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Sample records for mgo-based magnetic tunnel

  1. Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction.

    Science.gov (United States)

    Lee, Du-Yeong; Hong, Song-Hwa; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-08

    It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (~1.40 nm) was much shorter than that of Ta atoms (~2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered-cubic crystallinity.

  2. Evidence of a Symmetry-Dependent Metallic Barrier in Fully Epitaxial MgO Based Magnetic Tunnel Junctions

    Science.gov (United States)

    Greullet, F.; Tiusan, C.; Montaigne, F.; Hehn, M.; Halley, D.; Bengone, O.; Bowen, M.; Weber, W.

    2007-11-01

    We report on the experimental observation of tunneling across an ultrathin metallic Cr spacer layer that is inserted at the interface of a Fe/MgO/Fe(001) junction. We show how this remarkable behavior in a solid-state device reflects a quenching in the transmission of particular electronic states, as expected from the symmetry-filtering properties of the MgO barrier and the band structure of the bcc Cr(001) spacer in the epitaxial junction stack. This ultrathin Cr metallic barrier can promote quantum well states in an adjacent Fe layer.

  3. The study of origin of interfacial perpendicular magnetic anisotropy in ultra-thin CoFeB layer on the top of MgO based magnetic tunnel junction

    Science.gov (United States)

    Li, Zhi-Peng; Li, Shaoping; Zheng, Yuankai; Fang, Jason; Chen, Lifan; Hong, Liang; Wang, Haifeng

    2016-10-01

    A comprehensive microstructure study has been conducted experimentally for identifying the origin or mechanism of perpendicular magnetic anisotropy (PMA) in the ultra-thin (10 Å) CoFeB layer on the top of magnetic tunnel junction (MTJ). The high resolution transmission electron microscopy reveals that the feature of crystal structure in 10 Å-CoFeB layer is localized in nature at the CoFeB-MgO interface. On the other hand, the strain-relaxed crystalline structure is observed in the thick CoFeB (20 Å) layer at the CoFeB-MgO interface, associated with a series of dislocation formations. The electron energy loss spectroscopy further suggests that the local chemical stoichiometry of the ultra-thin 10 Å-CoFeB layer is notably changed at the CoFeB-MgO interface, compared with an atomic stoichiometry in a thick 20 Å-CoFeB layer. The origin of PMA mechanism is therefore identified experimentally as an interface effect, which can be attributed to a change of local atom bonding or lattice constant of the transition metal at the CoFeB-MgO based MTJ interface. Furthermore, such a local interfacial atom bonding change is seemly induced by the localized anisotropic strain and consistent with previous theoretical speculations and calculations. The observed experimental findings provide some perspective on microstructure and chemistry on PMA in ultra-thin CoFeB film at the MTJ interface, then deepening our understanding of the mechanism of PMA within MTJ stack and thus facilitating advancement for emerging spintronics technology.

  4. Tunneling magnetic force microscopy

    Science.gov (United States)

    Burke, Edward R.; Gomez, Romel D.; Adly, Amr A.; Mayergoyz, Isaak D.

    1993-01-01

    We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.

  5. X-ray absorption and magnetic circular dichroism studies of Co2FeAl in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Ebke, D.; Kugler, Z.; Thomas, P.; Schebaum, O.; Schafers, M.; Nissen, D.; Schmalhorst, J.; Hutten, A.; Arenholz, E.; Thomas, A.

    2010-01-11

    The bulk magnetic moment and the element specific magnetic moment of Co{sub 2}FeAl thin films were examined as a function of annealing temperature by alternating gradient magnetometer (AGM) and X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), respectively. A high magnetic moment can be achieved for all annealing temperatures and the predicted bulk and interface magnetic moment of about 5 {tilde A}{sub B} are reached via heating. We will also present tunnel magnetoresistance (TMR) values of up to 153% at room temperature and 260% at 13 K for MgO based magnetic tunnel junctions (MTJs) with Co{sub 2}FeAl and Co-Fe electrodes.

  6. Magnetic tunnel junctions (MTJs)

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    We review the giant tunnel magnetoresistance (TMR) in ferromagnetic-insulator-ferromagnetic junctions discovered in recent years, which is the magnetoresistance (MR) associated with the spin-dependent tunneling between two ferromagnetic metal films separated by an insulating thin tunnel barrier. The theoretical and experimental results including junction conductance, magnetoresistance and their temperature and bias dependences are described.

  7. Magnetic properties and high room temperature TMR ratios of Co{sub 2}FeAl in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Ebke, Daniel; Kugler, Zoe; Thomas, Patrick; Schebaum, Oliver; Schaefers, Markus; Nissen, Dennis; Schmalhorst, Jan; Huetten, Andreas; Thomas, Andy [Thin Films and Physics of Nanostructures, Physics Department, Bielefeld University (Germany)

    2010-07-01

    Spintronic devices have found a lot of attention in the recent years due to the possible new applications, e.g. a magnetic random access memory (MRAM). Therefore, materials with a high spin polarization such as half metallic Heusler compounds are eligible. In this work, we present low temperature tunnel magnetoresistance (TMR) values of up to 270% for MgO based magnetic tunnel junctions (MTJs) with Co{sub 2}FeAl and Co-Fe electrodes. A low temperature dependence leads to high room temperature TMR values of about 150%. The bulk magnetic moment and the element specific magnetic moment at the barrier interface were examined as a function of annealing temperature by alternating gradient magnetometer (AGM) and X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), respectively.

  8. Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi; Kato, Daisuke; Kuga, Kiyoshi; Kikuchi, Hiroshi; Shimidzu, Naoki [Science and Technology Research Laboratories, Japan Broadcasting Corporation (NHK), Kinuta, Setagaya, Tokyo 157-8510 (Japan); Matsui, Koichi [Department of Green and Sustainable Chemistry, Tokyo Denki University, Adachi, Tokyo 120-8551 (Japan)

    2014-05-28

    Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

  9. Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

    Energy Technology Data Exchange (ETDEWEB)

    Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P. [Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau 91767 (France); Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Xavier, S. [Thales Research and Technology, 1 avenue Augustin Fresnel, Palaiseau 91767 (France)

    2016-03-07

    We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

  10. Dynamical quenching of tunneling in molecular magnets

    Energy Technology Data Exchange (ETDEWEB)

    José Santander, María, E-mail: maria.jose.noemi@gmail.com [Recursos Educativos Quántica, Santiago (Chile); Departamento de Física, Universidad de Santiago de Chile and CEDENNA, Avda. Ecuador 3493, Santiago (Chile); Nunez, Alvaro S., E-mail: alnunez@dfi.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla 487-3, Santiago (Chile); Roldán-Molina, A. [Instituto de Física, Pontificia Universidad Católica de Valparaíso, Avenida Universidad 330, Curauma, Valparaíso (Chile); Troncoso, Roberto E., E-mail: r.troncoso.c@gmail.com [Centro para el Desarrollo de la Nanociencia y la Nanotecnología, CEDENNA, Avda. Ecuador 3493, Santiago 9170124 (Chile); Departamento de Física, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso (Chile)

    2015-12-15

    It is shown that a single molecular magnet placed in a rapidly oscillating magnetic field displays the phenomenon of quenching of tunneling processes. The results open a way to manipulate the quantum states of molecular magnets by means of radiation in the terahertz range. Our analysis separates the time evolution into slow and fast components thereby obtaining an effective theory for the slow dynamics. This effective theory presents quenching of the tunnel effect, in particular, stands out its difference with the so-called coherent destruction of tunneling. We support our prediction with numerical evidence based on an exact solution of Schrödinger's equation. - Highlights: • Single molecular magnets under rapidly oscillating magnetic fields is studied. • It is shown that this system displays the quenching of tunneling processes. • Our findings provide a control of quantum molecular magnets via terahertz radiation.

  11. Resonant tunnel magnetoresistance in a double magnetic tunnel junction

    KAUST Repository

    Useinov, Arthur

    2011-08-09

    We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FML/I/FMW/I/FMR, where the magnetization of the middle ferromagnetic metal layer FMW can be aligned parallel or antiparallel with respect to the fixed magnetizations of the left FML and right FMR ferromagnetic electrodes. The transmission coefficients for components of the spin-dependent current, and TMR are calculated as a function of the applied voltage. As a result, we found a high resonant TMR. Thus, DMTJ can serve as highly effective magnetic nanosensor for biological applications, or as magnetic memory cells by switching the magnetization of the inner ferromagnetic layer FMW.© Springer Science+Business Media, LLC 2011.

  12. Dependency of anti-ferro-magnetic coupling strength on Ru spacer thickness of [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer in perpendicular magnetic-tunnel-junctions fabricated on 12-inch TiN electrode wafer

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Kyo-Suk [MRAM Center, Department of Electronics, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701 (Korea, Republic of); Shim, Tae-Hun; Park, Jea-Gun, E-mail: parkjgL@hanyang.ac.kr [MRAM Center, Department of Electronics, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2014-07-21

    We investigated the Ru spacer-thickness effect on the anti-ferro-magnetic coupling strength (J{sub ex}) of a [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer fabricated with Co{sub 2}Fe{sub 6}B{sub 2}/MgO based perpendicular-magnetic-tunneling-junction spin-valves on 12-in. TiN electrode wafers. J{sub ex} peaked at a certain Ru spacer-thickness: specifically, a J{sub ex} of 0.78 erg/cm{sup 2} at 0.6 nm, satisfying the J{sub ex} criteria for realizing the mass production of terra-bit-level perpendicular-spin-transfer-torque magnetic-random-access-memory. Otherwise, J{sub ex} rapidly degraded when the Ru spacer-thickness was less than or higher than 0.6 nm. As a result, the allowable Ru thickness variation should be controlled less than 0.12 nm to satisfy the J{sub ex} criteria. However, the Ru spacer-thickness did not influence the tunneling-magneto-resistance (TMR) and resistance-area (RA) of the perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valves since the Ru spacer in the synthetic-anti-ferro-magnetic layer mainly affects the anti-ferro-magnetic coupling efficiency rather than the crystalline linearity of the Co{sub 2}Fe{sub 6}B{sub 2} free layer/MgO tunneling barrier/Co{sub 2}Fe{sub 6}B{sub 2} pinned layer, although Co{sub 2}Fe{sub 6}B{sub 2}/MgO based p-MTJ spin-valves ex-situ annealed at 275 °C achieved a TMR of ∼70% at a RA of ∼20 Ω μm{sup 2}.

  13. Perpendicular magnetic anisotropy in CoXPd100-X alloys for magnetic tunnel junctions

    Science.gov (United States)

    Clark, B. D.; Natarajarathinam, A.; Tadisina, Z. R.; Chen, P. J.; Shull, R. D.; Gupta, S.

    2017-08-01

    CoFeB/MgO-based perpendicular magnetic tunnel junctions (p-MTJ's) with high anisotropy and low damping are critical for spin-torque transfer random access memory (STT-RAM). Most schemes of making the pinned CoFeB fully perpendicular require ferrimagnets with high damping constants, a high temperature-grown L10 alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular CoxPd alloy-pinned Co20Fe60B20/MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the CoxPd alloy films can be tuned based on the layer thickness and composition. The films were characterized by alternating gradient magnetometry (AGM), energy-dispersive X-rays (EDX), and X-ray diffraction (XRD). Current-in-plane tunneling (CIPT) measurements have also been performed on the compositionally varied CoxPd MTJ stacks. The CoxPd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si/SiO2/MgO (13)/CoXPd100-x (50)/Ta (0.3)/CoFeB (1)/MgO (1.6)/CoFeB (1)/Ta (5)/Ru (10), with the numbers enclosed in parentheses being the layer thicknesses in nm, were sputtered onto thermally oxidized silicon substrates and in-situ lamp annealed at 400 °C for 5 min. CIPT measurements indicate that the highest TMR is observed for the CoPd composition with the highest perpendicular magnetic anisotropy.

  14. Characterization of magnetic tunnel junction test pads

    DEFF Research Database (Denmark)

    Østerberg, Frederik Westergaard; Kjær, Daniel; Nielsen, Peter Folmer

    2015-01-01

    We show experimentally as well as theoretically that patterned magnetic tunnel junctions can be characterized using the current-in-plane tunneling (CIPT) method, and the key parameters, the resistance-area product (RA) and the tunnel magnetoresistance (TMR), can be determined. The CIPT method...... on square tunnel junction pads with varying sizes and analyze the measured data using both the original and the modified CIPT model. Thus, we determine in which sample size range the modified CIPT model is needed to ensure validity of the extracted sample parameters, RA and TMR. In addition, measurements...... as a function of position on a square tunnel junction pad are used to investigate the sensitivity of the measurement results to probe misalignment....

  15. Seebeck Effect in Magnetic Tunnel Junctions

    OpenAIRE

    Walter, Marvin; Walowski, Jakob; Zbarsky, Vladyslav; Münzenberg, Markus; Schäfers, Markus; Ebke, Daniel; Reiss, Günter; Thomas, Andy; Peretzki, Patrick; Seibt, Michael; Moodera, Jagadeesh S.; Czerner, Michael; Bachmann, Michael; Heiliger, Christian

    2011-01-01

    Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, i.e., the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel j...

  16. Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

    Science.gov (United States)

    Parui, Subir; Ribeiro, Mário; Atxabal, Ainhoa; Bedoya-Pinto, Amilcar; Sun, Xiangnan; Llopis, Roger; Casanova, Fèlix; Hueso, Luis E.

    2016-08-01

    The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al2O3/NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

  17. Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Parui, Subir, E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Bedoya-Pinto, Amilcar [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Max Planck Institute of Microstructure Physics, D-06120 Halle (Germany); Sun, Xiangnan [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); National Center for Nanoscience and Technology, 100190 Beijing (China); Casanova, Fèlix; Hueso, Luis E., E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

    2016-08-01

    The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al{sub 2}O{sub 3}/NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

  18. Fabrication of magnetic tunnel junctions with epitaxial and textured ferromagnetic layers

    Science.gov (United States)

    Chang, Y. Austin; Yang, Jianhua Joshua

    2008-11-11

    This invention relates to magnetic tunnel junctions and methods for making the magnetic tunnel junctions. The magnetic tunnel junctions include a tunnel barrier oxide layer sandwiched between two ferromagnetic layers both of which are epitaxial or textured with respect to the underlying substrate upon which the magnetic tunnel junctions are grown. The magnetic tunnel junctions provide improved magnetic properties, sharper interfaces and few defects.

  19. Room Temperature Magnetic Barrier Layers in Magnetic Tunnel Junctions

    Energy Technology Data Exchange (ETDEWEB)

    Nelson-Cheeseman, B. B.; Wong, F. J.; Chopdekar, R. V.; Arenholz, E.; Suzuki, Y.

    2010-03-09

    We investigate the spin transport and interfacial magnetism of magnetic tunnel junctions with highly spin polarized LSMO and Fe3O4 electrodes and a ferrimagnetic NiFe2O4 (NFO) barrier layer. The spin dependent transport can be understood in terms of magnon-assisted spin dependent tunneling where the magnons are excited in the barrier layer itself. The NFO/Fe3O4 interface displays strong magnetic coupling, while the LSMO/NFO interface exhibits clear decoupling as determined by a combination of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. This decoupling allows for distinct parallel and antiparallel electrode states in this all-magnetic trilayer. The spin transport of these devices, dominated by the NFO barrier layer magnetism, leads to a symmetric bias dependence of the junction magnetoresistance at all temperatures.

  20. Fully magnetic manganite spin filter tunnel junctions

    Science.gov (United States)

    Prasad, Bhagwati; Blamire, Mark G.

    2016-09-01

    In this paper we demonstrate spintronic devices which combine magnetic tunnel junctions with a spin-filtering tunnel barrier. These consist of an ultrathin ferromagnetic insulating barrier, Sm0.75Sr0.25MnO3, sandwiched between two ferromagnetic half-metallic manganite electrodes, La0.7Sr0.3MnO3 and La0.7Ca0.3MnO3, in a nanopillar structure. Depending on the relative magnetic configurations of barrier and electrode layers, three resistance states are well defined, which therefore represent a potential three-state memory concept. These results open the way for the development of spintronic devices by exploiting the many degrees of freedom of perovskite manganite heterostructure systems.

  1. Interfacial capacitance effects in magnetic tunneling junctions

    CERN Document Server

    Landry, G; Du, J; Xiao, J Q

    2001-01-01

    We have investigated the AC transport properties of magnetic tunnel junctions (MTJ) in order to characterize interfacial properties. One such property is interfacial charge accumulation, which leads to a voltage drop in the electrodes of the MTJ and the measured capacitance differing from the geometrical capacitance. Through measurement of capacitance spectra, we have extracted an interfacial capacitance of 16 mu F/cm sup 2 per interface and a screening length of 0.55 A for FeNi electrodes.

  2. Gamma Radiation Tolerance of Magnetic Tunnel Junctions

    Science.gov (United States)

    Ren, Fanghui; Jander, Albrecht; Dhagat, Pallavi; Nordman, Cathy

    2011-10-01

    Determining the radiation tolerance of magnetic tunnel junctions (MTJ), which are the storage elements of non-volatile magnetoresistive random access memories (MRAM), is important for investigating their potential application in space. In this effort, the effect of gamma radiation on MTJs with MgO tunnel barriers was studied. Experimental and control groups of samples were characterized by ex situ measurements of the magnetoresistive hysteresis loops and I-V curves. The experimental group was exposed to gamma rays from a ^60Co source. The samples initially received a dose of 5.9 Mrad (Si) after which they were again characterized electrically and magnetically. Irradiation was then continued for a cumulative dose of 10 Mrad and the devices re-measured. The result shows no change in magnetic properties such as coercivity or exchange coupling due to irradiation. After correcting for differences in temperature at the time of testing, the tunneling magnetoresistance was also found to be unchanged. Thus, it has been determined that MgO-based MTJs are highly tolerant of gamma radiation, particularly in comparison to silicon field-effect transistors which have been shown to degrade with gamma ray exposure even as low as 100 Krad [Zhiyuan Hu. et al., IEEE trans. on Nucl. Sci., vol. 58, 2011].

  3. Magnetic instability induced by tunnel current in single Co nanoparticles

    OpenAIRE

    Birk, F. Tijiwa; Jiang, W.; Davidović, D.

    2011-01-01

    Measurements of magnetic hysteresis loops in single Co nanoparticles at dilution refrigerator temperatures are presented. The nanoparticles are in electric contact with bulk Al leads via tunnel junctions. The tunnel current versus magnetic field displays a magnetic hysteresis loop. The magnetic switching field is reduced by current, and the magnetization of the nanoparticle can be switched by applying a voltage pulse, demonstrating that the magnetic stability of the nanoparticle is diminished...

  4. Dependency of tunneling magnetoresistance ratio on Pt seed-layer thickness for double MgO perpendicular magnetic tunneling junction spin-valves with a top Co2Fe6B2 free layer ex-situ annealed at 400 °C

    Science.gov (United States)

    Takemura, Yasutaka; Lee, Du-Yeong; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-01

    For the double MgO based perpendicular magnetic tunneling junction (p-MTJ) spin-valves with a top Co2Fe6B2 free layer ex situ annealed at 400 °C, the tunneling-magnetoresistance ratio (TMR) strongly depended on the platinum (Pt) seed layer thickness (t Pt): it peaked (˜134%) at a specific t Pt (3.3 nm). The TMR ratio was initially and slightly increased from 113%-134% by the enhancement of the magnetic moment of the Co2Fe6B2 pinned layer when t Pt increased from 2.0-3.3 nm, and then rapidly decreased from 134%-38.6% by the degrading face-centered-cubic crystallinity of the MgO tunneling barrier when t Pt increased from 3.3-14.3 nm.

  5. Spin-valley filter and tunnel magnetoresistance in asymmetrical silicene magnetic tunnel junctions

    Science.gov (United States)

    Wang, Dali; Huang, Zeyuan; Zhang, Yongyou; Jin, Guojun

    2016-05-01

    The spin and valley transports and tunnel magnetoresistance are studied in a silicene-based asymmetrical magnetic tunnel junction consisting of a ferromagnetic tunnel barrier, sandwiched between a ferromagnetic electrode and a normal electrode. For such an asymmetrical silicene junction, a general formulism is established. The numerical results show that the spin-valley resolved conductances strongly depend on the magnetization orientation of the ferromagnetic tunnel barrier, and the fully spin-valley polarized current can be realized by tuning a perpendicularly applied electric field. We also find that the tunnel magnetoresistance in this case can be effectively modified by the external electric field when the conductance is fully spin-valley polarized. In particular, the exchange field in the ferromagnetic electrode can further substantially enhance the tunnel magnetoresistance of the system. Our work provides a practical method for electric and magnetic manipulation of valley/spin polarization and tunnel magnetoresistance.

  6. Seebeck effect in magnetic tunnel junctions.

    Science.gov (United States)

    Walter, Marvin; Walowski, Jakob; Zbarsky, Vladyslav; Münzenberg, Markus; Schäfers, Markus; Ebke, Daniel; Reiss, Günter; Thomas, Andy; Peretzki, Patrick; Seibt, Michael; Moodera, Jagadeesh S; Czerner, Michael; Bachmann, Michael; Heiliger, Christian

    2011-10-01

    Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, that is, the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge-based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In this respect, it is the analogue to the tunnelling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configurations are of the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. The geometric centre of the electronic density of states relative to the Fermi level determines the size of the Seebeck effect. Experimentally, we realized 8.8% magneto-Seebeck effect, which results from a voltage change of about -8.7 μV K⁻¹ from the antiparallel to the parallel direction close to the predicted value of -12.1 μV K⁻¹. In contrast to the spin-Seebeck effect, it can be measured as a voltage change directly without conversion of a spin current.

  7. Tantalum oxide barrier in magnetic tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Guanghua Yu; Tingting Ren; Wei Ji; Jiao Teng; Fengwu Zhu

    2004-01-01

    Tantalum as an insulating barrier can take the place of Al in magnetic tunnel junctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectron spectroscopy (XPS) was used to characterize the oxidation states of Ta barrier.The experimental results show that the chemical state of tantalum is pure Ta5+ and the thickness of the oxide is 1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usually used in MTJs to form an intermetallic compound,NiTa2. A magnetic "dead layer" could be produced in the NiFe/Ta interface. The "dead layer" is likely to influence the spinning electron transport and the magnetoresistance effect.

  8. Superpoissonian shot noise in organic magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Cascales, Juan Pedro; Martinez, Isidoro; Aliev, Farkhad G., E-mail: farkhad.aliev@uam.es [Dpto. Fisica Materia Condensada C3, Instituto Nicolas Cabrera (INC), Condensed Matter Physics Institute (IFIMAC), Universidad Autonoma de Madrid, Madrid 28049 (Spain); Hong, Jhen-Yong; Lin, Minn-Tsong, E-mail: mtlin@phys.ntu.edu.tw [Department of Physics, National Taiwan University, Taipei 10617, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Szczepański, Tomasz; Dugaev, Vitalii K. [Department of Physics, Rzeszów University of Technology, al. Powstańców Warszawy 6, 35-959 Rzeszów (Poland); Barnaś, Józef [Faculty of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland and Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179 Poznań (Poland)

    2014-12-08

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here, we investigate conductance and shot noise in magnetic tunnel junctions with 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10% and 40%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5–2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers.

  9. Annealing free magnetic tunnel junction sensors

    Science.gov (United States)

    Knudde, S.; Leitao, D. C.; Cardoso, S.; Freitas, P. P.

    2017-04-01

    Annealing is a major step in the fabrication of magnetic tunnel junctions (MTJs). It sets the exchange bias between the pinned and antiferromagnetic layers, and helps to increase the tunnel magnetoresistance (TMR) in both amorphous and crystalline junctions. Recent research on MTJs has focused on MgO-based structures due to their high TMR. However, the strict process control and mandatory annealing step can limit the scope of the application of these structures as sensors. In this paper, we present AlOx-based MTJs that are produced by ion beam sputtering and remote plasma oxidation and show optimum transport properties with no annealing. The microfabricated devices show TMR values of up to 35% and using NiFe/CoFeB free layers provides tunable linear ranges, leading to coercivity-free linear responses with sensitivities of up to 5.5%/mT. The top-pinned synthetic antiferromagnetic reference shows a stability of about 30 mT in the microfabricated devices. Sensors with linear ranges of up to 60 mT are demonstrated. This paves the way for the integration of MTJ sensors in heat-sensitive applications such as flexible substrates, or for the design of low-footprint on-chip multiaxial sensing devices.

  10. Tunneling magnetoresistance phenomenon utilizing graphene magnet electrode

    Energy Technology Data Exchange (ETDEWEB)

    Hashimoto, T.; Kamikawa, S.; Haruyama, J., E-mail: J-haru@ee.aoyama.ac.jp [Faculty of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara, Kanagawa 252-5258 (Japan); Soriano, D. [Institut Català de Nanociència i Nanotecnologia (ICN2), Campus de la UAB, Edifici ICN2, 08193 Bellaterra, Barcelona (Spain); Pedersen, J. G. [Institut Català de Nanociència i Nanotecnologia (ICN2), Campus de la UAB, Edifici ICN2, 08193 Bellaterra, Barcelona (Spain); Department of Micro-and Nanotechnology, DTU Nanotech, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Roche, S. [Institut Català de Nanociència i Nanotecnologia (ICN2), Campus de la UAB, Edifici ICN2, 08193 Bellaterra, Barcelona (Spain); ICREA - Institucio Catalana de Recerca i Estudis Avancats, 08010 Barcelona (Spain)

    2014-11-03

    Using magnetic rare-metals for spintronic devices is facing serious problems for the environmental contamination and the limited material-resource. In contrast, by fabricating ferromagnetic graphene nanopore arrays (FGNPAs) consisting of honeycomb-like array of hexagonal nanopores with hydrogen-terminated zigzag-type atomic structure edges, we reported observation of polarized electron spins spontaneously driven from the pore edge states, resulting in rare-metal-free flat-energy-band ferromagnetism. Here, we demonstrate observation of tunneling magnetoresistance (TMR) behaviors on the junction of cobalt/SiO{sub 2}/FGNPA electrode, serving as a prototype structure for future rare-metal free TMR devices using magnetic graphene electrodes. Gradual change in TMR ratios is observed across zero-magnetic field, arising from specified alignment between pore-edge- and cobalt-spins. The TMR ratios can be controlled by applying back-gate voltage and by modulating interpore distance. Annealing the SiO{sub 2}/FGNPA junction also drastically enhances TMR ratios up to ∼100%.

  11. Anomalous Tunnel Magnetoresistance and Spin Transfer Torque in Magnetic Tunnel Junctions with Embedded Nanoparticles

    Science.gov (United States)

    Useinov, Arthur; Ye, Lin-Xiu; Useinov, Niazbeck; Wu, Te-Ho; Lai, Chih-Huang

    2015-12-01

    The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature.

  12. Quantum tunneling of the magnetic moment in a free nanoparticle

    Energy Technology Data Exchange (ETDEWEB)

    O' Keeffe, M.F. [Physics Department, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, 10468-1589 (United States); Chudnovsky, E.M., E-mail: eugene.chudnovsky@lehman.cuny.edu [Physics Department, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, 10468-1589 (United States); Garanin, D.A. [Physics Department, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, New York, 10468-1589 (United States)

    2012-09-15

    We study tunneling of the magnetic moment in a particle that has full rotational freedom. Exact energy levels are obtained and the ground-state magnetic moment is computed for a symmetric rotor. The effect of mechanical freedom on spin tunneling manifests itself in a strong dependence of the magnetic moment on the moments of inertia of the rotor. The energy of the particle exhibits quantum phase transitions between states with different values of the magnetic moment. Particles of various shapes are investigated and the quantum phase diagram is obtained. - Highlights: Black-Right-Pointing-Pointer We obtain an exact analytical solution of a tunneling spin in a mechanical rotator. Black-Right-Pointing-Pointer The quantum phase diagram shows magnetic moment dependence on rotator shape and size. Black-Right-Pointing-Pointer Our work explains magnetic properties of free atomic clusters and magnetic molecules.

  13. Josephson tunnel junctions in a magnetic field gradient

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Koshelets, V.P.

    2011-01-01

    We measured the magnetic field dependence of the critical current of high-quality Nb-based planar Josephson tunnel junctions in the presence of a controllable nonuniform field distribution. We found skewed and slowly changing magnetic diffraction patterns quite dissimilar from the Fraunhofer-like...... be suppressed by an asymmetric magnetic field profile. © 2011 American Institute of Physics....

  14. Magnetic interaction between spatially extended superconducting tunnel junctions

    DEFF Research Database (Denmark)

    Grønbech-Jensen, Niels; Samuelsen, Mogens Rugholm

    2002-01-01

    A general description of magnetic interactions between superconducting tunnel junctions is given. The description covers a wide range of possible experimental systems, and we explicitly explore two experimentally relevant limits of coupled junctions. One is the limit of junctions with tunneling...... been considered through arrays of superconducting weak links based on semiconductor quantum wells with superconducting electrodes. We use the model to make direct interpretations of the published experiments and thereby propose that long-range magnetic interactions are responsible for the reported...

  15. Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

    KAUST Repository

    Useinov, A. N.

    2011-08-24

    We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.

  16. Magnetic tunnel junction based spintronic logic devices

    Science.gov (United States)

    Lyle, Andrew Paul

    The International Technology Roadmap for Semiconductors (ITRS) predicts that complimentary metal oxide semiconductor (CMOS) based technologies will hit their last generation on or near the 16 nm node, which we expect to reach by the year 2025. Thus future advances in computational power will not be realized from ever-shrinking device sizes, but rather by 'outside the box' designs and new physics, including molecular or DNA based computation, organics, magnonics, or spintronic. This dissertation investigates magnetic logic devices for post-CMOS computation. Three different architectures were studied, each relying on a different magnetic mechanism to compute logic functions. Each design has it benefits and challenges that must be overcome. This dissertation focuses on pushing each design from the drawing board to a realistic logic technology. The first logic architecture is based on electrically connected magnetic tunnel junctions (MTJs) that allow direct communication between elements without intermediate sensing amplifiers. Two and three input logic gates, which consist of two and three MTJs connected in parallel, respectively were fabricated and are compared. The direct communication is realized by electrically connecting the output in series with the input and applying voltage across the series connections. The logic gates rely on the fact that a change in resistance at the input modulates the voltage that is needed to supply the critical current for spin transfer torque switching the output. The change in resistance at the input resulted in a voltage margin of 50--200 mV and 250--300 mV for the closest input states for the three and two input designs, respectively. The two input logic gate realizes the AND, NAND, NOR, and OR logic functions. The three input logic function realizes the Majority, AND, NAND, NOR, and OR logic operations. The second logic architecture utilizes magnetostatically coupled nanomagnets to compute logic functions, which is the basis of

  17. Magnetostatic effects on switching in small magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Bapna, Mukund; Piotrowski, Stephan K.; Oberdick, Samuel D.; Majetich, Sara A., E-mail: sara@cmu.edu [Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Li, Mingen; Chien, C.-L. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218 (United States)

    2016-01-11

    Perpendicular CoFeB/MgO/CoFeB magnetic tunnel junctions with diameters under 100 nm are investigated by conductive atomic force microscopy. Minor loops of the tunnel magnetoresistance as a function of applied magnetic field reveal the hysteresis of the soft layer and an offset due to the magnetostatic field of the hard layer. Within the hysteretic region, telegraph noise is observed in the tunnel current. Simulations show that in this range, the net magnetic field in the soft layer is spatially inhomogeneous, and that antiparallel to parallel switching tends to start near the edge, while parallel to antiparallel reversal favors nucleation in the interior of the soft layer. As the diameter of the tunnel junction is decreased, the average magnitude of the magnetostatic field increases, but the spatial inhomogeneity across the soft layer is reduced.

  18. Magnetic quantum tunneling: insights from simple molecule-based magnets.

    Science.gov (United States)

    Hill, Stephen; Datta, Saiti; Liu, Junjie; Inglis, Ross; Milios, Constantinos J; Feng, Patrick L; Henderson, John J; del Barco, Enrique; Brechin, Euan K; Hendrickson, David N

    2010-05-28

    This perspectives article takes a broad view of the current understanding of magnetic bistability and magnetic quantum tunneling in single-molecule magnets (SMMs), focusing on three families of relatively simple, low-nuclearity transition metal clusters: spin S = 4 Ni(II)(4), Mn(III)(3) (S = 2 and 6) and Mn(III)(6) (S = 4 and 12). The Mn(III) complexes are related by the fact that they contain triangular Mn(III)(3) units in which the exchange may be switched from antiferromagnetic to ferromagnetic without significantly altering the coordination around the Mn(III) centers, thereby leaving the single-ion physics more-or-less unaltered. This allows for a detailed and systematic study of the way in which the individual-ion anisotropies project onto the molecular spin ground state in otherwise identical low- and high-spin molecules, thus providing unique insights into the key factors that control the quantum dynamics of SMMs, namely: (i) the height of the kinetic barrier to magnetization relaxation; and (ii) the transverse interactions that cause tunneling through this barrier. Numerical calculations are supported by an unprecedented experimental data set (17 different compounds), including very detailed spectroscopic information obtained from high-frequency electron paramagnetic resonance and low-temperature hysteresis measurements. Comparisons are made between the giant spin and multi-spin phenomenologies. The giant spin approach assumes the ground state spin, S, to be exact, enabling implementation of simple anisotropy projection techniques. This methodology provides a basic understanding of the concept of anisotropy dilution whereby the cluster anisotropy decreases as the total spin increases, resulting in a barrier that depends weakly on S. This partly explains why the record barrier for a SMM (86 K for Mn(6)) has barely increased in the 15 years since the first studies of Mn(12)-acetate, and why the tiny Mn(3) molecule can have a barrier approaching 60% of this

  19. Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2012-06-01

    In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.

  20. Planar Josephson tunnel junctions in a transverse magnetic field

    DEFF Research Database (Denmark)

    Monacoa, R.; Aarøe, Morten; Mygind, Jesper

    2007-01-01

    Traditionally, since the discovery of the Josephson effect in 1962, the magnetic diffraction pattern of planar Josephson tunnel junctions has been recorded with the field applied in the plane of the junction. Here we discuss the static junction properties in a transverse magnetic field where...... demagnetization effects imposed by the tunnel barrier and electrodes geometry are important. Measurements of the junction critical current versus magnetic field in planar Nb-based high-quality junctions with different geometry, size, and critical current density show that it is advantageous to use a transverse...

  1. Thermally induced dynamics in ultrathin magnetic tunnel junctions

    NARCIS (Netherlands)

    Ogrodnik, P.; Bauer, G.E.W.; Xia, K.

    2013-01-01

    We consider the magnetization dynamics induced by thermally induced spin transfer torques in thin Fe|MgO|Fe tunnel junctions. The magnetization dynamics is described by the Landau-Lifshitz-Gilbert equation, including the thermal torques as computed from first principles. We show that the angular ske

  2. Magnetic tunnel junctions with Co:TiO2 magnetic semiconductor electrodes

    NARCIS (Netherlands)

    Lee, Y.J.; Abhishek Kumar, A.K.; Kumar, A.; Vera Marun, I.J.; de Jong, Machiel Pieter; Jansen, R.

    2010-01-01

    Spin-polarized tunneling is investigated in magnetic tunnel junctions containing an ultrathin interfacial layer of Co:TiO2 magnetic semiconductor. The Co:TiO2 layers (0 to 1 nm thick) are inserted at the SrTiO3/Co interface in La0.67Sr0.33MnO3/SrTiO3/Co tunnel junctions. For all junctions we find a

  3. Flexible MgO Barrier Magnetic Tunnel Junctions.

    Science.gov (United States)

    Loong, Li Ming; Lee, Wonho; Qiu, Xuepeng; Yang, Ping; Kawai, Hiroyo; Saeys, Mark; Ahn, Jong-Hyun; Yang, Hyunsoo

    2016-07-01

    Flexible MgO barrier magnetic tunnel junction (MTJ) devices are fabricated using a transfer printing process. The flexible MTJ devices yield significantly enhanced tunneling magnetoresistance of ≈300% and improved abruptness of switching, as residual strain in the MTJ structure is released during the transfer process. This approach could be useful for flexible electronic systems that require high-performance memory components. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Characterization of Magnetic Tunnel Junctions For Spin Transfer Torque Magnetic Random Access Memory

    Science.gov (United States)

    Dill, Joshua Luchay

    This thesis details two experimental methods for quantifying magnetic tunnel junction behavior, namely write error rates and field modulated spin-torque ferromagnetic resonance. The former examines how reliably an applied spin-transfer torque can excite magnetization dynamics that lead to a reversal of magnetization direction while the latter studies steady state dynamics provided by an oscillating spin-transfer torque. These characterization techniques reveal write error rate behavior for a particular composition magnetic tunnel junction that qualitatively deviates from theoretical predictions. Possible origins of this phenomenon are also investigated with the field modulated spin-torque ferromagnetic resonance technique. By understanding the dynamics of magnetic moments predicted by theory, one can experimentally confirm or disprove these theories in order to accurately model and predict tunnel junction behavior. By having a better model for what factors are important in magnetization dynamics, one can optimize these factors in terms of improving magnetic tunnel junctions for their use as computer memory.

  5. Tunnel magnetoresistance in magnetic tunnel junctions with ZnS barrier

    Energy Technology Data Exchange (ETDEWEB)

    Guth, M.; Da Costa, V.; Schmerber, G.; Dinia, A.; van den Berg, H. A. M.

    2001-06-01

    A first experimental evidence of a significant tunneling magnetoresistance signal of about 5% at 300 K for a magnetic tunnel junction consisting of hard and soft magnetic layers separated by a 2 nm ZnS semiconducting barrier is reported. The samples have been grown by sputtering on Si(111) substrate at room temperature and have the following structure: Fe{sub 6nm}Cu{sub 30nm}CoFe{sub 1.8nm}Ru{sub 0.8nm}CoFe{sub 3nm}ZnS{sub x}CoFe{sub 1nm}Fe{sub 4nm}Cu{sub 10nm}Ru{sub 3nm}. The hard magnetic bottom electrode consists of the artificial antiferromagnetic structure in which the rigidity is ensured by the antiferromagnetic exchange coupling between two FeCo layers through a Ru spacer layer. Barrier impedance scanning microscope (BISM) measurements reveal a good homogeneity of the barrier thickness. Electric transport measurements over square tunnel elements with lateral sizes between 3 and 100 {mu}m, exhibit a typical tunnel current{endash}voltage variations and tunnel resistance of 2{endash}3 k{Omega}{mu}m2 with small variations which never exceed a factor of 2, which is in good agreement with the BISM results. This good reproducibility of the junctions is very promising for MRAMs and transistors applications. {copyright} 2001 American Institute of Physics.

  6. L10-MnGa based magnetic tunnel junction for high magnetic field sensor

    Science.gov (United States)

    Zhao, X. P.; Lu, J.; Mao, S. W.; Yu, Z. F.; Wang, H. L.; Wang, X. L.; Wei, D. H.; Zhao, J. H.

    2017-07-01

    We report on the investigation of the magnetic tunnel junction structure designed for high magnetic field sensors with a perpendicularly magnetized L10-MnGa reference layer and an in-plane magnetized Fe sensing layer. A large linear tunneling magnetoresistance ratio up to 27.4% and huge dynamic range up to 5600 Oe have been observed at 300 K, with a low nonlinearity of 0.23% in the optimized magnetic tunnel junction (MTJ). The field response of tunneling magnetoresistance is discussed to explain the field sensing properties in the dynamic range. These results indicate that L10-MnGa based orthogonal MTJ is a promising candidate for a high performance magnetic field sensor with a large dynamic range, high endurance and low power consumption.

  7. Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    You, Chun-Yeol [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of)

    2014-01-28

    We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.

  8. Giant thermal spin-torque-assisted magnetic tunnel junction switching.

    Science.gov (United States)

    Pushp, Aakash; Phung, Timothy; Rettner, Charles; Hughes, Brian P; Yang, See-Hun; Parkin, Stuart S P

    2015-05-26

    Spin-polarized charge currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin currents from temperature gradients, and their associated thermal-spin torques (TSTs), have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe.

  9. Enhanced voltage-controlled magnetic anisotropy in magnetic tunnel junctions with an MgO/PZT/MgO tunnel barrier

    Science.gov (United States)

    Chien, Diana; Li, Xiang; Wong, Kin; Zurbuchen, Mark A.; Robbennolt, Shauna; Yu, Guoqiang; Tolbert, Sarah; Kioussis, Nicholas; Khalili Amiri, Pedram; Wang, Kang L.; Chang, Jane P.

    2016-03-01

    Compared with current-controlled magnetization switching in a perpendicular magnetic tunnel junction (MTJ), electric field- or voltage-induced magnetization switching reduces the writing energy of the memory cell, which also results in increased memory density. In this work, an ultra-thin PZT film with high dielectric constant was integrated into the tunneling oxide layer to enhance the voltage-controlled magnetic anisotropy (VCMA) effect. The growth of MTJ stacks with an MgO/PZT/MgO tunnel barrier was performed using a combination of sputtering and atomic layer deposition techniques. The fabricated MTJs with the MgO/PZT/MgO barrier demonstrate a VCMA coefficient, which is ˜40% higher (19.8 ± 1.3 fJ/V m) than the control sample MTJs with an MgO barrier (14.3 ± 2.7 fJ/V m). The MTJs with the MgO/PZT/MgO barrier also possess a sizeable tunneling magnetoresistance (TMR) of more than 50% at room temperature, comparable to the control MTJs with an MgO barrier. The TMR and enhanced VCMA effect demonstrated simultaneously in this work make the MgO/PZT/MgO barrier-based MTJs potential candidates for future voltage-controlled, ultralow-power, and high-density magnetic random access memory devices.

  10. Tunneling spectroscopy of a magnetic adatoms on topological insulator surfaces

    Science.gov (United States)

    Misiorny, M.; Bjerngaard, M.; Paaske, J.

    In this communication, we address the question of how the presence of a magnetic impurity on a topological insulator (TI) surface manifests in the inelastic electron tunneling spectroscopy (IETS) when such a system is probed by a STM. For this purpose, we consider a single magnetic adatom with arbitrary spin, whose dynamics is governed by the local magnetic anisotropy. The spin is exchange-coupled to two-dimensional helical surface electrons, corresponding to the surface of a three-dimensional TI like Bi2Se3, with its characteristic hexagonally warped Dirac cone band structure. Employing an effective exchange-tunneling model, we calculate the non-linear differential conductance from a spin-polarized STM tip to the helical substrate, valid in the perturbative regime of weak exchange-tunneling and including the nonequilibrium pumping of the adatom spin states. The interplay between the magnetic anisotropy and the spin-momentum locked surface electrons is shown to give a number of specific imprints in the IETS, which could be investigated by spin-resolved scanning tunneling spectroscopy. M. Misiorny, M. Bjerngaard and J. Paaske, manuscript in preparation Work supported by the Polish Ministry of Science and Education as `Iuventus Plus' project (IP2014 030973) in years 2015-2016.

  11. Temperature dependence of magnetocurrent in a magnetic tunnel transistor

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Min, B.C.; Sanderink, J.G.M.; Lodder, J.C.; Jansen, R.

    2005-01-01

    The temperature dependence of magnetocurrent (MC) and transfer ratio has been investigated in a magnetic tunnel transistor (MTT) with a ferromagnetic (FM) emitter of Co or Ni80Fe20. MTT devices of sizes ranging from 10 to 100 µm in diameter were fabricated using a standard photolithography process a

  12. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Science.gov (United States)

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-01

    Heulser alloys Fe2Cr1-xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  13. A magnetic tunnel to shelter hyperpolarized fluids

    Energy Technology Data Exchange (ETDEWEB)

    Milani, Jonas, E-mail: jonas.milani@epfl.ch; Vuichoud, Basile; Bornet, Aurélien; Miéville, Pascal; Mottier, Roger [Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Batochime, CH-1015 Lausanne (Switzerland); Jannin, Sami [Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Batochime, CH-1015 Lausanne (Switzerland); Bruker BioSpin AG, Industriestrasse 26, CH-8117 Fällanden (Switzerland); Bodenhausen, Geoffrey [Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Batochime, CH-1015 Lausanne (Switzerland); Département de Chimie, École Normale Supérieure-PSL Research University, 24 rue Lhomond, F-75005 Paris (France); Sorbonne Universités, UPMC Univ Paris 06, LBM, 4 place Jussieu, F-75005 Paris (France); CNRS, UMR 7203 LBM, F-75005 Paris (France)

    2015-02-15

    To shield solutions carrying hyperpolarized nuclear magnetization from rapid relaxation during transfer through low fields, the transfer duct can be threaded through an array of permanent magnets. The advantages are illustrated for solutions containing hyperpolarized {sup 1}H and {sup 13}C nuclei in a variety of molecules.

  14. On-chip measurement of the Brownian relaxation frequency of magnetic beads using magnetic tunneling junctions

    DEFF Research Database (Denmark)

    Donolato, M.; Sogne, E.; Dalslet, Bjarke Thomas

    2011-01-01

    We demonstrate the detection of the Brownian relaxation frequency of 250 nm diameter magnetic beads using a lab-on-chip platform based on current lines for exciting the beads with alternating magnetic fields and highly sensitive magnetic tunnel junction (MTJ) sensors with a superparamagnetic free...

  15. Spin transfer torque with spin diffusion in magnetic tunnel junctions

    KAUST Repository

    Manchon, Aurelien

    2012-08-09

    Spin transport in magnetic tunnel junctions in the presence of spin diffusion is considered theoretically. Combining ballistic tunneling across the barrier and diffusive transport in the electrodes, we solve the spin dynamics equation in the metallic layers. We show that spin diffusion mixes the transverse spin current components and dramatically modifies the bias dependence of the effective spin transfer torque. This leads to a significant linear bias dependence of the out-of-plane torque, as well as a nonconventional thickness dependence of both spin torque components.

  16. Magnetoresistance of galfenol-based magnetic tunnel junction

    Science.gov (United States)

    Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Panaccione, G.; Eddrief, M.; Marangolo, M.; Torelli, P.

    2015-12-01

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe1-xGax) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  17. Backhopping in magnetic tunnel junctions: Micromagnetic approach and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Frankowski, Marek, E-mail: wsong@unb.ca; Skowroński, Witold; Czapkiewicz, Maciej; Stobiecki, Tomasz

    2015-01-15

    Micromagnetic simulations of Current Induced Magnetization Switching (CIMS) loops in CoFeB/MgO/CoFeB exchange-biased Magnetic Tunnel Junctions (MTJ) are discussed. Our model uses the Landau–Lifshitz–Gilbert equation with the Slonczewski's Spin-Transfer-Torque (STT) component. The current density for STT is calculated from the applied bias voltage and tunnel magnetoresistance which depends on the local magnetization vectors arrangement. We take into account the change in the anti-parallel state resistance with increasing bias voltage. Using such model we investigate influence of the interlayer exchange coupling, between free and reference layers across the barrier, on the backhopping effect in anti-parallel to parallel switching. We compare our simulated CIMS loops with the experimental data obtained from MTJs with different MgO barrier thicknesses. - Highlights: • We model Current Induced Magnetization Switching in magnetic tunnel junctions. • We investigate interlayer exchange coupling influence on backhopping effect. • Experimental results are reproduced with good qualitative agreement. • Ferromagnetic coupling decreases backhopping occurrence probability.

  18. Probing momentum distributions in magnetic tunnel junctions via hot-electron decay

    NARCIS (Netherlands)

    Jansen, R.; Banerjee, T.; Park, B.G.; Lodder, J.C.

