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Sample records for establishing exchange bias

  1. The Electrically Controlled Exchange Bias

    NASA Astrophysics Data System (ADS)

    Harper, Jacob

    Controlling magnetism via voltage in the virtual absence of electric current is the key to reduce power consumption while enhancing processing speed, integration density and functionality in comparison with present-day information technology. Almost all spintronic devices rely on tailored interface magnetism. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is therefore a key challenge to better spintronics. However, there is no direct interaction between magnetization and electric fields, thus making voltage control of magnetism in general a scientific challenge. The significance of controlled interface magnetism started with the exchange-bias effect. Exchange bias is a coupling phenomenon at magnetic interfaces that manifests itself prominently in the shift of the ferromagnetic hysteresis loop along the magnetic-field axis. Various attempts on controlling exchange bias via voltage utilizing different scientific principles have been intensively studied recently. The majority of present research is emphasizing on various complex oxides. Our approach can be considered as a paradigm shift away from complex oxides. We focus on a magnetoelectric antiferromagnetic simple oxide Cr2O3. From a combination of experimental and theoretical efforts, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This is a significant scientific breakthrough providing a new route towards potentially revolutionizing information technology. In addition, a second path of electrically controlled exchange bias is introduced by exploiting the piezoelectric property of BaTiO3. An exchange-bias Co

  2. Exchange bias mediated by interfacial nanoparticles (invited)

    SciTech Connect

    Berkowitz, A. E.; Sinha, S. K.; Fullerton, E. E.; Smith, D. J.

    2015-05-07

    The objective of this study on the iconic exchange-bias bilayer Permalloy/CoO has been to identify those elements of the interfacial microstructure and accompanying magnetic properties that are responsible for the exchange-bias and hysteretic properties of this bilayer. Both epitaxial and polycrystalline samples were examined. X-ray and neutron reflectometry established that there existed an interfacial region, of width ∼1 nm, whose magnetic properties differed from those of Py or CoO. A model was developed for the interfacial microstructure that predicts all the relevant properties of this system; namely; the temperature and Permalloy thickness dependence of the exchange-bias, H{sub EX}, and coercivity, H{sub C}; the much smaller measured values of H{sub EX} from what was nominally expected; the different behavior of H{sub EX} and H{sub C} in epitaxial and polycrystalline bilayers. A surprising result is that the exchange-bias does not involve direct exchange-coupling between Permalloy and CoO, but rather is mediated by CoFe{sub 2}O{sub 4} nanoparticles in the interfacial region.

  3. 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

  4. Electric Control of Exchange Bias Training

    NASA Astrophysics Data System (ADS)

    Echtenkamp, W.; Binek, Ch.

    2013-11-01

    Voltage-controlled exchange bias training and tunability are introduced. Isothermal voltage pulses are used to reverse the antiferromagnetic order parameter of magnetoelectric Cr2O3, and thus continuously tune the exchange bias of an adjacent CoPd film. Voltage-controlled exchange bias training is initialized by tuning the antiferromagnetic interface into a nonequilibrium state incommensurate with the underlying bulk. Interpretation of these hitherto unreported effects contributes to new understanding in electrically controlled magnetism.

  5. 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

  6. Asymmetric Magnetization Reversal in Exchange Bias Systems*

    NASA Astrophysics Data System (ADS)

    Fitzsimmons, Michael

    2001-03-01

    Polarized neutron reflectometry measured the in-plane projection of the net-magnetization vector of polycrystalline Fe films exchange-coupled to (110) FeF2 antiferromagnetic (AF) films of controlled crystalline quality. For the sample with the single crystal AF film, we observed perpendicular exchange coupling across the ferromagnetic (F)-AF interface on either side of the hysteresis loop at coercivity. Perpendicular exchange coupling was observed regardless of cooling field orientation parallel or perpendicular to the AF anisotropy axis. Yet, for one orientation the exchange bias was zero; thus, perpendicular exchange coupling is not a sufficient condition for exchange bias. For samples with twinned AF films, an asymmetry in the spin flip scattering on either side of the hysteresis loop, and consequently in the magnetization reversal process, was observed. The origin of the asymmetry is explained by frustration of perpendicular exchange coupling, which enhances exchange bias and leads to 45° exchange coupling across the F-AF interface. The easy axis in the ferromagnet, which gives rise to asymmetric magnetization reversal in the twinned samples, is not present in samples with (110) textured polycrystalline AF films; and consequently exchange bias is reduced. *Work supported by the U.S. Department of Energy, BES-DMS under Contract No. W-7405-Eng-36, Grant No. DE-FG03-87ER-45332 and funds from the University of California Collaborative University and Laboratory Assisted Research. ÝWork in collaboration with A. Hoffmann, P. Yashar, J. Groves, R. Springer, P. Arendt (LANL), C. Leighton, K. Liu, Ivan K. Schuller (UCSD), J. Nogués (UAB), C.F. Majkrzak, J.A. Dura (NIST), H. Fritzsche (HMI), V. Leiner, H. Lauter (ILL).

  7. Exchange bias of conetic thin films

    NASA Astrophysics Data System (ADS)

    Eggers, Tatiana; Kirby, Hillary; Jayathilaka, Priyanga; Campbell, Scott; Miller, Casey

    2012-02-01

    In this work, we study the exchange bias and coercivity of Ni77Fe14Cu5Mo4 (Conetic, also known as mu-metal) exchange coupled with FeMn as functions of Conetic thickness and buffer layer material. The samples studied were BL(30nm)/Conetic(9nm-30nm)/FeMn(10nm)/Ta(5nm), where BL = Cu or Ta. All samples were grown by magnetron sputtering in a deposition field of ˜150 Oe during growth to set the exchange bias axis. Room temperature hysteresis loops were measured by a magneto-optical Kerr effect magnetometer as a function of applied-field angle. For each variety of sample, the exchange bias and coercivity were inversely proportional to Conetic thickness. With Cu buffer layers grown on Si, the Heb decreased from 300 Oe to 62 Oe, and Hc decreased from 99 Oe to 9 Oe. Similar results were found when the Cu buffer layer was grown on SiOx, though the maximum coercivity was only 67 Oe. For the samples grown on Si(001)/Ta(5nm), the exchange bias decreased from 80 Oe to 14 Oe, while the coercivity increases only slightly from 2 Oe to 10 Oe. These results indicate a trade-off between preserving the softness of the ferromagnet and having a large exchange, which may be useful for tuning the performance of low-field sensing materials

  8. Exchange bias studied with polarized neutron reflectivity

    SciTech Connect

    te Velthuis, S. G. E.

    2000-01-05

    The role of Polarized Neutron Reflectivity (PNR) for studying natural and synthetic exchange biased systems is illustrated. For a partially oxidized thin film of Co, cycling of the magnetic field causes a considerable reduction of the bias, which the onset of diffuse neutron scattering shows to be due to the loosening of the ferromagnetic domains. On the other hand, PNR measurements of a model exchange bias junction consisting of an n-layered Fe/Cr antiferromagnetic (AF) superlattice coupled with an m-layered Fe/Cr ferromagnetic (F) superlattice confirm the predicted collinear magnetization in the two superlattices. The two magnetized states of the F (along or opposite to the bias field) differ only in the relative orientation of the F and adjacent AF layer. The possibility of reading clearly the magnetic state at the interface pinpoints the commanding role that PNR is having in solving this intriguing problem.

  9. 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.

  10. Depth profile of uncompensated spins in an exchange bias system

    SciTech Connect

    Roy, S.; Fitzsimmons, M.R.; Park, S.; Dorn, M.; Petracic, O.; Roshchin, Igor V.; Li, Zhi-Pan; Morales, R.; Misra, A.; Zhang, X.; Chesnel, K.; Kortright, J.B.; Sinha, S.K.; Schuller, Ivan K.

    2005-05-17

    We have used the unique spatial sensitivity of polarized neutron and soft x-ray beams in reflection geometry to measure the depth dependence of magnetization across the interface between a ferromagnet and antiferromagnet. The new uncompensated magnetization near the interface responds to applied field, while the uncompensated spins in the antiferromagnetic bulk are pinned, thus providing a means to establish exchange bias.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Exchange bias in nearly perpendicularly coupled ferromagnetic/ferromagnetic system

    NASA Astrophysics Data System (ADS)

    Bu, K. M.; Kwon, H. Y.; Oh, S. W.; Won, C.

    2012-04-01

    Exchange bias phenomena appear not only in ferromagnetic/antiferromagnetic systems but also in ferromagnetic/ferromagnetic systems in which two layers are nearly perpendicularly coupled. We investigated the origin of the symmetry-breaking mechanism and the relationship between the exchange bias and the system's energy parameters. We compared the results of computational Monte Carlo simulations with those of theoretical model calculation. We found that the exchange bias exhibited nonlinear behaviors, including sign reversal and singularities. These complicated behaviors were caused by two distinct magnetization processes depending on the interlayer coupling strength. The exchange bias reached a maximum at the transition between the two magnetization processes.

  16. Dynamics of Exchange-Biased Magnetic Vortices

    NASA Astrophysics Data System (ADS)

    Chen, T. Y.; Chan, M. K.; Crowell, P. A.

    2009-03-01

    We have studied magnetization dynamics in micron-sized circular disks composed of ferromagnetic (FM)-antiferromagnetic (AFM) bilayers. The patterned samples of FeMn/NiFe are field-cooled (FC) or zero-field cooled (ZFC) from above the blocking temperature to room temperature. Time-resolved Kerr microscopy measurements show that the vortex gyrotropic mode fluctuates in frequency as the vortex core is displaced by a static in-plane magnetic field. The average gyrotropic frequency and the magnitude of its fluctuations, which are due to pinning of the vortex core, are larger than in single layer FM films. The enhancement of the gyrotropic frequency is largest in the ZFC samples, in which the effective field due to exchange coupling is expected to enhance pinning of the vortex core at the center of the disk. We find, however, that micromagnetic simulations incorporating uniform or vortex-like exchange-bias fields do not explain our results quantitatively. We interpret this discrepancy as a consequence of randomly orientated AFM domains, which are comparable in size to the vortex core. This work was supported by NSF and the Univ. of Minnesota Graduate School.

  17. 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.

  18. Ferromagnetic behavior and exchange bias effect in akaganeite nanorods

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We report ferromagnetic-like properties and exchange bias effect in akaganeite (β-FeOOH) nanorods. They exhibit a Néel temperature TN = 259 K and ferromagnetic-like hysteresis behavior both below and above TN. An exchange bias effect is observed below TN 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.

  19. Effect of grain cutting in exchange biased nanostructures

    NASA Astrophysics Data System (ADS)

    Carpenter, R.; Vick, A. J.; Hirohata, A.; Vallejo-Fernandez, G.; O'Grady, K.

    2014-05-01

    The effect of sub-500 nm patterning on exchange bias in thin films has been studied. Experimental results are compared to the York model of exchange bias which has been modified to take into account grain cutting at the edges of the structures. Exchange bias (Hex) was found to decrease with element size. The form of the variation of Hex with element size matches that of the experiment. Numerical agreement has not been achieved for Hex. However, the predictions of the median blocking temperature ⟨TB⟩ agree with experiment. The disagreement for Hex is attributed to edge roughness of the structures which will affect the quality of the interface which is dominant in structures of this scale.

  20. 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.

  1. 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.

  2. 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.

  3. A bias-exchange approach to protein folding.

    PubMed

    Piana, Stefano; Laio, Alessandro

    2007-05-01

    By suitably extending a recent approach [Bussi, G.; et al. J. Am. Chem. Soc. 2006, 128, 13435] we introduce a powerful methodology that allows the parallel reconstruction of the free energy of a system in a virtually unlimited number of variables. Multiple metadynamics simulations of the same system at the same temperature are performed, biasing each replica with a time-dependent potential constructed in a different set of collective variables. Exchanges between the bias potentials in the different variables are periodically allowed according to a replica exchange scheme. Due to the efficaciously multidimensional nature of the bias the method allows exploring complex free energy landscapes with high efficiency. The usefulness of the method is demonstrated by performing an atomistic simulation in explicit solvent of the folding of a Triptophane cage miniprotein. It is shown that the folding free energy landscape can be fully characterized starting from an extended conformation with use of only 40 ns of simulation on 8 replicas. PMID:17419610

  4. 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.

  5. 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...

  6. 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...

  7. 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.

  8. Exchange-bias-like effect of an uncompensated antiferromagnet

    NASA Astrophysics Data System (ADS)

    Henne, Bastian; Ney, Verena; de Souza, Mariano; Ney, Andreas

    2016-04-01

    The exchange bias effect is usually defined as horizontal shift of the field-cooled magnetization loop when an antiferromagnet is directly coupled to a ferromagnet. Uncompensated spins at the interface between the two layers are believed to cause this phenomenon. The presence of such, on the other hand, would infer a vertical, i.e., a magnetization-like shift stemming from the antiferromagnet. Observations of this effect are sparse, especially in the absence of a ferromagnet. We present a model system based on extremely Co doped ZnO in which the uncompensated spins of antiferromagnetic Co-O-Co… configurations lead to this vertical shift and therefore to a field-resistant magnetization. A simple Stoner-Wohlfarth-like model based on configurations of different sizes is used to explain the occurrence of this exchange-bias-like shift and a narrow opening of the magnetization curves.

  9. Role of anisotropy configuration in exchange-biased systems.

    SciTech Connect

    Jimenez, E.; Camarero, J.; Perna, P.; Mikuszeit, N.; Teran, F. J.; Sort, J.; Nogues, J.; Garcia-Martin, J. M.; Hoffmann, A.; Dieny, B.; Miranda, R.

    2011-01-01

    We present a systematic study of the anisotropy configuration effects on the magnetic properties of exchange-biased ferromagnetic/antiferromagnetic (FM/AFM) Co/IrMn bilayers. The interfacial unidirectional anisotropy is set extrinsically via a field cooling procedure with the magnetic field misaligned by an angle {beta}{sub FC} with respect to the intrinsic FM uniaxial anisotropy. High resolution angular dependence in-plane resolved Kerr magnetometry measurements have been performed for three different anisotropy arrangements, including collinear {beta}{sub FC} = 0 and two opposite noncollinear cases. The symmetry breaking of the induced noncollinear configurations results in a peculiar nonsymmetric magnetic behavior of the angular dependence of magnetization reversal, coercivity, and exchange bias. The experimental results are well reproduced without any fitting parameter by using a simple model including the induced anisotropy configuration. Our finding highlights the importance of the relative angle between anisotropies in order to properly account for the magnetic properties of exchange-biased FM/AFM systems.

  10. 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

  11. Magnetoelectricity coupled exchange bias in BaMnF4.

    PubMed

    Zhou, Shuang; Wang, Ji; Chang, Xiaofeng; Wang, Shuangbao; Qian, Bin; Han, Zhida; Xu, Qingyu; Du, Jun; Wang, Peng; Dong, Shuai

    2015-01-01

    Multiferroic BaMnF4 powder was prepared by hydrothermal method. Hysteretic field dependent magnetization curve at 5 K confirms the weak ferromagnetism aroused from the canted antiferromagnetic spins by magnetoelectric coupling. The blocking temperature of 65 K for exchange bias coincides well with the peak at 65 K in the zero-field cooled temperature-dependent magnetization curve, which has been assigned to the onset temperature of two-dimensional antiferromagnetism. An upturn kink of exchange field and coercivity with decreasing temperature was observed from 40 K to 20 K, which is consistent with the two-dimensional to three-dimensional antiferromagnetic transition at Néel temperature (~26 K). In contrast to the conventional mechanism of magnetization pinned by interfacial exchange coupling in multiphases, the exchange bias in BaMnF4 is argued to be a bulk effect in single phase, due to the magnetization pinned by the polarization through magnetoelectric coupling. PMID:26671575

  12. Magnetoelectricity coupled exchange bias in BaMnF4

    PubMed Central

    Zhou, Shuang; Wang, Ji; Chang, Xiaofeng; Wang, Shuangbao; Qian, Bin; Han, Zhida; Xu, Qingyu; Du, Jun; Wang, Peng; Dong, Shuai

    2015-01-01

    Multiferroic BaMnF4 powder was prepared by hydrothermal method. Hysteretic field dependent magnetization curve at 5 K confirms the weak ferromagnetism aroused from the canted antiferromagnetic spins by magnetoelectric coupling. The blocking temperature of 65 K for exchange bias coincides well with the peak at 65 K in the zero-field cooled temperature-dependent magnetization curve, which has been assigned to the onset temperature of two-dimensional antiferromagnetism. An upturn kink of exchange field and coercivity with decreasing temperature was observed from 40 K to 20 K, which is consistent with the two-dimensional to three-dimensional antiferromagnetic transition at Néel temperature (~26 K). In contrast to the conventional mechanism of magnetization pinned by interfacial exchange coupling in multiphases, the exchange bias in BaMnF4 is argued to be a bulk effect in single phase, due to the magnetization pinned by the polarization through magnetoelectric coupling. PMID:26671575

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

    DOE PAGESBeta

    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

  14. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  16. 45 CFR 155.100 - Establishment of a State Exchange.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 45 Public Welfare 1 2014-10-01 2014-10-01 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...

  17. 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...

  18. 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...

  19. Origins of Asymmetric Magnetization Reversal in Exchange Biased Multilayers

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Wang, Shuoguo; Li, Yang; Chen, Ning; Liu, Shuai; Li, Minghua; Yu, Guanghua; Department of Materials Physics; Chemistry, University of Science; Technology Beijing Team; State Key Laboratory Of Magnetism, Beijing National LaboratoryCondensed Matter Physics, Institu Team; University of Puerto Rico At Mayaguez Team

    2011-03-01

    Novel asymmetric magnetization reversal behaviors (ARBs) as well as positive exchange bias (EB) are observed by using the alternating gradient force magnetometer (AGM) in both Co/FeMn bilayer with an oblique out-of-plane exchange anisotropy and the Co/FeMn bilayer in which Co layer has a quite heavy thickness. There are two different ARBs, arised from the ferromagnetic and the antiferromagnetic layer respectively under the perpendicular magnetization. Our results show that two intrinsic origins of the ARBs (i.e. the competing anisotropy and the inhomogeneity of the magnetic structure) coexist. Both of them are indispensable for the development of the ARBs in our Co/FeMn multilayers. This work was supported by the National Science Foundation under Grant no. DMR-0821284, NASA under Grant Nos. NNX10AM80H and NNX07AO30A.

  20. Memory effect versus exchange bias for maghemite nanoparticles

    NASA Astrophysics Data System (ADS)

    Nadeem, K.; Krenn, H.; Szabó, D. V.

    2015-11-01

    We studied the temperature dependence of memory and exchange bias effects and their dependence on each other in maghemite (γ-Fe2O3) nanoparticles by using magnetization studies. Memory effect in zero field cooled process in nanoparticles is a fingerprint of spin-glass behavior which can be due to i) surface disordered spins (surface spin-glass) and/or ii) randomly frozen and interacting nanoparticles core spins (super spin-glass). Temperature region (25-70 K) for measurements has been chosen just below the average blocking temperature (TB=75 K) of the nanoparticles. Memory effect (ME) shows a non-monotonous behavior with temperature. It shows a decreasing trend with decreasing temperature and nearly vanishes below 30 K. However it also decreased again near the blocking temperature of the nanoparticles e.g., 70 K. Exchange bias (EB) in these nanoparticles arises due to core/shell interface interactions. The EB increases sharply below 30 K due to increase in core/shell interactions, while ME starts vanishing below 30 K. We conclude that the core/shell interface interactions or EB have not enhanced the ME but may reduce it in these nanoparticles.

  1. 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.

  2. 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.

  3. 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.

  4. Monte Carlo study on exchange bias and coercivity properties in coupled ferromagnetic/antiferromagnetic films

    NASA Astrophysics Data System (ADS)

    Jiang, Liqin; Shen, Shuangjuan; Zhang, Jian-Min; Feng, Qian; Huang, Zhigao

    2015-12-01

    Based on Monte Carlo simulation, a model consisting of an antiferromagnetic (AFM) film coupled to a ferromagnetic (FM) film is developed to study the exchange bias and coercivity phenomenon. It is suggested that exchange bias is a consequence of exchange coupling in the AFM/FM interface, and the AFM anisotropy needs to have a threshold value for the occurrence of exchange bias. Simultaneously, exchange bias and coercivity as functions of the value of anisotropy, exchange coupling and film thickness are studied. By inducing a thickness dependence of the anisotropy in FM film, the coercivity can be reduced or enhanced by choosing suitable magnetic parameters, which can better account for the discrepancies found in previous studies. The results also provide evidence for the absence of a direct correlation between coercivity and exchange bias, which is in agreement with other studies.

  5. Domain wall pinning for racetrack memory using exchange bias

    NASA Astrophysics Data System (ADS)

    Polenciuc, I.; Vick, A. J.; Allwood, D. A.; Hayward, T. J.; Vallejo-Fernandez, G.; O'Grady, K.; Hirohata, A.

    2014-10-01

    The pinning of domain walls in ferromagnetic (F) wires is one possible technique for the creation of a solid state magnetic memory. Such a system has been under consideration for some time but one of the main limitations is the control of, and non-uniformity of the domain wall pinning. Techniques such as the lithographic definition of notches and steps in the substrate have had some success in creating local pins but have the disadvantage of being expensive to fabricate and the reproducibility of the domain wall pinning strength is limited. In this letter, we report on an alternative strategy to create pins of reproducible strength using crossed ferromagnetic and antiferromagnetic (AF) wires such that exchange bias can be introduced at the crossing points. Such a system has the advantage of ease of fabrication and creating domain wall pins of controlled strength by varying the width of the AF wire. We have achieved domain wall pinning field strengths of up to 37 Oe in a system where the AF wire is deposited above the F wire which is comparable to the values achieved using notches.

  6. 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.

  7. 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.

  8. Texture and magnetic properties of exchange bias systems

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    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 (KAF) of the antiferromagnet (AF) layer, with an optimum NiCr seed layer of 6 nm to give a maximum value of KAF of 1.2×107 ergs/cc.

  9. Exchange bias in Fe and Ni codoped CuO nanocomposites

    NASA Astrophysics Data System (ADS)

    Liu, K. L.; Yuan, S. L.; Duan, H. N.; Zheng, X. F.; Yin, S. Y.; Tian, Z. M.; Wang, C. H.; Huo, S. X.

    2010-01-01

    Exchange bias nanocomposites were obtained by the chemical concentration precipitation method, in which the ferrimagnetic MFe2O4 (M=Cu,Ni) particles were embedded in the antiferromagnetic (AFM) CuO matrix. The dependence of magnetization on temperature measurements show that the exchange bias effect in these composites is ascribed to the exchange coupling at the interface between the ferrimagnetic particles and spin-glass-like phase. With continuous introduction of magnetic Ni ions, the existence of domain state structure and the formation of soft magnetic phase in AFM matrix are responsible for the different behaviors of the exchange bias field and coercivity in these nanocomposites.

  10. On the exchange bias in single and polycrystalline ferro/antiferromagnetic bilayers

    SciTech Connect

    Li, Zhanjie; Zhang, Shufeng

    2001-06-01

    By incorporating a random interfacial exchange interaction into the Landau{endash}Lifshitz{endash}Gilbert equation, a unified picture of exchange bias for single crystals, textured crystals, twin structures, and polycrystals of antiferromagnets is presented. It is found that the lateral interaction in the antiferromagnet is a key element governing the exchange bias and magnetization reversal of the ferromagnet. {copyright} 2001 American Institute of Physics.

  11. Controllable exchange bias in Fe/metamagnetic FeRh bilayers

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  12. 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.

  13. 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.

  14. 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.

  15. Positive exchange bias observed in Pt-inserted Cr2O3/Co exchange coupled bilayers

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    We investigated the effect of Pt insertion on a Cr2O3/Co exchange coupling system. The perpendicular exchange bias μ0Hex decreased with increasing Pt insertion layer thickness, and we observed positive μ0Hex for samples with relatively thick Pt insertion layers. We also examined the cooling field μ0Hfc dependence of μ0Hex for the samples. At small μ0Hfc, all samples exhibited negative μ0Hex. With increasing μ0Hfc, a shift of μ0Hex from negative to positive was observed. In the past, similar behaviors were observed for FeF2/Fe systems exhibiting positive μ0Hex. In addition, the μ0Hfc dependence of μ0Hex 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) Cr2O3 surface spin is affected by the external magnetic field and (2) the coupling at the Cr2O3/Pt/Co interface is antiferromagnetic.

  16. 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.

  17. Isothermal switching of perpendicular exchange bias by pulsed high magnetic field

    NASA Astrophysics Data System (ADS)

    Shiratsuchi, Yu; Wakatsu, Kohei; Nakamura, Tetsuya; Oikawa, Hiroto; Maenou, Satoru; Narumi, Yasuo; Tazoe, Kou; Mitsumata, Chiharu; Kinoshita, Toyohiko; Nojiri, Hiroyuki; Nakatani, Ryoichi

    2012-06-01

    Isothermal switching of a perpendicular exchange bias by a strong pulsed magnetic field has been investigated using a Pt/Co/α-Cr2O3 thin film system. The switching of the perpendicular exchange bias is accompanied by the spin reversal of interfacial uncompensated antiferromagnetic Cr spins. We have also demonstrated that the switching of the exchange bias is reversible by changing the pulsed magnetic field direction. The mechanism of the demonstrated switching is discussed from the viewpoint of the spin flop transition of the α-Cr2O3 layer.

