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Sample records for exchange bias coupling

  1. 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.

  2. 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

  3. 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

  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. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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

  19. 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).

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. Exchange coupling between laterally adjacent nanomagnets.

    PubMed

    Dey, H; Csaba, G; Bernstein, G H; Porod, W

    2016-09-30

    We experimentally demonstrate exchange-coupling between laterally adjacent nanomagnets. Our results show that two neighboring nanomagnets that are each antiferromagnetically exchange-coupled to a common ferromagnetic bottom layer can be brought into strong ferromagnetic interaction. Simulations show that interlayer exchange coupling effectively promotes ferromagnetic alignment between the two nanomagnets, as opposed to antiferromagnetic alignment due to dipole-coupling. In order to experimentally demonstrate the proposed scheme, we fabricated arrays of pairs of elongated, single-domain nanomagnets. Magnetic force microscopy measurements show that most of the pairs are ferromagnetically ordered. The results are in agreement with micromagnetic simulations. The presented scheme can achieve coupling strengths that are significantly stronger than dipole coupling, potentially enabling far-reaching applications in Nanomagnet Logic, spin-wave devices and three-dimensional storage and computing. PMID:27535227

  19. 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

  20. 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.

  1. Magnetization dynamics in exchange coupled antiferromagnet spin superfluids

    NASA Astrophysics Data System (ADS)

    Liu, Yizhou; Barlas, Yafis; Yin, Gen; Zang, Jiadong; Lake, Roger

    Antiferromagnets (AFMs) are commonly used as the exchange bias layer in magnetic recording and spintronic devices. Recently, several studies on the spin transfer torque and spin pumping in AFMs reveal much more interesting physics in AFMs. Properties of AFMs such as the ultrafast switching within picoseconds and spin superfluidity demonstrate the potential to build AFM based spintronic devices. Here, we study the magnetization dynamics in an exchange coupled AFM systems. Beginning from the Landau-Lifshitz-Gilbert equation, we derive a Josephson-like equation for the exchange coupled system. We investigate the detailed magnetization dynamics by employing spin injection and spin pumping theory. We also propose a geometry that could be used to measure this magnetization dynamics. This work was supported as part of the Spins and Heat in Nanoscale Electronic Systems (SHINES) an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #SC0012670.

  2. 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.

  3. 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.

  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. 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

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. Strong Electron-Hole Exchange in Coherently Coupled Quantum Dots

    NASA Astrophysics Data System (ADS)

    Fält, Stefan; Atatüre, Mete; Türeci, Hakan E.; Zhao, Yong; Badolato, Antonio; Imamoglu, Atac

    2008-03-01

    We have investigated few-body states in vertically stacked quantum dots. Because of a small interdot tunneling rate, the coupling in our system is in a previously unexplored regime where electron-hole exchange plays a prominent role. By tuning the gate bias, we are able to turn this coupling off and study a complementary regime where total electron spin is a good quantum number. The use of differential transmission allows us to obtain unambiguous signatures of the interplay between electron and hole-spin interactions. Small tunnel coupling also enables us to demonstrate all-optical charge sensing, where a conditional exciton energy shift in one dot identifies the charging state of the coupled partner.

  11. 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.

  12. 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.

  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. 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

  15. 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.

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

    PubMed Central

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

    2014-01-01

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

  17. Exchange coupled ferrite nanocomposites through chemical synthesis.

    PubMed

    Dai, Qilin; Patel, Ketan; Ren, Shenqiang

    2016-08-16

    Exchange coupling between magnetically hard and soft phases has the potential to yield a large gain in the energy product. In this work, we present a scalable chemical synthetic route to produce magnetic iron oxide based nanocomposites, consisting of cobalt ferrite (CoFe2O4) and strontium ferrite (SrFe12O19) components. PMID:27476744

  18. Quantifying exchange coupling in segregated granular materials

    NASA Astrophysics Data System (ADS)

    Morrison, C.; Saharan, L.; Ikeda, Y.; Takano, K.; Hrkac, G.; Thomson, T.

    2013-11-01

    The volume of a magnetic grain, together with its anisotropy, determines the probability of thermally activated reversal. Thus for grain volume distributions where the median volume is close to the superparamagnetic limit there will be a sub-set of grains which are either superparamagnetic on the time scale of a typical magnetic measurement (10 s), or the reverse due to magnetostatic fields from surrounding grains. We use this effect to probe exchange coupling in segregated granular materials, using CoCrPt-SiOx granular recording media as model systems. As the film thickness is reduced below 10 nm, the remanent magnetization of these films decreases, due to thermal activation and magnetostatic reversal. Varying film thickness and temperature allows us to thermally select a population of grains that contribute to the measurement. Exchange coupling is characterized by the angle dependence of remanent coercivity where we associate a breaking of symmetry from the Stoner-Wohlfarth model towards the Kondorsky model as a measure of the incoherency of reversal. Combining these models allows an estimate to be made of the volume fraction of grains that are exchange coupled and we find that, for well segregated CoCrPt-SiOx media, approximately 8% of the magnetic volume undergoes some degree of exchange coupling.

  19. Antenna-coupled arrays of voltage-biased superconducting bolometers

    SciTech Connect

    Myers, Michael J.; Lee, Adrian T.; Richards, P.L.; Schwan, D.; Skidmore, J.T.; Smith, A.D.; Spieler, H.; Yoon, Jongsoo

    2001-07-23

    We report on the development of antenna-coupled Voltage-biased Superconducting Bolometers (VSBs) which use Transition-edge Sensors (TES). Antenna coupling can greatly simplify the fabrication of large multi-frequency bolometer arrays compared to horn-coupled techniques. This simplification can make it practical to implement 1000+ element arrays that fill the focal plane of mm/sub-mm wave telescopes. We have designed a prototype device with a double-slot dipole antenna, integrated band-defining filters, and a membrane-suspended bolometer. A test chip has been constructed and will be tested shortly.

  20. 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.

  1. Micro-fluid exchange coupling apparatus

    NASA Technical Reports Server (NTRS)

    Johnson, J. E., Jr.; Swartz, P. F. (Inventor)

    1980-01-01

    In a macro-fluid exchange, a hollow needle, such as a syringe needle, is provided for penetrating the fluid conduit of the animal. The syringe needle is coupled to a plenum chamber having an inlet and outlet port. The plenum chamber is coupled to the syringe needle via the intermediary of a standard quick disconnect coupling fitting. The plenum chamber is carried at the end of a drive rod which is coupled to a micrometer drive head. The micrometer drive head is slidably and pivotably coupled to a pedestal for adjusting the height and angle of inclination of the needle relative to a reference base support. The needle is positioned adjacent to the incised trachea or a blood vessel of a small animal and the micrometer drive head is operated for penetrating the fluid conduit of the animal.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Long distance coupling of resonant exchange qubits

    NASA Astrophysics Data System (ADS)

    Russ, Maximilian; Burkard, Guido

    2015-11-01

    We investigate the effectiveness of a microwave cavity as a mediator of interactions between two resonant exchange (RX) qubits in semiconductor quantum dots (QDs) over long distances, limited only by the extension of the cavity. Our interaction model includes the orthonormalized Wannier orbitals constructed from Fock-Darwin states under the assumption of a harmonic QD confinement potential. We calculate the qubit-cavity coupling strength in a Jaynes-Cummings Hamiltonian and find that dipole transitions between two states with an asymmetric charge configuration constitute the relevant RX qubit-cavity coupling mechanism. The effective coupling between two RX qubits in a shared cavity yields a universal two-qubit iswap gate with gate times on the order of nanoseconds over distances on the order of up to a millimeter.

  14. Long distance coupling of resonant exchange qubits

    NASA Astrophysics Data System (ADS)

    Russ, Maximilian; Burkard, Guido

    We investigate the effectiveness of a microwave cavity as a mediator of interactions between two resonant exchange (RX) qubits in semiconductor quantum dots (QDs) over long distances, limited only by the extension of the cavity. Our interaction model includes the orthonormalized Wannier orbitals constructed from Fock-Darwin states under the assumption of a harmonic QD confinement potential. We calculate the qubit-cavity coupling strength gr in a Jaynes Cummings Hamiltonian, and find that dipole transitions between two states with an asymmetric charge configuration constitute the relevant RX qubit-cavity coupling mechanism. The effective coupling between two RX qubits in a shared cavity yields a universal two-qubit iSWAP-gate with gate times on the order of nanoseconds over distances on the order of up to a millimeter. Funded by ARO through Grant No. W911NF-15-1-0149.

  15. Manipulation by exchange coupling in layered magnetic structures

    SciTech Connect

    Moskalenko, M. A.; Uzdin, V. M.; Zabel, H.

    2014-02-07

    Exchange coupling in magnetic heterostructures can be modified via introduction of additional magnetic spacer layers at the interfaces. The magnetic characteristics and the spacer layer thickness determine the functional properties of the whole system. We show that the hysteresis loop area of trilayer spring magnets with two different soft magnetic layers (s1, s2) and one hard magnetic layer (h) with the sequence s1/s2/h can be increased as compared to both bilayer structures s1/h and s2/h with the same total thickness of the soft layers and for definite thickness ratios of the soft layers and their sequences. For ferrimagnetic spin valves, the perpendicular exchange bias effect can be tuned via the thickness of non-magnetic spacer layers at the interface, which determine the exchange coupling between ferrimagnets. A simple quasi one-dimensional phenomenological model is able to describe the magnetic hysteresis of even complex layered structures and to predict optimal geometrical and magnetic parameters of such heterostructures.

  16. TRP-Na(+)/Ca(2+) Exchanger Coupling.

    PubMed

    Harper, Alan G S; Sage, Stewart O

    2016-01-01

    Na(+)/Ca(2+) exchangers (NCXs) have traditionally been viewed principally as a means of Ca(2+) removal from non-excitable cells. However there has recently been increasing interest in the operation of NCXs in reverse mode acting as a means of eliciting Ca(2+) entry into these cells. Reverse mode exchange requires a significant change in the normal resting transmembrane ion gradients and membrane potential, which has been suggested to occur principally via the coupling of NCXs to localised Na(+) entry through non-selective cation channels such as canonical transient receptor potential (TRPC) channels. Here we review evidence for functional or physical coupling of NCXs to non-selective cation channels, and how this affects NCX activity in non-excitable cells. In particular we focus on the potential role of nanojunctions, where the close apposition of plasma and intracellular membranes may help create the conditions needed for the generation of localised rises in Na(+) concentration that would be required to trigger reverse mode exchange. PMID:27161225

  17. 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.

  18. 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.

  19. 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.

  20. Exchange-coupled nanocomposites: chemical synthesis, characterization and applications.

    PubMed

    Liu, Fei; Hou, Yanglong; Gao, Song

    2014-12-01

    Nanocomposites containing soft and hard magnetic phases have attracted immense attention for energy-related and biomedical applications. With exchange coupling between nanoscale grains in the composites, magnetization of the soft magnetic phase can rotate coherently with that of the hard magnetic phase. In particular, good control of the soft and hard phases at the nanoscale in the composites is of great importance for effective exchange coupling, allowing us to make the best of the strengths of soft and hard magnetic phases and to optimize the magnetic properties for targeted applications. In this review, we present the recent progress in the chemical synthesis and applications of exchange-coupled nanocomposites. Firstly, the principle of nanomagnetism and exchange coupling is introduced. Secondly, the characterization of exchange-coupled nanocomposites is summarized. Thirdly, the chemical methods for the production of different exchange-coupled nanocomposites are presented. Finally, applications of exchange-coupled nanocomposites in magnetic energy storage and biomedicine are addressed. PMID:25130706

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Information Filtering via Biased Random Walk on Coupled Social Network

    PubMed Central

    Dong, Qiang; Fu, Yan

    2014-01-01

    The recommender systems have advanced a great deal in the past two decades. However, most researchers focus their attentions on mining the similarities among users or objects in recommender systems and overlook the social influence which plays an important role in users' purchase process. In this paper, we design a biased random walk algorithm on coupled social networks which gives recommendation results based on both social interests and users' preference. Numerical analyses on two real data sets, Epinions and Friendfeed, demonstrate the improvement of recommendation performance by taking social interests into account, and experimental results show that our algorithm can alleviate the user cold-start problem more effectively compared with the mass diffusion and user-based collaborative filtering methods. PMID:25147867

  17. Information filtering via biased random walk on coupled social network.

    PubMed

    Nie, Da-Cheng; Zhang, Zi-Ke; Dong, Qiang; Sun, Chongjing; Fu, Yan

    2014-01-01

    The recommender systems have advanced a great deal in the past two decades. However, most researchers focus their attentions on mining the similarities among users or objects in recommender systems and overlook the social influence which plays an important role in users' purchase process. In this paper, we design a biased random walk algorithm on coupled social networks which gives recommendation results based on both social interests and users' preference. Numerical analyses on two real data sets, Epinions and Friendfeed, demonstrate the improvement of recommendation performance by taking social interests into account, and experimental results show that our algorithm can alleviate the user cold-start problem more effectively compared with the mass diffusion and user-based collaborative filtering methods. PMID:25147867

  18. 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.

  19. 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

  20. 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.

  1. Sources of tropical Atlantic coupled model biases derived from initialised hindcasts and partially coupled sensitivity experiments

    NASA Astrophysics Data System (ADS)

    Deppenmeier, Anna-Lena; Hazeleger, Wilco; Haarsma, Rein; Prodhomme, Chloé; Exarchou, Eleftheria; Doblas-Reyes, Francisco J.

    2016-04-01

    State-of-the-art coupled general circulation models (CGCMs) still fail to simulate the mean state and variability of the tropical Atlantic (TA) climate correctly. We investigate the importance of air-sea interaction at different regions in the TA by means of performing partially coupled sensitivity experiments with the state-of-the-art CGCM EC-Earth3.1. All simulations are intialised from the observed climate state. By studying the initial drift in sensitivity experiments we obtain insight into the tropical dynamics and sources of model bias. We test the influence of realistic wind stress forcing over different regions of the TA on the development of SST as well as other oceanic biases. A series of hindcasts fully initialised in May and run until the end of August are performed with prescribed ERA-Interim zonal and meridional wind stresses over three different regions: firstly, we force the entire TA from 15N - 30S. Secondly, we force the equatorial band only between 5N - 5S, and finally we force the coastal area of the Angola Benguela upwelling region between 0W and the coast and between 5S - 30N. Our setup only affects the oceanic forcing and leaves the atmosphere free to adapt, such that we can identify the air-sea interaction processes in the different regions and their effect on the SST bias in the fully coupled system. The differences between forcing the entire TA and the equatorial region only are very small, which hints to the great importance of the relatively narrow equatorial region. The coastal upwelling area does not strongly affect the equatorial region in our model. We identify the equatorial band as most susceptible to errors in the wind stress forcing and, due to the strong atmosphere-ocean coupling, as source of the main biases in our model. The partially coupled experiments with initialised seasonal hindcasts appear to be a powerful tool to identify the sources of model biases and to identify relevant air-sea interaction processes in the TA.

  2. 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

  3. 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.

  4. Exchange-coupled nanocomposite magnets by nanoparticle self-assembly.

    PubMed

    Zeng, Hao; Li, Jing; Liu, J P; Wang, Zhong L; Sun, Shouheng

    2002-11-28

    Exchange-spring magnets are nanocomposites that are composed of magnetically hard and soft phases that interact by magnetic exchange coupling. Such systems are promising for advanced permanent magnetic applications, as they have a large energy product--the combination of permanent magnet field and magnetization--compared to traditional, single-phase materials. Conventional techniques, including melt-spinning, mechanical milling and sputtering, have been explored to prepare exchange-spring magnets. However, the requirement that both the hard and soft phases are controlled at the nanometre scale, to ensure efficient exchange coupling, has posed significant preparation challenges. Here we report the fabrication of exchange-coupled nanocomposites using nanoparticle self-assembly. In this approach, both FePt and Fe3O4 particles are incorporated as nanometre-scale building blocks into binary assemblies. Subsequent annealing converts the assembly into FePt-Fe3Pt nanocomposites, where FePt is a magnetically hard phase and Fe3Pt a soft phase. An optimum exchange coupling, and therefore an optimum energy product, can be obtained by independently tuning the size and composition of the individual building blocks. We have produced exchange-coupled isotropic FePt-Fe3Pt nanocomposites with an energy product of 20.1 MG Oe, which exceeds the theoretical limit of 13 MG Oe for non-exchange-coupled isotropic FePt by over 50 per cent. PMID:12459779

  5. 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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  8. 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.

  9. 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

  10. 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.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Bias-dependence of luminescent coupling efficiency in multijunction solar cells.

    PubMed

    Jia, Jieyang; Miao, Yu; Kang, Yangsen; Huo, Yijie; Mazouchi, Mojgan; Chen, Yusi; Zhao, Li; Deng, Huiyang; Supaniratisai, Pakapol; AlQahtani, Sara H; Harris, James S

    2015-04-01

    In this work, we demonstrate an improved method to simulate the characteristics of multijunction solar cell by introducing a bias-dependent luminescent coupling efficiency. The standard two-diode equivalent-circuit model with constant luminescent coupling efficiency has limited accuracy because it does not include the recombination current from photogenerated carriers. Therefore, we propose an alternative analytical method with bias-dependent luminescent coupling efficiency to model multijunction cell behavior. We show that there is a noticeable difference in the J-V characteristics and cell performance generated by simulations with a constant vs. bias-dependent coupling efficiency. The results indicate that introducing a bias-dependent coupling efficiency produces more accurate modeling of multijunction cell behavior under real operating conditions. PMID:25968788

  3. 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.

  4. 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.

  5. Study of exchange bias and training effect in NiCr2O4

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  6. Magnetic exchange coupling through superconductors: A trilayer study

    NASA Astrophysics Data System (ADS)

    Sá de Melo, C. A.

    2000-11-01

    The possibility of magnetic exchange coupling between two ferromagnets (F) separated by a superconductor (S) spacer is analyzed using the functional integral method. For this coupling to occur three prima facie conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity to ferromagnetic boundaries. Third, roughness of the F/S interfaces must be small. Under these conditions, when the superconductor is cooled to below its critical temperature, the magnetic coupling changes. The appearance of the superconducting gap introduces a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below the the critical temperature of the superconductor, as well as strongly temperature-dependent. However, at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above the critical temperature of the superconductor the magnetic coupling decay length is controlled by the thermal length.

  7. 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

  8. 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.

  9. FAST TRACK COMMUNICATION: Interlayer exchange coupling across a ferroelectric barrier

    NASA Astrophysics Data System (ADS)

    Zhuravlev, M. Ye; Vedyayev, A. V.; Tsymbal, E. Y.

    2010-09-01

    A new magnetoelectric effect is predicted originating from the interlayer exchange coupling between two ferromagnetic layers separated by an ultrathin ferroelectric barrier. It is demonstrated that ferroelectric polarization switching driven by an external electric field leads to a sizable change in the interlayer exchange coupling. The effect occurs in asymmetric ferromagnet/ferroelectric/ferromagnet junctions due to a change in the electrostatic potential profile across the junction affecting the interlayer coupling. The predicted phenomenon indicates the possibility of switching the magnetic configuration by reversing the polarization of the ferroelectric barrier layer.

  10. A Novel Method for Analyzing Extremely Biased Agonism at G Protein–Coupled Receptors

    PubMed Central

    Zhou, Lei; Ehlert, Frederick J.; Bohn, Laura M.

    2015-01-01

    Seven transmembrane receptors were originally named and characterized based on their ability to couple to heterotrimeric G proteins. The assortment of coupling partners for G protein–coupled receptors has subsequently expanded to include other effectors (most notably the βarrestins). This diversity of partners available to the receptor has prompted the pursuit of ligands that selectively activate only a subset of the available partners. A biased or functionally selective ligand may be able to distinguish between different active states of the receptor, and this would result in the preferential activation of one signaling cascade more than another. Although application of the “standard” operational model for analyzing ligand bias is useful and suitable in most cases, there are limitations that arise when the biased agonist fails to induce a significant response in one of the assays being compared. In this article, we describe a quantitative method for measuring ligand bias that is particularly useful for such cases of extreme bias. Using simulations and experimental evidence from several κ opioid receptor agonists, we illustrate a “competitive” model for quantitating the degree and direction of bias. By comparing the results obtained from the competitive model with the standard model, we demonstrate that the competitive model expands the potential for evaluating the bias of very partial agonists. We conclude the competitive model provides a useful mechanism for analyzing the bias of partial agonists that exhibit extreme bias. PMID:25680753

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Effect of interlayer exchange coupling on magnetic chiral structures

    SciTech Connect

    Kang, S. P.; Kwon, H. Y.; Kim, H. S.; Shim, J. H.; Won, C.

    2015-07-28

    We numerically investigated the effect of interlayer exchange coupling on magnetic chiral structures, such as a helical/cycloidal spin structure and magnetic skyrmion crystal (SkX), which are produced in a magnetic system involving the Dzyaloshinskii-Moriya interaction (DMI). We report the existence of a phase transition where the length scale of magnetic structure discontinuously changes, and that there can be a novel magnetic structure around the phase boundary that exhibits double-ordering lengths of magnetic structure. Therefore, the system has multiple ground phases determined by the ratio of interlayer exchange coupling strength and DMI strength. Furthermore, we investigated the critical condition of the external perpendicular field required for the SkX. The critical field is significantly reduced under the effect of interlayer exchange coupling, which can stabilize the SkX without the external field.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Magnetic Exchange Coupling in Ferromagnetic/Superconducting/Ferromagnetic Multilayers

    NASA Astrophysics Data System (ADS)

    de Melo, C. A. R. Sa

    2001-03-01

    The possibility of magnetic exchange coupling between ferromagnets (F) separated by superconductor (S) spacers in F/S/F multilayers is analysed theoretically [1,2]. Ideal systems for the observation of magnetic coupling through superconductors are complex oxide multilayers consisting of Colossal Magneto-Resistance (CMR) Ferromagnets and High Critical Temperature Cuprate Superconductors. For this coupling to occur, three "prima facie" conditions need to be satisfied. First, an indirect exchange coupling between the ferromagnets must exist when the superconductor is in its normal state. Second, superconductivity must not be destroyed due to the proximity of ferromagnetic boundaries. Third, roughness of the F/S interfaces must be small. Under these conditions, when the superconductor is cooled below its critical temperature T_c, the magnetic coupling changes. The appearance of the superconducting gap introduces a new length scale (the coherence length of the superconductor) and modifies the temperature dependence of the indirect exchange coupling existent in the normal state. The magnetic coupling is oscillatory both above and below T_c, as well as strongly temperature-dependent. However at low temperatures the indirect exchange coupling decay length is controlled by the coherence length of the superconductor, while at temperatures close to and above Tc the magnetic coupling decay length is controlled by the thermal length. [I would like to thank the Georgia Institute of Technology, NSF (Grant No. DMR-9803111) and NATO (Grant No. CRG-972261) for financial support.] [1] C. A. R. Sa de Melo, Phys. Rev. Lett. 79, 1933 (1997). [2] C. A. R. Sa de Melo, Phys. Rev. B 62, 12303 (2000).

  3. 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

  4. Micromagnetic simulation of exchange coupled ferri-/ferromagnetic heterostructures

    PubMed Central

    Oezelt, Harald; Kovacs, Alexander; Reichel, Franz; Fischbacher, Johann; Bance, Simon; Gusenbauer, Markus; Schubert, Christian; Albrecht, Manfred; Schrefl, Thomas

    2015-01-01

    Exchange coupled ferri-/ferromagnetic heterostructures are a possible material composition for future magnetic storage and sensor applications. In order to understand the driving mechanisms in the demagnetization process, we perform micromagnetic simulations by employing the Landau–Lifshitz–Gilbert equation. The magnetization reversal is dominated by pinning events within the amorphous ferrimagnetic layer and at the interface between the ferrimagnetic and the ferromagnetic layer. The shape of the computed magnetization reversal loop corresponds well with experimental data, if a spatial variation of the exchange coupling across the ferri-/ferromagnetic interface is assumed. PMID:25937693

  5. Micromagnetic simulation of exchange coupled ferri-/ferromagnetic heterostructures

    NASA Astrophysics Data System (ADS)

    Oezelt, Harald; Kovacs, Alexander; Reichel, Franz; Fischbacher, Johann; Bance, Simon; Gusenbauer, Markus; Schubert, Christian; Albrecht, Manfred; Schrefl, Thomas

    2015-05-01

    Exchange coupled ferri-/ferromagnetic heterostructures are a possible material composition for future magnetic storage and sensor applications. In order to understand the driving mechanisms in the demagnetization process, we perform micromagnetic simulations by employing the Landau-Lifshitz-Gilbert equation. The magnetization reversal is dominated by pinning events within the amorphous ferrimagnetic layer and at the interface between the ferrimagnetic and the ferromagnetic layer. The shape of the computed magnetization reversal loop corresponds well with experimental data, if a spatial variation of the exchange coupling across the ferri-/ferromagnetic interface is assumed.

  6. Ferromagnetic resonance of exchange-coupled perpendicularly magnetized bilayers

    NASA Astrophysics Data System (ADS)

    Devolder, Thibaut

    2016-04-01

    Strong ferromagnetic interlayer exchange couplings J in perpendicularly magnetized systems are becoming increasingly desirable for applications. We study whether ferromagnetic interlayer exchange couplings can be measured by a combination of broadband ferromagnetic resonance methods and magnetometry hysteresis loops. For this, we model the switching and the eigenexcitations in bilayer systems comprising a soft layer coupled to a thicker harder layer that possesses higher perpendicular magnetic anisotropy. For large J > 0, the switching fields are essentially independent of J but the frequency of the optical eigenmode of the bilayer and the linewidth of the acoustical and optical eigenmode are directly sensitive to the coupling. We derive a corpus of compact analytical expressions to analyze these frequencies, their linewidth and discuss the meaning thereof. We illustrate this corpus on a system mimicking the fixed layers of a magnetic tunnel junction meant for spin torque applications.

  7. Improvement of bias stability for a micromachined gyroscope based on dynamic electrical balancing of coupling stiffness

    NASA Astrophysics Data System (ADS)

    Su, Jianbin; Xiao, Dingbang; Wu, Xuezhong; Hou, Zhanqiang; Chen, Zhihua

    2013-07-01

    We present a dynamic electrical balancing of coupling stiffness for improving the bias stability of micromachined gyroscopes, which embeds the coupling stiffness in a closed-loop system to make the micromachined gyroscope possess more robust bias stability by suppressing the variation of coupling stiffness. The effect of the dynamic electrical balancing control is theoretically analyzed and implemented using a silicon micromachined gyroscope as an example case. It has been experimentally shown that, comparing with open loop detection, the proposed method increased the stability of the amplitude of the mechanical quadrature signal by 38 times, and therefore improved the bias stability by 5.2 times from 89 to 17 deg/h, and the temperature stability of scale factor by 2.7 times from 622 to 231 ppm/°C. Experimental results effectively indicated the theoretical model of dynamic electrical balancing of coupling stiffness.

  8. Interlayer exchange coupling effect of L1(0) CoPt based exchange coupled composite media.

    PubMed

    Yang, Yang; Pandey, K K M; Chen, J S; Chow, G M; Hu, J F

    2011-03-01

    In this work, effects of exchange coupling of soft magnetic layer on switching field and magnetization reversal behaviour of CoPt-SiO2(soft)/CoPt-SiO2(hard) exchange coupled media were investigated. With increasing the thickness of the soft layer, both the coercivity and magnetization squareness of composite media decreased. Soft layer thickness 4 nm and below was more effective to significantly reduce the switching field than that above 4 nm. More incoherent switching behavior was observed with increasing soft layer thickness. PMID:21449436

  9. Exchange coupling between localized defect states in graphene nanoflakes

    NASA Astrophysics Data System (ADS)

    Droth, Matthias; Burkard, Guido

    2014-03-01

    Graphene nanoflakes are interesting because electrons are naturally confined in these quasi zero-dimensional structures, thus eluding the need for a bandgap. Defects inside the graphene lattice lead to localized states and the spins of two such localized states may be used for spintronics. We perform a tight-binding description on the entire system and, by virtue of a Schrieffer-Wolff-transformation on the bonding and antibonding states, we extract the coupling strength between the localized states. The coupling strength allows us to estimate the exchange coupling, which governs the dynamics of singlet-triplet spintronics.