    2007-01-01

    The tunnel momentum distribution in a (magnetic) tunnel junction is probed by analyzing the decay of the hot electrons in the Co metal anode after tunneling, using a three-terminal transistor structure in which the hot-electron attenuation is sensitive to the tunnel momentum distribution. Solid stat

  19. Neural coding using telegraphic switching of magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Suh, Dong Ik; Bae, Gi Yoon; Oh, Heong Sik; Park, Wanjun, E-mail: wanjun@hanyang.ac.kr [Department of Electronic Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2015-05-07

    In this work, we present a synaptic transmission representing neural coding with spike trains by using a magnetic tunnel junction (MTJ). Telegraphic switching generates an artificial neural signal with both the applied magnetic field and the spin-transfer torque that act as conflicting inputs for modulating the number of spikes in spike trains. The spiking probability is observed to be weighted with modulation between 27.6% and 99.8% by varying the amplitude of the voltage input or the external magnetic field. With a combination of the reverse coding scheme and the synaptic characteristic of MTJ, an artificial function for the synaptic transmission is achieved.

  20. Magnetic tunnel junctions with integrated thermometers for magnetothermopower measurements

    Science.gov (United States)

    Böhnert, T.; Serrano-Guisan, S.; Paz, E.; Lacoste, B.; Ferreira, R.; Freitas, P. P.

    2017-05-01

    Magnetic tunnel junction (MTJ) micropillars were fabricated with integrated thermometers and a heater line (HL) for thermovoltage measurements. This novel thermometer configuration enabled a direct measurement of ΔT across the MTJ micropillar. The MTJ devices were patterned from a CoFeB/MgO/CoFeB stack, with a 1.2 nm to 1.6 nm MgO wedge across the wafer, resulting in resistance area products in the range of 0.7 kΩ · µm2  MTJ structure and the thermopower were estimated with a noticeable improvement of the measurement accuracy. The studied MTJ structures showed tunneling magnetoresistance (TMR) ratios up to 125%, and tunneling magnetothermopower (TMTP) up to 35%.

  1. Impurity-limited quantum transport variability in magnetic tunnel junctions

    Science.gov (United States)

    Zhuang, Jianing; Wang, Yin; Zhou, Yan; Wang, Jian; Guo, Hong

    2017-08-01

    We report an extensive first-principles investigation of impurity-induced device-to-device variability of spin-polarized quantum tunneling through Fe/MgO/Fe magnetic tunnel junctions (MTJ). In particular, we calculated the tunnel magnetoresistance ratio (TMR) and the average values and variances of the currents and spin transfer torque (STT) of an interfacially doped Fe/MgO/Fe MTJ. Further, we predicted that N-doped MgO can improve the performance of a doped Fe/MgO/Fe MTJ. Our firstprinciples calculations of the fluctuations of the on/off currents and STT provide vital information for future predictions of the long-term reliability of spintronic devices, which is imperative for high-volume production.

  2. Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy.

    Science.gov (United States)

    Zhao, Weisheng; Zhao, Xiaoxuan; Zhang, Boyu; Cao, Kaihua; Wang, Lezhi; Kang, Wang; Shi, Qian; Wang, Mengxing; Zhang, Yu; Wang, You; Peng, Shouzhong; Klein, Jacques-Olivier; de Barros Naviner, Lirida Alves; Ravelosona, Dafine

    2016-01-12

    Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ) becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM) for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS) circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

  3. Tunneling magnetoresistance phenomenon utilizing graphene magnet electrode

    DEFF Research Database (Denmark)

    Hashimoto, T.; Kamikawa, S.; Soriano, D.

    2014-01-01

    Using magnetic rare-metals for spintronic devices is facing serious problems for the environmental contamination and the limited material-resource. In contrast, by fabricating ferromagnetic graphene nanopore arrays (FGNPAs) consisting of honeycomb-like array of hexagonal nanopores with hydrogen-t...

  4. The SPS tunnel with a dipole magnet

    CERN Multimedia

    1976-01-01

    The SPS uses about 800 6-m long dipole magnets to bend the beam around its path. Particle beams come into the SPS from the smaller PS accelerator at 26 GeV. The SPS then accelerates the beam further up to 450 GeV when the beam is extracted and transferred to the LHC or CERN Neutrinos to Gran Sasso (CNGS).

  5. Advanced optical position sensors for magnetically suspended wind tunnel models

    Science.gov (United States)

    Lafleur, S.

    1985-01-01

    A major concern to aerodynamicists has been the corruption of wind tunnel test data by model support structures, such as stings or struts. A technique for magnetically suspending wind tunnel models was considered by Tournier and Laurenceau (1957) in order to overcome this problem. This technique is now implemented with the aid of a Large Magnetic Suspension and Balance System (LMSBS) and advanced position sensors for measuring model attitude and position within the test section. Two different optical position sensors are discussed, taking into account a device based on the use of linear CCD arrays, and a device utilizing area CID cameras. Current techniques in image processing have been employed to develop target tracking algorithms capable of subpixel resolution for the sensors. The algorithms are discussed in detail, and some preliminary test results are reported.

  6. Low-temperature phonoemissive tunneling rates in single molecule magnets

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yun, E-mail: yl2192@gmail.com [University of Illinois, Department of Physics, 1110 W. Green St., Urbana, IL 61801 (United States); Garg, Anupam, E-mail: agarg@northwestern.edu [Northwestern University, Department of Physics and Astronomy, 2145 Sheridan Rd., Evanston, IL 60208 (United States)

    2016-03-15

    Tunneling between the two lowest energy levels of single molecule magnets with Ising type anisotropy, accompanied by the emission or absorption of phonons, is considered. Quantitatively accurate calculations of the rates for such tunneling are performed for a model Hamiltonian especially relevant to the best studied example, Fe{sub 8}. Two different methods are used: high-order perturbation theory in the spin–phonon interaction and the non-Ising-symmetric parts of the spin Hamiltonian, and a novel semiclassical approach based on spin-coherent-state-path-integral instantons. The methods are found to be in good quantitative agreement with other, and consistent with previous approaches to the problem. The implications of these results for magnetization of molecular solids of these molecules are discussed briefly.

  7. Field-like spin torque in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Y-H; Kioussis, N; Kalitsov, A [Department of Physics, California State University, Northridge, CA 91330-8268 (United States); Butler, W H [MINT Center, University of Alabama, P. O. Box 870209, Tuscaloosa, AL (United States); Car, R, E-mail: nick.kioussis@csun.ed [Department of Chemistry, Princeton University, Princeton, New Jersey 08544-0001 (United States)

    2010-01-01

    We show that the exchange splitting asymmetry between the left and right ferromagnetic leads in non-collinear magnetic tunnel junctions (MTJ) tunes the bias behavior of the field-like spin torque, T{sub p}erpendicular. These results can be understood by our recently derived general expression, which relates the non-collinear T{sub p}erpendicular to the algebraic sum of four independent non-equilibrium interlayer exchange couplings (IEC) solely in collinear configurations.

  8. Large influence of capping layers on tunnel magnetoresistance in magnetic tunnel junctions

    Science.gov (United States)

    Zhou, Jiaqi; Zhao, Weisheng; Wang, Yin; Peng, Shouzhong; Qiao, Junfeng; Su, Li; Zeng, Lang; Lei, Na; Liu, Lei; Zhang, Youguang; Bournel, Arnaud

    2016-12-01

    It has been reported in experiments that capping layers, which enhance the perpendicular magnetic anisotropy (PMA) of magnetic tunnel junctions (MTJs), induce a great impact on the tunnel magnetoresistance (TMR). To explore the essential influence caused by the capping layers, we carry out ab initio calculations on TMR in the X(001)|CoFe(001)|MgO(001)|CoFe(001)|X(001) MTJ, where X represents the capping layer material, which can be tungsten, tantalum, or hafnium. We report TMR in different MTJs and demonstrate that tungsten is an ideal candidate for a giant TMR ratio. The transmission spectrum in Brillouin zone is presented. It can be seen that in the parallel condition of MTJ, sharp transmission peaks appear in the minority-spin channel. This phenomenon is attributed to the resonant tunnel transmission effect, and we explained it by the layer-resolved density of states. In order to explore transport properties in MTJs, the density of scattering states was studied from the point of band symmetry. It has been found that CoFe|tungsten interface blocks scattering states transmission in the anti-parallel condition. This work reports TMR and transport properties in MTJs with different capping layers and proves that tungsten is a proper capping layer material, which would benefit the design and optimization of MTJs.

  9. Field-tuned quantum tunnelling of the magnetization in small magnetic particles

    NARCIS (Netherlands)

    García-Pablos, D.; García, N.; Raedt, H. De

    1998-01-01

    We present staircase magnetization curves for single-spin models of uniaxial magnets as obtained from the numerically exact solution of the time-dependent Schrödinger equation. Steps are shown to correspond to field-tuned tunnelling between different pairs of nearly degenerate energy levels. The rol

  10. Electric-field manipulation of magnetization rotation and tunneling magnetoresistance of magnetic tunnel junctions at room temperature

    Science.gov (United States)

    Chen, Aitian; Li, Peisen; Li, Dalai; Zhao, Yonggang; Zhang, Sen; Yang, Lifeng; Liu, Yan; Zhu, Meihong; Zhang, Huiyun; Han, Xiufeng

    2015-03-01

    Recent studies on the electric-field control of tunneling magnetoresistance (TMR) have attracted considerable attention for low power consumption. So far two methods have been demonstrated for electric-field control of TMR. One method uses ferroelectric or multiferroic barriers, which is limited by low temperature. The other is nanoscale thin film magnetic tunnel junction (MTJ), but the assistance of a magnetic field is required. Therefore, electric-field control of TMR at room temperature without a magnetic field is highly desired. One promising way is to employ strain-mediated coupling in ferromagnetic/piezoelectric structure. Though MTJs/piezoelectric has been predicted by theory, experiment work is still lacking. We deposited CoFeB/AlOx/CoFeB on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric single crystal. Under external electric fields, PMN-PT will produce a piezostrain due to piezoelectric effect, and the piezostrain transfers to ferromagnetic film to change the magnetic anisotropy. We demonstrate a reversible, continuous magnetization rotation and manipulation of TMR at room temperature by electric fields without the assistance of a magnetic field.

  11. Tailoring the properties of a magnetic tunnel junction to be used as a magnetic field sensor

    OpenAIRE

    Nguyen, Hugo; Persson, Anders

    2011-01-01

    A magnetic tunnel junction (MTJ) can be used as an effective magnetic field sensor thank to its high magnetoresistance ratio. To be used as a magnetic field sensor in different applications, the possibility of tuning the performance of the MTJ is important. Different means of tuning, such as voltage and magnetic field biasing, can be used. In this work, an external magnetic field from a permanent magnet was used to bias the sensing layer of a MTJ along its hard axis, and the effect of the bia...

  12. Giant thermal spin torque assisted magnetic tunnel junction switching

    Science.gov (United States)

    Pushp, Aakash

    Spin-polarized charge-currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer-torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin-currents from temperature gradients, and their associated thermal-spin-torques (TSTs) have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge-currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe. Reference: A. Pushp*, T. Phung*, C. Rettner, B. P. Hughes, S.-H. Yang, S. S. P. Parkin, 112, 6585-6590 (2015).

  13. Giant thermal spin-torque–assisted magnetic tunnel junction switching

    Science.gov (United States)

    Pushp, Aakash; Phung, Timothy; Rettner, Charles; Hughes, Brian P.; Yang, See-Hun; Parkin, Stuart S. P.

    2015-01-01

    Spin-polarized charge currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin currents from temperature gradients, and their associated thermal-spin torques (TSTs), have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe. PMID:25971730

  14. Minimization of the energy costs for operating magnetic tunnel junctions

    Science.gov (United States)

    Farhat, Ilyas A. H.; Gale, E.; Isakovic, A. F.

    2015-03-01

    Increasing prospects of utilizing the STT-MRAM calls for the re-assessment of the overall energy (power) cost of operating magnetic tunnel junctions and related elements. This motivates our design, nanofabrication and characterization of simple tri-layer magnetic tunnel junctions which show measurable decrease in the operating energy cost. The MTJs we report about rely on nanoengineering interfaces between the insulating and magnetic layers in such a way that the area of the hysteresis loops can be controlled in one or both magnetic layers. Our TMR coefficient ranges from 45% to 130%, depending on the MTJ layer materials, and can be anticipated to be further increased. We also report the study of the TMR dependence on the RA product, as an important interface parameter. Lastly, we present an analysis of MTJ parameters affected by our approach and a perspective on further improvements, focusing on the device design parameters relevant for the integration of this type of MTJs. This work is supported by the SRC-ATIC Grant 2012-VJ-2335. A part of this work is being performed at Cornell University CNF, a member of NNIN. We thank CNF staff for the support.

  15. Tunnel magnetoresistance in thermally robust Mo/CoFeB/MgO tunnel junction with perpendicular magnetic anisotropy

    Directory of Open Access Journals (Sweden)

    B. Fang

    2015-06-01

    Full Text Available We report on tunnel magnetoresistance and electric-field effect in the Mo buffered and capped CoFeB/MgO magnetic tunnel junctions (MTJs with perpendicular magnetic anisotropy. A large tunnel magnetoresistance of 120% is achieved. Furthermore, this structure shows greatly improved thermal stability and stronger electric-field-induced modulation effect in comparison with the Ta/CoFeB/MgO-based MTJs. These results suggest that the Mo-based MTJs are more desirable for next generation spintronic devices.

  16. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Pu, E-mail: Vicky-sg1015@hotmail.com [Department of Electrical and Computer Engineering, National University of Singapore (Singapore); Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Lim, Sze-Ter; Han, Gu-Chang, E-mail: HAN-Guchang@dsi.a-star.edu.sg [Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Teo, Kie-Leong, E-mail: eleteokl@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore (Singapore)

    2015-12-21

    Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  17. Magnetoresistance of galfenol-based magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Gobaut, B., E-mail: benoit.gobaut@elettra.eu [Sincrotrone Trieste S.C.p.A., S.S. 14 Km 163.5, Area Science Park, 34149 Trieste (Italy); Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Rafaqat, H. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); ICTP, Trieste (Italy); Roddaro, S. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127 Pisa (Italy); Rossi, G. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano (Italy); Eddrief, M.; Marangolo, M. [Sorbonne Universités, UPMC Paris 06, CNRS-UMR 7588, Institut des Nanosciences de Paris, 75005, Paris (France)

    2015-12-15

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe{sub 1-x}Ga{sub x}) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  18. Tunneling for Dirac Fermions in Constant Magnetic Field

    CERN Document Server

    Choubabi, El Bouazzaoui; Jellal, Ahmed

    2009-01-01

    The tunneling effect of two-dimensional Dirac fermions in a constant magnetic field is studied. This can be done by using the continuity equation at some points to determine the corresponding reflexion and transmission coefficients. For this, we consider a system made of graphene as superposition of two different regions where the second is characterized by an energy gap t'. In fact, we treat concrete systems to practically give two illustrations: barrier and diode. For each case, we discuss the transmission in terms of the ratio of the energy conservation and t'. Moreover, we analyze the resonant tunneling by introducing a scalar Lorentz potential where it is shown that a total transmission is possible.

  19. Spin-transfer torque switched magnetic tunnel junctions in magnetic random access memory

    Science.gov (United States)

    Sun, Jonathan Z.

    2016-10-01

    Spin-transfer torque (or spin-torque, or STT) based magnetic tunnel junction (MTJ) is at the heart of a new generation of magnetism-based solid-state memory, the so-called spin-transfer-torque magnetic random access memory, or STT-MRAM. Over the past decades, STT-based switchable magnetic tunnel junction has seen progress on many fronts, including the discovery of (001) MgO as the most favored tunnel barrier, which together with (bcc) Fe or FeCo alloy are yielding best demonstrated tunnel magneto-resistance (TMR); the development of perpendicularly magnetized ultrathin CoFeB-type of thin films sufficient to support high density memories with junction sizes demonstrated down to 11nm in diameter; and record-low spin-torque switching threshold current, giving best reported switching efficiency over 5 kBT/μA. Here we review the basic device properties focusing on the perpendicularly magnetized MTJs, both in terms of switching efficiency as measured by sub-threshold, quasi-static methods, and of switching speed at super-threshold, forced switching. We focus on device behaviors important for memory applications that are rooted in fundamental device physics, which highlights the trade-off of device parameters for best suitable system integration.

  20. Magnetic tunnel junction on a magnetostrictive substrate: An ultrasensitive magnetic-field sensor

    Science.gov (United States)

    Pertsev, N. A.

    2016-09-01

    The concept of a magnetic tunnel junction (MTJ) fabricated on an active substrate made of a highly magnetostrictive ferromagnetic material is described theoretically. It is shown that, under certain conditions, such hybrid device exhibits strongly enhanced sensitivity of the tunnel current to the external magnetic field. This feature results from the field-induced substrate deformations, which create lattice strains in the MTJ due to the interfacial mechanical interaction. If the free electrode of MTJ is made of a cubic ferromagnet like Co40Fe60 having strong magnetoelastic coupling between the magnetization and strains, the field-induced magnetization reorientation here may be enhanced by the strain effect drastically. This reorientation should lead to a change in the junction's electrical conductance because the magnetization of the reference electrode may be pinned by adjacent antiferromagnetic layer to keep its initial direction. Taking into account additional strain effects on the height and width of the tunnel barrier and the effective mass of tunneling electrons, we performed numerical calculations of the conductance magnetosensitivity for the CoFe/MgO/CoFeB junctions mechanically coupled to the FeGaB film grown on Si and found that such hybrid device is promising as an ultrasensitive room-temperature magnetic-field sensor.

  1. Coexistance of Giant Tunneling Electroresistance and Magnetoresistance in an All-Oxide Composite Magnetic Tunnel Junction

    KAUST Repository

    Caffrey, Nuala Mai

    2012-11-30

    We propose, by performing advanced abinitio electron transport calculations, an all-oxide composite magnetic tunnel junction, within which both large tunneling magnetoresistance (TMR) and tunneling electroresistance (TER) effects can coexist. The TMR originates from the symmetry-driven spin filtering provided by an insulating BaTiO3 barrier to the electrons injected from the SrRuO3 electrodes. Following recent theoretical suggestions, the TER effect is achieved by intercalating a thin insulating layer, here SrTiO3, at one of the SrRuO3/BaTiO3 interfaces. As the complex band structure of SrTiO3 has the same symmetry as that of BaTiO3, the inclusion of such an intercalated layer does not negatively alter the TMR and in fact increases it. Crucially, the magnitude of the TER also scales with the thickness of the SrTiO3 layer. The SrTiO3 thickness becomes then a single control parameter for both the TMR and the TER effect. This protocol offers a practical way to the fabrication of four-state memory cells. © 2012 American Physical Society.

  2. Magnetic resonance neurography of median neuropathies proximal to the carpal tunnel

    Energy Technology Data Exchange (ETDEWEB)

    Thawait, Gaurav K. [Johns Hopkins Hospital, The Russell H. Morgan Department of Radiology and Radiological Science, Baltimore, MD (United States); The Johns Hopkins Hospital, Russell H. Morgan Department of Radiology and Radiological Science, Baltimore, MD (United States); Subhawong, Ty K.; Eng, John; Carrino, John A.; Chhabra, Avneesh [Johns Hopkins Hospital, The Russell H. Morgan Department of Radiology and Radiological Science, Baltimore, MD (United States); Thawait, Shrey K. [Yale University, Bridgeport Hospital, Department of Radiology, Bridgeport, CT (United States); Andreisek, Gustav [University Hospital Zurich, Department of Radiology, Zurich (Switzerland); Belzberg, Alan J. [Johns Hopkins Hospital, Department of Neurosurgery, Baltimore, MD (United States)

    2012-06-15

    This review provides magnetic resonance neurography (MRN) imaging appearances of median neuropathy proximal to the carpal tunnel. Carpal tunnel syndrome (CTS) and its imaging have been extensively described in the literature; however, there is a relative paucity of information on the MR imaging appearances of different pathologies of the median nerve proximal to the carpal tunnel. (orig.)

  3. Temperature dependence of microwave oscillations in magnetic tunnel junctions with a perpendicularly magnetized free layer

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Peng; Feng, Jiafeng, E-mail: hxwei@iphy.ac.cn, E-mail: jiafengfeng@iphy.ac.cn; Wei, Hongxiang, E-mail: hxwei@iphy.ac.cn, E-mail: jiafengfeng@iphy.ac.cn; Han, Xiufeng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Fang, Bin; Zhang, Baoshun; Zeng, Zhongming [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Ruoshui Road 398, Suzhou 215123 (China)

    2015-01-05

    We experimentally study the temperature dependence of the spin-transfer-torque-induced microwave oscillations in MgO-based magnetic tunnel junction nanopillars with a perpendicularly magnetized free layer. We demonstrate that the oscillation frequency increases rapidly with decreasing temperature, which is mainly ascribed to the temperature dependence of both the saturation magnetization and the perpendicular magnetic anisotropy. We also find that a strong temperature dependence of the output power while a nonmonotonic temperature dependence of spectral linewidth are maintained for a constant dc bias in measured temperature range. Possible mechanisms leading to the different dependences of oscillation frequency, output power, and linewidth are discussed.

  4. Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges

    Directory of Open Access Journals (Sweden)

    Mengxing Wang

    2015-08-01

    Full Text Available Magnetic tunnel junction (MTJ, which arises from emerging spintronics, has the potential to become the basic component of novel memory, logic circuits, and other applications. Particularly since the first demonstration of current induced magnetization switching in MTJ, spin transfer torque magnetic random access memory (STT-MRAM has sparked a huge interest thanks to its non-volatility, fast access speed, and infinite endurance. However, along with the advanced nodes scaling, MTJ with in-plane magnetic anisotropy suffers from modest thermal stability, high power consumption, and manufactural challenges. To address these concerns, focus of research has converted to the preferable perpendicular magnetic anisotropy (PMA based MTJ, whereas a number of conditions still have to be met before its practical application. This paper overviews the principles of PMA and STT, where relevant issues are preliminarily discussed. Centering on the interfacial PMA in CoFeB/MgO system, we present the fundamentals and latest progress in the engineering, material, and structural points of view. The last part illustrates potential investigations and applications with regard to MTJ with interfacial PMA.

  5. Spin-Polarization in Quasi-Magnetic Tunnel Junctions

    Science.gov (United States)

    Xie, Zheng-Wei; Li, Ling

    2017-05-01

    Spin polarization in ferromagnetic metal/insulator/spin-filter barrier/nonmagnetic metal, referred to as quasi-magnetic tunnel junctions, is studied within the free-electron model. Our results show that large positive or negative spin-polarization can be obtained at high bias in quasi-magnetic tunnel junctions, and within large bias variation regions, the degree of spin-polarization can be linearly tuned by bias. These linear variation regions of spin-polarization with bias are influenced by the barrier thicknesses, barrier heights and molecular fields in the spin-filter (SF) layer. Among them, the variations of thickness and heights of the insulating and SF barrier layers have influence on the value of spin-polarization and the linear variation regions of spin-polarization with bias. However, the variations of molecular field in the SF layer only have influence on the values of the spin-polarization and the influences on the linear variation regions of spin-polarization with bias are slight. Supported by the Key Natural Science Fund of Sichuan Province Education Department under Grant Nos 13ZA0149 and 16ZA0047, and the Construction Plan for Scientific Research Innovation Team of Universities in Sichuan Province under Grant No 12TD008.

  6. Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Weisheng Zhao

    2016-01-01

    Full Text Available Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., <1 nm to reduce the resistance area for the spin transfer torque switching in the nanopillar. These failure issues limit the research and development of STT-MRAM to widely achieve commercial products. In this paper, we give a full analysis of failure mechanisms for PMA-MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

  7. Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy.

    Science.gov (United States)

    Jeong, Jaewoo; Ferrante, Yari; Faleev, Sergey V; Samant, Mahesh G; Felser, Claudia; Parkin, Stuart S P

    2016-01-18

    Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn-Ge termination layers that are oppositely magnetized to the higher moment Mn-Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible.

  8. Termination layer compensated tunnelling magnetoresistance in ferrimagnetic Heusler compounds with high perpendicular magnetic anisotropy

    Science.gov (United States)

    Jeong, Jaewoo; Ferrante, Yari; Faleev, Sergey V.; Samant, Mahesh G.; Felser, Claudia; Parkin, Stuart S. P.

    2016-01-01

    Although high-tunnelling spin polarization has been observed in soft, ferromagnetic, and predicted for hard, ferrimagnetic Heusler materials, there has been no experimental observation to date of high-tunnelling magnetoresistance in the latter. Here we report the preparation of highly textured, polycrystalline Mn3Ge films on amorphous substrates, with very high magnetic anisotropy fields exceeding 7 T, making them technologically relevant. However, the small and negative tunnelling magnetoresistance that we find is attributed to predominant tunnelling from the lower moment Mn-Ge termination layers that are oppositely magnetized to the higher moment Mn-Mn layers. The net spin polarization of the current reflects the different proportions of the two distinct termination layers and their associated tunnelling matrix elements that result from inevitable atomic scale roughness. We show that by engineering the spin polarization of the two termination layers to be of the same sign, even though these layers are oppositely magnetized, high-tunnelling magnetoresistance is possible.

  9. Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices.

    Science.gov (United States)

    Liu, Luqiao; Pai, Chi-Feng; Ralph, D C; Buhrman, R A

    2012-11-02

    We show that a direct current in a tantalum microstrip can induce steady-state magnetic oscillations in an adjacent nanomagnet through spin torque from the spin Hall effect (SHE). The oscillations are detected electrically via a magnetic tunnel junction (MTJ) contacting the nanomagnet. The oscillation frequency can be controlled using the MTJ bias to tune the magnetic anisotropy. In this 3-terminal device, the SHE torque and the MTJ bias therefore provide independent controls of the oscillation amplitude and frequency, enabling new approaches for developing tunable spin torque nano-oscillators.

  10. Magnetic tunnel junctions using perpendicularly magnetized synthetic antiferromagnetic reference layer for wide-dynamic-range magnetic sensors

    Science.gov (United States)

    Nakano, T.; Oogane, M.; Furuichi, T.; Ando, Y.

    2017-01-01

    We developed CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with a perpendicularly magnetized synthetic antiferromagnetic (p-SAF) reference layer for magnetic sensor applications. The MTJs exhibited linear tunnel magnetoresistance curves to out-of-plane applied magnetic fields with dynamic ranges more than ±2.5 kOe, which are wider than those in CoFeB/MgO/CoFeB-MTJs reported to date. The performance metrics of MTJ sensors, i.e., sensitivity and nonlinearity, depend significantly on the anisotropy field of the free layer. We explained the dependences by a simple model based on the Stoner-Wohlfarth and Slonczewski models, which gives us a guideline to design the sensor performance metrics. These findings demonstrated that MTJs with a p-SAF reference layer are promising candidates for wide-dynamic-range magnetic sensors.

  11. Synthesis of magnetic tunnel junctions with full in situ atomic layer and chemical vapor deposition processes

    Energy Technology Data Exchange (ETDEWEB)

    Mantovan, R., E-mail: roberto.mantovan@mdm.imm.cnr.it [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Vangelista, S.; Kutrzeba-Kotowska, B.; Cocco, S.; Lamperti, A.; Tallarida, G. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (MB) (Italy); Mameli, D. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Dipartimento di Scienze Chimiche, Universita di Cagliari, Cittadella Universitaria, 09042 Monserrato, Cagliari (Italy); Fanciulli, M. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Dipartimento di Scienza dei Materiali, Universita degli studi Milano-Bicocca, Via R Cozzi 53, 20125 Milano (Italy)

    2012-05-01

    Magnetic tunnel junctions, i.e. the combination of two ferromagnetic electrodes separated by an ultrathin tunnel oxide barrier, are core elements in a large variety of spin-based devices. We report on the use of combined chemical vapor and atomic layer deposition processes for the synthesis of magnetic tunnel junctions with no vacuum break. Structural, chemical and morphological characterizations of selected ferromagnetic and oxide layers are reported, together with the evidence of tunnel magnetoresistance effect in patterned Fe/MgO/Co junctions.

  12. Magnetic Tunnel Junction as an On-Chip Temperature Sensor.

    Science.gov (United States)

    Sengupta, Abhronil; Liyanagedera, Chamika Mihiranga; Jung, Byunghoo; Roy, Kaushik

    2017-09-18

    Temperature sensors are becoming an increasingly important component in System-on-Chip (SoC) designs with increasing transistor scaling, power density and associated heating effects. This work explores a compact nanoelectronic temperature sensor based on a Magnetic Tunnel Junction (MTJ) structure. The MTJ switches probabilistically depending on the operating temperature in the presence of thermal noise. Performance evaluation of the proposed MTJ temperature sensor, based on experimentally measured device parameters, reveals that the sensor is able to achieve a conversion rate of 2.5K samples/s with energy consumption of 8.8 nJ per conversion (1-2 orders of magnitude lower than state-of-the-art CMOS sensors) for a linear sensing regime of 200-400 K.

  13. Shape Biased Low Power Spin Dependent Tunneling Magnetic Field Sensors

    Science.gov (United States)

    Tondra, Mark; Qian, Zhenghong; Wang, Dexin; Nordman, Cathy; Anderson, John

    2001-10-01

    Spin Dependent Tunneling (SDT) devices are leading candidates for inclusion in a number of Unattended Ground Sensor applications. Continued progress at NVE has pushed their performance to 1OOs of pT I rt. Hz 1 Hz. However, these sensors were designed to use an applied field from an on-chip coil to create an appropriate magnetic sensing configuration. The power required to generate this field (^100mW) is significantly greater than the power budget (^lmW) for a magnetic sensor in an Unattended Ground Sensor (UGS) application. Consequently, a new approach to creating an ideal sensing environment is required. One approach being used at NVE is "shape biasing." This means that the physical layout of the SDT sensing elements is such that the magnetization of the sensing film is correct even when no biasing field is applied. Sensors have been fabricated using this technique and show reasonable promise for UGS applications. Some performance trade-offs exist. The power is easily tinder 1 MW, but the sensitivity is typically lower by a factor of 10. This talk will discuss some of the design details of these sensors as well as their expected ultimate performance.

  14. Tunneling conductance studies in the ion-beam sputtered CoFe/Mg/MgO/NiFe magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Braj Bhusan; Chaudhary, Sujeet [Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)

    2013-06-03

    Magnetic tunnel junctions consisting of CoFe(10 nm)/Mg(1 nm)/MgO(3.5 nm)/NiFe(10 nm) are grown at room temperature using dual ion beam sputtering via in-situ shadow masking. The effective barrier thickness and average barrier height are estimated to be 3.5 nm (2.9 nm) and 0.69 eV (1.09 eV) at 290 K (70 K), respectively. The tunnel magnetoresistance value of 0.2 % and 2.3 % was observed at 290 K and 60 K, respectively. The temperature dependence of tunneling conductance revealed the presence of localized states present within the forbidden gap of the MgO barrier leading to finite inelastic spin independent tunneling contributions, which degrade the TMR value.

  15. MgGa2O4 spinel barrier for magnetic tunnel junctions: Coherent tunneling and low barrier height

    Science.gov (United States)

    Sukegawa, Hiroaki; Kato, Yushi; Belmoubarik, Mohamed; Cheng, P.-H.; Daibou, Tadaomi; Shimomura, Naoharu; Kamiguchi, Yuuzo; Ito, Junichi; Yoda, Hiroaki; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro

    2017-03-01

    Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel junctions (MTJs) were fabricated by magnetron sputtering. A tunnel magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was observed, suggesting a TMR enhancement by the coherent tunneling effect in the MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good lattice matching with the Fe layers owing to slight tetragonal lattice distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance and current-voltage characteristics revealed that the height of the MgGa2O4 barrier is much lower than that of an MgAl2O4 barrier. This study demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a large TMR ratio at a low resistance area product.

  16. Time-resolved measurement of the tunnel magneto-Seebeck effect in a single magnetic tunnel junction.

    Science.gov (United States)

    Boehnke, Alexander; Walter, Marvin; Roschewsky, Niklas; Eggebrecht, Tim; Drewello, Volker; Rott, Karsten; Münzenberg, Markus; Thomas, Andy; Reiss, Günter

    2013-06-01

    Recently, several groups have reported spin-dependent thermoelectric effects in magnetic tunnel junctions. In this paper, we present a setup for time-resolved measurements of thermovoltages and thermocurrents of a single micro- to nanometer-scaled tunnel junction. An electrically modulated diode laser is used to create a temperature gradient across the tunnel junction layer stack. This laser modulation technique enables the recording of time-dependent thermovoltage signals with a temporal resolution only limited by the preamplifier for the thermovoltage. So far, time-dependent thermovoltage could not be interpreted. Now, with the setup presented in this paper, it is possible to distinguish different Seebeck voltage contributions to the overall measured voltage signal in the μs time regime. A model circuit is developed that explains those voltage contributions on different sample types. Further, it will be shown that a voltage signal arising from the magnetic tunnel junction can only be observed when the laser spot is directly centered on top of the magnetic tunnel junction, which allows a lateral separation of the effects.

  17. Spin transport in nanoscale spin valves and magnetic tunnel junctions

    Science.gov (United States)

    Patibandla, Sridhar

    relaxation in high- and low-mobility materials respectively. Chapter 5 discusses the first ever reported results on the fabrication of manganese doped germanium dilute magnetic semiconductor nanowires (DMS) using electrochemical deposition techniques. The magnetic measurements conducted on these nanowires show ferromagnetism with a Curie temperature of about 220K. Chapter 6 discusses the spin transport studies conducted in nanoscale organic spin valves with tunnel barriers interposed between the ferromagnet and the organic spacer layer. Two dimensional organic spin valves with tunnel injectors were also studied and the experimental details are discussed.

  18. Output voltage calculations in double barrier magnetic tunnel junctions with asymmetric voltage behavior

    KAUST Repository

    Useinov, Arthur

    2011-10-22

    In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR-V curves, output voltages and I-V characteristics for negative and positive values of applied voltages were carried out using MTJs with CoFeB/MgO interfaces as an example. Asymmetry of the experimental TMR-V curves is explained by different values of the minority and majority Fermi wave vectors for the left and right sides of the tunnel barrier, which arises due to different annealing regimes. Electron tunneling in DMTJs was simulated in two ways: (i) Coherent tunneling, where the DMTJ is modeled as one tunnel system and (ii) consecutive tunneling, where the DMTJ is modeled by two single barrier junctions connected in series. © 2012 Elsevier B.V. All rights reserved.

  19. Switching Properties of sub-100 nm Perpendicular Magnetic Tunnel Junctions

    Science.gov (United States)

    Tryputen, Larysa; Piotrowski, Stephan; Bapna, Mukund; Chien, Chia-Ling; Wang, Weigang; Majetich, Sara; Ross, Caroline

    2015-03-01

    Perpendicular magnetic tunnel junctions (p-MTJs) have great potential for realizing high-density non-volatile memory and logic devices. It is critical to solve scalability problem to implement such devices, to achieve low resistance area and to reduce switching current density while maintaining thermal stability. We present our recent results on fabrication of high resolution Ta/CoFeB/MgO/CoFeB/Ta p-MTJ devices and characterization of their switching properties as well as topography and current mapping by using nanoscale Conductive Atomic Force Microscopy. Our patterning method is based on using hydrogen silsesquioxane resist mask combined with ion beam etching. It allows to fabricate p-MTJ devices down to 40 nm in diameter while maintaining the magnetic quality of the multilayers. Repeatable, consistent switching behaviour has been observed in the obtained p-MTJ devices of 500 nm down to 40 nm with 10 - 800 mV voltage applied. Switching field increased as device diameter decreased, from 580 Oe at 500 nm (MR = 10%) to 410 Oe at 80 nm (MR = 9%). We discuss the effect of device sizes on the switching properties. This work was supported in part by C-SPIN, one of the six centers of STARnet, a Semiconductor Research Corporation Program sponsored by MARCO and DARPA and in part through the National Science Foundation through NCN-Needs Program, Contract 12207020-EEC.

  20. Development and process control of magnetic tunnel junctions for magnetic random access memory devices

    Science.gov (United States)

    Kula, Witold; Wolfman, Jerome; Ounadjela, Kamel; Chen, Eugene; Koutny, William

    2003-05-01

    We report on the development and process control of magnetic tunnel junctions (MTJs) for magnetic random access memory (MRAM) devices. It is demonstrated that MTJs with high magnetoresistance ˜40% at 300 mV, resistance-area product (RA) ˜1-3 kΩ μm2, low intrinsic interlayer coupling (Hin) ˜2-3 Oe, and excellent bit switching characteristics can be developed and fully integrated with complementary metal-oxide-semiconductor circuitry into MRAM devices. MTJ uniformity and repeatability level suitable for mass production has been demonstrated with the advanced processing and monitoring techniques.

  1. Micromagnetic simulation of electric-field-assisted magnetization switching in perpendicular magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Chikako Yoshida

    2017-05-01

    Full Text Available The feasibility of a voltage assisted unipolar switching in perpendicular magnetic tunnel junction (MTJ has been studied using a micromagnetic simulation. Assuming a linear modulation of anisotropy field with voltage, both parallel (P to anti-parallel (AP and AP to P switchings were observed by application of unipolar voltage pulse without external magnetic field assistance. In latter case, the final P state can only be achieved with an ultrashort voltage pulse which vanishes before spin transfer torque (STT becomes dominant to restore the initial AP state. In addition, it was found that the larger change in anisotropy field is required for the MTJ with smaller diameter.

  2. Micromagnetic simulation of electric-field-assisted magnetization switching in perpendicular magnetic tunnel junction

    Science.gov (United States)

    Yoshida, Chikako; Noshiro, Hideyuki; Yamazaki, Yuichi; Sugii, Toshihiro; Tanaka, Tomohiro; Furuya, Atsushi; Uehara, Yuji

    2017-05-01

    The feasibility of a voltage assisted unipolar switching in perpendicular magnetic tunnel junction (MTJ) has been studied using a micromagnetic simulation. Assuming a linear modulation of anisotropy field with voltage, both parallel (P) to anti-parallel (AP) and AP to P switchings were observed by application of unipolar voltage pulse without external magnetic field assistance. In latter case, the final P state can only be achieved with an ultrashort voltage pulse which vanishes before spin transfer torque (STT) becomes dominant to restore the initial AP state. In addition, it was found that the larger change in anisotropy field is required for the MTJ with smaller diameter.

  3. Perpendicularly magnetized ferrimagnetic [Mn50Ga50/Co2FeAl] superlattice and the utilization in magnetic tunnel junctions

    Directory of Open Access Journals (Sweden)

    Q. L. Ma

    2015-08-01

    Full Text Available The ferrimagnetic superlattice (SL [MnGa/Co2FeAl]n exhibiting perpendicular magnetic anisotropy opened a new method for spintronics materials used in magnetic random access memory, because of the high anisotropy, small damping constant and tunable magnetization. In this work, we fabricated SLs with different MnGa composition and studied the MnGa composition dependence of the structure and magnetic properties of the SLs. Furthermore, we fabricated fully perpendicular magnetic tunnel junctions with SLs as both top and bottom electrodes. A clear tunnel magnetoresistance (TMR effect with TMR ratio of 1.3% at room temperature was observed.

  4. FeGa/MgO/Fe/GaAs(001) magnetic tunnel junction: Growth and magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Gobaut, B., E-mail: benoit.gobaut@elettra.eu [Sincrotrone Trieste S.C.p.A., S.S. 14-km 163.5, Area Science Park, 34012 Trieste (Italy); Ciprian, R.; Salles, B.R.; Krizmancic, D. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy); Rossi, G. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy); Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano (Italy); Panaccione, G. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy); Eddrief, M.; Marangolo, M. [Sorbonne Universites, UPMC Univ Paris 06, UMR 7588, INSP, 4 place Jussieu, 75005 Paris (France); CNRS, UMR 7588, Institut des NanoSciences de Paris, 4 place Jussieu, 75005 Paris (France); Torelli, P. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy)

    2015-06-01

    Research on spintronics and on multiferroics leads now to the possibility of combining the properties of these materials in order to develop new functional devices. Here we report the integration of a layer of magnetostrictive material into a magnetic tunnel junction. A FeGa/MgO/Fe heterostructure has been grown on a GaAs(001) substrate by molecular beam epitaxy (MBE) and studied by X-ray magnetic circular dichroism (XMCD). The comparison between magneto optical Kerr effect (MOKE) measurements and hysteresis performed in total electron yield allowed distinguishing the ferromagnetic hysteresis loop of the FeGa top layer from that of the Fe buried layer, evidencing a different switching field of the two layers. This observation indicates an absence of magnetic coupling between the two ferromagnetic layers despite the thickness of the MgO barrier of only 2.5 nm. The in-plane magnetic anisotropy has also been investigated. Overall results show the good quality of the heterostructure and the general feasibility of such a device using magnetostrictive materials in magnetic tunnel junction.

  5. Effect of Anti-Diffusion Oxide Layer on Enhanced Thermal Stability of Magnetic Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zong-Zhi; ZHAO Hui; Cardoso S.; Freitas P. P.

    2006-01-01

    @@ Magnetic tunnel junctions (MTJs) with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance (TMR) signals as high as 39% after anneal at 380℃ .

  6. Interaction-Induced Oscillations of the Tunneling Density of States in a Nonquantizing Magnetic Field

    Energy Technology Data Exchange (ETDEWEB)

    Rudin, A.; Aleiner, I.; Glazman, L. [Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    1997-01-01

    We study tunneling into an interacting disordered two-dimensional electron gas in a nonquantizing magnetic field, which does not cause the standard de Haasvan Alphen oscillations. Interaction induces a new type of oscillation in the tunneling density of states with the characteristic period of cyclotron quantum {h_bar}{omega}{sub c}. {copyright} {ital 1997} {ital The American Physical Society}

  7. Magnetism of Semiconductor-Based Magnetic Tunnel Junctions under Electric Field from First Principles

    Energy Technology Data Exchange (ETDEWEB)

    Kan, E.; Xiang, H.; Yang, J.; Whangbo, M. H.

    2009-06-01

    Semiconductor magnetic tunnel junctions (MTJs), composed of diluted magnetic semiconductors (DMSs) sandwiching a semiconductor barrier, have potential applications in spintronics but their development has been slow due to the difficulty of controlling the magnetism of DMSs. In terms of density functional calculations for model semiconductor MTJs, (Zn,Co)O/ZnO/(Zn,Co)O and (Ga,Mn)N/GaN/(Ga,Mn)N, we show that the magnetic coupling between the transition metal ions in each DMS electrode of such semiconductor MTJs can be switched from ferromagnetic to antiferromagnetic, or vice versa, under the application of external electric field across the junctions. Our results suggest a possible avenue for the application of semiconductor MTJs.

  8. Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach.

    Science.gov (United States)

    Yang, Chao-Yao; Chang, Shu-Jui; Lee, Min-Han; Shen, Kuei-Hung; Yang, Shan-Yi; Lin, Horng-Ji; Tseng, Yuan-Chieh

    2015-11-24

    We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport.

  9. Charge and spin current oscillations in a tunnel junction induced by magnetic field pulses

    Science.gov (United States)

    Dartora, C. A.; Nobrega, K. Z.; Cabrera, G. G.

    2016-08-01

    Usually, charge and spin transport properties in tunnel junctions are studied in the DC bias regime and/or in the adiabatic regime of time-varying magnetic fields. In this letter, the temporal dynamics of charge and spin currents in a tunnel junction induced by pulsed magnetic fields is considered. At low bias voltages, energy and momentum of the conduction electrons are nearly conserved in the tunneling process, leading to the description of the junction as a spin-1/2 fermionic system coupled to time-varying magnetic fields. Under the influence of pulsed magnetic fields, charge and spin current can flow across the tunnel junction, displaying oscillatory behavior, even in the absence of DC bias voltage. A type of spin capacitance function, in close analogy to electric capacitance, is predicted.

  10. Effectively Blocked Mechanism in Quantum Tunnelling of n-Coupled Single-Molecular Magnets

    Institute of Scientific and Technical Information of China (English)

    CHEN Zhi-De

    2005-01-01

    @@ We present theoretical study on quantum tunnelling in n-coupled single-molecule magnets (SMMs) by spincoherent-state path integral. It is found that, due to weak coupling between SMMs, the tunnelling process involving more than one-spin-flip is effectively blocked and the main contribution to the relaxation of the magnetization comes from the tunnelling processes involving just one-spin-flip. Starting from the negative saturated magnetization, the effect of the antiferromagnetic on tunnelling coupling is found to be qualitatively different from the ferromagnetic coupling. A criterion is developed to determine both the nature and the strength of the exchange coupling from the position of the first resonance of a spherical sample with homogeneous magnetization.

  11. Magnetic tunnel junctions with non-collinear anisotropy axes for sensor applications

    CERN Document Server

    Grigorenko, A N

    2003-01-01

    Magnetic tunnel junctions (MTJ) with non-collinear anisotropy axes of magnetic layers have been fabricated for reading head and sensor applications. It is shown that crossed anisotropies of magnetic layers improve sensor sensitivity and time-response compared to the conventional case of aligned anisotropies. The developed micromagnetic model is in good agreement with magnetoresistive properties of fabricated junctions.

  12. Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

    Science.gov (United States)

    Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; Andersen, Brian M.

    2017-02-01

    The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors--one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability.

  13. Scanning tunnelling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets

    Science.gov (United States)

    Gastiasoro, Maria N.; Eremin, Ilya; Fernandes, Rafael M.; Andersen, Brian M.

    2017-01-01

    The combination of electronic correlations and Fermi surfaces with multiple nesting vectors can lead to the appearance of complex multi-Q magnetic ground states, hosting unusual states such as chiral density waves and quantum Hall insulators. Distinguishing single-Q and multi-Q magnetic phases is however a notoriously difficult experimental problem. Here we propose theoretically that the local density of states (LDOS) near a magnetic impurity, whose orientation may be controlled by an external magnetic field, can be used to map out the detailed magnetic configuration of an itinerant system and distinguish unambiguously between single-Q and multi-Q phases. We demonstrate this concept by computing and contrasting the LDOS near a magnetic impurity embedded in three different magnetic ground states relevant to iron-based superconductors—one single-Q and two double-Q phases. Our results open a promising avenue to investigate the complex magnetic configurations in itinerant systems via standard scanning tunnelling spectroscopy, without requiring spin-resolved capability. PMID:28176779

  14. All-electric-controlled spin current switching in single-molecule magnet-tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Zhang Zheng-Zhong; Shen Rui; Sheng Li; Wang Rui-Qiang; Wang Bai-Gen; Xing Ding-Yu

    2011-01-01

    A single-molecule magnet (SMM)coupled to two normal metallic electrodes can both switch spin-up and spindown electronic currents within two different windows of SMM gate voltage. Such spin current switching in the SMM tunnel junction arises from spin-selected single electron resonant tunneling via the lowest unoccupied molecular orbit of the SMM. Since it is not magnetically controlled but all-electrically controlled, the proposed spin current switching effect may have potential applications in future spintronics.

  15. Negative tunnelling magnetoresistance in spin filtering magnetic junctions with spin-orbit coupling

    Institute of Scientific and Technical Information of China (English)

    Li Yun

    2011-01-01

    We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer-Büttiker formalism and taking into account the spin-orbit coupling (SOC). It is shown that spin-flip scattering induced by SOC is stronger in parallel alignment of magnetization of the ferromegnet barrier (FB) and the ferromagnetic electrode than that in antiparallel case. The increase of negative tunnelling magnetoresistance with bias is in agreement with recent experimental observation.