  18. Exchange bias field induced symmetry-breaking of magnetization rotation in two-dimension

    NASA Astrophysics Data System (ADS)

    Cui, B.; Song, C.; Sun, Y.; Wang, Y. Y.; Zhao, Y. L.; Li, F.; Wang, G. Y.; Zeng, F.; Pan, F.

    2014-10-01

    We investigate the effect of strain-induced intrinsic exchange bias field (HEB) on the magnetization rotation process in a nominally "single" layered La2/3Sr1/3MnO3 (LSMO) film. The intrinsic exchange bias appears when the LSMO film is grown on LaAlO3 substrate. The HEB is proved to be an effective approach to tuning the in-plane magnetization rotation, producing a 360° instead of 180° periodicity in the anisotropic magnetoresistance curves measured in a low external magnetic field. The planar Hall effect curves are asymmetric when the in-plane magnetization rotate between two orthogonal axes of LSMO, helped or hindered by the HEB. Our study reveals that the HEB in but not limited to LSMO with phase separation exhibits an unprecedentedly two-dimensional effect rather than merely establishing a reference magnetization direction as achieved in ferromagnetic/antiferromagnetic bilayers, thus furthering the cognition of manipulating the magnetization orientation.

  19. 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.

  20. Exchange Bias and Unusual Initial Magnetization in Nanocrystalline Spinel Ferrite Thin Films

    NASA Astrophysics Data System (ADS)

    Alaan, Urusa; Gollapudi, Sreenivasulu; Yu, Kin Man; Shafer, Padraic; Arenholz, Elke; Srinivasan, Gopalan; Suzuki, Yuri

    2015-03-01

    We report on unconventional magnetic behavior in nanocrystalline (Mn,Zn,Fe)3O4 (MZFO) thin films grown at room temperature. Structural studies show no secondary phases, yet these films are exchange biased, with magnetic hysteresis loops shifted by as much as ~ 200 Oe at 10 K after field-cooling. The samples can be ``trained'' so that successive magnetization loops exhibit reduced exchange bias. Shifts of the hysteresis loops exist even after cooling in zero field, indicating that the MZFO is not externally biased. We attribute the exchange bias to disordered, grain-boundary-like regions that bias more ordered MZFO. Annealing experiments that improved sample crystallinity decreased the exchange bias. Higher annealing temperatures resulted in reduced coercivities, higher magnetizations, and even the elimination of the exchange bias. Annealing also removed an unusual crossover of the initial magnetization curve outside of the saturated magnetization loop. This behavior has been seen in so-called ``mictomagnetic'' alloys. Using x-ray magnetic circular dichroism measurements, we have shown that cation disorder was reduced with annealing, and correlated the atypical initial magnetization with the degree of disorder. We gratefully acknowledge the National Science Foundation for funding this research.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

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

    PubMed

    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

  7. 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.

  8. Anomalous positive exchange bias in nanostructured FeMn/Co/FeMn networks

    NASA Astrophysics Data System (ADS)

    Jiang, Changjun; Xue, Desheng; Fan, Xiaolong; Guo, Dangwei; Liu, Qingfang

    2007-08-01

    FeMn/Co/FeMn multilayers are sputtered onto porous alumina templates and silicon, respectively. The FeMn/Co/FeMn multilayer on the porous alumina templates forms an interconnected network nanostructure, while the FeMn/Co/FeMn multilayer on the silicon substrate forms a continuous film. The SQUID testing results show that the exchange bias (HE) and coercivity (Hc) of the FeMn/Co/FeMn multilayer on the porous alumina templates strongly depend on the temperature. A positive exchange bias loops shift is observed at 250 K under field-cooled conditions. However, this is not found in the FeMn/Co/FeMn multilayer on silicon for the same layer thickness. We attribute the positive exchange bias loops shift of the network nanostructured FeMn/Co/FeMn multilayer to the decreased exchange coupling due to the existence of the holes in the interconnected nanostructure.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    Spin glass behavior and exchange bias effect have been observed in antiferromagnetic SrMn3O6-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 SrMn3O6-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.

  10. 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.

  11. 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.

  12. Magnetic exchange bias of more than 1 Tesla in a natural mineral intergrowth

    NASA Astrophysics Data System (ADS)

    McEnroe, Suzanne A.; Carter-Stiglitz, Brian; Harrison, Richard J.; Robinson, Peter; Fabian, Karl; McCammon, Catherine

    2007-10-01

    Magnetic exchange bias is a phenomenon whereby the hysteresis loop of a `soft' magnetic phase is shifted by an amount HE along the applied field axis owing to its interaction with a `hard' magnetic phase. Since the discovery of exchange bias fifty years ago, the development of a general theory has been hampered by the uncertain nature of the interfaces between the hard and soft phases, commonly between an antiferromagnetic phase and a ferro- or ferrimagnetic phase. Exchange bias continues to be the subject of investigation because of its technological applications and because it is now possible to manipulate magnetic materials at the nanoscale. Here we present the first documented example of exchange bias of significant magnitude (>1 T) in a natural mineral. We demonstrate that exchange bias in this system is due to the interaction between coherently intergrown magnetic phases formed through a natural process of phase separation during slow cooling over millions of years. Transmission electron microscopy studies show that these intergrowths have a known crystallographic orientation with a known crystallographic structure and that the interfaces are coherent.

  13. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  15. Magnetoelectric coupling and exchange bias effects in multiferroic NdCrO3.

    PubMed

    Indra, A; Dey, K; Midya, A; Mandal, P; Gutowski, O; Rütt, U; Majumdar, S; Giri, S

    2016-04-27

    We report ferroelectricity around  ∼88 K that appears well below T N (∼25 K), unlike other members of RCrO3 series. A synchrotron diffraction study suggests that the occurrence of ferroelectricity in NdCrO3 is coupled to the structural transformation from centrosymmetric Pnma to a non-centrosymmetric Pna21 space group. A strong magnetoelectric coupling is observed in the electric polarization [P(T)]. This coupling is significantly influenced by the magnetic field cooling effect, suggesting an exchange bias effect in P(T). This exchange bias effect is also revealed by the systematic shift of the magnetic hysteresis loops below T N. The rare occurrence of an exchange bias effect in both the magnetic and electric polarizations associated with a strong magnetoelectric coupling is of fundamental interest, as well as being attractive for technological applications close to liquid nitrogen temperature. PMID:27009362

  16. Magnetoelectric coupling and exchange bias effects in multiferroic NdCrO3

    NASA Astrophysics Data System (ADS)

    Indra, A.; Dey, K.; Midya, A.; Mandal, P.; Gutowski, O.; Rütt, U.; Majumdar, S.; Giri, S.

    2016-04-01

    We report ferroelectricity around  ∼88 K that appears well below T N (∼25 K), unlike other members of RCrO3 series. A synchrotron diffraction study suggests that the occurrence of ferroelectricity in NdCrO3 is coupled to the structural transformation from centrosymmetric Pnma to a non-centrosymmetric Pna21 space group. A strong magnetoelectric coupling is observed in the electric polarization [P(T)]. This coupling is significantly influenced by the magnetic field cooling effect, suggesting an exchange bias effect in P(T). This exchange bias effect is also revealed by the systematic shift of the magnetic hysteresis loops below T N. The rare occurrence of an exchange bias effect in both the magnetic and electric polarizations associated with a strong magnetoelectric coupling is of fundamental interest, as well as being attractive for technological applications close to liquid nitrogen temperature.

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

    NASA Astrophysics Data System (ADS)

    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.

    2015-03-01

    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.

  18. 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...

  19. 45 CFR 155.1050 - Establishment of Exchange network adequacy standards.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 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...

  20. 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...

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

    DOE PAGESBeta

    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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Exchange bias effect in BiFeO3-NiO nanocomposite

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Kaushik; Sarkar, Babusona; Dev Ashok, Vishal; Das, Kajari; Sinha Chaudhuri, Sheli; Mitra, Amitava; De, S. K.

    2014-01-01

    Ferromagnetic BiFeO3 nanocrystals of average size 11 nm were used to form nanocomposites (x)BiFeO3/(100 - x)NiO, x = 0, 20, 40, 50, 60, 80, and 100 by simple solvothermal process. The ferromagnetic BiFeO3 nanocrystals embedded in antiferromagnetic NiO nanostructures were confirmed from X-ray diffraction and transmission electron microscope studies. The modification of cycloidal spin structure of bulk BiFeO3 owing to reduction in particle size compared to its spin spiral wavelength (62 nm) results in ferromagnetic ordering in pure BiFeO3 nanocrystals. High Neel temperature (TN) of NiO leads to significant exchange bias effect across the BiFeO3/NiO interface at room temperature. A maximum exchange bias field of 123.5 Oe at 300 K for x = 50 after field cooling at 7 kOe has been observed. The exchange bias coupling causes an enhancement of coercivity up to 235 Oe at 300 K. The observed exchange bias effect originates from the exchange coupling between the surface uncompensated spins of BiFeO3 nanocrystals and NiO nanostructures.

  8. 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.

  9. Mircomagnetic Simulation of Amorphous TbFeCo Thin Films with Self Exchange Bias

    NASA Astrophysics Data System (ADS)

    Ma, Chung; Li, Xiaopu; Lu, Jiwei; Poon, Joseph

    Amorphous ferrimagnetic TbFeCo thin films are found to exhibit self exchange bias effect near compensation temperature by magnetic hysteresis loop measurement. Atom probe tomography, scanning transmission electron microscopy, and energy dispersive spectroscopy mapping have revealed two nanoscale amorphous phases with different Tb concentrations distributed within the amorphous films. The observed exchange anisotropy originates from the exchange interaction between the two nanoscale amorphous phases. Here, we present a computational model of TbFeCo with two nanoscale amorphous phases using micromagnetic simulation. To obtain a structure similar to the two nanoscale amorphous phases, two kinds of cells with different Tb concentration are distributed within the simulated space. Each cell contains separated Tb and FeCo components, forming two antiferromagnetically coupled sublattices. Using this model, we show exchange bias effect near compensation temperature, in agreement with experimental results. The effect can be tuned by controlling the microstructure and composition. The work was supported by the Defense Threat Reduction Agency grant.

  10. Exchange bias through a Cu interlayer in an IrMn/Co system

    NASA Astrophysics Data System (ADS)

    Geshev, J.; Nicolodi, S.; Pereira, L. G.; Nagamine, L. C. C. M.; Schmidt, J. E.; Deranlot, C.; Petroff, F.; Rodríguez-Suárez, R. L.; Azevedo, A.

    2007-06-01

    Ferromagnetic resonance (FMR) and magnetization (MAG) measurements were used to study the exchange interaction between the antiferromagnetic and ferromagnetic layers in an IrMn/Cu/Co system as a function of the Cu spacer thickness. Although the experimental angular variations of the exchange-bias fields HebFMR and HebMAG coincide, the coupling strengths J and the Co layers’ anisotropy fields HU , obtained via numerical simulations, are different. For all Cu thicknesses JFMR>JMAG and HUFMRexchange coupling decreases exponentially with the spacer thickness and is a short-range interaction. These characteristics were explained in the framework of a model considering polycrystalline magnetic layers with independent easy axis distributions, taking into account the rotatable anisotropy. The role of antiferromagnetic grains at the interface with different sizes and different magnetic stabilities is essential for understanding the behavior of this exchange-biased system.

  11. Tunable exchange bias in dilute magnetic alloys - chiral spin glasses

    NASA Astrophysics Data System (ADS)

    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.

  12. Influence of ion bombardment induced patterning of exchange bias in pinned artificial ferrimagnets on the interlayer exchange coupling

    SciTech Connect

    Hoeink, V.; Schmalhorst, J.; Reiss, G.; Weis, T.; Lengemann, D.; Engel, D.; Ehresmann, A.

    2008-06-15

    Artificial ferrimagnets have many applications as, e.g., pinned reference electrodes in magnetic tunnel junctions. It is known that the application of ion bombardment (IB) induced patterning of the exchange bias coupling of a single layer reference electrode in magnetic tunnel junctions with He ions is possible. For applications as, e.g., special types of magnetic logic, a combination of the IB induced patterning of the exchange bias coupling and the implementation of an artificial ferrimagnet as reference electrode is desirable. Here, investigations for a pinned artificial ferrimagnet with a Ru interlayer, which is frequently used in magnetic tunnel junctions, are presented. It is shown that in this kind of samples the exchange bias can be increased or rotated by IB induced magnetic patterning with 10 keV He ions without a destruction of the antiferromagnetic interlayer exchange coupling. An IrMn/Py/Co/Cu/Co stack turned out to be more sensitive to the influence of IB than the Ru based artificial ferrimagnet.

  13. Giant zero field cooled spontaneous exchange bias effect in phase separated La1.5Sr0.5CoMnO6

    NASA Astrophysics Data System (ADS)

    Krishna Murthy, J.; Venimadhav, A.

    2013-12-01

    We report a giant zero field cooled exchange bias (ZEB) effect (˜0.65 T) in La1.5Sr0.5CoMnO6 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.

  14. Piezoelectric manipulation of Co/CoO exchange-bias bilayer system at low-temperature

    NASA Astrophysics Data System (ADS)

    Rizwan, Syed; Ali, S. I.; Zhang, Q. T.; Zhang, S.; Zhao, Y. G.; Anis-ur-Rehman, M.; Tufail, Muhammad; Han, X. F.

    2013-09-01

    The spintronics devices based on electric field is a key challenge today and the exchange bias effect is the basic structure used in these devices. We have studied the electric field control of annealed Co/CoO exchange bias system fabricated on the (011)-Pb(Mg1/3Nb2/3)O3-PbTiO3 piezoelectric substrate. The Co/CoO heterostructure was cooled down from above the Neel temperature (TN = 291 K) down to 15 K in the presence of electric and magnetic fields; the sample was cooled every time for each electric field measurement in order to avoid the training effect. The exchange bias effect was found to increase by 44% at the highest electric field value of 8 kV/cm measured at 15 K. The electric field tuning of exchange bias is attributed to the different magnetization reversal processes for left and right branches of magnetic hysteresis loop. Our results reinforce the possibility for the use of electric field as a tool to control the future spintronics devices.

  15. 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.

  16. Role of interface coupling inhomogeneity in domain evolution in exchange bias

    PubMed Central

    Benassi, Andrea; Marioni, Miguel A.; Passerone, Daniele; Hug, Hans J.

    2014-01-01

    Models of exchange-bias in thin films have been able to describe various aspects of this technologically relevant effect. Through appropriate choices of free parameters the modelled hysteresis loops adequately match experiment, and typical domain structures can be simulated. However, the use of these parameters, notably the coupling strength between the systems' ferromagnetic (F) and antiferromagnetic (AF) layers, obscures conclusions about their influence on the magnetization reversal processes. Here we develop a 2D phase-field model of the magnetization process in exchange-biased CoO/(Co/Pt)×n that incorporates the 10 nm-resolved measured local biasing characteristics of the antiferromagnet. Just three interrelated parameters set to measured physical quantities of the ferromagnet and the measured density of uncompensated spins thus suffice to match the experiment in microscopic and macroscopic detail. We use the model to study changes in bias and coercivity caused by different distributions of pinned uncompensated spins of the antiferromagnet, in application-relevant situations where domain wall motion dominates the ferromagnetic reversal. We show the excess coercivity can arise solely from inhomogeneity in the density of biasing- and anti-biasing pinned uncompensated spins in the antiferromagnet. Counter to conventional wisdom, irreversible processes in the latter are not essential. PMID:24676050

  17. Rotatable anisotropy driven training effects in exchange biased Co/CoO films

    NASA Astrophysics Data System (ADS)

    Dias, T.; Menéndez, E.; Liu, H.; Van Haesendonck, C.; Vantomme, A.; Temst, K.; Schmidt, J. E.; Giulian, R.; Geshev, J.

    2014-06-01

    The training effect for exchange bias in field-cooled Co/CoO bilayers films is investigated. Previous experiments on the same system have shown that, starting from the ascending branch of the first hysteresis loop, coherent magnetization rotation is the dominant reversal mechanism. This is confirmed by the performed numerical simulations, which also indicate that the training is predominantly caused by changes of the rotatable anisotropy parameters of uncompensated spins at the Co/CoO interface. Moreover, in contrast with what is commonly assumed, the exchange coupling between the rotatable spins and the ferromagnetic layer is stronger than the coupling between the ferromagnet and the spins responsible for the bias. Thus, uncompensated spins strongly coupled to the ferromagnet contribute to the coercivity rather than to the bias, whatever the strength of their magnetic anisotropy.

  18. 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

  19. 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.

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

    PubMed Central

    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

  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. Monte-Carlo modeling of exchange bias properties in amorphous magnets

    NASA Astrophysics Data System (ADS)

    Hu, Yong; Du, An

    2015-11-01

    We explore the effect of interfacial disorder on exchange bias properties of a soft ferromagnet with a negligible intrinsic anisotropy exchange coupled to a hard amorphous magnet with a random magnetic anisotropy, based on an extensive Monte Carlo simulation. The interfacial disorder is introduced by using a '±J'' model. As compared to the conventionally crystalline ferromagnet/antiferromagnet bilayers, pronounced values and sign inversion in the exchange field are obtained at low temperature after cooling even under a weak field. However, the coercivity in the amorphous system not only shows smaller values, but also exhibits an opposite trend. Different from the ordered crystalline systems, the intrinsic properties of the Harris-Plischke-Zuckermann Hamiltonian rather than the domain structure determine the coercive fields and the shapes of hysteresis loops with different temperatures and cooling fields in the random magnetic anisotropy model, and hence the exchange bias. This theoretical work opens a new avenue for magnetism of the exchange bias and for its applications.

  3. 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.

  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. FORC analysis of ferro-ferromagnetic exchange bias in nanocrystalline ribbons

    NASA Astrophysics Data System (ADS)

    Martínez-García, J. C.; Rivas, M.; García, J. A.

    2016-04-01

    Horizontal shift and distortion of the hysteresis loops can be induced in some Co-based nanocrystalline systems in which soft and hard ferromagnetic phases coexist. As all the aspects of the phenomenon can be well explained in terms of the exchange interaction between the two phases, it has been identified as an induced ferro-ferromagnetic exchange bias. In this work we use the differential analysis based on first-order reversal curves to analyse this particular kind of exchange bias, through the comparison of the FORC diagrams corresponding to samples with different crystallization degrees. A detailed study of the evolution of such diagrams is presented, pointing in each case to the more outstanding features of the spots corresponding to the different phases as well as to their interactions.

  6. Giant exchange bias in Mn2FeGa with hexagonal structure

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Zhang, Y. J.; Zhang, H. G.; Zhang, X. J.; Ma, X. Q.

    2016-07-01

    In this study, we present the experimental observation that polycrystalline Mn2+xFe1-xGa (x = -0.2, 0, 0.2, 0.4) compounds can be synthesized to be D019-type (Ni3Sn-type) hexagonal structure with space group P63/mmc. A giant exchange bias field up to 1.32 kOe was achieved in hexagonal Mn2FeGa alloy at 5 K. A cluster glass state is confirmed by ac susceptibility measurement under different driving frequencies. Interestingly, robust horizontal and vertical shifts in magnetic hysteresis loop were simultaneously observed at 5 K under high cooling field up to 90 kOe. The large exchange bias is originated from the large exchange anisotropy between cluster glass phase and ferrimagnetic matrix. The vertical shift is thought to be attributed to the incomplete reversal of frozen cluster spins.

  7. 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.

  8. 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.

  9. Detection and in situ switching of unreversed interfacial antiferromagnetic spins in a perpendicular-exchange-biased system.

    PubMed

    Shiratsuchi, Yu; Noutomi, Hayato; Oikawa, Hiroto; Nakamura, Tetsuya; Suzuki, Motohiro; Fujita, Toshiaki; Arakawa, Kazuto; Takechi, Yuichiro; Mori, Hirotaro; Kinoshita, Toyohiko; Yamamoto, Masahiko; Nakatani, Ryoichi

    2012-08-17

    By using the perpendicular-exchange-biased Pt/Co/α-Cr(2)O(3) system, we provide experimental evidence that the unreversed uncompensated Cr spins exist at the Co/α-Cr(2)O(3) interface. The unreversed uncompensated Cr spin manifests itself in both the vertical shift of an element-specific magnetization curve and the relative peak intensity of soft-x-ray magnetic circular dichroism spectrum. We also demonstrate an in situ switching of the interfacial Cr spins and correspondingly a reversal of the exchange bias without interfacial atomic diffusion. Such switching shows the direct relationship between the interfacial antiferromagnetic spins and origin of the exchange bias. The demonstrated switching of exchange bias would likely offer a new design of advanced spintronics devices, using the perpendicular-exchange-biased system, with low power consumption and ultrafast operation. PMID:23006398

  10. Detection and In Situ Switching of Unreversed Interfacial Antiferromagnetic Spins in a Perpendicular-Exchange-Biased System

    NASA Astrophysics Data System (ADS)

    Shiratsuchi, Yu; Noutomi, Hayato; Oikawa, Hiroto; Nakamura, Tetsuya; Suzuki, Motohiro; Fujita, Toshiaki; Arakawa, Kazuto; Takechi, Yuichiro; Mori, Hirotaro; Kinoshita, Toyohiko; Yamamoto, Masahiko; Nakatani, Ryoichi

    2012-08-01

    By using the perpendicular-exchange-biased Pt/Co/α-Cr2O3 system, we provide experimental evidence that the unreversed uncompensated Cr spins exist at the Co/α-Cr2O3 interface. The unreversed uncompensated Cr spin manifests itself in both the vertical shift of an element-specific magnetization curve and the relative peak intensity of soft-x-ray magnetic circular dichroism spectrum. We also demonstrate an in situ switching of the interfacial Cr spins and correspondingly a reversal of the exchange bias without interfacial atomic diffusion. Such switching shows the direct relationship between the interfacial antiferromagnetic spins and origin of the exchange bias. The demonstrated switching of exchange bias would likely offer a new design of advanced spintronics devices, using the perpendicular-exchange-biased system, with low power consumption and ultrafast operation.

  11. Tailoring perpendicular exchange bias in [Pt/Co]-IrMn multilayers

    SciTech Connect

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

    2005-02-01

    In [Pt/Co] multilayers (ML) exchange coupled to IrMn, the magnitudes of the exchange bias field H{sub E} and coercivity H{sub C} measured along the perpendicular to film direction, can be tailored by (i) varying the thickness of the Co layers (t{sub Co}) inside the ML and/or (ii) inserting a Pt spacer between the ML and the antiferromagnetic (AFM) layer. An unusual peak in the ferromagnetic (FM) thickness dependence of exchange bias properties is observed. This is ascribed to a reduction of the perpendicular effective magnetic anisotropy for either very small or too large values of t{sub Co}. Moreover, for low values of t{sub Co}, the insertion of an ultrathin Pt spacer between the [Pt/Co] ML and the IrMn brings about a significant increase of H{sub E} and H{sub C}. However, such an effect is not observed for thicker Co layers. This behavior is explained by the two-fold role of the Pt spacer, i.e., it strengthens the perpendicular orientation of the Co magnetization in the ML but it also tends to reduce exchange bias due to the short-range character of the FM-AFM interactions.

  12. Large exchange bias in polycrystalline MnN/CoFe bilayers at room temperature

    NASA Astrophysics Data System (ADS)

    Meinert, Markus; Büker, Björn; Graulich, Dominik; Dunz, Mareike

    2015-10-01

    We report on the new polycrystalline exchange bias system MnN/CoFe, which shows exchange bias of up to 1800 Oe at room temperature with a coercive field around 600 Oe. The room-temperature values of the interfacial exchange energy and the effective uniaxial anisotropy are estimated to be Jeff=0.41 mJ /m2 and Keff=37 kJ /m3 . The thermal stability was found to be tunable by controlling the nitrogen content of MnN. The maximum blocking temperature exceeds 325 ∘C, however the median blocking temperature in the limit of thick MnN is 160 ∘C . Good oxidation stability through self-passivation was observed, enabling the use of MnN in lithographically defined microstructures. As a proof of principle we demonstrate a simple giant magnetoresistance stack exchange biased with MnN, which shows clear separation between parallel and antiparallel magnetic states. These properties come along with a surprisingly simple manufacturing process for the MnN films.

  13. Exchange-bias phenomena and modeling in nanocrystalline powders of MnO/FeCo and NiO/Fe

    NASA Astrophysics Data System (ADS)

    Cornejo, D. R.; Padrón Hernández, E.; Azevedo, A.; Rezende, S. M.

    2005-05-01

    An approach towards the modeling of the magnetic behavior in heterogeneous systems of exchange-coupled antiferromagnetic (AF) and ferromagnetic (FM) particles with composition (AF)x+(FM)1-x is presented. The model is based on the Preisach hysteresis model and correctly predicts the correlation between the exchange-bias field and the mean grain size of the material, as established from the measurements of the hysteresis loops in mechanically alloyed (MnO)+(α-FeCo). The model was also used to calculate the unidirectional anisotropy interface energies in both this and (NiO)x+(α-Fe)1-x system; in the latter case, the predicted value was in full agreement with that reported for antiferromagnetic layers of NiO.