  10. 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.

  11. Effect of bias application to plasma density in weakly magnetized inductively coupled plasma

    SciTech Connect

    Kim, Hyuk; Lee, Woohyun; Park, Wanjae; Whang, Ki-Woong

    2013-07-15

    Independent control of the ion flux and energy can be achieved in a dual frequency inductively coupled plasma (ICP) system. Typically, the plasma density is controlled by the high-frequency antenna radio-frequency (RF) power and the ion energy is controlled by the low-frequency bias RF power. Increasing the bias power has been known to cause a decrease in the plasma density in capacitively coupled discharge systems as well as in ICP systems. However, an applied axial magnetic field was found to sustain or increase the plasma density as bias power is increased. Measurements show higher electron temperatures but lower plasma densities are obtained in ordinary ICP systems than in magnetized ICP systems under the same neutral gas pressure and RF power levels. Explanations for the difference in the behavior of plasma density with increasing bias power are given in terms of the difference in the heating mechanism in ordinary unmagnetized and magnetized ICP systems.

  12. 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

  13. 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.

  14. A Coupled Nonlinear Spacecraft Attitude Controller and Observer with an Unknown Gyro Misalignment and Gyro Bias

    NASA Technical Reports Server (NTRS)

    Thienel, Julie; Sanner, Robert M.

    2002-01-01

    A nonlinear control scheme for attitude control of a spacecraft is combined with a nonlinear gyro misalignment and bias observer for the case of constant gyro misalignment and bias. A persistency of excitation analysis shows the observer gyro bias estimates converge to the true bias values exponentially fast. The convergence of the misalignment estimates is also presented. Then; the resulting coupled, closed loop dynamics are proven by a Lyapunov analysis to be globally stable, with asymptotically perfect tracking. The analysis is extended to consider the effects of noise in addition to the gyro misalignment and bias. A simulation of the proposed observer-controller design is given for a rigid spacecraft tracking a specified, time-varying attitude sequence to illustrate the theoretical claims.

  15. Biased ligands at G-protein-coupled receptors: promise and progress.

    PubMed

    Violin, Jonathan D; Crombie, Aimee L; Soergel, David G; Lark, Michael W

    2014-07-01

    Drug discovery targeting G protein-coupled receptors (GPCRs) is no longer limited to seeking agonists or antagonists to stimulate or block cellular responses associated with a particular receptor. GPCRs are now known to support a diversity of pharmacological profiles, a concept broadly referred to as functional selectivity. In particular, the concept of ligand bias, whereby a ligand stabilizes subsets of receptor conformations to engender novel pharmacological profiles, has recently gained increasing prominence. This review discusses how biased ligands may deliver safer, better tolerated, and more efficacious drugs, and highlights several biased ligands that are in clinical development. Biased ligands targeting the angiotensin II type 1 receptor and the μ opioid receptor illustrate the translation of the biased ligand concept from basic biology to clinical drug development. PMID:24878326

  16. 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.

  17. 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

  18. 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.

  19. Investigating the mechanisms of seasonal ENSO phase locking bias in the ACCESS coupled model

    NASA Astrophysics Data System (ADS)

    Rashid, Harun A.; Hirst, Anthony C.

    2016-02-01

    The mechanisms of coupled model bias in seasonal ENSO phase locking are investigated using versions 1.0 and 1.3 of the CSIRO-BOM ACCESS coupled model (hereafter, ACCESS1.0 and ACCESS1.3, respectively). The two ACCESS coupled models are mostly similar in construction except for some differences, the most notable of which are in the cloud and land surface schemes used in the models. ACCESS1.0 simulates a realistic seasonal phase locking, with the ENSO variability peaking in December as in observations. On the other hand, the simulated ENSO variability in ACCESS1.3 peaks in March, a bias shown to be shared by many other CMIP5 models. To explore the mechanisms of this model bias, we contrast the atmosphere-ocean feedbacks associated with ENSO in both ACCESS model simulations and also compare the key feedbacks with those in other CMIP5 models. We find evidence that the ENSO phase locking bias in ACCESS1.3 is primarily caused by incorrect simulations of the shortwave feedback and the thermocline feedback in this model. The bias in the shortwave feedback is brought about by unrealistic SST-cloud interactions leading to a positive cloud feedback bias that is largest around March, in contrast to the strongest negative cloud feedback found in ACCESS1.0 simulations and observations at that time. The positive cloud feedback bias in ACCESS1.3 is the result of a dominant role played by the low-level clouds in its modeled SST-cloud interactions in the tropical eastern Pacific. Two factors appear to contribute to the dominance of low-level clouds in ACCESS1.3: the occurrence of a stronger mean descending motion bias and, to a lesser extent, a larger mean SST cold bias during March-April in ACCESS1.3 than in ACCESS1.0. A similar association is found between the positive cloud feedback bias and the biases in spring-time mean descending motion and SST for a group of CMIP5 models that show a seasonal phase locking bias similar to ACCESS1.3. Significant differences are also found

  20. 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.

  1. Are atmospheric biases responsible for the tropical Atlantic SST biases in the CNRM-CM5 coupled model?

    NASA Astrophysics Data System (ADS)

    Voldoire, A.; Claudon, M.; Caniaux, G.; Giordani, H.; Roehrig, R.

    2014-12-01

    southeastern Atlantic regions, to comprehensively address the Atlantic SST bias. As pointed out in Richter (Clim Dyn, doi:10.1007/s00382-012-1624-5, 2013), the need to improve the atmospheric component of the CNRM-CM model is emphasized, even though strong positive coupling feedbacks are highlighted.

  2. Structural insights into biased G protein-coupled receptor signaling revealed by fluorescence spectroscopy

    PubMed Central

    Rahmeh, Rita; Damian, Marjorie; Cottet, Martin; Orcel, Hélène; Mendre, Christiane; Durroux, Thierry; Sharma, K. Shivaji; Durand, Grégory; Pucci, Bernard; Trinquet, Eric; Zwier, Jurriaan M.; Deupi, Xavier; Bron, Patrick; Banères, Jean-Louis; Mouillac, Bernard; Granier, Sébastien

    2012-01-01

    G protein-coupled receptors (GPCRs) are seven-transmembrane proteins that mediate most cellular responses to hormones and neurotransmitters, representing the largest group of therapeutic targets. Recent studies show that some GPCRs signal through both G protein and arrestin pathways in a ligand-specific manner. Ligands that direct signaling through a specific pathway are known as biased ligands. The arginine-vasopressin type 2 receptor (V2R), a prototypical peptide-activated GPCR, is an ideal model system to investigate the structural basis of biased signaling. Although the native hormone arginine-vasopressin leads to activation of both the stimulatory G protein (Gs) for the adenylyl cyclase and arrestin pathways, synthetic ligands exhibit highly biased signaling through either Gs alone or arrestin alone. We used purified V2R stabilized in neutral amphipols and developed fluorescence-based assays to investigate the structural basis of biased signaling for the V2R. Our studies demonstrate that the Gs-biased agonist stabilizes a conformation that is distinct from that stabilized by the arrestin-biased agonists. This study provides unique insights into the structural mechanisms of GPCR activation by biased ligands that may be relevant to the design of pathway-biased drugs. PMID:22493271

  3. Bidirectional private key exchange using delay-coupled semiconductor lasers.

    PubMed

    Porte, Xavier; Soriano, Miguel C; Brunner, Daniel; Fischer, Ingo

    2016-06-15

    We experimentally demonstrate a key exchange cryptosystem based on the phenomenon of identical chaos synchronization. In our protocol, the private key is symmetrically generated by the two communicating partners. It is built up from the synchronized bits occurring between two current-modulated bidirectionally coupled semiconductor lasers with additional self-feedback. We analyze the security of the exchanged key and discuss the amplification of its privacy. We demonstrate private key generation rates up to 11  Mbit/s over a public channel. PMID:27304310

  4. Spin–orbit coupling induced magnetoresistance oscillation in a dc biased two-dimensional electron system.

    PubMed

    Wang, C M; Lei, X L

    2014-06-11

    We study dc-current effects on the magnetoresistance oscillation in a two-dimensional electron gas with Rashba spin-orbit coupling, using the balance-equation approach to nonlinear magnetotransport. In the weak current limit the magnetoresistance exhibits periodical Shubnikov-de Haas oscillation with changing Rashba coupling strength for a fixed magnetic field. At finite dc bias, the period of the oscillation halves when the interbranch contribution to resistivity dominates. With further increasing current density, the oscillatory resistivity exhibits phase inversion, i.e., magnetoresistivity minima (maxima) invert to maxima (minima) at certain values of the dc bias, which is due to the current-induced magnetoresistance oscillation. PMID:25932474

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. Exchangers man the pumps: Functional interplay between proton pumps and proton-coupled Ca(2+) exchangers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tonoplast-localised proton-coupled Ca(2+) transporters encoded by cation/H(+) exchanger (CAX) genes play a critical role in sequestering Ca(2+) into the vacuole. These transporters may function in coordination with Ca(2+) release channels, to shape stimulus-induced cytosolic Ca(2+) elevations. Recen...

  12. Exchange coupling in metallic multilayers with a top FeRh layer

    NASA Astrophysics Data System (ADS)

    Yamada, S.; Tanikawa, K.; Hirayama, J.; Kanashima, T.; Taniyama, T.; Hamaya, K.

    2016-05-01

    We study magnetic properties of metallic multilayers with FeRh/ferromagnet interfaces grown by low-temperature molecular beam epitaxy. Room-temperature coercivity of the ferromagnetic layers is significantly enhanced after the growth of FeRh, proving the existence of the exchange coupling between the antiferromagnetic FeRh layer and the ferromagnetic layer. However, exchange bias is not clearly observed probably due to the presence of disordered structures, which result from the lattice strain at the FeRh/ferromagnet interfaces due to the lattice mismatch. We infer that the lattice matched interface between FeRh and ferromagnetic layers is a key parameter for controlling magnetic switching fields in such multilayer systems.

  13. Understanding the systematic air temperature biases in a coupled climate system model through a process-based decomposition method

    NASA Astrophysics Data System (ADS)

    Ren, R.-C.; Yang, Yang; Cai, Ming; Rao, Jian

    2015-10-01

    A quantitative attribution analysis is performed on the systematic atmospheric temperature biases in a coupled climate system model (flexible global ocean-atmosphere-land system model, spectral version 2) in reference to the European Center for Medium-Range Weather Forecasts, Re-analysis Interim data during 1979-2005. By adopting the coupled surface-atmosphere climate feedback response analysis method, the model temperature biases are related to model biases in representing the radiative processes including water vapor, ozone, clouds and surface albedo, and the non-radiative processes including surface heat fluxes and other dynamic processes. The results show that the temperature biases due to biases in radiative and non-radiative processes tend to compensate one another. In general, the radiative biases tend to dominate in the summer hemisphere, whereas the non-radiative biases dominate in the winter hemisphere. The temperature biases associated with radiative processes due to biases in ozone and water vapor content are the main contributors to the total temperature bias in the tropical and summer stratosphere. The overestimated surface albedo in both polar regions always results in significant cold biases in the atmosphere above in the summer season. Apart from these radiative biases, the zonal-mean patterns of the temperature biases in both boreal winter and summer are largely determined by model biases in non-radiative processes. In particular, the stronger non-radiative process biases in the northern winter hemisphere are responsible for the relatively larger `cold pole' bias in the northern winter polar stratosphere.

  14. Biased ligands for better cardiovascular drugs: dissecting G-protein-coupled receptor pharmacology.

    PubMed

    DeWire, Scott M; Violin, Jonathan D

    2011-07-01

    Drug discovery efforts targeting G-protein-coupled receptors (GPCR) have been immensely successful in creating new cardiovascular medicines. Currently marketed GPCR drugs are broadly classified as either agonists that activate receptors or antagonists that prevent receptor activation by endogenous stimuli. However, GPCR couple to a multitude of intracellular signaling pathways beyond classical G-protein signals, and these signals can be independently activated by biased ligands to vastly expand the potential for new drugs at these classic targets. By selectively engaging only a subset of a receptor's potential intracellular partners, biased ligands may deliver more precise therapeutic benefit with fewer side effects than current GPCR-targeted drugs. In this review, we discuss the history of biased ligand research, the current understanding of how biased ligands exert their unique pharmacology, and how research into GPCR signaling has uncovered previously unappreciated capabilities of receptor pharmacology. We focus on several receptors to illustrate the approaches taken and discoveries made, and how these are steadily illuminating the intricacies of GPCR pharmacology. Discoveries of biased ligands targeting the angiotensin II type 1 receptor and of separable pharmacology suggesting the potential value of biased ligands targeting the β-adrenergic receptors and nicotinic acid receptor GPR109a highlight the powerful clinical promise of this new category of potential therapeutics. PMID:21737816

  15. Exchange coupling in metals as understood then and now

    SciTech Connect

    Watson, R.E. )

    1989-01-01

    The first US magnetism conference occurred in 1952 and featured an invited session on exchange coupling in metals with Zener, Slater, Wohlfarth and Van Vleck speaking. All were concerned with intra- and interatomic exchange with Zener discussing coupling via conduction electron polarization while Wohlfarth and Slater were preoccupied with itinerant ferromagnetism. Van Vleck verbalized the Hubbard Hamiltonian (prior to its derivation). That meeting may be viewed as the ultimate discussion of magnetism prior to modern day computation and many of the ideas expressed there underlie our computational activities today. Solutions of the Hubbard Hamiltonian and electronic structure calculations, as applied to magnetism, come to mind. We will concentrate on the latter here, since solving the Hubbard Hamiltonian will be of great concern elsewhere in this meeting, and we will attempt to juxtapose current findings with some of the thoughts of that pioneering meeting. 30 refs., 5 figs.

  16. Bimagnetic nanoparticles with enhanced exchange coupling and energy products

    NASA Astrophysics Data System (ADS)

    Nandwana, Vikas; Chaubey, Girija S.; Yano, Kazuaki; Rong, Chuan-bing; Liu, J. Ping

    2009-01-01

    Bimagnetic FePt/Fe3O4 nanoparticles with core/shell or heterodimer structure have been prepared using a sequential synthetic method. The dimension of both FePt and Fe3O4 was tuned by varying the synthesis parameters. The as-synthesized bimagnetic nanoparticles were superparamagnetic at room temperature. After being annealed in a reducing atmosphere, the FePt/Fe3O4 bimagnetic nanoparticles were converted to a hard magnetic nanocomposite with enhanced energy products due to the exchange coupling between the hard and soft magnetic phases. It was found that the exchange coupling in nanocomposites made from the core/shell nanoparticles is stronger than that from the heterodimer nanoparticles. By tuning the dimensions of the FePt and Fe3O4 phases, the energy product up to 17.8 MGOe was achieved in the annealed nanocomposites, which is 36% higher than the isotropic single-phase FePt counterpart.

  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. 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.

  19. Magnetic properties of epitaxial-grown exchange-coupled FePt/FeRh bilayer films

    NASA Astrophysics Data System (ADS)

    Lu, Wei; He, Chenchong; Chen, Zhe; Fan, Junwei; Yan, Biao

    2012-07-01

    In this paper, (001) textured FeRh/FePt bilayer thin film was fabricated by sputtering and the temperature-dependent magnetic behavior of FePt/FeRh bilayers was investigated in detail. The magnetic regime passes from exchange bias to exchange spring when the temperature increases from low to high, resulting from the first-order antiferromagnetic (AFM) to ferromagnetic (FM) phase transition in ordered FeRh alloy layer. Controlling the temperature-allowed modification of the hysteresis loops of exchange-spring-like FeRh/FePt bilayer due to the nanoscale soft/hard interface exchange coupling, our experimental results clearly show that the coercive field decreases strongly at the temperature where FeRh completely transforms to ferromagnetic state. In an exchange-spring-like FeRh/FePt bilayer film, the out-of-plane magnetization reversal process was in two steps and resulted from domain wall nucleation and propagation from the FeRh layer into the FePt layer.

  20. 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.

  1. 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.

  2. 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.

  3. 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).

  4. Intergrain Exchange Coupling in PrCo/Co Films

    NASA Astrophysics Data System (ADS)

    Liu, J. P.; Shan, Z. S.; Sellmyer, D. J.

    1997-03-01

    Magnetic hardening and the intergrain exchange coupling in the PrCo/Co multilayer films have been investigated. The PrCo/Co multilayer thin films with Cr underlayer and cover layer were prepared by sputtering and followed by heat treatment. The as-deposited PrCo layer is amorphous and magnetically soft. Considerable coercivity is developed after the films are annealed at 500(C for 40 minutes. The maximum coercivity is 10 kOe. From the hysteresis loop it can be seen that the ratio Mr/Ms is larger than 0.5, suggesting an intergrain exchange coupling. It is interesting to note that the coercivity of the films with the Co interlayers is as large as that of the single-layer films, if the thickness of Co layers is less than 6 nm. This may be connected to the theoretical prediction that the intergrain exchange coupling remains strong if the dimension of the soft phase is less than the twice of the domain wall thickness in the hard phase (typically 3 nm in the rare earth-transition metal phases). Moreover, the insertion of Co layer enhances the magnetization remarkably. In the best situation, we obtained a maximum energy product of the film of 20 MGOe at room temperature.

  5. 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

  6. 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.

  7. 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.

  8. Coupled bias-variance tradeoff for cross-pose face recognition.

    PubMed

    Li, Annan; Shan, Shiguang; Gao, Wen

    2012-01-01

    Subspace-based face representation can be looked as a regression problem. From this viewpoint, we first revisited the problem of recognizing faces across pose differences, which is a bottleneck in face recognition. Then, we propose a new approach for cross-pose face recognition using a regressor with a coupled bias-variance tradeoff. We found that striking a coupled balance between bias and variance in regression for different poses could improve the regressor-based cross-pose face representation, i.e., the regressor can be more stable against a pose difference. With the basic idea, ridge regression and lasso regression are explored. Experimental results on CMU PIE, the FERET, and the Multi-PIE face databases show that the proposed bias-variance tradeoff can achieve considerable reinforcement in recognition performance. PMID:21724510

  9. Magnetic interactions in exchange-coupled yet unbiased IrMn/NiCu bilayers.

    PubMed

    Cichelero, R; Harres, A; Sossmeier, K D; Schmidt, J E; Geshev, J

    2013-10-23

    This paper reports experimental and model magnetization results obtained on exchange-coupled ferromagnet/antiferromagnet (FM/AF) bilayers that show zero net bias. The coercivity of the films, either irradiated with He or implanted with Ge ions at 40 keV, varies significantly with the fluence used. We employed the remanence plots technique in order to estimate the nature of the interactions present and check if there exists a correlation between their type and the coercivity variations. The analysis of the remanence plots through numerical simulations based on the Landau-Lifshitz-Gilbert equation demonstrated that outcomes of interactions within the FM layer could be distinguished from those coming from coupling at the FM/AF interface and that demagnetizing interaction effects could be achieved without the presence of dipolar interactions. Our findings indicate that such experiments could give selective information on modifications caused by a post-deposition treatment in each layer of the film. PMID:24065441

  10. Fulfilling the Promise of "Biased" G Protein–Coupled Receptor Agonism

    PubMed Central

    Maudsley, Stuart; Bohn, Laura M.

    2015-01-01

    The fact that over 30% of current pharmaceuticals target heptahelical G protein–coupled receptors (GPCRs) attests to their tractability as drug targets. Although GPCR drug development has traditionally focused on conventional agonists and antagonists, the growing appreciation that GPCRs mediate physiologically relevant effects via both G protein and non–G protein effectors has prompted the search for ligands that can "bias" downstream signaling in favor of one or the other process. Biased ligands are novel entities with distinct signaling profiles dictated by ligand structure, and the potential prospect of biased ligands as better drugs has been pleonastically proclaimed. Indeed, preclinical proof-of-concept studies have demonstrated that both G protein and arrestin pathway-selective ligands can promote beneficial effects in vivo while simultaneously antagonizing deleterious ones. But along with opportunity comes added complexity and new challenges for drug discovery. If ligands can be biased, then ligand classification becomes assay dependent, and more nuanced screening approaches are needed to capture ligand efficacy across several dimensions of signaling. Moreover, because the signaling repertoire of biased ligands differs from that of the native agonist, unpredicted responses may arise in vivo as these unbalanced signals propagate. For any given GPCR target, establishing a framework relating in vitro efficacy to in vivo biologic response is crucial to biased drug discovery. This review discusses approaches to describing ligand efficacy in vitro, translating ligand bias into biologic response, and developing a systems-level understanding of biased agonism in vivo, with the overall goal of overcoming current barriers to developing biased GPCR therapeutics. PMID:26134495

  11. Fulfilling the Promise of "Biased" G Protein-Coupled Receptor Agonism.

    PubMed

    Luttrell, Louis M; Maudsley, Stuart; Bohn, Laura M

    2015-09-01

    The fact that over 30% of current pharmaceuticals target heptahelical G protein-coupled receptors (GPCRs) attests to their tractability as drug targets. Although GPCR drug development has traditionally focused on conventional agonists and antagonists, the growing appreciation that GPCRs mediate physiologically relevant effects via both G protein and non-G protein effectors has prompted the search for ligands that can "bias" downstream signaling in favor of one or the other process. Biased ligands are novel entities with distinct signaling profiles dictated by ligand structure, and the potential prospect of biased ligands as better drugs has been pleonastically proclaimed. Indeed, preclinical proof-of-concept studies have demonstrated that both G protein and arrestin pathway-selective ligands can promote beneficial effects in vivo while simultaneously antagonizing deleterious ones. But along with opportunity comes added complexity and new challenges for drug discovery. If ligands can be biased, then ligand classification becomes assay dependent, and more nuanced screening approaches are needed to capture ligand efficacy across several dimensions of signaling. Moreover, because the signaling repertoire of biased ligands differs from that of the native agonist, unpredicted responses may arise in vivo as these unbalanced signals propagate. For any given GPCR target, establishing a framework relating in vitro efficacy to in vivo biologic response is crucial to biased drug discovery. This review discusses approaches to describing ligand efficacy in vitro, translating ligand bias into biologic response, and developing a systems-level understanding of biased agonism in vivo, with the overall goal of overcoming current barriers to developing biased GPCR therapeutics. PMID:26134495

  12. Characterizing formation of interfacial domain wall and exchange coupling strength in laminated exchange coupled composites

    NASA Astrophysics Data System (ADS)

    Hou, H.-C.; Kirby, B. J.; Gao, K. Z.; Lai, C.-H.

    2013-04-01

    We have studied the N-dependent switching behavior of composite magnets, comprised of a hard CoPtCr-SiO2 (CPCS) film and a laminated soft [Pt/CPCS]N multilayer. First order reversal curve magnetometry provides evidence of interfacial domain wall (iDW) assisted reversal for N ≥ 5. The magnetic depth profiles determined from polarized neutron reflectometry (PNR) explicitly demonstrate that the composite magnets are more rigidly coupled for N = 3 than for N = 7, and suggest that for N = 7 reversal occurs via formation of iDW. By fitting the PNR profile into the energy surface calculations, we can further deduce the vertical coupling strength in the laminated soft layer.

  13. 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

  14. Magnetic Exchange Couplings in Transition Metal Complexes from DFT

    NASA Astrophysics Data System (ADS)

    Peralta, Juan

    In this talk I will review our current efforts for the evaluation of magnetic exchange couplings in transition metal complexes from density functional theory. I will focus on the performance of different DFT approximations, including a variety of hybrid density functionals, and show that hybrid density functionals containing approximately 30% Hartree-Fock type exchange are in general among the best choice in terms of accuracy. I will also describe a novel computational method to evaluate exchange coupling parameters using analytic self-consistent linear response theory. This method avoids the explicit evaluation of energy differences, which can become impractical for large systems. Our approach is based on the evaluation of the transversal magnetic torque between two magnetic centers for a given spin configuration using explicit constraints of the local magnetization direction via Lagrange multipliers. This method is applicable in combination with any modern density functional with a noncollinear spin generalization and can be utilized as a ``black-box''. I will show proof-of-concept calculations in frustrated Fe7IIIdisk-shaped clusters, and dinuclear CuII, FeIII, and heteronuclear complexes. NSF DMR-1206920.

  15. Skin Temperature Analysis and Bias Correction in a Coupled Land-Atmosphere Data Assimilation System

    NASA Technical Reports Server (NTRS)

    Bosilovich, Michael G.; Radakovich, Jon D.; daSilva, Arlindo; Todling, Ricardo; Verter, Frances

    2006-01-01

    In an initial investigation, remotely sensed surface temperature is assimilated into a coupled atmosphere/land global data assimilation system, with explicit accounting for biases in the model state. In this scheme, an incremental bias correction term is introduced in the model's surface energy budget. In its simplest form, the algorithm estimates and corrects a constant time mean bias for each gridpoint; additional benefits are attained with a refined version of the algorithm which allows for a correction of the mean diurnal cycle. The method is validated against the assimilated observations, as well as independent near-surface air temperature observations. In many regions, not accounting for the diurnal cycle of bias caused degradation of the diurnal amplitude of background model air temperature. Energy fluxes collected through the Coordinated Enhanced Observing Period (CEOP) are used to more closely inspect the surface energy budget. In general, sensible heat flux is improved with the surface temperature assimilation, and two stations show a reduction of bias by as much as 30 Wm(sup -2) Rondonia station in Amazonia, the Bowen ratio changes direction in an improvement related to the temperature assimilation. However, at many stations the monthly latent heat flux bias is slightly increased. These results show the impact of univariate assimilation of surface temperature observations on the surface energy budget, and suggest the need for multivariate land data assimilation. The results also show the need for independent validation data, especially flux stations in varied climate regimes.

  16. Roles of Surface and Interface Spins in Exchange Coupled Nanostructures

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong

    Exchange bias (EB) in magnetic nanostructures has remained a topic of global interest because of its potential use in spin valves, MRAM circuits, magnetic tunnel junctions, and spintronic devices. The exploration of EB on the nanoscale provides a novel approach to overcoming the superparamagnetic limit and increasing the thermoremanence of magnetic nanoparticles, a critical bottleneck for magnetic data storage applications. Recent advances in chemical synthesis have given us a unique opportunity to explore the EB in a variety of nanoparticle systems ranging from core/shell nanoparticles of Fe/γFe2O3, Co/CoO,and FeO/Fe3O4 to hollow nanoparticles of γFe2O3 and hybrid composite nanoparticles of Au/Fe3O4. Our studies have addressed the following fundamental and important questions: (i) Can one decouple collective contributions of the interface and surface spins to the EB in a core/shell nanoparticle system? (ii) Can the dynamic and static response of the core and shell be identified separately? (iii) Can one tune ``minor loop'' to ``exchange bias'' effects in magnetic hollow nanoparticles by varying the number of surface spins? (iv) Can one decouple collective contributions of the inner and outer surface spins to the EB in a hollow nanoparticle system? (v) Can EB be induced in a magnetic nanoparticle by forming its interface with a non-magnetic metal? Such knowledge is essential to tailor EB in magnetic nanostructures for spintronics applications. In this talk, we will discuss the aforementioned findings in terms of our experimental and atomistic Monte Carlo studies. The work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award No. DE-FG02-07ER46438.

  17. Stabilization of magnetic helix in exchange-coupled thin films.

    PubMed

    Dzemiantsova, L V; Meier, G; Röhlsberger, R

    2015-01-01

    Based on micromagnetic simulations, we report on a novel magnetic helix in a soft magnetic film that is sandwiched between and exchange-coupled to two hard magnetic layers with different anisotropies. We show that such a confined helix stays stable without the presence of an external magnetic field. The magnetic stability is determined by the energy minimization and is a result of an internal magnetic field created by the exchange interaction. We show that this internal field stores a magnetic energy density of a few kJ/m(3). We also find that it dramatically modifies ferromagnetic resonances, such that the helix can be used as a ferromagnetic resonance filter and a fast acting attenuator. PMID:26537574

  18. Stabilization of magnetic helix in exchange-coupled thin films

    PubMed Central

    Dzemiantsova, L. V.; Meier, G.; Röhlsberger, R.