  16. Spin-glass behavior in zero magnetic field using tunnel resistance

    Energy Technology Data Exchange (ETDEWEB)

    Takeuchi, Y. [Department of Applied Physics and Physico-Infomatics, Faculty of Science and Technology, Keio University, Yokohama 223-8522 (Japan)]. E-mail: takeuchi@az.appi.keio.ac.jp; Komatsu, K. [Department of Applied Physics and Physico-Infomatics, Faculty of Science and Technology, Keio University, Yokohama 223-8522 (Japan); Maki, H. [Department of Applied Physics and Physico-Infomatics, Faculty of Science and Technology, Keio University, Yokohama 223-8522 (Japan); Taniyama, T. [Materials and Structures Laboratory, Tokyo Institute of Technology, 4529 Nagatsuta, Midori, Yokohama 226-8503 (Japan); Sato, T. [Department of Applied Physics and Physico-Infomatics, Faculty of Science and Technology, Keio University, Yokohama 223-8522 (Japan)

    2007-03-15

    The measurement of spin glass in zero magnetic field is essential to investigate the intrinsic nature of spin glass. We pay attention to tunnel resistance between spin-glass layers. The temperature dependence of tunnel resistance between spin-glass layers with the structure of AgMn/Al{sub 2}O{sub 3}/AgMn was measured, and was compared with that of Al/Al{sub 2}O{sub 3}/AgMn. For the junction of AgMn/Al{sub 2}O{sub 3}/AgMn, tunnel resistance shows a peak around the spin-glass transition temperature, but no peak was observed for the junction of Al/Al{sub 2}O{sub 3}/AgMn. The results indicate that the magnetic correlation between spin-glass layers is reflected to tunnel resistance. The singularity of the tunnel resistance between spin-glass layers is discussed by the droplet theory.

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

    Science.gov (United States)

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

    2016-06-01

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

  18. The need for control of magnetic parameters for energy efficient performance of magnetic tunnel junctions

    Science.gov (United States)

    Farhat, I. A. H.; Gale, E.; Alpha, C.; Isakovic, A. F.

    2017-07-01

    Optimizing energy performance of Magnetic Tunnel Junctions (MTJs) is the key for embedding Spin Transfer Torque-Random Access Memory (STT-RAM) in low power circuits. Due to the complex interdependencies of the parameters and variables of the device operating energy, it is important to analyse parameters with most effective control of MTJ power. The impact of threshold current density, Jco , on the energy and the impact of HK on Jco are studied analytically, following the expressions that stem from Landau-Lifshitz-Gilbert-Slonczewski (LLGS-STT) model. In addition, the impact of other magnetic material parameters, such as Ms , and geometric parameters such as tfree and λ is discussed. Device modelling study was conducted to analyse the impact at the circuit level. Nano-magnetism simulation based on NMAGTM package was conducted to analyse the impact of controlling HK on the switching dynamics of the film.

  19. The importance of Fe surface states for spintronic devices based on magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Chantis, Athanasios N [Los Alamos National Laboratory

    2008-01-01

    In this article we give a review of our recent theoretical studies of the influence of Fe(001) surface (interface) states on spin-polarized electron transport across magnetic tunnel junctions with Fe electrodes. We show that minority-spin surface (interface) states are responsible for at least two effects which are important for spin electronics. First, they can produce a sizable tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a single Fe electrode. The effect is driven by a Rashba shift of the resonant surface band when the magnetization changes direction. This can introduce a new class of spintronic devices, namely, tunneling magnetoresistance junctions with a single ferromagnetic electrode. Second, in Fe/GaAs(001) magnetic tunnel junctions minority-spin interface states produce a strong dependence of the tunneling current spin polarization on applied electrical bias. A dramatic sign reversal within a voltage range of just a few tenths of an eV is predicted. This explains the observed sign reversal of spin polarization in recent experiments of electrical spin injection in Fe/GaAs(001) and related reversal of tunneling magnetoresistance through vertical Fe/GaAs/Fe trilayers.

  20. Realistic tunnelling states for the magnetic effects in non-metallic real glasses

    Science.gov (United States)

    Jug, Giancarlo; Bonfanti, Silvia; Kob, Walter

    2016-03-01

    The discovery of magnetic and compositional effects in the low-temperature properties of multi-component glasses has prompted the need to extend the standard two-level systems (2LSs) tunnelling model. A possible extension assumes that a subset of tunnelling quasi-particles is moving in a three-welled potential (TWP) associated with the ubiquitous inhomogeneities of the disordered atomic structure of the glass. We show that within an alternative, cellular description of the intermediate-range atomic structure of glasses the tunnelling TWP can be fully justified. We then review how the experimentally discovered magnetic effects can be explained within the approach where only localized atomistic tunnelling 2LSs and quasi-particles tunnelling in TWPs are allowed. We discuss the origin of the magnetic effects in the heat capacity, dielectric constant (real and imaginary parts), polarization echo and SQUID magnetization in several glassy systems. We conclude by commenting on a strategy to reveal the mentioned tunnelling states (2LSs and TWPs) by means of atomistic computer simulations and discuss the microscopic nature of the tunnelling states in the context of the potential energy landscape of glass-forming systems

  1. Inelastic electron tunneling spectroscopy of CoFeB/ MgO/ CoFeB based magnetic tunnel junctions in high magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Walter, Marvin; Zbarskyy, Vladyslav; Muenzenberg, Markus [I. Phys. Inst., Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Seibt, Michael [IV. Phys. Inst., Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Drewello, Volker; Schaefers, Markus; Reiss, Guenter; Thomas, Andy [Bielefeld University, Physics Department, 33501 Bielefeld (Germany)

    2010-07-01

    Magnetic tunnel junctions (MTJs) showing a high tunnel magnetoresistance (TMR) are important for the fabrication of MRAM devices when combined with current induced switching. We discuss inelastic electron tunneling spectroscopy (IETS) measurements on CoFeB/MgO/CoFeB magnetic tunnel junctions. The junctions are prepared by means of magnetron sputtering of CoFeB and e-beam evaporation of stoichiometric MgO. Structuring of the multilayer is done using a photolithography process and Argon ion-milling. The IETS measurements are carried out at low temperatures down to 4.2 K, high magnetic fields up to 9 T and in parallel as well as antiparallel electrode configuration in order to distinguish between different kind of excitations such as e.g. magnons and phonons. Furthermore, oxygen vacancies in the MgO barrier are controlled through variation of the sample temperature during e-beam growth to investigate the influences of these vacancies on the tunneling spectra of MTJs.

  2. Enhanced annealing stability and perpendicular magnetic anisotropy in perpendicular magnetic tunnel junctions using W layer

    Science.gov (United States)

    Chatterjee, Jyotirmoy; Sousa, Ricardo C.; Perrissin, Nicolas; Auffret, Stéphane; Ducruet, Clarisse; Dieny, Bernard

    2017-05-01

    The magnetic properties of the perpendicular storage electrode (buffer/MgO/FeCoB/Cap) were studied as a function of annealing temperature by replacing Ta with W and W/Ta cap layers with variable thicknesses. W in the cap boosts up the annealing stability and increases the effective perpendicular anisotropy by 30% compared to the Ta cap. Correspondingly, an increase in the FeCoB critical thickness characterizing the transition from perpendicular to in-plane anisotropy was observed. Thicker W layer in the W(t)/Ta 1 nm cap layer makes the storage electrode highly robust against annealing up to 570 °C. The stiffening of the overall stack resulting from the W insertion due to its very high melting temperature seems to be the key mechanism behind the extremely high thermal robustness. The Gilbert damping constant of FeCoB with the W/Ta cap was found to be lower when compared with the Ta cap and stable with annealing. The evolution of the magnetic properties of bottom pinned perpendicular magnetic tunnel junctions (p-MTJ) stack with the W2/Ta1 nm cap layer shows back-end-of-line compatibility with increasing tunnel magnetoresistance up to the annealing temperature of 425 °C. The pMTJ thermal budget is limited by the synthetic antiferromagnetic hard layer which is stable up to 425 °C annealing temperature while the storage layer is stable up to 455 °C.

  3. Demonstration of the Potential of Magnetic Tunnel Junctions for a Universal RAM Technology

    Science.gov (United States)

    Gallagher, William J.

    2000-03-01

    Over the past four years, tunnel junctions with magnetic electrodes have emerged as promising devices for future magnetoresistive sensing and for information storage. This talk will review advances in these devices, focusing particularly on the use of magnetic tunnel junctions for magnetic random access memory (MRAM). Exchange-biased versions of magnetic tunnel junctions (MTJs) in particular will be shown to have useful properties for forming magnetic memory storage elements in a novel cross-point architecture. Exchange-biased MTJ elements have been made with areas as small as 0.1 square microns and have shown magnetoresistance values exceeding 40 The potential of exchange-biased MTJs for MRAM has been most seriously explored in a demonstration experiment involving the integration of 0.25 micron CMOS technology with a special magnetic tunnel junction "back end." The magnetic back end is based upon multi-layer magnetic tunnel junction growth technology which was developed using research-scale equipment and one-inch size substrates. For the demonstration, the CMOS wafers processed through two metal layers were cut into one-inch squares for depositions of bottom-pinned exchange-biased magnetic tunnel junctions. The samples were then processed through four additional lithographic levels to complete the circuits. The demonstration focused attention on a number of processing and device issues that were addressed successfully enough that key performance aspects of MTJ MRAM were demonstrated in 1 K bit arrays, including reads and writes in less than 10 ns and nonvolatility. While other key issues remain to be addressed, these results suggest that MTJ MRAM might simultaneously provide much of the functionality now provided separately by SRAM, DRAM, and NVRAM.

  4. Magnetic fingerprint of individual Fe4 molecular magnets under compression by a scanning tunnelling microscope.

    Science.gov (United States)

    Burgess, Jacob A J; Malavolti, Luigi; Lanzilotto, Valeria; Mannini, Matteo; Yan, Shichao; Ninova, Silviya; Totti, Federico; Rolf-Pissarczyk, Steffen; Cornia, Andrea; Sessoli, Roberta; Loth, Sebastian

    2015-01-01

    Single-molecule magnets (SMMs) present a promising avenue to develop spintronic technologies. Addressing individual molecules with electrical leads in SMM-based spintronic devices remains a ubiquitous challenge: interactions with metallic electrodes can drastically modify the SMM's properties by charge transfer or through changes in the molecular structure. Here, we probe electrical transport through individual Fe4 SMMs using a scanning tunnelling microscope at 0.5 K. Correlation of topographic and spectroscopic information permits identification of the spin excitation fingerprint of intact Fe4 molecules. Building from this, we find that the exchange coupling strength within the molecule's magnetic core is significantly enhanced. First-principles calculations support the conclusion that this is the result of confinement of the molecule in the two-contact junction formed by the microscope tip and the sample surface.

  5. Magnetic fingerprint of individual Fe4 molecular magnets under compression by a scanning tunnelling microscope

    Science.gov (United States)

    Burgess, Jacob A.J.; Malavolti, Luigi; Lanzilotto, Valeria; Mannini, Matteo; Yan, Shichao; Ninova, Silviya; Totti, Federico; Rolf-Pissarczyk, Steffen; Cornia, Andrea; Sessoli, Roberta; Loth, Sebastian

    2015-01-01

    Single-molecule magnets (SMMs) present a promising avenue to develop spintronic technologies. Addressing individual molecules with electrical leads in SMM-based spintronic devices remains a ubiquitous challenge: interactions with metallic electrodes can drastically modify the SMM's properties by charge transfer or through changes in the molecular structure. Here, we probe electrical transport through individual Fe4 SMMs using a scanning tunnelling microscope at 0.5 K. Correlation of topographic and spectroscopic information permits identification of the spin excitation fingerprint of intact Fe4 molecules. Building from this, we find that the exchange coupling strength within the molecule's magnetic core is significantly enhanced. First-principles calculations support the conclusion that this is the result of confinement of the molecule in the two-contact junction formed by the microscope tip and the sample surface. PMID:26359203

  6. Detection of HIV-1 antigen based on magnetic tunnel junction sensor and magnetic nanoparticles

    CERN Document Server

    Li, L; Zhou, Y; Pong, P W T

    2016-01-01

    In recent years, it is evidenced that the individuals newly infected HIV are transmitting the virus prior to knowing their HIV status. Identifying individuals that are early in infection with HIV antibody negative (window period) remains problematic. In the newly infected individuals, HIV antigen p24 is usually present in their serum or plasma 7-10 days before the HIV antibody. After antibody production initiates, the p24 antigen is bound into immune complexes. That means the detectable p24 antigens in serum/plasma are short-lived, and their amount is in the pg/ml range. Thus, a rapid quantitative bio-detection system with high-sensitivity is required to achieve early disease diagnosis. Magnetoresistive (MR) biosensor with ultra-high sensitivity possesses great potential in this area. In this study, a p24 detection assay using MgO-based magnetic tunnel junction (MTJ) sensor and 20-nm magnetic nanoparticles is reported.

  7. TRANSPORT AND INSTALLATION OF CRYO-MAGNETS IN CERN'S LARGE HADRON COLLIDER TUNNEL

    CERN Document Server

    Artoos, K; Coin, A; Gielen, M; Hauviller, Claude; Kershaw, K

    2004-01-01

    The arcs of the Large Hadron Collider (LHC) will contain around 1700 main superconducting dipoles and quadrupoles. The long and heavy magnets are supported on fragile composite support posts inside a cryostat to reduce the heat in-leak to the magnets' super fluid helium bath. The presence of fragile components and the need to avoid geometry changes make the cryo-magnets very difficult to handle and transport. The transport and installation of the LHC cryo-magnets in the LEP tunnels originally designed for smaller, lighter LEP magnets has required development of completely new handling solutions. The paper explains the constraints imposed by the cryo-magnet characteristics, the existing tunnel infrastructure and schedule considerations. The development and realisation of transport and handling solutions are described, starting from conceptual design, through manufacture and testing to the installation of the first cryo-magnet. Integration studies to verify and reserve space needed for manoeuvre and the prepara...

  8. Modeling of switching energy of magnetic tunnel junction devices with tilted magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Surawanitkun, C. [Science and Technology Program, Nongkhai Campus, Khon Kaen University, Nongkhai 43000 (Thailand); Kaewrawang, A. [KKU-Seagate Cooperation Research Laboratory, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002 (Thailand); Siritaratiwat, A., E-mail: apirat@kku.ac.th [KKU-Seagate Cooperation Research Laboratory, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002 (Thailand); Kruesubthaworn, A. [Science and Technology Program, Nongkhai Campus, Khon Kaen University, Nongkhai 43000 (Thailand); Sivaratana, R. [Seagate Technology, 1627, Teparak, Samutprakarn 10200 (Thailand); Jutong, N. [Institute of Physics, University of Augsburg, 86135 Augsburg (Germany); Mewes, C.K.A.; Mewes, T. [Department of Physics & Astronomy, MINT Center, University of Alabama, Tuscaloosa, AL 35487 (United States)

    2015-05-01

    For spin transfer torque (STT), the switching energy and thermal stability of magnetic tunnel junctions (MTJ) bits utilized in memory devices are important factors that have to be considered simultaneously. In this article, we examined the minimum energy for STT induced magnetization switching in MTJ devices for different in-plane angles of the magnetization in the free layer and the pinned layer with respect to the major axis of the elliptical cylinder of the cell. Simulations were performed by comparing the analytical solution with macrospin and full micromagnetic calculations. The results show good agreement of the switching energy calculated by using the three approaches for different initial angles of the magnetization of the free layer. Also, the low-energy location specifies the suitable value of both time and current in order to reduce the heat effect during the switching process. - Highlights: • Switching energy model was firstly examined with tiled magnetization in STT-RAM. • Simulation was performed by analytical solution, macrospin and micromagnetic models. • Low energy results from three models show agreement for tilt angle in free layer. • We also found an optimal tilt angle of the pinned layer. • Low-energy location specifies the suitable switching location to reduce heat effect.

  9. Spin-transfer torque and specific features of magnetic-state switching in vacuum tunnel nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Demin, G. D., E-mail: gddemin@gmail.com; Popkov, A. F.; Dyuzhev, N. A. [National Research University of Electronic Technology “MIET” (Russian Federation)

    2015-12-15

    The specific features of spin-transfer torque in vacuum tunnel structures with magnetic electrodes are investigated using the quasi-classical Sommerfeld model of electron conductivity, which takes into account the exchange splitting of the spin energy subbands of free electrons. Using the calculated voltage dependences of the transferred torques for a tunnel structure with cobalt electrodes and noncollinear magnetic moments in the electrodes, diagrams of stable spin states on the current–field parameter plane in the in-plane geometry of the initial magnetization are obtained.

  10. A first dipole magnet was delivered to its final location in the LHC tunnel (1)

    CERN Multimedia

    2005-01-01

    On 7 March at 2.00 p.m., the first 35-tonne dipole magnet was lowered down through the PMI2 shaft, reaching the floor of the TI2 transfer tunnel thirty minutes later. The magnet was transported to its final location between Points 8 and 1 by a specially designed vehicle.

  11. Phonon-assisted and magnetic field induced Kondo tunneling in single molecular devices

    Energy Technology Data Exchange (ETDEWEB)

    Kikoin, K [School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Kiselev, M N [The Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)

    2007-12-15

    We consider the Kondo tunneling induced by multiphonon emission/absorption processes in magnetic molecular complexes with low-energy singlet-triplet spin gap and show that the number of assisting phonons may be changed by varying the Zeeman splitting of excited triplet state. As a result, the structure of multiphonon Kondo resonances may be scanned by means of magnetic field tuning.

  12. Static properties of small Josephson tunnel junctions in a transverse magnetic field

    DEFF Research Database (Denmark)

    Monaco, R.; Aarøe, Morten; Mygind, Jesper;

    2008-01-01

    The magnetic field distribution in the barrier of small planar Josephson tunnel junctions is numerically simulated in the case when an external magnetic field is applied perpendicular to the barrier plane. The simulations allow for heuristic analytical solutions for the Josephson static phase pro...

  13. Magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy

    Science.gov (United States)

    Ning, Keyu; Liu, Houfang; Ju, Zhenyi; Fang, Chi; Wan, Caihua; Cheng, Jinglei; Liu, Xiao; Li, Linsen; Feng, Jiafeng; Wei, Hongxiang; Han, Xiufeng; Yang, Yi; Ren, Tian-Ling

    2017-01-01

    As one invigorated filed of spin caloritronics combining with spin, charge and heat current, the magneto-Seebeck effect has been experimentally and theoretically studied in spin tunneling thin films and nanostructures. Here we analyze the tunnel magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy (p-MTJs) under various measurement temperatures. The large tunnel magneto-Seebeck (TMS) ratio up to -838.8% for p-MTJs at 200 K is achieved, with Seebeck coefficient S in parallel and antiparallel states of 6.7 mV/K and 62.9 mV/K, respectively. The temperature dependence of the tunnel magneto-Seebeck can be attributed to the contributing transmission function and electron states at the interface between CoFeB electrode and MgO barrier.

  14. Magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy

    Directory of Open Access Journals (Sweden)

    Keyu Ning

    2017-01-01

    Full Text Available As one invigorated filed of spin caloritronics combining with spin, charge and heat current, the magneto-Seebeck effect has been experimentally and theoretically studied in spin tunneling thin films and nanostructures. Here we analyze the tunnel magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy (p-MTJs under various measurement temperatures. The large tunnel magneto-Seebeck (TMS ratio up to −838.8% for p-MTJs at 200 K is achieved, with Seebeck coefficient S in parallel and antiparallel states of 6.7 mV/K and 62.9 mV/K, respectively. The temperature dependence of the tunnel magneto-Seebeck can be attributed to the contributing transmission function and electron states at the interface between CoFeB electrode and MgO barrier.

  15. Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

    DEFF Research Database (Denmark)

    Grove-Rasmussen, Kasper; Grap, S.; Paaske, Jens;

    2012-01-01

    By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level...... renormalization. By comparison to a one- and two-shell model, this is shown to be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel renormalization....

  16. Electrical switching in Fe /Cr/MgO/Fe magnetic tunnel junctions

    Science.gov (United States)

    Halley, D.; Majjad, H.; Bowen, M.; Najjari, N.; Henry, Y.; Ulhaq-Bouillet, C.; Weber, W.; Bertoni, G.; Verbeeck, J.; Van Tendeloo, G.

    2008-05-01

    Hysteretic resistance switching is observed in epitaxial Fe /Cr/MgO/Fe magnetic tunnel junctions under bias voltage cycling between negative and positive values of about 1V. The junctions switch back and forth between high- and low-resistance states, both of which depend on the device bias history. A linear dependence is found between the magnitude of the tunnel magnetoresistance and the crafted resistance of the junctions. To explain these results, a model is proposed that considers electron transport both by elastic tunneling and by defect-assisted transmission.

  17. Influence of External Magnetic Fields on Tunneling of Spin-1 Bose Condensate

    Institute of Scientific and Technical Information of China (English)

    YU Zhao-Xian; JIAO Zhi-Yong; SUN Jin-Zuo

    2005-01-01

    In this letter, we have studied the influence of the external magnetic fields on tunneling of the spin-1 Bose condensate. We find that the population transfer between spin-0 and spin-±1 exhibits the step structure under the external cosinusoidal magnetic field and a combination of static and cosinusoidal one, respectively. Compared with the longitudinal component of the external magnetic field, the smaller the transverse component of the magnetic field is, the larger the time scale of exhibiting the step structure does. The tunneling current may exhibit periodically oscillation behavior when the ratio of the transverse component of the magnetic field is smaller than that of the longitudinal component, otherwise it exhibits a damply oscillating behavior. This means that the dynamical spin localization can be adjusted by the external magnetic fields.

  18. Electrical control of memristance and magnetoresistance in oxide magnetic tunnel junctions

    KAUST Repository

    Zhang, Kun

    2015-01-01

    Electric-field control of magnetic and transport properties of magnetic tunnel junctions has promising applications in spintronics. Here, we experimentally demonstrate a reversible electrical manipulation of memristance, magnetoresistance, and exchange bias in Co/CoO–ZnO/Co magnetic tunnel junctions, which enables the realization of four nonvolatile resistance states. Moreover, greatly enhanced tunneling magnetoresistance of 68% was observed due to the enhanced spin polarization of the bottom Co/CoO interface. The ab initio calculations further indicate that the spin polarization of the Co/CoO interface is as high as 73% near the Fermi level and plenty of oxygen vacancies can induce metal–insulator transition of the CoO1−v layer. Thus, the electrical manipulation mechanism on the memristance, magnetoresistance and exchange bias can be attributed to the electric-field-driven migration of oxygen ions/vacancies between very thin CoO and ZnO layers.

  19. Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

    Energy Technology Data Exchange (ETDEWEB)

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Kersell, Heath; Chang, Hao [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rosenmann, Daniel; Miller, Dean; Freeland, John W. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hla, Saw-Wai [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rose, Volker, E-mail: vrose@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

    2016-01-28

    A tunneling smart tip of a synchrotron X-ray scanning tunneling microscope provides simultaneously localized topographic, elemental and magnetic information. Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L{sub 2,3}-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

  20. High resolution imaging of tunnels by magnetic resonance neurography

    Energy Technology Data Exchange (ETDEWEB)

    Subhawong, Ty K.; Thawait, Shrey K.; Machado, Antonio J.; Carrino, John A.; Chhabra, Avneesh [Johns Hopkins Hospital, The Russell H. Morgan Department of Radiology and Radiological Science, Baltimore, MD (United States); Wang, Kenneth C. [Baltimore VA Medical Center, Department of Radiology, Baltimore, MD (United States); Williams, Eric H. [Dellon Institute for Peripheral Nerve Surgery, Towson, MD (United States); Hashemi, Shahreyar Shar [Johns Hopkins Hospital, Division of Plastic and Reconstructive Surgery, Baltimore, MD (United States)

    2012-01-15

    Peripheral nerves often traverse confined fibro-osseous and fibro-muscular tunnels in the extremities, where they are particularly vulnerable to entrapment and compressive neuropathy. This gives rise to various tunnel syndromes, characterized by distinct patterns of muscular weakness and sensory deficits. This article focuses on several upper and lower extremity tunnels, in which direct visualization of the normal and abnormal nerve in question is possible with high resolution 3T MR neurography (MRN). MRN can also serve as a useful adjunct to clinical and electrophysiologic exams by discriminating adhesive lesions (perineural scar) from compressive lesions (such as tumor, ganglion, hypertrophic callous, or anomalous muscles) responsible for symptoms, thereby guiding appropriate treatment. (orig.)

  1. High resolution imaging of tunnels by magnetic resonance neurography

    Science.gov (United States)

    Wang, Kenneth C.; Thawait, Shrey K.; Williams, Eric H.; Hashemi, Shahreyar Shar; Machado, Antonio J.; Carrino, John A.; Chhabra, Avneesh

    2011-01-01

    Peripheral nerves often traverse confined fibro-osseous and fibro-muscular tunnels in the extremities, where they are particularly vulnerable to entrapment and compressive neuropathy. This gives rise to various tunnel syndromes, characterized by distinct patterns of muscular weakness and sensory deficits. This article focuses on several upper and lower extremity tunnels, in which direct visualization of the normal and abnormal nerve in question is possible with high resolution 3T MR neurography (MRN). MRN can also serve as a useful adjunct to clinical and electrophysiologic exams by discriminating adhesive lesions (perineural scar) from compressive lesions (such as tumor, ganglion, hypertrophic callous, or anomalous muscles) responsible for symptoms, thereby guiding appropriate treatment. PMID:21479520

  2. A 4-fold-symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy and tunnel magnetoresistance.

    Science.gov (United States)

    Wen, Zhenchao; Sukegawa, Hiroaki; Furubayashi, Takao; Koo, Jungwoo; Inomata, Koichiro; Mitani, Seiji; Hadorn, Jason Paul; Ohkubo, Tadakatsu; Hono, Kazuhiro

    2014-10-08

    A 4-fold-symmetry hexagonal Ru emerging in epitaxial MgO/Ru/Co2 FeAl/MgO heterostructures is reported, in which an approximately Ru(022¯3) growth attributes to the lattice matching between MgO, Ru, and Co2 FeAl. Perpendicular magnetic anisotropy of the Co2 FeAl/MgO interface is substantially enhanced. The magnetic tunnel junctions (MTJs) incorporating this structure give rise to the largest tunnel magnetoresistance for perpendicular MTJs using low damping Heusler alloys.

  3. Magnetic Tunnel Junctions Incorporating a Near-Zero-Moment Ferromagnetic Semiconductor

    Science.gov (United States)

    Warring, H.; Trodahl, H. J.; Plank, N. O. V.; Natali, F.; Granville, S.; Ruck, B. J.

    2016-10-01

    We present a fully semiconductor-based magnetic tunnel junction that uses spin-orbit coupled materials made of intrinsic ferromagnetic semiconductors. Unlike more common approaches, one of the electrodes consists of a near-zero magnetic-moment ferromagnetic semiconductor, samarium nitride, with the other electrode composed of the more conventional ferromagnetic semiconductor gadolinium nitride. Fabricated tunnel junctions show a magnetoresistance as high as 200%, implying strong spin polarization in both electrodes. In contrast to conventional tunnel junctions, the resistance is largest at high fields, a direct result of the orbital-dominant magnetization in samarium nitride that requires that the spin in this electrode must align opposite to that in the gadolinium nitride when the magnetization is saturated. The magnetoresistance at intermediate fields is controlled by the formation of a twisted magnetization phase in the samarium nitride, a direct result of the orbital-dominant ferromagnetism. Thus, an alternative type of functionality can be brought to magnetic tunnel junctions by the use of different electrode materials, in contrast to the usual focus on tuning the barrier properties.

  4. Novel modeling and dynamic simulation of magnetic tunnel junctions for spintronic sensor development

    Science.gov (United States)

    Ji, Yu; Liu, Jie; Yang, Chunsheng

    2017-01-01

    Spintronic magnetic sensors with the integration of magnetic materials and microstructures have been enabling people to make use of the electron spin and charge properties in many applications. The high demand for such sensors has in turn spurred the technology developments in both novel materials and their atomic-level controls. Few works, however, have been carried out and reported thus far in modeling and simulation of these spintronic magnetic sensing units based on magnetic tunnel junction (MTJ) technology. Accordingly, this paper proposes a novel modeling approach as well as an iterative simulation methodology for MTJs. A more comprehensive electrical tunneling model is established for better interpreting the conductance and current generated by the electron tunneling, and this model can also facilitate the iterative simulation of the micromagnetic dynamics. Given the improved tunneling model as well as the updated dynamic simulation, the electric characteristics of an MTJ with an external magnetic field can be conveniently computed, which provides a reliable benchmark for the future development of novel spintronic magnetic sensors.

  5. Backhopping effect in magnetic tunnel junctions: Comparison between theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Skowroński, Witold, E-mail: skowron@agh.edu.pl; Wrona, Jerzy; Stobiecki, Tomasz [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Krakow (Poland); Ogrodnik, Piotr, E-mail: piotrogr@if.pw.edu.pl [Faculty of Physics, Warsaw University of Technology, Ul. Koszykowa 75, 00-662 Warsaw (Poland); Institute of Molecular Physics, Polish Academy of Sciences, Ul. Smoluchowskiego 17, 60-179 Poznań (Poland); Świrkowicz, Renata [Faculty of Physics, Warsaw University of Technology, Ul. Koszykowa 75, 00-662 Warsaw (Poland); Barnaś, Józef [Institute of Molecular Physics, Polish Academy of Sciences, Ul. Smoluchowskiego 17, 60-179 Poznań (Poland); Reiss, Günter [Thin Films and Physics of Nanostructures, Bielefeld University, 33615 Bielefeld (Germany); Dijken, Sebastiaan van [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland)

    2013-12-21

    We report on magnetic switching and backhopping effects due to spin-transfer-torque in magnetic tunnel junctions. Experimental data on current-induced switching in junctions with a MgO tunnel barrier reveal random back-and-forth switching between magnetization states, which appears when the current direction favors the parallel magnetic configuration. The effect depends on the barrier thickness t{sub b} and is not observed in tunnel junctions with very thin MgO tunnel barriers, t{sub b} < 0.95 nm. The switching dependence on bias voltage and barrier thickness is explained in terms of the macrospin model, with the magnetization dynamics described by the modified Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the competition between in-plane and out-of-plane torque components can result in a non-deterministic switching behavior at high bias voltages, in agreement with experimental observations. When the barrier thickness is reduced, the overall coupling between the magnetic layers across the barrier becomes ferromagnetic, which suppresses the backhopping effect.

  6. Enhancement of thermal spin transfer torque by double-barrier magnetic tunnel junctions with a nonmagnetic metal spacer

    Science.gov (United States)

    Chen, C. H.; Tseng, P.; Yang, Y. Y.; Hsueh, W. J.

    2017-01-01

    Enhancement of thermal spin transfer torque in a double-barrier magnetic tunnel junction with a nonmagnetic-metal spacer is proposed in this study. The results indicate that, given the same temperature difference, thermal spin transfer torque and charge current density for the proposed double barrier magnetic tunnel junction configuration can be approximately twice as much as that of the traditional single-barrier magnetic tunnel junctions. This enhancement can be attributed to the resonant tunneling mechanism in the double-barrier structure.

  7. Field-tuned quantum tunneling of the magnetization

    NARCIS (Netherlands)

    García-Pablos, D.; García, N.; Raedt, H. De

    1998-01-01

    The response of the magnetization to a time-dependent applied magnetic field in single-spin models for uniaxial magnets is studied. We present staircase magnetization curves obtained from the numerically exact solution of the time-dependent Schrodinger equation. Steps are shown to correspond to fiel

  8. The Usefulness of the Preoperative Magnetic Resonance Imaging Findings in the Evaluation of Tarsal Tunnel Syndrome

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Hyun Jin; Lee, Sheen Woo; Jeong, Yu Mi; Choi, Hye Young; Kim, Hyung Sik [Dept. of Radiology, Gil Hospital, Gacheon University College of Medicine, Incheon (Korea, Republic of); Park, Hong Gi; Kwak, Ji Hoon [Dept. of Orthopedic Surgery, Gil Hospital, Gacheon University College of Medicine, Incheon (Korea, Republic of)

    2012-02-15

    The purpose of this study was to access the diverse conditions that lead to the clinical manifestations of tarsal tunnel syndrome and evaluate the usefulness of magnetic resonance imaging (MRI) in preoperative evaluation. Thirty-three patients who underwent ankle MRI and surgery under the impression of tarsal tunnel syndrome were retrospectively analyzed. The findings on ankle MRI were categorized into space occupying lesions within the tarsal tunnel, space occupying lesions of the tunnel wall, and non-space occupying lesions. Associated plantar muscle atrophy was also evaluated. Medical records were reviewed for correlation of nerve conduction velocity (NCV) and surgical findings. There were 21 space occupying lesions of the tarsal tunnel, and eight lesions of tarsal tunnel wall. There were three cases with accessory muscle, three with tarsal coalition, five with ganglion cysts, one neurogenic tumor, five flexor retinaculum hypertrophy, three varicose veins, and nine with tenosynovitis of the posterior tibialis, flexor digitorum longus, or flexor hallucis longus tendon. One patient was found to have a deltoid ligament sprain. Of the 32, eight patients experienced fatty atrophic change within any one of the foot muscles. NCV was positive in 79% of the MRI-positive lesions. MRI provides detailed information on ankle anatomy, which includes that of tarsal tunnel and beyond. Pathologic conditions that cause or mimic tarsal tunnel syndrome are well demonstrated. MRI can enhance surgical planning by indicating the extent of decompression required, and help with further patient management. Patients with tarsal tunnel syndrome can greatly benefit from preoperative MRI. However, it should be noted that not all cases with tarsal tunnel syndrome have MRI-demonstrable causes.

  9. Magnetic-field-induced suppression of tunnelling into a two-dimensional electron system

    Energy Technology Data Exchange (ETDEWEB)

    Reker, T.; Chung, Y.C.; Im, H.; Klipstein, P.C.; Nicholas, R.J. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford (United Kingdom); Shtrikman, Hadas [Braun Center for Submicron Research, Weizmann Institute of Science, Rehovot (Israel)

    2002-06-10

    Tunnelling between a three-dimensional emitter contact and a two-dimensional electron system (2DES) is studied in magnetic fields aligned perpendicular to the barriers of a double-barrier heterostructure. The differential conductance around the Fermi energy exhibits a magnetic-field-dependent pseudogap. This pseudogap is shown to be thermally activated and to depend on the two-dimensional electron density. We attribute this pseudogap to an extra energy that an electron tunnelling from the emitter into the 2DES has to overcome as a result of the correlated state of the 2DES. (author)

  10. Voltage-controlled spin selection in a magnetic resonant tunneling diode.

    Science.gov (United States)

    Slobodskyy, A; Gould, C; Slobodskyy, T; Becker, C R; Schmidt, G; Molenkamp, L W

    2003-06-20

    We have fabricated all II-VI semiconductor resonant tunneling diodes based on the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the quantum well, and studied their current-voltage characteristics. When subjected to an external magnetic field the resulting spin splitting of the levels in the quantum well leads to a splitting of the transmission resonance into two separate peaks. This is interpreted as evidence of tunneling transport through spin polarized levels, and could be the first step towards a voltage controlled spin filter.

  11. Tunneling effect of the spin-2 Bose condensate driven by external magnetic fields

    OpenAIRE

    Yu, Zhao-xian; Jiao, Zhi-yong

    2003-01-01

    In this paper, we have studied tunneling effect of the spin-2 Bose condensate driven by external magnetic field. We find that the population transfers among spin-0 and spin-$\\pm1$, spin-0 and spin-$\\pm2$ exhibit the step structure under the external cosinusoidal magnetic field respectively, but there do not exist step structure among spin-$\\pm1$ and spin-$\\pm2$. The tunneling current among spin-$\\pm1$ and spin-$\\pm2$ may exhibit periodically oscillation behavior, but among spin-0 and spin-$\\p...

  12. Three-dimensional integration technology of magnetic tunnel junctions for magnetoresistive random access memory application

    Science.gov (United States)

    Yakushiji, Kay; Takagi, Hideki; Watanabe, Naoya; Fukushima, Akio; Kikuchi, Katsuya; Kurashima, Yuuichi; Sugihara, Atsushi; Kubota, Hitoshi; Yuasa, Shinji

    2017-06-01

    Three-dimensional integration processes (based on direct wafer bonding and back-surface silicon removal) for magnetic tunnel junctions with perpendicular magnetization (p-MTJs) were developed. Perfect wafer bonding, namely, bonding without interfacial voids, and damageless silicon removal were successfully demonstrated by using very flat tantalum cap layers. Moreover, p-MTJ nanopillars subjected to these processes exhibited no degradation in magnetoresistance or spin-transfer-torque (STT) switching. Magnetoresistive random access memory (MRAM) technology incorporating these processes (direct wafer bonding and back-surface silicon removal) will make it possible to integrate epitaxial MTJs (with a single-crystal tunnel barrier) and ferromagnetic electrode layers (based on new materials).

  13. Tunnelling Radiation of Charged and Magnetized Massive Particles from BTZ Black Holes

    Institute of Scientific and Technical Information of China (English)

    HE Tang-Mei; ZHANG Jing-Yi

    2007-01-01

    We investigate the tunnelling radiation of charged and magnetized massive particles from a Ba(n)ados-TeitelboimZanelli (BTZ) black hole by extending the Parikh-Wilczek tunnelling framework. In order to calculate the emission rate,we reconstruct the electromagnetic field tensor and the Lagrangian of the field corresponding to the source with electric and magnetic charges,and treat the charges as an equivalent electric charge for simplicity in the later calculation.The result supports Parikh-Wilczek's conclusion,that is,the Hawking thermal radiation actually deviates from perfect thermality and agrees with an underlying unitary theory.

  14. Tetragonal Heusler-Like Mn-Ga Alloys Based Perpendicular Magnetic Tunnel Junctions

    Science.gov (United States)

    Ma, Qinli; Sugihara, Atsushi; Suzuki, Kazuya; Zhang, Xianmin; Miyazaki, Terunobu; Mizukami, Shigemi

    2014-10-01

    Films of the Mn-based tetragonal Heusler-like alloys, such as Mn-Ga, exhibit a large perpendicular magnetic anisotropy (PMA), small damping constant, small saturation magnetization and large spin polarizations. These properties are attractive for the application to the next generation high density spin-transfer-torque (STT) magnetic random access memory (STT-MRAM). We reviewed the structure, magnetic properties and Gilbert damping of the alloy films with large PMA, and the current status of research on tunnel magnetoresistance (TMR) in perpendicular magnetic tunnel junctions (p-MTJs) based on Mn-based tetragonal Heusler-like alloy electrode, and also discuss the issues for the application of those to STT-MRAM.

  15. Shot noise of the spin inelastic tunneling through a quantum dot with single molecule-magnet

    Institute of Scientific and Technical Information of China (English)

    Chang Bo; Liang Jiu-Qing

    2011-01-01

    We have studied the quantum fluctuations of inelastic spin-electron scattering in quantum dot with an embedded biaxial single molecule-magnet and particularly investigated the zero-frequency shot noise and Fano factor in different magnetic fields. It is found that the shot noise and Fano factor exhibit a stepwise behaviour as bias increases in the presence of interaction between the electron and molecule-magnet for a weak magnetic field. As magnetic field becomes strong, a dip is displayed in the shot-noise-bias curve due to the suppression of inelastic shot noise caused by the quantum tunneling of magnetisation. Because of the spontaneous inelastic tunneling at zero bias, a small shot noise occurs, which results in the case of Fano factor F > 1. Moreover, our results show that the sweeping speed can also influence the shot noise and Fano factor obviously.

  16. Magnetic tunnel junctions using Co/Pt multilayered free layers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Machida, K; Funabashi, N; Aoshima, K; Kuga, K; Kikuchi, H; Shimidzu, N [Science and Technology Research Labs., Japan Broadcasting Corp. (NHK), 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan); Furukawa, K; Nakayama, T [Department of Electrical Engineering, Tokyo Denki University, 2-2 Kandanishikicho, Chiyoda-ku, Tokyo 101-8457 (Japan); Ishibashi, T, E-mail: machida.k-ge@nhk.or.jp [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188 (Japan)

    2011-07-06

    Co/Pt multilayered films with perpendicular magnetic anisotropy have a large magneto-optical Kerr effect. To use the films with a submicron magneto-optical light modulator driven by spin transfer switching, we fabricated two types of magnetic tunnel junctions (MTJs) with Co/Pt multilayered films for the free layers. One is an fcc-based MTJ, another is a bcc-based MTJ with CoFeB/MgO/CoFeB junction. The fcc-based MTJ with a Ag buffer layer on the bottom electrode showed a large coercive force of the pinned layer, a large Kerr rotation angle of 0.3 degree in the free layer and a tunnel magnetoresistance (TMR) ratio of 3.8%. In the CoFeB/MgO/CoFeB junction, an X-ray diffraction pattern of an MgO layer showed a large MgO(002)-orientation. However, the TMR ratio was less than 3 %. An MTJ with a Ta buffer layer between the CoFeB layer and the Co/Pt multilayered films in the free layer was prepared. The Ta buffer was used to alleviate a lattice mismatch between bcc-CoFeB/MgO/CoFeB and fcc-Co/Pt multilayer. The peak intensity of the MgO(002)-orientation was increased up to 2 times. This result suggests that the crystalline texture of the bcc-CoFeB/MgO/CoFeB junction is strongly influenced by the fcc-Co/Pt multilayered films.

  17. CMOS Interface Circuits for Spin Tunneling Junction Based Magnetic Random Access Memories

    Energy Technology Data Exchange (ETDEWEB)

    Ganesh Saripalli

    2002-12-31

    Magneto resistive memories (MRAM) are non-volatile memories which use magnetic instead of electrical structures to store data. These memories, apart from being non-volatile, offer a possibility to achieve densities better than DRAMs and speeds faster than SRAMs. MRAMs could potentially replace all computer memory RAM technologies in use today, leading to future applications like instan-on computers and longer battery life for pervasive devices. Such rapid development was made possible due to the recent discovery of large magnetoresistance in Spin tunneling junction devices. Spin tunneling junctions (STJ) are composite structures consisting of a thin insulating layer sandwiched between two magnetic layers. This thesis research is targeted towards these spin tunneling junction based Magnetic memories. In any memory, some kind of an interface circuit is needed to read the logic states. In this thesis, four such circuits are proposed and designed for Magnetic memories (MRAM). These circuits interface to the Spin tunneling junctions and act as sense amplifiers to read their magnetic states. The physical structure and functional characteristics of these circuits are discussed in this thesis. Mismatch effects on the circuits and proper design techniques are also presented. To demonstrate the functionality of these interface structures, test circuits were designed and fabricated in TSMC 0.35{micro} CMOS process. Also circuits to characterize the process mismatches were fabricated and tested. These results were then used in Matlab programs to aid in design process and to predict interface circuit's yields.

  18. CMOS Interface Circuits for Spin Tunneling Junction Based Magnetic Random Access Memories

    Energy Technology Data Exchange (ETDEWEB)

    Saripalli, Ganesh [Iowa State Univ., Ames, IA (United States)

    2002-01-01

    Magneto resistive memories (MRAM) are non-volatile memories which use magnetic instead of electrical structures to store data. These memories, apart from being non-volatile, offer a possibility to achieve densities better than DRAMs and speeds faster than SRAMs. MRAMs could potentially replace all computer memory RAM technologies in use today, leading to future applications like instan-on computers and longer battery life for pervasive devices. Such rapid development was made possible due to the recent discovery of large magnetoresistance in Spin tunneling junction devices. Spin tunneling junctions (STJ) are composite structures consisting of a thin insulating layer sandwiched between two magnetic layers. This thesis research is targeted towards these spin tunneling junction based Magnetic memories. In any memory, some kind of an interface circuit is needed to read the logic states. In this thesis, four such circuits are proposed and designed for Magnetic memories (MRAM). These circuits interface to the Spin tunneling junctions and act as sense amplifiers to read their magnetic states. The physical structure and functional characteristics of these circuits are discussed in this thesis. Mismatch effects on the circuits and proper design techniques are also presented. To demonstrate the functionality of these interface structures, test circuits were designed and fabricated in TSMC 0.35μ CMOS process. Also circuits to characterize the process mismatches were fabricated and tested. These results were then used in Matlab programs to aid in design process and to predict interface circuit's yields.

  19. Coulomb and tunneling-coupled trilayer systems at zero magnetic field

    Science.gov (United States)

    Miravet, D.; Proetto, C. R.; Bolcatto, P. G.

    2016-02-01

    The ground-state electronic configuration of three coupled bidimensional electron gases has been determined using a variational Hartree-Fock approach, at zero magnetic field. The layers are Coulomb coupled, and tunneling is present between neighboring layers. In the limit of small separation between layers, the tunneling becomes the dominant energy contribution, while for large distance between layers the physics is driven by the Hartree electrostatic energy. Transition from tunneling to Hartree dominated physics is shifted towards larger layer separation values as the total bidimensional density of the trilayers decreases. The interlayer exchange stabilizes a "balanced" configuration, where the three layers are approximately equally occupied; most of the experiments are performed in the vicinity of this balanced configuration. Several ground-state configurations are a consequence of a delicate interplay between tunneling and intersubband exchange.

  20. Diffusion-weighted magnetic resonance imaging of the ulnar nerve in cubital tunnel syndrome.

    Science.gov (United States)

    Iba, K; Wada, T; Tamakawa, M; Aoki, M; Yamashita, T

    2010-01-01

    Diffusion-weighted images based on magnetic resonance reveal the microstructure of tissues by monitoring the random movement of water molecules. In this study, we investigated whether this new technique could visualize pathologic lesions on ulnar nerve in cubital tunnel. Six elbows in six healthy males without any symptoms and eleven elbows in ten patients with cubital tunnel syndrome underwent on diffusion-weighted MRI. No signal from the ulnar nerve was detected in normal subjects. Diffusion-weighted MRI revealed positive signals from the ulnar nerve in all of the eleven elbows with cubital tunnel syndrome. In contrast, conventional T2W-MRI revealed high signal intensity in eight elbows and low signal intensity in three elbows. Three elbows with low signal MRI showed normal nerve conduction velocity of the ulnar nerve. Diffusion-weighted MRI appears to be an attractive technique for diagnosis of cubital tunnel syndrome in its early stages which show normal electrophysiological and conventional MRI studies.

  1. Direct Observation of Tunnelling through 100-nm-Wide All Metal Magnetic Junction into Si

    Institute of Scientific and Technical Information of China (English)

    Nam n. KIM; WANG Ke-Qiang; ZHANG Yu; WANG Jian-Qing

    2008-01-01

    @@ Nanoscaled spin-dependent tunnelling lines were patterned on doped Si and studied for tunnelling from the SDT ferromagnetic layer through an insulating barrier into Si. The injection contacts have the form of long strips with width and separation, ranging from 100 nm to 2 μm, and are patterned using e-beam lithography. The measured Ⅰ-Ⅴ characteristics versus temperature (80 to 300 K) on the 100 nm scaled devices between the layered-magnetic metals and the semiconductor clearly showed ballistic tunnelling, with weak dependence on the temperature.This is qualitatively different, at elevated temperatures, from 2-μm-wide scaled-up spin-dependent tunnelling structures, where thermal-ionic emission was observed to dominate carrier transport.