  14. 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.

  15. Interface induced manipulation of perpendicular exchange bias in Pt/Co/(Pt,Cr)/CoO thin films

    NASA Astrophysics Data System (ADS)

    Akdoğan, N.; Yağmur, A.; Öztürk, M.; Demirci, E.; Öztürk, O.; Erkovan, M.

    2015-01-01

    Perpendicular exchange bias has been manipulated by changing ferromagnetic film thickness and spacer layer in Pt/Co/(Pt,Cr)/CoO thin films. The exchange bias characteristics, blocking temperature, and magnetization of thin films strongly depend on the spacer layer (Pt,Cr) between ferromagnetic and antiferromagnetic layers. While Pt/Co/Pt/CoO thin films show perpendicular exchange bias, Pt/Co/Cr/CoO has exchange bias with easy magnetization axis in the film plane. We have also observed very small hysteretic behavior from the hard axis magnetization curve of Pt/Co/Cr/CoO film. This can be attributed to misalignment of the sample or small perpendicular contribution from Pt/Co bottom interface. We have also investigated the temperature and spacer layer dependent exchange bias properties of the samples. We observed higher HEB and HC for the thicker Co layer in the Pt/Co/Pt/CoO sample. In addition, onset of exchange bias effect starts at much lower temperatures for Pt/Co/Cr/CoO thin film. This clearly shows that Cr spacer layer not only removes the perpendicular exchange bias, but also reduces the exchange interaction between Co and CoO and thus lowers the TB.

  16. Ion irradiation effects on the exchange bias in IrMn/Co films

    SciTech Connect

    Schafer, D.; Grande, P. L.; Pereira, L. G.; Geshev, J.

    2011-01-15

    The present work reports on the influence of ion irradiation in exchange-coupled bilayers. Magnetron-sputtered IrMn{sub 4}/Co films were irradiated with 40 keV He{sup +} ions and the dependence of their magnetic properties was studied as function of ion fluence and current used during the irradiations. The effects of ion damage and electronic excitation were also studied through additional irradiations with H{sup +} and Ne{sup +} ions. The results show a clear dependence of the exchange-bias field on the defects caused by the ion bombardment. No correlations with other irradiation effects were observed.

  17. 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

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

    PubMed

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

    2016-01-01

    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

  19. Exchange bias in strained SrRuO3 thin films

    NASA Astrophysics Data System (ADS)

    Sow, Chanchal; Pramanik, A. K.; Anil Kumar, P. S.

    2014-11-01

    Recently, it was found that the ferromagnetic SrRuO3 when combined with another ferromagnet in thin film form gives rise to exchange bias (EB) effect. However, we observed EB in single, strained, SrRuO3 thin films grown on diamagnetic LaAlO3 (100) substrates. It displays the training effect, which essentially confirms EB. The temperature dependence of the EB reveals the blocking temperature to be around ˜75 K. The strength of the exchange bias decreases with the increase in thickness of the film. We observe tensile strain in the out of plane direction. Further, the presence of in-plane compressive strain is observed through asymmetric reciprocal space mapping. Finally, we find a direct link between strain and EB. The evolution of strain with thickness matches well with the nature of scaled EB. It has been shown earlier by first principle calculations that this strain can induce EB in thin films.

  20. 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.

  1. 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.

  2. 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.

  3. Exchange-bias-like coupling in a Cu-diluted-Fe/Tb multilayer

    NASA Astrophysics Data System (ADS)

    Mukherjee, Saumya; Kreuzpaintner, Wolfgang; Stahn, Jochen; Zheng, Jian-Guo; Bauer, Andreas; Böni, Peter; Paul, Amitesh

    2015-03-01

    Transition metal-rare earth (TM-RE) Fe/Tb-multilayer systems have been known to show exchange-bias-like shifts in the form of double hysteresis loop (DHL) along and opposite to the field cooling axis. Planar domain walls, with opposite handedness at the interfaces, are held responsible for such DHL. Here, we report on the formation of nanoparticulated Fe layers in the Cu-matrix within a Fe-Cu/Tb multilayer and their eventual low-temperature characteristics. AC susceptibility measurements indicate that these diluted magnetic clusters have a superspin-glass-type of freezing behavior. Eventually, this Fe-cluster/Tb interlayer interaction, which is conjectured to be mediated by the pinned moments within the individual clusters, has helped in increasing the exchange bias field in the system to a high value of ≈1.3 kOe, which gradually vanishes around 50 K. Polarized neutron reflectivity confirms a very strong antiferromagnetic (AF) coupling between the individual layers. The magnitude of the magnetic moment of each of the individual Tb or Fe-Cu layer remains similar, but due to the strong AF-coupling at the interfaces, the entire ferrimagnetic Fe-Cu/Tb entity flips its direction at a compensation field of around 3.7 kOe. This study shows that magnetic dilution can be an effective way to manipulate the possible domain walls or the clusters in TM and thereby the exchange bias in TM-RE systems.

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

    PubMed

    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. Mn(3+) and Mn(2+) 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 Mn(4+) very well. The uncoupled spins in 3d(3) orbitals of the Mn(4+) 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  6. Voltage Controlled Exchange Bias in a Cr2O3 based heterostructure

    NASA Astrophysics Data System (ADS)

    Echtenkamp, Will; Street, Mike; Binek, Christian

    2015-03-01

    Controlling magnetism by electrical means is 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. Isothermal electric control of exchange bias has been achieved near room temperature using bulk, single crystal, magnetoelectric Cr2O3, which has a voltage controlled net magnetization at the (0001) surface. Voltage control of magnetism in a Cr2O3 thin film system has presented significant challenges. In this study we explore the electric control of exchange bias in an all-thin-film system of decreasing chromia film thickness with significant implications for scalability of ultra-low power memory and logical devices. Cross-sectional HRTEM indicates that grain boundaries in the metallic bottom electrode propagate into the Cr2O3 thin film with detrimental effects on leakage currents. We address this issue via a three-step growth method for the deposition of epitaxial Pd on sapphire. The resulting microstructure of the films is analyzed by reflection high-energy electron diffraction, tunneling electron microscopy and x-ray diffraction. This project was supported by SRC through CNFD, an SRC-NRI Center, by C-SPIN, part of STARnet, and by the NSF through MRSEC DMR-0820521.

  7. 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

  8. 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. PMID:26523499

  9. Exchange bias of Ni nanoparticles embedded in an antiferromagnetic IrMn matrix

    NASA Astrophysics Data System (ADS)

    Kuerbanjiang, Balati; Wiedwald, Ulf; Haering, Felix; Biskupek, Johannes; Kaiser, Ute; Ziemann, Paul; Herr, Ulrich

    2013-11-01

    The magnetic properties of Ni nanoparticles (Ni-NPs) embedded in an antiferromagnetic IrMn matrix were investigated. The Ni-NPs of 8.4 nm mean diameter were synthesized by inert gas aggregation. In a second processing step, the Ni-NPs were in situ embedded in IrMn films or SiOx films under ultrahigh vacuum (UHV) conditions. Findings showed that Ni-NPs embedded in IrMn have an exchange bias field HEB = 821 Oe at 10 K, and 50 Oe at 300 K. The extracted value of the exchange energy density is 0.06 mJ m-2 at 10 K, which is in good accordance with the results from multilayered thin film systems. The Ni-NPs embedded in SiOx did not show exchange bias. As expected for this particle size, they are superparamagnetic at T = 300 K. A direct comparison of the Ni-NPs embedded in IrMn or SiOx reveals an increase of the blocking temperature from 210 K to around 400 K. The coercivity of the Ni-NPs exchange coupled to the IrMn matrix at 10 K is 8 times larger than the value for Ni-NPs embedded in SiOx. We studied time-dependent remanent magnetization at different temperatures. The relaxation behavior is described by a magnetic viscosity model which reflects a rather flat distribution of energy barriers. Furthermore, we investigated the effects of different field cooling processes on the magnetic properties of the embedded Ni-NPs. Exchange bias values fit to model calculations which correlate the contribution of the antiferromagnetic IrMn matrix to its grain size.

  10. Exchange bias of Ni nanoparticles embedded in an antiferromagnetic IrMn matrix.

    PubMed

    Kuerbanjiang, Balati; Wiedwald, Ulf; Haering, Felix; Biskupek, Johannes; Kaiser, Ute; Ziemann, Paul; Herr, Ulrich

    2013-11-15

    The magnetic properties of Ni nanoparticles (Ni-NPs) embedded in an antiferromagnetic IrMn matrix were investigated. The Ni-NPs of 8.4 nm mean diameter were synthesized by inert gas aggregation. In a second processing step, the Ni-NPs were in situ embedded in IrMn films or SiOx films under ultrahigh vacuum (UHV) conditions. Findings showed that Ni-NPs embedded in IrMn have an exchange bias field HEB = 821 Oe at 10 K, and 50 Oe at 300 K. The extracted value of the exchange energy density is 0.06 mJ m(-2) at 10 K, which is in good accordance with the results from multilayered thin film systems. The Ni-NPs embedded in SiOx did not show exchange bias. As expected for this particle size, they are superparamagnetic at T = 300 K. A direct comparison of the Ni-NPs embedded in IrMn or SiOx reveals an increase of the blocking temperature from 210 K to around 400 K. The coercivity of the Ni-NPs exchange coupled to the IrMn matrix at 10 K is 8 times larger than the value for Ni-NPs embedded in SiOx. We studied time-dependent remanent magnetization at different temperatures. The relaxation behavior is described by a magnetic viscosity model which reflects a rather flat distribution of energy barriers. Furthermore, we investigated the effects of different field cooling processes on the magnetic properties of the embedded Ni-NPs. Exchange bias values fit to model calculations which correlate the contribution of the antiferromagnetic IrMn matrix to its grain size. PMID:24141385

  11. Enhancement of perpendicular magnetic anisotropy of Co layer in exchange-biased Au/Co/NiO/Au polycrystalline system

    NASA Astrophysics Data System (ADS)

    Kuświk, P.; Szymański, B.; Anastaziak, B.; Matczak, M.; Urbaniak, M.; Ehresmann, A.; Stobiecki, F.

    2016-06-01

    The perpendicular exchange bias in NiO(antiferromagnet)/Co(ferromagnet) polycrystalline layer films is studied. It is found that the NiO layer forces the Co layer magnetization to be oriented perpendicular to the film plane in a greater thickness range than is found in the Au/Co/Au system. Simultaneously, a large coercivity and a significant perpendicular exchange bias field were observed that are owing to the interlayer exchange bias coupling between NiO and Co, which supports the perpendicular magnetic anisotropy of the Co layer. These findings are confirmed by magnetometry and magnetoresistance measurements.

  12. 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,…

  13. 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.

  14. Controlled rotation of the exchange-bias direction in IrMn/Cu/Co via ion irradiation

    SciTech Connect

    Schafer, D.; Geshev, J.; Nicolodi, S.; Pereira, L. G.; Schmidt, J. E.; Grande, P. L.

    2008-07-28

    Co/Cu/IrMn films were irradiated with 40 keV He{sup +} ions varying the fluence and the current, with magnetic field applied at 120 deg. with respect to the original exchange-bias direction. The angular variations of the exchange-bias field of the irradiated samples were compared with those of the as-made and the thermally annealed films. Gradual deviation of the exchange-bias direction with the fluence increase was observed. Complete reorientation of the easy axes of both ferromagnet and antiferromagnet toward that of the field applied during irradiation was achieved for fluences higher than 1x10{sup 15} ions/cm{sup 2}, accompanied with a significant enhancement of the exchange-bias field.

  15. 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.

  16. 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.

  17. Magnetization reversal and exchange bias effects in hard/soft ferromagnetic bilayers with orthogonal anisotropies

    NASA Astrophysics Data System (ADS)

    Navas, D.; Torrejon, J.; Béron, F.; Redondo, C.; Batallan, F.; Toperverg, B. P.; Devishvili, A.; Sierra, B.; Castaño, F.; Pirota, K. R.; Ross, C. A.

    2012-11-01

    The magnetization reversal processes are discussed for exchange-coupled ferromagnetic hard/soft bilayers made from Co0.66Cr0.22Pt0.12 (10 and 20 nm)/Ni (from 0 to 40 nm) films with out-of-plane and in-plane magnetic easy axes respectively, based on room temperature hysteresis loops and first-order reversal curve analysis. On increasing the Ni layer thicknesses, the easy axis of the bilayer reorients from out-of-plane to in-plane. An exchange bias effect, consisting of a shift of the in-plane minor hysteresis loops along the field axis, was observed at room temperature after in-plane saturation. This effect was associated with specific ferromagnetic domain configurations experimentally determined by polarized neutron reflectivity. On the other hand, perpendicular exchange bias effect was revealed from the out-of-plane hysteresis loops and it was attributed to residual domains in the magnetically hard layer.

  18. 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.

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

    DOE PAGESBeta

    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

  20. 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

  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. 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.

  3. Exchange-bias reversal in magnetically compensated ErFe O3 single crystal

    NASA Astrophysics Data System (ADS)

    Fita, I.; Wisniewski, A.; Puzniak, R.; Markovich, V.; Gorodetsky, G.

    2016-05-01

    An exchange-bias (EB) effect observed in single crystal ErFe O3 compensated ferrimagnet, exhibiting the EB field HEB increasing and diverging upon approaching compensation temperature Tcomp=45 K , and changing sign with crossing Tcomp, is reported. The EB sign may be changed to the opposite one by varying the field-cooling protocol, depending on whether Tcomp is crossed with decreasing or increasing temperature. Namely, a different EB sign with the same | HEB| and coercive field HC values is obtained approaching a given T with increasing and decreasing temperature and the HEB(T ) dependence completed in one way is a mirror image of that completed in another way.

  4. Recent advances in exchange bias of layered magnetic FM/AFM systems

    NASA Astrophysics Data System (ADS)

    Liu, ZhongYuan

    2013-01-01

    The exchange bias (EB) has been investigated in magnetic materials with the ferromagnetic (FM)/antiferromagnetic (AFM) contacting interfaces for more than half a century. To date, the significant progress has been made in the layered magnetic FM/AFM thin film systems. EB mechanisms have shown substantive research advances. Here some of the new advances are introduced and discussed with the emphasis on the influence of AFM layer, the interlayer EB coupling across nonmagnetic spacer, and the interlayer coupling across AFM layer, as well as EB related to multiferrioc materials and electrical control.

  5. Tunable misalignment of ferromagnetic and antiferromagnetic easy axes in exchange biased bilayers

    NASA Astrophysics Data System (ADS)

    Rodríguez-Suárez, R. L.; Vilela-Leão, L. H.; Bueno, T.; Mendes, J. B. S.; Landeros, P.; Rezende, S. M.; Azevedo, A.

    2012-06-01

    In this paper we report experiments that show how to tune the unidirectional anisotropy field in exchange biased Ni81Fe19/Ir20Mn80 bilayers grown by sputtering. During growth the samples are held in an obliquely inclined stage, and simultaneously a static magnetic field is applied along an arbitrary direction in the film plane. While the direction of the ferromagnetic anisotropy field is given by the tilted columnar microstructures induced by the oblique sputtering, the direction of the unidirectional field can be tuned by the application of the in situ magnetic field. The magnetic properties were investigated using the ferromagnetic resonance technique.

  6. On the controversial measurements of the exchange-bias field in magnetic bilayers

    NASA Astrophysics Data System (ADS)

    Rodríguez-Suárez, R. L.; Vilela Leão, L. H.; Aguiar, F. M.; Rezende, S. M.; Azevedo, A.

    2004-05-01

    The ferromagnetic/antiferromagnetic interface has been characterized in several exchange-biased bilayers, by field dependent AC-susceptibility. The uniaxial ( HU) and unidirectional ( HE) anisotropy field values have been compared with those obtained by ferromagnetic resonance and DC-magnetometry. The measurements of HE and HU in all of the analyzed samples gave values that are consistently lower when measured by FMR than those obtained by AC- and DC-magnetometry. We assume that the discrepant values might be well explained by the coupling dependence of the unstable AF grains at the interface.

  7. On the exchange bias effect in NiO nanoparticles with a core(antiferromagnetic)/shell (spin glass) morphology

    NASA Astrophysics Data System (ADS)

    Rinaldi-Montes, N.; Gorria, P.; Martínez-Blanco, D.; Fuertes, A. B.; Fernández Barquín, L.; Rodríguez Fernández, J.; de Pedro, I.; Fdez-Gubieda, M. L.; Alonso, J.; Olivi, L.; Aquilanti, G.; Puente-Orench, I.; Blanco, J. A.

    2015-11-01

    The unexpected appearance of magnetic hysteresis and exchange bias effects in nominally antiferromagnetic NiO nanoparticles is usually explained in terms of a core/shell morphology, where a spin glass-like shell is exchange coupled to an antiferromagnetic core. However, recent studies have challenged the validity of this assumption for small enough NiO nanoparticles. In this work we present proof of the core/shell model for NiO nanoparticles with sizes below 10 nm by combining neutron powder diffraction and magnetic measurements. In addition, we have verified that the exchange bias effect persists even when the particle size is reduced down to 4 nm.

  8. 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

  9. NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure

    SciTech Connect

    Mlynczak, E.; Luches, P.

    2013-06-21

    The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Moessbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using {sup 57}Fe-CEMS. An iron oxide phase (Fe{sup 3+}{sub 4}Fe{sup 2+}{sub 1}O{sub 7}), as thick as 31 A, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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, NiS2 nanoparticles obtained at 400 °C. As the temperature is increased, nanoparticles of phases with lesser sulphur content, NiS (600 °C) and Ni3S2 (800 °C) are formed. NiS2 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, Ni3S2 nanoparticles exhibit very weak temperature dependent magnetization. Electrical measurements show that both NiS2 and NiS are semiconductors whereas Ni3S2 is a metal.

  11. 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

  12. 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

  13. 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).

  14. The formation mechanism of 360° domain walls in exchange-biased polycrystalline ferromagnetic films

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    The formation mechanism of 360° domain walls (360DW) created in an exchange-biased bilayer of Co65.5Fe14.5B20/Ir22Mn78 is described. The structural and magnetic properties are experimentally characterized and incorporated into a micromagnetic model of exchange-bias for granular anti-ferromagnetic films. This model is used to study and explain the formation mechanism of 360DWs in the ferromagnetic layer, which occur due to interface coupling to the antiferromagnetic layer. The validity of the resulting calculated magnetization maps are examined by comparing simulated and experimental Fresnel-contrast images of the bilayer. Energy barrier simulations are used to explain the dependence of the areal size and spatial frequency of the 360DW on the anisotropy energy of the anti-ferromagnetic layer. These calculations also show how such structures can form at room temperature at relatively low applied magnetic fields. Calculations based on this model are in agreement with imaging using Lorentz transmission electron microscopy and the measured macro-magnetic properties.

  15. Free energy surface of an intrinsically disordered protein: comparison between temperature replica exchange molecular dynamics and bias-exchange metadynamics.

    PubMed

    Zerze, Gül H; Miller, Cayla M; Granata, Daniele; Mittal, Jeetain

    2015-06-01

    Intrinsically disordered proteins (IDPs), which are expected to be largely unstructured under physiological conditions, make up a large fraction of eukaryotic proteins. Molecular dynamics simulations have been utilized to probe structural characteristics of these proteins, which are not always easily accessible to experiments. However, exploration of the conformational space by brute force molecular dynamics simulations is often limited by short time scales. Present literature provides a number of enhanced sampling methods to explore protein conformational space in molecular simulations more efficiently. In this work, we present a comparison of two enhanced sampling methods: temperature replica exchange molecular dynamics and bias exchange metadynamics. By investigating both the free energy landscape as a function of pertinent order parameters and the per-residue secondary structures of an IDP, namely, human islet amyloid polypeptide, we found that the two methods yield similar results as expected. We also highlight the practical difference between the two methods by describing the path that we followed to obtain both sets of data. PMID:26575570

  16. 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.

  17. Electrical Pulse Modification and Reversal of the Exchange-Bias in Magnetic Tunnel Junction Structures

    NASA Astrophysics Data System (ADS)

    Li, Yun; Tseng, Hsin-Wei; Ralph, Dan; Buhrman, Robert

    2010-03-01

    The use of antiferromagnetic layers to exchange-bias (EB) the reference layer is common in spin-torque (ST) experiments. Previous work has shown that the EB in both MTJs and spin valves can be degraded or reversed by electrical pulses, with the effect being attributed to heating or possibly to ST effects in the spin valve case. We have studied EB modification due to individual electrical pulses in the presence of a small external field (<50Oe) in FeCoB/MgO/FeCoB/IrMn MTJs as a function of MgO thickness. For MgO thickness = 1.7 nm, RA = 5 x 10^3φμm^2, pulses with Jc = 4 x 10^4A/cm^2 and V = 1.8 V, can repeatedly and reliably reverse the EB. For 1.3 nm barriers, RA =150φμm^2, much higher power pulses, Jc = 6 x 10^5A/cm^2 and V = 0.9 V, are required for reversal. Such results indicate that a combination of heating and ST, with the latter possibly involving the field-like spin torque component at high bias, is responsible for EB reversal in our MTJs. We will discuss the details of the EB reversal behavior and report the phase diagram for reversal as function of electrical and field bias.

  18. 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

  19. 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.

  20. Perpendicular exchange bias behaviors of CoPt/IrMn and CoPt/FeMn bilayers: A comparative study

    SciTech Connect

    Tsai, C. Y.; Lin, K. F.; Hsu, Jen-Hwa

    2015-05-07

    In this study, FeMn was introduced as an antiferromagnetic (AFM) layer to couple with a single-layered Co{sub 49}Pt{sub 51} alloy thin film, and it was compared with a Co{sub 49}Pt{sub 51}/IrMn bilayer system in exchange bias (EB) effect, to explore the mechanism of spontaneous perpendicular exchange bias (PEB), which has been recently observed in CoPt/IrMn bilayers. Bilayers of CoPt/IrMn and CoPt/FeMn were prepared under the same conditions by sputtering at room temperature without any inducing field. Although PEB was observed in as-grown CoPt/FeMn bilayers, the loop shape and PEB behavior were found to exhibit different characteristics from those of CoPt/IrMn bilayers. The CoPt (5 nm)/FeMn (10 nm) bilayer has a sheared loop that is similar to a double-shifted loop and a much lower squareness ratio (SQR = 0.52) and exchange bias field (H{sub e} = 180 Oe) than the CoPt (5 nm)/IrMn (10 nm) system, which has a rectangular loop shape and a high SQR of 0.97 and large H{sub e} of 290 Oe. The two systems present entirely different dependences of PEB on the thickness of the AFM layer. CoPt/IrMn exhibits behavior that is typical of most EB systems, but for CoPt/FeMn, this dependence is more complicated with an unusual peak at an AFM layer thickness of 10 nm. Based on the dissimilar loop shapes and dependences of PEB on AFM thickness, the mechanisms of the spontaneously established PEB in these two systems are considered to differ. Investigations of cross-sectional transmission electron microscopy revealed no apparent difference between the interfacial microstructures of the two systems. X-ray diffraction studies demonstrated the 〈111〉 texture of both systems. Therefore, different interfacial spin configurations may be responsible for the dissimilar PEB behaviors in these two FM/AFM bilayer systems.

  1. Exchange bias and antiferromagnetic interfacial exchange coupling in the mixed-spin oxide Li2/7Ni5/7O

    NASA Astrophysics Data System (ADS)

    Shi, C. X.; Ren, W. J.; Liu, W.; Zhang, Z. D.

    2014-01-01

    We present a detailed study on magnetic properties of mixed spin oxide Li2/7Ni5/7O, where small ferromagnetic (FM) clusters (with averaged diameter of ˜18 Å) immersed with an antiferromagnetic (AFM) host. The exchange bias (EB) with shifts of the hysteresis loop along both the field and magnetization axes is found, which is due to the interfacial interaction between the FM clusters and the AFM host. An AFM interfacial exchange coupling is deduced from the exchange interactions between Ni ions. The type and strength of this interfacial exchange interaction are discussed in terms of the EB at low temperature.

  2. Bridging exchange bias effect in NiO and Ni(core)@NiO(shell) nanoparticles

    NASA Astrophysics Data System (ADS)

    Rinaldi-Montes, Natalia; Gorria, Pedro; Martínez-Blanco, David; Fuertes, Antonio B.; Fernández Barquín, Luis; Puente-Orench, Inés; Blanco, Jesús A.

    2016-02-01

    Among all bi-magnetic core(transition metal)@shell(transition metal oxide) nanoparticles (NPs), Ni@NiO ones show an onset temperature for the exchange bias (EB) effect far below the Néel temperature of bulk antiferromagnetic NiO. In this framework, the role played by the magnetism of NiO at the nanoscale is investigated by comparing the microstructure and magnetic properties of NiO and Ni@NiO NPs. With the aim of bridging the two systems, the diameter of the NiO NPs (~4 nm) is chosen to be comparable to the shell thickness of Ni@NiO ones (~2 nm). The EB effect in Ni@NiO NPs is attributed to the exchange coupling between the core and the shell, with an interfacial exchange energy of ΔE~0.06 erg cm-2, thus comparable to previous reports on Ni/NiO interfaces both in thin film and NP morphologies. In contrast, the EB detected in NiO NPs is explained in a picture where uncompensated spins located on a magnetically disordered surface shell are exchange coupled to the antiferromagnetic core. In all the studied NPs, the variation of the EB field as a function of temperature is described according to a negative exponential law with a similar decay constant, yielding a vanishing EB effect around T~40-50 K. In addition, the onset temperature for the EB effect in both NiO and Ni@NiO NPs seems to follow a universal dependence with the NiO crystallite size.