    2015-01-01

    Based on micromagnetic simulations, we report on a novel magnetic helix in a soft magnetic film that is sandwiched between and exchange-coupled to two hard magnetic layers with different anisotropies. We show that such a confined helix stays stable without the presence of an external magnetic field. The magnetic stability is determined by the energy minimization and is a result of an internal magnetic field created by the exchange interaction. We show that this internal field stores a magnetic energy density of a few kJ/m3. We also find that it dramatically modifies ferromagnetic resonances, such that the helix can be used as a ferromagnetic resonance filter and a fast acting attenuator. PMID:26537574

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  6. What is biased efficacy? Defining the relationship between intrinsic efficacy and free energy coupling.

    PubMed

    Onaran, H Ongun; Rajagopal, Sudarshan; Costa, Tommaso

    2014-12-01

    A G protein-coupled receptor (GPCR) is only biologically active when associated with a transduction protein, but it can also switch function by interacting with different types of transduction proteins. Biased agonism arises when the ligand induces the receptor to engage distinct transduction proteins with different efficacies. We briefly review the concept of ligand efficacy, from the classical empirical idea to the current mechanistic views of allosteric regulation in proteins. A combination of these theoretically distinct ideas and methodologies allows us to distinguish true ligand bias from divergences of signalling caused by the system. We also demonstrate a rigorous mathematical connection between the intrinsic efficacy of classical receptor theory and the energetic effect that makes a ligand capable of stabilizing receptor-transducer association in the ternary complex model. This relationship unifies different definitions of efficacy and provides a rational basis for quantifying biased agonism. PMID:25448316

  7. 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.

  8. Nature of magnetization reversal in exchange-coupled polycrystalline NiO-Co bilayers

    NASA Astrophysics Data System (ADS)

    Chopra, Harsh Deep; Yang, David X.; Chen, P. J.; Brown, H. J.; Swartzendruber, L. J.; Egelhoff, W. F.

    2000-06-01

    The nature of magnetization reversal in exchange-coupled NiO-Co polycrystalline bilayers was investigated. As-deposited bilayers exhibit a moderate value of exchange bias HE (=-0.9 mT) and a significantly enhanced coercivity (HNiO-Coc=12.4 mT), which is roughly 5 times the coercivity of a reference Co single film (HCoc=2.7 mT). Real time investigation of magnetization reversal in exchange-coupled NiO-Co bilayers shows that reversal is highly local and nonuniform in nature. It is preceded by the formation of precursors or embryos of reversed domains as the applied field reaches a critical value ≅8.8-9.0 mT. Once this critical applied field value is reached, numerous reversed domains are formed. Growths of such reversed domains occur primarily by the abrupt nucleation and the subsequent coalescence together of reversed domains; wall motion is not the dominant growth mode. Clear evidence is presented which shows that the strength of exchange bias varies at the microscopic scale across the sample. This manifests itself as different microscopic regions switching abruptly at different fields, and a given microscopic area switching at different fields in the positive and negative field directions. When the applied field is along the unidirectional anisotropy, reversal of a given strongly coupled microscopic region is aided by exchange bias, and such a region switches first; the same region undergoes reversal last when the polarity of the applied field is changed to oppose unidirectional anisotropy. Significantly, it was found that, locally, the measured value of exchange bias may vary by a factor of 3 or more from the macroscopically measured value of HE (=-0.9 mT) obtained from the shift of the M-H loop. High-resolution transmission electron microscopy (HRTEM) shows that that the local variation in HE may be explained by considering the underlying microstructure and interfacial topography of the NiO-Co interface. HRTEM results show that the NiO surface parallel to the

  9. Evaluation of FOXFET biased ac-coupled silicon strip detector prototypes for CDF SVX upgrade

    SciTech Connect

    Laakso, M. Research Inst. for High Energy Physics , Helsinki )

    1992-03-01

    Silicon microstrip detectors for high-precision charged particle position measurements have been used in nuclear and particle physics for years. The detectors have evolved from simple surface barrier strip detectors with metal strips to highly complicated double-sided AC-coupled junction detectors. The feature of AC-coupling the readout electrodes from the diode strips necessitates the manufacture of a separate biasing structure for the strips, which comprises a common bias line together with a means for preventing the signal from one strip from spreading to its neighbors through the bias line. The obvious solution to this is to bias the strips through individual high value resistors. These resistors can be integrated on the detector wafer by depositing a layer of resistive polycrystalline silicon and patterning it to form the individual resistors. To circumvent the extra processing step required for polysilicon resistor processing and the rather difficult tuning of the process to obtain uniform and high enough resistance values throughout the large detector area, alternative methods for strip biasing have been devised. These include the usage of electron accumulation layer resistance for N{sup +}{minus} strips or the usage of the phenomenon known as the punch-through effect for P{sup +}{minus} strips. In this paper we present measurement results about the operation and radiation resistance of detectors with a punch-through effect based biasing structure known as a Field OXide Field-Effect Transistor (FOXFET), and present a model describing the FOXFET behavior. The studied detectors were prototypes for detectors to be used in the CDF silicon vertex detector upgrade.

  10. On the bilinear exchange coupling in ferromagnetic multilayers

    NASA Astrophysics Data System (ADS)

    Tilioua, M.

    2009-04-01

    We investigate a mathematical model describing the bilinear interlayer exchange coupling (IEC) of ferromagnets through spacers. We propose an extension in the case of the Maxwell system of the results obtained in Hamdache K and Tilioua M (2004 SIAM J. Appl. Math. 64 1077-97). The model couples the Landau-Lifshitz-Gilbert (LLG) equations with the Maxwell system. The Hoffmann interfacial boundary condition is considered to take into account bilinear IEC. The behavior of the electromagnetic field in the two cases of a thin and large nonmagnetic spacer is discussed. For example we obtain that the magnetic field in the nonmagnetic spacer vanishes in the case of a thin spacer. However the electric field depends explicitly on the initial data. Various other convergence results are also given.

  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. 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

  14. 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

  15. Tailoring coercivity of unbiased exchange-coupled ferromagnet/antiferromagnet bilayers

    SciTech Connect

    Sossmeier, K. D.; Schafer, D.; Bastos, A. P. O.; Schmidt, J. E.; Geshev, J.

    2012-07-01

    This paper reports experimental results obtained on unconventional exchange-coupled ferromagnet/antiferromagnet (FM/AF) system showing zero net bias. The Curie temperature of the FM (NiCu) is lower than the blocking temperature of the AF (IrMn). Samples were either annealed or irradiated with He, Ar, or Ge ions at 40 keV. Due to the exchange coupling at the FM/AF interface, the coercivity (H{sub C}) of the as-deposited FM/AF bilayer is rather higher than that of the corresponding FM single layer. We found that by choosing a proper ion fluence or annealing temperature, it is possible to controllably vary H{sub C}. Ion irradiation of the FM single layer has lead to only a decrease of H{sub C} and annealing or He ion irradiation has not caused important changes at the FM/AF interface; nevertheless, a twofold increase of H{sub C} was obtained after these treatments. Even more significant enhancement of H{sub C} was attained after Ge ion irradiation and attributed to ion-implantation-induced modification of only the FM layer; damages of the FM/AF interface, on the other hand, decrease the coercivity.

  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. 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.

  19. Evaluation of a regional air-quality model with bidirectional NH3 exchange coupled to an agroecosystem model

    NASA Astrophysics Data System (ADS)

    Bash, J. O.; Cooter, E. J.; Dennis, R. L.; Walker, J. T.; Pleim, J. E.

    2013-03-01

    Atmospheric ammonia (NH3) is the primary atmospheric base and an important precursor for inorganic particulate matter and when deposited NH3 contributes to surface water eutrophication, soil acidification and decline in species biodiversity. Flux measurements indicate that the air-surface exchange of NH3 is bidirectional. However, the effects of bidirectional exchange, soil biogeochemistry and human activity are not parameterized in air quality models. The US Environmental Protection Agency's (EPA) Community Multiscale Air-Quality (CMAQ) model with bidirectional NH3 exchange has been coupled with the United States Department of Agriculture's (USDA) Environmental Policy Integrated Climate (EPIC) agroecosystem model. The coupled CMAQ-EPIC model relies on EPIC fertilization timing, rate and composition while CMAQ models the soil ammonium (NH4+) pool by conserving the ammonium mass due to fertilization, evasion, deposition, and nitrification processes. This mechanistically coupled modeling system reduced the biases and error in NHx (NH3 + NH4+) wet deposition and in ambient aerosol concentrations in an annual 2002 Continental US (CONUS) domain simulation when compared to a 2002 annual simulation of CMAQ without bidirectional exchange. Fertilizer emissions estimated in CMAQ 5.0 with bidirectional exchange exhibits markedly different seasonal dynamics than the US EPA's National Emissions Inventory (NEI), with lower emissions in the spring and fall and higher emissions in July.

  20. Cosmic voids in coupled dark energy cosmologies: the impact of halo bias

    NASA Astrophysics Data System (ADS)

    Pollina, Giorgia; Baldi, Marco; Marulli, Federico; Moscardini, Lauro

    2016-01-01

    In this work, we analyse the properties of cosmic voids in standard and coupled dark energy cosmologies. Using large numerical simulations, we investigate the effects produced by the dark energy coupling on three statistics: the filling factor, the size distribution and the stacked profiles of cosmic voids. We find that the bias of the tracers of the density field used to identify the voids strongly influences the properties of the void catalogues, and, consequently, the possibility of using the identified voids as a probe to distinguish coupled dark energy models from the standard Λ cold dark matter cosmology. In fact, on one hand coupled dark energy models are characterized by an excess of large voids in the cold dark matter distribution as compared to the reference standard cosmology, due to their higher normalization of linear perturbations at low redshifts. Specifically, these models present an excess of large voids with Reff > 20, 15, 12h-1 Mpc , at z = 0, 0.55, 1, respectively. On the other hand, we do not find any significant difference in the properties of the voids detected in the distribution of collapsed dark matter haloes. These results imply that the tracer bias has a significant impact on the possibility of using cosmic void catalogues to probe cosmology.

  1. 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.

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

    SciTech Connect

    Sharma, Jyoti; Suresh, K. G.

    2015-02-16

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  4. An Air-Coupled Multiple Moving Membrane Micromachined Ultrasonic Transducer With Inverse Biasing Functionality.

    PubMed

    Emadi, Arezoo; Buchanan, Douglas A

    2016-08-01

    A novel air-coupled multiple moving membrane-capacitive micromachined ultrasonic transducer ( [Formula: see text]-CMUT) with individually biased deflectable plates has been developed. Unlike the conventional capacitive micromachined ultrasonic transducer, this device cell structure includes an additional deflectable plate that is suspended underneath the transducer top plate. This added flexible plate contributes to the device signal transmission and reception. It is demonstrated that due to the presence of this added moving plate, the transducer is capable of operating under inverse bias condition, where the driving voltage is sandwiched between two grounded electrodes. COMSOL electromechanical simulations were conducted to investigate the influence of the transducer additional moving plate. A set of three individuals and an array of [Formula: see text]-CMUT transducers were fabricated using a sacrificial technique and with resonant frequencies ranging from 0.8 to 2.1 MHz. Electrical, optical, and pitch-catch acoustic measurements were performed to characterize the transducers properties under inverse bias condition. The experimental results are shown to be in good agreement with the simulation results for all of the fabricated transducers. It is shown that these transducers are fully functional under both normal and inverse bias conditions without any degradation in the transducer performance. PMID:27254861

  5. Coupling and tuning of modal frequencies in direct current biased microelectromechanical systems arrays

    SciTech Connect

    Kambali, Prashant N.; Swain, Gyanadutta; Pandey, Ashok Kumar; Buks, Eyal; Gottlieb, Oded

    2015-08-10

    Understanding the coupling of different modal frequencies and their tuning mechanisms has become essential to design multi-frequency MEMS devices. In this work, we fabricate a MEMS beam with fixed boundaries separated from two side electrodes and a bottom electrode. Subsequently, we perform experiments to obtain the frequency variation of in-plane and out-of-plane mechanical modes of the microbeam with respect to both DC bias and laser heating. We show that the frequencies of the two modes coincide at a certain DC bias, which in turn can also be varied due to temperature. Subsequently, we develop a theoretical model to predict the variation of the two modes and their coupling due to a variable gap between the microbeam and electrodes, initial tension, and fringing field coefficients. Finally, we discuss the influence of frequency tuning parameters in arrays of 3, 33, and 40 microbeams, respectively. It is also found that the frequency bandwidth of a microbeam array can be increased to as high as 25 kHz for a 40 microbeam array with a DC bias of 80 V.

  6. Coupling and tuning of modal frequencies in direct current biased microelectromechanical systems arrays

    NASA Astrophysics Data System (ADS)

    Kambali, Prashant N.; Swain, Gyanadutta; Pandey, Ashok Kumar; Buks, Eyal; Gottlieb, Oded

    2015-08-01

    Understanding the coupling of different modal frequencies and their tuning mechanisms has become essential to design multi-frequency MEMS devices. In this work, we fabricate a MEMS beam with fixed boundaries separated from two side electrodes and a bottom electrode. Subsequently, we perform experiments to obtain the frequency variation of in-plane and out-of-plane mechanical modes of the microbeam with respect to both DC bias and laser heating. We show that the frequencies of the two modes coincide at a certain DC bias, which in turn can also be varied due to temperature. Subsequently, we develop a theoretical model to predict the variation of the two modes and their coupling due to a variable gap between the microbeam and electrodes, initial tension, and fringing field coefficients. Finally, we discuss the influence of frequency tuning parameters in arrays of 3, 33, and 40 microbeams, respectively. It is also found that the frequency bandwidth of a microbeam array can be increased to as high as 25 kHz for a 40 microbeam array with a DC bias of 80 V.

  7. 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.

  8. Room temperature skyrmion ground state stabilized through interlayer exchange coupling

    SciTech Connect

    Chen, Gong Schmid, Andreas K.; Mascaraque, Arantzazu; N'Diaye, Alpha T.

    2015-06-15

    Possible magnetic skyrmion device applications motivate the search for structures that extend the stability of skyrmion spin textures to ambient temperature. Here, we demonstrate an experimental approach to stabilize a room temperature skyrmion ground state in chiral magnetic films via exchange coupling across non-magnetic spacer layers. Using spin polarized low-energy electron microscopy to measure all three Cartesian components of the magnetization vector, we image the spin textures in Fe/Ni films. We show how tuning the thickness of a copper spacer layer between chiral Fe/Ni films and perpendicularly magnetized Ni layers permits stabilization of a chiral stripe phase, a skyrmion phase, and a single domain phase. This strategy to stabilize skyrmion ground states can be extended to other magnetic thin film systems and may be useful for designing skyrmion based spintronics devices.

  9. Optimization of perpendicular recording on exchange coupled composite media

    NASA Astrophysics Data System (ADS)

    Tang, Yuhui; Zhu, Jian-Gang; Hong, Sooyoul; Che, Xiaodong

    2008-04-01

    Using micromagnetic modeling, the recording performance of exchange coupled composite (ECC) media with perpendicular heads was systematically studied. The simulations indicated that the switching field angular dependency of ECC media is similar to the continuous media switching behavior. By tuning the magnetic properties of the soft/hard layers, it was found that a soft layer with high saturation magnetization and low anisotropy energy caused large dc noise and unfavorable Adjacent Track Erasure (ATE) performance in recording, which is mainly due to the small nucleation field. A quantitative optimization of ECC media was given. Recording with different head designs on ECC media was also evaluated and this showed that large head field gradients at both the trailing edge and track edges are crucial to the implementation of ECC media at high recording areal density.

  10. Exchange-coupled magnetic nanoparticles for efficient heat induction

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Hyun; Jang, Jung-Tak; Choi, Jin-Sil; Moon, Seung Ho; Noh, Seung-Hyun; Kim, Ji-Wook; Kim, Jin-Gyu; Kim, Il-Sun; Park, Kook In; Cheon, Jinwoo

    2011-07-01

    The conversion of electromagnetic energy into heat by nanoparticles has the potential to be a powerful, non-invasive technique for biotechnology applications such as drug release, disease treatment and remote control of single cell functions, but poor conversion efficiencies have hindered practical applications so far. In this Letter, we demonstrate a significant increase in the efficiency of magnetic thermal induction by nanoparticles. We take advantage of the exchange coupling between a magnetically hard core and magnetically soft shell to tune the magnetic properties of the nanoparticle and maximize the specific loss power, which is a gauge of the conversion efficiency. The optimized core-shell magnetic nanoparticles have specific loss power values that are an order of magnitude larger than conventional iron-oxide nanoparticles. We also perform an antitumour study in mice, and find that the therapeutic efficacy of these nanoparticles is superior to that of a common anticancer drug.

  11. High energy products in exchange-coupled nanocomposite films

    SciTech Connect

    Liu, J.P.; Liu, Y.; Skomski, R.; Sellmyer, D.J.

    1999-09-01

    Several systems of nanocomposite thin films have been prepared by plasma sputtering and heat treatment. By choosing suitable multilayer structures of the as-deposited films and subsequent heat-treatment processes, the nanostructures of the films have been tailored. The thermal processing is the key to control the morphology. Appropriate heat-treatment processes have been found for the systems studied, which result in the desired nanostructures. For the first time a nearly ideal nanostructure with the soft-phase grains embedded homogeneously in the hard phase grains has been obtained for the FePt-Fe{sub 1{minus}x}Pt{sub x} (x{approximately}0.3) system. Effective intergrain exchange coupling has been realized. As a consequence, high energy products up to 50 MGOe have been achieved.

  12. Energy exchange in strongly coupled plasmas with electron drift

    SciTech Connect

    Akbari-Moghanjoughi, M.; Ghorbanalilu, M.

    2015-11-15

    In this paper, the generalized viscoelastic collisional quantum hydrodynamic model is employed in order to investigate the linear dielectric response of a quantum plasma in the presence of strong electron-beam plasma interactions. The generalized Chandrasekhar's relativistic degeneracy pressure together with the electron-exchange and Coulomb interaction effects are taken into account in order to extend current research to a wide range of plasma number density relevant to big planetary cores and astrophysical compact objects. The previously calculated shear viscosity and the electron-ion collision frequencies are used for strongly coupled ion fluid. The effect of the electron-beam velocity on complex linear dielectric function is found to be profound. This effect is clearly interpreted in terms of the wave-particle interactions and their energy-exchange according to the sign of the imaginary dielectric function, which is closely related to the wave attenuation coefficient in plasmas. Such kinetic effect is also shown to be in close connection with the stopping power of a charged-particle beam in a quantum plasma. The effect of many independent plasma parameters, such as the ion charge-state, electron beam-velocity, and relativistic degeneracy, is shown to be significant on the growing/damping of plasma instability or energy loss/gain of the electron-beam.

  13. Energy exchange in strongly coupled plasmas with electron drift

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.; Ghorbanalilu, M.

    2015-11-01

    In this paper, the generalized viscoelastic collisional quantum hydrodynamic model is employed in order to investigate the linear dielectric response of a quantum plasma in the presence of strong electron-beam plasma interactions. The generalized Chandrasekhar's relativistic degeneracy pressure together with the electron-exchange and Coulomb interaction effects are taken into account in order to extend current research to a wide range of plasma number density relevant to big planetary cores and astrophysical compact objects. The previously calculated shear viscosity and the electron-ion collision frequencies are used for strongly coupled ion fluid. The effect of the electron-beam velocity on complex linear dielectric function is found to be profound. This effect is clearly interpreted in terms of the wave-particle interactions and their energy-exchange according to the sign of the imaginary dielectric function, which is closely related to the wave attenuation coefficient in plasmas. Such kinetic effect is also shown to be in close connection with the stopping power of a charged-particle beam in a quantum plasma. The effect of many independent plasma parameters, such as the ion charge-state, electron beam-velocity, and relativistic degeneracy, is shown to be significant on the growing/damping of plasma instability or energy loss/gain of the electron-beam.

  14. Wealth distribution of simple exchange models coupled with extremal dynamics

    NASA Astrophysics Data System (ADS)

    Bagatella-Flores, N.; Rodríguez-Achach, M.; Coronel-Brizio, H. F.; Hernández-Montoya, A. R.

    2015-01-01

    Punctuated Equilibrium (PE) states that after long periods of evolutionary quiescence, species evolution can take place in short time intervals, where sudden differentiation makes new species emerge and some species extinct. In this paper, we introduce and study the effect of punctuated equilibrium on two different asset exchange models: the yard sale model (YS, winner gets a random fraction of a poorer player's wealth) and the theft and fraud model (TF, winner gets a random fraction of the loser's wealth). The resulting wealth distribution is characterized using the Gini index. In order to do this, we consider PE as a perturbation with probability ρ of being applied. We compare the resulting values of the Gini index at different increasing values of ρ in both models. We found that in the case of the TF model, the Gini index reduces as the perturbation ρ increases, not showing dependence with the agents number. While for YS we observe a phase transition which happens around ρc = 0.79. For perturbations ρ <ρc the Gini index reaches the value of one as time increases (an extreme wealth condensation state), whereas for perturbations greater than or equal to ρc the Gini index becomes different to one, avoiding the system reaches this extreme state. We show that both simple exchange models coupled with PE dynamics give more realistic results. In particular for YS, we observe a power low decay of wealth distribution.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. Direct manipulation of the uncompensated antiferromagnetic spins in exchange coupled system by GeV ion irradiation

    SciTech Connect

    Paul, Amitesh; Boeni, P.; Paul, N.; Hoepfner, Britta; Lauermann, Iver; Lux-Steiner, M.; Trautmann, C.; Mattauch, S.

    2012-06-18

    Incident ion energy to matrix electrons of a material is dissipated within a narrow cylinder surrounding the swift heavy ion path. The temperature of the lattice exceeds the melting point and upon quenching causes nanometric modifications. We present here a unique ex situ approach in manipulating the uncompensated spins in antiferromagnetic layers of ferro-/antiferromagnetic exchange coupled systems on a nanometric scale. We use the impact of relativistic heavy ion (1-2 GeV) irradiation on such systems. We find an increase in the bias field and a restoration of the reversal via domain nucleation in the trained state. These are identified as plausible results of ion-induced antiferromagnetic ordering with little or no effect on the layer structure. This study demonstrates, therefore, the possibility of nanoscale tailoring of exchange coupled systems that survive even in the trained state.

  6. 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

  7. A hybrid model of radio frequency biased inductively coupled plasma discharges: description of model and experimental validation in argon

    NASA Astrophysics Data System (ADS)

    Wen, De-Qi; Liu, Wei; Gao, Fei; Lieberman, M. A.; Wang, You-Nian

    2016-08-01

    A hybrid model, i.e. a global model coupled bidirectionally with a parallel Monte-Carlo collision (MCC) sheath model, is developed to investigate an inductively coupled discharge with a bias source. This hybrid model can self-consistently reveal the interaction between the bulk plasma and the radio frequency (rf) bias sheath. More specifically, the plasma parameters affecting characteristics of rf bias sheath (sheath length and self-bias) are calculated by a global model and the effect of the rf bias sheath on the bulk plasma is determined by the voltage drop of the rf bias sheath. Moreover, specific numbers of ions are tracked in the rf bias sheath and ultimately the ion energy distribution function (IEDF) incident on the bias electrode is obtained. To validate this model, both bulk plasma density and IEDF on the bias electrode in an argon discharge are compared with experimental measurements, and a good agreement is obtained. The advantage of this model is that it can quickly calculate the bulk plasma density and IEDF on the bias electrode, which are of practical interest in industrial plasma processing, and the model could be easily extended to serve for industrial gases.

  8. 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

  9. Strong exchange coupling in lanthanide bis-(phthalocyaninato) sandwich compounds

    SciTech Connect

    Trojan, K.L.; Hatfield, W.E.; Kepler, K.D.; Kirk, M.L. )

    1991-04-15

    Bis (phthalocyaninato) lanthanide sandwich compounds, which have the formula Pc{sup 2-}LnPc{sup 1-}, have been synthesized for Ln=terbium, holmium, and lutecium. Low-temperature magnetic susceptibility data for Ho(Pc){sub 2} and Tb(Pc){sub 2} show a reduction in moment from that which is expected for the lanthanide free ion value, which correlates with an antiferromagnetic exchange between the lanthanide {ital f} electrons and the phthalocyaninato ligand radical electron. The {ital g} factors determined from least-squares fitting of the Curie--Weiss law to the magnetic data show excellent agreement to the {ital g} factors calculated for the strongly coupled state. Magnetic moments calculated from the experimentally determined Curie constants are also in good agreement with those expected for the strongly coupled state. Low-temperature magnetic susceptibility data for Lu(Pc){sub 2} follows the Curie--Weiss law with a limiting moment of 1.8 {mu}{sub {ital B}} at 100 K. Since lutecium has a {sup 1}{ital S}{sub 0} ground state, only the phthalocyanine(1-) ligand would be expected to contribute to the magnetic susceptibility in this system. Room-temperature electron paramagnetic resonance measurements show no transitions at or near {ital g}=2, indicative of a free radical, due to the strong antiferromagnetic coupling of the ligand radical electron with the lanthanide {ital f} electrons. In the case of LuPc{sub 2}, where no unpaired {ital f} electrons exist, a transition at {ital g}=2.00 is present.

  10. 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.

  11. 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

  12. 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.

  13. ESTIMATING GASEOUS EXCHANGES BETWEEN THE ATMOSPHERE AND PLANTS USING A COUPLED BIOCHEMICAL DRY DEPOSITION MODEL

    EPA Science Inventory

    To study gaseous exchanges between the soil, biosphere and atmosphere, a biochemical model was coupled with the latest version of Meyers Multi-Layer Deposition Model. The biochemical model describes photosynthesis and respiration and their coupling with stomatal resistance for...

  14. Allosteric and Biased G Protein-Coupled Receptor Signaling Regulation: Potentials for New Therapeutics

    PubMed Central

    Khoury, Etienne; Clément, Stéphanie; Laporte, Stéphane A.

    2014-01-01

    G protein-coupled receptors (GPCRs) are seven-transmembrane proteins that participate in many aspects of the endocrine function and are important targets for drug development. They transduce signals mainly, but not exclusively, via hetero-trimeric G proteins, leading to a diversity of intracellular signaling cascades. Ligands binding at the hormone orthosteric sites of receptors have been classified as agonists, antagonists, and/or inverse agonists based on their ability to mainly modulate G protein signaling. Accumulating evidence also indicates that such ligands, alone or in combination with other ones such as those acting outside the orthosteric hormone binding sites (e.g., allosteric modulators), have the ability to selectively engage subsets of signaling responses as compared to the natural endogenous ligands. Such modes of functioning have been variously referred to as “functional selectivity” or “ligand-biased signaling.” In this review, we provide an overview of the current knowledge regarding GPCR-biased signaling and their functional regulation with a focus on the evolving concept that receptor domains can also be targeted to allosterically bias signaling, and discuss the usefulness of such modes of regulation for the design of more efficient therapeutics. PMID:24847311

  15. Implementation of Coupled Skin Temperature Analysis and Bias Correction in a Global Atmospheric Data Assimilation System

    NASA Technical Reports Server (NTRS)

    Radakovich, Jon; Bosilovich, M.; Chern, Jiun-dar; daSilva, Arlindo

    2004-01-01

    The NASA/NCAR Finite Volume GCM (fvGCM) with the NCAR CLM (Community Land Model) version 2.0 was integrated into the NASA/GMAO Finite Volume Data Assimilation System (fvDAS). A new method was developed for coupled skin temperature assimilation and bias correction where the analysis increment and bias correction term is passed into the CLM2 and considered a forcing term in the solution to the energy balance. For our purposes, the fvDAS CLM2 was run at 1 deg. x 1.25 deg. horizontal resolution with 55 vertical levels. We assimilate the ISCCP-DX (30 km resolution) surface temperature product. The atmospheric analysis was performed 6-hourly, while the skin temperature analysis was performed 3-hourly. The bias correction term, which was updated at the analysis times, was added to the skin temperature tendency equation at every timestep. In this presentation, we focus on the validation of the surface energy budget at the in situ reference sites for the Coordinated Enhanced Observation Period (CEOP). We will concentrate on sites that include independent skin temperature measurements and complete energy budget observations for the month of July 2001. In addition, MODIS skin temperature will be used for validation. Several assimilations were conducted and preliminary results will be presented.