  2. Time-dependent dielectric breakdown of MgO magnetic tunnel junctions and novel test method

    Science.gov (United States)

    Kim, Kyungjun; Choi, Chulmin; Oh, Youngtaek; Sukegawa, Hiroaki; Mitani, Seiji; Song, Yunheub

    2017-04-01

    Time-dependent dielectric breakdown (TDDB), which is used to measure reliability, depends on both the thickness of the tunnel barrier and bias voltage. In addition, the heat generated by self-heating in a magnetic tunneling junction (MTJ) affects TDDB. Therefore, we investigated TDDB with the self-heating effect for a MgO tunnel barrier with thicknesses of 1.1 and 1.2 nm by the constant voltage stress (CVS) method. Using the results of this experiment, we predicted a TDDB of 1.0 nm for the tunnel barrier. Also, we suggested the use of not only the CVS method, which is a common way of determining TDDB, but also the constant current stress (CCS) method, which compensates for the disadvantages of the CVS method.

  3. Large magnetocapacitance effect in magnetic tunnel junctions based on Debye-Fröhlich model

    Energy Technology Data Exchange (ETDEWEB)

    Kaiju, Hideo, E-mail: kaiju@es.hokudai.ac.jp; Takei, Masashi; Misawa, Takahiro; Nishii, Junji [Research Institute for Electronic Science, Hokkaido University, Sapporo, Hokkaido 001-0020 (Japan); Nagahama, Taro [School of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628 (Japan); Xiao, Gang [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States)

    2015-09-28

    The frequency dependence of tunneling magnetocapacitance (TMC) in magnetic tunnel junctions (MTJs) is investigated theoretically and experimentally. According to the calculation based on Debye-Fröhlich model combined with Julliere formula, the TMC ratio strongly depends on the frequency and it has the maximum peak at a specific frequency. The calculated frequency dependence of TMC is in good agreement with the experimental results obtained in MgO-based MTJs with a tunneling magnetoresistance (TMR) ratio of 108%, which exhibit a large TMC ratio of 155% at room temperature. This calculation also predicts that the TMC ratio can be as large as about 1000% for a spin polarization of 87%, while the TMR ratio is 623% for the same spin polarization. These theoretical and experimental findings provide a deeper understanding on AC spin-dependent transport in the MTJs and will open up wider opportunities for device applications, such as highly sensitive magnetic sensors and impedance-tunable devices.

  4. Magnetic Breakdown and Klein Tunneling in a Type-II Weyl Semimetal

    Science.gov (United States)

    O'Brien, T. E.; Diez, M.; Beenakker, C. W. J.

    2016-06-01

    The band structure of a type-II Weyl semimetal has pairs of electron and hole pockets that coexist over a range of energies and touch at a topologically protected conical point. We identify signatures of this Weyl point in the magnetic quantum oscillations of the density of states, observable in thermodynamic properties. Tunneling between the electron and hole pockets in a magnetic field is the momentum space counterpart of Klein tunneling at a p -n junction in real space. This magnetic breakdown happens at a characteristic field strength that vanishes when the Fermi level approaches the Weyl point. The topological distinction between connected and disconnected pairs of type-II Weyl cones can be distinguished by the qualitatively different dependence of the quantum oscillations on the direction of the magnetic field.

  5. Voltage-induced magnetization dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions

    Science.gov (United States)

    Miura, Katsuya; Yabuuchi, Shin; Yamada, Masaki; Ichimura, Masahiko; Rana, Bivas; Ogawa, Susumu; Takahashi, Hiromasa; Fukuma, Yasuhiro; Otani, Yoshichika

    2017-01-01

    Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (Vrec) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions. PMID:28209976

  6. Voltage-induced magnetization dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions

    Science.gov (United States)

    Miura, Katsuya; Yabuuchi, Shin; Yamada, Masaki; Ichimura, Masahiko; Rana, Bivas; Ogawa, Susumu; Takahashi, Hiromasa; Fukuma, Yasuhiro; Otani, Yoshichika

    2017-02-01

    Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (Vrec) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions.

  7. All-optical detection of magnetization precession in tunnel junctions under applied voltage

    Science.gov (United States)

    Sasaki, Yuta; Suzuki, Kazuya; Sugihara, Atsushi; Kamimaki, Akira; Iihama, Satoshi; Ando, Yasuo; Mizukami, Shigemi

    2017-02-01

    An all-optical time-resolved magneto-optical Kerr effect measurement of a micron-sized tunnel junction with a CoFeB electrode was performed. The femtosecond (fs) laser-induced magnetization precession was clearly observed at various magnetic field angles. The frequency f and relaxation time τ of the magnetization precession varied with the voltage applied via a MgO barrier. The precession dynamics were in accordance with Kittel’s ferromagnetic resonance mode, and the voltage-induced changes in f and τ were well explained by the voltage-induced change in the perpendicular magnetic anisotropy of -36 fJ/Vm.

  8. Thermoelectricity and disorder of FeCo/MgO/FeCo magnetic tunnel junctions

    NARCIS (Netherlands)

    Wang, S.Z.; Xia, K.; Bauer, G.E.W.

    2014-01-01

    We compute the thermoelectric transport parameterized by the Seebeck coefficient and thermal/electric conductance of random-alloy FeCo/MgO/FeCo(001) magnetic tunnel junctions (MTJs) from first principles using a generalized Landauer-Büttiker formalism. The thermopower is found to be typically smalle

  9. Static properties of small Josephson tunnel junctions in an oblique magnetic field

    DEFF Research Database (Denmark)

    Monaco, Roberto; Aarøe, Morten; Mygind, Jesper;

    2009-01-01

    We have carried out a detailed experimental investigation of the static properties of planar Josephson tunnel junctions in presence of a uniform external magnetic field applied in an arbitrary orientation with respect to the barrier plane. We considered annular junctions, as well as rectangular j...

  10. Simultaneous topographic and elemental chemical and magnetic contrast in scanning tunneling microscopy

    Science.gov (United States)

    Rose, Volker; Preissner, Curt A; Hla, Saw-Wai; Wang, Kangkang; Rosenmann, Daniel

    2014-09-30

    A method and system for performing simultaneous topographic and elemental chemical and magnetic contrast analysis in a scanning, tunneling microscope. The method and system also includes nanofabricated coaxial multilayer tips with a nanoscale conducting apex and a programmable in-situ nanomanipulator to fabricate these tips and also to rotate tips controllably.

  11. Comparison of the magneto-Peltier and magneto-Seebeck effects in magnetic tunnel junctions

    NARCIS (Netherlands)

    Shan, J.; Dejene, F. K.; Leutenantsmeyer, J. C.; Flipse, J.; Munzenberg, M.; van Wees, B. J.

    2015-01-01

    Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction v

  12. Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Yang, G.; Li, D. L.; Wang, S. G., E-mail: Sgwang@iphy.ac.cn; Ma, Q. L.; Liang, S. H.; Wei, H. X.; Han, X. F. [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Hesjedal, T.; Ward, R. C. C. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Kohn, A.; Elkayam, A.; Tal, N. [Department of Materials Engineering and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Zhang, X.-G. [Department of Physics and Quantum Theory Project, University of Florida, Gainesville, Florida 32611 (United States); Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493 (United States)

    2015-02-28

    Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.

  13. Temperature and bias voltage dependence of Co/Pd multilayer-based magnetic tunnel junctions with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Kugler, Zoe, E-mail: zkugler@physik.uni-bielefeld.d [Bielefeld University, Department of Physics, Universitaetsstr. 25, 33615 Bielefeld (Germany); Drewello, Volker; Schaefers, Markus; Schmalhorst, Jan; Reiss, Guenter; Thomas, Andy [Bielefeld University, Department of Physics, Universitaetsstr. 25, 33615 Bielefeld (Germany)

    2011-01-15

    Temperature- and bias voltage-dependent transport measurements of magnetic tunnel junctions (MTJs) with perpendicularly magnetized Co/Pd electrodes are presented. Magnetization measurements of the Co/Pd multilayers are performed to characterize the electrodes. The effects of the Co layer thickness in the Co/Pd bilayers, the annealing temperature, the Co thickness at the MgO barrier interface, and the number of bilayers on the tunneling magneto resistance (TMR) effect are investigated. TMR-ratios of about 11% at room temperature and 18.5% at 13 K are measured and two well-defined switching fields are observed. The results are compared to measurements of MTJs with Co-Fe-B electrodes and in-plane anisotropy.

  14. Tunnel magnetoresistance in full-epitaxial magnetic tunnel junctions with a top electrode consisting of a perpendicularly magnetized D022-Mn3Ge film

    Science.gov (United States)

    Sugihara, Atsushi; Suzuki, Kazuya; Miyazaki, Terunobu; Mizukami, Shigemi

    2015-07-01

    We grew a magnetic tunnel junction (MTJ) with a top electrode consisting of a Mn3Ge film using a thin Co-Fe alloy film as a seed layer. X-ray diffraction showed that the Mn3Ge had (001)-oriented D022 structure epitaxially grown on an MgO(001) substrate. Magnetic hysteresis loops suggested that the D022-Mn3Ge film possessed perpendicular magnetic anisotropy. A magnetoresistance (MR) ratio of 11.3% was observed in the microfabricated MTJ at room temperature. The resistance-field curve suggested that the top-Co-Fe and D022-Mn3Ge layer are weakly coupled antiferromagnetically. The optimization of top-Co-Fe composition would improve MR ratio.

  15. Spin-wave thermal population as temperature probe in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Le Goff, A., E-mail: adrien.le-goff@u-psud.fr; Devolder, T. [Institut d' Electronique Fondamentale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); Nikitin, V. [SAMSUNG Electronics Corporation, 601 McCarthy Blvd Milpitas, California 95035 (United States)

    2016-07-14

    We study whether a direct measurement of the absolute temperature of a Magnetic Tunnel Junction (MTJ) can be performed using the high frequency electrical noise that it delivers under a finite voltage bias. Our method includes quasi-static hysteresis loop measurements of the MTJ, together with the field-dependence of its spin wave noise spectra. We rely on an analytical modeling of the spectra by assuming independent fluctuations of the different sub-systems of the tunnel junction that are described as macrospin fluctuators. We illustrate our method on perpendicularly magnetized MgO-based MTJs patterned in 50 × 100 nm{sup 2} nanopillars. We apply hard axis (in-plane) fields to let the magnetic thermal fluctuations yield finite conductance fluctuations of the MTJ. Instead of the free layer fluctuations that are observed to be affected by both spin-torque and temperature, we use the magnetization fluctuations of the sole reference layers. Their much stronger anisotropy and their much heavier damping render them essentially immune to spin-torque. We illustrate our method by determining current-induced heating of the perpendicularly magnetized tunnel junction at voltages similar to those used in spin-torque memory applications. The absolute temperature can be deduced with a precision of ±60 K, and we can exclude any substantial heating at the spin-torque switching voltage.

  16. Superfluidity enhanced by spin-flip tunnelling in the presence of a magnetic field

    Science.gov (United States)

    Zheng, Jun-Hui; Wang, Daw-Wei; Juzeliūnas, Gediminas

    2016-01-01

    It is well-known that when the magnetic field is stronger than a critical value, the spin imbalance can break the Cooper pairs of electrons and hence hinder the superconductivity in a spin-singlet channel. In a bilayer system of ultra-cold Fermi gases, however, we demonstrate that the critical value of the magnetic field at zero temperature can be significantly increased by including a spin-flip tunnelling, which opens a gap in the spin-triplet channel near the Fermi surface and hence reduces the influence of the effective magnetic field on the superfluidity. The phase transition also changes from first order to second order when the tunnelling exceeds a critical value. Considering a realistic experiment, this mechanism can be implemented by applying an intralayer Raman coupling between the spin states with a phase difference between the two layers. PMID:27633848

  17. Vector spin modeling for magnetic tunnel junctions with voltage dependent effects

    Energy Technology Data Exchange (ETDEWEB)

    Manipatruni, Sasikanth, E-mail: sasikanth.manipatruni@intel.com; Nikonov, Dmitri E.; Young, Ian A. [Exploratory Integrated Circuits, Components Research, Intel Corp., Hillsboro, Oregon 97124 (United States)

    2014-05-07

    Integration and co-design of CMOS and spin transfer devices requires accurate vector spin conduction modeling of magnetic tunnel junction (MTJ) devices. A physically realistic model of the MTJ should comprehend the spin torque dynamics of nanomagnet interacting with an injected vector spin current and the voltage dependent spin torque. Vector spin modeling allows for calculation of 3 component spin currents and potentials along with the charge currents/potentials in non-collinear magnetic systems. Here, we show 4-component vector spin conduction modeling of magnetic tunnel junction devices coupled with spin transfer torque in the nanomagnet. Nanomagnet dynamics, voltage dependent spin transport, and thermal noise are comprehended in a self-consistent fashion. We show comparison of the model with experimental magnetoresistance (MR) of MTJs and voltage degradation of MR with voltage. Proposed model enables MTJ circuit design that comprehends voltage dependent spin torque effects, switching error rates, spin degradation, and back hopping effects.

  18. Simulation of electric-field and spin-transfer-torque induced magnetization switching in perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiangli; Zhang, Zongzhi, E-mail: zzzhang@fudan.edu.cn [Department of Optical Science and Engineering, Shanghai Ultra-Precision Optical Engineering Center, Fudan University, Shanghai 200433 (China); Liu, Yaowen [School of Physical Science and Engineering, Tongji University, Shanghai 200092 (China); Jin, Q. Y. [State Key Laboratory of Precision Spectroscopy and Department of Physics, East China Normal University, Shanghai 200062 (China)

    2015-05-07

    Macrospin simulations are performed to model the magnetization switching driven by the combined action of electric-field and spin-polarized electric current (spin-transfer torque; STT) in MgO/CoFeB based magnetic tunnel junctions with interfacial perpendicular magnetic anisotropy. The results indicate that at low current case, the free layer magnetization shows a fast toggle-like switching, the final parallel or antiparallel magnetization state is determined by the electric-field effect, and the STT just helps or resists it to reach the final state depending on the current direction. However, with the increase of current strength, the contribution of STT effect gradually increases, which eventually achieves a deterministic magnetization switching state. Simulations further demonstrate that by appropriately tuning the parameters of applied electric-field and current the power consumption can be easily reduced by two orders of magnitude.

  19. Large influence of capping layers on tunnel magnetoresistance in CoFe/MgO/CoFe magnetic tunnel junctions

    CERN Document Server

    Zhou, Jiaqi; Wang, Yin; Peng, Shouzhong; Qiao, Junfeng; Su, Li; Zeng, Lang; Lei, Na; Zhang, Youguang; Bournel, Arnaud

    2016-01-01

    We report the first-principles theoretical investigations of the tunnel magnetoresistance(TMR) effect in the symmetric capping layer/CoFe(001)/MgO(001)/CoFe(001)/capping layer magnetic tunnel junctions(MTJs) with Ta, Hf and Ir used as capping layer materials. Spin-resolved conductance and TMR ratios are shown and it is found that the TMR ratio is sensitive to the capping layer material. The spin polarization of s state in Co atom at the CoFe/capping layer interface is presented to explain the influence on TMR ratio caused by different capping layers, and we can obtain a high spin polarization value and a giant TMR ratio when Ir is used, demonstrating that Ir is an ideal capping layer material. We also study the spin-polarized transport properties in the Brillouin zone. In the parallel condition, a central broad peak is found in the majority-spin channel due to the {\\Delta}1 state, while sharp transmission probability peaks at some k||-points appear in the minority-spin channel. The sharp peak phenomenon is at...

  20. Tunneling magnetoresistance in Fe{sub 3}Si/MgO/Fe{sub 3}Si(001) magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Tao, L. L.; Liang, S. H.; Liu, D. P.; Wei, H. X.; Han, X. F., E-mail: xfhan@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Wang, Jian [Department of Physics and the Center of Theoretical and Computational Physics, The University of Hong Kong, Hong Kong (China)

    2014-04-28

    We present a theoretical study of the tunneling magnetoresistance (TMR) and spin-polarized transport in Fe{sub 3}Si/MgO/Fe{sub 3}Si(001) magnetic tunnel junction (MTJ). It is found that the spin-polarized conductance and bias-dependent TMR ratios are rather sensitive to the structure of Fe{sub 3}Si electrode. From the symmetry analysis of the band structures, we found that there is no spin-polarized Δ{sub 1} symmetry bands crossing the Fermi level for the cubic Fe{sub 3}Si. In contrast, the tetragonal Fe{sub 3}Si driven by in-plane strain reveals half-metal nature in terms of Δ{sub 1} state. The giant TMR ratios are predicted for both MTJs with cubic and tetragonal Fe{sub 3}Si electrodes under zero bias. However, the giant TMR ratio resulting from interface resonant transmission for the former decreases rapidly with the bias. For the latter, the giant TMR ratio can maintain up to larger bias due to coherent transmission through the majority-spin Δ{sub 1} channel.

  1. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning....... This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low...... coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6...

  2. Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Clément, P.-Y.; Baraduc, C., E-mail: claire.baraduc@cea.fr; Chshiev, M.; Diény, B. [Univ. Grenoble Alpes, INAC-SPINTEC, F-38000 Grenoble (France); CNRS, INAC-SPINTEC, F-38000 Grenoble (France); CEA, INAC-SPINTEC, F-38000 Grenoble (France); Ducruet, C. [Crocus-Technology, 5, Place Robert Schuman, F-38054 Grenoble (France); Vila, L. [Univ. Grenoble Alpes, INAC-SP2M, F-38000 Grenoble, France and CEA, INAC-SP2M, F-38000 Grenoble (France)

    2015-09-07

    Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pave the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated.

  3. Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

    Science.gov (United States)

    Clément, P.-Y.; Baraduc, C.; Ducruet, C.; Vila, L.; Chshiev, M.; Diény, B.

    2015-09-01

    Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pave the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated.

  4. Influence of hydrogen patterning gas on electric and magnetic properties of perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, J. H., E-mail: juno@fris.tohoku.ac.jp [Graduate School of Engineering, Tohoku University, Sendai (Japan); Semiconductor R and D Center, Samsung Electronics Co., Ltd., Hwasung (Korea, Republic of); Endoh, T. [Graduate School of Engineering, Tohoku University, Sendai (Japan); Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai (Japan); Kim, Y.; Kim, W. K.; Park, S. O. [Semiconductor R and D Center, Samsung Electronics Co., Ltd., Hwasung (Korea, Republic of)

    2014-05-07

    To identify the degradation mechanism in magnetic tunnel junctions (MTJs) using hydrogen, the properties of the MTJs were measured by applying an additional hydrogen etch process and a hydrogen plasma process to the patterned MTJs. In these studies, an additional 50 s hydrogen etch process caused the magnetoresistance (MR) to decrease from 103% to 14.7% and the resistance (R) to increase from 6.5 kΩ to 39 kΩ. Moreover, an additional 500 s hydrogen plasma process decreased the MR from 103% to 74% and increased R from 6.5 kΩ to 13.9 kΩ. These results show that MTJs can be damaged by the hydrogen plasma process as well as by the hydrogen etch process, as the atomic bonds in MgO may break and react with the exposed hydrogen gas. Compounds such as MgO hydrate very easily. We also calculated the damaged layer width (DLW) of the patterned MTJs after the hydrogen etching and plasma processes, to evaluate the downscaling limitations of spin-transfer-torque magnetic random-access memory (STT-MRAM) devices. With these calculations, the maximum DLWs at each side of the MTJ, generated by the etching and plasma processes, were 23.8 nm and 12.8 nm, respectively. This result validates that the hydrogen-based MTJ patterning processes cannot be used exclusively in STT-MRAMs beyond 20 nm.

  5. Changes in the carpal tunnel due to action of the flexor tendons : Visualization with magnetic resonance imaging

    NARCIS (Netherlands)

    Ham, SJ; Kolkman, WFA; Heeres, J; den Boer, JA; Vierhout, PAM

    1996-01-01

    Successive cross-sectional areas (CSA) of the carpal tunnel were measured with the fingers in both extension and full flexion in 12 healthy volunteers using magnetic resonance imaging. During flexion, lumbrical muscles could be observed to move into the carpal tunnel up to different revels in all vo

  6. Experimental investigations of SiO{sub 2} based ferrite magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Ravi, S., E-mail: sravi@mepcoeng.ac.in [Department of Physics, Mepco Schlenk Engineering College, Sivakasi (India); Karthikeyan, A. [Department of Physics, Mepco Schlenk Engineering College, Sivakasi (India); Aravindan, V. [Energy Research Institute, Nanyang Technological University (Singapore); Pugazhvadivu, K.S.; Tamilarasan, K. [Department of Physics, Kongu Engineering College, Perundurai (India)

    2013-09-01

    Highlights: • CoFe{sub 2}O{sub 4}/SiO{sub 2}/Co–NiFe{sub 2}O{sub 4} magnetic junction was fabricated using RF/DC sputtering. • Spin transport through nanostructure silicon oxide with ferrite as free and pinned layer is our first report. • Magnetization studies were done to justify the free layer and pinned layer for our multilayer. • Magnetoresistance behavior shows a sharp discriminating between parallel and antiparallel alignment with TMR value of 16%. -- Abstract: We report experimental results of ferrite based magnetic tunnel junction. Ferrite junction and spin transport through SiO{sub 2} were interesting since they can readily replace the conventional electronics. We fabricated a cobalt ferrite/SiO{sub 2}/cobalt nickel ferrite based magnetic tunnel junction over a copper coated n-silicon substrate using a RF/DC magnetron sputtering. The tunneling magnetoresistance shows a very good response to applied field and we achieved a TMR of about 16%. Although theoretically it was predicted infinite TMR for half metallic ferromagnetic junction, the deviation was explained on the basis of incoherent scattering along the interfaces.

  7. Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces

    Science.gov (United States)

    Ngo, Thach D. N.; Chang, Jung-Won; Lee, Kyujoon; Han, Seungju; Lee, Joon Sung; Kim, Young Heon; Jung, Myung-Hwa; Doh, Yong-Joo; Choi, Mahn-Soo; Song, Jonghyun; Kim, Jinhee

    2015-08-01

    Complex oxide systems have attracted considerable attention because of their fascinating properties, including the magnetic ordering at the conducting interface between two band insulators, such as LaAlO3 and SrTiO3. However, the manipulation of the spin degree of freedom at the LaAlO3/SrTiO3 heterointerface has remained elusive. Here, we have fabricated hybrid magnetic tunnel junctions consisting of Co and LaAlO3/SrTiO3 ferromagnets with the insertion of a Ti layer in between, which clearly exhibit magnetic switching and the tunnelling magnetoresistance effect below 10 K. The magnitude and sign of the tunnelling magnetoresistance are strongly dependent on the direction of the rotational magnetic field parallel to the LaAlO3/SrTiO3 plane, which is attributed to a strong Rashba-type spin-orbit coupling in the LaAlO3/SrTiO3 heterostructure. Our study provides a further support for the existence of the macroscopic ferromagnetism at LaAlO3/SrTiO3 heterointerfaces and opens a novel route to realize interfacial spintronics devices.

  8. Resonant tunneling in truly axial symmetry Mn12 single-molecule magnets: sharp crossover between thermally assisted and pure quantum tunneling.

    Science.gov (United States)

    Wernsdorfer, W; Murugesu, M; Christou, G

    2006-02-10

    Magnetization measurements of a truly axial symmetry molecular nanomagnet with a spin ground state of S = 10 show resonant tunneling. This compound has the same magnetic anisotropy as but the molecules are better isolated and the crystals have less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The results establish a sharp crossover between thermally assisted and pure quantum tunneling, as had been previously predicted.

  9. Investigation of magnetic sensor properties of magnetic tunnel junctions with superparamagnetic free layer at low frequencies for biomedical imaging applications

    Science.gov (United States)

    Ishikawa, Kyohei; Oogane, Mikihiko; Fujiwara, Kousuke; Jono, Junichi; Tsuchida, Masaaki; Ando, Yasuo

    2016-12-01

    The magnetic sensor properties of magnetic tunnel junctions (MTJs) with a superparamagnetic (SP) free layer were systematically investigated at low frequencies (<10 Hz). We prepared four varieties of MTJs with various SP properties by changing the annealing temperature. The temperature dependence of magnetoresistance curves and the signal/noise property at 285 K were evaluated. We found that the SP free layer has the advantage of detecting very small and low-frequency AC magnetic fields compared with a ferromagnetic free layer. The SP free layer strongly suppressed magnetic 1/f noise at low frequencies and expressed a very linear response to a small magnetic field. The obtained properties in MTJs with the SP free layer are suitable for detecting biomagnetic fields. The detectivity was 111 nT at low frequencies (from 0.1 to 10 Hz), which is one of the highest values in single-MTJ sensors.

  10. Assisted Writing in Spin Transfer Torque Magnetic Tunnel Junctions

    Science.gov (United States)

    Ganguly, Samiran; Ahmed, Zeeshan; Datta, Supriyo; Marinero, Ernesto E.

    2015-03-01

    Spin transfer torque driven MRAM devices are now in an advanced state of development, and the importance of reducing the current requirement for writing information is well recognized. Different approaches to assist the writing process have been proposed such as spin orbit torque, spin Hall effect, voltage controlled magnetic anisotropy and thermal excitation. In this work,we report on our comparative study using the Spin-Circuit Approach regarding the total energy, the switching speed and energy-delay products for different assisted writing approaches in STT-MTJ devices using PMA magnets.

  11. Free- and reference-layer magnetization modes versus in-plane magnetic field in a magnetic tunnel junction with perpendicular magnetic easy axis

    Science.gov (United States)

    Mazraati, Hamid; Le, Tuan Q.; Awad, Ahmad A.; Chung, Sunjae; Hirayama, Eriko; Ikeda, Shoji; Matsukura, Fumihiro; Ohno, Hideo; Åkerman, Johan

    2016-09-01

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  12. BEOL compatible high tunnel magneto resistance perpendicular magnetic tunnel junctions using a sacrificial Mg layer as CoFeB free layer cap

    Energy Technology Data Exchange (ETDEWEB)

    Swerts, J., E-mail: Johan.Swerts@imec.be; Mertens, S.; Lin, T.; Couet, S.; Tomczak, Y.; Sankaran, K.; Pourtois, G.; Kim, W.; Meersschaut, J.; Souriau, L.; Radisic, D.; Van Elshocht, S.; Kar, G.; Furnemont, A. [imec, Kapeldreef 75, Leuven 3001 (Belgium)

    2015-06-29

    Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface of the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-induced damage during the Ta deposition. The Ta-capped CoFeB free layer using the sacrificial Mg interlayer has significantly better electrical and magnetic properties than the equivalent stack without protective layer. We demonstrate a tunnel magneto resistance increase up to 30% in bottom pinned magnetic tunnel junctions and tunnel magneto resistance values of 160% at resistance area product of 5 Ω.μm{sup 2}. Moreover, the free layer maintains perpendicular magnetic anisotropy after 400 °C annealing.

  13. BEOL compatible high tunnel magneto resistance perpendicular magnetic tunnel junctions using a sacrificial Mg layer as CoFeB free layer cap

    Science.gov (United States)

    Swerts, J.; Mertens, S.; Lin, T.; Couet, S.; Tomczak, Y.; Sankaran, K.; Pourtois, G.; Kim, W.; Meersschaut, J.; Souriau, L.; Radisic, D.; Van Elshocht, S.; Kar, G.; Furnemont, A.

    2015-06-01

    Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface of the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-induced damage during the Ta deposition. The Ta-capped CoFeB free layer using the sacrificial Mg interlayer has significantly better electrical and magnetic properties than the equivalent stack without protective layer. We demonstrate a tunnel magneto resistance increase up to 30% in bottom pinned magnetic tunnel junctions and tunnel magneto resistance values of 160% at resistance area product of 5 Ω.μm2. Moreover, the free layer maintains perpendicular magnetic anisotropy after 400 °C annealing.

  14. Spin-dependent electron transport through a magnetic resonant tunneling diode

    Science.gov (United States)

    Havu, P.; Tuomisto, N.; Väänänen, R.; Puska, M. J.; Nieminen, R. M.

    2005-06-01

    Electron-transport properties in nanostructures can be modeled, for example, by using the semiclassical Wigner formalism or the quantum-mechanical Green’s function formalism. We compare the performance and the results of these methods in the case of magnetic resonant-tunneling diodes. We have implemented the two methods within the self-consistent spin-density-functional theory. Our numerical implementation of the Wigner formalism is based on the finite-difference scheme whereas for the Green’s function formalism the finite-element method is used. As a specific application, we consider the device studied by Slobodskyy [Phys. Rev. Lett. 90, 246601 (2003)] and analyze their experimental results. The Wigner and Green’s function formalisms give similar electron densities and potentials but, surprisingly, the former method requires much more computer resources in order to obtain numerically accurate results for currents. Both of the formalisms can be used to model magnetic resonant tunneling diode structures.

  15. Magnetic-Field-Modulated Resonant Tunneling in Ferromagnetic-Insulator-Nonmagnetic Junctions

    Science.gov (United States)

    Song, Yang; Dery, Hanan

    2014-07-01

    We present a theory for resonance-tunneling magnetoresistance (MR) in ferromagnetic-insulator-nonmagnetic junctions. The theory sheds light on many of the recent electrical spin injection experiments, suggesting that this MR effect rather than spin accumulation in the nonmagnetic channel corresponds to the electrically detected signal. We quantify the dependence of the tunnel current on the magnetic field by quantum rate equations derived from the Anderson impurity model, with the important addition of impurity spin interactions. Considering the on-site Coulomb correlation, the MR effect is caused by competition between the field, spin interactions, and coupling to the magnetic lead. By extending the theory, we present a basis for operation of novel nanometer-size memories.

  16. Electron Holography of Barrier Structures in Co/ZrAlOx/Co Magnetic Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhe; ZHU Tao; SHEN Feng; SHENG Wen-Ting; WANG Wei-Gang; XIAO John Q; ZHANG Ze

    2005-01-01

    @@ We investigate the potential profiles and elemental distribution of barriers in Co/ZrAlOx/Co magnetic tunnel junctions (MTJs) using electron holography (EH) and scanning transmission electron microscopy. The MTJ barriers are introduced by oxidizing a bilayer consisting with a uniform 0.45-nm Al layer and a wedge-shaped Zr layer (0-2 nm). From the scanning transmission electron microscopy, AlOx and ZrOx layers are mixed together,indicating that compact AlOx layer cannot be formed in such a bilayer structure of barriers. The EH results reveal that there are no sharp interfaces between the barrier and magnetic electrodes, which may be responsible for a smaller tunnelling magnetoresistance compared with the MTJs of Co/AlOx/Co.

  17. Behavioural model of Spin Torque Transfer Magnetic Tunnel Junction, Using Verilog-A

    Science.gov (United States)

    Garg, Rishubh; Kumar, Deepak; Jindal, Navneet; Negi, Nandita; Ahuja, Chetna

    2012-11-01

    A novel simple and efficient model of Spin Torque Transfer Magnetic Tunnel Junction (STT-MTJ) is presented. The model is implemented using Verilog-A. The model accurately emulates the main properties of an STT-MTJ which includes Tunnel Magneto resistance Ratio (TMR), its dependence on the voltage bias and the Critical switching current. The novelty of the model lies in the fact that the voltage dependence of TMR has been modeled using a single equation dividing it into three different operating regions. A register based on the model is also developed. The model can be used for faster simulations of hybrid Magnetic CMOS circuits and in various other wide range of applications. The models were verified using Synopsys Hspice 2010.

  18. All-Optical Switching of Magnetic Tunnel Junctions with Single Subpicosecond Laser Pulses

    Science.gov (United States)

    Chen, Jun-Yang; He, Li; Wang, Jian-Ping; Li, Mo

    2017-02-01

    The magnetic tunnel junction (MTJ) is one of the most important building blocks of spintronic logic and memory components for beyond-CMOS computation and communication. Although switching of MTJs without magnetic field has been achieved by charge and spin current injection, the operation speed is limited fundamentally by the spin-precession time to many picoseconds. We report the demonstration of ultrafast all-optical switching of an MTJ using single subpicosecond infrared laser pulses. This optically switchable MTJ uses ferrimagnetic Gd(Fe,Co) as the free layer and its switching is read out by measuring its tunneling magnetoresistance with a Δ R /R ratio of 0.6%. A switching repetition rate at MHz has been demonstrated, but the fundamental upper limit should be higher than tens of GHz rate. This result represents an important step toward integrated optospintronic devices that combines spintronics and photonics technologies to enable ultrafast conversion between fundamental information carriers of electron spins and photons.

  19. Observation of thermally driven field-like spin torque in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Bose, Arnab, E-mail: arnabbose@ee.iitb.ac.in; Jain, Sourabh; Asam, Nagarjuna; Bhuktare, Swapnil; Singh, Hanuman; Tulapurkar, Ashwin A. [Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai 400076 (India); Shukla, Amit Kumar; Konishi, Katsunori; Lam, Duc Duong; Fujii, Yuya; Miwa, Shinji; Suzuki, Yoshishige [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan)

    2016-07-18

    We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 10{sup 9 }A/m{sup 2} can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgO tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque.

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

    Science.gov (United States)

    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.

  1. Oscillatory behavior of the tunnel magnetoresistance due to thickness variations in Ta|CoFe|MgO magnetic tunnel junctions: A first-principles study

    Science.gov (United States)

    Sankaran, K.; Swerts, J.; Couet, S.; Stokbro, K.; Pourtois, G.

    2016-09-01

    To investigate the impact of both the CoFe ferromagnetic layer thickness and the capping paramagnetic layer on the tunnel magnetoresistance (TMR), we performed first-principles simulations on epitaxial magnetic tunnel junctions contacted with either CoFe or Ta paramagnetic capping layers. We observed a strong oscillation of the TMR amplitude with respect to the thickness of the ferromagnetic layer. The TMR is found to be amplified whenever the MgO spin tunnel barrier is thickened. Quantization of the electronic structure of the ferromagnetic layers is found to be at the origin of this oscillatory behavior. Metals such as Ta contacting the magnetic layer are found to enhance the amplitude of the oscillations due to the occurrence of an interface dipole. The latter drives the band alignment and tunes the nature of the spin channels that are active during the tunneling process. Subsequently, the regular transmission spin channels are modulated in the magnetic tunnel junction stack and other complex ones are being activated.

  2. High sensitivity microwave detection using a magnetic tunnel junction in the absence of an external applied magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Gui, Y. S.; Bai, L. H.; Hu, C.-M. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Xiao, Y.; Guo, H. [Department of Physics, Center for the Physics of Materials, McGill University, Montreal, Quebec H3A 2T8 (Canada); Hemour, S.; Zhao, Y. P.; Wu, K. [Ecole Polytechnique de Montreal, Montreal, Quebec H3T 1J4 (Canada); Houssameddine, D. [Everspin Technologies, 1347 N. Alma School Road, Chandler, Arizona 85224 (United States)

    2015-04-13

    In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5000 mV/mW.

  3. Enhancement of electric-field-induced change of magnetic anisotropy by interface engineering of MgO magnetic tunnel junctions

    Science.gov (United States)

    Bonaedy, Taufik; Choi, Jun Woo; Jang, Chaun; Min, Byoung-Chul; Chang, Joonyeon

    2015-06-01

    Electric-field-induced modification of magnetic anisotropy is studied using tunnel magnetoresistance of the Co40Fe40B20/ MgO/ Co40Fe40B20 and Co40Fe40B20/ Hf (0.08 nm)/ MgO/ Co40Fe40B20 magnetic tunnel junctions. In both systems, the interfacial perpendicular magnetic anisotropy is increased with increasing electron density at the MgO interface. A quantitative comparison between the two systems reveals that the change of magnetic anisotropy energy with electric field is significantly enhanced in Co40Fe40B20/ Hf/ MgO/ Co40Fe40B20 compared to Co40Fe40B20/ MgO/ Co40Fe40B20. The sub-monolayer Hf insertion at the Co40Fe40B20/MgO interface turns out to be critical to the enhanced electric field control of the magnetic anisotropy, indicating the interface sensitive nature of the effect.

  4. Magnetization distribution and spin transport of graphene/h-BN/graphene nanoribbon-based magnetic tunnel junction

    Science.gov (United States)

    Zhang, Y.; Yan, X. H.; Guo, Y. D.; Xiao, Y.

    2017-09-01

    Motivated by recent electronic transport measurement of boron nitride-graphene hybrid atomic layers, we studied magnetization distribution, transmission and current-bias relation of graphene/h-BN/graphene (C/BN/C) nanoribbon-based magnetic tunnel junctions (MTJ) based on density functional theory and non-equilibrium Green's function methods. Three types of MTJs, i.e. asymmetric, symmetric (S) and symmetric (SS), and two types of lead magnetization alignment, i.e. parallel (PC) and antiparallel (APC), are considered. The results show that the magnetization distribution is closely related to the interface structure. Especially for asymmetric MTJ, the B/N atoms at the C/BN interface are spin-polarized and give finite magnetic moments. More interesting, it is found that the APC transmission of asymmetric MTJ with the thinnest barrier dominates over the PC one. By analyzing the projected density of states, one finds that the unusual higher APC transmission than PC is due to the coupling of electronic states of left ZGNR and right ZGNR. By integrating transmission, we calculate the current-bias voltage relation and find that the APC current is larger than PC current at small bias voltage and therefore reproduces a negative tunnel magnetoresistance. The results reported here will be useful and important for the design of C/BN/C-based MTJ.

  5. Interface characterization of epitaxial Fe/MgO/Fe magnetic tunnel junctions.

    Science.gov (United States)

    Wang, S G; Ward, R C C; Hesjedal, T; Zhang, X G; Wang, C; Kohn, A; Ma, Q L; Zhang, Jia; Liu, H F; Han, X F

    2012-02-01

    Following predictions by first-principles theory of a huge tunnel magnetoresistance (TMR) effect in epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs), measured magnetoresistance (MR) ratios of about 200% at room temperature (RT) have been reported in MgO-based epitaxial MTJs. Recently, a MR ratio of about 600% has been reported at RT in MgO-based MTJs prepared by magnetron sputtering, using amorphous CoFeB as the ferromagnetic electrode. These MTJs show great potential for application in spintronic devices. Fully epitaxial MTJs are excellent model systems that enhance our understanding of the spin-dependent tunneling process as the interface is well defined and can be fully characterized. Both theoretical calculations and experimental results clearly indicate that the interfacial structure plays a crucial role in the coherent tunneling across a single crystal MgO barrier, especially in epitaxial MgO-based MTJs grown by molecular beam epitaxy (MBE). Surface X-ray diffraction, Auger electron spectroscopy, X-ray absorption spectra, and X-ray magnetic circular dichroism techniques have been reported previously for interface characterization. However, no consistent viewpoint has been reached on the interfacial structures (such as FeO layer formation at the bottom Fe/MgO interface), and it is still an open issue. In this article, our recent studies on the interface characterization of MgO-based epitaxial MTJs by X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and spin-dependent tunneling spectroscopy, will be presented.

  6. Multiferroic tunnel junctions and ferroelectric control of magnetic state at interface (invited)

    KAUST Repository

    Yin, Y. W.

    2015-03-03

    As semiconductor devices reach ever smaller dimensions, the challenge of power dissipation and quantum effect place a serious limit on the future device scaling. Recently, a multiferroic tunnel junction (MFTJ) with a ferroelectric barrier sandwiched between two ferromagnetic electrodes has drawn enormous interest due to its potential applications not only in multi-level data storage but also in electric field controlled spintronics and nanoferronics. Here, we present our investigations on four-level resistance states, giant tunneling electroresistance (TER) due to interfacial magnetoelectric coupling, and ferroelectric control of spin polarized tunneling in MFTJs. Coexistence of large tunneling magnetoresistance and TER has been observed in manganite/(Ba, Sr)TiO3/manganite MFTJs at low temperatures and room temperature four-resistance state devices were also obtained. To enhance the TER for potential logic operation with a magnetic memory, La0.7Sr0.3MnO3/BaTiO3/La0.5Ca0.5MnO3 /La0.7Sr0.3MnO3 MFTJs were designed by utilizing a bilayer tunneling barrier in which BaTiO3 is ferroelectric and La0.5Ca0.5MnO3 is close to ferromagnetic metal to antiferromagnetic insulator phase transition. The phase transition occurs when the ferroelectric polarization is reversed, resulting in an increase of TER by two orders of magnitude. Tunneling magnetoresistance can also be controlled by the ferroelectric polarization reversal, indicating strong magnetoelectric coupling at the interface.

  7. Magnetic Tunnel Junction-Based On-Chip Microwave Phase and Spectrum Analyzer

    Science.gov (United States)

    Fan, Xin; Chen, Yunpeng; Xie, Yunsong; Kolodzey, James; Wilson, Jeffrey D.; Simons, Rainee N.; Xiao, John Q.

    2014-01-01

    A magnetic tunnel junction (MTJ)-based microwave detector is proposed and investigated. When the MTJ is excited by microwave magnetic fields, the relative angle between the free layer and pinned layer alternates, giving rise to an average resistance change. By measuring the average resistance change, the MTJ can be utilized as a microwave power sensor. Due to the nature of ferromagnetic resonance, the frequency of an incident microwave is directly determined. In addition, by integrating a mixer circuit, the MTJ-based microwave detector can also determine the relative phase between two microwave signals. Thus, the MTJbased microwave detector can be used as an on-chip microwave phase and spectrum analyzer.

  8. Spin-dependent tunneling time in periodic diluted-magnetic-semiconductor/nonmagnetic-barrier superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ping-Fan; Guo, Yong, E-mail: guoy66@tsinghua.edu.cn [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)

    2016-02-01

    We investigate the tunneling time (dwell time) in periodic diluted-magnetic-semiconductor/nonmagnetic-barrier (DMS/NB) superlattices subjected to an external magnetic field. It is found that spin-dependent resonant bands form in the spectra of dwell time, which can be effectively manipulated by not only the external magnetic field but also the geometric parameters of the system. Moreover, an intuitive semiclassical delay is defined to illustrate the behavior of the dwell time, and the former one is shown to be the result of “smoothing out” the latter one. We also find that the dwell time in diluted-magnetic-semiconductor/semiconductor superlattices behaves surprisingly different from the DMS/NB case, especially for spin-down electrons.

  9. Probing the Influence of Thermal Spin Torque on Magnetic Tunnel Junction Switching

    Science.gov (United States)

    Phung, Timothy; Pushp, Aakash; Rettner, Charles; Hughes, Brian; Yang, See-Hun; Parkin, Stuart

    2013-03-01

    It has been established in the past few years that heat flow within a ferromagnet can induce a spin current and an associated voltage. This so called Spin Seebeck effect, initially reported in ferromagnetic metals, has also been observed in magnetic semiconductors, magnetic insulators as well as in strongly spin orbit coupled systems. An open question has been whether heat induced spin currents can be used in switching a magnetic tunnel junction (MTJ) via thermal spin torque (TST). In order to answer this question, we investigate the MTJ switching with TST induced by sharp temperature gradients on the order of 1-10 K/nm. We will describe our experimental setup and present data that show the various roles that temperature plays on the saturation magnetization of the material and on the induced spin currents that influence MTJ switching.

  10. Micromagnetic model for studies on Magnetic Tunnel Junction switching dynamics, including local current density

    Energy Technology Data Exchange (ETDEWEB)

    Frankowski, Marek, E-mail: mfrankow@agh.edu.pl; Czapkiewicz, Maciej; Skowronski, Witold; Stobiecki, Tomasz

    2014-02-15

    We present a model introducing the Landau–Lifshitz–Gilbert equation with a Slonczewski's Spin-Transfer-Torque (STT) component in order to take into account spin polarized current influence on the magnetization dynamics, which was developed as an Object Oriented MicroMagnetic Framework extension. We implement the following computations: magnetoresistance of vertical channels is calculated from the local spin arrangement, local current density is used to calculate the in-plane and perpendicular STT components as well as the Oersted field, which is caused by the vertical current flow. The model allows for an analysis of all listed components separately, therefore, the contribution of each physical phenomenon in dynamic behavior of Magnetic Tunnel Junction (MTJ) magnetization is discussed. The simulated switching voltage is compared with the experimental data measured in MTJ nanopillars.

  11. Influence of spin-orbit interaction within the insulating barrier on the electron transport in magnetic tunnel junctions

    Science.gov (United States)

    Vedyayev, A.; Ryzhanova, N.; Strelkov, N.; Titova, M.; Chshiev, M.; Rodmacq, B.; Auffret, S.; Cuchet, L.; Nistor, L.; Dieny, B.

    2017-02-01

    We present a theory of the anisotropy of tunneling magnetoresistance (ATMR) phenomenon in magnetic tunnel junctions (MTJs) attributed to Rashba spin-orbit interaction in the insulating barrier. ATMR represents the difference of tunnel magnetoresistance (TMR) amplitude measured with in-plane and out-of-plane magnetic configurations. It is demonstrated that within the spin-polarized free-electron model the change of conductance associated with the ATMR is exactly twice the change of conductance measured at full saturation (i.e., in parallel configuration of magnetizations) between in-plane and out-of-plane configuration, i.e., the tunneling anisotropic magnetoresistance (TAMR). Both ATMR and TAMR are closely related to the TMR amplitude and spin-orbit constant. The predicted ATMR phenomenon is confirmed experimentally, showing a few percent value in the case of the widely studied CoFeB/MgO/CoFeB based MTJ.

  12. Theory of spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

    CERN Document Server

    Schüler, Michael; Berakdar, Jamal

    2012-01-01

    The inelastic scanning tunneling microscopy (STM) has been shown recently (Loth et al. Science 329, 1628 (2010)) to be extendable as to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze theoretically this novel tool by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin-configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is nonpertubative and hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the prediction of simple analytical models and compared with experiments.

  13. Symmetry dependent spin injection from Fe/MgO in single crystal based magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Hehn, Michel; Greullet, Fanny; Bernos, Julien; Tiusan, Coriolan; Bellouard, Christine; Montaigne, Francois; Lacour, Daniel; Alnot, Marc; Lu, Yuan; Lengaigne, Gwladys [LPM, Vandoeuvre les Nancy (France); Halley, David; Weber, Wolfgang [IPCMS, 67 - Strasbourg (France)

    2009-07-01

    The transport in crystalline magnetic tunnel junctions (MTJ) attracted the interest of the international community after the theoretical predictions of Butler et al of giant tunnel magnetoresistance (TMR) effects. In these model systems the electrons are classified with respect to the symmetry of their associated electronic Bloch wave function. The large predicted TMR ratio is related to a symmetry dependent attenuation rate within the MgO single crystal barrier combined with a half metallic property of a specific symmetry in the Fe electrode. After a brief introduction to the physics of the transport in Fe/MgO/Fe MTJ, I show how to exploit the symmetry dependence of the tunnel conductivity to engineer novel MTJs functionalities. We demonstrate that, a suitably chosen Cr(001) epitaxial metallic spacer layer quenches the transmission of particular electronic states, therefore acting as an additional symmetry dependent tunnel barrier for electrons at the Fermi level. Moreover, we show that this ultrathin Cr metallic barrier can promote quantum well states in an adjacent Fe layer. These results confirm the transport mechanism proposed by Butler et al. Extension to other materials are also discussed.

  14. Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallic C o2MnSi electrodes

    Science.gov (United States)

    Hu, Bing; Moges, Kidist; Honda, Yusuke; Liu, Hong-xi; Uemura, Tetsuya; Yamamoto, Masafumi; Inoue, Jun-ichiro; Shirai, Masafumi

    2016-09-01

    In order to elucidate the origin of the temperature (T ) dependence of spin-dependent tunneling conductance (G ) of magnetic tunnel junctions (MTJs), we experimentally investigated the T dependence of G for the parallel and antiparallel magnetization alignments, GP and GAP, of high-quality C o2MnSi (CMS)/MgO/CMS MTJs having systematically varied spin polarizations (P ) at 4.2 K by varying the Mn composition α in C o2M nαSi electrodes that exhibited giant tunneling magnetoresistance ratios. Results showed that GP normalized by its value at 4.2 K exhibited a notable, nonmonotonic T dependence although its variation with T was significantly smaller than that of GAP normalized by its value at 4.2 K, indicating that an analysis of the experimental GP(T ) is critical to revealing the origin of the T dependence of G . By analyzing the experimental GP(T ) , we clarified that both spin-flip inelastic tunneling via a thermally excited magnon and spin-conserving elastic tunneling in which P decays with increasing T play key roles. The experimental GAP(T ) , including its stronger T dependence for higher P at 4.2 K, was also consistently explained with this model. Our findings provide a unified picture for understanding the origin of the T dependence of G of MTJs with a wide range of P , including MTJs with high P close to a half-metallic value.