  3. Magnetoelectric switching of perpendicular exchange bias in Pt/Co/α-Cr2O3/Pt stacked films

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We report the realization of magnetoelectric switching of the perpendicular exchange bias in Pt/Co/α-Cr2O3/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.

  4. Perpendicular exchange bias effect in sputter-deposited CoFe/IrMn bilayers

    SciTech Connect

    Chen, J. Y. Thiyagarajah, Naganivetha; Xu, H. J.; Coey, J. M. D.

    2014-04-14

    CoFe/IrMn bilayers with perpendicular magnetization for various IrMn layer thicknesses exhibit unusual two-step hysteresis loops with both positive and negative loop shifts. Observed at room temperature in the as-grown state, they provide direct evidence of large antiferromagnetic domain formation at the IrMn interface. The exchange bias field reaches 100 mT with an IrMn layer thickness of 4 nm after field annealing at 200 °C–300 °C in 800 mT, which is at least three times as large as the coercivity, and may be useful for reference layers of spin-valves or magnetic tunnel junctions with perpendicular magnetic anisotropy.

  5. Uniaxial spin-transfer torque in an exchange-biased spin valve.

    PubMed

    Xu, Jian-qing; Jin, Guojun

    2011-07-27

    We study the effects of uniaxial spin-transfer torque (USTT) on the ferromagnetic (F) as well as antiferromagnetic (AF) layers in an exchange-biased (EB) spin valve. By analytically treating the free-energy functional of the F/AF bilayer and numerically solving the Landau-Lifshitz-Gilbert equation for magnetic moments, we can reproduce and explain two existing experimental facts relevant to USTT: one is that the EB field can be reversed by both positive and negative pulsed currents, and the other is that the critical current to excite the F moments is greatly increased in the presence of an AF layer and independent of external fields. We also derive the angular dependence of the critical currents to excite AF and F moments, which suggests a possible way to quantitatively determine USTT in experiments. PMID:21727307

  6. 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.

  7. 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.

  8. Exchange bias in ferrite hollow nanoparticles originated by complex internal magnetic structure

    NASA Astrophysics Data System (ADS)

    De Biasi, Emilio; Lima, Enio, Jr.; Vargas, Jose M.; Zysler, Roberto D.; Arbiol, Jordi; Ibarra, Alfonso; Goya, Gerardo F.; Ibarra, M. Ricardo

    2015-10-01

    Iron-oxide hollow nanospheres (HNS) may present unusual magnetic behavior as a consequence of their unique morphology. Here, we report the unusual magnetic behavior of HNS that are 9 nm in diameter. The magnetic properties of HNS originate in their complex magnetic structure, as evidenced by Mössbauer spectroscopy and magnetization measurements. We observe a bias in the hysteresis when measured at very low temperature in the field cooling protocol (10 kOe). In addition, dc (static) and ac (dynamic) magnetization measurements against temperature and applied field reveal a frustrated order of the system below 10 K. High-resolution transmission electron microscopy (HRTEM) studies reveal that the HNS are composed of small crystalline clusters of about 2 nm in diameter, which behave as individual magnetic entities. Micromagnetic simulations (using conjugate gradient in order to minimize the total energy of the system) reproduce the experimentally observed magnetic behavior. The model considers the hollow particles as constituted by small ordered clusters embedded in an antiferromagnetic environment (spins localized outside the clusters). In addition, the surface spins (in both inner and outer surfaces of the HNS) are affected by a local surface anisotropy. The strong effective magnetic anisotropy field of the clusters induces the bias observed when the system is cooled in the presence of a magnetic external field. This effect propagates through the exchange interaction into the entire particle.

  9. 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.

  10. A supramolecular aggregate of four exchange-biased single-molecule magnets.

    PubMed

    Nguyen, Tu N; Wernsdorfer, Wolfgang; Abboud, Khalil A; Christou, George

    2011-12-28

    The reaction between 3-phenyl-1,5-bis(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH(2)) and triangular [Mn(III)(3)O(O(2)CMe)(py)(3)](ClO(4)) (1) affords [Mn(12)O(4)(O(2)CMe)(12)(pdpd)(6))](ClO(4))(4) (3). Complex 3 has a rectangular shape and consists of four [Mn(III)(3)O](7+) triangular units linked covalently by the dioximate ligands into a supramolecular [Mn(3)](4) tetramer. Solid-state dc and ac magnetic susceptibility measurements revealed that [Mn(3)](4) contains four Mn(3) single-molecule magnets (SMMs), each with an S = 6 ground state. Magnetization versus dc-field sweeps on a single crystal gave hysteresis loops below 1 K that exhibited exchange-biased quantum tunneling of magnetization steps, confirming 3 to be a supramolecular aggregate of four weakly exchange-coupled SMM units. PMID:22136491

  11. 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.

  12. Correlations between coercivity and exchange bias in epitaxial NiO-Co(110) bilayers

    NASA Astrophysics Data System (ADS)

    Dubourg, S.; Bobo, J. F.; Ousset, J. C.; Warot, B.; Snoeck, E.

    2002-05-01

    We have sputtered epitaxial NiO-Co samples on MgO (110) substrates. NiO epitaxially grows on the isostructural fcc MgO substrate but, due to surface energy minimization, its surface morphology is saw-tooth-like with terraces aligned along [001] direction and either (100) or (010) termination planes. The obtained nanostructures are 80-200 Å wide facets with micron-size length. Subsequently deposited Co layers adopt a fcc structure conformal with the NiO nanofacets. It consists thus in a set of connected nanostripes as evidenced by complementary structural characterizations. Shape anisotropy induces a strong easy axis along the stripe edges [001] and a hard axis along the [-110] MgO direction. Magnetization loops recorded along [001] have a total squareness. Thermal treatments were done in zero field for investigating the NiO/Co exchange thermal stability and activation. We observed thermally assisted exchange bias field (HE) variations on 1000 Oe field treated samples for various temperatures between 300 K and 400 K. Similar experiments were also performed on polycrystalline bilayers for comparison. For all samples (polycrystalline and epitaxial), thermal treatments induce a HE raise with a kinetics related to the anneal temperature. However, while the coercive field HC of epitaxial samples is significantly reduced, one of the polycrystalline samples remains constant. The ferromagnetic domain wall pinning at antiferromagnetic antiphase boundaries explains both results.

  13. 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

  14. 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.

  15. 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

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

    DOE PAGESBeta

    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

  17. 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.

  18. 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.

  19. 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.

  20. Exchange Bias as a Probe of the Incommensurate Spin-Density Wave in Epitaxial Fe/Cr(001)

    NASA Astrophysics Data System (ADS)

    Parker, J. S.; Wang, L.; Steiner, K. A.; Crowell, P. A.; Leighton, C.

    2006-12-01

    We report clear multiple period oscillations in the temperature dependence of exchange bias in an Fe thin film exchange coupled to a neighboring Cr film. The oscillations arise due to an incommensurate spin-density wave in the Cr, with wave vector perpendicular to the Fe/Cr(001) interface. The exchange bias and coercivity allow for a determination of the extent of the thermally driven wavelength expansion, the (strain-suppressed) spin-flip transition temperature, and the Cr Néel temperature, which show a crossover from bulklike to finite-size behavior at a Cr thickness of ˜1100Å. The data are consistent with a transition from a transverse to longitudinal wave on cooling.

  1. Giant spontaneous exchange bias effect in Sm1.5Ca0.5CoMnO6 perovskite

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Sahoo, R. C.; Dasgupta, Papri; Poddar, A.; Nath, T. K.

    2016-04-01

    We report here on the enormously large value of the spontaneous exchange bias (SEB) of ~5.1 kOe in the Sm1.5Ca0.5CoMnO6 bulk double perovskite system after zero-field cooling from an unmagnetized state. Depending on the path used for measuring the magnetic hysteresis loop, P-type or N-type, the EB field varies significantly. Dc and ac magnetization reveals a super-spin-glass-like (SSG) state below 19 K. The EB effect has been observed below the glassy transition temperature. The conventional exchange bias (CEB) as well as the SEB increase with a decrease in temperature and show monotonic variation. All these interesting features can be explained through the multimagnetic phase of double perovskite and the onset of unidirectional anisotropy driven by interface exchange coupling between the SSG, turned isothermally into a field-induced superferromagnetic shell and antiferromagnetic core.

  2. 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

    ... Care Act; Establishment of Exchanges and Qualified Health Plans; Proposed Rule, 76 FR 41866 (July 15...) Requirements Under the Patient Protection and Affordable Care Act; Interim Final Rule, 75 FR 74864, 74918-20... of the Patient Protection and Affordable Care Act and the Health Care and Education...

  3. 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.

  4. 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

  5. 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.

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

    PubMed

    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

  7. 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

  8. Probing boundary magnetization through exchange bias in heterostructures with competing anisotropy

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Binek, Christian

    2013-03-01

    Cr2O3 (chromia) is a magnetoelectric antiferromagnet with a bulk TN of 307 K. It has been utilized for electrically controlled exchange bias (EB) by taking advantage of voltage-controllable boundary magnetization (BM) occurring as a generic property in magnetoelectric single domain antiferromagnets.[2] In the perpendicular Cr2O3(0001)/CoPd EB system the EB-field shows an order parameter type T-dependence close to TN reflecting the T-dependence of the BM. At about 150 K a decrease of the EB-field sets in with decreasing temperature suggesting canting of the BM. To evidence this mechanism we use EB as a probe. Specifically, we investigate EB in Permalloy(5nm)/Cr2O3 (0001)(100nm) with Permalloy and chromia having competing anisotropies. We measure easy axis magnetic hysteresis loops via longitudinal magneto-optical Kerr effect for various temperatures after perpendicular and in-plane magnetic field-cooling. The T-dependence of the EB field supports the canting mechanism. In addition to the all thin film EB system, we explore a Permalloy(10nm)/Cr2O3(0001 single crystal) heterostructure where magnetoelectric annealing allows selecting Cr2O3 single domain states. Here the effect of T-dependent canting of the BM is compared with findings in the complementary perpendicular EB system. Financial support by NSF through MRSEC and the Nanoelectronic Research Initiative.

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

    NASA Astrophysics Data System (ADS)

    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 108 to 107 A cm-2. In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 × 106 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.

  10. Modeling of exchange bias in the antiferromagnetic (core)/ferromagnetic (shell) nanoparticles with specialized shapes

    NASA Astrophysics Data System (ADS)

    Hu, Yong; Liu, Yan; Du, An

    2011-11-01

    Zero-field-cooled (ZFC) and field-cooled (FC) hysteresis loops of egg- and ellipsoid-shaped nanoparticles with inverted ferromagnetic (FM)-antiferromagnetic (AFM) core-shell morphologies are simulated using a modified Monte Carlo method, which takes into account both the thermal fluctuations and energy barriers during the rotation of spin. Pronounced exchange bias (EB) fields and reduced coercivities are obtained in the FC hysteresis loops. The analysis of the microscopic spin configurations allows us to conclude that the magnetization reversal occurs by means of the nucleation process during both the ZFC and FC hysteresis branches. The nucleation takes place in the form of "sparks" resulting from the energy competition and the morphology of the nanoparticle. The appearance of EB in the FC hysteresis loops is only dependent on that the movements of "sparks" driven by magnetic field at both branches of hysteresis loops are not along the same axis, which is independent of the strength of AFM anisotropy. The tilt of "spark" movement with respect to the symmetric axis implies the existence of additional unidirectional anisotropy at the AFM/FM interfaces as a consequence of the surplus magnetization in the AFM core, which is the commonly accepted origin of EB. Our simulations allow us to clarify the microscopic mechanisms of the observed EB behavior, not accessible in experiments.

  11. 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.

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

    PubMed

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

    2016-05-18

    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. PMID:27092595

  13. 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

  14. Cyanide Single-Molecule Magnets Exhibiting Solvent Dependent Reversible "On" and "Off" Exchange Bias Behavior.

    PubMed

    Pinkowicz, Dawid; Southerland, Heather I; Avendaño, Carolina; Prosvirin, Andrey; Sanders, Codi; Wernsdorfer, Wolfgang; Pedersen, Kasper S; Dreiser, Jan; Clérac, Rodolphe; Nehrkorn, Joscha; Simeoni, Giovanna G; Schnegg, Alexander; Holldack, Karsten; Dunbar, Kim R

    2015-11-18

    The syntheses, structures, and magnetic properties of four new complex salts, (PPN){[Mn(III)(salphen)(MeOH)]2[M(III)(CN)6]}·7MeOH (Mn2M·7MeOH) (M = Fe, Ru, Os and Co; PPN(+) = bis(triphenylphosphoranylidene)ammonium cation; H2salphen = N,N'-bis(salicylidene)-1,2-diaminobenzene), and a mixed metal Co/Os analogue (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH were undertaken. It was found that all compounds exhibit switchable single-molecule magnet (SMM) and exchange-bias behavior depending on the interstitial methanol content. The pristine (PPN){[Mn(salphen)(MeOH)]2[Os(CN)6]}·7MeOH (Mn2Os·7MeOH) behaves as an SMM with an effective barrier for the magnetization reversal, (Ueff/kB), of 17.1 K. Upon desolvation, Mn2Os exhibits an increase of Ueff/kB to 42.0 K and an opening of the hysteresis loop observable at 1.8 K. Mn2Os·7MeOH shows also exchange-bias behavior with magnetic hysteresis loops exhibiting a shift in the quantum tunneling to 0.25 T from zero-field. The Fe(III) and Ru(III) analogues were prepared as reference compounds for assessing the effect of the 5d versus 4d and 3d metal ions on the SMM properties. These compounds are also SMMs and exhibit similar effects but with lower energy barriers. These findings underscore the importance of introducing heavy transition elements into SMMs to improve their slow relaxation of the magnetization properties. The (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)(CN)6]}·7MeOH (Mn2Co·7MeOH) analogue with a diamagnetic Co(III) central atom and the mixed Co/Os (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH (Mn2Co/Os·7MeOH) "magnetically diluted" system with a 9:1 Co/Os metal ratio were prepared in order to further probe the nature of the energy barrier increase upon desolvation of Mn2Os. In addition, inelastic neutron scattering and frequency-domain Fourier-transform THz electron paramagnetic resonance spectra obtained on Mn2Os·7MeOH and Mn2Os in combination with the magnetic data

  15. 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

  16. Switching of perpendicular exchange bias in Pt/Co/Pt/α-Cr2O3/Pt layered structure using magneto-electric effect

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Switching of the perpendicular exchange bias polarity using a magneto-electric (ME) effect of α-Cr2O3 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.

  17. 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.

  18. 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.

  19. Effect of the exchange bias on the magnetization hysteresis of a ferromagnetic film in contact with an antiferromagnet

    NASA Astrophysics Data System (ADS)

    Grechnev, A. G.; Kovalev, A. S.; Pankratova, M. L.

    2013-12-01

    The transformation of the hysteretic field dependence of the magnetization of a ferromagnetic thin layer in contact with a magnetically hard antiferromagnet is considered. It is shown that this interaction leads to a shift of the hysteresis loop from the configuration symmetric with respect to magnetic field (exchange bias). Furthermore, upon increasing the magnitude of the exchange interaction, within a narrow range of the magnitudes, there occurs a qualitative change in the hysteresis loop shape and its subsequent disappearance; hence the field dependence of the magnetization becomes monotonous and single-valued.

  20. Thermal Decay and Reversal of Exchange Bias Field of CoFe/PtMn Bilayer after Ga+ Irradiation

    NASA Astrophysics Data System (ADS)

    Zhou, Guang-Hong; Zhu, Yu-Fu; Lin, Yue-Bin

    2011-05-01

    An applied field is used to perform Ga+ ion irradiation on a CoFe/PtMn bilayer. Effects of the applied field and energy transfer between Ga+ ions and antiferromagnetic (AFM) atoms on the exchange bias field Hex are investigated. A partially reversed Hex is found in CoFe/PtMn specimens irradiated at a dose of 1 × 1014 ions/cm2 with an applied field anti-parallel to the original exchange bias direction. We believe that the rapid energy transfer and local temperature increase originating from the interaction between Ga+ ions and AFM atoms result in spin reversal and the formation of reversed AFM domains when specimens are irradiated with anti-parallel fields. The decrease in Hex when annealing the film in a negative saturation field indicates a thermal decay process. The AFM moments are reversed by thermal activation over an energy barrier distribution, which may change in some way as the temperature increases.

  1. Compensation temperatures and exchange bias in La1.5Ca0.5CoIrO6

    NASA Astrophysics Data System (ADS)

    Coutrim, L. T.; Bittar, E. M.; Stavale, F.; Garcia, F.; Baggio-Saitovitch, E.; Abbate, M.; Mossanek, R. J. O.; Martins, H. P.; Tobia, D.; Pagliuso, P. G.; Bufaiçal, L.

    2016-05-01

    We report on the study of magnetic properties of the La1.5Ca0.5CoIrO6 double perovskite. Via ac magnetic susceptibility we have observed evidence of weak ferromagnetism and reentrant spin glass behavior on an antiferromagnetic matrix. Regarding the magnetic behavior as a function of temperature, we have found that the material displays up to three inversions of its magnetization, depending on the appropriate choice of the applied magnetic field. At low temperature, the material exhibits exchange bias effect when it is cooled in the presence of a magnetic field. Also, our results indicate that this effect may be observed even when the system is cooled at zero field. Supported by other measurements and also by electronic structure calculations, we discuss the magnetic reversals and spontaneous exchange bias effect in terms of magnetic phase separation and magnetic frustration of Ir4 + ions located between the antiferromagnetically coupled Co ions.

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

    DOE PAGESBeta

    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. The effect of interface roughness on exchange bias in La0.7Sr0.3MnO3-BiFeO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Vafaee, Mehran; Finizio, Simone; Deniz, Hakan; Hesse, Dietrich; Zabel, Hartmut; Jakob, Gerhard; Kläui, Mathias

    2016-02-01

    We characterized the interfaces of heterostructures with different stack sequences of La0.7Sr0.3MnO3/BiFeO3 (LSMO/BFO) and BFO/LSMO using TEM revealing sharp and rough interfaces, respectively. Magnetometry and magnetoresistance measurements do not show a detectable exchange bias coupling for the multistack with sharp interface. Instead, the heterostructures with rough and chemically intermixed interfaces exhibit a sizable exchange bias coupling. Furthermore, we find a temperature-dependent irreversible magnetization behavior and an exponential decay of coercive and exchange bias fields with temperature suggesting a possible spin-glass-like state at the interface of both stacks.

  5. 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.

  6. 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

  7. High-Temperature Regeneration of Perpendicular Exchange Bias in a Pt/Co/Pt/α-Cr2O3/Pt Thin Film System

    NASA Astrophysics Data System (ADS)

    Shiratsuchi, Yu; Takechi, Yuichiro; Toyoki, Kentaro; Nakano, Yuuta; Onoue, Satoshi; Mitsumata, Chiharu; Nakatani, Ryoichi

    2013-12-01

    We found the regeneration of perpendicular exchange bias at high temperature in the Pt-capping/Co/Pt-spacer/α-Cr2O3/Pt-buffer thin film with an ultrathin (0.2 nm) Pt-spacer layer after the disappearance at low temperature. Abrupt changes in the coercivity accompany the abrupt disappearance and regeneration of exchange bias. The direction of the regenerated exchange bias could be reversed by altering the ferromagnetic spin orientation during temperature rise. The exchange bias did not regenerate when the Pt spacer layer was grown at a slow growth rate, suggesting that the growth mode of Pt on the α-Cr2O3 layer affects the regeneration feature.

  8. 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.

  9. Coexistence of perpendicular and in-plane exchange bias using a single ferromagnetic layer in Pt/Co/Cr/CoO thin film

    NASA Astrophysics Data System (ADS)

    Öztürk, Mustafa; Demirci, Erdem; Erkovan, Mustafa; Öztürk, Osman; Akdoğan, Numan

    2016-04-01

    We studied the temperature dependence of magnetization and exchange bias in a Pt/Co/Cr/CoO multilayer thin film. These magnetic multilayers are of particular interest since the easy axis of ultra-thin Co is strongly affected by the interfacial anisotropies of neighbouring Pt and Cr layers. The room temperature measurements show that the sample has a magnetic easy axis only in the film plane. However, upon cooling the sample, the easy axis of the magnetization departs from its initial orientation and typical easy-axis hysteresis loops are obtained for both in-plane and perpendicular directions. In accordance with this change in the magnetization direction at lower temperatures, the sample shows an unexpected coexistence of perpendicular and in-plane exchange bias below the antiferromagnetic transition of CoO. The temperature dependence of the exchange bias field for both directions is also significantly different. Along the film plane, the exchange bias field monotonically decreases and disappears at 220 K with increasing temperature. For the perpendicular direction, however, the exchange bias field increases and reaches a maximum value at 80 K. Then it decreases and disappears at 150 K with further increasing temperature. The mechanisms behind this anomalous temperature dependence of the exchange bias as well as the step-like behaviour in the hysteresis curves are discussed.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    Patterned hard-soft 2D magnetic lateral composites have been fabricated by e-beam lithography plus dry etching techniques on sputter-deposited NdCo5 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.

  16. 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.

  17. Unravelling the tunable exchange bias-like effect in magnetostatically-coupled two dimensional hybrid (hard/soft) composites

    NASA Astrophysics Data System (ADS)

    Hierro-Rodriguez, A.; Teixeira, J. M.; Rodriguez-Rodriguez, G.; Rubio, H.; Vélez, M.; Álvarez-Prado, L. M.; Martín, J. I.; Alameda, J. M.

    2015-06-01

    Hybrid 2D hard-soft composites have been fabricated by combining soft (Co73Si27) and hard (NdCo5) magnetic materials with in-plane and out-of-plane magnetic anisotropies, respectively. They have been microstructured in a square lattice of CoSi anti-dots with NdCo dots within the holes. The magnetic properties of the dots allow us to introduce a magnetostatic stray field that can be controlled in direction and sense by their last saturating magnetic field. The magnetostatic interactions between dot and anti-dot layers induce a completely tunable exchange bias-like shift in the system’s hysteresis loops. Two different regimes for this shift are present depending on the lattice parameter of the microstructures. For large parameters, dipolar magnetostatic decay is observed, while for the smaller one, the interaction between the adjacent anti-dot’s characteristic closure domain structures enhances the exchange bias-like effect as clarified by micromagnetic simulations.

  18. 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.

  19. 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

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

    DOE PAGESBeta

    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.

  2. Quantifying biases in non-steady state chamber measurements of soil-atmosphere gas exchange

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Limitations of non-steady state (NSS) chamber methods for determining soil-to-atmosphere trace gas exchange rates have been recognized for several decades. Of these limitations, the so-called “chamber effect” is one of the most challenging to overcome. The chamber effect can be defined as the inhere...

  3. Epitaxial Growth of Intermetallic MnPt Films on Oxides and Large Exchange Bias.

    PubMed

    Liu, Zhiqi; Biegalski, Michael D; Hsu, Shang-Lin; Shang, Shunli; Marker, Cassie; Liu, Jian; Li, Li; Fan, Lisha; Meyer, Tricia L; Wong, Anthony T; Nichols, John A; Chen, Deyang; You, Long; Chen, Zuhuang; Wang, Kai; Wang, Kevin; Ward, Thomas Z; Gai, Zheng; Lee, Ho Nyung; Sefat, Athena S; Lauter, Valeria; Liu, Zi-Kui; Christen, Hans M

    2016-01-01

    High-quality epitaxial growth of inter-metallic 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. Moreover, highly ordered antiferromagnetic MnPt films exhibit superiorly large exchange coupling with a ferromagnetic layer. PMID:26539758

  4. 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

  5. Enhanced Anion Exchange for Selective Sulfate Extraction: Overcoming the Hofmeister Bias

    SciTech Connect

    Fowler, Christopher J; Haverlock, Tamara; Moyer, Bruce A; Shriver, James A.; Gross, Mr. Dustin E.; Marquez, Manuel; Sessler, Jonathan L.; Hossain, Alamgir; Bowman-James, Kristin

    2008-01-01

    Synergism in liquid-liquid extraction, typified by the combination of a neutral extractant with a cation-exchanger to enhance selectively cation extraction strength, has been used and understood for over five decades.1 Surprisingly, analogous synergism in anion extraction has not yet been developed. In this Communication we present a simple way to achieve non-Hofmeister selectivity in liquid-liquid anion exchange by combining a synthetic hydrogen-bond-donating (HBD) anion receptor with a standard quaternary ammonium type extractant. Specifically, we show that the fluorinated calixpyrroles 1 and 22 and the tetraamide macrocycles 3 5,3 may be used to enhance the solvent extraction of sulfate from nitrate by Aliquat 336-nitrate (A336-nitrate).