  16. From exchange coupling to magnetic memory: how domains remembers at nanoscale

    NASA Astrophysics Data System (ADS)

    Chesnel, Karine; Nelson, Joseph; Wilcken, Brian; Kevan, Steve; Carey, Matthew; Fullerton, Eric

    2009-10-01

    Magnetic memory, the ability of a material to remember its magnetic domain configuration throughout magnetization, offers potential technological interest for the data storage industry. One way to quantify the magnetic memory is to use Coherent X-ray Resonant Magnetic Scattering (XRMS) tools, at synchrotron facilities. The light is tuned to resonant edges of magnetic element to optimize the magneto-optical contrast. When illuminated by coherent beam, the sample produces speckle patterns. Our approach is to cross-correlate patterns recorded at different field values throughout the magnetization cycle, and at different temperatures. We have studied the return point memory (RPM) that characterizes the memory after a full cycle, and developed a q-selective correlation analysis to study the spatial dependency of the memory. We will give here an overview of different type of memory behaviors, first showing disorder induced memory in thin CoPt films and influence of roughness, then demonstrating the ability to control the magnetic memory by inducing exchange bias [1]. We will see how the local exchange couplings pin the magnetic domain in the ferromagnetic layer and lead the large memory enhancement at different spatial scales. [0pt] [1] K.Chesnel et al, PRB 78, 132409 (2008)

  17. From exchange coupling to magnetic memory: how domains remember at nanoscale

    NASA Astrophysics Data System (ADS)

    Gay, Karine; Nelson, Joseph; Fullerton, Eric; Carey, Matt; Kevan, Steve

    2010-03-01

    Magnetic memory, the ability of a material to remember its magnetic domain configuration throughout magnetization, offers potential technological interest for the data storage industry. One way to quantify the magnetic memory is to use Coherent X-ray Resonant Magnetic Scattering (XRMS), at synchrotron facilities. The light is tuned to resonant edges to optimize the magneto-optical contrast. When illuminated by coherent beam, the sample produces speckle patterns. Our approach is to cross-correlate patterns recorded at different field values throughout the magnetization cycle, and at different temperatures. We have studied the return point memory (RPM) that characterizes the memory after a full cycle, and developed a q-selective correlation analysis to study the spatial dependency of the memory. We will give here an overview of different type of memory behaviors, first showing disorder induced memory in thin CoPt films and influence of roughness, then demonstrating the ability to control the magnetic memory by inducing exchange bias (1). We will see how the local exchange couplings pin the magnetic domain in the ferromagnetic layer and lead the large memory enhancement at different spatial scales and under different field cooling conditions. (1) K.Chesnel et al, PRB 78, 132409 (2008)

  18. 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.

  19. Longitudinal biases in the Seychelles Dome simulated by 35 ocean-atmosphere coupled general circulation models

    NASA Astrophysics Data System (ADS)

    Nagura, Motoki; Sasaki, Wataru; Tozuka, Tomoki; Luo, Jing-Jia; Behera, Swadhin K.; Yamagata, Toshio

    2013-02-01

    Seychelles Dome refers to the shallow climatological thermocline in the southwestern Indian Ocean, where ocean wave dynamics efficiently affect sea surface temperature, allowing sea surface temperature anomalies to be predicted up to 1-2 years in advance. Accurate reproduction of the dome by ocean-atmosphere coupled general circulation models (CGCMs) is essential for successful seasonal predictions in the Indian Ocean. This study examines the Seychelles Dome as simulated by 35 CGCMs, including models used in phase five of the Coupled Model Intercomparison Project (CMIP5). Among the 35 CGCMs, 14 models erroneously produce an upwelling dome in the eastern half of the basin whereas the observed Seychelles Dome is located in the southwestern tropical Indian Ocean. The annual mean Ekman pumping velocity in these models is found to be almost zero in the southern off-equatorial region. This result is inconsistent with observations, in which Ekman upwelling acts as the main cause of the Seychelles Dome. In the models reproducing an eastward-displaced dome, easterly biases are prominent along the equator in boreal summer and fall, which result in shallow thermocline biases along the Java and Sumatra coasts via Kelvin wave dynamics and a spurious upwelling dome in the region. Compared to the CMIP3 models, the CMIP5 models are even worse in simulating the dome longitudes.

  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. 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. Engineering the interlayer exchange coupling in magnetic trilayers

    NASA Astrophysics Data System (ADS)

    Chang, Ching-Hao; Dou, Kun-Peng; Chen, Ying-Chin; Hong, Tzay-Ming; Kaun, Chao-Cheng

    2015-11-01

    When the thickness of metal film approaches the nanoscale, itinerant carriers resonate between its boundaries and form quantum well states (QWSs), which are crucial to account for the film’s electrical, transport and magnetic properties. Besides the classic origin of particle-in-a-box, the QWSs are also susceptible to the crystal structures that affect the quantum resonance. Here we investigate the QWSs and the magnetic interlayer exchange coupling (IEC) in the Fe/Ag/Fe (001) trilayer from first-principles calculations. We find that the carriers at the Brillouin-zone center (belly) and edge (neck) separately form electron- and hole-like QWSs that give rise to an oscillatory feature for the IEC as a function of the Ag-layer thickness with long and short periods. Since the QWS formation sensitively depends on boundary conditions, one can switch between these two IEC periods by changing the Fe-layer thickness. These features, which also occur in the magnetic trilayers with other noble-metal spacers, open a new degree of freedom to engineer the IEC in magnetoresistance devices.

  3. Engineering the interlayer exchange coupling in magnetic trilayers.

    PubMed

    Chang, Ching-Hao; Dou, Kun-Peng; Chen, Ying-Chin; Hong, Tzay-Ming; Kaun, Chao-Cheng

    2015-01-01

    When the thickness of metal film approaches the nanoscale, itinerant carriers resonate between its boundaries and form quantum well states (QWSs), which are crucial to account for the film's electrical, transport and magnetic properties. Besides the classic origin of particle-in-a-box, the QWSs are also susceptible to the crystal structures that affect the quantum resonance. Here we investigate the QWSs and the magnetic interlayer exchange coupling (IEC) in the Fe/Ag/Fe (001) trilayer from first-principles calculations. We find that the carriers at the Brillouin-zone center (belly) and edge (neck) separately form electron- and hole-like QWSs that give rise to an oscillatory feature for the IEC as a function of the Ag-layer thickness with long and short periods. Since the QWS formation sensitively depends on boundary conditions, one can switch between these two IEC periods by changing the Fe-layer thickness. These features, which also occur in the magnetic trilayers with other noble-metal spacers, open a new degree of freedom to engineer the IEC in magnetoresistance devices. PMID:26596253

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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.

  9. Enhanced interlayer exchange coupling in antiferromagnetically coupled ultrathin (Co70Fe30/Pd) multilayers

    NASA Astrophysics Data System (ADS)

    Meng, Zhaoliang; Qiu, Jinjun; Han, Guchang; Teo, Kie Leong

    2015-12-01

    We report the studies of magnetization reversal and magnetic interlayer coupling in synthetic antiferromagnetic (SAF) [Pd/Co70Fe30]9/Ru(tRu)/Pd(tPd)/[Co70Fe30/Pd]9 structure as functions of inserted Pd layer (tPd) and Ru layer (tRu) thicknesses. We found the exchange coupling field (Hex) and perpendicular magnetic anisotropy (PMA) can be controlled by both the tPd and tRu, The Hex shows a Ruderman-Kittel-Kasuya-Yosida-type oscillatory decay dependence on tRu and a maximum interlayer coupling strength Jex = 0.522 erg/cm2 is achieved at tPd + tRu ≈ 0.8 nm in the as-deposited sample. As it is known that a high post-annealing stability of SAF structure is required for magnetic random access memory applications, the dependence of Hex and PMA on the post-annealing temperature (Ta) is also investigated. We found that both high PMA of the top Co70Fe30/Pd multilayer is maintained and Hex is enhanced with increasing Ta up to 350 °C for tRu > 0.7 nm in our SAF structure.

  10. 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

  11. Biased signaling through G-protein-coupled PROKR2 receptors harboring missense mutations.

    PubMed

    Sbai, Oualid; Monnier, Carine; Dodé, Catherine; Pin, Jean-Philippe; Hardelin, Jean-Pierre; Rondard, Philippe

    2014-08-01

    Various missense mutations in the gene coding for prokineticin receptor 2 (PROKR2), a G-protein-coupled receptor, have been identified in patients with Kallmann syndrome. However, the functional consequences of these mutations on the different signaling pathways of this receptor have not been studied. We first showed that the wild-type PROKR2 can activate different G-protein subtypes (Gq, Gs, and Gi/o) and recruit β-arrestins in transfected HEK-293 cells. We then examined, for each of these signaling pathways, the effects of 9 mutations that did not significantly impair cell surface targeting or ligand binding of the receptor. Four mutant receptors showing defective Gq signaling (R85C, R85H, R164Q, and V331M) could still recruit β-arrestins on ligand activation, which may cause biased signaling in vivo. Conversely, the R80C receptor could activate the 3 types of G proteins but could not recruit β-arrestins. Finally, the R268C receptor could recruit β-arrestins and activate the Gq and Gs signaling pathways but could not activate the Gi/o signaling pathway. Our results validate the concept that mutations in the genes encoding membrane receptors can bias downstream signaling in various ways, possibly leading to pathogenic and, perhaps in some cases, protective (e.g., R268C) effects. PMID:24830383

  12. 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.

  13. Zero-bias microwave detectors based on array of nanorectifiers coupled with a dipole antenna

    NASA Astrophysics Data System (ADS)

    Kasjoo, Shahrir R.; Singh, Arun K.; Mat Isa, Siti S.; Ramli, Muhammad M.; Mohamad Isa, Muammar; Ahmad, Norhawati; Mohd Nor, Nurul I.; Khalid, Nazuhusna; Song, Ai Min

    2016-04-01

    We report on zero-bias microwave detection using a large array of unipolar nanodevices, known as the self-switching diodes (SSDs). The large array was realized in a single lithography step without the need of interconnection layers, hence allowing for a simple and low-cost fabrication process. The SSD array was coupled with a narrowband dipole antenna with a resonant frequency of 890 MHz, to form a simple rectenna (rectifying antenna). The extrinsic voltage responsivity and noise-equivalent-power (NEP) of the rectenna were ∼70 V/W and ∼0.18 nW/Hz1/2, respectively, measured in the far-field region at unbiased condition. Nevertheless, the estimated intrinsic voltage responsivity can achieve up to ∼5 kV/W with NEP of ∼2.6 pW/Hz1/2.

  14. 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.

  15. 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.

  16. 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.

  17. Antiferromagnetic Interlayer Exchange Coupling in All-Semiconducting EuS/PbS/EuS Trilayers

    NASA Technical Reports Server (NTRS)

    Smits, C. J. P.; Filip, A. T.; Swagten, H. J. M.; Koopmans, B.; deJonge, W. J. M.; Chernyshova, M.; Kowalczyk, L.; Grasza, K.; Szczerbakow, A.; Story, T.

    2003-01-01

    A comprehensive experimental study on the antiferromagnetic interlayer exchange coupling in high quality epitaxial all-semiconducting EuSPbSEuS trilayers is reported. The influence of substrates, the thickness of the non-magnetic PbS spacer layer, and of temperature, was investigated by means of SQUID magnetometry. In trilayers with a PbS thickness between 4 and 12 deg A the low temperature hysteresis loops showed the signature of antiferromagnetic coupling. The value of the interlayer exchange coupling energy was determined by simulating the data with a modified Stoner model, including Zeeman, anisotropy, and exchange coupling energies. An important observation was of a strong dependence of the interlayer exchange coupling energy on temperature, consistent with a power law dependence of the exchange coupling constant on the saturation magnetization of the EuS layers. While no theoretical description is readily available, we conjecture that the observed behavior is due to a dependence of the interlayer exchange coupling energy on the exchange splitting of the EuS conduction band.

  18. 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.

  19. Origin and control of magnetic exchange coupling in between focused electron beam deposited cobalt nanostructures

    SciTech Connect

    Nikulina, E.; Idigoras, O.; Porro, J. M.; Berger, A.; Vavassori, P.; Chuvilin, A.; Ikerbasque, Basque Foundation for Science, Alameda Urquijo 36-5, 48011 Bilbao

    2013-09-16

    We demonstrate the existence and control of inter-particle magnetic exchange coupling in densely packed nanostructures fabricated by focused electron beam induced deposition. With Xe beam post-processing, we have achieved the controlled reduction and eventual elimination of the parasitic halo-like cobalt deposits formed in the proximity of intended nanostructures, which are the identified source of the magnetic exchange coupling. The elimination of the halo-mediated exchange coupling is demonstrated by magnetic measurements using Kerr microscopy on Co pillar arrays. Electron microscopy studies allowed us to identify the mechanisms underlying this process and to verify the efficiency and opportunities of the described nano-scale fabrication approach.

  20. Quantifying exchange coupling in f-ion pairs using the diamagnetic substitution method

    SciTech Connect

    Lukens, Wayne W.; Walter, Marc D.

    2010-04-01

    One of the challenges in the chemistry of actinide and lanthanide (f-ion) is quantifying exchange coupling between f-ions. While qualitative information about exchange coupling may be readily obtained using the diamagnetic substitution approach, obtaining quantitative information is much more difficult. This article describes how exchange coupling may be quantified using the susceptibility of a magnetically isolated analog, as in the diamagnetic substitution approach, along with the anisotropy of the ground state as determined by EPR spectroscopy. Several examples are used to illustrate and test this approach.

  1. Evaluation of a regional air-quality model with bi-directional NH3 exchange coupled to an agro-ecosystem model

    NASA Astrophysics Data System (ADS)

    Bash, J. O.; Cooter, E. J.; Dennis, R. L.; Walker, J. T.; Pleim, J. E.

    2012-08-01

    Atmospheric ammonia (NH3) is the primary atmospheric base and an important precursor for inorganic particulate matter and when deposited NH3 contributes to surface water eutrophication, soil acidification and decline in species biodiversity. Flux measurements indicate that the air-surface exchange of NH3 is bi-directional. However, the effects of bi-directional exchange, soil biogeochemistry and human activity are not parameterized in air quality models. The US Environmental Protection Agency (EPA)'s Community Multiscale Air-Quality (CMAQ) model with bi-directional NH3 exchange has been coupled with the United States Department of Agriculture (USDA)'s Environmental Policy Integrated Climate (EPIC) agro-ecosystem model's nitrogen geochemistry algorithms. CMAQ with bi-directional NH3 exchange coupled to EPIC connects agricultural cropping management practices to emissions and atmospheric concentrations of reduced nitrogen and models the biogeochemical feedback on NH3 air-surface exchange. This coupled modeling system reduced the biases and error in NHx (NH3 + NH4+) wet deposition and in ambient aerosol concentrations in an annual 2002 Continental US (CONUS) domain simulation when compared to a 2002 annual simulation of CMAQ without bi-directional exchange. Fertilizer emissions estimated in CMAQ 5.0 with bi-directional exchange exhibits markedly different seasonal dynamics than the US EPA's National Emissions Inventory (NEI), with lower emissions in the spring and fall and higher emissions in July.

  2. 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.

  3. 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.

  4. A new reversal mode in exchange coupled antiferromagnetic/ferromagnetic disks: distorted viscous vortex

    DOE PAGESBeta

    Gilbert, Dustin A.; Ye, Li; Varea, Aïda; Agramunt-Puig, Sebastià; del Valle, Nuria; Navau, Carles; López-Barbera, José Francisco; Buchanan, Kristen S.; Hoffmann, Axel; Sánchez, Alvar; et al

    2015-04-28

    Magnetic vortices have generated intense interest in recent years due to their unique reversal mechanisms, fascinating topological properties, and exciting potential applications. In addition, the exchange coupling of magnetic vortices to antiferromagnets has also been shown to lead to a range of novel phenomena and functionalities. Here we report a new magnetization reversal mode of magnetic vortices in exchange coupled Ir20Mn80/Fe20Ni80 microdots: distorted viscous vortex reversal. In contrast to the previously known or proposed reversal modes, the vortex is distorted close to the interface and viscously dragged due to the uncompensated spins of a thin antiferromagnet, which leads to unexpectedmore » asymmetries in the annihilation and nucleation fields. These results provide a deeper understanding of the physics of exchange coupled vortices and may also have important implications for applications involving exchange coupled nanostructures.« less

  5. A new reversal mode in exchange coupled antiferromagnetic/ferromagnetic disks: distorted viscous vortex

    SciTech Connect

    Gilbert, Dustin A.; Ye, Li; Varea, Aïda; Agramunt-Puig, Sebastià; del Valle, Nuria; Navau, Carles; López-Barbera, José Francisco; Buchanan, Kristen S.; Hoffmann, Axel; Sánchez, Alvar; Sort, Jordi; Liu, Kai; Nogués, Josep

    2015-04-28

    Magnetic vortices have generated intense interest in recent years due to their unique reversal mechanisms, fascinating topological properties, and exciting potential applications. In addition, the exchange coupling of magnetic vortices to antiferromagnets has also been shown to lead to a range of novel phenomena and functionalities. Here we report a new magnetization reversal mode of magnetic vortices in exchange coupled Ir20Mn80/Fe20Ni80 microdots: distorted viscous vortex reversal. In contrast to the previously known or proposed reversal modes, the vortex is distorted close to the interface and viscously dragged due to the uncompensated spins of a thin antiferromagnet, which leads to unexpected asymmetries in the annihilation and nucleation fields. These results provide a deeper understanding of the physics of exchange coupled vortices and may also have important implications for applications involving exchange coupled nanostructures.

  6. A Coupled Nonlinear Spacecraft Attitude Controller/Observer With an Unknown Constant Gyro Bias

    NASA Technical Reports Server (NTRS)

    Deutschmann, Julie; Sanner, Robert M.; Bauer, Frank H. (Technical Monitor)

    2001-01-01

    A nonlinear control scheme for attitude control of a spacecraft is combined with a nonlinear gyro bias observer for the case of constant gyro bias. The closed loop system is proven to be globally stable, with zero tracking error, thus proving a separation principle for the given system. The nonlinear observer incorporates persistency of excitation, resulting in exponential convergence of the gyro bias error.

  7. Southern Ocean albedo, inter-hemispheric energy transports and the double ITCZ: global impacts of biases in a coupled model

    NASA Astrophysics Data System (ADS)

    Hawcroft, Matt; Haywood, Jim M.; Collins, Mat; Jones, Andy; Jones, Anthony C.; Stephens, Graeme

    2016-06-01

    A causal link has been invoked between inter-hemispheric albedo, cross-equatorial energy transport and the double-Intertropical Convergence Zone (ITCZ) bias in climate models. Southern Ocean cloud biases are a major determinant of inter-hemispheric albedo biases in many models, including HadGEM2-ES, a fully coupled model with a dynamical ocean. In this study, targeted albedo corrections are applied in the Southern Ocean to explore the dynamical response to artificially reducing these biases. The Southern Hemisphere jet increases in strength in response to the increased tropical-extratropical temperature gradient, with increased energy transport into the mid-latitudes in the atmosphere, but no improvement is observed in the double-ITCZ bias or atmospheric cross-equatorial energy transport, a finding which supports other recent work. The majority of the adjustment in energy transport in the tropics is achieved in the ocean, with the response further limited to the Pacific Ocean. As a result, the frequently argued teleconnection between the Southern Ocean and tropical precipitation biases is muted. Further experiments in which tropical longwave biases are also reduced do not yield improvement in the representation of the tropical atmosphere. These results suggest that the dramatic improvements in tropical precipitation that have been shown in previous studies may be a function of the lack of dynamical ocean and/or the simplified hemispheric albedo bias corrections applied in that work. It further suggests that efforts to correct the double ITCZ problem in coupled models that focus on large-scale energetic controls will prove fruitless without improvements in the representation of atmospheric processes.

  8. Coercivity and exchange coupling in PrCo:Co nanocomposite films

    NASA Astrophysics Data System (ADS)

    Liu, J. P.; Liu, Y.; Sellmyer, D. J.

    1998-06-01

    Magnetic hysteresis and intergrain exchange coupling in nanostructured PrCo:Co composite films have been investigated. The composite thin films were made by multilayer sputtering and subsequent annealing. It is found that the coercivity mechanism is related to film morphology, especially the Co phase fraction. Evidence for the hard-soft-phase exchange coupling has been found and high energy products have been obtained.

  9. Coercivity and exchange coupling in PrCo:Co nanocomposite films

    SciTech Connect

    Liu, J.P.; Liu, Y.; Sellmyer, D.J.

    1998-06-01

    Magnetic hysteresis and intergrain exchange coupling in nanostructured PrCo:Co composite films have been investigated. The composite thin films were made by multilayer sputtering and subsequent annealing. It is found that the coercivity mechanism is related to film morphology, especially the Co phase fraction. Evidence for the hard-soft-phase exchange coupling has been found and high energy products have been obtained. {copyright} {ital 1998 American Institute of Physics.}

  10. Exchange coupled CoPd/TbCo magneto-optic storage films

    SciTech Connect

    Gambino, R.J.; Ruf, R.R.; Rishi, R. )

    1989-09-01

    Films of CoPd with weak perpendicular anisotropy are shown to exchange couple to square loop TbCo films on both the Tb and Co sides of compensation. The exchange is sensitive to reactive impurities at the interface and is broken under conditions that produce as little as one monolayer of paramagnetic compound. Even when the coupling at the interface is strong, the authors show that only a limited thickness of the CoPd layer is spin oriented perpendicular.

  11. A Cu(II)2 Paramagnetic Chemical Exchange Saturation Transfer Contrast Agent Enabled by Magnetic Exchange Coupling.

    PubMed

    Du, Kang; Harris, T David

    2016-06-29

    The ability of magnetic exchange coupling to enable observation of paramagnetic chemical exchange saturation transfer (PARACEST) in transition metal ions with long electronic relaxation times (τs) is demonstrated. Metalation of the dinucleating, tetra(carboxamide) ligand HL with Cu(2+) in the presence of pyrophosphate (P2O7)(4-) affords the complex [LCu(II)2(P2O7)](-). Solution-phase variable-temperature magnetic susceptibility data reveal weak ferromagnetic superexchange coupling between the two S = 1/2 Cu(II) centers, with a coupling constant of J = +2.69(5) cm(-1), to give an S = 1 ground state. This coupling results in a sharpened NMR line width relative to a GaCu analogue, indicative of a shortening of τs. Presaturation of the amide protons in the Cu2 complex at 37 °C leads to a 14% intensity decrease in the bulk water (1)H NMR signal through the CEST effect. Conversely, no CEST effect is observed in the GaCu complex. These results provide the first example of a Cu-based PARACEST magnetic resonance contrast agent and demonstrate the potential to expand the metal ion toolbox for PARACEST agents through introduction of magnetic exchange coupling. PMID:27276533

  12. Exchange coupling in transition metal monoxides: Electronic structure calculations

    SciTech Connect

    Fischer, Guntram; Daene, Markus W; Ernst, Arthur; Bruno, Patrick; Lueders, Martin; Szotek, Zdzislawa; Temmerman, Walter M; Wolfam, Hergert

    2009-01-01

    An ab initio study of magnetic-exchange interactions in antiferromagnetic and strongly correlated 3d transition metal monoxides is presented. Their electronic structure is calculated using the local self-interaction correction approach, implemented within the Korringa-Kohn-Rostoker band-structure method, which is based on multiple scattering theory. The Heisenberg exchange constants are evaluated with the magnetic force theorem. Based on these the corresponding Neel temperatures TN and spin-wave dispersions are calculated. The Neel temperatures are obtained using mean-field approximation, random-phase approximation and Monte Carlo simulations. The pressure dependence of TN is investigated using exchange constants calculated for different lattice constants. All the calculated results are compared to experimental data.

  13. Paramagnetic molecule induced strong antiferromagnetic exchange coupling on a magnetic tunnel junction based molecular spintronics device

    NASA Astrophysics Data System (ADS)

    Tyagi, Pawan; Baker, Collin; D'Angelo, Christopher

    2015-07-01

    This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs) were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the tunnel junction’s perimeter. These MTJMSDs exhibited molecule-induced strong antiferromagnetic coupling. We simulated the 3D atomic model analogous to the MTJMSD and studied the effect of molecule’s magnetic couplings with the two FM electrodes. Simulations show that when a molecule established ferromagnetic coupling with one electrode and antiferromagnetic coupling with the other electrode, then theoretical results effectively explained the experimental findings. Our studies suggest that in order to align MTJMSDs’ electrodes antiparallel to each other, the exchange coupling strength between a molecule and FM electrodes should be ˜50% of the interatomic exchange coupling for the FM electrodes.

  14. Paramagnetic molecule induced strong antiferromagnetic exchange coupling on a magnetic tunnel junction based molecular spintronics device.

    PubMed

    Tyagi, Pawan; Baker, Collin; D'Angelo, Christopher

    2015-07-31

    This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs) were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the tunnel junction's perimeter. These MTJMSDs exhibited molecule-induced strong antiferromagnetic coupling. We simulated the 3D atomic model analogous to the MTJMSD and studied the effect of molecule's magnetic couplings with the two FM electrodes. Simulations show that when a molecule established ferromagnetic coupling with one electrode and antiferromagnetic coupling with the other electrode, then theoretical results effectively explained the experimental findings. Our studies suggest that in order to align MTJMSDs' electrodes antiparallel to each other, the exchange coupling strength between a molecule and FM electrodes should be ∼50% of the interatomic exchange coupling for the FM electrodes. PMID:26159362

  15. 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.

  16. 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.

  17. Unravelling intrinsic efficacy and ligand bias at G protein coupled receptors: A practical guide to assessing functional data.

    PubMed

    Stott, Lisa A; Hall, David A; Holliday, Nicholas D

    2016-02-01

    Stephenson's empirical definition of an agonist, as a ligand with binding affinity and intrinsic efficacy (the ability to activate the receptor once bound), underpins classical receptor pharmacology. Quantifying intrinsic efficacy using functional concentration response relationships has always presented an experimental challenge. The requirement for realistic determination of efficacy is emphasised by recent developments in our understanding of G protein coupled receptor (GPCR) agonists, with recognition that some ligands stabilise different active conformations of the receptor, leading to pathway-selective, or biased agonism. Biased ligands have potential as therapeutics with improved selectivity and clinical efficacy, but there are also pitfalls to the identification of pathway selective effects. Here we explore the basics of concentration response curve analysis, beginning with the need to distinguish ligand bias from other influences of the functional system under study. We consider the different approaches that have been used to quantify and compare biased ligands, many of which are based on the Black and Leff operational model of agonism. Some of the practical issues that accompany these analyses are highlighted, with opportunities to improve estimates in future, particularly in the separation of true agonist intrinsic efficacy from the contributions of system dependent coupling efficiency. Such methods are by their nature practical approaches, and all rely on Stephenson's separation of affinity and efficacy parameters, which are interdependent at the mechanistic level. Nevertheless, operational analysis methods can be justified by mechanistic models of GPCR activation, and if used wisely are key elements to biased ligand identification. PMID:26478533

  18. A hybrid model in inductively coupled plasma discharges with bias source: Description of model and experimental validation in Ar discharge

    NASA Astrophysics Data System (ADS)

    Wen, De-Qi; Liu, Wei; Liu, Yong-Xin; Gao, Fei; Wang, You-Nian

    2015-09-01

    Traditional fluid simulation and Particle-in-Cell/Monte-Carlo collision (PIC/MCC) are very time consuming in inductively coupled plasma. In this work, a hybrid model, i.e. global model coupled bidirectional with parallel Monte-Carlo collision (MCC) sheath model, is developed to investigate inductively coupled plasma discharge with bias source. The global model is applied to calculate plasma density in bulk plasma. The sheath model is performed to consistently calculate the electric field, ion kinetic and the sheath thickness above the bias electrode. Moreover, specific numbers of ions are tracked and ultimately ion energy distribution functions (IEDFs) incident into bias electrode are obtained from MCC module. It is found that as the bias amplitude increases, the energy width of both IEDFs becomes wider, and the total outlines of IEDFs move towards higher energy. The results from the model are validated by experimental measurement and a qualitative agreement is obtained. The advantage of this model is that plasma density, ion flux and IEDF, which are widely concerned in the actual process, could be obtained within an hour. This work was supported by the National Natural Science Foundation of China (NSFC) (Grant No. 11205025 and 11335004) and (Grant No.11405018), the Important National Science and Technology Specific Project (Grant No. 2011ZX02403-001).