  15. Optimized electrode configuration for current-in-plane characterization of magnetic tunnel junction stacks

    Science.gov (United States)

    Cagliani, A.; Kjær, D.; Østerberg, F. W.; Hansen, O.; Nielsen, P. F.; Petersen, D. H.

    2017-02-01

    The current-in-plane tunneling technique (CIPT) has been a crucial tool in the development of magnetic tunnel junction stacks suitable for magnetic random access memories (MRAM) for more than a decade. The MRAM development has now reached the maturity to make the transition from the R&D phase to the pilot production phase. This will require an improvement in the repeatability of the CIPT metrology technique. Here, we present an analytical model that can be used to simulate numerically the repeatability of a CIPT measurement for an arbitrary MTJ stack prior to any CIPT measurement. The model describes mathematically the main sources of error arising when a micro multi-electrode probe is used to perform a CIPT measurement. The numerically simulated repeatability values obtained on four different MTJ stacks are verified by experimental data and the model is used to optimize the choice of electrodes on a multi-electrode probe to reach up to 36% improvement on the repeatability for the resistance area product and the tunneling magnetoresistance measurement, without any hardware modification.

  16. Vortex domain structures and dc current dependence of magneto-resistances in magnetic tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Wei Hong-Xiang; Lu Qing-Feng; Zhao Su-Fen; Zhang Xie-Qun; Feng Jia-Feng; Han Xiu-Feng

    2004-01-01

    Microfabrication and the magneto-transport characteristics of the magnetic tunnel junctions (MTJs) with a spin-valve-type structure of Ta (5nm)/Ni7gFe21 (25nm)/Ir22Mn78 (12nm)/Co75Fe25 (4nm)/Al(0.8nm) oxide/Co75Fe25(4nm)/Ni7gFe21 (20nm)/Ta(5nm) were investigated in this paper. A series of experimental data measured with a MTJ was used to verify a magnon-assisted tunnelling model and theory. Furthermore, a micromagnetics simulation shows that the butterfly-like vortex domain structures can be formed under a current-induced Oersted field, which decreases the net magnetization values of the ferromagnetic electrodes under a large dc current (i.e., in high voltage regimes). It is one of the main reasons for the tunnel magnetoresistance ratios to decrease significantly at high voltage biasing.

  17. Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

    Science.gov (United States)

    Chen, Xiaobin; Zhou, Chenyi; Zhang, Zhaohui; Chen, Jingzhe; Zheng, Xiaohong; Zhang, Lei; Hu, Can-Ming; Guo, Hong

    2017-03-01

    The phenomenon of spin transfer torque (STT) has attracted a great deal of interest due to its promising prospects in practical spintronic devices. In this paper, we report a theoretical investigation of STT in a noncollinear magnetic tunnel junction under ac modulation based on the nonequilibrium Green's-function formalism, and we derive a closed formulation for predicting the time-averaged STT. Using this formulation, the ac STT of a carbon-nanotube-based magnetic tunnel junction is analyzed. Under ac modulation, the low-bias linear (quadratic) dependence of the in-plane (out-of-plane) torque on bias still holds, and the sinθ dependence on the noncollinear angle is maintained. By photon-assisted tunneling, the bias-induced components of the in-plane and out-of-plane torques can be enhanced significantly, about 12 and 75 times, respectively. Our analysis reveals the condition for achieving optimized STT enhancement and suggests that ac modulation is a very effective way for electrical manipulation of STT.

  18. Current-induced magnetization switching with a spin-polarized scanning tunneling microscope

    Science.gov (United States)

    Krause, Stefan

    2008-03-01

    In present data storage applications magnetic nanostructures are switched by external magnetic fields. Due to their non-local character, however, cross-talk between adjacent nanomagnets may occur. An elegant method to circumvent this problem is magnetization switching by spin-polarized currents, as observed in GMR,1] as well as in TMR,2] studies. However, the layered structures of these devices do not provide any insight to the details of the spatial distribution of the switching processes. Spin-polarized scanning tunneling microscopy (SP-STM) is a well-established tool to reveal the magnetic structure of surfaces at spatial resolution down to the atomic scale. Besides, SP-STM takes advantage of a perfect TMR junction consisting of an isolating vacuum barrier separating two magnetic electrodes, which are represented by the foremost tip atom and the sample. Our experiments demonstrate that SP-STM serves as a tool to manipulate the switching behavior of uniaxial superparamagnetic nanoislands,3]. Furthermore, we show how SP-STM can be used to switch the magnetization of quasistable magnetic nanoislands at low temperature (T=31,). Besides its scientific relevance to investigate the details of current-induced magnetization switching (CIMS), this technique opens perspectives for future data storage technologies based on SP-STM. [1] J. A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000). [2] Y. Liu et al., Appl. Phys. Lett. 82, 2871 (2003). [3] S. Krause et al., Science 317, 1537 (2007).

  19. Detection of endogenous magnetic nanoparticles with a tunnelling magneto resistance sensor.

    Science.gov (United States)

    Ionescu, A; Darton, N J; Vyas, K; Llandro, J

    2010-09-28

    The magnetotactic bacterium Magnetospirillum sp. has been cultured and the properties of its endogenous magnetic nanoparticles characterized. Electron-microscopic analyses indicate that the endogenous magnetite nanoparticles in Magnetospirillum sp. are coated with a 3-4 nm thick transparent shell, forming a magnetosome. These magnetite nanoparticles had diameters of 50.9+/-13.3 nm, in good agreement with the diameter of 40.6+/-1.2 nm extracted from magnetometry. Each Magnetospirillum sp. bacterium contained chains of 5-25 magnetosomes. Superconducting quantum interference device magnetometry results indicate that the extrinsic superparamagnetic response of the bacterial solution at room temperature can be attributed to the reversal of the magnetization by physical rotation of the nanoparticles. The intrinsic blocking temperature of a sample of freeze-dried bacteria was estimated to be 282+/-13 K. A tunnelling magneto resistance sensor was used to detect the stray fields of endogenous magnetic nanoparticles in static and quasi-dynamic modes. Based on the tunnelling magneto resistance sensor results, the magnetic moment per bacterium was estimated to be approximately 2.6 x 10(-13) emu. The feasibility of this detection method either as a mass-coverage device or as part of an integrated microfluidic circuit for detection and sorting of magnetosome-containing cells was demonstrated.

  20. Perpendicular magnetic anisotropy influence on voltage-driven spin-diode effect in magnetic tunnel junctions: A micromagnetic study

    Science.gov (United States)

    Frankowski, Marek; Chȩciński, Jakub; Skowroński, Witold; Stobiecki, Tomasz

    2017-05-01

    We study the influence of the perpendicular magnetic anisotropy on the voltage-induced ferromagnetic resonance in magnetic tunnel junctions (MTJs). An MTJ response to the applied radio-frequency voltage excitation is investigated using micromagnetic calculations with the free layer oriented both in-plane and out-of-plane. Our model allows for a quantitative description of the magnetic system parameters such as resonance frequency, sensitivity or quality factor and for a distinction between material-dependent internal damping and disorder-dependent effective damping. We find that the sensitivity abruptly increases up to three orders of magnitude near the anisotropy transition regime, while the quality factor declines due to effective damping increase. We attribute the origin of this behaviour to the changes of the exchange energy in the system, which is calculated using micromagnetic approach.

  1. Radio-frequency shot-noise measurement in a magnetic tunnel junction with a MgO barrier

    Energy Technology Data Exchange (ETDEWEB)

    Rehman, Mushtaq; Park, Junghwan; Song, Woon; Chong, Yonuk [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Lee, Yeonsub; Min, Byoungchul; Shin, Kyungho [Korea Institute of Science and Technology, Seoul (Korea, Republic of); Ryu, Sangwan [Chonnam National University, Gwangju (Korea, Republic of); Khim, Zheong [Seoul National University, Seoul (Korea, Republic of)

    2010-10-15

    We measured the noise power of a magnetic tunnel junction in the frequency range of 710 {approx} 1200 MHz. A low-noise cryogenic HEMT amplifier was used to measure the small noise signal at a high frequency with wide bandwidth. The MgO-barrier tunnel junction showed large tunnel magnetoresistance ratio of 215% at low temperature, which indicates electronic transport through the tunnel barrier without any significant spin-flip scattering. In the bias-dependent noise measurement, however, the zero-bias shot noise was enhanced compared to the value expected from a perfect tunnel barrier or the value observed from a good Al-AlO{sub x}-Al tunnel junction. We assume that this enhanced noise comes from inelastic tunneling processes through the barrier, which may be related to the observed zero-bias anomaly in the differential resistance of the tunnel junctions. We present a simple phenomenological model for how the inelastic scattering process can enhance the zero-bias noise in a tunnel junction.

  2. Disorder Scattering in Magnetic Tunnel Junctions: Theory of Nonequilibrium Vertex Correction

    Science.gov (United States)

    Ke, Youqi; Xia, Ke; Guo, Hong

    2008-04-01

    We report a first principles formalism and its numerical implementation for treating quantum transport properties of nanoelectronic devices with atomistic disorder. We develop a nonequilibrium vertex correction (NVC) theory to handle the configurational average of random disorder at the density matrix level so that disorder effects to nonlinear and nonequilibrium quantum transport can be calculated from atomic first principles in a self-consistent and efficient manner. We implement the NVC into a Keldysh nonequilibrium Green’s function (NEGF) -based density functional theory (DFT) and apply the NEGF-DFT-NVC formalism to Fe/vacuum/Fe magnetic tunnel junctions with interface roughness disorder. Our results show that disorder has dramatic effects on the nonlinear spin injection and tunnel magnetoresistance ratio.

  3. Degradation of magnetic tunnel junctions with thin AlOx barrier

    Directory of Open Access Journals (Sweden)

    Tadashi Mihara, Yoshinari Kamakura, Masato Morifuji and Kenji Taniguchi

    2007-01-01

    Full Text Available The degradation of magnetic tunnel junctions (MTJs with AlOx barrier was experimentally investigated. Constant voltage stress (CVS measurement was carried out to monitor the time evolution of the conductance and tunneling magnetoresistance (TMR of MTJs. The gradual increase of the stress-induced leakage current (SILC was observed prior to the breakdown, following a power law function of stress time with an exponent of about 0.2–0.4, which is similar to the case of the ultrathin gate oxide films in MOSFETs. The measured TMR for SILC suggests that the spin-dependent current component would be involved in the early stage of degradation, while spin-independent conduction becomes dominant before the breakdown resulting in a decrease of TMR.

  4. Observation of thermal spin-transfer torque via ferromagnetic resonance in magnetic tunnel junctions

    Science.gov (United States)

    Zhang, Zhaohui; Bai, Lihui; Chen, Xiaobin; Guo, Hong; Fan, X. L.; Xue, D. S.; Houssameddine, D.; Hu, C.-M.

    2016-08-01

    The thermal spin-transfer torque (TSTT) in magnetic tunneling junctions (MTJs) was systematically studied using electrical detection of ferromagnetic resonance (FMR). Evidence for the existence of TSTT in MTJs is observed. A temperature difference was applied across an MTJ acting as a TSTT on the free layer of the MTJ. The FMR of the free layer was then excited by a microwave current and electrically detected as a dc voltage. We found that the FMR line shape was changed by the TSTT, indicated by the ratio of dispersive and Lorentz components of the FMR spectra (D /L ). D /L increases by increasing the temperature difference. In addition, we analyze the magnetization orientation dependence of TSTT and provide solid evidence that this dependence differs from the magnetization orientation dependence of spin-transfer torque driven by a dc bias.

  5. Fabrication of superconducting tunnel junctions with embedded coil for applying magnetic field

    Science.gov (United States)

    Yamaguchi, Kenji; Nakagawa, Hiroshi; Aoyagi, Masahiro; Naruse, Masato; Myoren, Hiroaki; Taino, Tohru

    2016-11-01

    We have proposed and demonstrated a superconducting tunnel junction (STJ) with an embedded coil for applying a magnetic field. The STJ was fabricated on the coil, which was embedded in a Si substrate. The coil in the Si substrate consists of superconducting microstrip lines and applies a magnetic field to the STJ to suppress the dc Josephson current. The embedded coil was designed with a line and space of 3 μm and a thickness of 120 nm. To planarize the coil, we employed chemical mechanical polishing (CMP) in our fabrication process. In this STJ, the maximum current of the embedded coil was 28 mA, which corresponded to the maximum magnetic field of 11.76 mT.

  6. Novel handheld magnetometer probe based on magnetic tunnelling junction sensors for intraoperative sentinel lymph node identification.

    Science.gov (United States)

    Cousins, A; Balalis, G L; Thompson, S K; Forero Morales, D; Mohtar, A; Wedding, A B; Thierry, B

    2015-06-03

    Using magnetic tunnelling junction sensors, a novel magnetometer probe for the identification of the sentinel lymph node using magnetic tracers was developed. Probe performance was characterised in vitro and validated in a preclinical swine model. Compared to conventional gamma probes, the magnetometer probe showed excellent spatial resolution of 4.0 mm, and the potential to detect as few as 5 μg of magnetic tracer. Due to the high sensitivity of the magnetometer, all first-tier nodes were identified in the preclinical experiments, and there were no instances of false positive or false negative detection. Furthermore, these preliminary data encourage the application of the magnetometer probe for use in more complex lymphatic environments, such as in gastrointestinal cancers, where the sentinel node is often in close proximity to other non-sentinel nodes, and high spatial resolution detection is required.

  7. Size and voltage dependence of effective anisotropy in sub-100-nm perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Piotrowski, Stephan K.; Bapna, Mukund; Oberdick, Samuel D.; Majetich, Sara A.; Li, Mingen; Chien, C. L.; Ahmed, Rizvi; Victora, R. H.

    2016-07-01

    Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The 1.23 -nm Co40Fe40B20 recording layer coercivity exhibits a size dependence which suggests single-domain behavior for diameters ≤100 nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy Keff using two different techniques. Keff is extracted both from distributions of the switching fields of the recording and reference layers and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that Keff increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that Keff can be controlled with a voltage down to the smallest size measured, 64 nm.

  8. Three-terminal magnetic tunneling junction device with perpendicular anisotropy CoFeB sensing layer

    Energy Technology Data Exchange (ETDEWEB)

    Honjo, H., E-mail: hr-honjou@aist.go.jp; Nebashi, R.; Tokutome, K.; Miura, S.; Sakimura, N.; Sugibayashi, T. [Green Platform Research Laboratories, NEC Corporation, Tsukuba (Japan); Fukami, S.; Kinoshita, K.; Murahata, M.; Kasai, N. [Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); Ishihara, K. [Smart Energy Research Laboratories, NEC Corporation, Tsukuba (Japan); Ohno, H. [Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); WPI Advanced Institute for Materials Research, Tohoku University, Sendai (Japan)

    2014-05-07

    We demonstrated read and write characteristics of a three terminal memory device with a perpendicular anisotropy-free layer of a strip of [Co/Ni] and a low-switching perpendicular-anisotropy CoFeB/MgO sensing layer. This new design of the cell results in a small cell area. The switching magnetic field of the sensing layer can be decreased by changing sputtering gas for the Ta-cap from Ar to Kr. An electron energy-loss spectroscopy analysis of the cross-section of the magnetic tunneling junction (MTJ) revealed that the boron content in CoFeB with a Kr-sputtered Ta-cap was smaller than that with an Ar-sputtered one. A change in resistance for the MTJ was observed that corresponded to the magnetic switching of the Co/Ni wire and its magnetoresistance ratio and critical current were 90% and 0.8 mA, respectively.

  9. Quantum dynamical calculations in clusters of spin 1/2 particles : Resonant coherent quantum tunneling on the magnetization reversal

    NARCIS (Netherlands)

    García-Pablos, D.; García, N.; Serena, P.A.; Raedt, H. De

    1996-01-01

    We investigate the reversal of magnetization and the coherence of tunneling when an external magnetic field is rotated instantaneously in systems of a few (N) spin 1/2 particles described by an anisotropic Heisenberg Hamiltonian at T=0. The temporal evolution is calculated by a numerically exact sol

  10. Quantum dynamical calculations in clusters of spin-1/2 particles: resonant coherent quantum tunneling on the magnetization reversal

    NARCIS (Netherlands)

    García-Pablos, D.; García, N.; Serena, P.A.; Raedt, H. De

    1996-01-01

    We investigate the reversal of magnetization and the coherence of tunneling when an external magnetic field is rotated instantaneously in systems of a few (N) spin 1/2 particles described by an anisotropic Heisenberg Hamiltonian at T=0. The temporal evolution is calculated by a numerically exact sol

  11. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Miwa, Shinji, E-mail: miwa@mp.es.osaka-u.ac.jp; Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Kotani, Yoshinori; Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198 (Japan)

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  12. Spin asymmetry calculations of the TMR-V curves in single and double-barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2011-10-01

    Spin-polarization asymmetry is the key parameter in asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) in magnetic tunnel junctions. In this paper, we study the value of the TMR as a function of the applied voltage Va in the single as well as double barrier magnetic tunnel junctions (SMTJ & DMTJ, which are constructed from CoFeB/MgO interfaces) and numerically estimate the possible difference of the TMR-V a curves for negative and positive voltages in the homojunctions. As a result, we found that AVB may help to determine the exact values of Fermi wave vectors for minority and majority conducting spin sub-bands. Moreover, significant asymmetry of the experimental TMR-Va curves, which arises due to different annealing regimes, is explained by different heights of the tunnel barriers and values of the spin asymmetry. The numerical TMR-V a data are in good agreement with experimental ones. © 2011 IEEE.

  13. Perpendicular magnetic tunnel junction with a strained Mn-based nanolayer

    Science.gov (United States)

    Suzuki, K. Z.; Ranjbar, R.; Okabayashi, J.; Miura, Y.; Sugihara, A.; Tsuchiura, H.; Mizukami, S.

    2016-07-01

    A magnetic tunnel junction with a perpendicular magnetic easy-axis (p-MTJ) is a key device for spintronic non-volatile magnetoresistive random access memory (MRAM). Co-Fe-B alloy-based p-MTJs are being developed, although they have a large magnetisation and medium perpendicular magnetic anisotropy (PMA), which make it difficult to apply them to a future dense MRAM. Here, we demonstrate a p-MTJ with an epitaxially strained MnGa nanolayer grown on a unique CoGa buffer material, which exhibits a large PMA of more than 5 Merg/cm3 and magnetisation below 500 emu/cm3 these properties are sufficient for application to advanced MRAM. Although the experimental tunnel magnetoresistance (TMR) ratio is still low, first principles calculations confirm that the strain-induced crystal lattice distortion modifies the band dispersion along the tetragonal c-axis into the fully spin-polarised state; thus, a huge TMR effect can be generated in this p-MTJ.

  14. Resonant spin-transfer torque in asymmetric double barrier magnetic tunnel junctions (MTJs)

    Science.gov (United States)

    Daqiq, Reza; Ghobadi, Nader

    2017-02-01

    The substitution effect of a Ferro-magnet (FM) electrode by a half-metallic FM material La0.7Sr0.3MnO3 (LSMO) on charge current and spin-transfer torque (STT) components is studied in MgO-based double barrier magnetic tunnel junctions (DBMTJs) with a middle non-magnetic metal (NM) layer. Using non-equilibrium Green's function (NEGF) formalism, it is observed that the current and STT components show oscillatory behavior due to quantum well states in the middle NM layer and resonant tunneling effect. We also study effect of difference in the thickness of the MgO insulators. Bias dependence demonstrate the magnitude enhancement of the current and in-plane STT in new asymmetric DBMTJs (A-DBMTJs) compared with symmetric DBMTJs (S-DBMTJs), however, perpendicular STT decreases in the A-DBMTJs. Results also show different behavior compared with conventional asymmetric MTJs and spin valves (SVs). Therefore, one can design new memory devices by means of suitable insulator and FM electrodes with proper thicknesses.

  15. Perpendicular magnetic tunnel junction with a strained Mn-based nanolayer.

    Science.gov (United States)

    Suzuki, K Z; Ranjbar, R; Okabayashi, J; Miura, Y; Sugihara, A; Tsuchiura, H; Mizukami, S

    2016-07-26

    A magnetic tunnel junction with a perpendicular magnetic easy-axis (p-MTJ) is a key device for spintronic non-volatile magnetoresistive random access memory (MRAM). Co-Fe-B alloy-based p-MTJs are being developed, although they have a large magnetisation and medium perpendicular magnetic anisotropy (PMA), which make it difficult to apply them to a future dense MRAM. Here, we demonstrate a p-MTJ with an epitaxially strained MnGa nanolayer grown on a unique CoGa buffer material, which exhibits a large PMA of more than 5 Merg/cm(3) and magnetisation below 500 emu/cm(3); these properties are sufficient for application to advanced MRAM. Although the experimental tunnel magnetoresistance (TMR) ratio is still low, first principles calculations confirm that the strain-induced crystal lattice distortion modifies the band dispersion along the tetragonal c-axis into the fully spin-polarised state; thus, a huge TMR effect can be generated in this p-MTJ.

  16. Comparison of the magneto-Peltier and magneto-Seebeck effects in magnetic tunnel junctions

    Science.gov (United States)

    Shan, J.; Dejene, F. K.; Leutenantsmeyer, J. C.; Flipse, J.; Münzenberg, M.; van Wees, B. J.

    2015-07-01

    Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction varies as the magnetic configuration changes from a parallel (P) to an antiparallel (AP) configuration. Here we report a study on its reciprocal effect, the magneto-Peltier effect, where the heat flow carried by the tunneling electrons is altered by changing the magnetic configuration of the MTJ. The magneto-Peltier signal that reflects the change in the temperature difference across the junction between the P and AP configurations scales linearly with the applied current in the small bias but is greatly enhanced in the large-bias regime, due to higher-order Joule heating mechanisms. By carefully extracting the linear response which reflects the magneto-Peltier effect, and comparing it with the magneto-Seebeck measurements performed on the same device, we observe results consistent with Onsager reciprocity. We estimate a magneto-Peltier coefficient of 13.4 mV in the linear regime using a three-dimensional thermoelectric model. Our result opens up the possibility of programmable thermoelectric devices based on the Peltier effect in MTJs.

  17. Hawking Tunneling Radiation of a Particle with Electric and Magnetic Charge from Kerr-Newman-Kasuya Black Hole

    Institute of Scientific and Technical Information of China (English)

    ZHAO Wei-Qin; LEI Jie-Hong; LIU Zhi-Xiang; YANG Shu-Zheng

    2008-01-01

    Extending the Parikh's quantum tunneling method of an uncharged particle, we investigate the quantum radiation characteristics of a particle with electric and magnetic charge via tunneling from the event horizon of theKerr-Newman-Kasuya black hole. The derived result supports the Parikh's opinion and the correction to the thermal spectrum is of precisely the form that satisfies the underlying unitary quantum theory, and finally provides a might explanation to the black hole information puzzle.

  18. Sub-nanometer atomic layer deposition for spintronics in magnetic tunnel junctions based on graphene spin-filtering membranes.

    Science.gov (United States)

    Martin, Marie-Blandine; Dlubak, Bruno; Weatherup, Robert S; Yang, Heejun; Deranlot, Cyrile; Bouzehouane, Karim; Petroff, Frédéric; Anane, Abdelmadjid; Hofmann, Stephan; Robertson, John; Fert, Albert; Seneor, Pierre

    2014-08-26

    We report on the successful integration of low-cost, conformal, and versatile atomic layer deposited (ALD) dielectric in Ni–Al2O3–Co magnetic tunnel junctions (MTJs) where the Ni is coated with a spin-filtering graphene membrane. The ALD tunnel barriers, as thin as 0.6 nm, are grown layer-by-layer in a simple, low-vacuum, ozone-based process, which yields high-quality electron-transport barriers as revealed by tunneling characterization. Even under these relaxed conditions, including air exposure of the interfaces, a significant tunnel magnetoresistance is measured highlighting the robustness of the process. The spin-filtering effect of graphene is enhanced, leading to an almost fully inversed spin polarization for the Ni electrode of −42%. This unlocks the potential of ALD for spintronics with conformal, layer-by-layer control of tunnel barriers in magnetic tunnel junctions toward low-cost fabrication and down-scaling of tunnel resistances.

  19. Magnetic tunneling junctions with permalloy electrodes: a study of barrier, thermal annealing, and interlayer coupling

    Energy Technology Data Exchange (ETDEWEB)

    Liu Xiaoyong E-mail: xiaoyong_liu@brown.edu; Ren Cong; Ritchie, Lance; Schrag, B.D.; Xiao Gang; Li Laifeng

    2003-11-01

    Magnetic properties of Ni{sub 81}Fe{sub 19}/Al{sub 2}O{sub 3}/Ni{sub 81}Fe{sub 19} tunneling junctions are studied for different Al thicknesses and plasma oxidation times. A maximal magnetoresistance of 34% is obtained with Al thickness of 20 A. Magnetometry reveals large exchange bias fields ({approx}400 Oe) over a wide range of barrier thicknesses, indicating junctions of high quality. Transport measurements conducted on junctions before and after thermal annealing show a dramatic improvement in barrier quality after annealing. Interlayer coupling fields have been measured as a function of barrier thickness for different oxidation times.

  20. Spontaneous fluxon production in annular Josephson tunnel junctions in the presence of a magnetic field

    DEFF Research Database (Denmark)

    Monaco, Roberto; Aarøe, Morten; Mygind, Jesper;

    2008-01-01

    We report on the spontaneous production of fluxons in annular Josephson tunnel junctions during a thermal quench in the presence of a symmetry-breaking magnetic field. The dependence on field intensity B of the probability (f) over bar (1) to trap a single defect during the N-S phase transition...... depends drastically on the sample circumferences. We show that this can be understood in the framework of the same picture of spontaneous defect formation that leads to the experimentally well attested scaling behavior of (f) over bar (1) with quench rate in the absence of an external field....

  1. Strength of the symmetry spin-filtering effect in magnetic tunnel junctions

    Science.gov (United States)

    Faleev, Sergey V.; Mryasov, Oleg N.; Parkin, Stuart S. P.

    2016-11-01

    We developed a general theory that allows us to predict the power factor n in the asymptotics of the tunneling magnetoresistance (TMR), TMR∝Nn , in the limit of large number of the tunnel barrier layers, N , for a magnetic tunnel junction (MTJ) system that has the so-called symmetry spin-filtering properties. Within this theory the only information required to determine n is the knowledge of the symmetries of the wave functions of the bulk electrode and barrier materials at the Γ point in the in-plane surface Brillouin zone. In particular, we show that for a MTJ that has the in-plane square symmetry only three values for the power factor are allowed: n =0 ,1 , and 2 for the asymptotics of the TMR enhanced due to the symmetry spin-filtering mechanism. To verify our theory we performed the density functional theory calculations of transmission functions and TMR for a Fe/MgO/Fe MTJ which confirm predicted values of the power factor n =0 ,1 , or 2 in specific ranges of energies (in particular, n =1 at the Fermi energy).

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

    Directory of Open Access Journals (Sweden)

    Qiang Hao

    2016-02-01

    Full Text Available 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.

  3. Origins of large light induced voltage in magnetic tunnel junctions grown on semiconductor substrates

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Y.; Lin, W.; Petit-Watelot, S.; Hehn, M.; Rinnert, H.; Lu, Y.; Montaigne, F.; Lacour, D.; Andrieu, S.; Mangin, S., E-mail: stephane.mangin@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine- BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex (France)

    2016-01-14

    Recently, the study of interactions between electron spins and heat currents has given rise to the field of “Spin Caloritronics”. Experimental studies of these interactions have shown a possibility to combine the use of heat and light to power magnetic tunnel junction (MTJ) devices. Here we present a careful study of an MTJ device on Si substrate that can be powered entirely by light. We analyze the influence of the material properties, device geometry, and laser characteristics on the electric response of the sample. We demonstrate that by engineering the MTJ and its electrical contact, a large photovoltage reaching 100 mV can be generated. This voltage originates from the Si substrate and depends on the MTJ magnetic configuration. Finally, we discuss the origin of the photo-voltage in terms of Seebeck and photovoltaic effects.

  4. Short-Term Plasticity and Long-Term Potentiation in Magnetic Tunnel Junctions: Towards Volatile Synapses

    Science.gov (United States)

    Sengupta, Abhronil; Roy, Kaushik

    2016-02-01

    Synaptic memory is considered to be the main element responsible for learning and cognition in humans. Although traditionally nonvolatile long-term plasticity changes are implemented in nanoelectronic synapses for neuromorphic applications, recent studies in neuroscience reveal that biological synapses undergo metastable volatile strengthening followed by a long-term strengthening provided that the frequency of the input stimulus is sufficiently high. Such "memory strengthening" and "memory decay" functionalities can potentially lead to adaptive neuromorphic architectures. In this paper, we demonstrate the close resemblance of the magnetization dynamics of a magnetic tunnel junction (MTJ) to short-term plasticity and long-term potentiation observed in biological synapses. We illustrate that, in addition to the magnitude and duration of the input stimulus, the frequency of the stimulus plays a critical role in determining long-term potentiation of the MTJ. Such MTJ synaptic memory arrays can be utilized to create compact, ultrafast, and low-power intelligent neural systems.

  5. Magnetic Tunnel Junction-Based On-Chip Microwave Phase and Spectrum Analyzer

    Science.gov (United States)

    Fan, Xin; Chen, Yunpeng; Xie, Yunsong; Kolodzey, James; Wilson, Jeffrey D.; Simons, Rainee N.; Xiao, John Q.

    2014-01-01

    A magnetic tunnel junction (MTJ)-based microwave detector is proposed and investigated. When the MTJ is excited by microwave magnetic fields, the relative angle between the free layer and pinned layer alternates, giving rise to an average resistance change. By measuring the average resistance change, the MTJ can be utilized as a microwave power sensor. Due to the nature of ferromagnetic resonance, the frequency of an incident microwave is directly determined. In addition, by integrating a mixer circuit, the MTJ-based microwave detector can also determine the relative phase between two microwave signals. Thus, the MTJ-based microwave detector can be used as an on-chip microwave phase and spectrum analyzer.

  6. Tunnel Junctions between Metals and Magnetic Perovskites and their use in Spin Polarized Spectroscopy

    Science.gov (United States)

    Mieville, Laurent; Worledge, Daniel; Geballe, Theodore H.; Char, Kookrin

    1998-03-01

    The recently reported "colossal" magnetoresistance (CMR) effect in (La_1-xA_x)MnO3 (where A stands for alkaline earth element) has shed new light on the magnetic properties exhibited by some members of the perovskite family with the generic formula ABO_3. We have studied the interface resistance between metals (Al, Nb and Pd) and magnetic perovskites ((La_0.66Sr_0.34)MnO_3, SrRuO3 and (La_0.5Sr_0.5)CoO_3) thin films grown by pulsed laser deposition. Low temperature measurements of tunnel junctions which aim to measure directly the amount of spin polarized carriers present in these perovskites will be also reviewed.

  7. Scanning Tunneling Microscopy of the π Magnetism of a Single Carbon Vacancy in Graphene

    Science.gov (United States)

    Zhang, Yu; Li, Si-Yu; Huang, Huaqing; Li, Wen-Tian; Qiao, Jia-Bin; Wang, Wen-Xiao; Yin, Long-Jing; Bai, Ke-Ke; Duan, Wenhui; He, Lin

    2016-10-01

    Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the π magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this π magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the π magnetism experimentally elusive. Here, we report direct experimental evidence of π magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective g factor around the atomic defect is measured to be about 40, which is about 20 times larger than the g factor for electron spins.

  8. Scanning Tunneling Microscopy of the π Magnetism of a Single Carbon Vacancy in Graphene.

    Science.gov (United States)

    Zhang, Yu; Li, Si-Yu; Huang, Huaqing; Li, Wen-Tian; Qiao, Jia-Bin; Wang, Wen-Xiao; Yin, Long-Jing; Bai, Ke-Ke; Duan, Wenhui; He, Lin

    2016-10-14

    Pristine graphene is strongly diamagnetic. However, graphene with single carbon atom defects could exhibit paramagnetism. Theoretically, the π magnetism induced by the monovacancy in graphene is characteristic of two spin-split density-of-states (DOS) peaks close to the Dirac point. Since its prediction, many experiments have attempted to study this π magnetism in graphene, whereas only a notable resonance peak has been observed around the atomic defects, leaving the π magnetism experimentally elusive. Here, we report direct experimental evidence of π magnetism by using a scanning tunneling microscope. We demonstrate that the localized state of the atomic defects is split into two DOS peaks with energy separations of several tens of meV. Strong magnetic fields further increase the energy separations of the two spin-polarized peaks and lead to a Zeeman-like splitting. Unexpectedly, the effective g factor around the atomic defect is measured to be about 40, which is about 20 times larger than the g factor for electron spins.

  9. Analytical description of ballistic spin currents and torques in magnetic tunnel junctions

    KAUST Repository

    Chshiev, M.

    2015-09-21

    In this work we demonstrate explicit analytical expressions for both charge and spin currents which constitute the 2×2 spinor in magnetic tunnel junctions with noncollinear magnetizations under applied voltage. The calculations have been performed within the free electron model in the framework of the Keldysh formalism and WKB approximation. We demonstrate that spin/charge currents and spin transfer torques are all explicitly expressed through only three irreducible quantities, without further approximations. The conditions and mechanisms of deviation from the conventional sine angular dependence of both spin currents and torques are shown and discussed. It is shown in the thick barrier approximation that all tunneling transport quantities can be expressed in an extremely simplified form via Slonczewski spin polarizations and our effective spin averaged interfacial transmission probabilities and effective out-of-plane polarizations at both interfaces. It is proven that the latter plays a key role in the emergence of perpendicular spin torque as well as in the angular dependence character of all spin and charge transport considered. It is demonstrated directly also that for any applied voltage, the parallel component of spin current at the FM/I interface is expressed via collinear longitudinal spin current components. Finally, spin transfer torque behavior is analyzed in a view of transverse characteristic length scales for spin transport.

  10. Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

    Directory of Open Access Journals (Sweden)

    Liang Liu

    2014-12-01

    Full Text Available We report on the low frequency (LF noise measurements in magnetic tunnel junctions (MTJs below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlOx/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlOx-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

  11. Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Liang; Xiang, Li; Guo, Huiqiang; Wei, Jian, E-mail: weijian6791@pku.edu.cn [International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China and Collaborative Innovation Center of Quantum Matter, Beijing (China); Li, D. L.; Yuan, Z. H.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn; Han, X. F. [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland)

    2014-12-15

    We report on the low frequency (LF) noise measurements in magnetic tunnel junctions (MTJs) below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlO{sub x}/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlO{sub x}-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN) is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

  12. Influence of the thermal interface resistance on the thermovoltage of a magnetic tunnel junction

    Science.gov (United States)

    Böhnert, Tim; Dutra, Roberta; Sommer, Rubem L.; Paz, Elvira; Serrano-Guisan, Santiago; Ferreira, Ricardo; Freitas, Paulo P.

    2017-03-01

    In the field of spin caloritronics recent theoretical models suggested a significant influence of the interfaces of the magnetic tunnel junction (MTJ) on the thermal transport. In this work magnetothermopower measurements are carried out on CoFeB/MgO/CoFeB nanopillars and an unexpected increase of the thermovoltage with the diameter of the nanopillars is observed. To understand this behavior the thermal profiles are computed by finite element simulations. The observed behavior with the pillar diameter could only be reproduced in simulations by considering a far lower effective thermal conductivity of the MgO than the intrinsic thin-film value. In agreement with theoretical predictions, a finite thermal conductivity of the MgO/CoFeB interface can explain this observation. This is experimental evidence of the influence of the thermal resistance of the MgO/CoFeB interfaces on magnetothermovoltage measurements and is in agreement with recent theoretical predictions. The measured magnetothermovoltage is around 4.5 μV and the simulated temperature difference is about 2 K across the tunnel barrier, which resulted in a magnetic contribution of the thermopower of Δ SMTJ≈-2.25 μ V K-1 . This value was about 20 times smaller than the result obtained by the typically used thermal conductivity of MgO thin films.

  13. Thermal Transport and Nonequilibrium Temperature Drop Across a Magnetic Tunnel Junction

    Science.gov (United States)

    Zhang, Jia; Bachman, Michael; Czerner, Michael; Heiliger, Christian

    2015-07-01

    In the field of spin caloritronics, spin-dependent transport phenomena are observed in a number of current experiments where a temperature gradient across a nanostructured interface is applied. The interpretation of these experiments is not clear as both phonons and electrons may contribute to thermal transport. Therefore, it still remains an open question how the temperature drop across a magnetic nanostructured interface arises microscopically. We answer this question for the case of a magnetic tunnel junction (MTJ) where the tunneling magneto-Seebeck effect occurs. Our explanation may be extended to other types of nanostructured interfaces. We explicitly calculate phonon and electron thermal conductance across Fe /MgO /Fe MTJs in an ab initio approach using a Green function method. Furthermore, we are able to calculate the electron and phonon temperature profile across the Fe /MgO /Fe MTJ by estimating the electron-phonon interaction in the Fe leads. Our results show that there is an electron-phonon temperature imbalance at the Fe-MgO interfaces. As a consequence, a revision of the interpretation of current experimental measurements may be necessary.

  14. Zero-field spin transfer oscillators based on magnetic tunnel junction having perpendicular polarizer and planar free layer

    Science.gov (United States)

    Fang, Bin; Feng, Jiafeng; Gan, Huadong; Malmhall, Roger; Huai, Yiming; Xiong, Rongxin; Wei, Hongxiang; Han, Xiufeng; Zhang, Baoshun; Zeng, Zhongming

    2016-12-01

    We experimentally studied spin-transfer-torque induced magnetization oscillations in an asymmetric MgO-based magnetic tunnel junction device consisting of an in-plane magnetized free layer and an out-of-plane magnetized polarizer. A steady auto-oscillation was achieved at zero magnetic field and room temperature, with an oscillation frequency that was strongly dependent on bias currents, with a large frequency tunability of 1.39 GHz/mA. Our results suggest that this new structure has a high potential for new microwave device designs.

  15. Zero-field spin transfer oscillators based on magnetic tunnel junction having perpendicular polarizer and planar free layer

    Directory of Open Access Journals (Sweden)

    Bin Fang

    2016-12-01

    Full Text Available We experimentally studied spin-transfer-torque induced magnetization oscillations in an asymmetric MgO-based magnetic tunnel junction device consisting of an in-plane magnetized free layer and an out-of-plane magnetized polarizer. A steady auto-oscillation was achieved at zero magnetic field and room temperature, with an oscillation frequency that was strongly dependent on bias currents, with a large frequency tunability of 1.39 GHz/mA. Our results suggest that this new structure has a high potential for new microwave device designs.

  16. Origin of magnetic contrast in spin-polarized scanning tunneling spectroscopy. Experiments on ultra-thin Mn films

    CERN Document Server

    Yamada, T K; Heijnen, G M M; Kempen, H V; Mizoguchi, T

    2003-01-01

    Normalized differential tunneling conductivities obtained with Fe-coated W tips show a spin-polarized peak around +0.8 V on ultrathin bct Mn films grown on Fe(001)-whiskers. This spin-polarized peak results in a clear magnetic contrast in spectroscopic images. Our normalization removes the influence of the tunneling probability and makes the spectroscopic curves most reliable for a derivation of the spin-resolved sample density of states (DOS) at positive voltages. From this analysis we conclude that the magnetic contrast in our spectroscopic maps is caused by a highly polarized DOS. Furthermore, a tip polarization of about 15% is found. (author)

  17. Proximity detector circuits: an attractive alternative to tunnel diode oscillators for contactless measurements in pulsed magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Altarawneh, Moaz M [Los Alamos National Laboratory; Mielke, Charles H [Los Alamos National Laboratory

    2009-01-01

    A new radio frequency oscillator circuit based on a proximity detector integrated circuit is described as an alternative for the traditional tunnel diode oscillator used for pulsed magnetic field measurements at low temperatures. The new circuit has been successfully applied to measure the superconducting upper critical field in Ba{sub 0.55}K{sub 0.45}Fe{sub 2}As{sub 2} single crystfl.ls up to 60 T. The new circuit design avoids many of the problems associated with tunnel diode circuits while keeping the advantages of contact less measurements in pulsed magnets.

  18. Thick CoFeB with perpendicular magnetic anisotropy in CoFeB-MgO based magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    V. B. Naik

    2012-12-01

    Full Text Available We have investigated the effect of an ultra-thin Ta insertion in the CoFeB (CoFeB/Ta/CoFeB free layer (FL on magnetic and tunneling magnetoresistance (TMR properties of a CoFeB-MgO system with perpendicular magnetic anisotropy (PMA. It is found that the critical thickness (tc to sustain PMA is doubled (tc = 2.6 nm in Ta-inserted CoFeB FL as compared to single CoFeB layer (tc = 1.3 nm. While the effective magnetic anisotropy is found to increase with Ta insertion, the saturation magnetization showed a slight reduction. As the CoFeB thickness increasing, the thermal stability of Ta inserted structure is significantly increased by a factor of 2.5 for total CoFeB thickness less than 2 nm. We have observed a reasonable value of TMR for a much thicker CoFeB FL (thickness = 2-2.6 nm with Ta insertion, and without significant increment in resistance-area product. Our results reveal that an ultra-thin Ta insertion in CoFeB might pay the way towards developing the high-density memory devices with enhanced thermal stability.

  19. Soft errors in 10-nm-scale magnetic tunnel junctions exposed to high-energy heavy-ion radiation

    Science.gov (United States)

    Kobayashi, Daisuke; Hirose, Kazuyuki; Makino, Takahiro; Onoda, Shinobu; Ohshima, Takeshi; Ikeda, Shoji; Sato, Hideo; Inocencio Enobio, Eli Christopher; Endoh, Tetsuo; Ohno, Hideo

    2017-08-01

    The influences of various types of high-energy heavy-ion radiation on 10-nm-scale CoFeB-MgO magnetic tunnel junctions with a perpendicular easy axis have been investigated. In addition to possible latent damage, which has already been pointed out in previous studies, high-energy heavy-ion bombardments demonstrated that the magnetic tunnel junctions may exhibit clear flips between their high- and low-resistance states designed for a digital bit 1 or 0. It was also demonstrated that flipped magnetic tunnel junctions still may provide proper memory functions such as read, write, and hold capabilities. These two findings proved that high-energy heavy ions can produce recoverable bit flips in magnetic tunnel junctions, i.e., soft errors. Data analyses suggested that the resistance flips stem from magnetization reversals of the ferromagnetic layers and that each of them is caused by a single strike of heavy ions. It was concurrently found that an ion strike does not always result in a flip, suggesting a stochastic process behind the flip. Experimental data also showed that the flip phenomenon is dependent on the device and heavy-ion characteristics. Among them, the diameter of the device and the linear energy transfer of the heavy ions were revealed as the key parameters. From their dependences, the physical mechanism behind the flip was discussed. It is likely that a 10-nm-scale ferromagnetic disk loses its magnetization due to a local temperature increase induced by a single strike of heavy ions; this demagnetization is followed by a cooling period associated with a possible stochastic recovery process. On the basis of this hypothesis, a simple analytical model was developed, and it was found that the model accounts for the results reasonably well. This model also predicted that magnetic tunnel junctions provide sufficiently high soft-error reliability for use in space, highlighting their advantage over their counterpart conventional semiconductor memories.

  20. Unidirectional Spin-Dependent Molecule-Ferromagnet Hybridized States Anisotropy in Cobalt Phthalocyanine Based Magnetic Tunnel Junctions

    Science.gov (United States)

    Barraud, Clément; Bouzehouane, Karim; Deranlot, Cyrile; Fusil, Stéphane; Jabbar, Hashim; Arabski, Jacek; Rakshit, Rajib; Kim, Dong-Jik; Kieber, Christophe; Boukari, Samy; Bowen, Martin; Beaurepaire, Eric; Seneor, Pierre; Mattana, Richard; Petroff, Frédéric

    2015-05-01

    Organic or molecular spintronics is a rising field of research at the frontier between condensed matter physics and chemistry. It aims to mix spin physics and the richness of chemistry towards designing new properties for spin electronics devices through engineering at the molecular scale. Beyond the expectation of a long spin lifetime, molecules can be also used to tailor the spin polarization of the injected current through the spin-dependent hybridization between molecules and ferromagnetic electrodes. In this Letter, we provide direct evidence of a hybrid interface spin polarization reversal due to the differing hybridization between phthalocyanine molecules and each cobalt electrode in Co /CoPc /Co magnetic tunnel junctions. Tunnel magnetoresistance and anisotropic tunnel magnetoresistance experiments show that interfacial hybridized electronic states have a unidirectional anisotropy that can be controlled by an electric field and that spin hybridization at the bottom and top interfaces differ, leading to an inverse tunnel magnetoresistance.

  1. Nonlinear damping effects in spin torque dynamics of magnetic tunnel junctions

    Science.gov (United States)

    Barsukov, Igor; Chen, Yu-Jin; Lee, Han Kyu; Goncalves, Alexandre; Katine, Jordan; Arias, Rodrigo; Ivanov, Boris; Krivorotov, Ilya

    2015-03-01

    Performance of nanoscale spin torque devices such as memory (STT-MRAM) and auto-oscillators critically depends on magnetic relaxation. It is commonly assumed that magnetization dynamics in the presence of spin torque can be understood as simple competition between antidamping arising from spin torque and Gilbert damping of the free layer. However our experiments reveal that the situation is more complex and that nonlinear damping processes in the free layer of magnetic tunnel junction (MTJ) nanopillars can strongly alter spin torque driven dynamics. We study elliptical MTJ nanopillars with in-plane magnetizations of the free layer and SAF layers by spin torque ferromagnetic resonance. We find an excitation spectrum associated with standing spin waves of the free layer. By varying the external field, the energy of a higher-order spin wave mode becomes twice the energy of the main mode. This opens up a nonlinear, resonant relaxation channel, giving rise to a damping increase of approximately 20 percent. With increasing spin torque provided by a DC bias current, we find that this relaxation channel competes with antidamping in a nonlinear manner, increasingly contributing to and even dominating the relaxation at subcritical currents.

  2. Synthesis and Study of Optical properties of MgO based TM oxide (TM=Cu, Mn and Zn) nanocomposites

    Science.gov (United States)

    Tamizh Selvi, K.; Alamelumangai, K.; Priya, M.; Rathnakumari, M.; Kumar, P. Suresh; Sagadevan, Suresh

    2016-11-01

    A nanocomposite of MgO based transition metal (TM) oxide (TM=Zn, Mn, and Cu) was synthesized using sol-gel method. The powder x-ray diffraction confirmed the phase purity and particle size. The surface morphology and elemental composition were examined by High resolution scanning electron microscopy and energy-dispersive x-ray spectroscopy. The change in optical band gap of the synthesized nanocomposites, by increasing the Mg content was determined using UV-vis spectra and the luminescent properties were analyzed using photoluminescence spectra.