  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. 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

  8. 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.

  9. Exchange bias and magnetic properties induced by intrinsic structural distortion in CaMn3O6 nanoribbons

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    Single-crystalline CaMn3O6 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 CaMn3O6 (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.

  10. Effect of antiferromagnetic layer thickness on exchange bias, training effect, and magnetotransport properties in ferromagnetic/antiferromagnetic antidot arrays

    SciTech Connect

    Gong, W. J.; Liu, W. Feng, J. N.; Zhang, Z. D.; Kim, D. S.; Choi, C. J.

    2014-04-07

    The effect of antiferromagnetic (AFM) layer on exchange bias (EB), training effect, and magnetotransport properties in ferromagnetic (FM) /AFM nanoscale antidot arrays and sheet films Ag(10 nm)/Co(8 nm)/NiO(t{sub NiO})/Ag(5 nm) at 10 K is studied. The AFM layer thickness dependence of the EB field shows a peak at t{sub NiO} = 2 nm that is explained by using the random field model. The misalignment of magnetic moments in the three-dimensional antidot arrays causes smaller decrease of EB field compared with that in the sheet films for training effect. The anomalous magnetotransport properties, in particular positive magnetoresistance (MR) for antidot arrays but negative MR for sheet films are found. The training effect and magnetotransport properties are strongly affected by the three-dimensional spin-alignment effects in the antidot arrays.

  11. Magnetization reversal in epitaxial exchange-biased IrMn/FeGa bilayers with anisotropy geometries controlled by oblique deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Yao; Zhan, Qingfeng; Zuo, Zhenghu; Yang, Huali; Zhang, Xiaoshan; Dai, Guohong; Liu, Yiwei; Yu, Ying; Wang, Jun; Wang, Baomin; Li, Run-Wei

    2015-05-01

    We fabricated epitaxial exchange biased (EB) IrMn/FeGa bilayers by oblique deposition and systematically investigated their magnetization reversal. Two different configurations with the uniaxial magnetic anisotropy Ku parallel and perpendicular to the unidirectional anisotropy Ke b were obtained by controlling the orientation of the incident FeGa beam during deposition. A large ratio of Ku/Ke b was obtained by obliquely depositing the FeGa layer to achieve a large Ku while reducing the IrMn thickness to obtain a small Ke b. Besides the previously reported square loops, conventional asymmetrically shaped loops, and one-sided and two-sided two-step loops, unusual asymmetrically shaped loops with a three-step magnetic transition for the descending branch and a two-step transition for the ascending branch and biased three-step loops were observed at various field orientations in the films of both IrMn (tIrMn=1.5 to 20 nm)/FeGa (10 nm) with Ku⊥ Ke b and IrMn (tIrMn≤2 nm)/FeGa (10 nm) with Ku|| Ke b . Considering the geometries of anisotropies, a model based on domain wall nucleation and propagation was employed to quantitatively describe the angular dependent behaviors of IrMn/FeGa bilayers. The biased three-step magnetic switching was predicted to take place when | Ku|> ɛ90°+Ke b , where ɛ90° is the 90° domain wall nucleation energy, and the EB leads to the appearance of the unusual asymmetrically shaped hysteresis loops.

  12. Exchange bias of spin valve structure with a top-pinned Co{sub 40}Fe{sub 40}B{sub 20}/IrMn

    SciTech Connect

    You, C. Y.; Furubayashi, T.; Takahashi, Y. K.; Goripati, H. S.; Hono, K.

    2008-07-07

    We have investigated the exchange bias of a directly top-pinned Co{sub 40}Fe{sub 40}B{sub 20}/IrMn structure. An exchange bias was realized on the as-deposited samples, in which Co{sub 40}Fe{sub 40}B{sub 20} exhibits a fully amorphous structure. A current-in-plane giant magnetoresistance effect was demonstrated on simple Ru/CoFeB/Cu/CoFeB/IrMn/Ru stacks prior to and after annealing. The amorphous CoFeB layer partially crystallized from the interface with a Cu spacer layer after annealed at 280 deg. C.

  13. 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

  14. 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.

  15. 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.

  16. Fast laser annealing induced exchange bias in poly-crystalline BiFeO3/Co bilayers

    NASA Astrophysics Data System (ADS)

    Zhang, Y. Q.; Ruan, X. Z.; Liu, B.; Xu, Z. Y.; Xu, Q. Y.; Shen, J. D.; Li, Q.; Wang, J.; You, B.; Tu, H. Q.; Gao, Y.; Zhang, W.; Xu, Y. B.; Du, J.

    2016-03-01

    The conventional field cooling process for antiferromagnetic/ferromagnetic bilayer system might strongly damage the interface of BiFeO3 (BFO) with metallic ferromagnetic layer, leading to significant deterioration of exchange bias (EB). In this paper, a field cooling process with fast laser annealing has been proposed and applied on polycrystalline-BFO/Co bilayers, which can effectively modify the EB. In those samples with obvious EB, it is found that the exchange field (HE) increases abruptly when the laser fluence rises to a critical value, and decreases when the laser fluence is large enough. On the other hand, in those samples with negligible HE, EB could be easily induced after field cooling with proper laser fluence. In addition, the sign of HE could also be changed, depending on the direction of the cooling field. In contrast, after field cooling by conventional heat treatment, EB could be neither induced nor enhanced. The feasibility of fast laser annealing accompanied with field cooling to enhance or induce EB in the BFO/Co bilayer can be understood by much less interfacial diffusion in comparison with conventional field cooling.

  17. 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

  18. 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. PMID:26222013

  19. 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.

  20. 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.

  1. Exchange bias induced by the fully strained La{sub 2/3}Ca{sub 1/3}MnO{sub 3} dead layers

    SciTech Connect

    Xie, Q. Y.; Wu, X. S.; Gao, J.; Jia, Q. J.

    2014-05-07

    A pure compressively strained La{sub 2/3}Ca{sub 1/3}MnO{sub 3} (LCMO) dead layer grown on (001)-oriented LaAlO{sub 3} substrate can show all the rich phenomenon of large bias field shift, coercive field enhancement, and high blocking temperature. The obtained exchange bias field (∼350 Oe) and the enhanced coercivity of about 1160 Oe at 5 K under 500 Oe cooling field are superior to that have been reported in LCMO-based ferromagnetic/antiferromagnetic superlattices or nanoscale systems. Our results clearly demonstrate that the inhomogeneous magnetic dead layer of LCMO can induce a strong exchange bias effect, which may be exploited as a very simple structure for spin-valve device application.

  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. 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.

  4. Establishing and Enriching School-Community Ties in Small Schools. Small Schools Network Information Exchange Number 6.

    ERIC Educational Resources Information Center

    Regional Laboratory for Educational Improvement of the Northeast & Islands, Andover, MA.

    This information packet contains 14 articles reprinted from various books and journals. Establishing and enriching school-community ties in small schools is the theme for this "Information Exchange Packet," the sixth in a series developed for Small Schools Network members. The articles and their authors are: "Skills in Building Support for…

  5. 41 CFR 301-72.300 - What procedures must we establish to collect unused, partially used, and exchanged tickets?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 41 Public Contracts and Property Management 4 2012-07-01 2012-07-01 false What procedures must we establish to collect unused, partially used, and exchanged tickets? 301-72.300 Section 301-72.300 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL ALLOWANCES AGENCY RESPONSIBILITIES...

  6. 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.

  7. 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.

  8. 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

    ... 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...

  9. 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}.

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

    DOE PAGESBeta

    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

  11. Folding of Trp-cage Mini Protein Using Temperature and Biasing Potential Replica—Exchange Molecular Dynamics Simulations

    PubMed Central

    Kannan, Srinivasaraghavan; Zacharias, Martin

    2009-01-01

    The folding process of the 20 residue Trp-cage mini-protein was investigated using standard temperature replica exchange molecular dynamics (T-RexMD) simulation and a biasing potential RexMD (BP-RexMD) method. In contrast to several conventional molecular dynamics simulations, both RexMD methods sampled conformations close to the native structure after 10–20 ns simulation time as the dominant conformational states. In contrast, to T-RexMD involving 16 replicas the BP-RexMD method achieved very similar sampling results with only five replicas. The result indicates that the BP-RexMD method is well suited to study folding processes of proteins at a significantly smaller computational cost, compared to T-RexMD. Both RexMD methods sampled not only similar final states but also agreed on the sampling of intermediate conformations during Trp-cage folding. The analysis of the sampled potential energy contributions indicated that Trp-cage folding is favored by both van der Waals and to a lesser degree electrostatic contributions. Folding does not introduce any significant sterical strain as reflected by similar energy distributions of bonded energy terms (bond length, bond angle and dihedral angle) of folded and unfolded Trp-cage structures. PMID:19399241

  12. Calculation of adsorption free energy for solute-surface interactions using biased replica-exchange molecular dynamics

    PubMed Central

    Wang, Feng; Stuart, Steven J.; Latour, Robert A.

    2009-01-01

    The adsorption behavior of a biomolecule, such as a peptide or protein, to a functionalized surface is of fundamental importance for a broad range of applications in biotechnology. The adsorption free energy for these types of interactions can be determined from a molecular dynamics simulation using the partitioning between adsorbed and nonadsorbed states, provided that sufficient sampling of both states is obtained. However, if interactions between the solute and the surface are strong, the solute will tend to be trapped near the surface during the simulation, thus preventing the adsorption free energy from being calculated by this method. This situation occurs even when using an advanced sampling algorithm such as replica-exchange molecular dynamics (REMD). In this paper, the authors demonstrate the fundamental basis of this problem using a model system consisting of one sodium ion (Na+) as the solute positioned over a surface functionalized with one negatively charged group (COO−) in explicit water. With this simple system, the authors show that sufficient sampling in the coordinate normal to the surface cannot be obtained by conventional REMD alone. The authors then present a method to overcome this problem through the use of an adaptive windowed-umbrella sampling technique to develop a biased-energy function that is combined with REMD. This approach provides an effective method for the calculation of adsorption free energy for solute-surface interactions. PMID:19768127

  13. 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.

  14. Negative magnetization and exchange bias in Y1 - x Prx CrO3 with (0>x>0.3)

    NASA Astrophysics Data System (ADS)

    Verdin, E.; Duran, A.; Morales, F.; Escudero, E.

    2015-03-01

    Rare earth orthochromites compounds with perovskite structure have attracted great interest because its potential applications as data storage and spintronic. We report studies of the crystalline structure, thermal, and magnetic properties performed in the compound Y1-xPrxCrO3with 0exchange bias and magnetization reversal when the magnetization-temperature (M-T) curves were measured in field cooled mode (FC). All those changes are attributed to the influence of the Dzialoshinskii-Moriya indirect interaction that we related to the octahedral distortion, because the Pr substitution affecting the Cr-O bond lengths. This work was partially supported by DGAPA-UNAM, IN103213, IN10014, CONACyT-Mexico, Project 129293, BISSNANO, and by the Institute of Sciences Project PICCO 11-7, Distrito Federal, Mexico.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

    .../exchange_q_and_a.pdf.pdf . II. Provisions of the Proposed Regulation and Analysis and Responses to Public... Request for Comment (the RFC) on August 3, 2010 (75 FR 45584) inviting the public to provide input.... Response: The term ``benefit year'' is defined only for the purposes of this regulation and does not...

  20. 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...

  1. Magnetoelastically induced perpendicular magnetic anisotropy and perpendicular exchange bias of CoO/CoPt multilayer films

    NASA Astrophysics Data System (ADS)

    Guo, Lei; Wang, Yue; Wang, Jian; Muraishi, Shinji; Sannomiya, Takumi; Nakamura, Yoshio; Shi, Ji

    2015-11-01

    The effects of magnetoelastically induced perpendicular magnetic anisotropy (PMA) on perpendicular exchange bias (PEB) have been studied in [CoO5nm/CoPt5nm]5 multilayer films. After deposition at room temperature, [CoO5nm/CoPt5nm]5 multilayer films were post-annealed at 100 °C, 250 °C, 300 °C and 375 °C for 3 h. In-plane tensile stress of CoPt layer was calculated by sin2 φ method, and we found it increased gradually upon annealing from 0.99 GPa (as-deposited) up to 3.02 GPa (300 °C-annealed). As to the magnetic property, significant enhancement of PMA was achieved in [CoO5nm/CoPt5nm]5 multilayer films after annealing due to the increase of CoPt layer in-plane tensile stress. With the enhancement of magnetoelastically induced PMA, great improvement of PEB was also achieved in [CoO5nm/CoPt5nm]5 multilayer films, which increased from 130 Oe (as-deposited) up to 1060 Oe (300 °C-annealed), showing the same change tendency as PMA and the strong correlation with CoPt layer in-plane tensile stress. We consider it is the increase of CoPt layer in-plane tensile stress that leads to the enhancement of CoPt layer PMA, which is favorable for the spins in CoPt layer aligning to a more perpendicular direction. And thus the enhanced PMA with more perpendicular spins alignment in CoPt layer results in the improved PEB in [CoO5nm/CoPt5nm]5 multilayer films through enhanced perpendicular spins coupling at CoO/CoPt interfaces.

  2. Reentrant spin-glass behavior and bipolar exchange-bias effect in "Sn" substituted cobalt-orthotitanate

    NASA Astrophysics Data System (ADS)

    Nayak, S.; Joshi, D. C.; Krautz, M.; Waske, A.; Eckert, J.; Thota, S.

    2016-01-01

    We report the co-existence of longitudinal ferrimagnetic behavior with Néel temperature TN ˜ 46.1 K and reentrant transverse spin-glass state at 44.05 K in Tin (Sn) doped cobalt-orthotitanate (Co2TiO4). The ferrimagnetic ordering is resulting from different magnetic moments of Co2+ on the A-sites (3.87 μB) and B-sites (5.069 μB). The magnetic compensation temperature (TCOMP) shifts from 31.74 K to 27.1 K when 40 at. % of "Sn4+" substitutes "Ti4+" at B-sites where the bulk-magnetization of two-sublattices balance each other. For T > TN, the dc-magnetic susceptibility (χdc = M/Hdc) fits well with the Néel's expression for the two-sublattice model with antiferromagnetic molecular field constants NBB ˜ 15.44, NAB ˜ 32.01, and NAA ˜ 20.88. The frequency dependence of ac-magnetic susceptibility χac data follows the Vogel-Fulcher law, and the power-law of critical slowing-down with "zν" = 6.01 suggests the existence of spin-clusters (where "z" and "ν" being dynamic critical-exponent and correlation length of critical-exponent, respectively). This system exhibits unusual hysteresis loops with large bipolar exchange-bias effect (HEB ˜ 13.6 kOe at 7 K) after zero-field cooling process from an un-magnetized state, and a dramatic collapse of remanence (MR) and coercive field (HC) across TCOMP. The possible origins of such anomalous characteristics were discussed.

  3. 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.

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

    PubMed

    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

  5. Exchange bias in two-step artificially grown one-dimensional hybrid Co-BiFeO3 core-shell nanostructures.

    PubMed

    Ali, S S; Li, W J; Javed, K; Shi, D W; Riaz, S; Zhai, G J; Han, X F

    2016-01-29

    One-dimensional core-shell nanostructures consisting of a ferromagnetic cobalt core and a multiferroic BiFeO3 (BFO) shell were fabricated by an artificial two-step methodology. The coupling between the ferromagnetic core and multiferroic shell manifests a significant exchange bias effect which gives a clear demonstration of the anti-ferromagnetic functionality of the BFO shell material. Exchange biases of 30 Oe and 60 Oe are observed at 300 K and at 5 K, respectively. Superparamagnetic contributions at lower temperatures play an important role in contributing to overall magnetic behavior. Dominant shape anisotropy causes parallel alignment of the easy magnetization axis along the axis of core-shell nanowires. A coherent mode of the magnetization reversal mechanism is observed by the angular dependence of coercivity (H c). This versatile two-step methodology can be employed to fabricate and investigate many other hybrid nanostructures leading to a vast scope of investigation for researchers. PMID:26656305

  6. 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.

  7. 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

  8. 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.

  9. Large coercivity and exchange bias in [Fe1-δ(FeO)δ]x(TiO2)1-x granular films

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    [Fe1-δ(FeO)δ]x(TiO2)1-x (0≤δ≤0.91, 0.34≤x≤0.54) granular films were fabricated by magnetron sputtering. Large coercivity (HC = 10.5 kOe) and exchange-bias-field (HE = 6.5 kOe) at 5 K were found in the film with δ =0.84 and x = 0.48. AC susceptibility measurements exhibit a frequency (f) dependent peak Tf in the in-phase susceptibility curve. The fitting of the relation of Tf vs f with both the Vogel-Fulcher law and critical slowing down theory indicate that the evident enhancement of the HC and HE 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.

  10. 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

  11. 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.

  12. 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

  13. Exchange bias in two-step artificially grown one-dimensional hybrid Co-BiFeO3 core-shell nanostructures

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    One-dimensional core-shell nanostructures consisting of a ferromagnetic cobalt core and a multiferroic BiFeO3 (BFO) shell were fabricated by an artificial two-step methodology. The coupling between the ferromagnetic core and multiferroic shell manifests a significant exchange bias effect which gives a clear demonstration of the anti-ferromagnetic functionality of the BFO shell material. Exchange biases of 30 Oe and 60 Oe are observed at 300 K and at 5 K, respectively. Superparamagnetic contributions at lower temperatures play an important role in contributing to overall magnetic behavior. Dominant shape anisotropy causes parallel alignment of the easy magnetization axis along the axis of core-shell nanowires. A coherent mode of the magnetization reversal mechanism is observed by the angular dependence of coercivity (H c). This versatile two-step methodology can be employed to fabricate and investigate many other hybrid nanostructures leading to a vast scope of investigation for researchers.

  14. 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.

  15. Origin of spin-glass and exchange bias in La1/3Sr2/3FeO3-γ nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    The structure and the magnetic properties of nanopowdered samples of La1/3Sr2/3FeO3-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 La1/3Sr2/3FeO3-γ are associated to compact Fe3+ 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.

  16. 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

  17. 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.

  18. Effect of the Pt buffer layer on perpendicular exchange bias based on collinear/non-collinear coupling in a Cr2O3/Co3Pt interface

    NASA Astrophysics Data System (ADS)

    Ashida, T.; Sato, Y.; Nozaki, T.; Sahashi, M.

    2013-05-01

    In this study, we fabricated a Cr2O3 (0001) film without and with a Pt buffer layer and investigated its effect on perpendicular exchange coupling in a Cr2O3/Co3Pt interface. The results showed that the exchange bias field (μ0Hex) and blocking temperature (TB) of a Cr2O3 film without and with Pt were very different. The Cr2O3 film without Pt had a lower μ0Hex of 176 Oe and a lower TB of 75 K, whereas that with Pt had a higher μ0Hex of 436 Oe and a higher TB of 150 K. We discussed this difference in μ0Hex and TB values based on collinear/non-collinear coupling in a ferromagnetic and antiferromagnetic interface using Meiklejohn and Bean's exchange anisotropy model.

  19. 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

  20. 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...

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  2. 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

  3. 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

  4. Soft X-ray ARPES investigation of the nickelate Fermi surface in exchange biased LaNiO3-LaMnO3 superlattices

    NASA Astrophysics Data System (ADS)

    Bruno, Flavio; McKeown Walker, S.; de la Torre, A.; Tamai, A.; Gibert, M.; Catalano, S.; Triscone, J.-M.; Wang, Z.; Bisti, F.; Strocov, V.; Baumberger, F.

    2015-03-01

    We investigate (111)-oriented superlattices consisting of paramagnetic LaNiO3 (LNO) and ferromagnetic LaMnO3 (LMO). The field dependence of the magnetization in these heterostructures was measured at 5 K after cooling the sample in the presence of a 0.4 T field. Surprisingly, a shift of 15 mT in the magnetization loop towards negative fields along the magnetic field axis was observed. If the same measurement is repeated in a (111) LMO thin film, no exchange bias is observed which implies that LNO is the driving force for the biasing effect exhibited by the heterostructures. Since LNO is a well-known paramagnetic material, the existence of exchange bias in the superlattices implies the existence of an interface-induced magnetic order. Here we use soft x-ray angle resolved photoemission spectroscopy -SX ARPES- to study the electronic band structure of LNO layers in these heterostructures. Due to the increase in photoelectron escape depth in the 500 - 1000 eV energy range, we are able to map the LNO Fermi surface below 7 u.c. of LMO. In this talk we will discuss the similarities and differences in the electronic structure between thin films of (111)-LNO and buried LNO-LMO interfaces.

  5. 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

  6. 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.

  7. Exchange bias in phase-segregated Nd2/3Ca1/3MnO3 as a function of temperature and cooling magnetic fields

    NASA Astrophysics Data System (ADS)

    Fertman, Elena; Dolya, Sergiy; Desnenko, Vladimir; Pozhar, L. A.; KajÅaková, Marcela; Feher, Alexander

    2014-05-01

    Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal magnetoresistance perovskite below the Curie temperature TC ˜ 70 K and attributed to an antiferromagnetic-ferromagnetic (FM) spontaneous phase segregated state of this compound. Field cooled magnetic hysteresis loops exhibit shifts toward negative direction of the magnetic field axis. The values of exchange field HEB and coercivity HC are found to be strongly dependent of temperature and strength of the cooling magnetic field Hcool. These effects are attributed to evolution of the FM phase content and a size of FM clusters. A contribution to the total magnetization of the system due to the FM phase has been evaluated. The exchange bias effect decreases with increasing temperature up to TC and vanishes above this temperature with disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of the compound manifests itself through a training effect also observed while studying EB in Nd2/3Ca1/3MnO3.

  8. Exchange bias identifies lamellar magnetism as the origin of the natural remanent magnetization in titanohematite with ilmenite exsolution from Modum, Norway

    NASA Astrophysics Data System (ADS)

    Fabian, Karl; McEnroe, Suzanne A.; Robinson, Peter; Shcherbakov, Valera P.

    2008-04-01

    Large and stable negative magnetic anomalies in southwestern Sweden, southern Norway, the Adirondacks, USA, and Quebec, Canada, are related to rock units with a magnetic fraction consisting primarily of ilmeno-hematite or hemo-ilmenite. It has been suggested that the unusual magnetic stability of these rocks results from lamellar magnetism. This is a type of magnetic remanence, carried by uncompensated magnetic layers at interfaces between nanoscale exsolution structures of antiferromagnetic (AFM) hematite and paramagnetic ilmenite. Here we present the first direct proof that this lamellar magnetism indeed is responsible for the natural remanent magnetization (NRM) of a rock from Modum, Norway. Our argument expands a previous observation, that, in mineral grains from this rock, the cooling of a positive-induced remanence from room temperature to 5 K - which is well below the ordering temperature of ilmenite (57 K) - leads to a large negative shift of the low-temperature (LT) hysteresis loop. This can only be explained by exchange bias due to exchange coupling across the hematite-ilmenite interfaces. In a different experiment, we now have cooled the original NRM of untreated grains to 5 K, and then measured the hysteresis loop. Again, in several separate grains we observed large shifts of the hysteresis curves. This shows that exchange bias develops also from the untreated NRM. This observation proves that the moments, which carry the NRM, also participate in the exchange coupling at the hematite-ilmenite interfaces. Therefore, the NRM is not carried by defect moments or stress-induced moments, which occur in normal bulk hematite. A closer look at the NRM-induced LT loops shows that exchange bias acts in both field directions, though one direction is clearly predominant. This observation can be interpreted as a frozen equilibrium of different proportions of oppositely directed lamellar moments, a key feature of the original lamellar magnetism hypothesis. We discuss

  9. 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

  10. 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

  11. Exchange bias in Ag/FeCo/Ag core/shell/shell nanoparticles due to partial oxidation of FeCo intermediate shell

    NASA Astrophysics Data System (ADS)

    Takahashi, Mari; Mohan, Priyank; Mott, Derrick M.; Maenosono, Shinya

    2016-03-01

    Recently we developed magnetic-plasmonic Ag/FeCo/Ag core/shell/shell nanoparticles for the purpose of biological applications. In these heterostructured nanoparticles, exchange bias is observed as a result of the formation of an interface between ferromagnetic FeCo and antiferromagnetic CoxFe1-xO due to the partial oxidation of the FeCo intermediate shell. In this study we thoroughly characterized the surface oxide layer of the FeCo shell by XPS, XRD and SQUID magnetometer.

  12. 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.

  13. Ab initio study of the intrinsic exchange bias at the SrRuO3/SrMnO3 interface

    SciTech Connect

    Dong, Shuai; Zhang, Qinfang; Yunoki, Seiji; Liu, J.-M.; Dagotto, Elbio R

    2011-01-01

    In a recent publication [S. Dong et al., Phys. Rev. Lett. 103, 127201 (2009)], two (related) mechanisms were proposed to understand the intrinsic exchange bias present in oxides heterostructures involving G-type antiferromagnetic perovskites. The first mechanism is driven by the Dzyaloshinskii-Moriya interaction, which is a spin-orbit coupling effect. The second is induced by the ferroelectric polarization, and it is only active in heterostructures involving multiferroics. Using the SrRuO3/SrMnO3 superlattice as a model system, density- functional calculations are here performed to verify the two proposals. This proof-of-principle calculation provides convincing evidence that qualitatively supports both proposals.