  19. 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...

  20. Magnetic susceptibility and exchange coupling in the mineral ardennite

    USGS Publications Warehouse

    Thorpe, A.N.; Senftle, F.E.; Donnay, G.

    1969-01-01

    Ardennite, a rare silicate mineral, contains about 19 wt.% manganese. Some of the manganese atoms are in positions which are close enough to allow negative exchange and hence a reduction of the total magnetic susceptibility. It is shown that the susceptibility can be accounted for approximately by the treatment of Earnshaw and Lewis (1958) for S = 5 2 and a Hamiltonian H = -2g??Hb-2JS1??S2. ?? 1969.

  1. 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.

  2. 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

  3. 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).

  4. 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.

  5. An OSSE study using the GFDL ensemble coupled data assimilation system: Biased twin experiment for deep Argo array

    NASA Astrophysics Data System (ADS)

    Chang, Y. S.; Zhang, S.; Rosati, A.; Vecchi, G. A.; Yang, X.

    2014-12-01

    A "biased" twin experiment of coupled data assimilation with two CGCMs is designed to address two questions: 1) given atmospheric and oceanic observations and a biased numerical climate system, how to obtain balanced climate estimation? 2) Within the steady and coherent climate estimation framework, what is the impact of deep ocean Argo profiles? Based on the modern Argo observing system and artificial extension to the full depth, "observations" drawn from one CGCM are assimilated into the other. Our results show that the simultaneous atmospheric and oceanic constraints play a significant role for preventing the deep ocean drift. Within the bias magnitude in the twin experiment, the Argo extension to the full depth does not significantly improve the quality of climate estimation. More studies based on different assimilation models with improved spatial and temporal scales of the deep Argo array are demanding for further understanding the impact of deep Argo array.

  6. 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.

  7. 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.

  8. Energy Exchange in Driven Open Quantum Systems at Strong Coupling.

    PubMed

    Carrega, Matteo; Solinas, Paolo; Sassetti, Maura; Weiss, Ulrich

    2016-06-17

    The time-dependent energy transfer in a driven quantum system strongly coupled to a heat bath is studied within an influence functional approach. Exact formal expressions for the statistics of energy dissipation into the different channels are derived. The general method is applied to the driven dissipative two-state system. It is shown that the energy flows obey a balance relation, and that, for strong coupling, the interaction may constitute the major dissipative channel. Results in analytic form are presented for the particular value K=1/2 of strong Ohmic dissipation. The energy flows show interesting behaviors including driving-induced coherences and quantum stochastic resonances. It is found that the general characteristics persists for K near 1/2. PMID:27367367

  9. Energy Exchange in Driven Open Quantum Systems at Strong Coupling

    NASA Astrophysics Data System (ADS)

    Carrega, Matteo; Solinas, Paolo; Sassetti, Maura; Weiss, Ulrich

    2016-06-01

    The time-dependent energy transfer in a driven quantum system strongly coupled to a heat bath is studied within an influence functional approach. Exact formal expressions for the statistics of energy dissipation into the different channels are derived. The general method is applied to the driven dissipative two-state system. It is shown that the energy flows obey a balance relation, and that, for strong coupling, the interaction may constitute the major dissipative channel. Results in analytic form are presented for the particular value K =1/2 of strong Ohmic dissipation. The energy flows show interesting behaviors including driving-induced coherences and quantum stochastic resonances. It is found that the general characteristics persists for K near 1/2 .

  10. Effects of temperature on intergranular exchange coupling in L10 FePt thin films

    NASA Astrophysics Data System (ADS)

    Huang, Efrem Y.; Kryder, Mark H.

    2014-06-01

    The effects of temperature on intergranular exchange coupling for FePt:X:FePt (X = TaOx, SiOx, Cr) sputtered thin film stacks were investigated. In-plane FePt layers separated by a thin layer of segregant were used as an experimental model for the intergranular region in perpendicular recording media. Magnetic hysteresis was measured for varying segregant thicknesses (0.5 nm-1.5 nm) at varying temperatures (300 K-700 K). Exchange coupling energies were calculated using the reversal field, saturation magnetization, and coercivity. The intergranular exchange coupling energy was observed to be well-behaved, decreasing linearly with increasing temperature to 600 K. TaOx resulted in the lowest exchange coupling energy at any given temperature, while SiOx and Cr showed similar decoupling capabilities. At 600 K and beyond, antiferromagnetic behavior was observed. Exchange coupling was found to be negligible at operating temperatures above 600 K even with as little as 0.5 nm of TaOx segregant or 1 nm of SiOx segregant.

  11. Effects of exchange coupling between cap layer and oxide layer on the recording performance in perpendicular media

    NASA Astrophysics Data System (ADS)

    Zhang, Kezhao; Choe, Gunn; Duan, Shanlin

    2009-04-01

    To understand the effects of exchange coupling between the CoCr-alloy cap layer and the CoCrPt-oxide layer in perpendicular media, we measured switching dynamics and recording performances of a series of media with various exchange-coupling layer thicknesses on a high-precision spinstand. This study shows that the cap and the oxide layers have different switching dynamics and sufficiently strong exchange coupling is necessary for adequate thermal stability. Exchange coupling improves the signal-to-noise ratio (SNR) through improved writability and reduced noise from the cap. In the strong coupling region, overwrite and write widths can be varied without loss in SNR.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Wave-vector-dependent spin pumping as a probe of exchange-coupled magnons

    NASA Astrophysics Data System (ADS)

    Fukami, Masaya; Tateno, Yuma; Sekiguchi, Koji; Ando, Kazuya

    2016-05-01

    We demonstrate that short-wavelength exchange-coupled magnons can be identified electrically through the combination of their spin-pumping and damping properties in a metal/magnetic insulator heterostructure. We present clear wave-vector dependence of the spin pumping from parametrically excited exchange-coupled magnons in the heterostructure. The efficiency of spin pumping by dipole-exchange magnons was measured to be sensitive to their wave numbers and propagation angles, while the efficiency was found to be almost constant in the exchange limit. This dependence enabled us to uncover nontrivial dual bistability in the system originating from drastic change in dominant nonequilibrium magnon modes. These findings pave a path for direct electric access to short-wavelength spin dynamics that cannot be probed by optical techniques.

  18. Modelling interfacial coupling in thin film magnetic exchange springs at finite temperature

    NASA Astrophysics Data System (ADS)

    Saharan, L.; Morrison, C.; Miles, J. J.; Thomson, T.; Schrefl, T.; Hrkac, G.

    2013-10-01

    We report a numerical study that demonstrates the interface layer between a soft and hard magnetic phase, the exchange transition layer, is the dominant factor that influences the magnetization reversal process at room temperature and long measurement times. It is found that the exchange transition layer thickness affects the magnetization reversal and the coupling of a bi-layer system by lowering the switching field and changing the angle dependent magnetization reversal. We show that the change in angle dependence of reversal is due to an increased incoherency in the lateral spin behavior. Changing the value of exchange coupling in the exchange transition layer affects only the angle dependent behavior and does not lower the switching field.

  19. Magnetic patterning: local manipulation of the intergranular exchange coupling via grain boundary engineering

    PubMed Central

    Huang, Kuo-Feng; Liao, Jung-Wei; Hsieh, Cheng-Yu; Wang, Liang-Wei; Huang, Yen-Chun; Wen, Wei-Chih; Chang, Mu-Tung; Lo, Shen-Chuan; Yuan, Jun; Lin, Hsiu-Hau; Lai, Chih-Huang

    2015-01-01

    Magnetic patterning, with designed spatial profile of the desired magnetic properties, has been a rising challenge for developing magnetic devices at nanoscale. Most existing methods rely on locally modifying magnetic anisotropy energy or saturation magnetization, and thus post stringent constraints on the adaptability in diverse applications. We propose an alternative route for magnetic patterning: by manipulating the local intergranular exchange coupling to tune lateral magnetic properties. As demonstration, the grain boundary structure of Co/Pt multilayers is engineered by thermal treatment, where the stress state of the multilayers and thus the intergranular exchange coupling can be modified. With Ag passivation layers on top of the Co/Pt multilayers, we can hinder the stress relaxation and grain boundary modification. Combining the pre-patterned Ag passivation layer with thermal treatment, we can design spatial variations of the magnetic properties by tuning the intergranular exchange coupling, which diversifies the magnetic patterning process and extends its feasibility for varieties of new devices. PMID:26156786

  20. Ignition calculations using a reduced coupled-mode electron- ion energy exchange model*

    NASA Astrophysics Data System (ADS)

    Garbett, W. J.; Chapman, D. A.

    2016-03-01

    Coupled-mode models for electron-ion energy exchange can predict large deviations from standard binary collision models in some regimes. A recently developed reduced coupled-mode model for electron-ion energy exchange, which accurately reproduces full numerical results over a wide range of density and temperature space, has been implemented in the Nym hydrocode and used to assess the impact on ICF capsule fuel assembly and performance. Simulations show a lack of sensitivity to the model, consistent with results from a range of simpler alternative models. Since the coupled-mode model is conceptually distinct to models based on binary collision theory, this result provides increased confidence that uncertainty in electron-ion energy exchange will not impact ignition attempts.

  1. Strain-modulated antiferromagnetic spin orientation and exchange coupling in Fe/CoO(001)

    SciTech Connect

    Zhu, J.; Li, Q.; Li, J. X.; Ding, Z.; Wu, Y. Z.; Hua, C. Y.; Huang, M. J.; Lin, H.-J.; Hu, Z.; Won, C.

    2014-05-21

    The effect of CoO spin orientation on exchange coupling was investigated in single-crystalline Fe/CoO/MnO/MgO(001) systems. An antiferromagnetic CoO spin reorientation transition from the in-plane direction to the out-of-plane direction was found to be associated with the in-plane strain transition in CoO film from compression to expansion. The induced uniaxial anisotropies by exchange coupling at the Fe/CoO interface are significantly stronger for the in-plane CoO spin orientation than for the out-of-plane CoO spin orientation. Our study provides a way to modify the exchange coupling in the ferromagnetic (FM)/antiferromagnetic (AFM) bilayer by modulating the strain in the AFM film.

  2. Density functional study on anisotropic magnetic exchange couplings in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Oh, Hyungju; Choi, Hyoung Joon

    2013-03-01

    Iron-based superconductors exhibit many different antiferromagnetically ordered ground states. An understanding of the magnetic exchange couplings and ground-state Hamiltonian in the parent compounds of these materials is important because such an information could be the basis to unveil the mechanism of unconventional superconductivity. By performing first-principles calculations of the electronic and magnetic properties with non-collinear spin configurations, we study the anisotropic magnetic exchange couplings in iron-based superconductors. We obtain magnetic excitations using the anisotropic magnetic exchange couplings, and compare the results with published inelastic neutron scattering data. This work was supported by the NRF of Korea (Grant No. 2011-0018306). Computational resources have been provided by KISTI Supercomputing Center (Project No. KSC-2012-C2-14).

  3. Experimental modeling of intergranular exchange coupling for perpendicular thin film media

    NASA Astrophysics Data System (ADS)

    Sokalski, Vincent; Laughlin, David E.; Zhu, Jian-Gang

    2009-09-01

    We present an experimental model system that enables quantitative assessment of intergranular exchange coupling in CoCrPt-oxide perpendicular magnetic recording media. A thin film structure consisting of a high coercivity CoPt unicrystal layer and a lower coercivity CoPt layer separated by a thin oxide interlayer is used to model perpendicularly magnetized grains separated by oxide grain boundaries. Exchange coupling energy between the CoPt layers was obtained for SiOx, TiOx, and CrOx interlayers by measuring field shifts from the lower coercivity layer. Cr segregation in CoCrPt grains to grain boundaries is also modeled experimentally and found to significantly suppress exchange coupling.

  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.

    2015-02-01

    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

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. Enhancing Inter-phase Exchange Coupling in SmCo5/Co Nanocomposite Materials

    NASA Astrophysics Data System (ADS)

    Wu, Dangxin; Zhang, Qiming; Liu, J. P.

    2006-10-01

    Exchange-coupled hard/soft phase nanocomposite magnets were proposed to increase the maximum energy product by combining the large anisotropy of hard phase materials and the high saturation magnetization of soft phase materials. To understand the inter-phase exchange coupling is very important for design of nanocomposite magnets. In this work, we performed first-principles calculations to investigate the inter-phase exchange coupling between hard phase SmCo5 and soft phase Co using superlattice model. The calculations were based on Density Functional Theory, using projector augmented wave (PAW) method and linear-muffin-tin-orbital (LMTO) method in the atomic sphere approximation. The atomic structures were optimized and the electronic ground state was obtained. Then the noncollinear magnetic calculations were performed to calculate the exchange interactions. We found that the total energy is a quadratic function of angle (θ) between the directions of magnetic moments of hard phase and middle layer of soft phase. We found that Fe doped soft phase strengths the exchange coupling between SmCo5/Co in our models, which in turn may lead to higher maximum energy product.

  12. Thermodynamics of information exchange between two coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Kutvonen, Aki; Sagawa, Takahiro; Ala-Nissila, Tapio

    2016-03-01

    We propose a setup based on two coupled quantum dots where thermodynamics of a measurement can be quantitatively characterized. The information obtained in the measurement can be utilized by performing feedback in a manner apparently breaking the second law of thermodynamics. In this way the setup can be operated as a Maxwell's demon, where both the measurement and feedback are performed separately by controlling an external parameter. This is analogous to the case of the original Szilard engine. Since the setup contains both the microscopic demon and the engine itself, the operation of the whole measurement-feedback cycle can be explained in detail at the level of single realizations. In addition, we derive integral fluctuation relations for both the bare and coarse-grained entropy productions in the setup.

  13. Impact of orthogonal exchange coupling on magnetic anisotropy in antiferromagnetic oxides/ferromagnetic systems.

    PubMed

    Kuświk, Piotr; Gastelois, Pedro Lana; Głowiński, Hubert; Przybylski, Marek; Kirschner, Jürgen

    2016-10-26

    The influence of interface exchange coupling on magnetic anisotropy in the antiferromagnetic oxide/Ni system is investigated. We show how interfacial exchange coupling can be employed not only to pin the magnetization of the ferromagnetic layer but also to support magnetic anisotropy to orient the easy magnetization axis perpendicular to the film plane. The fact that this effect is only observed below the Néel temperature of all investigated antiferromagnetic oxides with significantly different magnetocrystalline anisotropies gives evidence that antiferromagnetic ordering is a source of the additional contribution to the perpendicular effective magnetic anisotropy. PMID:27589202

  14. Enhanced exchange-coupling effect in Nd-Fe-B/Fe-B nanocomposite magnet.

    PubMed

    Cha, Hyungil; Kim, Changwoo; Ji, Eunsun; Kim, Younghwan; Jadhav, Abhijit; Kang, Dongin; Kang, Youngsoo

    2010-01-01

    Soft phase magnetic Fe-B nanoparticles were prepared by coprecipitation and the hard phase magnetic Nd-Fe-B nanoparticles were obtained from mechanical ball mill of the bulk Nd-Fe-B with a shaker mill. Also mechanical ball mill technique was applied to the mixture of Nd-Fe-B and Fe-B nanoparticles to build up an exchange-coupled nanocomposite magnet. It was loaded in electronic furnace and annealed under a flow of hydrogen at 953 K for 30 min. The exchange coupled interaction of isotropic magnets was characterized by smooth hysteresis loop with a high value of remanence (Mr/Ms > 0.5). PMID:20352831

  15. Real-Time PPP Based on the Coupling Estimation of Clock Bias and Orbit Error with Broadcast Ephemeris.

    PubMed

    Pan, Shuguo; Chen, Weirong; Jin, Xiaodong; Shi, Xiaofei; He, Fan

    2015-01-01

    Satellite orbit error and clock bias are the keys to precise point positioning (PPP). The traditional PPP algorithm requires precise satellite products based on worldwide permanent reference stations. Such an algorithm requires considerable work and hardly achieves real-time performance. However, real-time positioning service will be the dominant mode in the future. IGS is providing such an operational service (RTS) and there are also commercial systems like Trimble RTX in operation. On the basis of the regional Continuous Operational Reference System (CORS), a real-time PPP algorithm is proposed to apply the coupling estimation of clock bias and orbit error. The projection of orbit error onto the satellite-receiver range has the same effects on positioning accuracy with clock bias. Therefore, in satellite clock estimation, part of the orbit error can be absorbed by the clock bias and the effects of residual orbit error on positioning accuracy can be weakened by the evenly distributed satellite geometry. In consideration of the simple structure of pseudorange equations and the high precision of carrier-phase equations, the clock bias estimation method coupled with orbit error is also improved. Rovers obtain PPP results by receiving broadcast ephemeris and real-time satellite clock bias coupled with orbit error. By applying the proposed algorithm, the precise orbit products provided by GNSS analysis centers are rendered no longer necessary. On the basis of previous theoretical analysis, a real-time PPP system was developed. Some experiments were then designed to verify this algorithm. Experimental results show that the newly proposed approach performs better than the traditional PPP based on International GNSS Service (IGS) real-time products. The positioning accuracies of the rovers inside and outside the network are improved by 38.8% and 36.1%, respectively. The PPP convergence speeds are improved by up to 61.4% and 65.9%. The new approach can change the

  16. Real-Time PPP Based on the Coupling Estimation of Clock Bias and Orbit Error with Broadcast Ephemeris

    PubMed Central

    Pan, Shuguo; Chen, Weirong; Jin, Xiaodong; Shi, Xiaofei; He, Fan

    2015-01-01

    Satellite orbit error and clock bias are the keys to precise point positioning (PPP). The traditional PPP algorithm requires precise satellite products based on worldwide permanent reference stations. Such an algorithm requires considerable work and hardly achieves real-time performance. However, real-time positioning service will be the dominant mode in the future. IGS is providing such an operational service (RTS) and there are also commercial systems like Trimble RTX in operation. On the basis of the regional Continuous Operational Reference System (CORS), a real-time PPP algorithm is proposed to apply the coupling estimation of clock bias and orbit error. The projection of orbit error onto the satellite-receiver range has the same effects on positioning accuracy with clock bias. Therefore, in satellite clock estimation, part of the orbit error can be absorbed by the clock bias and the effects of residual orbit error on positioning accuracy can be weakened by the evenly distributed satellite geometry. In consideration of the simple structure of pseudorange equations and the high precision of carrier-phase equations, the clock bias estimation method coupled with orbit error is also improved. Rovers obtain PPP results by receiving broadcast ephemeris and real-time satellite clock bias coupled with orbit error. By applying the proposed algorithm, the precise orbit products provided by GNSS analysis centers are rendered no longer necessary. On the basis of previous theoretical analysis, a real-time PPP system was developed. Some experiments were then designed to verify this algorithm. Experimental results show that the newly proposed approach performs better than the traditional PPP based on International GNSS Service (IGS) real-time products. The positioning accuracies of the rovers inside and outside the network are improved by 38.8% and 36.1%, respectively. The PPP convergence speeds are improved by up to 61.4% and 65.9%. The new approach can change the

  17. 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.

  18. O2 activation by binuclear Cu sites: Noncoupled versus exchange coupled reaction mechanisms

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Solomon, Edward I.

    2004-09-01

    Binuclear Cu proteins play vital roles in O2 binding and activation in biology and can be classified into coupled and noncoupled binuclear sites based on the magnetic interaction between the two Cu centers. Coupled binuclear Cu proteins include hemocyanin, tyrosinase, and catechol oxidase. These proteins have two Cu centers strongly magnetically coupled through direct bridging ligands that provide a mechanism for the 2-electron reduction of O2 to a µ-2:2 side-on peroxide bridged species. This side-on bridged peroxo-CuII2 species is activated for electrophilic attack on the phenolic ring of substrates. Noncoupled binuclear Cu proteins include peptidylglycine -hydroxylating monooxygenase and dopamine -monooxygenase. These proteins have binuclear Cu active sites that are distant, that exhibit no exchange interaction, and that activate O2 at a single Cu center to generate a reactive CuII/O2 species for H-atom abstraction from the C-H bond of substrates. O2 intermediates in the coupled binuclear Cu enzymes can be trapped and studied spectroscopically. Possible intermediates in noncoupled binuclear Cu proteins can be defined through correlation to mononuclear CuII/O2 model complexes. The different intermediates in these two classes of binuclear Cu proteins exhibit different reactivities that correlate with their different electronic structures and exchange coupling interactions between the binuclear Cu centers. These studies provide insight into the role of exchange coupling between the Cu centers in their reaction mechanisms.

  19. Ion Energy Distribution Control Using Ion Mass Ratios in Inductively Coupled Plasmas With a Pulsed DC Bias on the Substrate

    NASA Astrophysics Data System (ADS)

    Logue, Michael D.; Kushner, Mark J.

    2012-10-01

    In many applications requiring energetic ion bombardment, such as plasma etching, gas mixtures containing several ion species are used. In cases where two ions have significantly different masses, it may be feasible to selectively control the ion energy distributions (IEDs) by preferentially extracting the lighter ion mass with a controllable energy. In this work, we investigate the possibility of using a pulsed DC substrate bias in an inductively coupled plasma (ICP) to obtain this control. Pulsing of the substrate bias in the afterglow of a pulsed ICP plasma should allow for shifting of the IED peak energy by an amount approximately equal to the applied bias. If short enough pulses are used it may be possible to obtain a higher flux at high energy of the lower mass ion compared to the higher mass ion. A computational investigation of IEDs in low pressure (a few to 100 mTorr) ICPs sustained in gas mixtures such as Ar/H2 or Xe/H2 (having large mass differences) was conducted as a proof of principle. The model is the Hybrid Plasma Equipment Model with which electron energy distributions (EEDs) and IEDs as a function of position and time are obtained using Monte Carlo simulations. We have found a selective ability to mass and energy discriminate ion fluxes when using sufficiently short bias pulses. Results from the model for plasmas densities, electron temperatures, EEDs and IEDs will be discussed.

  20. Tilt engineering of exchange coupling at G-type SrMnO3/(La,Sr)MnO3 interfaces.

    PubMed

    Li, F; Song, C; Wang, Y Y; Cui, B; Mao, H J; Peng, J J; Li, S N; Wang, G Y; Pan, F

    2015-01-01

    With the recent realization of hybrid improper ferroelectricity and room-temperature multiferroic by tilt engineering, "functional" octahedral tilting has become a novel concept in multifunctional perovskite oxides, showing great potential for property manipulation and device design. However, the control of magnetism by octahedral tilting has remained a challenging issue. Here a qualitative and quantitative tilt engineering of exchange coupling, one of the magnetic properties, is demonstrated at compensated G-type antiferromagnetic/ferromagnetic (SrMnO3/La2/3Sr1/3MnO3) interfaces. According to interfacial Hamiltonian, exchange bias (EB) in this system originates from an in-plane antiphase rotation (a(-)) in G-type antiferromagnetic layer. Based on first-principles calculation, tilt patterns in SrMnO3 are artificially designed in experiment with different epitaxial strain and a much stronger EB is attained in the tensile heterostructure than the compressive counterpart. By controlling the magnitude of octahedral tilting, the manipulation of exchange coupling is even performed in a quantitative manner, as expected in the theoretical estimation. This work realized the combination of tilt engineering and exchange coupling, which might be significant for the development of multifunctional materials and antiferromagnetic spintronics. PMID:26531154

  1. Tilt engineering of exchange coupling at G-type SrMnO3/(La,Sr)MnO3 interfaces

    PubMed Central

    Li, F.; Song, C.; Wang, Y. Y.; Cui, B.; Mao, H. J.; Peng, J. J.; Li, S. N.; Wang, G. Y.; Pan, F.

    2015-01-01

    With the recent realization of hybrid improper ferroelectricity and room-temperature multiferroic by tilt engineering, “functional” octahedral tilting has become a novel concept in multifunctional perovskite oxides, showing great potential for property manipulation and device design. However, the control of magnetism by octahedral tilting has remained a challenging issue. Here a qualitative and quantitative tilt engineering of exchange coupling, one of the magnetic properties, is demonstrated at compensated G-type antiferromagnetic/ferromagnetic (SrMnO3/La2/3Sr1/3MnO3) interfaces. According to interfacial Hamiltonian, exchange bias (EB) in this system originates from an in-plane antiphase rotation (a−) in G-type antiferromagnetic layer. Based on first-principles calculation, tilt patterns in SrMnO3 are artificially designed in experiment with different epitaxial strain and a much stronger EB is attained in the tensile heterostructure than the compressive counterpart. By controlling the magnitude of octahedral tilting, the manipulation of exchange coupling is even performed in a quantitative manner, as expected in the theoretical estimation. This work realized the combination of tilt engineering and exchange coupling, which might be significant for the development of multifunctional materials and antiferromagnetic spintronics. PMID:26531154

  2. 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.

  3. 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.

  4. On the scaling of rf and dc self-bias voltages with pressure in electronegative capacitively coupled plasmas

    SciTech Connect

    Agarwal, Ankur; Dorf, Leonid; Rauf, Shahid; Collins, Ken

    2012-03-15

    Higher gas densities and lower diffusion losses at higher operating pressures typically lead to increased charged species densities (and hence flux) for a constant power deposition in capacitively coupled plasmas (CCP). As a result, one would expect that the bias radio-frequency (rf) voltage required to deposit a given power in a CCP reactor decreases with increasing operating pressure. These observations may not hold true in multiple frequency CCPs, commonly used for dielectric etching in microelectronics fabrication, due to nonlinear interactions between the rf sources. Wafer-based measurements of the rf and self-generated direct current (dc) bias voltages in a dual-frequency capacitively coupled electronegative plasma were made, which indicate that the rf and dc voltages vary nonmonotonically with pressure. These experimental results are presented in this paper and a computational plasma model is used to explain the experimental observations for varying 60 MHz and 13 MHz powers in the Ar/CF{sub 4}/CHF{sub 3} plasma over a pressure range of 25 to 400 mTorr. The authors found that while the ion density increases with pressure, the increase is most dominant near the electrode with the high frequency source (60 MHz). The rf and dc bias voltages are ultimately influenced by both charged species density magnitudes and spatial profiles.

  5. 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.

  6. Tropical Indian Ocean surface salinity bias in Climate Forecasting System coupled models and the role of upper ocean processes

    NASA Astrophysics Data System (ADS)

    Parekh, Anant; Chowdary, Jasti S.; Sayantani, Ojha; Fousiya, T. S.; Gnanaseelan, C.

    2016-04-01

    In the present study sea surface salinity (SSS) biases and seasonal tendency over the Tropical Indian Ocean (TIO) in the coupled models [Climate Forecasting System version 1 (CFSv1) and version 2 (CFSv2)] are examined with respect to observations. Both CFSv1 and CFSv2 overestimate SSS over the TIO throughout the year. CFSv1 displays improper SSS seasonal cycle over the Bay of Bengal (BoB), which is due to weaker model precipitation and improper river runoff especially during summer and fall. Over the southeastern Arabian Sea (AS) weak horizontal advection associated with East Indian coastal current during winter limits the formation of spring fresh water pool. On the other hand, weaker Somali jet during summer results for reduced positive salt tendency in the central and eastern AS. Strong positive precipitation bias in CFSv1 over the region off Somalia during winter, weaker vertical mixing and absence of horizontal salt advection lead to unrealistic barrier layer during winter and spring. The weaker stratification and improper spatial distribution of barrier layer thickness (BLT) in CFSv1 indicate that not only horizontal flux distribution but also vertical salt distribution displays large discrepancies. Absence of fall Wyrtki jet and winter equatorial currents in this model limit the advection of horizontal salt flux to the eastern equatorial Indian Ocean. The associated weaker stratification in eastern equatorial Indian Ocean can lead to deeper mixed layer and negative Sea Surface Temperature (SST) bias, which in turn favor positive Indian Ocean Dipole bias in CFSv1. It is important to note that improper spatial distribution of barrier layer and stratification can alter the air-sea interaction and precipitation in the models. On the other hand CFSv2 could produce the seasonal evolution and spatial distribution of SSS, BLT and stratification better than CFSv1. However CFSv2 displays positive bias in evaporation over the whole domain and negative bias in

  7. 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.