  3. In-plane magnetic field effect on switching voltage and thermal stability in electric-field-controlled perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Grezes, C.; Rojas Rozas, A.; Ebrahimi, F.; Alzate, J. G.; Cai, X.; Katine, J. A.; Langer, J.; Ocker, B.; Khalili Amiri, P.; Wang, K. L.

    2016-07-01

    The effect of in-plane magnetic field on switching voltage (Vsw) and thermal stability factor (Δ) are investigated in electric-field-controlled perpendicular magnetic tunnel junctions (p-MTJs). Dwell time measurements are used to determine the voltage dependence of the energy barrier height for various in-plane magnetic fields (Hin), and gain insight into the Hin dependent energy landscape. We find that both Vsw and Δ decrease with increasing Hin, with a dominant linear dependence. The results are reproduced by calculations based on a macrospin model while accounting for the modified magnetization configuration in the presence of an external magnetic field.

  4. Negative tunneling magnetoresistance of Fe/MgO/NiO/Fe magnetic tunnel junction: Role of spin mixing and interface state

    Science.gov (United States)

    Zhang, Y.; Yan, X. H.; Guo, Y. D.; Xiao, Y.

    2017-08-01

    Motivated by a recent tunneling magnetoresistance (TMR) measurement in which the negative TMR is observed in MgO/NiO-based magnetic tunnel junctions (MTJs), we have performed systematic calculations of transmission, current, and TMR of Fe/MgO/NiO/Fe MTJ with different thicknesses of NiO and MgO layers based on noncollinear density functional theory and non-equilibrium Green's function theory. The calculations show that, as the thickness of NiO and MgO layers is small, the negative TMR can be obtained which is attributed to the spin mixing effect and interface state. However, in the thick MTJ, the spin-flipping scattering becomes weaker, and thus, the MTJs recover positive TMR. Based on our theoretical results, we believe that the interface state at Fe/NiO interface and the spin mixing effect induced by noncollinear interfacial magnetization will play important role in determining transmission and current of Fe/MgO/NiO/Fe MTJ. The results reported here will be important in understanding the electron tunneling in MTJ with the barrier made by transition metal oxide.

  5. The effect of the ferromagnetic metal layer on tunnelling conductance and magnetoresistance in double magnetic planar junctions

    Institute of Scientific and Technical Information of China (English)

    谢征微; 李伯臧; 李玉现

    2002-01-01

    Based on the free-electron approximation, we investigate the effect of the ferromagnetic metal layer on the tunnelling magnetoresistance (TMR) and tunnelling conductance (TC) in the double magnetic tunnel junctions (DMTJs)of the structure NM/FM/Ⅰ(S)/NM/Ⅰ(S)/FM/NM, where FM, NM and Ⅰ(S) represent the ferromagnetic metal, nonmagnetic metal and insulator (semiconductor), respectively. The FM, Ⅰ(S) and inner NM layers are of finite thickness,while the thickness of the outer NM layer is infinite. The calculated results show that, due to the spin-dependent interfacial potential barriers caused by electronic band mismatch between the various magnetic and nonmagnetic layers,the dependences of the TMR and TC on the thicknesses of the FM layers exhibit oscillations, and a much higher TMR can be obtained for suitable thicknesses of FM layers.

  6. Methyl quantum tunneling and nitrogen-14 NQR NMR studies using a SQUID magnetic resonance spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Black, Bruce Elmer [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1993-07-01

    Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) techniques have been very successful in obtaining molecular conformation and dynamics information. Unfortunately, standard NMR and NQR spectrometers are unable to adequately detect resonances below a few megahertz due to the frequency dependent sensitivity of their Faraday coil detectors. For this reason a new spectrometer with a dc SQUID (Superconducting Quantum Interference Device) detector, which has no such frequency dependence, has been developed. Previously, this spectrometer was used to observe 11B and 27Al NQR resonances. The scope of this study was increased to include 23Na, 51V, and 55Mn NQR transitions. Also, a technique was presented to observe 14N NQR resonances through cross relaxation of the nitrogen polarization to adjacent proton spins. When the proton Zeeman splitting matches one nitrogen quadrupoler transition the remaining two 14N transitions can be detected by sweeping a saturating rf field through resonance. Additionally, simultaneous excitation of two nitrogen resonances provides signal enhancement which helps to connect transitions from the same site. In this way, nitrogen-14 resonances were observed in several amino acids and polypeptides. This spectrometer has also been useful in the direct detection of methyl quantum tunneling splittings at 4.2 K. Tunneling, frequencies of a homologous series of carboxylic acids were measured and for solids with equivalent crystal structures, an exponential correlation between the tunneling frequency and the enthalpy of fusion is observed. This correlation provides information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.

  7. Methyl Quantum Tunneling and NITROGEN-14 Nqr Studies Using a DC SQUID Magnetic Resonance Spectrometer.

    Science.gov (United States)

    Black, Bruce Elmer

    Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) techniques have been very successful in obtaining molecular conformation and dynamics information. Unfortunately, standard NMR and NQR spectrometers are unable to adequately detect resonances below a few megahertz due to the frequency dependent sensitivity of their Faraday coil detectors. For this reason a new spectrometer with a dc SQUID (Superconducting Quantum Interference Device) detector, which has no such frequency dependence, has been developed. Previously, this spectrometer was used to observe ^ {11}B and ^{27} Al NQR resonances. I have increased the scope of this study to include ^{23}Na, ^{51}V, and ^ {55}Mn NQR transitions. Also, I present a technique to observe ^{14}N NQR resonances through cross relaxation of the nitrogen polarization to adjacent proton spins. When the proton Zeeman splitting matches one nitrogen quadrupolar transition the remaining two ^ {14}N transitions can be detected by sweeping a saturating rf field through resonance. Additionally, simultaneous excitation of two nitrogen resonances provides signal enhancement which helps to connect transitions from the same site. In this way, we have observed nitrogen -14 resonances in several amino acids and polypeptides. This spectrometer has also been useful in the direct detection of methyl quantum tunneling splittings at 4.2 K. Tunneling frequencies of a homologous series of carboxylic acids were measured and for solids with equivalent crystal structures, an exponential correlation between the tunneling frequency and the enthalpy of fusion is observed. This correlation provides information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.

  8. Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling

    Science.gov (United States)

    Chavent, A.; Ducruet, C.; Portemont, C.; Vila, L.; Alvarez-Hérault, J.; Sousa, R.; Prejbeanu, I. L.; Dieny, B.

    2016-09-01

    Understanding quantitatively the heating dynamics in magnetic tunnel junctions submitted to current pulses is very important in the context of spin-transfer-torque magnetic random-access memory development. Here we provide a method to probe the heating of magnetic tunnel junctions using the Ruderman-Kittel-Kasuya-Yoshida coupling of a synthetic ferrimagnetic storage layer as a thermal sensor. The temperature increase versus applied bias voltage is measured thanks to the decrease of the spin-flop field with temperature. This method allows distinguishing spin-transfer torque effects from the influence of temperature on the switching field. The heating dynamics is then studied in real time by probing the conductance variation due to spin-flop rotation during heating. This approach provides a method for measuring fast heating in spintronic devices, particularly magnetic random-access memory using thermally assisted or spin-transfer torque writing.

  9. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Science.gov (United States)

    Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, J.-Q.

    2016-11-01

    We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  10. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Directory of Open Access Journals (Sweden)

    Chao Zhang

    2016-11-01

    Full Text Available We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  11. A Novel Design and Fabrication of Magnetic Random Access Memory Based on Nano-ring-type Magnetic Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    X.F.Han; M. Ma; Y. Wang; Z.C. Wen; D.P. Liu; W.S.Zhan; H.X. Wei; Z.L.Peng; H.D. Yang; J.F. Feng; G.X.Du; Z.B.Sun; L.X. Jiang; Q.H. Qin

    2007-01-01

    Nano-ring-type magnetic tunnel junctions (NR-MTJs) with the layer structure of Ta(5)/Ir22Mn78(10)/Co75Fe25(2)/Ru(0.75)/Co60Fe20B20(3)/Al(0.6)-oxide/Co60Fe20B20(2.5)/Ta(3)/Ru(5) (thickness unit: nm)were nano-fabricated on the Si(100)/SiO2 substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography (EBL) and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunnelling magnetoresistance (TMR & R) versus driving current (I) loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co60Fe20B20 layer relative to the reference Co60Fe20B20 layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch2 even 6 Gbite/inch2 are possible using both 1 NR-MTJ+1 transistor structure and current switching mechanism based on based on our fabricated 4×4 MRAM demo devices.

  12. Magnetotransport in MgO-based magnetic tunnel junctions grown by molecular beam epitaxy (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Andrieu, S., E-mail: stephane.andrieu@univ-lorraine.fr; Bonell, F.; Hauet, T.; Montaigne, F. [Institut Jean Lamour, Nancy University/CNRS, Bd des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy (France); Calmels, L.; Snoeck, E. [CEMES, CNRS and Toulouse University, 29 rue Jeanne Marvig, 31055 Toulouse (France); Lefevre, P.; Bertran, F. [Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette cedex (France)

    2014-05-07

    The strong impact of molecular beam epitaxy growth and Synchrotron Radiation characterization tools in the understanding of fundamental issues in nanomagnetism and spintronics is illustrated through the example of fully epitaxial MgO-based Magnetic Tunnel Junctions (MTJs). If ab initio calculations predict very high tunnel magnetoresistance (TMR) in such devices, some discrepancy between theory and experiments still exists. The influence of imperfections in real systems has thus to be considered like surface contaminations, structural defects, unexpected electronic states, etc. The influence of possible oxygen contamination at the Fe/MgO(001) interface is thus studied, and is shown to be not so detrimental to TMR as predicted by ab initio calculations. On the contrary, the decrease of dislocations density in the MgO barrier of MTJs using Fe{sub 1−x}V{sub x} electrodes is shown to significantly increase TMR. Finally, unexpected transport properties in Fe{sub 1−X}Co{sub x}/MgO/Fe{sub 1−X}Co{sub x} (001) are presented. With the help of spin and symmetry resolved photoemission and ab initio calculation, the TMR decrease for Co content higher than 25% is shown to come from the existence of an interface state and the shift of the empty Δ1 minority spin state towards the Fermi level.

  13. Transport through artificial single-molecule magnets:Spin-pair state sequential tunneling and Kondo effects

    Institute of Scientific and Technical Information of China (English)

    Niu Peng-Bin; Wang Qiang; Nie Yi-Hang

    2013-01-01

    The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn+2 ion (S =5/2) are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with (2S+ 1) sublevels.In the sequential tunneling regime,the differential conductance exhibits (2S + 1) possible peaks,corresponding to resonance tunneling via (2S + 1) sublevels.At low temperature,Kondo physics dominates transport and (2S + 1) Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.

  14. AlOx barrier growth in magnetic tunnel junctions for sensor applications

    Science.gov (United States)

    Knudde, S.; Farinha, G.; Leitao, D. C.; Ferreira, R.; Cardoso, S.; Freitas, P. P.

    2016-08-01

    Magnetic tunnel junction (MTJ) research has been focused on MgO-based crystalline structures due to high tunnel magnetoresistance (TMR), despite requiring a more severe process control than previous generations of MTJ stacks based on amorphous barriers (e.g. AlOx). In this work, we study the electrical transport properties in AlOx barriers in MTJ sensors fabricated using Ion beam sputtering and remote plasma oxidation. Amorphous barriers were prepared from oxidation of thin Al films, deposited in single step barrier (SSB-Al 1 nm/oxidation) or double step barrier (DSB-Al 0.5 nm/oxidation/Al 0.5 nm/oxidation) structures. We show tunable resistance-area products (RxA) ranging from ≈ 10 Ω μ m2 (suited for nano devices) up to ≈ 100 k Ω μ m2 (suited for large area sensors) with TMR above 30%. For all geometries studied, the structures have a coercivity free linear response and require none or one annealing step. This makes them very competitive for all industrial applications where the TMR level is not the dominant specification to meet.

  15. Influence of exchange bias on magnetic losses in CoFeB/MgO/CoFeB tunnel junctions

    Science.gov (United States)

    Stearrett, Ryan; Wang, W. G.; Kou, Xiaoming; Feng, J. F.; Coey, J. M. D.; Xiao, J. Q.; Nowak, E. R.

    2012-07-01

    The strength of the exchange bias field is found to influence the low-frequency magnetoresistive noise associated with the magnetic reference layer in sputtered-deposited and electron-beam-evaporated CoFeB/MgO/CoFeB tunnel junctions. The noise is due to magnetic losses arising in the reference layer. The losses are parameterized by a phase lag ɛ which exhibits a nontrivial dependence on the externally applied field. The general trend found among all devices is that the losses are largest in the antiparallel state. The effect of exchange bias on the reference layer's noise is investigated at a field corresponding to maximum resistance susceptibility, Href. Higher values for the phase lag at Href, ɛref, are found in devices having a large exchange bias field. We also observed that Href and ɛref are larger in devices having thicker seed layers. This characteristic is also evident in double-barrier magnetic tunnel junctions. Prolonged thermal annealing is found to decrease ɛref, reduce Href, and alter the field profile of the resistance susceptibility of the reference layer to resemble that of a more magnetically soft behavior. In addition to its impact on the magnetoresistive noise, the incorporation of exchange bias layers into the materials stack also affects the tunneling magnetoresistance ratio with higher values found at smaller exchange bias fields. We attribute the magnitude of the magnetic losses, and hence the magnetoresistive noise, from the reference layer to disorder in its magnetic microstructure. Our results indicate that the nature and degree of disorder are correlated to the strength of the exchange bias coupling. The origin of this correlation may be due to a competition between different microstructures among various layers, one that leads to coherent tunneling (large tunneling magnetoresistance) in MgO-based tunneling devices and the other which promotes strong exchange bias coupling. A decrease in the exchange bias either through degradation

  16. Scalable and thermally robust perpendicular magnetic tunnel junctions for STT-MRAM

    Science.gov (United States)

    Gottwald, M.; Kan, J. J.; Lee, K.; Zhu, X.; Park, C.; Kang, S. H.

    2015-01-01

    Thermal budget, stack thickness, and dipolar offset field control are crucial for seamless integration of perpendicular magnetic junctions (pMTJ) into semiconductor integrated circuits to build scalable spin-transfer-torque magnetoresistive random access memory. This paper is concerned with materials and process tuning to deliver thermally robust (400 °C, 30 min) and thin (i.e., fewer layers and integration-friendly) pMTJ utilizing Co/Pt-based bottom pinned layers. Interlayer roughness control is identified as a key enabler to achieve high thermal budgets. The dipolar offset fields of the developed film stacks at scaled dimensions are evaluated by micromagnetic simulations. This paper shows a path towards achieving sub-15 nm-thick pMTJ with tunneling magnetoresistance ratio higher than 150% after 30 min of thermal excursion at 400 °C.

  17. Scalable and thermally robust perpendicular magnetic tunnel junctions for STT-MRAM

    Energy Technology Data Exchange (ETDEWEB)

    Gottwald, M. [QUALCOMM Europe Incorporated, Kapeldreef 75, 3001 Heverlee (Belgium); Kan, J. J.; Lee, K.; Zhu, X.; Park, C.; Kang, S. H. [Corporate Research and Development, Qualcomm Technologies Incorporated, San Diego, California 92121-1714 (United States)

    2015-01-19

    Thermal budget, stack thickness, and dipolar offset field control are crucial for seamless integration of perpendicular magnetic junctions (pMTJ) into semiconductor integrated circuits to build scalable spin-transfer-torque magnetoresistive random access memory. This paper is concerned with materials and process tuning to deliver thermally robust (400 °C, 30 min) and thin (i.e., fewer layers and integration-friendly) pMTJ utilizing Co/Pt-based bottom pinned layers. Interlayer roughness control is identified as a key enabler to achieve high thermal budgets. The dipolar offset fields of the developed film stacks at scaled dimensions are evaluated by micromagnetic simulations. This paper shows a path towards achieving sub-15 nm-thick pMTJ with tunneling magnetoresistance ratio higher than 150% after 30 min of thermal excursion at 400 °C.

  18. Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

    Energy Technology Data Exchange (ETDEWEB)

    Tsang, Juine-Kai [Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Physics

    1980-01-01

    Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data.

  19. Huge spin-transfer torque in a magnetic tunnel junction by a superlattice barrier

    Science.gov (United States)

    Chen, C. H.; Tseng, P.; Ko, C. W.; Hsueh, W. J.

    2017-09-01

    Huge spin-transfer torque (STT) in a magnetic tunnel junction (MTJ) achieved by superlattice barrier composed of alternate layers of a nonmagnetic metal and an insulator is proposed. The magnitude of the STT depends on the number of cells in the superlattice barrier and the nonmagnetic metal layer's thickness. The result shows that the STT of the novel superlattice-barrier MTJ can reach values up to four orders of magnitude greater than those of traditional single-barrier stacks based on three cells superlattice by designing the nonmagnetic metal layer's thickness. In addition, the spin-transfer torque of the proposed MTJ can also be thousands of magnitude greater than those of traditional double-barrier MTJs.

  20. Magnetic tunnel junction design margin exploration for self-reference sensing scheme.

    Science.gov (United States)

    Sun, Z; Li, H; Wang, X

    2012-04-01

    This work investigates the magnetic tunnel junction (MTJ) design requirements for the application of nondestructive self-reference sensing scheme, a novel sensing scheme featuring high tolerance of process variations, fast sensing speed, and no impact on device reliability. Unlike the conventional sensing scheme that requires a large TMR ratio and the uniform antiparallel and parallel resistances for MTJs, the nondestructive self-reference sensing scheme is more sensitive to the roll-off slope of MTJ's R-I or R-V curve. Our purpose is to provide a guidance to facilitate MTJ design used in the nondestructive self-reference scheme. In this work, we comprehensively investigate and analyze the design matrix by considering MTJ device physical properties, such as bias voltage dependent conductance, spin torque, etc. The manuscript suggests the approaches to optimize MTJ design for better trade-off between device properties and circuit design.

  1. Very strong antiferromagnetic interlayer exchange coupling with iridium spacer layer for perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Yakushiji, Kay; Sugihara, Atsushi; Fukushima, Akio; Kubota, Hitoshi; Yuasa, Shinji

    2017-02-01

    We systematically studied the interlayer exchange coupling (IEC) in a perpendicular synthetic antiferromagnetically coupled structure having an Ir spacer layer for perpendicular magnetic tunnel junctions (p-MTJs). We found a broader peak in IEC energy density (Jex) versus spacer thickness (tIr) compared with the case of using a Ru spacer. The highest IEC energy density was 2.6 erg/cm2 at a tIr of about 5 nm. The p-MTJ nanopillars had a high magnetoresistance ratio (131%) as well as a high spin-transfer torque (STT) switching efficiency (about 2). An Ir spacer can be used to make a stable reference layer for STT magnetoresistive random access memory.

  2. Magnetic properties and tun-neling magnetoresistance in FeCo-SiO2 granular films

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Fefv(SiO2)1-fv granular films were fabricated by rf sputtering (fv represents the Fe volume fraction). The microstructure, magnetic properties as well as the tunneling magnetoresistance effect (TMR) were systematically studied. It was found that the maximum TMR ratio is about -3.3% at fv = 0.33. Under the same condition, a series of (Fe100-x Cox)0.33(SiO2)0.67 were prepared. TMR value reaches -4.5% at x = 53, while the microstructure of the film still keeps as that of Fe0.33(SiO2)0.67. The higher TMR ratio is con-tributed to the elevating of the spin polarization of particles. This is consistent with Inoue's theory.

  3. Double-pinned magnetic tunnel junction sensors with spin-valve-like sensing layers

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Z. H.; Huang, L.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn; Wen, Z. C.; Li, D. L.; Han, X. F. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P. O. Box 603, Beijing 100190 (China); Nakano, Takafumi; Naganuma, Hiroshi, E-mail: naganuma@mlab.apph.tohoku.ac.jp [Department of Applied Physics, Tohoku University, Sendai, Miyagi 980-8579 (Japan); Yu, T. [Department of Applied Physics, Tohoku University, Sendai, Miyagi 980-8579 (Japan); College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China)

    2015-08-07

    MgO magnetic tunnel junction (MTJ) sensors with spin-valve-like sensing layers of Ir{sub 22}Mn{sub 78} (6)/Ni{sub 80}Fe{sub 20} (t{sub NiFe} = 20–70)/Ru (0.9)/Co{sub 40}Fe{sub 40}B{sub 20} (3) (unit: nm) have been fabricated. A linear field dependence of magnetoresistance for these MTJ sensors was obtained by carrying out a two-step field annealing process. The sensitivity and linear field range can be tuned by varying the thickness of NiFe layer and annealing temperature, and a high sensitivity of 37%/mT has been achieved in the MTJ sensors with 70 nm NiFe at the optimum annealing temperature of 230 °C. Combining the spin-valve-like sensing structure and a soft magnetic NiFe layer, MTJ sensors with relatively wide field sensing range have been achieved and could be promising for showing high sensitivity magnetic field sensing applications.

  4. SPICE modelling of magnetic tunnel junctions written by spin-transfer torque

    Energy Technology Data Exchange (ETDEWEB)

    Guo, W; Prenat, G; De Mestier, N; Baraduc, C; Dieny, B [SPINTEC, UMR(8191), INAC, CEA/CNRS/UJF, 17 Av. des Martyrs, 38054 Grenoble Cedex 9 (France); Javerliac, V; El Baraji, M, E-mail: guillaume.prenat@cea.f [CROCUS Technology, 5 Place Robert Schuman, 38025 Grenoble (France)

    2010-06-02

    Spintronics aims at extending the possibility of conventional electronics by using not only the charge of the electron but also its spin. The resulting spintronic devices, combining the front-end complementary metal oxide semiconductor technology of electronics with a magnetic back-end technology, employ magnetic tunnel junctions (MTJs) as core elements. With the intent of simulating a circuit without fabricating it first, a reliable MTJ electrical model which is applicable to the standard SPICE (Simulation Program with Integrated Circuit Emphasis) simulator is required. Since such a model was lacking so far, we present a MTJ SPICE model whose magnetic state is written by using the spin-transfer torque effect. This model has been developed in the C language and validated on the Cadence Virtuoso Platform with a Spectre simulator. Its operation is similar to that of the standard BSIM (Berkeley Short-channel IGFET Model) SPICE model of the MOS transistor and fully compatible with the SPICE electrical simulator. The simulation results obtained using this model have been found in good accord with those theoretical macrospin calculations and results.

  5. A Survey on the Modeling of Magnetic Tunnel Junctions for Circuit Simulation

    Directory of Open Access Journals (Sweden)

    Hyein Lim

    2016-01-01

    Full Text Available Spin-transfer torque-based magnetoresistive random access memory (STT-MRAM is a promising candidate for universal memory that may replace traditional memory forms. It is expected to provide high-speed operation, scalability, low-power dissipation, and high endurance. MRAM switching technology has evolved from the field-induced magnetic switching (FIMS technique to the spin-transfer torque (STT switching technique. Additionally, material technology that induces perpendicular magnetic anisotropy (PMA facilitates low-power operation through the reduction of the switching current density. In this paper, the modeling of magnetic tunnel junctions (MTJs is reviewed. Modeling methods and models of MTJ characteristics are classified into two groups, macromodels and behavioral models, and the most important characteristics of MTJs, the voltage-dependent MTJ resistance and the switching behavior, are compared. To represent the voltage dependency of MTJ resistance, some models are based on physical mechanisms, such as Landau-Lifshitz-Gilbert (LLG equation or voltage-dependent conductance. Some behavioral models are constructed by adding fitting parameters or introducing new physical parameters to represent the complex switching behavior of an MTJ over a wide range of input current conditions. Other models that are not based on physical mechanisms are implemented by simply fitting to experimental data.

  6. Perpendicular magnetic tunnel junction with thin CoFeB/Ta/Co/Pd/Co reference layer

    Energy Technology Data Exchange (ETDEWEB)

    Gan, Huadong, E-mail: huadong@avalanche-technology.com; Malmhall, Roger; Wang, Zihui; Yen, Bing K; Zhang, Jing; Wang, Xiaobin; Zhou, Yuchen; Hao, Xiaojie; Jung, Dongha; Satoh, Kimihiro; Huai, Yiming [Avalanche Technology, 46600 Landing Parkway, Fremont, California 94538 (United States)

    2014-11-10

    Integration of high density spin transfer torque magnetoresistance random access memory requires a thin stack (less than 15 nm) of perpendicular magnetic tunnel junction (p-MTJ). We propose an innovative approach to solve this challenging problem by reducing the thickness and/or moment of the reference layer. A thin reference layer structure of CoFeB/Ta/Co/Pd/Co has 60% magnetic moment of the conventional thick structure including [Co/Pd] multilayers. We demonstrate that the perpendicular magnetization of the CoFeB/Ta/Co/Pd/Co structure can be realized by anti-ferromagnetically coupling to a pinned layer with strong perpendicular anisotropy via Ruderman-Kittel-Kasuya-Yosida exchange interaction. The pMTJ with thin CoFeB/Ta/Co/Pd/Co reference layer has a comparable TMR ratio (near 80%) as that with thick reference layer after annealing at 280 °C. The pMTJ with thin reference layer has a total thickness less than 15 nm, thereby significantly increasing the etching margin required for integration of high density pMTJ array on wafers with form factor of 300 mm and beyond.

  7. Brief rapid thermal treatment effect on patterned CoFeB-based magnetic tunneling junctions

    Science.gov (United States)

    Wu, Kuo-Ming; Huang, Chao-Hsien; Wang, Yung-Hung; Kao, Ming-Jer; Tsai, Ming-Jinn; Wu, Jong-Ching; Horng, Lance

    2007-05-01

    The brief thermal treatment effects on the magnetoresistance of microstructured Co60Fe20B20-based magnetic tunneling junctions have been studied. The elliptical shape of devices with long/short axis of 4/2μm was patterned out of film stack of seed layer (20)/PtMn(15)/Co60Fe20B20(3)/Al(0.7)oxide/C60Fe20B20(20)/capping layer (48) (thickness unit in nanometers) combining conventional lithography and inductively coupled plasma reactive ion beam etching technologies. The thermal annealing was carried out with device loading into a furnace with preset temperatures ranging from 100to400°C for only 5min in the absence of any external magnetic field. The magnetoresistance was found to increase with increasing annealing temperatures up to 250°C and then decrease at higher annealing temperatures. In addition, the magnetoresistance ratio of around 35%, similar to that of as-fabricated devices, sustains up to annealing temperature of 350°C. This survival of magnetoresistance at higher annealing temperature is due to boron conservation in the amorphous CoFeB ferromagnetic layer at higher annealing temperature for only a short time, which is manifested using x-ray diffractometer technique.

  8. HfO2 and SiO2 as barriers in magnetic tunneling junctions

    Science.gov (United States)

    Shukla, Gokaran; Archer, Thomas; Sanvito, Stefano

    2017-05-01

    SiO2 and HfO2 are both high-k, wide-gap semiconductors, currently used in the microelectronic industry as gate barriers. Here we investigate whether the same materials can be employed to make magnetic tunnel junctions, which in principle can be amenable for integration in conventional Si technology. By using a combination of density functional theory and the nonequilibrium Green's functions method for quantum transport we have studied the transport properties of Co [0001 ] /SiO2[001 ] /Co [0001 ] and Fe [001 ] /HfO2[001 ] /Fe [001 ] junctions. In both cases we found a quite large magnetoresistance, which is explained through the analysis of the real band structure of the magnets and the complex one of the insulator. We find that there is no symmetry spin filtering for the Co-based junction since the high transmission Δ2' band crosses the Fermi level, EF, for both spin directions. However, the fact that Co is a strong ferromagnet makes the orbital contribution to the two Δ2' spin subbands different, yielding magnetoresistance. In contrast for the Fe-based junction symmetry filtering is active for an energy window spanning between the Fermi level and 1 eV below EF, with Δ1 symmetry contributing to the transmission.

  9. Massive Dirac fermion transport in a gapped graphene-based magnetic tunnel junction

    Science.gov (United States)

    Soodchomshom, Bumned; Tang, I.-Ming; Hoonsawat, Rassmidara

    2009-08-01

    The spin transport in a graphene-based magnetic (NG/ferromagnetic barrier (FB)/NG) tunnel junction with the graphene sheet being grown on a SiC substrate is investigated. Zhou et al. [Nat. Mater. 6 (2007) 770] has shown that in these epitaxial grown graphene sheets, the electrons behave like massive relativistic particles with an energy gap of 2 Δ∼260 meV opening up in the energy spectrum of the massive relativistic electron. Basing on assumption that gap in graphene can occur under the influence of the magnetic field, we find that in the case of thick ferromagnetic graphene barriers, the electronic gap causes the barrier to behave as a strong insulator when the gate potential is in the range 400-130 meVswitched from a 100% spin up current to a 100% spin down current by small variation of V G from V G E f , the features of a perfect spin filtering electronic junction.

  10. A New Circuit Model for Spin-Torque Oscillator Including Perpendicular Torque of Magnetic Tunnel Junction

    Directory of Open Access Journals (Sweden)

    Hyein Lim

    2013-01-01

    Full Text Available Spin-torque oscillator (STO is a promising new technology for the future RF oscillators, which is based on the spin-transfer torque (STT effect in magnetic multilayered nanostructure. It is expected to provide a larger tunability, smaller size, lower power consumption, and higher level of integration than the semiconductor-based oscillators. In our previous work, a circuit-level model of the giant magnetoresistance (GMR STO was proposed. In this paper, we present a physics-based circuit-level model of the magnetic tunnel junction (MTJ-based STO. MTJ-STO model includes the effect of perpendicular torque that has been ignored in the GMR-STO model. The variations of three major characteristics, generation frequency, mean oscillation power, and generation linewidth of an MTJ-STO with respect to the amount of perpendicular torque, are investigated, and the results are applied to our model. The operation of the model was verified by HSPICE simulation, and the results show an excellent agreement with the experimental data. The results also prove that a full circuit-level simulation with MJT-STO devices can be made with our proposed model.

  11. Effect of Low-Frequency AC Magnetic Susceptibility and Magnetic Properties of CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

    Directory of Open Access Journals (Sweden)

    Yuan-Tsung Chen

    2014-01-01

    Full Text Available In this investigation, the low-frequency alternate-current (AC magnetic susceptibility (χac and hysteresis loop of various MgO thickness in CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ determined coercivity (Hc and magnetization (Ms and correlated that with χac maxima. The multilayer films were sputtered onto glass substrates and the thickness of intermediate barrier MgO layer was varied from 6 to 15 Å. An experiment was also performed to examine the variation of the highest χac and maximum phase angle (θmax at the optimal resonance frequency (fres, at which the spin sensitivity is maximal. The results reveal that χac falls as the frequency increases due to the relationship between magnetization and thickness of the barrier layer. The maximum χac is at 10 Hz that is related to the maximal spin sensitivity and that this corresponds to a MgO layer of 11 Å. This result also suggests that the spin sensitivity is related to both highest χac and maximum phase angle. The corresponding maximum of χac is related to high exchange coupling. High coercivity and saturation magnetization contribute to high exchange-coupling χac strength.

  12. Trend of tunnel magnetoresistance and variation in threshold voltage for keeping data load robustness of metal–oxide–semiconductor/magnetic tunnel junction hybrid latches

    Energy Technology Data Exchange (ETDEWEB)

    Ohsawa, T. [Center for Spintronics Integrated Systems, Tohoku University, Sendai 980-8579 (Japan); Ikeda, S.; Hanyu, T.; Ohno, H. [Center for Spintronics Integrated Systems, Tohoku University, Sendai 980-8579 (Japan); Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai 980-8579 (Japan); Endoh, T., E-mail: tetsuo.endoh@cies.tohoku.ac.jp [Center for Spintronics Integrated Systems, Tohoku University, Sendai 980-8579 (Japan); Center for Innovative Integrated Electronic Systems, Tohoku University, Sendai 980-8579 (Japan); Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan)

    2014-05-07

    The robustness of data load of metal–oxide–semiconductor/magnetic tunnel junction (MOS/MTJ) hybrid latches at power-on is examined by using Monte Carlo simulation with the variations in magnetoresistances for MTJs and in threshold voltages for MOSFETs involved in 90 nm technology node. Three differential pair type spin-transfer-torque-magnetic random access memory cells (4T2MTJ, 6T2MTJ, and 8T2MTJ) are compared for their successful data load at power-on. It is found that the 4T2MTJ cell has the largest pass area in the shmoo plot in TMR ratio (tunnel magnetoresistance ratio) and V{sub dd} in which a whole 256 kb cell array can be powered-on successfully. The minimum TMR ratio for the 4T2MTJ in 0.9 V < V{sub dd} < 1.9 V is 140%, while the 6T2MTJ and the 8T2MTJ cells require TMR ratio larger than 170%.

  13. Novel compact model for multi-level spin torque magnetic tunnel junctions

    Science.gov (United States)

    Prajapati, Sanjay; Verma, Shivam; Kulkarni, Anant Aravind; Kaushik, Brajesh Kumar

    2016-10-01

    Spin-transfer torque (STT) and spin-orbit torque (SOT) based magnetic tunnel junction (MTJ) devices are emerging as strong contenders for the next generation memories. Conventional STT magneto-resistive random access memory (MRAM) offers lower power, non-volatility and CMOS process compatibility. However, higher current requirement during the write operation leads to tunnel barrier reliability issues and larger access devices. SOT-MRAM eliminates the reliability issues with strong spin polarized current (100%) and separate read/write current paths; however, the additional two access transistors in SOT-MRAM results into increased cell area. Multilevel cell (MLC) structure paves a way to circumvent the problems related to the conventional STT/SOT based MTJ devices and provides enhanced integration density at reduced cost per bit. Conventional STT/SOT-MRAM requires a unit cell area of 10-60 F2 and reported simulations have been based on available single-level MTJ compact models. However, till date no compact model exists that can capture the device physics of MLC-MTJ accurately. Hence, a novel compact model is proposed in this paper to capture the accurate device physics and behaviour of the MLC-MTJs. It is designed for MLCs with different MTJ configurations demonstrated so far, such as series and parallel free layer based MLC-MTJs. The proposed model is coded in Verilog-A, which is compatible with SPICE for circuit level simulations. The model is in close agreement with the experimental results exhibiting an average error of less than 15%.

  14. Effect of annealing on the temperature dependence of inelastic tunneling contributions vis-à-vis tunneling magnetoresistance and barrier parameters in CoFe/MgO/NiFe magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Bhusan Singh, Braj; Chaudhary, Sujeet, E-mail: sujeetc@physics.iitd.ac.in [Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110 016 (India)

    2014-02-28

    The effect of annealing on the changes in the inelastic tunneling contributions in tunneling conductance of ion beam sputtered CoFe/MgO/NiFe magnetic tunnel junctions (MTJs) is investigated. The inelastic contributions are evaluated using hopping conduction model of Glazman and Matveev in the temperature range of 25–300 K. The hopping through number of series of localized states present in the barrier due to structural defects increases from 9 (in as deposited MTJ) to 18 after annealing (at 200 °C/1 h); although no changes in the interface roughness of CoFe-MgO and MgO-NiFe interfaces are observed as revealed by the x-ray reflectance studies on planar MTJs. The bias dependence of tunneling magnetoresistance (TMR) at 25 K is found to get improved after annealing as revealed by the value V{sub 1/2} (the bias value at which the TMR reaches to half of its value at nearly zero bias); which is 78 mV (in MTJ annealed at 200 °C/1 h) 2.5 times the value of 33 mV (in as deposited MTJ). At 25 K the inelastic tunneling spectra revealed the presence of zero bias anomaly and magnon excitations in the range of 10–15 mV. While the barrier height exhibited a strong temperature dependence with nearly 100% increase from the value at 300 K to 25 K, the temperature dependence of TMR becomes steep after annealing.

  15. Similarities between normal- and super-currents in topological insulator magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Soodchomshom, Bumned, E-mail: Bumned@hotmail.co [ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rd. Bangkok 10400 (Thailand); Chantngarm, Peerasak [Department of Electronics and Telecommunication Engineering, Faculty of Engineering, Pathumwan Institute of Technology, Bangkok 10330 (Thailand)

    2010-11-15

    This work compares the normal-current in a NM/Fi/NM junction with the super-current in a SC/Fi/SC junction, where both are topological insulator systems. NM and Fi are normal region and ferromagnetic region of thickness d with exchange energy m playing a role of the mass of the Dirac electrons and with the gate voltage V{sub G}, respectively. SC is superconducting region induced by a s-wave superconductor. We show that, interestingly, the critical super-current passing through a SC/Fi/SC junction behaves quite similar to the normal-current passing through a NM/Fi/NM junction. The normal-current and super-current exhibit N-peak oscillation, found when currents are plotted as a function of the magnetic barrier strength {chi} {approx} md/hv{sub F}. With the barrier strength Z {approx} V{sub G}d/hv{sub F}, the number of peaks N is determined through the relation Z {approx} N{pi} + {sigma}{pi} (with 0 < {sigma}{<=}1 for {chi} < Z). The normal- and the super-currents also exhibit oscillating with the same height for all of peaks, corresponding to the Dirac fermion tunneling behavior. These anomalous oscillating currents due to the interplay between gate voltage and magnetic field in the barrier were not found in graphene-based NM/Fi/NM and SC/Fi/SC junctions. This is due to the different magnetic effect between the Dirac fermions in topological insulator and graphene.

  16. Epitaxial wurtzite-MgZnO barrier based magnetic tunnel junctions deposited on a metallic ferromagnetic electrode

    Energy Technology Data Exchange (ETDEWEB)

    Belmoubarik, M., E-mail: bmm-dhr@ecei.tohoku.ac.jp; Al-Mahdawi, M.; Sato, H.; Nozaki, T.; Sahashi, M. [Department of Electronic Engineering, Tohoku University, Sendai 890-8579 (Japan)

    2015-06-22

    An epitaxial wurtzite (WZ) Mg{sub 0.23}Zn{sub 0.77}O barrier based magnetic tunnel junction (MTJ), with electrode-barrier structure of Co{sub 0.30}Pt{sub 0.70} (111)/Mg{sub 0.23}Zn{sub 0.77}O (0001)/Co (0001), was fabricated. The good crystallinity and tunneling properties were experimentally confirmed. Electrical and magnetic investigations demonstrated its high resistance-area product of 1.05 MΩ μm{sup 2}, a maximum tunneling magneto-resistance (TMR) of 35.5%, and the existence of localized states within the tunneling barrier producing TMR rapid decrease and oscillation when increasing the applied bias voltage. The TMR value almost vanished at 200 K, which was attributed to the induced moment and strong spin-orbit coupling in Pt atoms at the Co{sub 0.30}Pt{sub 0.70}/Mg{sub 0.23}Zn{sub 0.77}O interface. Owing to the ferroelectric behavior in WZ-MgZnO materials, the fabrication of WZ-MgZnO barrier based MTJs deposited on a metallic ferromagnetic electrode will open routes for electrically controllable non-volatile devices that are compatible with CMOS technology.

  17. Bias dependence of spin transfer torque in Co2MnSi Heusler alloy based magnetic tunnel junctions

    Science.gov (United States)

    Zhang, Jie; Phung, Timothy; Pushp, Aakash; Ferrante, Yari; Jeong, Jaewoo; Rettner, Charles; Hughes, Brian P.; Yang, See-Hun; Jiang, Yong; Parkin, Stuart S. P.

    2017-04-01

    Heusler compounds are of interest as electrode materials for use in magnetic tunnel junctions (MTJs) due to their half metallic character, which leads to 100% spin polarization and high tunneling magnetoresistance. Most work to date has focused on the improvements to tunneling magnetoresistance that can stem from the use of Heusler electrodes, while there is much less work investigating the influence of Heusler electrodes on the spin transfer torque properties of MTJs. Here, we investigate the bias dependence of the anti-damping like and field-like spin transfer torque components in both symmetric (Co2MnSi/MgO/Co2MnSi) and asymmetric (Co2MnSi/MgO/CoFe) structure Heusler based MTJs using spin transfer torque ferromagnetic resonance. We find that while the damping like torque is linear with respect to bias for both MTJ structures, the asymmetric MTJ structure has an additional linear component to the ordinarily quadratic field like torque bias dependence and that these results can be accounted for by a free electron tunneling model. Furthermore, our results suggest that the low damping and low saturation magnetization properties of Heusler alloys are more likely to lead significant improvements to spin torque switching efficiency rather than their half metallic character.

  18. Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure

    Science.gov (United States)

    Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

    2016-09-01

    For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

  19. A link between the coercivity and microstructure of high moment Fe films and their use in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Georgieva, M.T. [Institute for Materials Research, Maxwell Building, The University of Salford, Salford M5 4WT (United Kingdom)]. E-mail: milena.georgieva@mdm.infm.it; Telling, N.D. [Institute for Materials Research, Maxwell Building, The University of Salford, Salford M5 4WT (United Kingdom); Magnetic Spectroscopy Group, CCLRC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Grundy, P.J. [Institute for Materials Research, Maxwell Building, The University of Salford, Salford M5 4WT (United Kingdom)

    2006-01-25

    Magnetron sputtered single Fe films have been 'softened' magnetically by controlled N-doping during the sputter deposition. This technique allows a reduction in grain size and coercivity of the Fe films, without decreasing the saturation magnetization and without the formation of any crystalline FeN phases. We describe this effect through a modification of the random magnetocrystalline anisotropy model, by taking the film thickness into account. The coercivities calculated in this way are in good agreement with those obtained experimentally. It is demonstrated that N-doping can be samples increased as to control the switching field of the 'free' layer in magnetic trilayer films of the MTJ type. It is thus possible to construct an all Fe-electrode magnetic tunnel junction (MTJ) that displays the tunneling magnetoresistance (TMR) effect by altering the switching field of one Fe layer using N-doping. The ability to control the magnetic softness of high magnetic moment materials is important in regard to their incorporation into TMR devices.

  20. Impact of lattice strain on the tunnel magnetoresistance in Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2013-08-19

    The objective of this work is to describe the tunnel electron current in single-barrier magnetic tunnel junctions within an approach that goes beyond the single-band transport model. We propose a ballistic multichannel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single-crystal magnetic Fe(110) electrodes for Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 tunnel junctions, where the electronic band structures of Fe and La0.67Sr0.33MnO3 are derived by ab initio calculations.

  1. Comprehensive and Macrospin-Based Magnetic Tunnel Junction Spin Torque Oscillator Model - Part I: Analytical Model of the MTJ STO

    OpenAIRE

    Chen, Tingsu; Eklund, Anders; Iacocca, Ezio; Rodriguez, Saul; Malm, Gunnar; Åkerman, Johan; Rusu, Ana

    2014-01-01

    Magnetic tunnel junction (MTJ) spin torque oscillators (STO) have shown the potential to be used in a wide range of microwave and sensing applications. To evaluate potential uses of MTJ STO technology in various applications, an analytical model that can capture MTJ STO's characteristics, while enabling system- and circuit-level designs, is of great importance. An analytical model based on macrospin approximation is necessary for these designs since it allows implementation in hardware descri...

  2. Influence of the MgO barrier thickness on the lifetime characteristics of magnetic tunnelling junctions for sensors

    Science.gov (United States)

    Conca, A.; Casper, F.; Paul, J.; Lehndorff, R.; Jakob, G.; Kläui, M.; Hillebrands, B.; Leven, B.

    2016-06-01

    Magnetic tunnelling junctions increasingly enter the market for magnetic sensor applications. Thus, technological parameters such as the lifetime characteristics become more and more important. Here, an analysis of the lifetime characteristics of magnetic tunnelling junctions using the Weibull statistical distribution for CoFeB/MgO/CoFeB junctions is presented. The Weibull distribution is governed by two parameters, the characteristic lifetime η of the population and the shape parameter β, which gives information about the presence of an infant mortality. The suitability of the Weibull distribution is demonstrated for the description of dielectric breakdown processes in MgO-based tunnelling junctions at different voltages. A study of the dependence of the characteristic lifetime extrapolated to the low voltage regime, and the β parameter on the nominal barrier thickness and the resistance  ×  area product of the MgO barrier is shown. The influence of the RF deposition power for the MgO barrier and an annealing step on the Weibull parameters is also discussed.

  3. High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications.

    Science.gov (United States)

    Chen, Jun-Yang; Lau, Yong-Chang; Coey, J M D; Li, Mo; Wang, Jian-Ping

    2017-02-02

    The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices' robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications.

  4. Tunneling magnetoresistance sensor with pT level 1/f magnetic noise

    Directory of Open Access Journals (Sweden)

    James G. Deak

    2017-05-01

    Full Text Available Magnetoresistive devices are important components in a large number of commercial electronic products in a wide range of applications including industrial position sensors, automotive sensors, hard disk read heads, cell phone compasses, and solid state memories. These devices are commonly based on anisotropic magnetoresistance (AMR and giant magnetoresistance (GMR, but over the past few years tunneling magnetoresistance (TMR has been emerging in more applications. Here we focus on recent work that has enabled the development of TMR magnetic field sensors with 1/f noise of less than 100 pT/rtHz at 1 Hz. Of the commercially available sensors, the lowest noise devices have typically been AMR, but they generally have the largest die size. Based on this observation and modeling of experimental data size and geometry dependence, we find that there is an optimal design rule that produces minimum 1/f noise. This design rule requires maximizing the areal coverage of an on-chip flux concentrator, providing it with a minimum possible total gap width, and tightly packing the gaps with MTJ elements, which increases the effective volume and decreases the saturation field of the MTJ freelayers. When properly optimized using this rule, these sensors have noise below 60 pT/rtHz, and could possibly replace fluxgate magnetometers in some applications.

  5. Tunneling magnetoresistance sensor with pT level 1/f magnetic noise

    Science.gov (United States)

    Deak, James G.; Zhou, Zhimin; Shen, Weifeng

    2017-05-01

    Magnetoresistive devices are important components in a large number of commercial electronic products in a wide range of applications including industrial position sensors, automotive sensors, hard disk read heads, cell phone compasses, and solid state memories. These devices are commonly based on anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), but over the past few years tunneling magnetoresistance (TMR) has been emerging in more applications. Here we focus on recent work that has enabled the development of TMR magnetic field sensors with 1/f noise of less than 100 pT/rtHz at 1 Hz. Of the commercially available sensors, the lowest noise devices have typically been AMR, but they generally have the largest die size. Based on this observation and modeling of experimental data size and geometry dependence, we find that there is an optimal design rule that produces minimum 1/f noise. This design rule requires maximizing the areal coverage of an on-chip flux concentrator, providing it with a minimum possible total gap width, and tightly packing the gaps with MTJ elements, which increases the effective volume and decreases the saturation field of the MTJ freelayers. When properly optimized using this rule, these sensors have noise below 60 pT/rtHz, and could possibly replace fluxgate magnetometers in some applications.

  6. High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications

    Science.gov (United States)

    Chen, Jun-Yang; Lau, Yong-Chang; Coey, J. M. D.; Li, Mo; Wang, Jian-Ping

    2017-02-01

    The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices‘ robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications.