  14. 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, S. A.; Robinson, Peter; Miyajima, Nobuyoshi; Fabian, Karl; Dyar, Darby; Sklute, Elizabeth

    2016-04-01

    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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Anomalous coercivity enhancement with temperature and tunable exchange bias in Gd and Ti co-doped BiFeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Ahmmad, Bashir; Islam, M. Z.; Billah, Areef; Basith, M. A.

    2016-03-01

    We have investigated the effects of temperature on the magnetic properties of the Bi0.9Gd0.1Fe1-x Ti x O3 (x  =  0.00-0.20) multiferroic system. Unexpectedly, the coercive fields (H c ) of this multiferroic system increased with increasing temperature. The coercive fields and remanent magnetization were higher over a wide range of temperatures in sample x  =  0.10, i.e. in a sample with a composition Bi0.9Gd0.1Fe0.9Ti0.1O3 than those of x  =  0.00 and 0.20 compositions. Therefore, we carried out temperature-dependent magnetization experiments extensively for sample x  =  0.10. The magnetic hysteresis loops at different temperatures exhibit an asymmetric shift towards the magnetic field axes, which indicates the presence of an exchange bias effect in this material system. The hysteresis loops were also carried out at temperatures of 150 K and 250 K by cooling down the sample from 300 K in various cooling magnetic fields ({{H}\\text{cool}} ). The exchange bias field ({{H}\\text{EB}} ) values increased with {{H}\\text{cool}} and decreased with temperature. The {{H}\\text{EB}} values were tunable by field cooling at temperatures of up to 250 K.

  1. Intriguing photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates.

    PubMed

    Sung, Kil Dong; Lee, Tae Kwon; Jung, Jong Hoon

    2015-01-01

    To date, electric fields have been widely used to control the magnetic properties of BiFeO3-based antiferromagnet/ferromagnet heterostructures through application of an exchange bias. To extend the applicability of exchange bias, however, an alternative mechanism to electric fields is required. Here, we report the photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on an SrTiO3 substrate. Through an ex situ pulsed laser deposition technique, we successfully synthesized epitaxial BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates. By measuring magnetoresistance under light illumination, we investigated the effect of light illumination on resistance, exchange bias, and coercive field in BiFeO3/La2/3Sr1/3MnO3 thin films. After illumination of red and blue lights, the exchange bias was sharply reduced compared to that measured in the dark. With increasing light intensity, the exchange bias under red and blue lights initially decreased to zero and then appeared again. It is possible to reasonably explain these behaviors by considering photo-injection from SrTiO3 and the photo-conductivity of La2/3Sr1/3MnO3. This study may provide a fundamental understanding of the mechanism underlying photo-controlled exchange bias, which is significant for the development of new functional spintronic devices. PMID:25852417

  2. Exchange bias in sputtered FeNi/FeMn systems: Effect of short low-temperature heat treatments

    NASA Astrophysics Data System (ADS)

    Savin, Peter; Guzmán, Jorge; Lepalovskij, Vladimir; Svalov, Andrey; Kurlyandskaya, Galina; Asenjo, Agustina; Vas'kovskiy, Vladimir; Vazquez, Manuel

    2016-03-01

    Short (5 min) post-deposition thermal treatments under magnetic field at low temperature (up to 200 °C) performed in exchange-coupled FeNi(40 nm)/FeMn(20 nm) bilayer thin films prepared by magnetron sputtering are shown to be effective to significantly modify their exchange field (from around 40 Oe down to 27 Oe) between FeNi and FeMn layers. A similar exchange field decrease was observed for the first deposited FeNi layer of the FeNi(40 nm)/FeMn(20 nm)/FeNi(40 nm) trilayer films after the same thermal treatments. The exchange field value for the second FeNi layer was not substantially changed. The X-ray diffraction patterns indicates that such a heat treatment has no effect on the grain size and crystalline texture of the films, while atomic force microscope studies reveal an increase of the surface roughness after the treatment which is more noticeable in the case of the trilayer film. Analysis of the experimental results leads us to conclude that the variations of the exchange field after heat treatment are likely caused by a modification of interfacial roughness and/or interfacial magnetic structure, but unlikely by the changes in the microstructure and/or changes of composition of the antiferromagnetic FeMn layer.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. A study of spin-flipping in sputtered IrMn using Py-based exchange-biased spin-valves

    NASA Astrophysics Data System (ADS)

    Acharyya, R.; Nguyen, H. Y. T.; Pratt, W. P.; Bass, J.

    2011-04-01

    To study spin-flipping within the antiferromagnet IrMn, we extended prior current-perpendicular-to-plane giant magnetoresistance studies of Permalloy (Py)-based exchange-biased-spin-valves containing IrMn inserts to thicker IrMn layers—5 nm ≤ tIrMn ≤ 30 nm. Unexpectedly, AΔR = A(RAP - RP)—the difference in specific resistance between the antiparallel (AP) and parallel (P) magnetic states of the two Py layers—did not decrease with increasing tIrMn, for tIrMn ≥ 5 nm, but rather became constant to within our measuring uncertainty. This constant looks to be due mostly to a new, small magnetoresistance in thin Py layers. The constant complicates isolating the spin-diffusion length, lsfIrMn, in bulk IrMn, but lsfIrMn is probably short, ≤1 nm. Similar results were found with FeMn.

  9. 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.

  10. 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}.

  11. Optimization of magneto-resistive response of ion-irradiated exchange biased films through zigzag arrangement of magnetization

    SciTech Connect

    Trützschler, Julia; Sentosun, Kadir; McCord, Jeffrey; Langer, Manuel; Fassbender, Jürgen; Mönch, Ingolf; Mattheis, Roland

    2014-03-14

    Exchange coupled ferromagnetic-antiferromagnetic Ni{sub 81}Fe{sub 19}/Ir{sub 23}Mn{sub 77} films with a zigzag alignment of magnetization are prepared by local ion irradiation. The anisotropic magneto-resistive behavior of the magnetic thin film structures is correlated to the magnetic structure and modeled. A unique uniaxial field sensitivity along the net magnetization alignment is obtained through the orthogonally modulated and magnetic domain wall stabilized magnetic ground state. Controlling local thin film magnetization distributions and, thus, the overall magnetization response opens unique ways to tailor the magneto-resistive sensitivity of functional magnetic thin film devices.

  12. 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.

  13. 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.

  14. Pressure enhanced ferromagnetism and suppressed exchange bias in La0.9Ba0.1CoO3 cobaltite

    NASA Astrophysics Data System (ADS)

    Fita, I.; Puzniak, R.; Wisniewski, A.; Markovich, V.; Troyanchuk, I. O.; Pashkevich, Yu. G.

    2013-10-01

    Pressure effect on magnetic properties of La0.9Ba0.1CoO3 cobaltite, exhibiting the ferromagnetic (FM) cluster-glass behavior and exchange bias (EB) effect at low temperatures, was investigated up to 10 kbar. It was found that an applied pressure increases the temperature TCcl ≈ 190 K, below which the FM clusters appear, and enlarges the FM phase volume in the sample. Positive value of dTCcl/dP coefficient suggests a wide eg-electron bandwidth for Co ions sited inside the Ba-rich regions (FM clusters). The EB field HE increases sharply with decreasing temperature below the spin-glass (SG) like transition temperature Tf ≈ 38 K, in a consequence of the exchange coupling at the FM/SG interfaces. Applied pressure was found to suppress strongly the EB, in particular, HE reduces by a factor of ˜3 under pressure of 10 kbar at 30 K. It appears that under pressure, HE varies oppositely to the changes in FM phase volume that is very similar to the behavior observed for phase-separated FM/antiferromagnetic manganites. Overall, the pressure-induced diminution in HE is explained by considering an increase of the FM cluster size and by concomitant decrease of distance between clusters. The results show that for phase-separated FM/SG cobaltites, the EB effect may be controlled by external pressure.

  15. Spin dynamics and criteria for onset of exchange bias in superspin glass Fe/γ-Fe2O3 core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Chandra, Sayan; Khurshid, H.; Li, Wanfeng; Hadjipanayis, G. C.; Phan, M. H.; Srikanth, H.

    2012-07-01

    A detailed study is presented on Fe/γ-Fe2O3 core-shell structured nanoparticles (mean size ˜10 nm) to understand the spin dynamics of the core and shell independently and their role in triggering exchange bias (EB) phenomena. The particle dynamics critically slow down at Tg ˜ 68 K, below which they exhibit memory effect in field-cooled and zero-field-cooled protocols associated with a superspin glass state. The field dependence of mean blocking temperature fits the de Almeida-Thouless line and shows two different linear responses in the low and high field regimes corresponding to the core and shell, respectively. We show that the energy barrier distribution estimated from the temperature decay of isothermal remanent magnetization shows two maxima that mark the freezing temperatures of the core (Tf-cr ˜ 48 K) and shell (Tf-sh ˜ 21 K). Last, hysteresis measurements after field cooling reveal strong EB indicated by a loop shift associated with unidirectional anisotropy. The onset of EB is at 35 K when the ferromagnetic core is frozen and the moments in the ferrimagnetic shell begin to block, resulting in enhanced exchange coupling.

  16. Effect of exchange bias on the electrical resistivity of Pd doped NiMn thin films: Two-channel Kondo system

    NASA Astrophysics Data System (ADS)

    Öner, Y.; Kamer, O.; Ross, Joseph H.

    2006-12-01

    Electrical resistivity measurements have been carried out for both flash-evaporated reentrant spin glasses (RSGs) (Ni76-xPdx)Mn24 and Ni74.5Mn23.5Pd2, as well as Ni75Mn23Pd2, a pure SG. These measurements were carried out at temperatures down to 4K. We observed a very deep resistivity minimum at about 75K for Ni74Mn24Pd2. It was found previously [Öner et al., J. Appl. Phys. 89, 7044 (2001)] that this sample shows the largest coercivity and exchange unidirectional anisotropy among these films. In addition, magnetization measurements show that this takes place just on the border of the RSG such that it could be handled as a superparamagnetic sample. Previously it was assumed that the exchange bias created in the sample between the domains plays the dominant role in the resistivity minimum. On the other hand, in order to account for the temperature dependence of the resistivity below the minimum we have analyzed these data using the Kondo, two-channel Kondo, weak localization, and Cochrane models for structural disorder based on the Anderson mechanism. We have deduced that the two-channel Kondo model gives the best agreement with the data; a logarithmic temperature dependence Δρ(T )=βlog10(T/TK), was observed at the temperatures below Tf accompanied by a resistivity behavior Δρ(T )=ρ0m(0)(1-αT1/2), at lower temperatures. All parameters deduced from the fitting correlate consistently with the strength of the exchange anisotropy and coercivity in the RSG films, and thus provide a separate measure of the presence of antiferromagnetically coupled domains in these materials.

  17. Exchange bias of MnFe2O4@γFe2O3 and CoFe2O4@γFe2O3 core/shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Cabreira-Gomes, R.; G. Silva, F.; Aquino, R.; Bonville, P.; Tourinho, F. A.; Perzynski, R.; Depeyrot, J.

    2014-11-01

    We compare here exchange bias (EB) properties of chemically synthesized core-shell nanoparticles (NPs), based either on a core of soft ferrite (MnFe2O4) or hard ferrite (CoFe2O4) protected by a maghemite shell (γ-Fe2O3). These NPs dispersed in acidic solutions are electrostatically stabilized, yielding to stable colloidal dispersions with a strong interparticle repulsion and negligible dipolar interactions in the probed range of temperatures. Field cooled (FC) magnetic hysteresis loops of non-textured frozen dispersions (with magnetic anisotropy axis of NPs distributed at random) and those of a powder based on the same NPs present a shift along the H-axis, expressing the coupling between the spin-ordered cores and the disordered surface layer of the NPs. The bias field is found to present a maximum, larger for NPs based on harder ferrite core. It is obtained for a cooling field of the order of one half of the anisotropy field, which is much larger for the CoFe2O4 cores than for MnFe2O4 ones. In powders, particles are in contact leading to an interparticle exchange which is not present in the dilute solutions where exchange bias properties are only due to an intraparticle exchange between core and surface. The thermal dependence of the bias field is well described by a reduced exponential behavior with a characteristic freezing temperature of about 8 K.

  18. 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.

  19. 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.

  20. 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.

  1. The role of magnetic interactions in exchange bias properties of MnFe2O4@γ-Fe2O3 core/shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Silva, F. G.; Aquino, R.; Tourinho, F. A.; Stepanov, V. I.; Raikher, Yu L.; Perzynski, R.; Depeyrot, J.

    2013-07-01

    Low-temperature magnetic properties of assemblies of 3.3 nm sized nanoparticles (NPs) based on a MnFe2O4 core protected by a maghemite shell are investigated. These NPs are obtained by a chemical core/shell method developed for the synthesis of the electrostatically stabilized ferrofluid colloidal dispersions that we probe here. They are model systems where the interparticle interaction is tuned by the NP volume fractions, ranging here between 0.4% and 13.9%. It has been shown that these NPs consist of a well-ordered ferrimagnetic core surrounded by a disordered spin glass-like surface layer and that they display uniaxial magnetic anisotropy. We compare the magnetic hysteresis loops of non-textured frozen dispersions (with magnetic anisotropy axis of NPs distributed at random) with those of a powder based on the same NPs. After cooling under field the hysteresis loops shift along the H axis, expressing the coupling between the spin-ordered cores and the disordered surface layers. The negative H-shift provides an evaluation for the exchange bias (EB) field. The EB field is optimum for a cooling field of the order of the anisotropy field. A comparison between frozen dispersions and disordered powder allows us to distinguish the influence of intra- and interparticle interactions on the EB. Interparticle collective effects dominate in the powder while an intraparticle EB, eventually hindered by dipolar interactions at large volume fraction, is observed in frozen dispersions.

  2. 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.

  3. 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.

  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. Bridging amount of spin-glasses over ferromagnetic/antiferromagnetic thin films and bit-cell dispersion of exchange bias in corresponding TA-MRAM devices

    NASA Astrophysics Data System (ADS)

    Akmaldinov, Kamil; Ducruet, Clarisse; Alvarez-Herault, Jeremy; Baltz, Vincent

    2015-03-01

    For thermally-assisted magnetic random access memories (TA-MRAM), lowering bit-cells dispersions of exchange bias is necessary. In this study, we prove that spin-glass-like phases (SG) spread over the ferromagnetic/antiferromagnetic (F/AF) storage layer are the main cause of such distributions once the film is nanofabricated into a device. In particular, we show that the less the SG, the lower the bit-cell dispersion. More precisely, the amount of SG was varied from sample to sample by sputtering various AFs: IrMn, FeMn and their alloys. Blocking temperature distributions were measured to quantify the amount of SG at the wafer level. The wafers were then patterned to obtain 1kb devices and all the cells were tested electrically. Finally, the resulting loop shift cumulative distribution functions accounting for the bit-cell dispersions were correlated to the initial amount of SG. In addition to bridging the gap between fundamental SG and a technological application, we also demonstrated that blocking temperature distributions are a versatile method to qualify TA-MRAM production batches before processing. Univ. Grenoble-Alpes/CNRS/INAC-CEA, 38000 Grenoble, France.

  6. 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.

  7. Field-induced transitions from negative to positive exchange bias in nanoparticles with inverted ferromagnetic-antiferromagnetic core-shell morphology

    NASA Astrophysics Data System (ADS)

    Hu, Yong; Wu, Guo-Zhen; Liu, Yan; Du, An

    2012-03-01

    In an antiferromagnetic (core)/ferromagnetic (shell) nanoparticle, the transition behaviors from negative (NEB) to positive exchange bias (PEB) at low temperature after field cooling are studied in detail. The NEB field may exhibit an oscillatory behavior due to the competition between interfacial coupling and cooling field. The critical cooling fields, at which the transitions occur, exhibit a logarithmic decrement with the decrease of interfacial coupling, but indicate a linear decrease with the decrease of antiferromagnetic coupling or with the further dilution in the antiferromagnetic core. With the further increase of cooling field, the PEB field increases linearly and finally levels off. Moreover, the weaker antiferromagnetic coupling may enhance the NEB field value, whereas the suppression of PEB may be observed by diluting the antiferromagnetic core. The magnetization reversal by coherent rotation strongly depends on the variation of the magnetic parameters, because its occurrence just needs to consume a lower additional energy, which is the main reason for these unique phenomena. We have shed new light on the microscopic origin of the peculiar magnetic properties in the nanoparticles with such an inverted magnetic structure.

  8. Negative exchange bias in single-phase D y1 -xN dxCr O3 induced by Nd doping

    NASA Astrophysics Data System (ADS)

    McDannald, A.; dela Cruz, C. R.; Seehra, M. S.; Jain, M.

    2016-05-01

    Observation of significant negative exchange bias (HE) is reported in solid solutions of single-phase samples of D y1 -xN dxCr O3 for x = 0.33 ,0.67 , and 1 with corresponding Néel temperatures at TNCr= 175 K ,200 K , and 225 K, respectively, and the spin-reorientation transitions TS R at 48 K, 58 K, and 38 K, respectively. In contrast, no HE was observed for the sample with x =0 (i.e., DyCr O3 ) shows no HE below its TNCr= 145 K , and no reorientation of spins at lower temperatures was observed. More importantly, the (negative) HE for the x = 0.33 ,0.67 , and 1 samples is observed only in the temperature range between TN and TS R with the corresponding observation of magnetic coercivity. These results show that the canted antiferromagnetic Γ7 ,Cr structure of the C r3 + moments present between TNCr and TS R is essential for the observed HE. By comparing this result to the literature, common features of single-phase materials with HE were identified. The present bulk powder samples were prepared by the citrate method and structurally characterized by x-ray diffraction and Raman spectroscopy techniques. Neutron diffraction measurements for the x = 0.33 ,0.67 , and 1 samples at select temperatures were done to verify the presence of the Γ7 ,Cr structure between TNCr and TS R and the Γ1 ,Cr structure (with no canting of C r3 + moments) below TS R.

  9. Exchange bias and enhanced coercivity in phase separated La0.45Sr0.55MnO3 and Pr0.55(Ca0.65S0.35)0.45MnO3 films

    NASA Astrophysics Data System (ADS)

    Kim, Byeong-geon; Kumar, Ashvani; Ki, Sanghoon; Kim, Sangwoo; Dho, Joonghoe

    2011-12-01

    An epitaxial La0.45Sr0.55MnO3 (LSMO) film, which has a paramagnetic-to-ferromagnetic transition at ˜260 K and a partial ferromagnetic-to-antiferromagnetic transition at ˜150 K upon cooling, was synthesized on (001) (La0.18Sr0.82)(Al0.59Ta0.41)O3 with pulsed laser deposition. The x-ray diffraction pattern showed interference fringes around the (002) LSMO peak, indicating a successful growth of a high quality and smooth film. When the LSMO film was cooled down in a magnetic field of 5 kOe, it exhibited a large exchange bias (HEX) of ˜490 Oe and an enhanced coercivity (HC) of ˜800 at 10 K, respectively. The observed exchange bias effect, which is associated with phase coexistence of the ferromagnetic (FM) and antiferromagnetic (AF) phases, displayed a distinctive training effect, which is probably due to a competing spin order at the boundary between the FM and AF phases. Similarly, we also observed a large exchange bias and enhanced coercivity in a phase separated Pr0.55(Ca0.65S0.35)0.45MnO3 film, which had simultaneous FM and AF transitions at ˜150 K. Our results show that the exchange bias effect can be induced even in single layer films with a magnetic phase coexistence state of FM and AF phases, which may be exploited as a very simple structure for spin-valve devices.

  10. 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.

  11. 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.

  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. Intergroup bias.

    PubMed

    Hewstone, Miles; Rubin, Mark; Willis, Hazel

    2002-01-01

    This chapter reviews the extensive literature on bias in favor of in-groups at the expense of out-groups. We focus on five issues and identify areas for future research: (a) measurement and conceptual issues (especially in-group favoritism vs. out-group derogation, and explicit vs. implicit measures of bias); (b) modern theories of bias highlighting motivational explanations (social identity, optimal distinctiveness, uncertainty reduction, social dominance, terror management); (c) key moderators of bias, especially those that exacerbate bias (identification, group size, status and power, threat, positive-negative asymmetry, personality and individual differences); (d) reduction of bias (individual vs. intergroup approaches, especially models of social categorization); and (e) the link between intergroup bias and more corrosive forms of social hostility. PMID:11752497

  14. 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

  15. 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.

  16. Antisite disorder driven spontaneous exchange bias effect in La2-x Sr x CoMnO6 (0  ⩽  x  ⩽  1)

    NASA Astrophysics Data System (ADS)

    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 (Sr2+) doping in La2-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 Co2+ and Co3+ 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.

  17. Sympathetic bias.

    PubMed

    Levy, David M; Peart, Sandra J

    2008-06-01

    We wish to deal with investigator bias in a statistical context. We sketch how a textbook solution to the problem of "outliers" which avoids one sort of investigator bias, creates the temptation for another sort. We write down a model of the approbation seeking statistician who is tempted by sympathy for client to violate the disciplinary standards. We give a simple account of one context in which we might expect investigator bias to flourish. Finally, we offer tentative suggestions to deal with the problem of investigator bias which follow from our account. As we have given a very sparse and stylized account of investigator bias, we ask what might be done to overcome this limitation. PMID:17925315

  18. Hindsight Bias.

    PubMed

    Roese, Neal J; Vohs, Kathleen D

    2012-09-01

    Hindsight bias occurs when people feel that they "knew it all along," that is, when they believe that an event is more predictable after it becomes known than it was before it became known. Hindsight bias embodies any combination of three aspects: memory distortion, beliefs about events' objective likelihoods, or subjective beliefs about one's own prediction abilities. Hindsight bias stems from (a) cognitive inputs (people selectively recall information consistent with what they now know to be true and engage in sensemaking to impose meaning on their own knowledge), (b) metacognitive inputs (the ease with which a past outcome is understood may be misattributed to its assumed prior likelihood), and (c) motivational inputs (people have a need to see the world as orderly and predictable and to avoid being blamed for problems). Consequences of hindsight bias include myopic attention to a single causal understanding of the past (to the neglect of other reasonable explanations) as well as general overconfidence in the certainty of one's judgments. New technologies for visualizing and understanding data sets may have the unintended consequence of heightening hindsight bias, but an intervention that encourages people to consider alternative causal explanations for a given outcome can reduce hindsight bias. PMID:26168501

  19. 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

  20. 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.

  1. 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

  2. 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

  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. Proximity effects and exchange bias in Co/MnF2(111) heterostructures studied by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Suturin, S. M.; Fedorov, V. V.; Banshchikov, A. G.; Baranov, D. A.; Koshmak, K. V.; Torelli, P.; Fujii, J.; Panaccione, G.; Amemiya, K.; Sakamaki, M.; Nakamura, T.; Tabuchi, M.; Pasquali, L.; Sokolov, N. S.

    2013-01-01

    Cobalt nano-structured ultrathin films were grown on orthorhombic MnF2 by molecular beam epitaxy on CaF2 epitaxial layers deposited on Si(111) substrates. The Co film was grown at room temperature. It was found to be polycrystalline, forming nano-islands with height≈diameter≤10 nm. X-ray absorption evidences the chemical stability of the Co/MnF2 interface. Remarkably, x-ray magnetic circular dichroism (XMCD) demonstrates that the Co induces a net magnetization on the Mn ions close to the interface. The magnetic moments of these Mn ions couple antiparallel to the Co and rotate upon field reversal following the magnetization of the Co both below and high above the Néel temperature of MnF2 (TN = 67 K). The density of coupled Mn moments is found to be temperature dependent, with an equivalent thickness of ˜1.5 MnF2 monolayers at 20 K, decreasing to about ˜0.5 ML as the temperature is raised to 300 K. Interestingly, the intensity of the Mn XMCD signal appears to be related to the coercivity of the Co layer. This behavior is interpreted in terms of the competition between thermal fluctuations, exchange coupling between Co and Mn at the interface and, at low temperature, the antiferromagnetic order in MnF2.

  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. Role of Enzyme Flexibility in Ligand Access and Egress to Active Site: Bias-Exchange Metadynamics Study of 1,3,7-Trimethyluric Acid in Cytochrome P450 3A4.

    PubMed

    Paloncýová, Markéta; Navrátilová, Veronika; Berka, Karel; Laio, Alessandro; Otyepka, Michal

    2016-04-12

    Although the majority of enzymes have buried active sites, very little is known about the energetics and mechanisms associated with substrate and product channeling in and out. Gaining direct information about these processes is a challenging task both for experimental and theoretical techniques. Here, we present a methodology that enables following of a ligand during its passage to the active site of cytochrome P450 (CYP) 3A4 and mapping of the free energy associated with this process. The technique is based on a combination of a bioinformatics tool for identifying access channels and bias-exchange metadynamics and provides converged free energies in good agreement with experimental data. In addition, it identifies the energetically preferred escape routes, limiting steps, and amino acids residues lining the channel. The approach was applied to mapping of a complex channel network in a complex environment, i.e., CYP3A4 attached to a lipid bilayer mimicking an endoplasmic reticulum membrane. The results provided direct information about the energetics and conformational changes associated with the ligand channeling. The methodology can easily be adapted to study channeling through other flexible biomacromolecular channels. PMID:26967371

  7. 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.