  8. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    PubMed Central

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  9. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes.

    PubMed

    Ma, X; Fang, F; Li, Q; Zhu, J; Yang, Y; Wu, Y Z; Zhao, H B; Lüpke, G

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  10. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    SciTech Connect

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  11. Effects of Exchange Energy and Spin-Orbit Coupling on Bond Energies

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2004-01-01

    Since chemical reactions involve the breaking and making of bonds, understanding the relative strengths of bonds is of paramount importance in the study, teaching, and practice of chemistry. Further, it is showed that free atoms having p(super n) configuration with n = 2,3, or 4 are stabilized by exchange energy, and by spin-orbit coupling for n =…

  12. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    DOE PAGESBeta

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-28

    In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

  13. First principles calculations of interlayer exchange coupling in bcc Fe/Cu/Fe structures

    SciTech Connect

    Kowalewski, M.; Heninrich, B.; Schulthess, T.C.; Butler, W.H.

    1998-01-01

    The authors report on theoretical calculations of interlayer exchange coupling between two Fe layers separated by a modified Cu spacer. These calculations were motivated by experimental investigations of similar structures by the SFU group. The multilayer structures of interest have the general form: Fe/Cu(k)/Fe and Fe/Cu(m)/X(1)/Cu(n)/Fe where X indicates one AL (atomic layer) of foreign atoms X (Cr, Ag, or Fe) and k, m, n represent the number of atomic layers of Cu. The purpose of the experimental and theoretical work was to determine the effect of modifying the pure Cu spacer by replacing the central Cu atomic layer with the atomic layer of foreign atoms X. The first principles calculation were performed using the Layer Korringa-Kohn-Rostoker (LKKR) method. The theoretical thickness dependence of the exchange coupling between two semi-infinite Fe layers was calculated for pure Cu spacer thicknesses in the range of 0 < k < 16. The effect of the foreign atoms X on the exchange coupling was investigated using the structure with 9 AL Cu spacer as a reference sample. The calculated changes in the exchange coupling are in qualitative agreement with experiment.

  14. Exchange coupling in hybrid anisotropy magnetic multilayers quantified by vector magnetometry

    SciTech Connect

    Morrison, C. Miles, J. J.; Thomson, T.; Anh Nguyen, T. N.; Fang, Y.; Dumas, R. K.; Åkerman, J.

    2015-05-07

    Hybrid anisotropy thin film heterostructures, where layers with perpendicular and in-plane anisotropy are separated by a thin spacer, are novel materials for zero/low field spin torque oscillators and bit patterned media. Here, we report on magnetization reversal and exchange coupling in a archetypal Co/Pd (perpendicular)-NiFe (in-plane) hybrid anisotropy system studied using vector vibrating sample magnetometry. This technique allows us to quantify the magnetization reversal in each individual magnetic layer, and measure of the interlayer exchange as a function of non-magnetic spacer thickness. At large (>1 nm) spacer thicknesses Ruderman-Kittel-Kasuya-Yosida-like exchange dominates, with orange-peel coupling providing a significant contribution only for sub-nm spacer thickness.

  15. Exchange Coupling Inversion in a High-Spin Organic Triradical Molecule.

    PubMed

    Gaudenzi, R; Burzurí, E; Reta, D; Moreira, I de P R; Bromley, S T; Rovira, C; Veciana, J; van der Zant, H S J

    2016-03-01

    The magnetic properties of a nanoscale system are inextricably linked to its local environment. In adatoms on surfaces and inorganic layered structures, the exchange interactions result from the relative lattice positions, layer thicknesses, and other environmental parameters. Here, we report on a sample-dependent sign inversion of the magnetic exchange coupling between the three unpaired spins of an organic triradical molecule embedded in a three-terminal device. This ferro-to-antiferromagnetic transition is due to structural distortions and results in a high-to-low spin ground-state change in a molecule traditionally considered to be a robust high-spin quartet. Moreover, the flexibility of the molecule yields an in situ electric tunability of the exchange coupling via the gate electrode. These findings open a route to the controlled reversal of the magnetic states in organic molecule-based nanodevices by mechanical means, electrical gating, or chemical tailoring. PMID:26862681

  16. Exchange coupling in hybrid anisotropy magnetic multilayers quantified by vector magnetometry

    NASA Astrophysics Data System (ADS)

    Morrison, C.; Miles, J. J.; Anh Nguyen, T. N.; Fang, Y.; Dumas, R. K.; Åkerman, J.; Thomson, T.

    2015-05-01

    Hybrid anisotropy thin film heterostructures, where layers with perpendicular and in-plane anisotropy are separated by a thin spacer, are novel materials for zero/low field spin torque oscillators and bit patterned media. Here, we report on magnetization reversal and exchange coupling in a archetypal Co/Pd (perpendicular)-NiFe (in-plane) hybrid anisotropy system studied using vector vibrating sample magnetometry. This technique allows us to quantify the magnetization reversal in each individual magnetic layer, and measure of the interlayer exchange as a function of non-magnetic spacer thickness. At large (>1 nm) spacer thicknesses Ruderman-Kittel-Kasuya-Yosida-like exchange dominates, with orange-peel coupling providing a significant contribution only for sub-nm spacer thickness.

  17. Modulation of interlayer exchange coupling strength in magnetic tunnel junctions via strain effect

    SciTech Connect

    Jiang, Xin Li, Zhipeng; Zheng, Yuankai; Kaiser, Christian; Diao, Zhitao; Fang, Jason; Leng, Qunwen

    2015-09-15

    Interlayer exchange coupling of two ferromagnetic electrodes separated by a thin MgO tunnel barrier is investigated using magneto-optical Kerr effect. We find that the coupling field can be reduced by more than 40% as the thickness of a top Ta capping layer increases from 0.5 to 1.2 nm. In contrast, a similar film stack with an additional 3 nm Ru capping layer displays no such dependence on Ta thickness. Transmission electron microscopy study shows that the oxidation of the exposed Ta capping layer induces changes in the crystalline structures of the underlying films, giving rise to the observed reduction of the interlayer coupling field.

  18. Modulation of interlayer exchange coupling strength in magnetic tunnel junctions via strain effect

    NASA Astrophysics Data System (ADS)

    Jiang, Xin; Li, Zhipeng; Zheng, Yuankai; Kaiser, Christian; Diao, Zhitao; Fang, Jason; Leng, Qunwen

    2015-09-01

    Interlayer exchange coupling of two ferromagnetic electrodes separated by a thin MgO tunnel barrier is investigated using magneto-optical Kerr effect. We find that the coupling field can be reduced by more than 40% as the thickness of a top Ta capping layer increases from 0.5 to 1.2 nm. In contrast, a similar film stack with an additional 3 nm Ru capping layer displays no such dependence on Ta thickness. Transmission electron microscopy study shows that the oxidation of the exposed Ta capping layer induces changes in the crystalline structures of the underlying films, giving rise to the observed reduction of the interlayer coupling field.

  19. 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.

  20. On the use of a weak-coupling thermostat in replica-exchange molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Lin, Zhixiong; van Gunsteren, Wilfred F.

    2015-07-01

    In a molecular dynamics (MD) simulation, various thermostat algorithms, including Langevin dynamics (LD), Nosé-Hoover (NH), and weak-coupling (WC) thermostats, can be used to keep the simulation temperature constant. A canonical ensemble is generated by the use of LD and NH, while the nature of the ensemble produced by WC has not yet been identified. A few years ago, it was shown that when using a WC thermostat with particular values of the temperature coupling time for liquid water at ambient temperature and pressure, the distribution of the potential energy is less wide than the canonical one. This led to an artifact in temperature replica-exchange molecular dynamics (T-REMD) simulations in which the potential energy distributions appear not to be equal to the ones of standard MD simulations. In this paper, we re-investigate this problem. We show that this artifact is probably due to the ensemble generated by WC being incompatible with the T-REMD replica-exchange criterion, which assumes a canonical configurational ensemble. We also show, however, that this artifact can be reduced or even eliminated by particular choices of the temperature coupling time of WC and the replica-exchange time period of T-REMD, i.e., when the temperature coupling time is chosen very close to the MD time step or when the exchange time period is chosen large enough. An attempt to develop a T-REMD replica-exchange criterion which is likely to be more compatible with the WC configurational ensemble is reported. Furthermore, an exchange criterion which is compatible with a microcanonical ensemble is used in total energy REMD simulations.

  1. The effect of Arabian Sea optical properties on SST biases and the South Asian summer monsoon in a coupled GCM

    NASA Astrophysics Data System (ADS)

    Turner, A. G.; Joshi, M.; Robertson, E. S.; Woolnough, S. J.

    2012-08-01

    This study examines the effect of seasonally varying chlorophyll on the climate of the Arabian Sea and South Asian monsoon. The effect of such seasonality on the radiative properties of the upper ocean is often a missing process in coupled general circulation models and its large amplitude in the region makes it a pertinent choice for study to determine any impact on systematic biases in the mean and seasonality of the Arabian Sea. In this study we examine the effects of incorporating a seasonal cycle in chlorophyll due to phytoplankton blooms in the UK Met Office coupled atmosphere-ocean GCM HadCM3. This is achieved by performing experiments in which the optical properties of water in the Arabian Sea—a key signal of the semi-annual cycle of phytoplankton blooms in the region—are calculated from a chlorophyll climatology derived from Sea-viewing Wide Field-of-View Sensor (SeaWiFS) data. The SeaWiFS chlorophyll is prescribed in annual mean and seasonally-varying experiments. In response to the chlorophyll bloom in late spring, biases in mixed layer depth are reduced by up to 50% and the surface is warmed, leading to increases in monsoon rainfall during the onset period. However when the monsoons are fully established in boreal winter and summer and there are strong surface winds and a deep mixed layer, biases in the mixed layer depth are reduced but the surface undergoes cooling. The seasonality of the response of SST to chlorophyll is found to depend on the relative depth of the mixed layer to that of the anomalous penetration depth of solar fluxes. Thus the inclusion of the effects of chlorophyll on radiative properties of the upper ocean acts to reduce biases in mixed layer depth and increase seasonality in SST.

  2. 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.

  3. 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.

  4. Chemical trend of exchange coupling in diluted magnetic II-VI semiconductors: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Chanier, T.; Virot, F.; Hayn, R.

    2009-05-01

    We have calculated the chemical trend of magnetic exchange parameters ( Jdd , Nα , and Nβ ) of Zn-based II-VI semiconductors ZnA ( A=O , S, Se, and Te) doped with Co or Mn. We show that a proper treatment of electron correlations by the local spin-density approximation (LSDA)+U method leads to good agreement between experimental and theoretical values of the nearest-neighbor exchange coupling Jdd between localized 3d spins in contrast to the LSDA method. The exchange couplings between localized spins and doped electrons in the conduction band Nα are in good agreement with experiment as well. But the values for Nβ (coupling to doped holes in the valence band) indicate a crossover from weak coupling (for A=Te and Se) to strong coupling (for A=O ) and a localized hole state in ZnO:Mn. This hole localization explains the apparent discrepancy between photoemission and magneto-optical data for ZnO:Mn.

  5. Tunable photonic cavity coupled to a voltage-biased double quantum dot system: Diagrammatic nonequilibrium Green's function approach

    NASA Astrophysics Data System (ADS)

    Agarwalla, Bijay Kumar; Kulkarni, Manas; Mukamel, Shaul; Segal, Dvira

    2016-07-01

    We investigate gain in microwave photonic cavities coupled to voltage-biased double quantum dot systems with an arbitrarily strong dot-lead coupling and with a Holstein-like light-matter interaction, by employing the diagrammatic Keldysh nonequilibrium Green's function approach. We compute out-of-equilibrium properties of the cavity: its transmission, phase response, mean photon number, power spectrum, and spectral function. We show that by the careful engineering of these hybrid light-matter systems, one can achieve a significant amplification of the optical signal with the voltage-biased electronic system serving as a gain medium. We also study the steady-state current across the device, identifying elastic and inelastic tunneling processes which involve the cavity mode. Our results show how recent advances in quantum electronics can be exploited to build hybrid light-matter systems that behave as microwave amplifiers and photon source devices. The diagrammatic Keldysh approach is primarily discussed for a cavity-coupled double quantum dot architecture, but it is generalizable to other hybrid light-matter systems.

  6. Magnetic Exchange Couplings in Heterodinuclear Complexes Based on Differential Local Spin Rotations.

    PubMed

    Joshi, Rajendra P; Phillips, Jordan J; Peralta, Juan E

    2016-04-12

    We analyze the performance of a new method for the calculation of magnetic exchange coupling parameters for the particular case of heterodinuclear transition metals complexes of Cu, Ni, and V. This method is based on a generalized perturbative approach which uses differential local spin rotations via formal Lagrange multipiers (Phillips, J. J.; Peralta, J. E. J. Chem. Phys. 2013, 138, 174115). The reliability of the calculated couplings has been assessed by comparing with results from traditional energy differences with different density functional approximations and with experimental values. Our results show that this method to calculate magnetic exchange couplings can be reliably used for heteronuclear transition metal complexes, and at the same time, that it is independent from the different mapping schemes used in energy difference methods. PMID:26953521

  7. Coupled acoustic-gravity field for dynamic evaluation of ion exchange with a single resin bead.

    PubMed

    Kanazaki, Takahiro; Hirawa, Shungo; Harada, Makoto; Okada, Tetsuo

    2010-06-01

    A coupled acoustic-gravity field is efficient for entrapping a particle at the position determined by its acoustic properties rather than its size. This field has been applied to the dynamic observation of ion-exchange reactions occurring in a single resin bead. The replacement of counterions in an ion-exchange resin induces changes in its acoustic properties, such as density and compressibility. Therefore, we can visually trace the advancement of an ion-exchange reaction as a time change in the levitation position of a resin bead entrapped in the field. Cation-exchange reactions occurring in resin beads with diameters of 40-120 microm are typically completed within 100-200 s. Ion-exchange equilibrium or kinetics is often evaluated with off-line chemical analyses, which require a batch amount of ion exchangers. Measurements with a single resin particle allow us to evaluate ion-exchange dynamics and kinetics of ions including those that are difficult to measure by usual off-line analyses. The diffusion properties of ions in resins have been successfully evaluated from the time change in the levitation positions of resin beads. PMID:20462180

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

    SciTech Connect

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

    2014-05-07

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

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. Investigation on intergranular exchange coupling effect in Pr9Fe85.5B5.5 ribbons

    NASA Astrophysics Data System (ADS)

    Li, Z. B.; Zhang, M.; Wang, L. C.; Shen, B. G.; Zhang, X. F.; Li, Y. F.; Hu, F. X.; Sun, J. R.

    2014-02-01

    The intergranular exchange coupling effects are investigated via thermal activation of magnetization reversal in the magnetic relaxation process, combined with Henkel plots and the measurement of susceptibilities in three types of Pr9Fe85.5B5.5 ribbons. Exchange interaction between hard-hard grains is proposed in optimal melt-spun ribbons, as well as in over melt-spun ribbons even bearing a weak exchange coupling between soft-hard grains. In under melt-spun ribbons, the decoupled effect is proposed between hard-hard grains. These investigations may contribute to a clear understanding about the complicated nature of the intergranular exchange coupling in nanocomposite magnets.

  16. Coupled Brownian motors: Anomalous hysteresis and zero-bias negative conductance

    NASA Astrophysics Data System (ADS)

    Reimann, P.; Kawai, R.; Van den Broeck, C.; Hänggi, P.

    1999-03-01

    We introduce a model of interacting Brownian particles in a symmetric, periodic potential that undergoes a noise-induced non-equilibrium phase transition. The associated spontaneous symmetry breaking entails a ratchet-like transport mechanism. In response to an external force we identify several novel features; among the most prominent being a zero-bias negative conductance and a prima facie counterintuitive, anomalous hysteresis.

  17. Strong coupling theory for electron-mediated interactions in double-exchange models

    NASA Astrophysics Data System (ADS)

    Ishizuka, Hiroaki; Motome, Yukitoshi

    2015-07-01

    We present a theoretical framework for evaluating effective interactions between localized spins mediated by itinerant electrons in double-exchange models. Performing the expansion with respect to the spin-dependent part of the electron hopping terms, we show a systematic way of constructing the effective spin model in the large Hund's coupling limit. As a benchmark, we examine the accuracy of this method by comparing the results with the numerical solutions for the spin-ice type model on a pyrochlore lattice. We also discuss an extension of the method to the double-exchange models with Heisenberg and X Y localized spins.

  18. Tunable High-Field Magnetization in Strongly Exchange-Coupled Freestanding Co/CoO Core/Shell Coaxial Nanowires.

    PubMed

    Salazar-Alvarez, German; Geshev, Julian; Agramunt-Puig, Sebastià; Navau, Carles; Sanchez, Alvaro; Sort, Jordi; Nogués, Josep

    2016-08-31

    The exchange bias properties of Co/CoO coaxial core/shell nanowires were investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. First, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting predefined magnetization states to the antiferromagnetic (AFM) shell, as corroborated by micromagnetic simulations. Second, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops attributed to the AFM easy axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, was thus experimentally and theoretically demonstrated. PMID:27502034

  19. Coupling the WAM wave model to EC-Earth GCM: Will it reduce the Southern Ocean bias?

    NASA Astrophysics Data System (ADS)

    de Vries, Hylke

    2015-04-01

    In an attempt to accelerate progress on the reduction of the well-known ocean SST bias in the Southern Ocean (SO), research has been undertaken to include the WAM wave-model in to the EC-Earth GCM. EC-Earth v3.1 is based on the ECMWF IFS atmosphere model and uses NEMO to describe the ocean circulation. The SST bias in EC-Earth, as in many other coupled GCMs, is predominantly a summer problem. In that season mixed layer depths are shallow because strong radiative forcing leads to strong vertical temperature stratification. Realistic sea states and surface wave breaking will feedback on to the upper layers of the oceanic circulation, for example through enhanced vertical mixing. Without actual sea state information, NEMO relies on certain parameterizations that involve atmospheric surface windstress. However, during a "growing"/"decaying" sea state, the net stress entering the ocean is lower/higher than the atmospheric wind stress. Without real-time information of the sea state, ocean models such as NEMO can only assume a sea-state in equilibrium with the wind at all times, a situation which is rather rare. We present first results of the effect of including surface ocean waves (WAM) into EC-Earth. If only IFS-WAM interaction is included, effects on the SO bias are limited. The small changes in the wind patterns (and thereby windstress), induced by the wave-induced modified drag-coefficients, are clearly not large enough to substantially modify the SST pattern. If WAM-NEMO interactions are included as well the changes are more substantial (as they modify the vertical mixing), but not necessarily everywhere in the right direction regarding the SST bias.

  20. Coupling of lever arm swing and biased Brownian motion in actomyosin.

    PubMed

    Nie, Qing-Miao; Togashi, Akio; Sasaki, Takeshi N; Takano, Mitsunori; Sasai, Masaki; Terada, Tomoki P

    2014-04-01

    An important unresolved problem associated with actomyosin motors is the role of Brownian motion in the process of force generation. On the basis of structural observations of myosins and actins, the widely held lever-arm hypothesis has been proposed, in which proteins are assumed to show sequential structural changes among observed and hypothesized structures to exert mechanical force. An alternative hypothesis, the Brownian motion hypothesis, has been supported by single-molecule experiments and emphasizes more on the roles of fluctuating protein movement. In this study, we address the long-standing controversy between the lever-arm hypothesis and the Brownian motion hypothesis through in silico observations of an actomyosin system. We study a system composed of myosin II and actin filament by calculating free-energy landscapes of actin-myosin interactions using the molecular dynamics method and by simulating transitions among dynamically changing free-energy landscapes using the Monte Carlo method. The results obtained by this combined multi-scale calculation show that myosin with inorganic phosphate (Pi) and ADP weakly binds to actin and that after releasing Pi and ADP, myosin moves along the actin filament toward the strong-binding site by exhibiting the biased Brownian motion, a behavior consistent with the observed single-molecular behavior of myosin. Conformational flexibility of loops at the actin-interface of myosin and the N-terminus of actin subunit is necessary for the distinct bias in the Brownian motion. Both the 5.5-11 nm displacement due to the biased Brownian motion and the 3-5 nm displacement due to lever-arm swing contribute to the net displacement of myosin. The calculated results further suggest that the recovery stroke of the lever arm plays an important role in enhancing the displacement of myosin through multiple cycles of ATP hydrolysis, suggesting a unified movement mechanism for various members of the myosin family. PMID:24762409

  1. Resonant magnetoelectric coupling in trilayers of ferromagnetic alloys and piezoelectric lead zirconate titanate: The influence of bias magnetic field

    NASA Astrophysics Data System (ADS)

    Srinivasan, G.; de Vreugd, C. P.; Laletin, V. M.; Paddubnaya, N.; Bichurin, M. I.; Petrov, V. M.; Filippov, D. A.

    2005-05-01

    We present the first data and theory for the bias magnetic field dependence of magnetoelectric coupling in the electromechanical resonance (EMR) region for ferromagnetic-piezoelectric heterostructures. Trilayers of Permendur, a Co-Fe-V alloy, and lead zirconate titanate were studied. Measurements of the magnetoelectric (ME) voltage coefficient αE indicate a strong ME coupling in the low-frequency range and a giant ME effect due to EMR at 200-300kHz for radial modes and at ˜2.7MHz for thickness modes. Data were obtained for the bias field H dependence of two key parameters, the EMR frequency fr and the ME coefficient αE,R at resonance. With increasing H , an increase in fr and a rapid rise and fall in αE,R are measured. In our model we consider two mechanisms for the magnetic field influence on ME interactions: (i) a shift in the EMR frequency due to changes in compliance coefficients ( ΔE effect) and (ii) variation in the piezomagnetic coefficient that manifests as a change in αE,R . Theoretical profiles of αE vs frequency and estimates of frequency shift based on the ΔE effect are in excellent agreement with the data.

  2. 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.

  3. Mutual interactions of redox couples via electron exchange in silicate melts - Models for geochemical melt systems

    NASA Technical Reports Server (NTRS)

    Schreiber, Henry D.; Merkel, Robert C., Jr.; Schreiber, V. Lea; Balazs, G. Bryan

    1987-01-01

    The mutual interactions via electron exchange of redox couples in glass-forming melts were investigated both theoretically and experimentally. A thermodynamic approach for considering the mutual interactions leads to conclusion that the degree of mutual interaction in the melt should be proportional in part to the difference in relative reduction potentials of the interacting redox couples. Experimental studies verify this conclusion for numerous redox couples in several composition/temperature/oxygen fugacity regimes. Geochemical systems simultaneously possess many potentially multivalent elements; the stabilized redox states in the resulting magmas can be explained in part by mutual interactions and by redox buffering through the central Fe(III)- Fe(II) couples in the melts. The significance of these results for basaltic magmas of the earth, moon, and meteorites is addressed.

  4. Magnetic coupling and exchange stiffness in striped MnAs films

    NASA Astrophysics Data System (ADS)

    Tolinski, T.; Lindner, J.; Lenz, K.; Baberschke, K.; Ney, A.; Hesjedal, T.; Pampuch, C.; Däweritz, L.; Koch, R.; Ploog, K. H.

    2004-12-01

    We provide the first direct evidence of interactions in a self-organized pattern of coexisting ferromagnetic and paramagnetic MnAs stripe domains as a function of the coupling strength between the stripes (inter) and within one stripe (intra). The value of the intra exchange constant A = 17.7 × 10-10 erg/cm is determined unambiguously from spin wave resonance. Additionally, in-plane ferromagnetic resonance measurements reveal the presence of a strong coupling between the neighboring stripes, which can dominate the weak intra-stripe interaction.

  5. Magnetization process in a two-phase exchange-coupled system: A microscopic study

    SciTech Connect

    Ryan, D.H.; Feutrill, E.H.; Ding, J.

    1997-04-01

    The magnetization process in an exchange-coupled {alpha}-Fe+Nd{sub 2}Fe{sub 14}B nanocomposite has been studied by M{umlt o}ssbauer spectroscopy. Measurements in fields of up to 2 T confirm that the magnetization of the soft phase is strongly coupled to that of the hard phase. Analysis of magnetization curves and magic-angle spectra of saturated samples shows that the remanence is dominated by the hard phase. {copyright} {ital 1997 American Institute of Physics.}

  6. A Perspective on Designing Chiral Organic Magnetic Molecules with Unusual Behavior in Magnetic Exchange Coupling.

    PubMed

    Sarbadhikary, Prodipta; Shil, Suranjan; Panda, Anirban; Misra, Anirban

    2016-07-01

    A total of nine diradical-based organic chiral magnetic molecules with allene and cumulene couplers have been theoretically designed, and subsequently, their magnetic property has been studied by density functional theory. It is found that with an increase in length of the coupler, a remarkable increase in spin density within the coupler takes place. An increase in the length of the coupler reduces the energy of LUMO, and a smaller HOMO-LUMO gap facilitates stronger magnetic coupling and thereby a higher magnetic exchange coupling constant (J). This observation is supported by the occupation number of natural orbitals. PMID:27285309

  7. Influence of temperature on structure and magnetic properties of exchange coupled TbCo/FeNi bilayers.

    PubMed

    Svalov, A V; Balymov, K G; Fernández, A; Orue, I; Larrañaga, A; Vas'kovsky, V O; Gutiérrez, J; Kurlyandskaya, G V

    2012-09-01

    Among amorphous films of rare earth-transition metal (RE-TM) alloys as exchange-biasing layers in magnetoresistive heads and spin-valve sensors, the amorphous Tb-Co films have most high practical potential. In the present work the influence of the temperature and the heat treatment parameters on the structure and magnetic properties was studied for exchange bias FeNi/Tb35Co65 bilayers annealed in vacuum or a nitrogen flow. A simple explanation of the dependence of the magnetic properties on the temperature and the heat treatment parameters connected with structural changes in each one of the layers was proposed. PMID:23035518

  8. Spin orbital torque driven magnetization switching in magnetic tunnel junction with inter-layer exchange coupling

    SciTech Connect

    Xu, Lei; Ma, Zhongshui; Wei, Dan

    2015-01-14

    The switching processes of elliptically shaped magnetic tunnel junction bits with the structure Ta/CoFeB/MgO/CoFeB have been studied by the micromagnetic models. By comparing the tunneling magneto-resistance minor and major loops calculated by our model with related experimental results, we found that the inter-layer exchange coupling between the two CoFeB layers and a reduced saturation magnetization M{sub s} distribution at the edge of the elliptical bit should be included. The chosen strength of the inter-layer exchange coupling also matches well with experimental observations. The current induced magnetization switching is generated from the spin Hall effect in the Ta layer. The critical switching currents calculated by our model are coincident with experiment. This shows the reliability of our micromagnetic model with the spin orbital torque term.

  9. Exchange Coupling Nanophase Fe-Pd Ferromagnets Through Solid State Transformation

    SciTech Connect

    Shugart, Kathleen N.; Ludtka, Gerard Michael; Ludtka, Gail Mackiewicz-; Soffa, William A

    2011-01-01

    This study continues previous work on off stoichiometric Fe-Pd alloys using a combined reaction strategy during thermomechanical processing [1,2]. Severe plastic deformation of the initial disordered fcc gamma phase ( ), followed by heat treatment in the two phase field produces a nano-composite ferromagnet comprised of soft alpha-Fe/ferrite in a high-anisotropy L10 FePd matrix. The length scale and morphology of the transformation products have been characterized using x-ray diffraction, and scanning and transmission electron microscopy. The transformed microstructures exhibit strong texture retention similar to the stoichiometric alloy suggesting a massive ordering mode. The alloy has shown a proclivity to exchange couple at a length scale not in agreement with proposed theories of exchange coupling [3,4]. The magnetic properties were measured using standard vibrating sample magnetometry (VSM). This research has been supported by the National Science Foundation (NSF-DMR).