  7. High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications

    Science.gov (United States)

    Chen, Jun-Yang; Lau, Yong-Chang; Coey, J. M. D.; Li, Mo; Wang, Jian-Ping

    2017-01-01

    The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices‘ robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications. PMID:28150807

  8. MnGa-based fully perpendicular magnetic tunnel junctions with ultrathin Co2MnSi interlayers

    Science.gov (United States)

    Mao, Siwei; Lu, Jun; Zhao, Xupeng; Wang, Xiaolei; Wei, Dahai; Liu, Jian; Xia, Jianbai; Zhao, Jianhua

    2017-01-01

    Because tetragonal structured MnGa alloy has intrinsic (not interface induced) giant perpendicular magnetic anisotropy (PMA), ultra-low damping constant and high spin polarization, it is predicted to be a kind of suitable magnetic electrode candidate in the perpendicular magnetic tunnel junction (p-MTJ) for high density spin transfer torque magnetic random access memory (STT-MRAM) applications. However, p-MTJs with both bottom and top MnGa electrodes have not been achieved yet, since high quality perpendicular magnetic MnGa films can hardly be obtained on the MgO barrier due to large lattice mismatch and surface energy difference between them. Here, a MnGa-based fully p-MTJ with the structure of MnGa/Co2MnSi/MgO/Co2MnSi/MnGa is investigated. As a result, the multilayer is with high crystalline quality, and both the top and bottom MnGa electrodes show well PMA. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. Ultrathin Co2MnSi films are used to optimize the interface quality between MnGa and MgO barrier. A strong antiferromagnetic coupling in MnGa/Co2MnSi bilayer is confirmed with the interfacial exchange coupling constant of −5erg/cm2. This work proposes a novel p-MTJ structure for the future STT-MRAM progress. PMID:28233780

  9. MnGa-based fully perpendicular magnetic tunnel junctions with ultrathin Co2MnSi interlayers.

    Science.gov (United States)

    Mao, Siwei; Lu, Jun; Zhao, Xupeng; Wang, Xiaolei; Wei, Dahai; Liu, Jian; Xia, Jianbai; Zhao, Jianhua

    2017-02-24

    Because tetragonal structured MnGa alloy has intrinsic (not interface induced) giant perpendicular magnetic anisotropy (PMA), ultra-low damping constant and high spin polarization, it is predicted to be a kind of suitable magnetic electrode candidate in the perpendicular magnetic tunnel junction (p-MTJ) for high density spin transfer torque magnetic random access memory (STT-MRAM) applications. However, p-MTJs with both bottom and top MnGa electrodes have not been achieved yet, since high quality perpendicular magnetic MnGa films can hardly be obtained on the MgO barrier due to large lattice mismatch and surface energy difference between them. Here, a MnGa-based fully p-MTJ with the structure of MnGa/Co2MnSi/MgO/Co2MnSi/MnGa is investigated. As a result, the multilayer is with high crystalline quality, and both the top and bottom MnGa electrodes show well PMA. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. Ultrathin Co2MnSi films are used to optimize the interface quality between MnGa and MgO barrier. A strong antiferromagnetic coupling in MnGa/Co2MnSi bilayer is confirmed with the interfacial exchange coupling constant of -5erg/cm(2). This work proposes a novel p-MTJ structure for the future STT-MRAM progress.

  10. MnGa-based fully perpendicular magnetic tunnel junctions with ultrathin Co2MnSi interlayers

    Science.gov (United States)

    Mao, Siwei; Lu, Jun; Zhao, Xupeng; Wang, Xiaolei; Wei, Dahai; Liu, Jian; Xia, Jianbai; Zhao, Jianhua

    2017-02-01

    Because tetragonal structured MnGa alloy has intrinsic (not interface induced) giant perpendicular magnetic anisotropy (PMA), ultra-low damping constant and high spin polarization, it is predicted to be a kind of suitable magnetic electrode candidate in the perpendicular magnetic tunnel junction (p-MTJ) for high density spin transfer torque magnetic random access memory (STT-MRAM) applications. However, p-MTJs with both bottom and top MnGa electrodes have not been achieved yet, since high quality perpendicular magnetic MnGa films can hardly be obtained on the MgO barrier due to large lattice mismatch and surface energy difference between them. Here, a MnGa-based fully p-MTJ with the structure of MnGa/Co2MnSi/MgO/Co2MnSi/MnGa is investigated. As a result, the multilayer is with high crystalline quality, and both the top and bottom MnGa electrodes show well PMA. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. Ultrathin Co2MnSi films are used to optimize the interface quality between MnGa and MgO barrier. A strong antiferromagnetic coupling in MnGa/Co2MnSi bilayer is confirmed with the interfacial exchange coupling constant of -5erg/cm2. This work proposes a novel p-MTJ structure for the future STT-MRAM progress.

  11. Tunnel-diode resonator and nuclear magnetic resonance studies of low-dimensional magnetic and superconducting systems

    Science.gov (United States)

    Yeninas, Steven Lee

    This thesis emphasizes two frequency-domain techniques which uniquely employ radio frequency (RF) excitations to investigate the static and dynamic properties of novel magnetic and superconducting materials. The first technique is a tunnel-diode resonator (TDR) which detects bulk changes in the dynamic susceptibility, chi = dM/dH. The capability of TDR to operate at low temperatures (less than 100 mK) and high fields (up to 65 T in pulsed fields) was critical for investigations of the antiferromagnetically correlated magnetic molecules Cr12Cu2 and Cr12 Ln4 (Ln = Y, Eu, Gd, Tb, Dy, Ho, Er, Yb), and the superconductor SrFe2(As1--xPx) 2 (x = 0.35). Investigations of Cr12Cu 2 and Cr12Ln4 demonstrates the first implementation of TDR to experimentally investigate the lowlying energy spectra of magnetic molecules in pulsed magnetic fields. Zeeman splitting of the quantum spin states results in transitions between field-dependent ground state energy levels observed as peaks in dM/dH at 600 mK, and demonstrate good agreement with theoretical calculations using a isotropic Heisenberg spin Hamiltonian. Increasing temperature to 2.5 K, TDR reveals a rich spectrum of frequency-dependent level crossings from thermally populated excited states which cannot be observed by conventional static magnetometry techniques. The last study presented uses TDR in pulsed fields to determine the temperature-dependent upper-critical field Hc2 to investigate the effects of columnar defects arising from heavy ion irradiation of SrFe2(As 1--xPx)2. Results suggest irradiation uniformly suppresses Tc and Hc2, and does not introduce additional features on H c2(T) and the shapes of the anisotropic Hc2 curves indicates a nodal superconducting gap. The second technique is nuclear magnetic resonance (NMR) which yields site specific magnetic and electronic information arising from hyperfine interactions for select magnetic nuclei. NMR spectra and nuclear spin-lattice relaxation measurements are reported

  12. Optimization of the tunnel magnetoresistance of CoFeB/ MgO/ CoFeB - based magnetic tunnel junctions (MTJs) with e-beam evaporation barriers

    Energy Technology Data Exchange (ETDEWEB)

    Zbarskyy, Vladyslav; Walter, Marvin; Eilers, Gerrit; Muenzenberg, Markus [I. Physikalisches Institut, Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Peretzki, Patrick; Seibt, Michael [IV. Physikalisches Institut, Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany)

    2010-07-01

    The investigation of MTJs with a high tunnel magnetoresistance (TMR) is very important for the production of MRAM devices. All our CoFeB layers are prepared via magnetron sputtering and MgO barriers via e-beam evaporation. We investigate the magnetic switching properties of CoFeB/MgO/CoFeB MTJs with measurements of hysteresis curves - using the magneto-optical Kerr effect - and TMR curves, optimizing the thickness of the CoFeB layers. Another parameter we change to optimize the ferromagnetic CoFeB electrodes is the annealing temperature. Both influence the solid state epitaxy leading to crystallization directly at the MgO/CoFeB interface. The optimization of MgO barrier properties is also necessary for the quality of our devices. In this context we study the TMR behaviour with the variation of the sample temperature during the e-beam evaporation of MgO barrier.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, M., E-mail: mzhu@sunycnse.com; Chong, H.; Vu, Q. B.; Vo, T.; Brooks, R.; Stamper, H.; Bennett, S.; Piccirillo, J. [Colleges of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, New York 12203 (United States)

    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.

  14. Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    Directory of Open Access Journals (Sweden)

    J. Rogge

    2015-07-01

    Full Text Available We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs. By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR ratio of -10% is found for Co2FeAl (24 nm / BaO (5 nm / Fe (7 nm MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM, it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  15. A theoretical analysis of the spin dynamics of magnetic adatoms traced by time-resolved scanning tunneling spectroscopy

    Science.gov (United States)

    Schüler, M.; Pavlyukh, Y.; Berakdar, J.

    2012-04-01

    Inelastic scanning tunneling microscopy (STM) has recently been shown (Loth et al 2010 Science 329 1628) to be extendable to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze this novel tool theoretically by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is non-perturbative and, hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the predictions of simple analytical models and compared with experiments.

  16. Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

    DEFF Research Database (Denmark)

    Grove-Rasmussen, Kasper; Grap, S.; Paaske, Jens;

    2012-01-01

    By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level...

  17. Simulation Study on Understanding the Spin Transport in MgO Adsorbed Graphene Based Magnetic Tunnel Junction

    Science.gov (United States)

    Raturi, Ashish; Choudhary, Sudhanshu

    2016-11-01

    First principles calculations of spin-dependent electronic transport properties of magnetic tunnel junction (MTJ) consisting of MgO adsorbed graphene nanosheet sandwiched between two CrO2 half-metallic ferromagnetic (HMF) electrodes is reported. MgO adsorption on graphene opens bandgap in graphene nanosheet which makes it more suitable for use as a tunnel barrier in MTJs. It was found that MgO adsorption suppresses transmission probabilities for spin-down channel in case of parallel configuration (PC) and also suppresses transmission in antiparallel configuration (APC) for both spin-up and spin-down channel. Tunnel magneto-resistance (TMR) of 100% is obtained at all bias voltages in MgO adsorbed graphene-based MTJ which is higher than that reported in pristine graphene-based MTJ. HMF electrodes were found suitable to achieve perfect spin filtration effect and high TMR. I-V characteristics for both parallel and antiparallel magnetization states of junction are calculated. High TMR suggests its usefulness in spin valves and other spintronics-based applications.

  18. Aharonov-Casher-effect suppression of macroscopic tunneling of magnetic flux.

    Science.gov (United States)

    Friedman, Jonathan R; Averin, D V

    2002-02-04

    We suggest a system in which the amplitude of macroscopic flux tunneling can be modulated via the Aharonov-Casher effect. The system is an rf SQUID with the Josephson junction replaced by a Bloch transistor--two junctions separated by a small superconducting island on which the charge can be induced by an external gate voltage. When the Josephson coupling energies of the junctions are equal and the induced charge is q = e, destructive interference between tunneling paths brings the flux tunneling rate to zero. The device may also be useful as a qubit for quantum computation.

  19. Hyperfine-interaction-driven suppression of quantum tunneling at zero field in a holmium(III) single-ion magnet

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yan-Cong; Liu, Jun-Liang; Chen, Xiao-Ming; Tong, Ming-Liang [Key Lab. of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-Sen Univ., Guangzhou (China); Wernsdorfer, Wolfgang [Institut Neel, CNRS and Universite Joseph Fournier, Grenoble (France); Institute of Nanotechnology, Karlsruhe Institute of Technology (Germany); Physikalisches Institut, Karlsruhe Institute of Technology (Germany); Liu, Dan; Chibotaru, Liviu F. [Theory of Nanomaterials Group and INPAC-Institute of Nanoscale Physics and Chemistry, Katholieke Universiteit Leuven (Belgium)

    2017-04-24

    An extremely rare non-Kramers holmium(III) single-ion magnet (SIM) is reported to be stabilized in the pentagonal-bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm{sup -1}. The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field-induced QTMs can be observed even from the field-dependent alternating-current magnetic susceptibility in addition to single-crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal-field environment and the hyperfine interactions arising from {sup 165}Ho (I=7/2) with a natural abundance of 100 %. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Spin Transfer Torque Switching and Perpendicular Magnetic Anisotropy in Full Heusler Alloy Co2FeAl-BASED Tunnel Junctions

    Science.gov (United States)

    Sukegawa, H.; Wen, Z. C.; Kasai, S.; Inomata, K.; Mitani, S.

    2014-12-01

    Some of Co-based full Heusler alloys have remarkable properties in spintronics, that is, high spin polarization of conduction electrons and low magnetic damping. Owing to these properties, magnetic tunnel junctions (MTJs) using Co-based full Heusler alloys are potentially of particular importance for spintronic application such as magnetoresistive random access memories (MRAMs). Recently, we have first demonstrated spin transfer torque (STT) switching and perpendicular magnetic anisotropy (PMA), which are required for developing high-density MRAMs, in full-Heusler Co2FeAl alloy-based MTJs. In this review, the main results of the experimental demonstrations are shown with referring to related issues, and the prospect of MTJs using Heusler alloys is also discussed.

  1. Angle-resolved soft X-ray magnetic circular dichroism in a monatomic Fe layer facing an MgO(0 0 1) tunnel barrier

    Energy Technology Data Exchange (ETDEWEB)

    Mamiya, K. [Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Koide, T. [Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)]. E-mail: tsuneharu.koide@kek.jp; Ishida, Y. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Osafune, Y. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Fujimori, A. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Suzuki, Y. [Graduate School of Engineering Science, Osaka University, 1-3 Toyonaka, Osaka 560-8531 (Japan); NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Katayama, T. [NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Yuasa, S. [NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)

    2006-11-15

    The electronic and magnetic states of a monatomic Fe(0 0 1) layer directly facing an MgO(0 0 1) tunnel barrier were studied by angle-resolved X-ray magnetic circular dichroism (XMCD) at the Fe L {sub 2,3} edges in the longitudinal (L) and transverse (T) arrangements. A strong XMCD reveals no oxidation of the 1-ML Fe, showing its crucial role in giant tunnel magnetoresistance effects in Fe/MgO/Fe magnetic tunnel junctions. Sum-rule analyses of the angle-resolved XMCD give values of a spin moment, in-plane and out-of-plane orbital and magnetic dipole moments. Argument is given on their physical implication.

  2. Change of Electronic Structure and Magnetic Properties with MgO and Fe Thicknesses in Fe/MgO/Fe Magnetic Tunnel Junction

    Institute of Scientific and Technical Information of China (English)

    YANG Fan; BI Xiao-fang

    2006-01-01

    The effects of the thickness of MgO and Fe on the electronic structure and magnetic properties of Fe/MgO/Fe magnetic tunnel junction was studied using the first principle method. Two series of models with MgO of different thicknesses: Fe(3)MgO(t)Fe(3) (t=1,3,5,7) and with Fe of varied thicknesses: Fe(t)MgO(3)Fe(t) (t=3,4,5,6,7) were established. Calculated results show that in all the models the magnetic moment of Fe increases at the Fe/MgO interface and surface as compared with that of the inner layers. The magnetic moment of each Fe layer was found to be independent of MgO thicknesses, while the spin-polarization of Fe layer at the interface shows a slight change in function of the MgO thicknesses. The tunneling magnetoresistance (TMR) ratio estimated by the Julliere model has the same change tendency as the spin-polarization has, and the largest value is obtained at the MgO thickness of 5 atomic layers. When the Fe thickness increases, the spin-polarization of interface Fe layer follows up an increase with a decrease. The highest TMR value is achieved when the Fe thickness is of 4 atomic layers.

  3. Trigonal antiprismatic Co(ii) single molecule magnets with large uniaxial anisotropies: importance of Raman and tunneling mechanisms.

    Science.gov (United States)

    Zhang, Yuan-Zhu; Gómez-Coca, Silvia; Brown, Andrew J; Saber, Mohamed R; Zhang, Xuan; Dunbar, Kim R

    2016-10-19

    The air-stable mononuclear Co(ii) compounds [Co(II)(Tpm)2][ClO4]2 (1, Tpm = tris(pyrazol-1-yl)methane), [Co(II)(Tpm)2][BPh4]2·2MeCN (2) with trigonal antiprismatic geometry (trigonally elongated octahedral geometry) are reported. Magnetic and theoretical studies reveal that the complexes exhibit single-molecule magnet behavior with uniaxial anisotropy and a huge energy difference between ground and first excited Karmers' doublets (∼200 cm(-1)). Under applied DC fields, compounds 1 and 2 exhibit frequency and temperature dependence of the imaginary susceptibility. The fit of the data to an Orbach relaxation process yields effective energy barriers of 30.6(1) and 44.7(6) cm(-1) for 1 and 2, respectively, but there is no real state at that energy. The inclusion of tunneling, direct and Raman relaxation processes leads to the conclusion that the inclusion of an Orbach process is not required to provide a good fit to the data. More interestingly, a detailed study of the dependence of the relaxation time with field shows that for these Kramers' ions, tunneling is the predominant process at low temperature and that differences in the counteranion allow for a tuning of the Raman process at higher temperatures. These findings underscore the fact that large uniaxial anisotropy can be achieved in hexacoordinate Co(ii) trigonal antiprismatic complexes which is an unexplored geometry in mononuclear single molecule magnets.

  4. A compact model for magnetic tunnel junction (MTJ) switched by thermally assisted Spin transfer torque (TAS + STT)

    Science.gov (United States)

    Zhao, Weisheng; Duval, Julien; Klein, Jacques-Olivier; Chappert, Claude

    2011-12-01

    Thermally assisted spin transfer torque [TAS + STT] is a new switching approach for magnetic tunnel junction [MTJ] nanopillars that represents the best trade-off between data reliability, power efficiency and density. In this paper, we present a compact model for MTJ switched by this approach, which integrates a number of physical models such as temperature evaluation and STT dynamic switching models. Many experimental parameters are included directly to improve the simulation accuracy. It is programmed in the Verilog-A language and compatible with the standard IC CAD tools, providing an easy parameter configuration interface and allowing high-speed co-simulation of hybrid MTJ/CMOS circuits.

  5. A compact model for magnetic tunnel junction (MTJ) switched by thermally assisted Spin transfer torque (TAS + STT).

    Science.gov (United States)

    Zhao, Weisheng; Duval, Julien; Klein, Jacques-Olivier; Chappert, Claude

    2011-04-28

    Thermally assisted spin transfer torque [TAS + STT] is a new switching approach for magnetic tunnel junction [MTJ] nanopillars that represents the best trade-off between data reliability, power efficiency and density. In this paper, we present a compact model for MTJ switched by this approach, which integrates a number of physical models such as temperature evaluation and STT dynamic switching models. Many experimental parameters are included directly to improve the simulation accuracy. It is programmed in the Verilog-A language and compatible with the standard IC CAD tools, providing an easy parameter configuration interface and allowing high-speed co-simulation of hybrid MTJ/CMOS circuits.

  6. Interfacial spin-filter assisted spin transfer torque effect in Co/BeO/Co magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Y.-H., E-mail: yhtang@cc.ncu.edu.tw; Chu, F.-C. [Department of Physics, National Central University, Jung-Li 32001, Taiwan (China)

    2015-03-07

    The first-principles calculation is employed to demonstrate the spin-selective transport properties and the non-collinear spin-transfer torque (STT) effect in the newly proposed Co/BeO/Co magnetic tunnel junction. The subtle spin-polarized charge transfer solely at O/Co interface gives rise to the interfacial spin-filter (ISF) effect, which can be simulated within the tight binding model to verify the general expression of STT. This allows us to predict the asymmetric bias behavior of non-collinear STT directly via the interplay between the first-principles calculated spin current densities in collinear magnetic configurations. We believe that the ISF effect, introduced by the combination between wurtzite-BeO barrier and the fcc-Co electrode, may open a new and promising route in semiconductor-based spintronics applications.

  7. Contactless Measurement of Magnetic Nanoparticles on Lateral Flow Strips Using Tunneling Magnetoresistance (TMR Sensors in Differential Configuration

    Directory of Open Access Journals (Sweden)

    Huaming Lei

    2016-12-01

    Full Text Available Magnetic nanoparticles (MNPs are commonly used in biomedical detection due to their capability to bind with some specific antibodies. Quantification of biological entities could be realized by measuring the magnetic response of MNPs after the binding process. This paper presents a contactless scanning prototype based on tunneling magnetoresistance (TMR sensors for quantification of MNPs present in lateral flow strips (LFSs. The sensing unit of the prototype composes of two active TMR elements, which are parallel and closely arranged to form a differential sensing configuration in a perpendicular magnetic field. Geometrical parameters of the configuration are optimized according to theoretical analysis of the stray magnetic field produced by the test line (T-line while strips being scanned. A brief description of our prototype and the sample preparation is presented. Experimental results show that the prototype exhibits the performance of high sensitivity and strong anti-interference ability. Meanwhile, the detection speed has been improved compared with existing similar techniques. The proposed prototype demonstrates a good sensitivity for detecting samples containing human chorionic gonadotropin (hCG at a concentration of 25 mIU/mL. The T-line produced by the sample with low concentration is almost beyond the visual limit and produces a maximum stray magnetic field some 0.247 mOe at the sensor in the x direction.

  8. Magnetic tunnel contacts to silicon with low-work-function ytterbium nanolayers

    NARCIS (Netherlands)

    Patel, R.S.; Dash, S.P.; de Jong, Machiel Pieter; Jansen, R.

    2009-01-01

    Unambiguous proof of spin transport in semiconductor spintronic devices requires a control experiment to exclude spurious signals that arise from the presence of the ferromagnetic contacts. It is shown here that insertion of a low-work-function Yb nanolayer in ferromagnetic tunnel contacts to

  9. Inducing spin-dependent tunneling to probe magnetic correlations in optical lattices

    DEFF Research Database (Denmark)

    Pedersen, Kim-Georg; Andersen, Brian; Syljuåsen, Olav;

    2012-01-01

    We suggest a simple experimental method for probing antiferromagnetic spin correlations of two-component Fermi gases in optical lattices. The method relies on a spin selective Raman transition to excite atoms of one spin species to their first excited vibrational mode where the tunneling is large...

  10. Co2MnSi Heusler alloy as an enhancing layer of perpendicular magnetic anisotropy for MgO-based magnetic tunnel junctions with L10 ordered FePd

    Science.gov (United States)

    Bae, Taejin; Ko, Jungho; Lee, Sangho; Cha, Jongin; Hong, Jongill

    2016-01-01

    Ultra-thin Co2MnSi Heusler alloy improves perpendicular magnetic anisotropy of FePd in an MgO-based magnetic tunnel junction after annealing it just once at a temperature of as low as 400 °C. Co2MnSi as thin as 1.0 nm inserted between MgO and FePd facilitated phase-transformation of 3-nm-thick FePd to ordered L10 and led a change in magnetic anisotropy to perpendicular-to-the-plane. To make it even better, FePd also helped the phase-transformation of Co2MnSi to ordered B2 known to have high spin polarization, which makes the L10 FePd/B2 Co2MnSi bilayer promising for perpendicular-magnetic tunnel junction and improving both thermal stability and tunnel magnetoresistance.

  11. Preparation and characterization of a ferrimagnetic amorphous alloy of GdCo entering the design of magnetic tunnel junctions: ionizing radiations hardness of magnetic tunnel junctions; preparation et caracterisation d'un alliage amorphe ferrimagnetique de GdCo entrant dans la conception de jonctions tunnel magnetiques. Resistance des jonctions tunnel magnetiques aux rayonnements ionisants

    Energy Technology Data Exchange (ETDEWEB)

    Conraux, Y

    2005-10-15

    The magnetic random access memories (MRAM) are on the way to supplant the other forms of random access memories using the states of electric charge, and this thanks to their many technical advantages: not-volatility, speed, low consumption power, robustness. Also, the MRAM are alleged insensitive with the ionizing radiations, which was not checked in experiments until now. The current architecture of the MRAM is based on the use of magnetic tunnel junctions (MTJ). These MRAM can present an important disadvantage, because they are likely of present errors of addressing, in particular when integration (density of memory cells) is increasingly thorough. The work undertaken during this thesis relates to these two points: - to check the functional reliability of the MRAM containing JTM exposed to high energy ionizing radiations; - to study a ferrimagnetic amorphous alloy, GdCo, likely to enter the composition of JTM and allowing to free from the possible errors of addressing by a process of thermal inhibition of the memory cells. This work of thesis showed that the MRAM containing JTM preserve their functional properties fully when they are subjected to intense ionizing radiations, and that GdCo is a very interesting material from the point of view of the solid state physics and magnetism, that its physical properties are very promising as for its applications, and that its integration in a JTM still claims technological developments. (author)

  12. Magnetic tunnel junctions for magnetic field sensor by using CoFeB sensing layer capped with MgO film

    Energy Technology Data Exchange (ETDEWEB)

    Takenaga, Takashi, E-mail: takenaga@leap.or.jp; Tsuzaki, Yosuke; Yoshida, Chikako; Yamazaki, Yuichi; Hatada, Akiyoshi; Nakabayashi, Masaaki; Iba, Yoshihisa; Takahashi, Atsushi; Noshiro, Hideyuki; Tsunoda, Koji; Aoki, Masaki; Furukawa, Taisuke; Fukumoto, Hiroshi; Sugii, Toshihiro [Low-power Electronics Association and Project (LEAP), Tsukuba 305-8569 (Japan)

    2014-05-07

    We evaluated MgO-based magnetic tunnel junctions (MTJs) for magnetic field sensors with spin-valve-type structures in the CoFeB sensing layer capped by an MgO film in order to obtain both top and bottom interfaces of MgO/CoFeB exhibiting interfacial perpendicular magnetic anisotropy (PMA). Hysteresis of the CoFeB sensing layer in these MTJs annealed at 275 °C was suppressed at a thickness of the sensing layer below 1.2 nm by interfacial PMA. We confirmed that the CoFeB sensing layers capped with MgO suppress the thickness dependences of both the magnetoresistance ratio and the magnetic behaviors of the CoFeB sensing layer more than that of the MTJ with a Ta capping layer. MgO-based MTJs with MgO capping layers can improve the controllability of the characteristics for magnetic field sensors.

  13. State diagram of a perpendicular magnetic tunnel junction driven by spin transfer torque: A power dissipation approach

    Science.gov (United States)

    Lavanant, M.; Petit-Watelot, S.; Kent, A. D.; Mangin, S.

    2017-04-01

    The state diagram of a magnetic tunnel junction with perpendicularly magnetized electrodes in the presence of spin-transfer torques is computed in a macrospin approximation using a power dissipation model. Starting from the macrospin's energy we determine the stability of energy extremum in terms of power received and dissipated, allowing the consideration of non-conservative torques associated with spin transfer and damping. The results are shown to be in agreement with those obtained by direct integration of the Landau-Lifshitz-Gilbert-Slonczewski equation. However, the power dissipation model approach is faster and shows the reason certain magnetic states are stable, such as states that are energy maxima but are stabilized by spin transfer torque. Breaking the axial system, such as by a tilted applied field or tilted anisotropy, is shown to dramatically affect the state diagrams. Finally, the influence of a higher order uniaxial anisotropy that can stabilize a canted magnetization state is considered and the results are compared to experimental data.

  14. Dependency of tunneling magneto-resistance on Fe insertion-layer thickness in Co{sub 2}Fe{sub 6}B{sub 2}/MgO-based magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Kyo-Suk [MRAM Center, Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701 (Korea, Republic of); Park, Jea-Gun, E-mail: parkjgL@hanyang.ac.kr [MRAM Center, Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2015-04-21

    For Co{sub 2}Fe{sub 6}B{sub 2}/MgO-based perpendicular magnetic tunneling junctions spin valves with [Co/Pd]{sub n}-synthetic-antiferromagnetic (SyAF) layers, the tunneling-magneto-resistance (TMR) ratio strongly depends on the nanoscale Fe insertion-layer thickness (t{sub Fe}) between the Co{sub 2}Fe{sub 6}B{sub 2} pinned layer and MgO tunneling barrier. The TMR ratio rapidly increased as t{sub Fe} increased up to 0.4 nm by improving the crystalline linearity of a MgO tunneling barrier and by suppressing the diffusion of Pd atoms from a [Co/Pd]{sub n}-SyAF. However, it abruptly decreased by further increasing t{sub Fe} in transferring interfacial-perpendicular magnetic anisotropy into the IMA characteristic of the Co{sub 2}Fe{sub 6}B{sub 2} pinned layer. Thus, the TMR ratio peaked at t{sub Fe} = 0.4 nm: i.e., 120% at 29 Ωμm{sup 2}.

  15. From tunneling to contact in a magnetic atom: The non-equilibrium Kondo effect

    Science.gov (United States)

    Choi, Deung-Jang; Abufager, Paula; Limot, Laurent; Lorente, Nicolás

    2017-03-01

    A low-temperature scanning tunneling microscope was employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip. A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation, we show that the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA.

  16. Interface study of FeMgOFe magnetic tunnel junctions using 3D Atom Probe

    CERN Document Server

    Mazumder, B; Vella, A; Vurpillot, F; Deconihout, B

    2011-01-01

    A detailed interface study was conducted on a Fe/MgO/Fe system using laser assisted 3D atom probe. It exhibits an additional oxide formation at the second interface of the multilayer structure independent of laser wavelength, laser fluence and the thickness of the tunnel barrier. We have shown with the help of simulation that this phenomena is caused by the field evaporation of two layers having two different evaporation

  17. LETTER TO THE EDITOR: A CrO2-based magnetic tunnel junction

    Science.gov (United States)

    Barry, A.; Coey, J. M. D.; Viret, M.

    2000-02-01

    A tunnel junction based on the half-metallic oxide CrO2 uses a native oxide barrier layer and a cobalt top electrode. The I :V characteristic is fitted to the Simmons model with icons/Journals/Common/phi" ALT="phi" ALIGN="TOP"/> = 0.76 eV and t = 2.0 nm. The magnetoresistance is positive with icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> R /R = 1.0% at 77 K.

  18. Stochastic macromodel of magnetic tunnel junction resistance variation and critical current dependence on resistance variation for SPICE simulation

    Science.gov (United States)

    Choi, Juntae; Song, Yunheub

    2017-04-01

    The resistance distribution of a magnetic tunnel junction (MTJ) shows nonuniformity according to various MTJ parameters. Moreover, this resistance variation leads to write-current density variation, which can cause serious problems when designing peripheral circuits for spin transfer torque magnetoresistance random access memory (STT-MRAM) and commercializing gigabit STT-MRAM. Therefore, a macromodel of MTJ including resistance, tunneling magnetoresistance ratio (TMR), and critical current variations is required for circuit designers to design MRAM peripheral circuits, that can overcome the various effects of the variations, such as write failure and read failure, and realize STT-MRAM. In this study, we investigated a stochastic behavior macromodel of the write current dependence on the MTJ resistance variation. The proposed model can possibly be used to analyze the write current density in relation to the resistance and TMR variations of MTJ with various parameter variations. It can be very helpful for designing STT-MRAM circuits and simulating the operation of STT-MRAM devices considering MTJ variations.

  19. Spin transfer torque in non-collinear magnetic tunnel junctions exhibiting quasiparticle bands: a non-equilibrium Green's function study

    Science.gov (United States)

    Jaya, Selvaraj Mathi

    2017-06-01

    A non-equilibrium Green's function formulation to study the spin transfer torque (STT) in non-collinear magnetic tunnel junctions (MTJs) exhibiting quasiparticle bands is developed. The formulation can be used to study the magnetoresistance and spin current too. The formulation is used to study the STT in model tunnel junctions exhibiting multiple layers and quasiparticle bands. The many body interaction that gives rise to quasiparticle bands is assumed to be a s - f exchange interaction at the electrode regions of the MTJ. The quasiparticle bands are obtained using a many body procedure and the single particle band structure is obtained using the tight binding model. The bias dependence of the STT as well as the influence of band occupancy and s - f exchange coupling strength on the STT are studied. We find from our studies that the band occupancy plays a significant role in deciding the STT and the s - f interaction strength too influences the STT significantly. Anomalous behavior in both the parallel and perpendicular components of the STT is obtained from our studies. Our results obtained for certain values of the band occupation are found to show the trend observed from the experimental measurements of STT.

  20. Tunnel-diode resonator and nuclear magnetic resonance studies of low-dimensional magnetic and superconducting systems

    Energy Technology Data Exchange (ETDEWEB)

    Yeninas, Steven Lee [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    This thesis emphasizes two frequency-domain techniques which uniquely employ radio frequency (RF) excitations to investigate the static and dynamic properties of novel magnetic and superconducting materials.

  1. Design of high-throughput and low-power true random number generator utilizing perpendicularly magnetized voltage-controlled magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Hochul Lee

    2017-05-01

    Full Text Available A true random number generator based on perpendicularly magnetized voltage-controlled magnetic tunnel junction devices (MRNG is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA. This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps by implementing a 64×64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit due to the high energy efficiency of the voltage-controlled MTJ switching.

  2. Design of high-throughput and low-power true random number generator utilizing perpendicularly magnetized voltage-controlled magnetic tunnel junction

    Science.gov (United States)

    Lee, Hochul; Ebrahimi, Farbod; Amiri, Pedram Khalili; Wang, Kang L.

    2017-05-01

    A true random number generator based on perpendicularly magnetized voltage-controlled magnetic tunnel junction devices (MRNG) is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA). This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA) effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps) by implementing a 64 ×64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit) due to the high energy efficiency of the voltage-controlled MTJ switching.

  3. A compact model for magnetic tunnel junction (MTJ switched by thermally assisted Spin transfer torque (TAS + STT

    Directory of Open Access Journals (Sweden)

    Zhao Weisheng

    2011-01-01

    Full Text Available Abstract Thermally assisted spin transfer torque [TAS + STT] is a new switching approach for magnetic tunnel junction [MTJ] nanopillars that represents the best trade-off between data reliability, power efficiency and density. In this paper, we present a compact model for MTJ switched by this approach, which integrates a number of physical models such as temperature evaluation and STT dynamic switching models. Many experimental parameters are included directly to improve the simulation accuracy. It is programmed in the Verilog-A language and compatible with the standard IC CAD tools, providing an easy parameter configuration interface and allowing high-speed co-simulation of hybrid MTJ/CMOS circuits.

  4. Investigation of the Mn{sub 3−δ}Ga/MgO interface for magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    ViolBarbosa, C. E., E-mail: carlos.barbosa@cpfs.mpg.de; Ouardi, S.; Fecher, G. H.; Felser, C. [Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, 01187 Dresden (Germany); Kubota, T.; Mizukami, S.; Miyazaki, T. [WPI Advanced Institute for Materials Research, Tohoku University, 980-8577 Sendai (Japan); Kozina, X.; Ikenaga, E. [JASRI, SPring-8, Sayo-cho, Hyogo 679-5198 (Japan)

    2014-07-21

    The Mn{sub 3}Ga Heusler compound and related alloys are the most promising materials for the realization of spin-transfer-torque magnetoresistive memories. Mn–Ga films exhibits perpendicular magnetic anisotropy and high spin polarization and can be used to improve the performance of MgO-based magneto tunneling junctions. The interface between Mn–Ga and MgO films were chemically characterized by hard x-ray photoelectron spectroscopy. The experiment indicated the formation of Ga-O bonds at the interface and evidenced changes in the local environment of Mn atoms in the proximity of the MgO film. We show that the deposition of few monoatomic layers of Mg on top of Mn–Ga film, before the MgO deposition, strongly suppresses the oxidation of gallium.

  5. Superconducting scanning tunneling microscopy tips in a magnetic field: Geometry-controlled order of the phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Eltschka, Matthias, E-mail: m.eltschka@fkf.mpg.de; Jäck, Berthold; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Kondrashov, Oleg V. [Moscow Institute of Physics and Technology, 141700 Moscow (Russian Federation); Skvortsov, Mikhail A. [Moscow Institute of Physics and Technology, 141700 Moscow (Russian Federation); Skolkovo Institute of Science and Technology, 143026 Moscow (Russian Federation); L. D. Landau Institute for Theoretical Physics, 142432 Chernogolovka (Russian Federation); Kern, Klaus [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)

    2015-09-21

    The properties of geometrically confined superconductors significantly differ from their bulk counterparts. Here, we demonstrate the geometrical impact for superconducting scanning tunneling microscopy (STM) tips, where the confinement ranges from the atomic to the mesoscopic scale. To this end, we compare the experimentally determined magnetic field dependence for several vanadium tips to microscopic calculations based on the Usadel equation. For our theoretical model of a superconducting cone, we find a direct correlation between the geometry and the order of the superconducting phase transition. Increasing the opening angle of the cone changes the phase transition from first to second order. Comparing our experimental findings to the theory reveals first and second order quantum phase transitions in the vanadium STM tips. In addition, the theory also explains experimentally observed broadening effects by the specific tip geometry.

  6. Analysis of single-event upset of magnetic tunnel junction used in spintronic circuits caused by radiation-induced current

    Energy Technology Data Exchange (ETDEWEB)

    Sakimura, N., E-mail: n-sakimura@ap.jp.nec.com [Green Platform Research Laboratories, NEC Corporation, Tsukuba (Japan); Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); Nebashi, R.; Sugibayashi, T. [Green Platform Research Laboratories, NEC Corporation, Tsukuba (Japan); Natsui, M.; Hanyu, T. [Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); Ohno, H. [Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); WPI Advanced Institute for Materials Research, Tohoku University, Sendai (Japan)

    2014-05-07

    This paper describes the possibility of a switching upset of a magnetic tunnel junction (MTJ) caused by a terrestrial radiation-induced single-event-upset (SEU) current in spintronic integrated circuits. The current waveforms were simulated by using a 3-D device simulator in a basic circuit including MTJs designed using 90-nm CMOS parameters and design rules. The waveforms have a 400 -μA peak and a 200-ps elapsed time when neutron particles with a linear energy transfer value of 14 MeV cm{sup 2}/mg enter the silicon surface. The authors also found that the SEU current may cause soft errors with a probability of more than 10{sup −12} per event, which was obtained by approximate solution of the ordinary differential equation of switching probability when the intrinsic critical current (I{sub C0}) became less than 30 μA.

  7. Bias-voltage dependence of perpendicular spin-transfer torque in asymmetric MgO-based magnetic tunnel junctions

    KAUST Repository

    Oh, Se Chung

    2009-10-25

    Spin-transfer torque (STT) allows the electrical control of magnetic states in nanostructures. The STT in magnetic tunnel junctions (MTJs) is of particular importance owing to its potential for device applications. It has been demonstrated that the MTJ has a sizable perpendicular STT (, field-like torque), which substantially affects STT-driven magnetization dynamics. In contrast to symmetric MTJs where the bias dependence of is quadratic, it is theoretically predicted that the symmetry breaking of the system causes an extra linear bias dependence. Here, we report experimental results that are consistent with the predicted linear bias dependence in asymmetric MTJs. The linear contribution is quite significant and its sign changes from positive to negative as the asymmetry is modified. This result opens a way to design the bias dependence of the field-like term, which is useful for device applications by allowing, in particular, the suppression of the abnormal switching-back phenomena. © 2009 Macmillan Publishers Limited. All rights reserved.

  8. Compact-device model development for the energy-delay analysis of magneto-electric magnetic tunnel junction structures

    Science.gov (United States)

    Sharma, N.; Bird, J. P.; Dowben, P. A.; Marshall, A.

    2016-06-01

    We discuss the application of a novel class of device, the magneto-electric magnetic tunnel junction (ME-MTJ) to realize a variety of computational functions, including majority logic and the XNOR/XOR gate. We also develop a compact model to describe the operation of these devices, which function by utilizing the phenomenon of ‘voltage-controlled magnetism’ to switch the operational state of MTJs. The model breaks down the switching process into three key stages of operation: electrical-to-magnetic conversion, magnetization transfer, and final-state readout. Estimates for the switching energy and delay of these devices, obtained from this compact model, reveal significant improvements in both of these parameters when compared to conventional MTJs switched by spin-transfer-torque. In fact, the capacity to use the ME-MTJ to implement complex logical operations within a single device allows its energy costs to even approach those of low-power CMOS. The added benefits of non-volatility and compact circuit footprint, combined with their potential for heterogeneous integration with CMOS, make the ME devices of considerable interest for post-CMOS technology.

  9. Susceptibility of CoFeB/AlOx/Co Magnetic Tunnel Junctions to Low-Frequency Alternating Current

    Directory of Open Access Journals (Sweden)

    Yuan-Tsung Chen

    2013-10-01

    Full Text Available This investigation studies CoFeB/AlOx/Co magnetic tunneling junction (MTJ in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlOx. The low-frequency alternate-current magnetic susceptibility (χac and phase angle (θ of the CoFeB/AlOx/Co MTJ are determined using an cac analyzer. The driving frequency ranges from 10 to 25,000 Hz. These multilayered MTJs are deposited on a silicon substrate using a DC and RF magnetron sputtering system. Barrier layer thicknesses are 22, 26, and 30 Å. The X-ray diffraction patterns (XRD include a main peak at 2θ = 44.7° from hexagonal close-packed (HCP Co with a highly (0002 textured structure, with AlOx and CoFeB as amorphous phases. The full width at half maximum (FWHM of the Co(0002 peak, decreases as the AlOx thickness increases; revealing that the Co layer becomes more crystalline with increasing thickness. χac result demonstrates that the optimal resonance frequency (fres that maximizes the χac value is 500 Hz. As the frequency increases to 1000 Hz, the susceptibility decreases rapidly. However, when the frequency increases over 1000 Hz, the susceptibility sharply declines, and almost closes to zero. The experimental results reveal that the mean optimal susceptibility is 1.87 at an AlOx barrier layer thickness of 30 Å because the Co(0002 texture induces magneto-anisotropy, which improves the indirect CoFeB and Co spin exchange-coupling strength and the χac value. The results concerning magnetism indicate that the magnetic characteristics are related to the crystallinity of Co.

  10. Enhancement of magnetic coercivity and macroscopic quantum tunneling in monodispersed Co/CoO cluster assemblies

    OpenAIRE

    Peng, D. L.; Sumiyama, Kenji; Hihara, Takehiko; Yamamuro, S.; ヒハラ, タケヒコ; スミヤマ, ケンジ; 日原, 岳彦; 隅山, 兼治; Hihara, T.; Sumiyama, K.

    1999-01-01

    Magnetic properties have been measured for monodisperse-sized Co/CoO cluster assemblies prepared by a plasma-gas-condensation-type cluster beam deposition technique. The clear correlation obtained between exchange bias field and coercivity suggests the enhancement of uniaxial anisotropy owing to the exchange coupling between the ferromagnetic Co core and antiferromagnetic CoO shell, and magnetic disorder at the core-shell interface. A nonthermal magnetic relaxation observed below 8 K, being r...

  11. Individual flexor tendon identification within the carpal tunnel: A semi-automated analysis method for serial cross-section magnetic resonance images

    Directory of Open Access Journals (Sweden)

    Nicole M Kunze

    2009-12-01

    Full Text Available Nicole M Kunze1, Jessica E Goetz2, Daniel R Thedens3, Thomas E Baer2, Ericka A Lawler2, Thomas D Brown21Department of Biomedical Engineering, 2Department of Orthopaedics and Rehabilitation, 3Department of Radiology, University of Iowa, Iowa City, IA, USAAbstract: Carpal tunnel syndrome is commonly viewed as resulting from chronic mechanical insult of the median nerve by adjacent anatomical structures. Both the median nerve and its surrounding soft tissue structures are well visualized on magnetic resonance (MR images of the wrist and hand. Addressing nerve damage from impingement of flexor digitorum tendons co-occupying the tunnel is attractive, but to date has been restricted by a lack of means for making individual identifications of the respective tendons. In this image analysis work, we have developed a region-growing method to positively identify each individual digital flexor tendon within the carpal tunnel by tracking it from a more distal MR section where the respective tendon identities are unambiguous. Illustratively, the new method was applied to MRI scans from four different subjects in a variety of hand poses. Conventional shape measures yielded less discriminatory information than did evaluations of individual tendon location and arrangement. This new method of rapid identification of individual tendons will facilitate analysis of tendon/nerve interactions within the tunnel, thereby providing better information about mechanical insult of the median nerve.Keywords: carpal tunnel syndrome, magnetic resonance imaging, region growing, digital flexor tendons

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

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xin, E-mail: jiangxinyj@gmail.com; Li, Zhipeng; Zheng, Yuankai; Kaiser, Christian; Diao, Zhitao; Fang, Jason; Leng, Qunwen, E-mail: Qunwen.Leng@wdc.com [Western Digital Corporation, 44100 Osgood Road, Fremont, California 94539 (United States)

    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.

  13. Model of tunnelling through periodic array of quantum dots in a magnetic field

    Institute of Scientific and Technical Information of China (English)

    I.Yu.Popov; S.A.Osipov

    2012-01-01

    A two-dimensional periodic array of quantum dots with two laterally coupled leads in a magnetic field is considered.The model of electron transport through the system based on the theory of self-adjoint extensions of symmetric operators is suggested.We obtain the formula for the transmission coefficient and investigate its dependence on the magnetic field.

  14. Response of magnetic tunnel junction-based spin-torque oscillator to series of sub-nanosecond magnetic pulses

    Science.gov (United States)

    Nagasawa, Tazumi; Suto, Hirofumi; Kudo, Kiwamu; Mizushima, Koichi; Sato, Rie

    2016-11-01

    Spin-torque oscillator (STO) read heads with a high data transfer rate for hard disk drives have been proposed. To investigate the oscillation stability and frequency agility of the STO under magnetic pulses, we measured the response waveforms of the STO to a series of sub-nanosecond magnetic pulses and calculated the delay-detection output signal from the STO waveforms. We found that stable oscillation was maintained under the magnetic pulses and that the delay-detection output signal reproduced the applied pulse pattern. The results indicate that the STO read heads can operate at data transfer rates higher than 2 Gbits/s.

  15. Effects of in-plane magnetization orientation on magnetic and electronic properties in a Bcc Co (001)/rock salt MgO (001)/Bcc Co (001) magnetic tunnel junction system: ab initio calculations.

    Science.gov (United States)

    Yoo, Dong Su; Chae, Kisung; Chung, Yong-Chae

    2012-04-01

    Ab initio calculations were performed on a fully epitaxial bcc Co (001)/rock salt MgO (001)/bcc Co (001) magnetic tunnel junction system for two cases where the magnetization is parallel to bcc Co [100] and to bcc Co [110]. Structural optimization reveals that the two cases are equivalent systems and that the Co electrodes contract in the z-direction whereas the MgO insulating barrier expands. The magnetic moments of each monolayer vary slightly in each case; furthermore, only the magnetic moment at the surface of the Co atom shows any enhancement (12%). The layer decomposed density of states profiles reveals that the bonding character of the junction interface is derived mainly from the 2p-3d hybridization of the MgO and Co interfacial atoms.

  16. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    Energy Technology Data Exchange (ETDEWEB)

    Daqiq, Reza; Ghobadi, Nader

    2016-07-15

    We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching. - Highlights: • The quantum size effects are studied in double barrier magnetic tunnel junctions. • Spin torque (ST) components oscillate for increasing of middle spacer thicknesses. • Due to the resonant tunneling in the quantum well, oscillations have appeared. • By replacement a metal spacer with a semiconductor (ZnO) ST has increased. • The ST components vs. bias show gradually decreasing unlike spin valves or MTJs.

  17. Thermally induced perpendicular magnetic anisotropy in CoFeB/MgO/CoFeB based magnetic tunnel junction

    Science.gov (United States)

    Kulkarni, Prabhanjan D.; Khan, Jakeer; Predeep, P.; Chowdhury, P.

    2016-05-01

    Thin films of CoFeB/MgO/CoFeB based MTJ structure were deposited using UHV magnetron sputtering system and post annealing treatment in the temperature range from 100 to 400 °C has been carried out to understand their magnetic anisotropic properties. Though the as-deposited stack possesses in-plane magnetic anisotropy, the changeover to perpendicular magnetic anisotropy happens at temperature above 200 °C. The PMA is maximum (4.5 x 106 erg/cm3) when annealed at 300°C and the stack retains PMA till 350 °C, which is necessary in CMOS technology. The stack regains in-plane magnetic anisotropy at higher annealing temperatures due to intermixing at interfaces.