  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. 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.

  11. Patient Protection and Affordable Care Act; establishment of the Multi-State Plan Program for the Affordable Insurance Exchanges. Final rule.

    PubMed

    2014-02-24

    The U.S. Office of Personnel Management (OPM) is issuing a final rule implementing modifications to the Multi-State Plan (MSP) Program based on the experience of the Program to date. OPM established the MSP Program pursuant to the Affordable Care Act. This rule clarifies the approach used to enforce the applicable standards of the Affordable Care Act with respect to health insurance issuers that contract with OPM to offer MSP options; amends MSP standards related to coverage area, benefits, and certain contracting provisions under section 1334 of the Affordable Care Act; and makes non-substantive technical changes. PMID:25735057

  12. Distraction from emotional information reduces biased judgements.

    PubMed

    Lench, Heather C; Bench, Shane W; Davis, Elizabeth L

    2016-06-01

    Biases arising from emotional processes are some of the most robust behavioural effects in the social sciences. The goal of this investigation was to examine the extent to which the emotion regulation strategy of distraction could reduce biases in judgement known to result from emotional information. Study 1 explored lay views regarding whether distraction is an effective strategy to improve decision-making and revealed that participants did not endorse this strategy. Studies 2-5 focused on several established, robust biases that result from emotional information: loss aversion, desirability bias, risk aversion and optimistic bias. Participants were prompted to divert attention away from their feelings while making judgements, and in each study this distraction strategy resulted in reduced bias in judgement relative to control conditions. The findings provide evidence that distraction can improve choice across several situations that typically elicit robustly biased responses, even though participants are not aware of the effectiveness of this strategy. PMID:25787937

  13. Specific residues of the GDP/GTP exchange factor Bud5p are involved in establishment of the cell type-specific budding pattern in yeast.

    PubMed

    Kang, Pil Jung; Lee, Bongyong; Park, Hay-Oak

    2004-07-01

    Cells of the budding yeast undergo oriented cell division by choosing a specific site for growth depending on their cell type. Haploid a and alpha cells bud in an axial pattern whereas diploid a/alpha cells bud in a bipolar pattern. The Ras-like GTPase Rsr1p/Bud1p, its GDP-GTP exchange factor Bud5p, and its GTPase-activating protein Bud2p are essential for selecting the proper site for polarized growth in all cell types. Here we showed that specific residues at the N terminus and the C terminus of Bud5p were important for bipolar budding, while some residues were involved in both axial and bipolar budding. These bipolar-specific mutations of BUD5 disrupted proper localization of Bud5p in diploid a/alpha cells without affecting Bud5p localization in haploid alpha cells. In contrast, Bud5p expressed in the bud5 mutants defective in both budding patterns failed to localize in all cell types. Thus, these results identify specific residues of Bud5p that are likely to be involved in direct interaction with spatial landmarks, which recruit Bud5p to the proper bud site. Finally, we found a new start codon of BUD5, which extends the open reading frame to 210 bp upstream of the previously estimated start site, thus encoding a polypeptide of 608 amino acid residues. Bud5p with these additional N-terminal residues interacted with Bud8p, a potential bipolar landmark, suggesting that the N-terminal region is necessary for recognition of the spatial cues. PMID:15136576

  14. 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

  15. 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

  16. Correcting the bias against interdisciplinary research

    PubMed Central

    2014-01-01

    When making decisions about funding and jobs the scientific community should recognise that most of the tools used to evaluate scientific excellence are biased in favour of established disciplines and against interdisciplinary research. PMID:24692451

  17. Correcting the bias against interdisciplinary research.

    PubMed

    Shapiro, Ehud

    2014-01-01

    When making decisions about funding and jobs the scientific community should recognise that most of the tools used to evaluate scientific excellence are biased in favour of established disciplines and against interdisciplinary research. PMID:24692451

  18. Bias in Mental Tests.

    ERIC Educational Resources Information Center

    Bond, Lloyd

    1981-01-01

    While some forms of test bias (for example, bias in selection and prediction) appear amenable to definitional consensus, a definition of cultural bias will remain problematic so long as it is confused with the nature/nurture issue. (Author/BW)

  19. 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'…

  20. 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.

  1. Recalibrating Academic Bias

    ERIC Educational Resources Information Center

    Yancey, George

    2012-01-01

    Whether political and/or religious academic bias exists is a question with important ramifications for the educational institutions. Those arguing for the presence of such bias contend that political conservatives and the highly religious in academia are marginalized and face discrimination. The question of academic bias tends to be cast in a…

  2. 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.

  3. 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

  4. Renormalized halo bias

    SciTech Connect

    Assassi, Valentin; Baumann, Daniel; Green, Daniel; Zaldarriaga, Matias E-mail: dbaumann@damtp.cam.ac.uk E-mail: matiasz@ias.edu

    2014-08-01

    This paper provides a systematic study of renormalization in models of halo biasing. Building on work of McDonald, we show that Eulerian biasing is only consistent with renormalization if non-local terms and higher-derivative contributions are included in the biasing model. We explicitly determine the complete list of required bias parameters for Gaussian initial conditions, up to quartic order in the dark matter density contrast and at leading order in derivatives. At quadratic order, this means including the gravitational tidal tensor, while at cubic order the velocity potential appears as an independent degree of freedom. Our study naturally leads to an effective theory of biasing in which the halo density is written as a double expansion in fluctuations and spatial derivatives. We show that the bias expansion can be organized in terms of Galileon operators which aren't renormalized at leading order in derivatives. Finally, we discuss how the renormalized bias parameters impact the statistics of halos.

  5. 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

  6. 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

  7. 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

  8. Bias correction with Data Assimilation

    NASA Astrophysics Data System (ADS)

    Canter, Martin; Barth, Alexander

    2015-04-01

    With this work, we aim at developping a new method of bias correction using data assimilation. This method is based on the stochastic forcing of a model to correct bias. First, through a preliminary run, we estimate the bias of the model and its possible sources. Then, we establish a forcing term which is directly added inside the model's equations. We create an ensemble of runs and consider the forcing term as a control variable during the assimilation of observations. We then use this analysed forcing term to correct the bias of the model. Since the forcing is added inside the model, it acts as a source term, unlike external forcings such as wind. This procedure has been developed and successfully tested with a twin experiment on a Lorenz 95 model. Indeed, we were able to estimate and recover an artificial bias that had been added into the model. This bias had a spatial structure and was constant through time. The mean and behaviour of the corrected model corresponded to those the reference model. It is currently being applied and tested on the sea ice ocean NEMO LIM model, which is used in the PredAntar project. NEMO LIM is a global and low resolution (2 degrees) coupled model (hydrodynamic model and sea ice model) with long time steps allowing simulations over several decades. Due to its low resolution, the model is subject to bias in area where strong currents are present. We aim at correcting this bias by using perturbed current fields from higher resolution models and randomly generated perturbations. The random perturbations need to be constrained in order to respect the physical properties of the ocean, and not create unwanted phenomena. To construct those random perturbations, we first create a random field with the Diva tool (Data-Interpolating Variational Analysis). Using a cost function, this tool penalizes abrupt variations in the field, while using a custom correlation length. It also decouples disconnected areas based on topography. Then, we filter

  9. Lagrangian bias in the local bias model

    SciTech Connect

    Frusciante, Noemi; Sheth, Ravi K. E-mail: sheth@ictp.it

    2012-11-01

    It is often assumed that the halo-patch fluctuation field can be written as a Taylor series in the initial Lagrangian dark matter density fluctuation field. We show that if this Lagrangian bias is local, and the initial conditions are Gaussian, then the two-point cross-correlation between halos and mass should be linearly proportional to the mass-mass auto-correlation function. This statement is exact and valid on all scales; there are no higher order contributions, e.g., from terms proportional to products or convolutions of two-point functions, which one might have thought would appear upon truncating the Taylor series of the halo bias function. In addition, the auto-correlation function of locally biased tracers can be written as a Taylor series in the auto-correlation function of the mass; there are no terms involving, e.g., derivatives or convolutions. Moreover, although the leading order coefficient, the linear bias factor of the auto-correlation function is just the square of that for the cross-correlation, it is the same as that obtained from expanding the mean number of halos as a function of the local density only in the large-scale limit. In principle, these relations allow simple tests of whether or not halo bias is indeed local in Lagrangian space. We discuss why things are more complicated in practice. We also discuss our results in light of recent work on the renormalizability of halo bias, demonstrating that it is better to renormalize than not. We use the Lognormal model to illustrate many of our findings.

  10. 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

  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. 22 CFR 214.11 - Establishment and chartering requirements.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... MANAGEMENT Establishment of Advisory Committees § 214.11 Establishment and chartering requirements... Library of Congress, Exchange and Gift Division, Federal Advisory Committee Desk, Washington, DC 20540....

  14. Harassment, Bias, and Discrimination.

    ERIC Educational Resources Information Center

    Welliver, Paul W.

    1995-01-01

    Discusses a new principle which has been added to the AECT (Association for Educational Communications and Technology) Code of Professional Ethics regarding discrimination, harassment, and bias. An example is presented which illustrates a violation of a professional colleague's rights. (LRW)

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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

  20. 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. PMID:25218691

  1. 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

  2. Prediction Bias and Selection Bias: An Empirical Analysis.

    ERIC Educational Resources Information Center

    Cahan, Sorel; Gamliel, Eyal

    2001-01-01

    Proposed a definition of selection bias and studied the empirical relation between prediction bias and selection bias with respect to prominent social groups. Results show that, although the two biases are related, the relation is not isomorphic. It is mediated by the selection ratio, and for most selection ratios, it is only moderate. (SLD)

  3. Bias in Psychological Assessment: Heterosexism.

    ERIC Educational Resources Information Center

    Chernin, Jeffrey; Holden, Janice Miner; Chandler, Cynthia

    1997-01-01

    Explores heterosexist bias in seven widely used assessment instruments. Focuses on bias that is observable in the instruments themselves and in the ancillary materials. Describes three types of bias, how these biases manifest in various instruments, and makes recommendations for mental health practitioners and for professionals who develop…

  4. 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…

  5. 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…

  6. 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.

  7. 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.

  8. Propagation of biases in climate models from the synoptic to the regional scale: Implications for bias adjustment

    NASA Astrophysics Data System (ADS)

    Addor, Nans; Rohrer, Marco; Furrer, Reinhard; Seibert, Jan

    2016-03-01

    Bias adjustment methods usually do not account for the origins of biases in climate models and instead perform empirical adjustments. Biases in the synoptic circulation are for instance often overlooked when postprocessing regional climate model (RCM) simulations driven by general circulation models (GCMs). Yet considering atmospheric circulation helps to establish links between the synoptic and the regional scale, and thereby provides insights into the physical processes leading to RCM biases. Here we investigate how synoptic circulation biases impact regional climate simulations and influence our ability to mitigate biases in precipitation and temperature using quantile mapping. We considered 20 GCM-RCM combinations from the ENSEMBLES project and characterized the dominant atmospheric flow over the Alpine domain using circulation types. We report in particular a systematic overestimation of the frequency of westerly flow in winter. We show that it contributes to the generalized overestimation of winter precipitation over Switzerland, and this wet regional bias can be reduced by improving the simulation of synoptic circulation. We also demonstrate that statistical bias adjustment relying on quantile mapping is sensitive to circulation biases, which leads to residual errors in the postprocessed time series. Overall, decomposing GCM-RCM time series using circulation types reveals connections missed by analyses relying on monthly or seasonal values. Our results underscore the necessity to better diagnose process misrepresentation in climate models to progress with bias adjustment and impact modeling.

  9. 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

  10. 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)

  11. Test Bias and the Elimination of Racism

    ERIC Educational Resources Information Center

    Sedlacek, William E.

    1977-01-01

    Three types of test bias are discussed: content bias, atmosphere bias, and use bias. Use bias is considered the most important. Tests reflect the bias in society, and eliminating test bias means eliminating racism and sexism in society. A six-stage model to eliminate racism and sexism is presented. (Author)

  12. 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…

  13. Evaluating solutions to sponsorship bias.

    PubMed

    Doucet, M; Sismondo, S

    2008-08-01

    More than 40 primary studies, and three recent systematic reviews and meta-analyses, have shown a clear association between pharmaceutical industry funding of clinical trials and pro-industry results. Industry sponsorship biases published scientific research in favour of the sponsors, a result of the strong interest commercial sponsors have in obtaining favourable results. Three proposed remedies to this problem are widely agreed upon among those concerned with the level of sponsorship bias: financial disclosure, reporting standards and trial registries. This paper argues that all of these remedies either fail to address the mechanisms by which pharmaceutical companies' sponsorship leads to biased results-design bias, multiple trials with predictable outcomes, fraud, rhetorical effects and publication bias-or else only inadequately address those mechanisms. As a result, the policies normally proposed for dealing with sponsorship bias are unable to eliminate it. Only completely separating public clinical research from pharmaceutical industry funding can eliminate sponsorship bias. PMID:18667655

  14. 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

  15. Effect of epitaxial strain on the exchange-bias properties of [La0.67Ca0.33MnO3/La0.33Ca0.67MnO3]15 multilayers: Resonant x-ray scattering measurements

    NASA Astrophysics Data System (ADS)

    Christides, C.; Deen, P. P.; Moutis, N.; Houssakou, E.; Bouchenoire, L.; Prassides, K.

    2007-01-01

    Complementary x-ray synchrotron radiation diffraction (XRD) and resonant scattering (RXS) measurements were performed at the MnK -edge between 10 and 300K in order to analyze the effect of epitaxial strain and tetragonal lattice distortions on the exchange bias (EB) mechanism observed in [La2/3Ca1/3MnO3(FM)/La1/3Ca2/3MnO3(AF)]15 multilayers below a blocking temperature, TB , of 80K . XRD measurements showed that the c/a axial ratio, an indication of the tetragonal lattice distortion in pseudocubic lattice settings, reaches its maximum at the onset of the EB effect and the corresponding structural correlation length varies substantially at the onset of TB . The in-plane lattice parameter a at TB is close to the bulk lattice parameters of the antiferromagnetic (AF) layers, thus indicating that the EB effect is related with the accommodation of strain inside the ferromagnetic (FM) and AF layers. RXS measurements revealed a ferrodistortive (FD) state. The RXS intensity difference signal exhibits a main-edge feature and a postedge feature at ˜6.57keV that scales linearly with temperature and the c/a ratio up to 80K . The disappearance of the postedge feature above 80K(=TB) may signify a rearrangement of Mn-O-Mn bonding angles due to strain-driven effects at the FM/AF interfaces, inducing disorder in FD octahedral tilt ordering which may pin the local distortions below the TB .

  16. Undercontribution bias in health care spending account decisions.

    PubMed

    Schweitzer, M E; Hershey, J C

    1997-01-01

    Results from this work describe 239 responses to a mailed survey regarding employee benefits decisions at a large eastern university. The primary objective of this work is to test for an undercontribution bias in health care financing decisions. The results establish the existence of an undercontribution bias in both actual employee decisions and hypothetical flexible spending account contribution decisions. We describe this bias within the context of related biases including loss aversion, mental accounting, status quo and omission biases. Surprisingly, we find a significant order effect in this study and posit that preference construction in this context is an active, reference-dependent process. In addition, results from this work demonstrate the endogenous nature of health care flexible spending account expenditures. The results have important implications both for the descriptive framework of and the normative solution to the flexible spending account contribution decision. PMID:10167155

  17. 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

  18. 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)

  19. 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

  20. Synchronous Spin-Exchange Optical Pumping

    NASA Astrophysics Data System (ADS)

    Korver, A.; Thrasher, D.; Bulatowicz, M.; Walker, T. G.

    2015-12-01

    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) 2 π 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 /√{Hz } .

  1. 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

  2. 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

  3. Cognitive biases in dermatology training.

    PubMed

    Shokeen, Divya

    2016-07-01

    Cognitive biases are patterns that physicians develop based on predetermined judgments that can influence their decisions regarding patient care. Unfortunately, they are usually encountered on a daily basis in clinics. A few examples include affective, anchoring, availability, confirmation, zebra, and Sutton's biases. PMID:27529715

  4. Science exchanges

    NASA Astrophysics Data System (ADS)

    Richman, Barbara T.

    Dwindling scientific and technical exchange between the United States and the Soviet Union and prospects for enhancing such exchanges were discussed at an August 2 hearing by the Foreign Affairs Committee of the U.S. House of Representatives. The committee also heard overviews on the United States' approach to international exchange of science and technology. The hearing was the first in a series on current and future international science and technology programs.Four of eight science and technology agreements with the USSR that have expired in the last 15 months, including one on space, have not been renewed. The remaining four agreements have been extended into 1987 and 1988. Two others, including one on oceanography, are scheduled to run out in 1984.

  5. 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.

  6. Optimal design of crossflow heat exchangers

    SciTech Connect

    Van den Bulck, E. )

    1991-05-01

    The design of plate-fin and tube-fin crossflow heat exchangers is discussed. The transfer surface area of crossflow heat exchangers is used ineffectively because of the nonuniform distribution of the heat transfer across the volume of the exchanger. The optimal distribution of the transfer surface area for maximum heat exchanger effectiveness and constant total surface area is determined. It is found that a Dirac delta distribution of the transfer surface aligned along the diagonal of the crossflow exchanger gives the best performance; equal to that of a counterflow device. Design guidelines for optimal area allocation within crossflow heat exchangers are established. Compared to conventional designs, designs following these guidelines may lead to either a higher exchanger effectiveness for equal pressure drops and surface area, reduced pressure drops for equal exchanger effectiveness, or reduced weight and a near cubic form of the exchanger core for equal pressure drops and effectiveness.

  7. Eliminating bias in CEM systems

    SciTech Connect

    Jahnke, J.A.

    1995-12-31

    The emission of sulfur dioxide, nitrogen oxides, and particulate matter from fossil-fuel fired power plants and industrial sources, is a matter of public concern that has led to both State and Federal requirements for pollution control. The accuracy of continuous emission monitoring (CEM) system data has been an issue of considerable importance in the development and implementation of the Acid Rain Program. The more stringent relative accuracy requirements of this program, coupled with the importance of emission trading allowances, has led to the need to minimize systematic errors in emissions measurement. With the inclusion of the t-test for bias in the Acid Rain Regulations of 40 CFR Part 75, a method was introduced that could be used to uncover systematic error, or bias, in CEM system measurements. Once bias is detected, it is highly desirable to either eliminate the cause of the bias or to apply correction factors to minimize its effect. However, a problem occurs in determining the cause of the bias; a task that is often both difficult and time consuming. This paper explains the rationale behind the bias test as applied to CEM systems and summarizes potential sources of systematic error in both extractive and in-situ CEM systems. The paper examines a number of factors that contribute to CEM system measurement error. Methods are suggested for both the detection and correction of the resulting biases.

  8. 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.

  9. 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.

  10. 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

  11. Threat bias, not negativity bias, underpins differences in political ideology.

    PubMed

    Lilienfeld, Scott O; Latzman, Robert D

    2014-06-01

    Although disparities in political ideology are rooted partly in dispositional differences, Hibbing et al.'s analysis paints with an overly broad brush. Research on the personality correlates of liberal-conservative differences points not to global differences in negativity bias, but to differences in threat bias, probably emanating from differences in fearfulness. This distinction bears implications for etiological research and persuasion efforts. PMID:24970441

  12. Psychological biases in environmental judgments

    SciTech Connect

    Miller, A.

    1985-04-01

    Faced with a complex environment, all of us resort to cognitive over-simplifications and wishful thinking, in an attempt to achieve an often illusory control over our lives. The resulting biases in judgment may lead to unfortunate decisions, as well as exacerbating disputes over such matters as the interpretation of environmental data. The detrimental effects of such biases are sufficient to warrant greater attention to the phenomenon. As a step in this direction, a variety of cognitive and motivated biases are discussed, together with examples of their effect on environmental judgment.

  13. 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.

  14. Experimenter bias and subliminal perception

    ERIC Educational Resources Information Center

    Barber, Paul J.; Rushton, J. Philippe

    1975-01-01

    It has been suggested that subliminal perception phenomena may be in part due to experimenter bias effects. Two studies that obtained positive evidence of subliminal perception were therefore replicated with experimenters tested under blind and not blind conditions. (Editor)

  15. 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. PMID:25042425

  16. The North Atlantic Cold Bias

    NASA Astrophysics Data System (ADS)

    Greatbatch, Richard; Drews, Annika; Ding, Hui; Latif, Mojib; Park, Wonsun

    2016-04-01

    The North Atlantic cold bias, associated with a too zonal path of the North Atlantic Current and a missing "northwest corner", is a common problem in coupled climate and forecast models. The bias affects the North Atlantic and European climate mean state, variability and predictability. We investigate the use of a flow field correction to adjust the path of the North Atlantic Current as well as additional corrections to the surface heat and freshwater fluxes. Results using the Kiel Climate Model show that the flow field correction allows a northward flow into the northwest corner, largely eliminating the bias below the surface layer. A surface cold bias remains but can be eliminated by additionally correcting the surface freshwater flux, without adjusting the surface heat flux seen by the ocean model. A model version in which only the surface fluxes of heat and freshwater are corrected continues to exhibit the incorrect path of the North Atlantic Current and a strong subsurface bias. Removing the bias impacts the multi-decadal time scale variability in the model and leads to a better representation of the SST pattern associated with the Atlantic Multidecadal Variability than the uncorrected model.

  17. 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.

  18. 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.

  19. Negativity Bias in Dangerous Drivers

    PubMed Central

    Chai, Jing; Qu, Weina; Sun, Xianghong; Zhang, Kan; Ge, Yan

    2016-01-01

    The behavioral and cognitive characteristics of dangerous drivers differ significantly from those of safe drivers. However, differences in emotional information processing have seldom been investigated. Previous studies have revealed that drivers with higher anger/anxiety trait scores are more likely to be involved in crashes and that individuals with higher anger traits exhibit stronger negativity biases when processing emotions compared with control groups. However, researchers have not explored the relationship between emotional information processing and driving behavior. In this study, we examined the emotional information processing differences between dangerous drivers and safe drivers. Thirty-eight non-professional drivers were divided into two groups according to the penalty points that they had accrued for traffic violations: 15 drivers with 6 or more points were included in the dangerous driver group, and 23 drivers with 3 or fewer points were included in the safe driver group. The emotional Stroop task was used to measure negativity biases, and both behavioral and electroencephalograph data were recorded. The behavioral results revealed stronger negativity biases in the dangerous drivers than in the safe drivers. The bias score was correlated with self-reported dangerous driving behavior. Drivers with strong negativity biases reported having been involved in mores crashes compared with the less-biased drivers. The event-related potentials (ERPs) revealed that the dangerous drivers exhibited reduced P3 components when responding to negative stimuli, suggesting decreased inhibitory control of information that is task-irrelevant but emotionally salient. The influence of negativity bias provides one possible explanation of the effects of individual differences on dangerous driving behavior and traffic crashes. PMID:26765225

  20. 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)...

  1. 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.

  2. Heat exchanger

    DOEpatents

    Brackenbury, Phillip J.

    1986-04-01

    A heat exchanger comparising a shell attached at its open end to one side of a tube sheet and a detachable head connected to the other side of said tube sheet. The head is divided into a first and second chamber in fluid communication with a nozzle inlet and nozzle outlet, respectively, formed in said tube sheet. A tube bundle is mounted within said shell and is provided with inlets and outlets formed in said tube sheet in communication with said first and second chambers, respectively.

  3. The multiple outcomes bias in antidepressants research.

    PubMed

    Procopio, Marco

    2005-01-01

    Despite the widespread use of antidepressant medication, there are no signs that the burden of depression and suicide is decreasing in the industrialised world. This is generating mounting scepticism on the effectiveness of this class of drugs as an approach for the treatment of mood disorders. These doubts are also fuelled by the increasing awareness that the literature on antidepressants is fundamentally flawed and under the control of the pharmaceutical companies. This article describes systematically for the first time what is probably the most insidious and misleading of the biases that affect this area of research: the "multiple outcomes bias". Most trials on the effectiveness of antidepressants, instead of first establishing a hypothesis and then trying to demonstrate it, following the scientific method, start instead "data mining", without a clear hypothesis, and then select for publication, amongst a multitude of outcomes, only the ones that favour the antidepressant drug, ignoring the others. This method has obviously no scientific validity and is very misleading, allowing the manipulation of the data without any overt fraudulent action. There is the need to generate new research, independently funded and with clear hypotheses established "a priori ". What is at stake is not only the appraisal of the balance between benefits and potential damage to the patients when using this class of medications, after the realisation that they are not as harmless as believed. It is also to establish whether the research on antidepressant medication has gone on a "wild goose chase" over the last half century, concentrating almost exclusively on molecules that modify the monoaminergic transmission at synaptic level and virtually ignoring any other avenue. PMID:15922120

  4. 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.