  10. Spin signatures of exchange-coupled triplet pairs formed by singlet fission

    NASA Astrophysics Data System (ADS)

    Bayliss, Sam L.; Weiss, Leah R.; Rao, Akshay; Friend, Richard H.; Chepelianskii, Alexei D.; Greenham, Neil C.

    2016-07-01

    We study the effect of an exchange interaction on the magnetic-field-dependent photoluminescence in singlet fission materials. We show that, for strongly interacting triplet exciton pairs (intertriplet exchange interaction greater than the intratriplet spin-dipolar interaction), quantum beating and magnetic-field effects vanish apart from at specific magnetic fields where singlet and quintet levels are mixed by a level anticrossing. We characterize these effects and show that the absence of a magnetic-field effect or zero-field quantum beats does not necessarily mean that fission is inoperative. These results call for a reconsideration of the observations that are considered hallmarks of singlet fission and demonstrate how the spin coherence and exchange coupling of interacting triplet pairs can be measured through magneto-photoluminescence experiments.

  11. The charge-exchange induced coupling between plasma-gas counterflows in the heliosheath

    NASA Astrophysics Data System (ADS)

    Fahr, H. J.

    2003-06-01

    Many hydrodynamic models have been presented which give similar views of the interaction of the solar wind plasma bubble with the counterstreaming partially ionized interstellar medium. In the more recent of these models it is taken into account that the solar and interstellar hydrodynamic flows of neutral atoms and protons are coupled by mass-, momentum-, and energy-exchange terms due to charge exchange processes. We shall reinvestigate the theoretical basis of this coupling here by use of a simplified description of the heliospheric interface and describe the main physics of the H-atom penetration through the more or less standing well-known plasma wall ahead of the heliopause. Thereby we can show that the type of charge exchange coupling terms used in up-to-now hydrodynamic treatments unavoidably leads to an O-type critical point at the sonic point of the H-atom flow, thus not allowing for a continuation of the integration of the hydrodynamic set of differential equations. The remedy for this problem is given by a more accurate formulation of the momentum exchange term for quasi-and sub-sonic H-atom flows. With a refined momentum exchange term derived from basic kinetic Boltzmann principles, we instead arrive at a characteristic equation with an X-type critical point, allowing for a continuous solution from supersonic to subsonic flow conditions. This necessitates that the often treated problem of the propagation of inter-stellar H-atoms through the heliosheath has to be solved using these newly derived, differently effective plasma - gas friction forces. Substantially different results are to be expected from this context for the filtration efficiency of the heliospheric interface.

  12. 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.

  13. Exchange coupling driven omnidirectional rotatable anisotropy in ferrite doped CoFe thin film

    PubMed Central

    Chai, Guozhi; Phuoc, Nguyen N.; Ong, C. K.

    2012-01-01

    Isotropic magnetic materials with high resonant frequencies are useful for applications in microwave devices. Undoped CoFe thin films, as common soft magnetic materials with high saturation magnetization, show isotropic characteristics but no high frequency response. Here, we use ferrite doped CoFe thin film to realize a resonant frequency higher than 4.5 GHz at all orientations. The exchange coupling between ferrimagnet and ferromagnet is assumed to play a key role on the omnidirectional rotatable anisotropy. PMID:23145323

  14. Magnetism behaviours dominated by the interplay of magnetic anisotropy and exchange coupling in local Co discs.

    PubMed

    Yang, En-Cui; Liu, Zhong-Yi; Zhang, Lei; Yang, Na; Zhao, Xiao-Jun

    2016-05-10

    Disc-like Co core-derived (4,4)- and (3,6)-connected layers, {[Co7(C2H5OH)1.5(H2O)0.5(Hdatrz)2(μ3-OH)4(ip)5]·2.5H2O·C2H5OH}n () and [Co7(H2O)4(ade)2(μ3-OH)6(sip)2]n () (Hdatrz = 3,5-diamino-1,2,4-triazole, ade(-) = adeninate, ip(2-) = isophthalate and sip(3-) = 5-sulfoisophthalate) were solvothermally generated and structurally and magnetically characterized. The effect of magnetic anisotropy and exchange coupling from the local Co cores on the resulting magnetism properties are discussed. A crystallographically asymmetric Co core in exhibited an unusual single-molecule magnet (SMM)-like response under zero dc field resulting from strong anisotropy generated by two different types of Co(II) polyhedra and highly anisotropic exchange interactions. By contrast, a highly symmetric Co disc in belonging to the C2h point group showed only strong ferromagnetic exchange, to lead to an overall ST = 7/2 spin ground-state at low temperature. Thus, the interplay of magnetic anisotropy and exchange coupling has a great and complicated influence on the overall magnetic phenomena, which should be fully considered for the design and preparation of new Co(II)-SMMs. PMID:27089955

  15. Experiments and Simulations on a Heat Exchanger of an Automotive Exhaust Thermoelectric Generation System Under Coupling Conditions

    NASA Astrophysics Data System (ADS)

    Liu, X.; Yu, C. G.; Chen, S.; Wang, Y. P.; Su, C. Q.

    2014-06-01

    The present experimental and computational study investigates an exhaust gas waste heat recovery system for vehicles, using thermoelectric modules and a heat exchanger to produce electric power. It proposes a new plane heat exchanger of a thermoelectric generation (TEG) system, producing electricity from a limited hot surface area. To investigate the new plane heat exchanger, we make a coupling condition of heat-flow and flow-solid coupling analysis on it to obtain the temperature, heat, and pressure field of the heat exchanger, and compared it with the old heat exchanger. These fields couple together to solve the multi-field coupling of the flow, solid, and heat, and then the simulation result is compared with the test bench experiment of TEG, providing a theoretical and experimental basis for the present exhaust gas waste heat recovery system.

  16. 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.

  17. 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.

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. Exchange coupled L10-FePt/fcc-FePt nanomagnets: Synthesis, characterization and magnetic properties

    NASA Astrophysics Data System (ADS)

    Srivastava, Sachchidanand; Gajbhiye, Namdeo S.

    2016-03-01

    We report synthesis, characterization and magnetic properties of exchange-coupled L10-FePt/fcc-FePt nanomagnets. Structural and morphological characterization of exchange-coupled L10-FePt/fcc-FePt was carried out by powder X-ray diffraction, Mössbauer spectroscopy and transmission electron microscopy. Rietveld refinement of powder X-ray diffraction pattern has been used to quantify L10-FePt and fcc-FePt phases present in samples. Room temperature Mössbauer spectroscopy showed sextets of both L10-FePt and fcc-FePt phases with their respective hyperfine interaction parameters. Transmission electron microscopic (TEM and HRTEM) images confirmed nanocrystalline nature of exchange-coupled nanomagnets with particle size ranges from 15 nm to 50 nm after annealing for different time at 700 °C. Room temperature magnetic studies showed ferromagnetic nature of nanomagnets and maximum energy product (BH)max~10.92 MGOe was obtained for sample containing 89.0% volume fraction of L10-FePt phase.

  7. A Framework of Computing Multipolar Exchange Interactions in Systems with Strong Spin-Orbit Coupling

    NASA Astrophysics Data System (ADS)

    Pi, Shu-Ting

    We intro duce a theoretical framework for computations of anisotropic multipolar exchange interactions found in many spin-orbit coupled magnetic systems and propose a method to extract these coupling constants using a density functional total energy calculation. This method is develop ed using a multipolar expansion of lo cal density matrices for correlated orbitals that are responsible for magnetic degrees of freedom. Within the mean-field approximation, we show that each coupling constant can b e recovered from a series of total energy calculations via what we call the "pair-flip" technique. This technique flips the relative phase of a pair of multipoles and computes the corresponding total energy cost associated with the given exchange constant. To test it, we apply our method to Uranium Dioxide, which is a system known to have pseudospin J = 1 superexchange induced dipolar, and superexchange plus spin-lattice induced quadrupolar orderings. Our calculation reveals that the superexchange and spin-lattice contributions to the quadrupolar exchange interactions are about the same order with ferro- and antiferro-magnetic contributions, respectively. This highlights a competition rather than a cooperation between them. Our method could be a promising tool to explore magnetic properties of rare-earth compounds and hidden-order materials.

  8. Anisotropic multipolar exchange interactions in systems with strong spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Pi, Shu-Ting; Nanguneri, Ravindra; Savrasov, Sergey

    2014-07-01

    We introduce a theoretical framework for computations of anisotropic multipolar exchange interactions found in many spin-orbit coupled magnetic systems and propose a method to extract these coupling constants using a density functional total energy calculation. This method is developed using a multipolar expansion of local density matrices for correlated orbitals that are responsible for magnetic degrees of freedom. Within the mean-field approximation, we show that each coupling constant can be recovered from a series of total energy calculations via what we call the "pair-flip" technique. This technique flips the relative phase of a pair of multipoles and computes the corresponding total energy cost associated with the given exchange constant. To test it, we apply our method to uranium dioxide, which is a system known to have pseudospin J =1 superexchange induced dipolar, and superexchange plus spin-lattice induced quadrupolar orderings. Our calculation reveals that the superexchange and spin-lattice contributions to the quadrupolar exchange interactions are about the same order with ferro- and antiferromagnetic contributions, respectively. This highlights a competition rather than a cooperation between them. Our method could be a promising tool to explore magnetic properties of rare-earth compounds and hidden-order materials.

  9. Quantum interference and correlations in single dopants and exchange-coupled dopants in silicon

    NASA Astrophysics Data System (ADS)

    Salfi, Joe

    2015-03-01

    Quantum electronics exploiting the highly coherent states of single dopants in silicon invariably requires interactions between states and interfaces, and inter-dopant coupling by exchange interactions. We have developed a low temperature STM scheme for spatially resolved single-electron transport in a device-like environment, providing the first wave-function measurements of single donors and exchange-coupled acceptors in silicon. For single donors, we directly observed valley quantum interference due to linear superpositions of the valleys, and found that valley degrees of freedom are highly robust to the symmetry-breaking perturbation of nearby (3 nm) surfaces. For exchange-coupled acceptors, we measured the singlet-triplet splitting, and from the spatial tunneling probability, extracted enough information about the 2-body wavefunction amplitudes to determine the entanglement entropy, a measure of the quantum inseparability (quantum correlations) generated by the interactions between indistinguishable particles. Entanglement entropy of the J=3/2 holes was found to increase with increasing dopant distance, as Coulomb interactions overcome tunneling, coherently localizing spin towards a Heitler-London singlet, mimicing S=1/2 particles. In the future these capabilities will be exploited to peer into the inner workings of few-dopant quantum devices and shed new light on multi-dopant correlated states, engineered atom-by-atom. Work done collaboratively with J. A. Mol, R. Rahman, G. Klimeck, M. Y. Simmons, L. C. L. Hollenberg, and S. Rogge. Primary financial support from the ARC.

  10. Effect of annealing on magnetic exchange coupling in CoPt/Co bilayer thin films

    SciTech Connect

    Kim, J.; Barmak, K.; De Graef, M.; Lewis, L. H.; Crew, D. C.

    2000-05-01

    Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase nanocomposite permanent magnets. The bilayers were prepared by magnetron sputter deposition of near-equiatomic CoPt with a thickness of 25 nm onto oxidized Si wafers. In the as-deposited state, CoPt had the A1 (fcc) structure and was magnetically soft. Before reinsertion into the sputtering chamber for the deposition of 2.8-16.7 nm thick Co layers, the CoPt films were annealed at 700 degree sign C for 120 min to produce the magnetically hard, fully ordered L1{sub 0} phase. The presence of exchange coupling in the bilayers was verified by magnetic hysteresis and recoil measurements and showed that only for Co thicknesses below 6.3 nm was this layer (in its as-deposited state) coupled through its full thickness to the CoPt layer. Annealing the bilayer samples at 300 and 550 degree sign C for 20 min resulted in improvement of the interlayer magnetic coupling and produced clear differences in the magnetic reversal coherency and the recoil curves. However, for some samples, the improved coupling resulted in a decrease in coercivity, indicating that there is an optimum in the coupling strength for the attainment of high coercivity. Transmission electron microscopy studies of the bilayers in plan view showed that the increased interlayer coupling with annealing was a result of improved granular epitaxy of Co to CoPt. (c) 2000 American Institute of Physics.

  11. Overcoming Bias toward Same-Sex Couples: A Case Study from inside an MFT Ethics Classroom

    ERIC Educational Resources Information Center

    Charles, Laurie L.; Thomas, Dina; Thornton, Matthew L.

    2005-01-01

    This article illustrates a teaching case in which a marriage and family therapy (MFT) trainee learned to develop cultural sensitivity toward same-sex couples despite religious beliefs that put her at risk of discriminating against that population. The case took place during a marriage and family therapy ethics course in the spring of 2003. From…

  12. 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.

  13. Exchange coupling and magnetic anisotropy at Fe/FePt interfaces

    NASA Astrophysics Data System (ADS)

    Aas, C. J.; Hasnip, P. J.; Cuadrado, R.; Plotnikova, E. M.; Szunyogh, L.; Udvardi, L.; Chantrell, R. W.

    2013-11-01

    We perform fully relativistic first-principles calculations of the exchange interactions and the magnetocrystalline anisotropy energy (MAE) in an Fe/FePt/Fe sandwich system in order to elucidate how the presence of Fe/FePt (soft/hard magnetic) interfaces impacts on the magnetic properties of Fe/FePt/Fe multilayers. Throughout our study we make comparisons between a geometrically unrelaxed system and a geometrically relaxed system. We observe that the Fe layer at the Fe/FePt interface plays a crucial role inasmuch as its (isotropic) exchange coupling to the soft (Fe) phase of the system is substantially reduced. Moreover, this interfacial Fe layer has a substantial impact on the MAE of the system. We show that the MAE of the FePt slab, including the contribution from the Fe/FePt interface, is dominated by anisotropic intersite exchange interactions. Our calculations indicate that the change in the MAE of the FePt slab with respect to the corresponding bulk value is negative, i.e., the presence of Fe/FePt interfaces appears to reduce the perpendicular MAE of the Fe/FePt/Fe system. However, for the relaxed system, this reduction is marginal. It is also shown that the relaxed system exhibits a reduced interfacial exchange. Using a simple linear chain model, we demonstrate that the reduced exchange leads to a discontinuity in the magnetization structure at the interface.

  14. 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.

  15. 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.

  16. A Mean Field Analysis of the Exchange Coupling (J) For 2- and 3-D Structured Tetracyanoethylenide (TCNE -)-based Magnets

    SciTech Connect

    McConnell, Amber C.; Fishman, Randy Scott; Miller, Joel S.

    2012-01-01

    Mean field expressions based on the simple Heisenberg model were derived to correlate the inter- and intralayer exchange coupling to the critical temperatures, Tc, for several TCNE (tetracyanoethylene) based magnets with extended 2- and 3-D structure types. These expressions were used to estimate the exchange coupling, J, for 2-D ferrimagnetic [MII(TCNE)(NCMe)2]+ (M = Mn, Fe), 3-D antiferromagnetic MnII(TCNE)[C4(CN)8]1/2, and 3-D ferrimagnetic MnII(TCNE)3/2(I3)1/2. The sign and magnitude of the exchange coupling are in accord with previously reported magnetic data.

  17. A Mean Field Analysis of the Exchange Coupling (J) for Non-cubic Prussian Blue Analogue Magnets

    SciTech Connect

    DaSilva, Jack G.; McConnell, Amber C.; Fishman, Randy Scott; Miller, Joel S.

    2012-01-01

    Mean field expressions based on the simple Heisenberg model were derived to correlate the intra- and interlayer exchange couplings to the critical temperatures, Tc, for three metallocyanide-based magnets with extended 2- and 3-D structure types. These expressions were used to estimate the exchange coupling, J, for 2-D ferrimagnetic [NEt4]2MnII3(CN)8, 3-D antiferromagnetic [NEt4]MnII3(CN)7, and 3-D antiferromagnetic interpenetrating 3-D MnII(CN)2. The type and magnitude of the exchange coupling are in accord with the previously reported magnetic data.

  18. Exchange coupling between silicon donors: The crucial role of the central cell and mass anisotropy

    NASA Astrophysics Data System (ADS)

    Pica, G.; Lovett, B. W.; Bhatt, R. N.; Lyon, S. A.

    2014-06-01

    Donors in silicon are now demonstrated as one of the leading candidates for implementing qubits and quantum information processing. Single qubit operations, measurements, and long coherence times are firmly established, but progress on controlling two qubit interactions has been slower. One reason for this is that the interdonor exchange coupling has been predicted to oscillate with separation, making it hard to estimate in device designs. We present a multivalley effective mass theory of a donor pair in silicon, including both a central cell potential and the effective mass anisotropy intrinsic in the Si conduction band. We are able to accurately describe the single donor properties of valley-orbit coupling and the spatial extent of donor wave functions, highlighting the importance of fitting measured values of hyperfine coupling and the orbital energy of the 1s levels. Ours is a simple framework that can be applied flexibly to a range of experimental scenarios, but it is nonetheless able to provide fast and reliable predictions. We use it to estimate the exchange coupling between two donor electrons and we find a smoothing of its expected oscillations, and predict a monotonic dependence on separation if two donors are spaced precisely along the [100] direction.

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

    PubMed Central

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

    2015-01-01

    Interfacial exchange coupling and magnetization reversal characteristics in the perpendicular heterostructures consisting of an amorphous ferrimagnetic (FI) TbxCo100–x alloy layer exchange-coupled with a ferromagnetic (FM) [Co/Ni]N multilayer have been investigated. As compared with pure TbxCo100–x alloy, the magnetization compensation composition of the heterostructures shift to a higher Tb content, implying Co/Ni also serves to compensate the Tb moment in TbCo layer. The net magnetization switching field Hc⊥ and interlayer interfacial coupling field Hex, are not only sensitive to the magnetization and thickness of the switched TbxCo100–x or [Co/Ni]N layer, but also to the perpendicular magnetic anisotropy strength of the pinning layer. By tuning the layer structure we achieve simultaneously both large Hc⊥ = 1.31 T and Hex = 2.19 T. These results, in addition to the fundamental interest, are important to understanding of the interfacial coupling interaction in the FM/FI heterostructures, which could offer the guiding of potential applications in heat-assisted magnetic recording or all-optical switching recording technique. PMID:26074295

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

    PubMed

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

    2015-01-01

    Interfacial exchange coupling and magnetization reversal characteristics in the perpendicular heterostructures consisting of an amorphous ferrimagnetic (FI) TbxCo(100-x) alloy layer exchange-coupled with a ferromagnetic (FM) [Co/Ni]N multilayer have been investigated. As compared with pure TbxCo(100-x) alloy, the magnetization compensation composition of the heterostructures shift to a higher Tb content, implying Co/Ni also serves to compensate the Tb moment in TbCo layer. The net magnetization switching field Hc⊥ and interlayer interfacial coupling field Hex, are not only sensitive to the magnetization and thickness of the switched TbxCo(100-x) or [Co/Ni]N layer, but also to the perpendicular magnetic anisotropy strength of the pinning layer. By tuning the layer structure we achieve simultaneously both large Hc⊥ = 1.31 T and Hex = 2.19 T. These results, in addition to the fundamental interest, are important to understanding of the interfacial coupling interaction in the FM/FI heterostructures, which could offer the guiding of potential applications in heat-assisted magnetic recording or all-optical switching recording technique. PMID:26074295

  1. Magnetic proximity effect and interlayer exchange coupling of ferromagnetic/topological insulator/ferromagnetic trilayer

    NASA Astrophysics Data System (ADS)

    Li, Mingda; Cui, Wenping; Yu, Jin; Dai, Zuyang; Wang, Zhe; Katmis, Ferhat; Guo, Wanlin; Moodera, Jagadeesh

    2015-01-01

    The magnetic proximity effect between the topological insulator (TI) and ferromagnetic insulator (FMI) is considered to have great potential in spintronics. However, a complete determination of interfacial magnetic structure has been highly challenging. We theoretically investigate the interlayer exchange coupling of two FMIs separated by a TI thin film, and show that the particular electronic states of the TI contributing to the proximity effect can be directly identified through the coupling behavior between two FMIs, together with a tunability of the coupling constant. Such an FMI/TI/FMI structure not only serves as a platform to clarify the magnetic structure of the FMI/TI interface, but also provides insights in designing the magnetic storage devices with ultrafast response.

  2. Resonators coupled to voltage-biased Josephson junctions: From linear response to strongly driven nonlinear oscillations

    NASA Astrophysics Data System (ADS)

    Meister, S.; Mecklenburg, M.; Gramich, V.; Stockburger, J. T.; Ankerhold, J.; Kubala, B.

    2015-11-01

    Motivated by recent experiments in which a voltage-biased Josephson junction is placed in series with a resonator, the classical dynamics of the circuit is studied in various domains of parameter space. This problem can be mapped onto the dissipative motion of a single degree of freedom in a nonlinear time-dependent potential, where in contrast to conventional settings the nonlinearity appears in the driving while the static potential is purely harmonic. For long times the system approaches steady states which are analyzed in the underdamped regime over the full range of driving parameters including the fundamental resonance as well as higher harmonics and subharmonics. Observables such as the dc-Josephson current and the radiated microwave power give direct information about the underlying dynamics covering phenomena such as bifurcations, irregular motion, and up- and down-conversion. Due to their tunability, present and future setups provide versatile platforms to explore the changeover from linear response to strongly nonlinear behavior in driven dissipative systems under well defined conditions.

  3. Ledge-type Co/L10-FePt exchange-coupled composites

    NASA Astrophysics Data System (ADS)

    Speliotis, Th.; Giannopoulos, G.; Niarchos, D.; Li, W. F.; Hadjipanayis, G.; Barucca, G.; Agostinelli, E.; Laureti, S.; Peddis, D.; Testa, A. M.; Varvaro, G.

    2016-06-01

    FePt-based exchange-coupled composites consisting of a magnetically hard L10-FePt phase exchange-coupled with a soft ferromagnetic material are promising candidates for future ultra-high density (>1 Tbit/in2) perpendicular magnetic recording media, also being of interest for other applications including spin torque oscillators and micro-electro-mechanical systems, among others. In this paper, the effect of the thickness of a soft Co layer (3 < thCo < 20 nm) on the magnetic behavior of ledge-type fcc(100)-Co/L10(001)-FePt composites deposited on an MgO (100) substrate is systematically studied by combining morpho-structural analyses and angular magnetization measurements. Starting from a film consisting of isolated L10(001)-FePt islands, the ledge-type structure was obtained by depositing a Co layer that either covered the FePt islands or filled-up the inter-island region, gradually forming a continuous layer with increasing Co thickness. A perpendicular anisotropy was maintained up to thCo ˜ 9.5 nm and a significant reduction in the coercivity (about 50% for thCo ˜ 3 nm) with the increase in thCo was observed, indicating that, by coupling hard FePt and soft Co phases in a ledge-type configuration, the writability can be greatly improved. Recoil loops' measurements confirmed the exchange-coupled behavior, reinforcing a potential interest in these systems for future magnetic recording media.

  4. Using Ensemble Short-Term Initialized Coupled NASA GEOS5 Climate Model Integrations to Study Convective Bias Growth

    NASA Technical Reports Server (NTRS)

    Cohen, Charlie; Robertson, Franklin; Molod, Andrea

    2014-01-01

    The representation of convective processes, particularly deep convection in the tropics, remains a persistent problem in climate models. In fact structural biases in the distribution of tropical rainfall in the CMIP5 models is hardly different than that of the CMIP3 versions. Given that regional climate change at higher latitudes is sensitive to the configuration of tropical forcing, this persistent bias is a major issue for the credibility of climate change projections. In this study we use model output from integrations of the NASA Global Earth Observing System Five (GEOS5) climate modeling system to study the evolution of biases in the location and intensity of convective processes. We take advantage of a series of hindcast experiments done in support of the US North American Multi-Model Ensemble (NMME) initiative. For these experiments a nine-month forecast using a coupled model configuration is made approximately every five days over the past 30 years. Each forecast is started with an updated analysis of the ocean, atmosphere and land states. For a given calendar month we have approximately 180 forecasts with daily means of various quantities. These forecasts can be averaged to essentially remove "weather scales" and highlight systematic errors as they evolve. Our primary question is to ask how the spatial structure of daily mean precipitation over the tropics evolves from the initial state and what physical processes are involved. Errors in parameterized convection, various water and energy fluxes and the divergent circulation are found to set up on fast time scales (order five days) compared to errors in the ocean, although SST changes can be non-negligible over that time. For the month of June the difference between forecast day five versus day zero precipitation looks quite similar to the difference between the June precipitation climatology and that from the Global Precipitation Climatology Project (GPCP). We focus much of our analysis on the influence of

  5. Thickness dependence of exchange coupling in (111)-oriented perovskite oxide superlattices

    NASA Astrophysics Data System (ADS)

    Jia, Yue; Chopdekar, Rajesh V.; Arenholz, Elke; Liu, Zhiqi; Biegalski, Michael D.; Porter, Zachary D.; Mehta, Apurva; Takamura, Yayoi

    2016-03-01

    Epitaxial L a0.7S r0.3Mn O3(LSMO )/L a0.7S r0.3Fe O3 (LSFO) superlattices on (111)-oriented SrTi O3 substrates with sublayer thicknesses ranging from 3 to 60 unit cells (u.c.) were synthesized and characterized. Detailed analysis of their structural, electronic, and magnetic properties were performed to explore the effect of sublayer thickness on the magnetic structure and exchange coupling at (111)-oriented perovskite oxide interfaces. In the ultrathin limit (3-6 u.c.), we find that the antiferromagnetic (AF) properties of the LSFO sublayers are preserved with an out-of-plane canting of the AF spin axis, while the ferromagnetic (FM) properties of the LSMO sublayers are significantly depressed. For thicker LSFO layers (>9 u.c.), the out-of-plane canting of the AF spin axis is only present in superlattices with thick LSMO sublayers. As a result, exchange coupling in the form of spin-flop coupling exists only in superlattices which display both robust ferromagnetism and out-of-plane canting of the AF spin axis.

  6. Joint perpendicular anisotropy and strong interlayer exchange coupling in systems with thin vanadium spacers

    SciTech Connect

    Devolder, T. Le Goff, A.; Eimer, S.; Adam, J.-P.

    2015-04-28

    We study the influence of the insertion of a vanadium spacer layer between an FeCoB layer and a [Co/Ni] multilayer in an MgO substrate-based system mimicking the reference system of a perpendicular anisotropy magnetic tunnel junction. The anisotropy of the [Co/Ni] multilayer gradually improves with the vanadium thicknesses t, up to an optimized state for t = 8 Å, with little influence of the thermal annealing. The interlayer exchange coupling is ferromagnetic and very strong for t≤6 Å. It can be adjusted by thermal treatment at t = 8 Å from no coupling in the as-grown state to more than 2 mJ/m{sup 2} after 250 °C annealing. For this spacer thickness, the magnetic properties are consistent with the occurrence of a bcc (001) to an fcc (111) crystalline structure transition at the vanadium spacer. The remaining interlayer exchange coupling at t = 8 Å is still substantially higher than the one formerly obtained with a Tantalum spacer, which holds promise for further optimization of the reference layers of tunnel junctions meant for magnetic random access memories.

  7. Joint perpendicular anisotropy and strong interlayer exchange coupling in systems with thin vanadium spacers

    NASA Astrophysics Data System (ADS)

    Devolder, T.; Le Goff, A.; Eimer, S.; Adam, J.-P.

    2015-04-01

    We study the influence of the insertion of a vanadium spacer layer between an FeCoB layer and a [Co/Ni] multilayer in an MgO substrate-based system mimicking the reference system of a perpendicular anisotropy magnetic tunnel junction. The anisotropy of the [Co/Ni] multilayer gradually improves with the vanadium thicknesses t, up to an optimized state for t = 8 Å, with little influence of the thermal annealing. The interlayer exchange coupling is ferromagnetic and very strong for t ≤6 Å. It can be adjusted by thermal treatment at t = 8 Å from no coupling in the as-grown state to more than 2 mJ/m2 after 250 °C annealing. For this spacer thickness, the magnetic properties are consistent with the occurrence of a bcc (001) to an fcc (111) crystalline structure transition at the vanadium spacer. The remaining interlayer exchange coupling at t = 8 Å is still substantially higher than the one formerly obtained with a Tantalum spacer, which holds promise for further optimization of the reference layers of tunnel junctions meant for magnetic random access memories.

  8. XY ring exchange model with frustrated Ising coupling on the triangular lattice

    NASA Astrophysics Data System (ADS)

    Owerre, S. A.

    2016-07-01

    We investigate the nature of a Z2-invariant XY ring-exchange interaction with a frustrated Ising coupling on the triangular lattice. Within the limits of pure XY ring-exchange interaction, we show that the classical ground state is degenerate resulting from the Z2-invariance of the Hamiltonian. Quantum fluctuations lift these classical degenerate ground states and produce an unusual state whose excitation spectrum exhibits a gapped maximum quadratic dispersion near k = 0 and vanishes at the midpoints of each side of the Brillouin zone. This result is in contrast to a gapless quadratic dispersion near k = 0 in the U(1)-invariant counterpart. We also study the effects of frustration when competing with a classically frustrated Ising interaction. We provide a glimpse into the possible quantum phases that could emerge. A comprehensive understanding of this Hamiltonian, however, cannot be elucidated analytically and requires an explicit numerical simulation.

  9. Gate-tunable indirect exchange interaction in spin-orbit-coupled mesoscopic rings

    NASA Astrophysics Data System (ADS)

    Nikoofard, H.; Heidari Semiromi, E.

    2015-05-01

    We study the carrier-mediated exchange interaction, the so-called Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, between two magnetic impurity moments embedded in a semiconductor mesoscopic ring. We treat the ring in the presence of an Aharonov-Bohm-type magnetic flux and the Rashba and Dresselhaus spin-orbit interactions (RSOI and DSOI). Energy eigenvalues of the system are obtained within a tight-binding framework and the strength of the indirect exchange interaction vs. RSOI strengths are plotted for different values of DSOI strength. The results show that the type of the impurity magnetic order, ferromagnetic (F) or antiferromagnetic (AF), depends on the RSOI and DSOI strengths. This leads to a full electrical control on the magnetic alignment of the system through, e.g., an external gate voltage.

  10. Exchange coupling, antiphase boundaries, and the origin of self-reversed thermoremanent magnetization

    NASA Astrophysics Data System (ADS)

    Harrison, R. J.; Kasama, T.; White, T. A.; Simpson, E. T.; Dunin-Borkowski, R. E.

    2005-12-01

    Self-reversed thermoremanent magnetization (SR-TRM) in the ilmenite-hematite system is thought to result from negative exchange coupling between antiphase domains (APDs) and antiphase domain boundaries (APBs), which form during rapid cooling of the mineral after volcanic eruption. Here we present a study of exchange coupling at APBs using a combination of off-axis electron holography and Monte Carlo simulations. A solid solution containing 70% ilmenite and 30% hematite (ilm70) was synthesised at 1573 K, quenched through the cation ordering phase transition and annealed for 10 hours at 1023 K. The sample was examined using off-axis electron holography, a technique that allows the phase shift of a high-energy electron wave to be recorded in a transmission electron microscope (TEM). Quantitative analysis of the phase shift shows that three distinct types of magnetic wall exist in quenched ilmenite-hematite. The first type corresponds to conventional free-standing 180° Bloch walls. These walls are free to move within the interior of an APD under the influence of an applied magnetic field. The second type forms when a 180° reversal in magnetization coincides exactly with the position of an APB. These walls are referred to as a 180° `chemical' walls. The reversal of magnetization results from negative exchange coupling between adjacent APDs, and occurs without any out-of-plane rotation of the magnetic moments. Chemical walls have a magnetization profile distinct from conventional Bloch walls and have a smaller wall width. A third type of magnetic wall appears when the negative exchange coupling between adjacent APDs is overcome at sufficiently large fields, forcing the magnetization in adjacent APDs to point in the same direction. We refer to these walls as 0° magnetic walls. Monte Carlo simulations have been used to investigate the nature of exchange coupling between ordered/antiordered APDs and disordered APBs. APBs are enriched in Fe relative to the ordered

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. Effect of exchange coupling on magnetic property in Sm-Co/α-Fe layered system

    NASA Astrophysics Data System (ADS)

    C, X. Sang; G, P. Zhao; W, X. Xia; X, L. Wan; F, J. Morvan; X, C. Zhang; L, H. Xie; J, Zhang; J, Du; A, R. Yan; P, Liu

    2016-03-01

    The hysteresis loops as well as the spin distributions of Sm-Co/α-Fe bilayers have been investigated by both three-dimensional (3D) and one-dimensional (1D) micromagnetic calculations, focusing on the effect of the interface exchange coupling under various soft layer thicknesses ts. The exchange coupling coefficient Ahs between the hard and soft layers varies from 1.8 × 10-6 erg/cm to 0.45 × 10-6 erg/cm, while the soft layer thickness increases from 2 nm to 10 nm. As the exchange coupling decreases, the squareness of the loop gradually deteriorates, both pinning and coercive fields rise up monotonically, and the nucleation field goes down. On the other hand, an increment of the soft layer thickness leads to a significant drop of the nucleation field, the deterioration of the hysteresis loop squareness, and an increase of the remanence. The simulated loops based on the 3D and 1D methods are consistent with each other and in good agreement with the measured loops for Sm-Co/α-Fe multilayers. Project supported by the National Natural Science Foundation of China (Grant Nos. 11074179 and 10747007), the National Basic Research Program of China (Grant No. 2014CB643702), the Zhejiang Provincial Natural Science Foundation of China (Grant No. LY14E010006), the Construction Plan for Scientific Research Innovation Teams of Universities in Sichuan Province, China (Grant No. 12TD008), the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the Education Ministry, China, and the Program for Key Science and Technology Innovation Team of Zhejiang Province, China (Grant No. 2013TD08).

  16. MAGNETIC EXCHANGE-COUPLING IN CoPt/Co BILAYER THIN FILMS

    SciTech Connect

    KIM,J.; BARMAK,K.; LEWIS,L.H.; CREW,D.C.; WELCH,D.O.

    1999-04-05

    Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700 C and fully transformed from the FCC phase to the magnetically hard, ordered L1{sub 0} phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8--225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.

  17. 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.

  18. Carboxymethylated polyethylenimine-polymethylenepolyphenylene isocyanate chelating ion exchange resin preconcentration for inductively coupled plasma spectrometry

    SciTech Connect

    Horvath, A.; Barnes, R.M.

    1986-06-01

    A carboxymethylated polyethylenimine-polylmethylenepolyphenylene isocyanate chelating ion exchange resin was prepared, characterized, and used for metals preconcentration for inductively coupled plasma spectrometry. The uptake of copper, cadmium, lead, and zinc by the resin was quantitative in the presence of high concentrations of ammonium, calcium, magnesium, potassium, sodium, and acetate and citrate salts. These metals could be collected from artificial seawater, Dead Sea water, and dissolved bone with a recovery of nearly 100%. The resin also chelates heavy metals and rare earths. Complexed metals can be eluted from the resin column with strong acids. The resin does not change volume with ionic form changes and can be regenerated for repeated use.

  19. Interfacial exchange-coupling induced chiral symmetry breaking of spin-orbit effects

    NASA Astrophysics Data System (ADS)

    Perna, P.; Ajejas, F.; Maccariello, D.; Fernandez Cuñado, J. L.; Guerrero, R.; Niño, M. A.; Bollero, A.; Miranda, R.; Camarero, J.

    2015-12-01

    We demonstrate that the interfacial exchange coupling in ferromagnetic/antiferromagnetic (FM/AFM) systems induces symmetry breaking of the spin-orbit (SO) effects. This has been done by studying the field and angle dependencies of anisotropic magnetoresistance and vectorial-resolved magnetization hysteresis loops, measured simultaneously and reproduced with numerical simulations. We show how the induced unidirectional magnetic anisotropy at the FM/AFM interface results in strong asymmetric transport behaviors, which are chiral around the magnetization hard-axis direction. Similar asymmetric features are anticipated in other SO-driven phenomena.

  20. Calculation of the exchange coupling in Si:P donor systems

    NASA Astrophysics Data System (ADS)

    Starling, Timothy R.; Wellard, Cameron J.; Quiney, Harry M.; Haig, Wayne; Hollenberg, Lloyd C. L.

    2005-02-01

    We examine exchange coupling in the Kate quantum computer, which consists of isolated spin-1/2 31P donors in a pure Si lattice. A calculation is made using full configuration interaction, a reasonably large basis set, and a simple physical model. Basis set convergence was not obtained, and increasing the size of the matrix further appears to be computationally impractical. We therefore consider a Gaussian basis set approach. A brief description of the McMurchie-Davidson algorithm for the expansion of SGTF functions into Hermite polynomials is given. We also give the results of a single-donor computation in this basis.

  1. Zero bias maximum of differential conductance in coupled quantum dots: The effect of interdot Coulomb interaction

    NASA Astrophysics Data System (ADS)

    Rajput, Gagan; Chand, S.; Ahluwalia, P. K.; Sharma, K. C.

    2010-10-01

    In this paper, we present a theoretical study of correlated electronic transport through coupled double quantum dot (DQD) system attached to normal leads, using a generalised two impurity Anderson Hamiltonian in the presence of intra- and inter-dot Coulomb interactions. A generic formulation from which different structures, i.e. series, symmetric as well as asymmetric parallel and T-shape, can be obtained easily, is developed using Keldysh non-equilibrium Green functions method. The occupation numbers and correlators appearing in the formulation have been calculated in a self-consistent manner. A special attention is paid to investigate the ZBM in the differential conductance, which appears, develops and disappears over a particular range of interdot Coulomb interaction, in the configuration of interest. The ZBM is found to result from the renormalization of energy levels induced by the interdot Coulomb interaction and therefore an attempt has been made to understand it within the framework of local density of states. The interdot tunneling is found to enhance the effect of the interdot Coulomb interaction in inducing the ZBM in all the three configurations. Calculations for the T-shape configuration reveal that non-zero value of the interdot tunneling is an essential condition for the appearance of the ZBM in the differential conductance.

  2. The Look that Binds: Partner-Directed Altruistic Motivation and Biased Perception in Married Couples

    PubMed Central

    Petrican, Raluca; Todorov, Alexander; Burris, Christopher T.; Rosenbaum, R. Shayna; Grady, Cheryl

    2016-01-01

    A trustworthy appearance is regarded as a marker of a globally positive personality and, thus, evokes a host of benevolent responses from perceivers. Nevertheless, it is yet to be determined whether the reverse is also true, that is, whether social targets who evoke unambiguously benign motivations in perceivers are regarded as possessing a more trustworthy appearance (cf. Oosterhof & Todorov, 2008). To this end, elderly long-term married couples completed measures of partner-directed altruistic motivation, accommodative behaviors, marital satisfaction, and trust in the partner. They also completed a face-processing task involving spousal and stranger faces one year later. Higher motivation to prioritize a spouse’s well-being (but none of the other relationship functioning variables assessed) predicted perceiving one’s spouse’s emotionally neutral face as being more trustworthy-looking. Results are discussed in the context of the reciprocal relationship between higher-order motivational processes and basic perceptual mechanisms in shaping relational climates. PMID:27330235

  3. Attribution and impacts of warm SST biases over the eastern coastal Pacific and Atlantic in the coupled model SINTEX-F

    NASA Astrophysics Data System (ADS)

    Doi, T.; Richter, I.; Sasaki, W.; Luo, J.; Behera, S. K.; Masumoto, Y.

    2012-12-01

    Using a fully coupled ocean-atmosphere model of SINTEX-F (a basis of our seasonal prediction system), attribution and impacts of warm SST biases over the eastern coastal Pacific and Atlantic has been investigated. SINTEX-F has warm biases for annual mean SST in the eastern tropical Pacific and Atlantic, which is ubiquitous in other climate models (e.g. IPCC-CMIP3 and CMIP5 models). The warm SST biases could be due to the weak bias of southerly winds along the eastern coastal regions associated with the excessive southward migration bias of the ITCZ. We have to improve these biases, because they could contaminate the seasonal prediction skill over not only local regions, but also global climate. For further understanding and improving the SST biases, we explored impacts of warm SST biases in the eastern coastal Pacific and Atlantic by conducting two sensitivity experiments with SINTEX-F model; "Rest_EP run" and "Rest_EA run". In Rest_EP run, the simulated SST in the eastern coastal Pacific (90-70W, 20S-5N) is strongly restored to the observational monthly climatology, while Rest_EA run is same as Rest_EP run, but for restoring to the eastern coastal Atlantic (0-15E, 20S-5N). By comparison Rest_EP run with Control run, we found that the improvement of warm SST bias in the eastern coastal Pacific can cool global tropical SST, and fix 30% of the warm SST bias in the eastern tropical Atlantic relative to the Control run. On the other hands, the improvement of warm SST bias in the eastern coastal Atlantic warms the northern tropical Atlantic and the eastern equatorial Pacific, and does not much influence on the warm SST bias in the eastern tropical Pacific..Those responses of the improvement of the warm SST biases in the two eastern tropical regions are closely coupled with the ITCZ meridional migration and the zonal Walker circulation, which have strong impacts on the Amazonian rainfall.

  4. Strong Exchange Coupling in a Trimetallic Radical-Bridged Cobalt(II)-Hexaazatrinaphthylene Complex.

    PubMed

    Moilanen, Jani O; Chilton, Nicholas F; Day, Benjamin M; Pugh, Thomas; Layfield, Richard A

    2016-04-25

    Reducing hexaazatrinaphthylene (HAN) with potassium in the presence of 18-c-6 produces [{K(18-c-6)}HAN], which contains the S=1/2 radical [HAN](.-) . The [HAN](.-) radical can be transferred to the cobalt(II) amide [Co{N(SiMe3 )2 }2 ], forming [K(18-c-6)][(HAN){Co(N'')2 }3 ]; magnetic measurements on this compound reveal an S=4 spin system with strong cobalt-ligand antiferromagnetic exchange and J≈-290 cm(-1) (-2 J formalism). In contrast, the Co(II) centres in the unreduced analogue [(HAN){Co(N'')2 }3 ] are weakly coupled (J≈-4.4 cm(-1) ). The finding that [HAN](.-) can be synthesized as a stable salt and transferred to cobalt introduces potential new routes to magnetic materials based on strongly coupled, triangular HAN building blocks. PMID:26997130

  5. Sexual Satisfaction in Spanish Heterosexual Couples: Testing the Interpersonal Exchange Model of Sexual Satisfaction.

    PubMed

    Sánchez-Fuentes, María Del Mar; Santos-Iglesias, Pablo

    2016-04-01

    The study of sexual satisfaction in Spain is scarce and has proceeded atheoretically. This study aimed at examining sexual satisfaction in 197 Spanish heterosexual couples based on the Interpersonal Exchange Model of Sexual Satisfaction. Men and women reported equal satisfaction. Men's sexual satisfaction was predicted by their own relationship satisfaction, balance of sexual rewards and costs, and comparison level of sexual rewards and costs. Women's sexual satisfaction was predicted by their own relationship satisfaction, balance of sexual rewards and costs, comparison level of sexual rewards and costs, equality of sexual costs, and their partner's balance of sexual rewards and costs. These results provide with a better understanding of the mechanisms that explain sexual satisfaction in Spanish couples. Implications for research and therapy are discussed. PMID:25629546

  6. 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.

  7. Thermally activated switching at long time scales in exchange-coupled magnetic grains

    NASA Astrophysics Data System (ADS)

    Almudallal, Ahmad M.; Mercer, J. I.; Whitehead, J. P.; Plumer, M. L.; van Ek, J.; Fal, T. J.

    2015-10-01

    Rate coefficients of the Arrhenius-Néel form are calculated for thermally activated magnetic moment reversal for dual layer exchange-coupled composite (ECC) media based on the Langer formalism and are applied to study the sweep rate dependence of M H hysteresis loops as a function of the exchange coupling I between the layers. The individual grains are modeled as two exchange-coupled Stoner-Wohlfarth particles from which the minimum energy paths connecting the minimum energy states are calculated using a variant of the string method and the energy barriers and attempt frequencies calculated as a function of the applied field. The resultant rate equations describing the evolution of an ensemble of noninteracting ECC grains are then integrated numerically in an applied field with constant sweep rate R =-d H /d t and the magnetization calculated as a function of the applied field H . M H hysteresis loops are presented for a range of values I for sweep rates 105Oe /s ≤R ≤1010Oe /s and a figure of merit that quantifies the advantages of ECC media is proposed. M H hysteresis loops are also calculated based on the stochastic Landau-Lifshitz-Gilbert equations for 108Oe /s ≤R ≤1010Oe /s and are shown to be in good agreement with those obtained from the direct integration of rate equations. The results are also used to examine the accuracy of certain approximate models that reduce the complexity associated with the Langer-based formalism and which provide some useful insight into the reversal process and its dependence on the coupling strength and sweep rate. Of particular interest is the clustering of minimum energy states that are separated by relatively low-energy barriers into "metastates." It is shown that while approximating the reversal process in terms of "metastates" results in little loss of accuracy, it can reduce the run time of a kinetic Monte Carlo (KMC) simulation of the magnetic decay of an ensemble of dual layer ECC media by 2 -3 orders of magnitude

  8. Effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media

    NASA Astrophysics Data System (ADS)

    Tham, Kim Kong; Saito, Shin; Hasegawa, Daiji; Itagaki, Norikazu; Hinata, Shintaro; Ishibashi, Shinichi; Takahashi, Migaku

    2012-11-01

    The effect of inhomogeneous microstructure of granular layer on inter granular/inter layer exchange coupling in stacked perpendicular recording media is studied by varying SiO2 content of CoCrPt-SiO2 granular layer. From cross-section and plane-view TEM observation, it can be concluded that each magnetic grain at cap layer (CL) grows on one magnetic grain of granular layer (GL), and inhomogeneous nucleation site at GL leads to inhomogeneous initial growth of continuous layer at CL. This phenomenon leads to the increase of inter granular coupling fluctuation in CL. Evaluation of inter granular coupling between magnetic grains at GL in stacked media with CL deposited directly on GL shows average and fluctuation of exchange coupling constant of around 2.9 erg/cm2 and 0.6 erg/cm2. In order to reduce the inter granular coupling, spacer layer (SL) with Pd material was inserted between GL and CL. As a result, average and fluctuation of exchange coupling constant decrease to 1.4 erg/cm2 and 0.3 erg/cm2 which suggests that by inserting a SL with small ferromagnetic exchange coupling between GL and CL will make it possible to control the inter granular coupling between magnetic grains at GL with CoCrPt-oxide material.

  9. From ferromagnetic{endash}ferromagnetic to ferromagnetic{endash}antiferromagnetic exchange coupling in NiFe/MnNi bilayers

    SciTech Connect

    Spenato, David; Youssef, Jamal Ben; Le Gall, Henri; Ostorero, Jean

    2001-06-01

    The effect of the growth conditions and the Mn concentration on the exchange coupling between a ferromagnetic (F) NiFe and an antiferromagnetic (AF) MnNi layers were studied. We found that an F/AF coupling appears in the bilayers when the Mn concentration is more than 45%. Beyond this critical concentration the exchange field shows a maximum then decreases. The correlation between the exchange field and the microstructure of the film is discussed. We show that: (1) the enhancement of the exchange field is associated with the enhancement of the antiferromagnetic grain size and (2) the existence of the exchange field is associated with a third x-ray peak which may be an FeMnNi ternary allow type. This result was associated with interfacial diffusion confirmed by magnetization variation measurements before and after annealing. {copyright} 2001 American Institute of Physics.

  10. The effect of SiO2 content on activation volumes in exchange coupled composite media

    NASA Astrophysics Data System (ADS)

    Chureemart, J.; Lari, L.; Nolan, T. P.; O'Grady, K.

    2013-08-01

    The activation volume, Vact, and the physical grain volume, VTEM, have been investigated on identical structures of exchange coupled composite media with three different contents of silicon dioxide (SiO2) utilised for intergranular exchange decoupling. Time dependence measurements known as the waiting time method have been used to determine Vact. Transmission Electron Microscopy analysis has been carried out to investigate the grain size distribution and the composition distribution at the grain boundaries using bright field high resolution-scanning transmission electron microscopy (BF HR-STEM) and high angle annular dark-field (HAADF) modes. We found that Vact and VTEM decrease as the oxide content is increased. The activation volume and the single grain volume are in excellent agreement for the samples with the highest oxide content indicating complete exchange decoupling. The BF HR-STEM and HAADF STEM images indicate excellent SiO2 segregation at the grain boundaries. This result implies that the activation volume in advanced recording media can be estimated via the correlation to the grain size.

  11. Coupling of phytoplankton uptake and air-water exchange of persistent organic pollutants

    SciTech Connect

    Dachs, J.; Eisenreich, S.J.; Baker, J.E.; Ko, F.C.; Jeremiason, J.D.

    1999-10-15

    A dynamic model that couples air-water exchange and phytoplankton uptake of persistent organic pollutants has been developed and then applied to PCB data from a small experimental lake. A sensitivity analysis of the model, taking into account the influence of physical environmental conditions such as temperature, wind speed, and mixing depth as well as plankton-related parameters such as biomass and growth rate was carried out for a number of PCBs with different physical-chemical properties. The results indicate that air-water exchange dynamics are influenced not only by physical parameters but also by phytoplankton biomass and growth rate. New phytoplankton production results in substantially longer times to reach equilibrium. Phytoplankton uptake-induced depletion of the dissolved phase concentration maintains air and water phases out of equilibrium. Furthermore, PCBs in phytoplankton also take longer times to reach equilibrium with the dissolved water phase when the latter is supported by diffusive air-water exchange. However, both model analysis and model application to the Experimental Lakes Area of northwestern Ontario (Canada) suggest that the gas phase supports the concentrations of persistent organic pollutants, such as PCBs, in atmospherically driven aquatic environments.

  12. 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.

  13. 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.

  14. Structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films

    NASA Astrophysics Data System (ADS)

    Chowdhury, P.; Krishnan, M.; Barshilia, Harish C.; Sridhara Rao, D. V.; Kumar, Deepak; Shivakumara, C.

    2013-09-01

    We investigated the structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitargets successively. The growth of the films was carried out at elevated substrate temperature followed by in situ annealing. On Si (100) substrate, X-ray diffraction confirms the formation of textured (110) SmCo5 hard phase, whereas on MgO(110) substrate, the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along [100] direction. Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature. Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co. Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, tSm=3.2 nm and cobalt layer thickness, tCo=11.4 nm, the values of (BH)max were obtained as 20.1 MGOe and 12.38 MGOe with Hc value ∼3.0 kOe grown on MgO and Si substrates, respectively. Formation of SmCo5/Co exchange spring nanocomposite films with successive deposition of Sm and Co layers at 450 °C. This technique gives the textured growth of the film on Si and epitaxial growth on crystalline MgO Substrate. High (BH)max on MgO substrate and large anisotropy.

  15. Interlayer exchange coupling in perpendicularly magnetized synthetic ferrimagnet structure using CoCrPt and CoFeB

    NASA Astrophysics Data System (ADS)

    Watanabe, D.; Mizukami, S.; Wu, F.; Oogane, M.; Naganuma, H.; Ando, Y.; Miyazaki, T.

    2010-01-01

    Interlayer exchange coupling in synthetic ferrimagnet structures consisting of perpendicularly magnetized CoCrPt and in-plane magnetized CoFeB layers, which are coupled by a Ru thin spacer, were investigated. The magnetization of the CoFeB layer turned perpendicular to the film plane after annealing at 300°C because of the appearance of interlayer coupling from the CoCrPt layer. The coupling varied between antiferromagnetic and ferromagnetic depending on the Ru spacer thickness. The sign and strength of the coupling were also observed through analyses of magnetization curves and ferromagnetic resonance spectra.

  16. 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.

  17. Simulation of land-atmosphere gaseous exchange using a coupled land surface-biogeochemical model

    NASA Astrophysics Data System (ADS)

    Gu, C.; Riley, W. J.; Perez, T. J.; Pan, L.

    2009-12-01

    It is important to develop and evaluate biogeochemical models that on the one hand represent vegetation and soil dynamics and on the other hand provide energy and water fluxes in a temporal resolution suitable for biogeochemical processes. In this study, we present a consistent coupling between a common land surface model (CLM3.0) and a recently developed biogeochemical model (TOUGHREACT-N). The model TOUGHREACT-N (TR-N) is one of the few process-based models that simulate green house gases fluxes by using an implicit scheme to solve the diffusion equations governing soil heat and water fluxes. By coupling with CLM3.0, we have significantly improved TR-N by including realistic representations of surface water, energy, and momentum exchanges, through the use of improved formulations for soil evaporation, plant transpiration, vegetation growth, and plant nitrogen uptake embedded in CLM3.0. The coupled CLMTR-N model is a first step for a full coupling of land surface and biogeochemical processes. The model is evaluated with measurements of soil temperature, soil water content, and N2O and N2 gaseous emission data from fallow, corn, and forest sites in Venezuela. The results demonstrate that the CLMTR-N model simulates realistic diurnal variation of soil temperature, soil water content, and N gaseous fluxes. For example, mean differences between predicted and observed midday near-surface soil water content were 8, 11, and 4 % in July, August, and September. The sensitivity of the biogeochemical processes and resulting N emissions to variation in environmental drivers is high, which indicates the need to calculate biogeochemical processes in, at least, two hourly time steps using dynamically updated (rather than daily averaged) soil environmental conditions. The development in CLMTR-N of such a complex representation of processes will allow us to characterize relevant processes and simplifications appropriate for regional to global-scale coupled biogeochemical and

  18. Exchange interaction and the tunneling induced transparency in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Borges, Halyne; Alcalde, Augusto; Ulloa, Sergio

    2014-03-01

    Stacked semiconductor quantum dots coupled by tunneling are unique ``quantum molecule'' where it is possible to create a multilevel structure of excitonic states. This structure allows the investigation of quantum interference processes and their control via electric external fields. In this work, we investigate the optical response of a quantum molecule coherently driven by a polarized laser, considering the splitting in excitonic levels caused by isotropic and anisotropic exchange interactions. In our model we consider interdot transitions mediated by the the hole tunneling between states with the same total spin and, between bright and dark exciton states. Using realistic experimental parameters, we demonstrate that the excitonic states coupled by tunneling exhibit an enriched and controllable optical response. Our results show that through the appropriate control of the external electric field and light polarization, the tunneling coupling establishes an efficient destructive quantum interference path that creates a transparency window in the absorption spectra, whenever states of appropriate symmetry are mixed by the hole tunneling. We explore the relevant parameters space that would allows with the experiments. CAPES, INCT-IQ and MWN/CIAM-NSF.

  19. Modeling coupled thermal-mechanical processes of frozen soil induced by borehole heat exchanger

    NASA Astrophysics Data System (ADS)

    Shao, H.

    2015-12-01

    To utilize the shallow geothermal energy, heat pumps are often coupled with Borehole Heat Exchangers (BHE) to provide heating and cooling for buildings. In cold regions, soil freezing around the BHE is a potential problem which will dramatically influence the underground soil temperature distribution, subsequently the inlet and outlet refrigerant temperature of the BHE, and finally the efficiency of the heat pump. In this study, a numerical model has been developed to simulate the coupled temperature evolution both inside the BHE, and the propagating freezing front in the surrounding soil. The coupled model was validated against analytical solutions and experimental data. The influence of the freezing process on the overall system performance is investigated by comparing one long BHE configuration without freezing and another short one with latent heat from the frozen groundwater. It is found that when freezing happens, the coefficient of performance (COP) of the heat pump will decrease by around 0.5, leading to more electricity consumption. Furthermore, analysis of the simulation result reveals that the exploitation of latent heat through groundwater freezing is only economically attractive if electricity price is low and interest rate high, and it is not the case is most European countries.

  20. 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.