  5. A Lack of Left Visual Field Bias when Individuals with Autism Process Faces

    ERIC Educational Resources Information Center

    Dundas, Eva M.; Best, Catherine A.; Minshew, Nancy J.; Strauss, Mark S.

    2012-01-01

    It has been established that typically developing individuals have a bias to attend to facial information in the left visual field (LVF) more than in the right visual field. This bias is thought to arise from the right hemisphere's advantage for processing facial information, with evidence suggesting it to be driven by the configural demands of…

  6. 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…

  7. 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…

  8. 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,…

  9. 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…

  10. 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…

  11. 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…

  12. SYRCLE’s risk of bias tool for animal studies

    PubMed Central

    2014-01-01

    Background Systematic Reviews (SRs) of experimental animal studies are not yet common practice, but awareness of the merits of conducting such SRs is steadily increasing. As animal intervention studies differ from randomized clinical trials (RCT) in many aspects, the methodology for SRs of clinical trials needs to be adapted and optimized for animal intervention studies. The Cochrane Collaboration developed a Risk of Bias (RoB) tool to establish consistency and avoid discrepancies in assessing the methodological quality of RCTs. A similar initiative is warranted in the field of animal experimentation. Methods We provide an RoB tool for animal intervention studies (SYRCLE’s RoB tool). This tool is based on the Cochrane RoB tool and has been adjusted for aspects of bias that play a specific role in animal intervention studies. To enhance transparency and applicability, we formulated signalling questions to facilitate judgment. Results The resulting RoB tool for animal studies contains 10 entries. These entries are related to selection bias, performance bias, detection bias, attrition bias, reporting bias and other biases. Half these items are in agreement with the items in the Cochrane RoB tool. Most of the variations between the two tools are due to differences in design between RCTs and animal studies. Shortcomings in, or unfamiliarity with, specific aspects of experimental design of animal studies compared to clinical studies also play a role. Conclusions SYRCLE’s RoB tool is an adapted version of the Cochrane RoB tool. Widespread adoption and implementation of this tool will facilitate and improve critical appraisal of evidence from animal studies. This may subsequently enhance the efficiency of translating animal research into clinical practice and increase awareness of the necessity of improving the methodological quality of animal studies. PMID:24667063

  13. 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…

  14. 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,…

  15. 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

  16. Cognitive bias and unusual experiences in childhood.

    PubMed

    Hassanali, Nedah; Ruffell, Tamatha; Browning, Sophie; Bracegirdle, Karen; Ames, Catherine; Corrigall, Richard; Laurens, Kristin R; Hirsch, Colette; Kuipers, Elizabeth; Maddox, Lucy; Jolley, Suzanne

    2015-08-01

    Cognitive therapy is recommended for children with psychotic-like, or unusual, experiences associated with distress or impairment (UEDs; UK National Institute for Health and Care Excellence, 2013 [1]). Accurate models of the psychological underpinnings of childhood UEDs are required to effectively target therapies. Cognitive biases, such as the jumping to conclusions data-gathering bias (JTC), are implicated in the development and maintenance of psychosis in adults. In this study, we aimed to establish the suitability for children of a task developed to assess JTC in adults. Eighty-six participants (aged 5-14 years) were recruited from Child and Adolescent Mental Health Service (CAMHS) and community (school) settings, and completed the probabilistic reasoning ('Beads') task, alongside measures of intellectual functioning, general psychopathology, and UEDs. Self-reported reasoning strategy was coded as 'probabilistic' or 'other'. Younger children (5-10 years) were more likely than older children (11-14 years) to JTC (OR = 2.7, 95 % CI = 1.1-6.5, p = 0.03); and to use non-probabilistic reasoning strategies (OR = 9.4, 95 % CI = 1.7-48.8, p = 0.008). Both UED presence (OR = 5.1, 95 % CI = 1.2-21.9, p = 0.03) and lower IQ (OR = 0.9, 95 % CI = 0.9-1.0, p = 0.02) were significantly and independently associated with JTC, irrespective of age and task comprehension. Findings replicate research in adults, indicating that the 'Beads' task can be reliably employed in children to assess cognitive biases. Psychological treatments for children with distressing unusual experiences might usefully incorporate reasoning interventions. PMID:25395382

  17. 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.

  18. 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…

  19. 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…

  20. 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…

  1. Observer Biases in the Classroom.

    ERIC Educational Resources Information Center

    Kite, Mary E.

    1991-01-01

    Presents three student exercises that demonstrate common perceptual errors described in social psychological literature: actor-observer effect, false consensus bias, and priming effects. Describes methods to be followed and gives terms, sentences, and a story to be used in the exercises. Suggests discussion of the bases and impact of such…

  2. Cultural Bias in Testing ESL.

    ERIC Educational Resources Information Center

    Cargill-Power, C.

    Although cultural content is unavoidable as a backdrop for good language testing, cultural bias in testing English as a second language presents many dangers. A picture cue calling for a correct grammatical response may evoke an incorrect answer if the pictorial content is culturally coded. The cultural background behind a test must be accurately…

  3. 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,…

  4. 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.

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

    DOE PAGESBeta

    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

  6. Plasma exchange in endocrine ophthalmopathy.

    PubMed

    Berlin, G; Hjelm, H; Liedén, G; Tegler, L

    1990-01-01

    We studied the effects of intensive plasma exchange on endocrine ophthalmopathy in 12 patients with Graves' disease and one with Hashimoto's thyroiditis. All patients were euthyroid at the time of plasma exchange. All but five had concomitant treatment with azathioprine. Each patient had a treatment period consisting of six plasma exchanges performed in 2-3 weeks; two patients were treated in two periods. Each time a mean of 2.4 liters plasma was exchanged. There was a prompt reduction in the concentration of circulating immune complexes and/or thyrotropin receptor antibodies following plasma exchange. Six of the 13 patients improved their proptosis; their median duration of eye symptoms before treatment was less than 8 months. In patients suffering from eye symptoms for more than 1 year improvement was rare. Overall the Hertel values were 24.1 +/- 4.4 (SD) before and 22.8 +/- 3.4 after plasma exchange for the left eyes (P = 0.07) and 23.8 +/- 4.0 before and 23.0 +/- 3.8 after for the right eyes (P = 0.09). Nine patients altogether improved their ophthalmopathy index and periorbital oedema. In patients with disabling endocrine ophthalmopathy plasma exchange may sometimes be of value to induce a relief of the ophthalmopathy; when it is used it should be instituted before fibrotic changes occur. We suggest that concomitant immunosuppressive drugs should be given to prevent rebound phenomenon induced by plasma exchange. To establish the role of plasma exchange in the treatment of endocrine ophthalmopathy controlled studies should be performed. PMID:2228998

  7. Inference for blocked randomization under a selection bias model.

    PubMed

    Kennes, Lieven N; Rosenberger, William F; Hilgers, Ralf-Dieter

    2015-12-01

    We provide an asymptotic test to analyze randomized clinical trials that may be subject to selection bias. For normally distributed responses, and under permuted block randomization, we derive a likelihood ratio test of the treatment effect under a selection bias model. A likelihood ratio test of the presence of selection bias arises from the same formulation. We prove that the test is asymptotically chi-square on one degree of freedom. These results correlate well with the likelihood ratio test of Ivanova et al. (2005, Statistics in Medicine 24, 1537-1546) for binary responses, for which they established by simulation that the asymptotic distribution is chi-square. Simulations also show that the test is robust to departures from normality and under another randomization procedure. We illustrate the test by reanalyzing a clinical trial on retinal detachment. PMID:26099068

  8. 78 FR 10229 - Self-Regulatory Organizations; BATS Exchange, Inc.; Notice of Filing and Immediate Effectiveness...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-13

    ... effectiveness establishing Short Term Option Series Program on BATS). Other exchanges have also established... that are opened by other securities exchanges in option classes selected by such exchanges under their... compete on an equal playing field with other options exchanges in satisfying the high market demand...

  9. 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

  10. 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...

  11. 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...

  12. 45 CFR 155.106 - Election to operate an Exchange after 2014.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 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...

  13. From acclaim to blame: evidence of a person sensitivity decision bias.

    PubMed

    Moon, Henry; Conlon, Donald E

    2002-02-01

    In a series of studies, the authors established empirical support for a general decision-making bias that they termed a person sensitvity bias. Specifically, a person sensitivity bias consists of a person positivity bias (D. O. Sears, 1983) under positive performance conditions and a person negativity bias under negative performance conditions. The authors conducted the first empirical studies of a direct comparison between individuals and objects performing the same task under both positive and negative performance conditions. Two additional studies tested the boundaries of the sensitivity bias within negatively framed decision dilemmas. The results are discussed in terms of their relevance toward a more comprehensive theory of person-object evaluation differences. PMID:11916214

  14. Spin-Exchange-Pumped NMR Gyros

    NASA Astrophysics Data System (ADS)

    Walker, T. G.; Larsen, M. S.

    We present the basic theory governing spin-exchange pumped NMR gyros. We review the basic physics of spin-exchange collisions and relaxation as they pertain to precision NMR. We present a simple model of operation as an NMR oscillator and use it to analyze the dynamic response and noise properties of the oscillator. We discuss the primary systematic errors (differential alkali fields, quadrupole shifts, and offset drifts) that limit the bias stability, and discuss methods to minimize them. We give with a brief overview of a practical implementation and performance of an NMR gyro built by Northrop-Grumman Corporation, and conclude with some comments about future prospects.

  15. 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,…

  16. 78 FR 42823 - Patient Protection and Affordable Care Act; Exchange Functions: Standards for Navigators and Non...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-17

    ...This final rule addresses various requirements applicable to Navigators and non-Navigator assistance personnel in Federally- facilitated Exchanges, including State Partnership Exchanges, and to non-Navigator assistance personnel in State Exchanges that are funded through federal Exchange Establishment grants. It finalizes the requirement that Exchanges must have a certified application......

  17. Critical thickness investigation of magnetic properties in exchange-coupled bilayers

    NASA Astrophysics Data System (ADS)

    Rodríguez-Suárez, R. L.; Vilela-Leão, L. H.; Bueno, T.; Oliveira, A. B.; de Almeida, J. R. L.; Landeros, P.; Rezende, S. M.; Azevedo, A.

    2011-06-01

    We present a systematic investigation of the magnetic properties of two series of polycrystalline ferromagnetic-antiferromagnetic bilayers (FM-AF) of Ni81Fe19(10nm)/Ir20Mn80(tAF) grown by dc magnetron sputtering. One series was grown at an oblique angle of 50° and the other one was grown at 0°. Ferromagnetic resonance (FMR) was used to measure the exchange bias field HE, the rotatable anisotropy field HRA, and the FMR linewidth ΔH as a function of the antiferromagnetic layer thickness tAF. Three relaxation channels due to isotropic Gilbert damping, anisotropic two-magnon scattering, and mosaicity effects are simultaneously distinguished through the angular dependence of the FMR linewidth. In the regime of small IrMn layer thicknesses, not enough to establish the exchange bias anisotropy, the FMR linewidth shows a sharp peak due to the contribution of the two-magnon scattering mechanism. The results presented here are of general importance for understanding the dynamics of magnetization in the FM-AF structures.

  18. Measurement bias in activation-recovery intervals from unipolar electrograms.

    PubMed

    Western, David; Hanson, Ben; Taggart, Peter

    2015-02-15

    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

  19. Bias Adjustment of PERSIANN Rainfall for Hydrologic Applications

    NASA Astrophysics Data System (ADS)

    Hsu, K.; Braithwaite, D.; Imam, B.; Gao, X.; Sorooshian, S.

    2008-05-01

    The exchange of water and energy through the land and atmospheric interaction occurs at various space and time scales. Modeling these exchanges, in general, and more specifically, adequate capturing of land surface hydrologic processes such as soil moisture and runoff generation requires reliable modeling and measurement of precipitation at fine time scale. The maturity of Satellite-based rainfall estimates is now sufficient to consider the value of such products in improving land surface models. This study addresses the measurement and bias correction of PERSIANN (Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks) rainfall to sub-daily scale of 0.25ox0.25o with emphasis on its potential use in land-surface hydrologic applications. The satellite-based PERSIANN system estimates surface rainfall based on infrared temperature and local image texture from geostationary satellites. Model parameters of PERSIANN are frequently adjusted when passive microwave rainfall estimates from low-orbital satellites (EOS, TRMM, NOAA, and DMSP) are available. PERSIANN estimates rainfall at hourly and 0.25ox0.25o lat-long scales. Its products are accumulated to daily and monthly scales for various applications. In this presentation, PERSIANN bias adjustment using monthly estimates from the Global Precipitation Climatology Project (GPCP) product is explored. Hourly PERSIANN rainfall estimates are first aggregated both spatially and temporally to the monthly 2.5ox2.5o scale and subsequently adjusted using GCPC monthly estimates as reference. Values of bias in PERSIANN are used to adjust PERSIANN rainfall at the 0.25ox0.25o hourly scale. The effectiveness of bias adjustment is evaluated using radar and gauge measurements at sub- daily to monthly scales at a spatial resolution of 0.25ox0.25o lat-long. The potential use of adjusted PERSIANN in hydrologic applications will be presented and discussed.

  20. Recent developments in biased agonism

    PubMed Central

    Wisler, James W.; Xiao, Kunhong; Thomsen, Alex R.B.; Lefkowitz, Robert J.

    2014-01-01

    The classic paradigm of G protein-coupled receptor (GPCR) activation was based on the understanding that agonist binding to a receptor induces or stabilizes a conformational change to an “active” conformation. In the past decade, however, it has been appreciated that ligands can induce distinct “active” receptor conformations with unique downstream functional signaling profiles. Building on the initial recognition of the existence of such “biased ligands”, recent years have witnessed significant developments in several areas of GPCR biology. These include increased understanding of structural and biophysical mechanisms underlying biased agonism, improvements in characterization and quantification of ligand efficacy, as well as clinical development of these novel ligands. Here we review recent major developments in these areas over the past several years. PMID:24680426

  1. 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

  2. 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.

  3. 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. PMID:12158019

  4. Significant biases affecting abundance determinations

    NASA Astrophysics Data System (ADS)

    Wesson, Roger

    2015-08-01

    I have developed two highly efficient codes to automate analyses of emission line nebulae. The tools place particular emphasis on the propagation of uncertainties. The first tool, ALFA, uses a genetic algorithm to rapidly optimise the parameters of gaussian fits to line profiles. It can fit emission line spectra of arbitrary resolution, wavelength range and depth, with no user input at all. It is well suited to highly multiplexed spectroscopy such as that now being carried out with instruments such as MUSE at the VLT. The second tool, NEAT, carries out a full analysis of emission line fluxes, robustly propagating uncertainties using a Monte Carlo technique.Using these tools, I have found that considerable biases can be introduced into abundance determinations if the uncertainty distribution of emission lines is not well characterised. For weak lines, normally distributed uncertainties are generally assumed, though it is incorrect to do so, and significant biases can result. I discuss observational evidence of these biases. The two new codes contain routines to correctly characterise the probability distributions, giving more reliable results in analyses of emission line nebulae.

  5. 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.)

  6. 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)

  7. 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

  8. 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.

  9. 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

  10. 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…

  11. 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)

  12. 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…

  13. Begging the Question: Is Critical Thinking Biased?

    ERIC Educational Resources Information Center

    Alston, Kal

    1995-01-01

    Discusses whether critical thinking is biased, examining what is meant by critical thinking and bias and what the consequences are for addressing bias in different ways. The paper responds to the three previous papers in the critical thinking symposium in this issue of the journal. (SM)

  14. Assessing Gender Bias in Computer Software.

    ERIC Educational Resources Information Center

    Rosenthal, Nina Ribak; Demetrulias, Diana Mayer

    1988-01-01

    Discusses gender bias in educational software programs and describes two studies that explored the ability of preservice and inservice teachers to detect bias in software programs. Evaluation instruments used to measure gender bias are described, and the need for instruction in equity issues is discussed. (23 references) (LRW)

  15. 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…

  16. Computers, Gender Bias, and Young Children.

    ERIC Educational Resources Information Center

    Bhargava, Ambika; Kirova-Petrova, Anna; McNair, Shannan

    1999-01-01

    Discusses gender discrepancy in classroom computer access and use; suggests strategies to minimize gender biases. Argues that gender differences in computer usage are due to biased classroom practices, lack of female role models, home computer gender gaps, and scarcity of bias-free software. Maintains that increased teacher/parent awareness,…

  17. 75 FR 23196 - Exchange Visitor Program-Secondary School Students

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-03

    ... CFR part 68-- Exchange Visitor Program, establishing a student exchange program (14 FR 4592, July 22... regulations governing the Exchange Visitor Program, including the Secondary School Student category (See 58 FR 15196, Mar. 19, 1993, as amended at 59 FR 34761, July 7, 1994, redesignated at 64 FR 54539, Oct. 7,...

  18. 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...

  19. 45 CFR 155.200 - Functions of an Exchange.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 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...

  20. 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...

  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. 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

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF HEALTH AND...: Office of Consumer Information and Insurance Oversight, Department of Health and Human Services. ACTION..., 2010. The Department of Health and Human Services (HHS) invites public comments in advance of...

  3. 75 FR 55381 - Joint Industry Plan; Order Approving Amendment To Add EDGA Exchange, Inc. and EDGX Exchange, Inc...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-10

    ...), 66 FR 19814 (April 17, 2001). \\4\\ See Securities Exchange Act Release No. 61824 (April 1, 2010), 75 FR 18246 (April 9, 2010). II. Discussion The Joint-SRO Plan establishes procedures for market centers... COMMISSION Joint Industry Plan; Order Approving Amendment To Add EDGA Exchange, Inc. and EDGX Exchange,...

  4. Opinion Dynamics with Confirmation Bias

    PubMed Central

    Allahverdyan, Armen E.; Galstyan, Aram

    2014-01-01

    Background Confirmation bias is the tendency to acquire or evaluate new information in a way that is consistent with one's preexisting beliefs. It is omnipresent in psychology, economics, and even scientific practices. Prior theoretical research of this phenomenon has mainly focused on its economic implications possibly missing its potential connections with broader notions of cognitive science. Methodology/Principal Findings We formulate a (non-Bayesian) model for revising subjective probabilistic opinion of a confirmationally-biased agent in the light of a persuasive opinion. The revision rule ensures that the agent does not react to persuasion that is either far from his current opinion or coincides with it. We demonstrate that the model accounts for the basic phenomenology of the social judgment theory, and allows to study various phenomena such as cognitive dissonance and boomerang effect. The model also displays the order of presentation effect–when consecutively exposed to two opinions, the preference is given to the last opinion (recency) or the first opinion (primacy) –and relates recency to confirmation bias. Finally, we study the model in the case of repeated persuasion and analyze its convergence properties. Conclusions The standard Bayesian approach to probabilistic opinion revision is inadequate for describing the observed phenomenology of persuasion process. The simple non-Bayesian model proposed here does agree with this phenomenology and is capable of reproducing a spectrum of effects observed in psychology: primacy-recency phenomenon, boomerang effect and cognitive dissonance. We point out several limitations of the model that should motivate its future development. PMID:25007078

  5. 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.

  6. 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

  7. 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

  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. Unlearning Implicit Social Biases During Sleep **

    PubMed Central

    Hu, Xiaoqing; Antony, James W.; Creery, Jessica D.; Vargas, Iliana M.; Bodenhausen, Galen V.; Paller, Ken A.

    2015-01-01

    Although people may endorse egalitarianism and tolerance, social biases can remain operative and drive harmful actions in an unconscious manner. Here we investigated training to reduce implicit racial and gender bias. Forty participants processed counter-stereotype information paired with one sound for each type of bias. Biases were reduced immediately after training. During subsequent slow-wave sleep, one sound was unobtrusively presented to each participant, repeatedly, to reactivate one type of training. Corresponding bias reductions were fortified in comparison to the social bias not externally reactivated during sleep. This advantage remained one week later, the magnitude of which was associated with time in slow-wave and rapid-eye-movement sleep after training. We conclude that memory reactivation during sleep enhances counter-stereotype training, and that maintaining a bias reduction is sleep-dependent. PMID:26023137

  10. 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.

  11. 78 FR 30376 - Self-Regulatory Organizations; BATS Y-Exchange, Inc.; Notice of Filing and Immediate...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-22

    ... port is commonly referred to as a TCP/IP port, and represents a port established by the Exchange within... Exchange FIX, FIXDROP, BOE, DROP, TCP PITCH, and TOP ports. In addition, the Exchange proposes to...

  12. Exchange coupling and its applications in magnetic data storage.

    PubMed

    Li, Kebin; Wu, Yihong; Guo, Zaibing; Zheng, Yuankai; Han, Guchang; Qiu, Jinjun; Luo, Ping; An, Lihua; Zhou, Tiejun

    2007-01-01

    The continuing scaling of magnetic recording is facing more and more scientific and technological challenges because both the read sensor and recording bit are approaching sub-50 nm regime with the ever increasing areal density in hard disk drives. One of the key and indispensable elements for both high-sensitivity sensors and high-density media is the exchange bias between a ferromagnetic and an antiferromagnetic layer or the exchange coupling between two ferromagnets via a non-magnetic spacer. In the nanometer regime, the exchange coupling between ferromagnet and antiferromagnet or two ferromagnets through a conductive spacer is governed by the intergrain exchange interaction which has its origin in electron spins. Interlayer exchange coupling in multilayer or trilayer essentially originates from the quantum confinement effect. In this paper, we first review the physical origin and various theoretical models of the two types of exchange couplings, followed by a review of the applications of the exchange bias and interlayer exchange coupling in data storage with emphasis on the advanced read sensor and advanced media including perpendicular media and patterned media. PMID:17455474

  13. 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.

  14. Imputation for semiparametric transformation models with biased-sampling data

    PubMed Central

    Liu, Hao; Qin, Jing; Shen, Yu

    2012-01-01

    Widely recognized in many fields including economics, engineering, epidemiology, health sciences, technology and wildlife management, length-biased sampling generates biased and right-censored data but often provide the best information available for statistical inference. Different from traditional right-censored data, length-biased data have unique aspects resulting from their sampling procedures. We exploit these unique aspects and propose a general imputation-based estimation method for analyzing length-biased data under a class of flexible semiparametric transformation models. We present new computational algorithms that can jointly estimate the regression coefficients and the baseline function semiparametrically. The imputation-based method under the transformation model provides an unbiased estimator regardless whether the censoring is independent or not on the covariates. We establish large-sample properties using the empirical processes method. Simulation studies show that under small to moderate sample sizes, the proposed procedure has smaller mean square errors than two existing estimation procedures. Finally, we demonstrate the estimation procedure by a real data example. PMID:22903245

  15. Revival of test bias research in preemployment testing.

    PubMed

    Aguinis, Herman; Culpepper, Steven A; Pierce, Charles A

    2010-07-01

    We developed a new analytic proof and conducted Monte Carlo simulations to assess the effects of methodological and statistical artifacts on the relative accuracy of intercept- and slope-based test bias assessment. The main simulation design included 3,185,000 unique combinations of a wide range of values for true intercept- and slope-based test bias, total sample size, proportion of minority group sample size to total sample size, predictor (i.e., preemployment test scores) and criterion (i.e., job performance) reliability, predictor range restriction, correlation between predictor scores and the dummy-coded grouping variable (e.g., ethnicity), and mean difference between predictor scores across groups. Results based on 15 billion 925 million individual samples of scores and more than 8 trillion 662 million individual scores raise questions about the established conclusion that test bias in preemployment testing is nonexistent and, if it exists, it only occurs regarding intercept-based differences that favor minority group members. Because of the prominence of test fairness in the popular media, legislation, and litigation, our results point to the need to revive test bias research in preemployment testing. PMID:20604587

  16. 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.

  17. Selection bias in rheumatic disease research

    PubMed Central

    Choi, Hyon K.; Nguyen, Uyen-Sa; Niu, Jingbo; Danaei, Goodarz; Zhang, Yuqing

    2014-01-01

    The identification of modifiable risk factors for the development of rheumatic conditions and their sequelae is crucial for reducing the substantial worldwide burden of these diseases. However, the validity of such research can be threatened by sources of bias, including confounding, measurement and selection biases. In this Review, we discuss potentially major issues of selection bias—a type of bias frequently overshadowed by other bias and feasibility issues, despite being equally or more problematic—in key areas of rheumatic disease research. We present index event bias (a type of selection bias) as one of the potentially unifying reasons behind some unexpected findings, such as the ‘risk factor paradox’—a phenomenon exemplified by the discrepant effects of certain risk factors on the development versus the progression of osteoarthritis (OA) or rheumatoid arthritis (RA). We also discuss potential selection biases owing to differential loss to follow-up in RA and OA research, as well as those due to the depletion of susceptibles (prevalent user bias) and immortal time bias. The lesson remains that selection bias can be ubiquitous and, therefore, has the potential to lead the field astray. Thus, we conclude with suggestions to help investigators avoid such issues and limit the impact on future rheumatology research. PMID:24686510

  18. 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…

  19. Establishing and Managing Switchgrass

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Care should be taken in selecting switchgrass varieties, using only those specifically adapted to the region of interest. Good establishment practices include using high quality seed, an appropriate seeding rate, a well-prepared seedbed, cultipacking after planting, and both pre- and post-emergence...

  20. 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