  18. Perpendicular magnetic tunnel junctions with a synthetic storage or reference layer: A new route towards Pt- and Pd-free junctions

    Science.gov (United States)

    Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard

    2016-02-01

    We report here the development of Pt and Pd-free perpendicular magnetic tunnel junctions (p-MTJ) for STT-MRAM applications. We start by studying a p-MTJ consisting of a bottom synthetic Co/Pt reference layer and a synthetic FeCoB/Ru/FeCoB storage layer covered with an MgO layer. We first investigate the evolution of RKKY coupling with Ru spacer thickness in such a storage layer. The coupling becomes antiferromagnetic above 0.5 nm and its strength decreases monotonously with increasing Ru thickness. This contrasts with the behavior of Co-based systems for which a maximum in interlayer coupling is generally observed around 0.8 nm. A thin Ta insertion below the Ru spacer considerably decreases the coupling energy, without basically changing its variation with Ru thickness. After optimization of the non-magnetic and magnetic layer thicknesses, it appears that such a FeCoB/Ru/FeCoB synthetic storage layer sandwiched between MgO barriers can be made stable enough to actually be used as hard reference layer in single or double magnetic tunnel junctions, the storage layer being now a single soft FeCoB layer. Finally, we realize Pt- or Pd-free robust perpendicular magnetic tunnel junctions, still keeping the advantage of a synthetic reference layer in terms of reduction of stray fields at small pillar sizes.

  19. Study of CoFeB thickness and composition dependence in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction

    Science.gov (United States)

    Zhu, M.; Chong, H.; Vu, Q. B.; Brooks, R.; Stamper, H.; Bennett, S.

    2016-02-01

    We studied the CoFeB thickness and composition dependence of tunneling magnetoresistance (TMR) and resistance-area product (RA) in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction (MTJ), in which the bottom CoFeB is coupled to an in-plane exchange biased magnetic layer. This stack structure allows us to measure TMR and RA of the MTJs in sheet film format without patterning them, using current-in-plane-tunneling (CIPT) technique. The thickness ranges for both top and bottom CoFeB to exhibit perpendicular magnetic anisotropy are similar to what are seen in each single magnetic film stack. However, CIPT measurement revealed that there exists an optimal thickness for both top and bottom CoFeB to achieve the highest TMR value. Magnetic hysteresis loops also suggest the thickness-dependent coupling between the top and bottom CoFeB layers. We studied MTJs with two CoFeB compositions (Co40Fe40B20 and Co20Fe60B20) and found that Co20Fe60B20 MTJs give higher TMR and also wider perpendicular thickness range when used at the top layer.

  20. Reducing spin-torque switching current by incorporating an ultra-thin Ta layer with CoFeB free layer in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, R. S., E-mail: liurs7204@yahoo.com; Meng, H.; Naik, V. B.; Sim, C. H.; Yap, S.; Luo, P. [Data Storage Institute, A*STAR (Agency for Science Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore)

    2014-12-15

    We studied the spin torque switching in dual MgO layer based magnetic tunnel junctions (MTJs) by incorporating an ultra-thin (0.5 nm) Ta layer at the CoFeB free layer/top MgO layer interface. The Ta incorporated MTJ showed a significant reduction (∼30%) in critical switching current density (J{sub C0} ) as compared to that of the control MTJ whilst maintaining the same tunneling magnetoresistance as well as thermal stability. The reduction of J{sub C0} can be attributed to the perpendicular magnetic anisotropy arising from the incorporation of an ultrathin Ta layer with the MgO|CoFeB structure. This scheme of reducing J{sub C0} without degrading other properties may contribute to the development of spin-transfer-torque magnetic random access memory for low power applications.

  1. Non-Equilibrium Green's Function Calculation for Electron Transport through Magnetic Tunnel Junction

    Directory of Open Access Journals (Sweden)

    Sara Nobakht

    2014-06-01

    Full Text Available In this paper non-equilibrium Green's function method –dependent electron transport through non magnetic layer (insulator has been studied in one dimension .electron transport in multi-layer (magnetic/non magnetic/ magneticlayers is studied as quantum .the result show increasing the binding strength of the electrical insulator transition probability density case , the electron density , broad levels of disruption increases. Broad band connection increases the levels of disruption to electrical insulation and show non- conductive insulating state to semiconductor stat and even conductor

  2. A first dipole magnet was delivered to its final location in the LHC tunnel (2)

    CERN Multimedia

    2005-01-01

    The first superconducting magnet was transported to its final location between Points 8 and 1 by a specially designed vehicle. It was then positioned with great precision and unloaded using a transfer table.

  3. Comprehensive and Macrospin-Based Magnetic Tunnel Junction Spin Torque Oscillator Model- Part II: Verilog-A Model Implementation

    Science.gov (United States)

    Chen, Tingsu; Eklund, Anders; Iacocca, Ezio; Rodriguez, Saul; Malm, B. Gunnar; Akerman, Johan; Rusu, Ana

    2015-03-01

    The rapid development of the magnetic tunnel junction (MTJ) spin torque oscillator (STO) technology demands an analytical model to enable building MTJ STO-based circuits and systems so as to evaluate and utilize MTJ STOs in various applications. In Part I of this paper, an analytical model based on the macrospin approximation, has been introduced and verified by comparing it with the measurements of three different MTJ STOs. In Part II, the full Verilog-A implementation of the proposed model is presented. To achieve a reliable model, an approach to reproduce the phase noise generated by the MTJ STO has been proposed and successfully employed. The implemented model yields a time domain signal, which retains the characteristics of operating frequency, linewidth, oscillation amplitude and DC operating point, with respect to the magnetic field and applied DC current. The Verilog-A implementation is verified against the analytical model, providing equivalent device characteristics for the full range of biasing conditions. Furthermore, a system that includes an MTJ STO and CMOS RF circuits is simulated to validate the proposed model for system- and circuit-level designs. The simulation results demonstrate that the proposed model opens the possibility to explore STO technology in a wide range of applications.

  4. Fabrication of nano-sized magnetic tunnel junctions using lift-off process assisted by atomic force probe tip.

    Science.gov (United States)

    Jung, Ku Youl; Min, Byoung-Chul; Ahn, Chiyui; Choi, Gyung-Min; Shin, Il-Jae; Park, Seung-Young; Rhie, Kungwon; Shin, Kyung-Ho

    2013-09-01

    We present a fabrication method for nano-scale magnetic tunnel junctions (MTJs), employing e-beam lithography and lift-off process assisted by the probe tip of atomic force microscope (AFM). It is challenging to fabricate nano-sized MTJs on small substrates because it is difficult to use chemical mechanical planarization (CMP) process. The AFM-assisted lift-off process enables us to fabricate nano-sized MTJs on small substrates (12.5 mm x 12.5 mm) without CMP process. The e-beam patterning has been done using bi-layer resist, the poly methyl methacrylate (PMMA)/ hydrogen silsesquioxane (HSQ). The PMMA/HSQ resist patterns are used for both the etch mask for ion milling and the self-aligned mask for top contact formation after passivation. The self-aligned mask buried inside a passivation oxide layer, is readily lifted-off by the force exerted by the probe tip. The nano-MTJs (160 nm x 90 nm) fabricated by this method show clear current-induced magnetization switching with a reasonable TMR and critical switching current density.

  5. Investigation on etch characteristics of nanometer-sized magnetic tunnel junction stacks using a HBr/Ar plasma.

    Science.gov (United States)

    Kim, Eun Ho; Xiao, Yu Bin; Kong, Seon Mi; Chung, Chee Won

    2011-07-01

    The etch characteristics of CoFeB magnetic films and magnetic-tunnel-junction (MTJ) stacks masked with Ti films were investigated using an inductively coupled plasma reactive ion etching in a HBr/Ar gas mix. The etch rate, etch selectivity, and etch profile of the CoFeB films were obtained as a function of the HBr concentration. As the HBr gas was added to Ar, the etch rate of the CoFeB films, and the etch selectivity to the Ti hard mask, gradually decreased, but the etch profile of the CoFeB films was improved. The effects of the HBr concentration and etch parameters on the etch profile of the MTJ stacks with a nanometer-sized 70 x 100 nm2 pattern were explored. At 10% HBr concentration, low ICP RF power, and low DC-bias voltage, better etch profiles of the MTJ stacks were obtained without redeposition. It was confirmed that the protective layer containing hydrogen, and the surface bombardment of the Ar ions, played a key role in obtaining a steep sidewall angle in the etch profile. Fine-pattern transfer of the MTJ stacks with a high degree of anisotropy was achieved using a HBr/Ar gas chemistry.

  6. A novel low-cost high-throughput probe card scanner analyzer for characterization of magnetic tunnel junctions

    Science.gov (United States)

    Pong, Philip W. T.; Schmoueli, Moshe; Marcus, Eliezer; Egelhoff, William F., Jr.

    2007-09-01

    The advancement of the technology of magnetic tunnel junctions (MTJs) greatly hinges on the optimization of the magnetic materials, fabrication process, and annealing conditions which involve characterization of a large number of samples. As such, it is of paramount importance to have a rapid-turnaround characterization method since the characterization process can take even longer time than the fabrication. Conventionally, micropositioners and probe tips are manually operated to perform 4-point electrical measurement on each individual device which is a time-consuming, low-throughput process. A commercial automatic probe card analyzer can provide high turnaround; however, it is expensive and involves much cost and labor to install and maintain the equipment. In view of this, we have developed a novel low-cost, home-made, high-throughput probe card analyzer system for characterization of MTJs. It can perform fast 4-probe electrical measurements including current vs voltage, magnetoresistance, and bias dependence measurements with a high turnaround of about 500 devices per hour. The design and construction of the system is discussed in detail in this paper.

  7. Fabrication of L1{sub 0}-MnAl perpendicularly magnetized thin films for perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Hosoda, Masaki; Oogane, Mikihiko; Kubota, Miho; Saruyama, Haruaki; Iihama, Satoshi; Naganuma, Hiroshi; Ando, Yasuo [Department of Applied Physics, Graduate school of Engineering, Tohoku University, Aza-aoba 6-6-05, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Kubota, Takahide [WPI Advanced Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan)

    2012-04-01

    Structural and magnetic properties of MnAl thin films with different composition, growth temperature, and post-annealing temperature were investigated. The optimum condition for fabrication of L1{sub 0}-MnAl perpendicularly magnetized thin film deposited on Cr-buffered MgO single crystal substrate was revealed. The results of x ray diffraction indicated that the MnAl films annealed at proper temperature had a (001)-orientation and L1{sub 0}-ordered structure. The L1{sub 0}-ordered films were perpendicularly magnetized and had a large perpendicular anisotropy. In addition, low surface roughness was achieved. For the optimized fabrication condition, the saturation magnetization M{sub s} of 600 emu/cm{sup 3} and perpendicular magnetic anisotropy K{sub u} of 1.0 x 10{sup 7} erg/cm{sup 3} was obtained using the Mn{sub 48}Al{sub 52} target at deposition temperature of 200 deg. C and post-annealing temperature of 450 deg. C.

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

    Directory of Open Access Journals (Sweden)

    Xin Jiang

    2015-09-01

    Full Text Available 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.

  9. MgAl{sub 2}O{sub 4}(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target

    Energy Technology Data Exchange (ETDEWEB)

    Belmoubarik, Mohamed; Sukegawa, Hiroaki, E-mail: sukegawa.hiroaki@nims.go.jp; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047 (Japan)

    2016-03-28

    We developed a fabrication process of an epitaxial MgAl{sub 2}O{sub 4} barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl{sub 2}O{sub 4} spinel sintered target. Annealing the sputter-deposited MgAl{sub 2}O{sub 4} layer sandwiched between Fe electrodes led to the formation of a (001)-oriented cation-disorder spinel with atomically sharp interfaces and lattice-matching with the Fe electrodes. A large tunnel magnetoresistance ratio up to 245% at 297 K (436% at 3 K) was achieved in the Fe/MgAl{sub 2}O{sub 4}/Fe(001) MTJ as well as an excellent bias voltage dependence. These results indicate that the direct sputtering is an alternative method for the realization of high performance MTJs with a spinel-based tunnel barrier.

  10. A nanoliter volume nuclear magnetic resonance (NMR) system using tunneling magneto-resistive (TMR) sensors to recognize biomolecules

    Science.gov (United States)

    Gomez, Pablo

    The need to incorporate advanced engineering tools in biology, biochemistry and medicine is in great demand. Many of the existing instruments and tools are usually expensive and require special facilities. With the advent of nanotechnology in the past decade, new approaches to develop devices and tools have been generated by academia and industry. One such technology, NMR spectroscopy, has been used by biochemists for more than 2 decades to study the molecular structure of chemical compounds. However, NMR spectrometers are very expensive and require special laboratory rooms for their proper operation. High magnetic fields with strengths in the order of several Tesla make these instruments unaffordable to most research groups. This doctoral research proposes a new technology to develop NMR spectrometers that can operate at field strengths of less than 0.5 Tesla using an inexpensive permanent magnet and spin dependent nanoscale magnetic devices. This portable NMR system is intended to analyze samples as small as a few nanoliters. The main problem to resolve when downscaling the variables is to obtain an NMR signal with high Signal-To-Noise-Ratio (SNR). A special Tunneling Magneto-Resistive (TMR) sensor design was developed to achieve this goal. The minimum specifications for each component of the proposed NMR system were established. A complete NMR system was designed based on these minimum requirements. The goat was always to find cost effective realistic components. The novel design of the NMR system uses technologies such as Direct Digital Synthesis (DDS), Digital Signal Processing (DSP) and a special Backpropagation Neural Network that finds the best match of the NMR spectrum. The system was designed, calculated and simulated with excellent results. In addition, a general method to design TMR Sensors was developed. The technique was automated and a computer program was written to help the designer perform this task interactively.

  11. Perpendicular magnetic tunnel junction with enhanced anisotropy obtained by utilizing an Ir/Co interface

    Science.gov (United States)

    Yakushiji, Kay; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji

    2016-01-01

    A highly scalable perpendicularly magnetized storage layer of a spin-torque-switching magnetic random-access memory (STT-MRAM) was developed. This storage layer attains a perpendicular magnetic anisotropy (PMA) of above 0.9 erg/cm2 at a thickness of 2 nm. Such high PMA is suitable for pushing STT-MRAM technology beyond the 20 nm node. The key was to realize dual interfacial PMA at both the Ir/Co and FeB/MgO interfaces in the united structure of the storage layer. While a high PMA was retained, a high magnetoresistance ratio (100%) and a low resistance-area product (3.0 Ω µm2) were also achieved.

  12. Fe3O4/MgO/Fe Heteroepitaxial Structures for Magnetic Tunnel Junctions

    Energy Technology Data Exchange (ETDEWEB)

    Orna, J. [University of Zaragoza, Spain; Morellon, Luis [University of Zaragoza, Spain; Algarabel, Pedro A. [University of Zaragoza, Spain; Pardo, J. A. [University of Zaragoza, Spain; Sangiao, S [Instituto de Nanociencia de Aragón, Universidad de Zaragoza, Zaragoza, 50009 Spain; Magen, C [Oak Ridge National Laboratory (ORNL); Snoeck, E. [CEMES-CNRS, Toulouse, France; De Teresa, J M [Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, Zaragoza, 50009 Spain; Ibarra, M. Ricardo [University of Zaragoza, Spain

    2008-01-01

    In this work we report the growth and structural and magnetic characterization of heteroepitaxial Fe O/MgO/Fe junctions. All three layers have been deposited by pulsed laser deposition. Combining High Resolution Transmission Electron Microscopy and X-ray results, we have obtained for the heterostructure the epitaxy relation MgO(001) [100]//Fe O(001)[100]/MgO(001) [100]/Fe(001)[110]. All interfaces appear very sharp with relatively small root-mean square (rms) roughness, 0.2 nm. The magnetic coupling between Fe O and Fe electrodes is also very small, 0.03 mJ/

  13. Intrinsic spin dynamics in optically excited nanoscale magnetic tunnel junction arrays restored by dielectric coating

    Science.gov (United States)

    Jaris, M.; Yahagi, Y.; Mahato, B. K.; Dhuey, S.; Cabrini, S.; Nikitin, V.; Stout, J.; Hawkins, A. R.; Schmidt, H.

    2016-11-01

    We report the all-optical observation of intrinsic spin dynamics and extraction of magnetic material parameters from arrays of sub-100 nm spin-transfer torque magnetic random access memory (STT-MRAM) devices with a CoFeB/MgO interface. To this end, the interference of surface acoustic waves with time-resolved magneto-optic signals via magneto-elastic coupling was suppressed using a dielectric coating. The efficacy of this method is demonstrated experimentally and via modeling on a nickel nanomagnet array. The magnetization dynamics for both coated nickel and STT-MRAM arrays shows a restored field-dependent Kittel mode from which the effective damping can be extracted. We observe an increased low-field damping due to extrinsic contributions from magnetic inhomogeneities and variations in the nanomagnet shape, while the intrinsic Gilbert damping remains unaffected by patterning. The data are in excellent agreement with a local resonance model and have direct implications for the design of STT-MRAM devices as well as other nanoscale spintronic technologies.

  14. Device properties of the spin-valve transistor and the magnetic tunnel transistor

    NARCIS (Netherlands)

    van 't Erve, O.M.J.

    Spin electronics is a new research area, which not only uses the electron’s charge but also its spin. By using the electron spin dependent properties of magnetic materials one can make devices with a new functionality. This has lead to magnetoresistive devices that can change their resistance by 10

  15. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    Science.gov (United States)

    Daqiq, Reza; Ghobadi, Nader

    2016-07-01

    We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching.

  16. Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited MgAl2O4/Fe(001) magnetic tunnel junctions

    Science.gov (United States)

    Belmoubarik, Mohamed; Sukegawa, Hiroaki; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro

    2017-05-01

    We investigated the effect of an Mg-Al layer insertion at the bottom interface of epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions (MTJs) on their spin-dependent transport properties. The tunnel magnetoresistance (TMR) ratio and differential conductance spectra for the parallel magnetic configuration exhibited clear dependence on the inserted Mg-Al thickness. A slight Mg-Al insertion (thickness 0.2 nm) induced a reduction of TMR ratios and featureless conductance spectra, indicating a degradation of the bottom-Fe/MgAl2O4 interface. Therefore, a minimal Mg-Al insertion was found to be effective to maximize the TMR ratio for a sputtered MgAl2O4-based MTJ.

  17. Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited MgAl2O4/Fe(001 magnetic tunnel junctions

    Directory of Open Access Journals (Sweden)

    Mohamed Belmoubarik

    2017-05-01

    Full Text Available We investigated the effect of an Mg-Al layer insertion at the bottom interface of epitaxial Fe/MgAl2O4/Fe(001 magnetic tunnel junctions (MTJs on their spin-dependent transport properties. The tunnel magnetoresistance (TMR ratio and differential conductance spectra for the parallel magnetic configuration exhibited clear dependence on the inserted Mg-Al thickness. A slight Mg-Al insertion (thickness 0.2 nm induced a reduction of TMR ratios and featureless conductance spectra, indicating a degradation of the bottom-Fe/MgAl2O4 interface. Therefore, a minimal Mg-Al insertion was found to be effective to maximize the TMR ratio for a sputtered MgAl2O4-based MTJ.

  18. The Oscillator Strength of the Quantum Transitions in Multi-Resonant-Tunneling Structures Tours as Basic Elements of Quantum Cascade Lasers and Detectors in a Transverse Magnetic Field

    Directory of Open Access Journals (Sweden)

    I.V. Boyko

    2014-04-01

    Full Text Available Using the model of a closed resonant tunneling structure developed the theory of the electron energy spectrum and oscillator strengths of the quantum electronic transitions between energy levels of this nanostructure. It is shown that by changing the intensity of the magnetic field can be in a wide range of electromagnetic waves to adjust the operating frequency of the radiation of a quantum cascade laser or detector, working on quantum transitions between the first and the third energy electronic states.

  19. Improvements to an electromagnetic position sensor for a magnetic suspension wind tunnel

    Science.gov (United States)

    Daniels, Taumi S.; Tripp, John S.

    1988-01-01

    The original and improved designs for the Electromagnetic Position Sensor (EPS), an electronic instrument and associated multicoil sensor for the six-inch Magnetic Suspension and Balance System (MSBS) that measures aerodynamic model position, are compared. The EPS power amplifier and oscillator, input nulling stage, reference voltage generators, bandpass filter, summation and demodulation, and final stage are described. The effects of the MSBS and of model materials on the performance are addressed.

  20. Solid state magnetic field sensors for micro unattended ground networks using spin dependent tunneling

    Science.gov (United States)

    Tondra, Mark; Nordman, Catherine A.; Lange, Erik H.; Reed, Daniel; Jander, Albrect; Akou, Seraphin; Daughton, James

    2001-09-01

    Micro Unattended Ground Sensor Networks will likely employ magnetic sensors, primarily for discrimination of objects as opposed to initial detection. These magnetic sensors, then, must fit within very small cost, size, and power budgets to be compatible with the envisioned sensor suites. Also, a high degree of sensitivity is required to minimize the number of sensor cells required to survey a given area in the field. Solid state magnetoresistive sensors, with their low cost, small size, and ease of integration, are excellent candidates for these applications assuming that their power and sensitivity performance are acceptable. SDT devices have been fabricated into prototype magnetic field sensors suitable for use in micro unattended ground sensor networks. They are housed in tiny SOIC 8-pin packages and mounted on a circuit board with required voltage regulation, signal amplification and conditioning, and sensor control and communications functions. The best sensitivity results to date are 289 pT/rt. Hz at 1 Hz, and and 7 pT/rt. Hz at f > 10 kHz. Expected near term improvements in performance would bring these levels to approximately 10 pT/rt Hz at 1 Hz and approximately 1 pT/rt. Hz at > 1 kHz.

  1. A solid-state controllable power supply for a magnetic suspension wind tunnel

    Science.gov (United States)

    Daniels, Taumi S.; Tripp, John S.

    1991-01-01

    The NASA Langley 6-inch Magnetic Suspension and Balance System (6-in. MSBS) requires an independently controlled bidirectional dc power source for each of six positioning electromagnets. These electromagnets provide five-degree-of-freedom control over a suspended aerodynamic test model. Existing power equipment, which employs resistance-coupled thyratron-controlled rectifiers as well as ac to dc motor-generator converters, is obsolete, inefficient, and unreliable. A replacement six-phase bidirectional controlled bridge rectifier is proposed, which employs power MOSFET switches sequenced by hybrid analog/digital circuits. Full-load efficiency is 80 percent compared with 25 percent for the resistance-coupled thyratron system. Current feedback provides high control linearity, adjustable current limiting, and current overload protection. A quenching circuit suppresses inductive voltage impulses. It is shown that 20-kHz interference from positioning magnet power into MSBS electromagnetic model position sensors results predominantly from capacitively coupled electric fields. Hence, proper shielding and grounding techniques are necessary. Inductively coupled magnetic interference is negligible.

  2. Magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations and tunnel magnetoresistance effect at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Nagahama, Taro, E-mail: nagahama@eng.hokudai.ac.jp; Matsuda, Yuya; Tate, Kazuya; Kawai, Tomohiro; Takahashi, Nozomi; Hiratani, Shungo; Watanabe, Yusuke; Yanase, Takashi; Shimada, Toshihiro [Graduate School of Engineering, Hokkaido University, Kita13 Nishi8, Kitak-ku, Sapporo 060-8628 (Japan)

    2014-09-08

    Fe{sub 3}O{sub 4} is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe{sub 3}O{sub 4} electrodes have demonstrated a small tunnel magnetoresistance (TMR) effect. Not even the sign of the tunnel magnetoresistance ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe{sub 3}O{sub 4}(110) films exhibited in-plane uniaxial magnetic anisotropy. With respect to the squareness of hysteresis, Fe{sub 3}O{sub 4} (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe{sub 3}O{sub 4}(110) electrodes and obtained a TMR effect of −12% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe{sub 3}O{sub 4} predicted from band calculations.

  3. Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Ling, E-mail: lingtang@zjut.edu.cn; Xu, Zhi-Jun, E-mail: xzj@zjut.edu.cn; Zuo, Xian-Jun; Yang, Ze-Jin, E-mail: zejinyang@zjut.edu.cn [Department of Applied Physics, College of Science, Zhejiang University of Technology, Hangzhou 310023 (China); Gao, Qing-He [College of Science, Northeastern University, Shenyang 110004, China, Information Engineering College, Liaoning University of Traditional Chinese Medicine, Shenyang 110847 (China); Linghu, Rong-Feng, E-mail: linghu@gznu.edu.cn [School of Physics and Electronics Sciences, Guizhou Education University, Guiyang 550018 (China); Guo, Yun-Dong, E-mail: g308yd@126.com [College of Engineering and Technology, Neijiang Normal University, Neijiang 641112 (China)

    2016-04-28

    Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg{sub 3}BO{sub 4}), B atoms replacing O atoms (Mg{sub 4}BO{sub 3}), and B atoms occupying interstitial positions (Mg{sub 4}BO{sub 4}) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg{sub 3}BO{sub 4} and CoFe/Mg{sub 4}BO{sub 4} based MTJs, whereas a nearly symmetric STT curve is observed in the junctions based on CoFe/Mg{sub 4}BO{sub 3}. Furthermore, the asymmetry of the angular dependence of STT can be suppressed significantly by the disorder of B distribution. Such skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the interfacial resonance states induced by the B diffusion into MgO spacer.

  4. Atomic-Scale Structure and Local Chemistry of CoFeB-MgO Magnetic Tunnel Junctions.

    Science.gov (United States)

    Wang, Zhongchang; Saito, Mitsuhiro; McKenna, Keith P; Fukami, Shunsuke; Sato, Hideo; Ikeda, Shoji; Ohno, Hideo; Ikuhara, Yuichi

    2016-03-09

    Magnetic tunnel junctions (MTJs) constitute a promising building block for future nonvolatile memories and logic circuits. Despite their pivotal role, spatially resolving and chemically identifying each individual stacking layer remains challenging due to spatially localized features that complicate characterizations limiting understanding of the physics of MTJs. Here, we combine advanced electron microscopy, spectroscopy, and first-principles calculations to obtain a direct structural and chemical imaging of the atomically confined layers in a CoFeB-MgO MTJ, and clarify atom diffusion and interface structures in the MTJ following annealing. The combined techniques demonstrate that B diffuses out of CoFeB electrodes into Ta interstitial sites rather than MgO after annealing, and CoFe bonds atomically to MgO grains with an epitaxial orientation relationship by forming Fe(Co)-O bonds, yet without incorporation of CoFe in MgO. These findings afford a comprehensive perspective on structure and chemistry of MTJs, helping to develop high-performance spintronic devices by atomistic design.

  5. Effect of RF pulsing biasing on the etching of magnetic tunnel junction materials using CH3OH.

    Science.gov (United States)

    Jeon, Min Hwan; Yun, Deok Hyun; Yang, Kyung Chae; Youn, Ji Youm; Lee, Du Yeong; Shim, Tae Hun; Park, Jea Gun; Yeom, Geun Young

    2014-12-01

    The magnetic tunnel junction (MTJ)-related materials such as CoFeB, CoPt, MgO, and Ru, and W were etched using CH3OH in a pulse-biased inductively coupled plasma system and the effect of bias pulsing (100% 30% duty percentage) on the etch characteristics of the MTJ-related materials was investigated at the substrate temperature of 200 degrees C. The etch selectivity of MTJ-related materials over W was improved by using pulse-biasing possibly due to the formation of more stable and volatile etch products during the pulse-off time and the removal of the compounds more easily on the etched CoFeB surface during the pulse-on time. X-ray photoelectron spectroscopy also showed that the use of lower duty percentage decreases the residue thickness remaining on the etched MTJ materials indirectly indicated the higher volatility of the etch products by the bias pulsing. The etching of nano-patterned CoFeB masked with W also showed more anisotropic etch profile by pulse-biasing probably due to the increased the etch selectivity of CoFeB over W and the decreased redeposition of etch products on the sidewall of the CoFeB features. The most anisotropic CoFeB etch profiles could be observed by using CH3OH gas in the pulse biasing of 30% duty ratio.

  6. Addressing the challenges of using ferromagnetic electrodes in the magnetic tunnel junction-based molecular spintronics devices

    Science.gov (United States)

    Tyagi, Pawan; Friebe, Edward; Baker, Collin

    2015-11-01

    Addressing the challenges of using high-Curie temperature ferromagnetic (FM) electrodes is critical for molecular spintronics devices (MSDs) research. Two FM electrodes simultaneously chemically bonded with a thiol-functionalized molecule can produce novel MSDs to exploring new quantum mechanical phenomenon and computer technologies. For developing a commercially viable MSD, it is crucial to developing a device fabrication scheme that carefully considers FM electrodes' susceptibility to oxidation, chemical etching, and stress-induced deformations during fabrication and usage. This paper studies NiFe, an alloy extensively used in present-day memory devices and high-temperature engineering applications, as a candidate FM electrode for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe oxidized aggressively after heating beyond 90 °C. The NiFe surfaces, aged for several months or heated for several minutes below 90 °C, exhibited remarkable electrochemical activity and were found suitable for chemical bonding with the thiol-functionalized molecular device elements. NiFe also demonstrated excellent etching resistance against commonly used solvents and lithography related chemicals. Additionally, NiFe mitigated the adverse effects of mechanical stress by subsiding the stress-induced deformities. A magnetic tunnel junction-based MSD approach was designed by carefully considering the merits and limitations of NiFe. The device fabrication protocol considers the safe temperature limit to avoiding irreversible surface oxidation, the effect of mechanical stresses, surface roughness, and chemical etching. This paper provides foundational experimental insights in realizing a versatile MSD allowing a wide range of transport and magnetic studies.

  7. Addressing the challenges of using ferromagnetic electrodes in the magnetic tunnel junction-based molecular spintronics devices

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, Pawan, E-mail: ptyagi@udc.edu; Friebe, Edward; Baker, Collin [University of the District of Columbia, Department of Mechanical Engineering (United States)

    2015-11-15

    Addressing the challenges of using high-Curie temperature ferromagnetic (FM) electrodes is critical for molecular spintronics devices (MSDs) research. Two FM electrodes simultaneously chemically bonded with a thiol-functionalized molecule can produce novel MSDs to exploring new quantum mechanical phenomenon and computer technologies. For developing a commercially viable MSD, it is crucial to developing a device fabrication scheme that carefully considers FM electrodes’ susceptibility to oxidation, chemical etching, and stress-induced deformations during fabrication and usage. This paper studies NiFe, an alloy extensively used in present-day memory devices and high-temperature engineering applications, as a candidate FM electrode for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe oxidized aggressively after heating beyond ∼90 °C. The NiFe surfaces, aged for several months or heated for several minutes below ∼90 °C, exhibited remarkable electrochemical activity and were found suitable for chemical bonding with the thiol-functionalized molecular device elements. NiFe also demonstrated excellent etching resistance against commonly used solvents and lithography related chemicals. Additionally, NiFe mitigated the adverse effects of mechanical stress by subsiding the stress-induced deformities. A magnetic tunnel junction-based MSD approach was designed by carefully considering the merits and limitations of NiFe. The device fabrication protocol considers the safe temperature limit to avoiding irreversible surface oxidation, the effect of mechanical stresses, surface roughness, and chemical etching. This paper provides foundational experimental insights in realizing a versatile MSD allowing a wide range of transport and magnetic studies.

  8. Comparison of laser-induced and intrinsic tunnel magneto-Seebeck effect in CoFeB /MgAl2O4 and CoFeB/MgO magnetic tunnel junctions

    Science.gov (United States)

    Huebner, Torsten; Boehnke, Alexander; Martens, Ulrike; Thomas, Andy; Schmalhorst, Jan-Michael; Reiss, Günter; Münzenberg, Markus; Kuschel, Timo

    2016-06-01

    We present a comparison of the tunnel magneto-Seebeck effect for laser-induced and intrinsic heating. Therefore, Co40Fe40B20 /MgAl2O4 and Co25Fe55B20 /MgO magnetic tunnel junctions have been prepared. The TMS ratio of 3% in case of the MAO MTJ agrees well with ratios found for other barrier materials, while the TMS ratio of 23% of the MgO MTJ emphasizes the influence of the CoFe composition. We find results using the intrinsic method that differ in sign and magnitude in comparison to the results of the laser heating. The intrinsic contributions can alternatively be explained by the Brinkman model and the given junction properties. Especially, we are able to demonstrate that the symmetric contribution is solely influenced by the barrier asymmetry. Thus, we conclude that the symmetry analysis used for the intrinsic method is not suitable to unambiguously identify an intrinsic tunnel magneto-Seebeck effect.

  9. Electrical-field and spin-transfer torque effects in CoFeB/MgO-based perpendicular magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Chikako Yoshida

    2016-05-01

    Full Text Available The electric-field (E dependence of the magnetoresistance (RH loops for top-pinned perpendicular CoFeB/MgO-based magnetic tunnel junctions (MTJs in the presence of a spin-transfer torque (STT-current was measured. The E effects were distinguished from the STT-current effects using a micromagnetic simulation. The coercive field (Hc decreased and the RH loop shifted as both the positive and negative bias E increased owing to the STT current. Furthermore, E-assisted switching for an MTJ with a diameter of 20 nm, which exhibited a nearly coherent magnetization reversal, was demonstrated using micromagnetic simulation.

  10. Electrical-field and spin-transfer torque effects in CoFeB/MgO-based perpendicular magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, Chikako, E-mail: cyoshida@jp.fujitsu.com; Noshiro, Hideyuki; Yamazaki, Yuichi; Sugii, Toshihiro [Fujitsu limited, 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0197 (Japan); Furuya, Atsushi; Ataka, Tadashi; Tanaka, Tomohiro; Uehara, Yuji [Fujitsu limited, 4-1-1 Kamikodanaka, Nakahara-ku, Kawasaki, Kanagawa, 211-8588 (Japan)

    2016-05-15

    The electric-field (E) dependence of the magnetoresistance (RH) loops for top-pinned perpendicular CoFeB/MgO-based magnetic tunnel junctions (MTJs) in the presence of a spin-transfer torque (STT)-current was measured. The E effects were distinguished from the STT-current effects using a micromagnetic simulation. The coercive field (H{sub c}) decreased and the RH loop shifted as both the positive and negative bias E increased owing to the STT current. Furthermore, E-assisted switching for an MTJ with a diameter of 20 nm, which exhibited a nearly coherent magnetization reversal, was demonstrated using micromagnetic simulation.

  11. Elliptic annular Josephson tunnel junctions in an external magnetic field: the statics

    DEFF Research Database (Denmark)

    Monaco, Roberto; Granata, Carmine; Vettoliere, Antonio

    2015-01-01

    symmetric electrodes a transverse magnetic field is equivalent to an in-plane field applied in the direction of the current flow. Varying the ellipse eccentricity we reproduce all known results for linear and ring-shaped JTJs. Experimental data on high-quality Nb/Al-AlOx/Nb elliptic annular junctions...... or in the perpendicular direction. We report a detailed study of both short and long elliptic annular junctions having different eccentricities. For junctions having a normalized perimeter less than one the threshold curves are derived and computed even in the case with one trapped Josephson vortex. For longer junctions...

  12. On the tunneling effect for magnetic Schrodinger operators in antidot lattices

    CERN Document Server

    Frank, R L

    2004-01-01

    We study the Schr\\"odinger operator $(h\\mathbf{D}-\\mathbf{A})^2$ with periodic magnetic field $B= \\text{curl}\\,\\mathbf{A}$ in an antidot lattice $\\Omega_\\infty=\\R^2\\setminus\\bigcup_{\\alpha\\in\\Gamma}(U+\\alpha)$. Neumann boundary conditions lead to spectrum below $h\\inf B$. Under suitable assumptions on a "one-well problem" we prove that this spectrum is localized inside an exponentially small interval in the semi-classical limit $h\\rightarrow 0$. For this purpose we construct a basis of the corresponding spectral subspace with natural localization and symmetry properties.

  13. Noise spectroscopy of CoFeB/MgO/CoFeB magnetic tunnel junctions in the presence of thermal gradients

    Energy Technology Data Exchange (ETDEWEB)

    Liebing, N. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, d-38116 Braunschweig (Germany); Serrano-Guisan, S., E-mail: santiago.serrano-guisan@inl.int [International Iberian Nanotechnology Laboratory, Avenida Mestre Jose Veiga, 4715-330 Braga (Portugal); Rott, K.; Reiss, G. [University of Bielefeld, Department of Physics, Univesitätesstr. 25, d-33615 Bielefeld (Germany); Schumacher, H.W., E-mail: hans.w.schumacher@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, d-38116 Braunschweig (Germany)

    2016-02-15

    We present experimental data of the precessional dynamics of the free layer of CoFeB/MgO/CoFeB based magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The free layer precession is investigated by noise spectroscopy. Thermal gradients of the order of tens of mK/nm across the MTJ are generated by electrical heating. Without applied thermal gradients we find spin transfer torque modified magnetization precession. With increasing thermal gradients we generally observe a decrease of the precession frequency which could be related to an increasing overall free layer temperature. However an asymmetry of the line width behavior for parallel and antiparallel orientation points towards additional effects beyond thermal activation. This could be a hint for the modification of the precessional dynamics in magnetic tunnel junctions by thermal spin torques. - Highlights: • Thermal gradients induced magnetization dynamics on MTJ structures are explored. • Magnetic noise spectroscopy is carried out to study the efficiency of such effects. • A decrease of resonance frequency is observed at both MTJ states for large ∇T. • An asymmetric linewidth behavior is observed for both MTJ states under ∇T. • Additional thermal effects beyond thermal activation must be considered.

  14. Tunneling conductance through normal metal - superconductor junctions: effects of Rashba spin orbit coupling and magnetic field

    Science.gov (United States)

    Kapri, Priyadarshini; Ganguly, Sudin; Basu, Saurabh

    2016-10-01

    In a system consisting of a metal-(s-wave) superconductor junction, we study the conductance characteristics in presence of Rashba spin orbit coupling (RSOC) and an external magnetic field applied along the plane of the sample. With a selective inclusion of the Rashba coupling either in the metallic or in both we note that there is a distinct effect with regard to the magnitude of the Andreev peak that occurs at a biasing voltage lower than the superconducting gap energy. The height of the peak is sensitive to the RSOC (increases with increase in RSOC) for RSOC to be present only in the metallic region, (same is true when RSOC is present throughout the junction), while the peak height is fairly independent when RSOC is solely present in the superconducting region. The in-plane magnetic field has very interesting effects which show up in the form of having a conductance peak at zero bias, thereby making it possible to realize a Majorana bound state.

  15. A fully automated in vitro diagnostic system based on magnetic tunnel junction arrays and superparamagnetic particles

    Science.gov (United States)

    Lian, Jie; Chen, Si; Qiu, Yuqin; Zhang, Suohui; Shi, Stone; Gao, Yunhua

    2012-04-01

    A fully automated in vitro diagnostic (IVD) system for diagnosing acute myocardial infarction was developed using high sensitivity MTJ array as sensors and nano-magnetic particles as tags. On the chip is an array of 12 × 106 MTJ devices integrated onto a 3 metal layer CMOS circuit. The array is divided into 48 detection areas, therefore 48 different types of bio targets can be analyzed simultaneously if needed. The chip is assembled with a micro-fluidic cartridge which contains all the reagents necessary for completing the assaying process. Integrated with electrical, mechanical and micro-fluidic pumping devices and with the reaction protocol programed in a microprocessor, the system only requires a simple one-step analyte application procedure to operate and yields results of the three major AMI bio-markers (cTnI, MYO, CK-MB) in 15 mins.

  16. Perpendicular magnetic anisotropy in Ta|Co40Fe40B20|MgAl2O4 structures and perpendicular CoFeB|MgAl2O4|CoFeB magnetic tunnel junction

    KAUST Repository

    Tao, B. S.

    2014-09-08

    Magnetic properties of Co40Fe40B20(CoFeB) thin films sandwiched between Ta and MgAl2O4layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl2O4structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy Ki=1.22erg/cm2, which further increases to 1.30erg/cm2after annealing, while MgAl2O4/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0nm, while that for top CoFeB layer is between 0.8 and 1.4nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a core structure of CoFeB/MgAl2O4/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.

  17. Investigation of electromagnetic interference effects by ESD simulator on test parameters of tunneling magnetic recording heads

    Science.gov (United States)

    Kruesubthaworn, A.; Khunkitti, P.; Siritaratiwat, A.; Kaewrawang, A.; Mewes, T.; Mewes, C. K. A.

    2017-01-01

    Electrostatic discharge (ESD) has been an important issue in the manufacturing processes of hard disk drive. It can also generate electromagnetic interference (EMI) which could possibly damage magnetic recording heads. The aims of this work are to measure the EMI from ESD events and to examine the effects of EMI on the heads. The discharge current and the EMI generated by an ESD simulator were experimentally measured. Also, the EMI was applied to the heads to determine if this can cause changes of head parameters. Our results show that the discharge current waveform is consistent with the theoretical waveform of the IEC ESD standard. Additionally, we found that the EMI applied due to ESD at distances greater than 2 cm does not have any significant effect on the head parameters. Hence, further detailed experiments are proposed to evaluate the EMI effects on recording head parameters in order to improve the measurement methodologies to prevent the degradation of the heads performance and to increase the robustness of the heads.

  18. Modulations of interlayer exchange coupling through ultrathin MgO-based magnetic tunnel junctions: First-principles study

    Science.gov (United States)

    Wang, Shizhuo; Xia, Ke; Min, Tai; Ke, Youqi

    2017-07-01

    Ultrathin MgO-based magnetic tunnel junction (MTJ) features high electron/heat current density, presenting important applications in spintronics. Here, we report a first-principles study of the interlayer exchange coupling (IEC) through ultrathin MgO-based MTJs. We investigate the effects of different modulations on the IEC, including temperature, different interfacial disorders, and the type and thickness of the ferromagnetic (FM) materials. It is found that the interfacial disorders, such as oxygen vacancies, boron and carbon impurities, can significantly influence the magnitude and sign of the IEC. The presence of interfacial disorders enhances the anti-FM coupling contribution and reduces the FM coupling contribution to the total IEC, and can thus change the total IEC from FM to Anti-FM in the ultrathin MTJ. We also find that FM materials have important effects on IEC: the IEC with CoFe alloy exhibits much weaker dependence on the interfacial disorders and temperature than that with the Fe. Our first-principles results provide a good explanation for the serious inconsistency between previous experimental measurements. Moreover, by studying the junction structure Vacuum/FM1/MgO/FM2 (FM1, FM2=Fe, CoFe), we find that the ultrathin FM1 layers can dramatically enhance the FM IEC and the IEC enhancement significantly depends on the combination of FM1-FM2. We show that the enhanced FM IEC with ultrathin FM1 can be sustained with a considerable amount of surface roughness in FM1 and interfacial disorder.

  19. Etch characteristics of magnetic tunnel junction materials using bias pulsing in the CH4/N2O inductively coupled plasma.

    Science.gov (United States)

    Jeon, Min Hwan; Youn, Ji Youn; Yang, Kyung Chae; Yun, Deok Hyun; Lee, Du Yeong; Shim, Tae Hun; Park, Jea Gun; Yeom, Geun Young

    2014-12-01

    The etch characteristics of magnetic tunneling junction (MTJ) related materials such as CoFeB, MgO, FePt, Ru, and W as hard mask have been investigated as functions of rf pulse biasing, substrate heating, and CH4/N2O gas combination in an inductively coupled plasma system. When CH4/N2O gas ratio was varied, at CH4/N2O gas ratio of 2:1, not only the highest etch rates but also the highest etch selectivity over W could be obtained. By increasing the substrate temperature, the linear increase of both the etch rates of MTJ materials and the etch selectivity over W could be obtained. The use of the rf pulse biasing improved the etch selectivity of the MTJ materials over hard mask such as W further. The surface roughness and residual thickness remaining on the etched surface of the CoFeB were also decreased by using rf pulse biasing and with the decrease of rf duty percentage. The improvement of etch characteristics by substrate heating and rf pulse biasing was possibly related to the formation of more stable and volatile etch compounds and the removal of chemically reacted compounds more easily on the etched CoFeB surface. Highly selective etching of MTJ materials over the hard mask could be obtained by using the rf pulse biasing of 30% of duty ratio and by increasing the substrate temperature to 200 degrees C in the CH4/N2O (2:1) plasmas.

  20. First-principles study on magnetic tunneling junctions with semiconducting CuInSe2 and CuGaSe2 barriers

    Science.gov (United States)

    Masuda, Keisuke; Miura, Yoshio

    2017-02-01

    We theoretically investigate two magnetic tunneling junctions (MTJs) with different semiconductor barriers, CuInSe2 (CIS) and CuGaSe2 (CGS), sandwiched between Fe electrodes. We find that Δ1 wave functions provide dominant contributions to spin-dependent tunneling transport in both CIS- and CGS-based MTJs. We also find that the CGS-based MTJ has a much higher magnetoresistive (MR) ratio than the CIS-based MTJ, which indicates that a higher MR ratio is expected for a higher Ga concentration x in the recently reported CuIn1- x Ga x Se2-based MTJs. Furthermore, we show that the CIS- and CGS-based MTJs have much smaller resistance-area products (RA) than the conventional MgO-based MTJs.

  1. Large Voltage-Induced Changes in the Perpendicular Magnetic Anisotropy of an MgO-Based Tunnel Junction with an Ultrathin Fe Layer

    Science.gov (United States)

    Nozaki, Takayuki; Kozioł-Rachwał, Anna; Skowroński, Witold; Zayets, Vadym; Shiota, Yoichi; Tamaru, Shingo; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Suzuki, Yoshishige

    2016-04-01

    We study the voltage control of perpendicular magnetic anisotropy in an ultrathin Fe layer sandwiched between the Cr buffer and MgO tunneling barrier layers. A high-interface magnetic anisotropy energy of 2.1 mJ /m2 is achieved in the Cr/ultrathin Fe /MgO structure. A large voltage-induced perpendicular magnetic anisotropy change is observed under the negative-bias voltage applications for the case of the Fe layer thinner than 0.6 nm. The amplitude of the voltage-induced anisotropy energy change exhibits a strong Fe-thickness dependence and it reaches as high as 290 fJ /Vm . The observed high values of the surface anisotropy and voltage-induced anisotropy energy change demonstrate the feasibility of voltage-driven spintronic devices.

  2. Electric field control of spin re-orientation in perpendicular magnetic tunnel junctions—CoFeB and MgO thickness dependence

    Science.gov (United States)

    Meng, Hao; Naik, Vinayak Bharat; Liu, Ruisheng; Han, Guchang

    2014-07-01

    We report an investigation of electric-field (EF) control of spin re-orientation as functions of the thicknesses of CoFeB free layer (FL) and MgO layer in synthetic-antiferromagnetic pinned magnetic tunnel junctions with perpendicular magnetic anisotropy. It is found that the EF modulates the coercivity (Hc) of the FL almost linearly for all FL thicknesses, while the EF efficiency, i.e., the slope of the linearity, increases as the FL thickness increases. This linear variation in Hc is also observed for larger MgO thicknesses (≥1.5 nm), while the EF efficiency increases only slightly from 370 to 410 Oe nm/V when MgO thickness increases from 1.5 to 1.76 nm. We have further observed the absence of quasi-DC unipolar switching. We discuss its origin and highlight the underlying challenges to implement the EF controlled switching in a practical magnetic memory.

  3. Quenching the Quantum Tunneling of Magnetization in Heterometallic Octanuclear {TM(III)4 Dy(III)4 } (TM=Co and Cr) Single-Molecule Magnets by Modification of the Bridging Ligands and Enhancing the Magnetic Exchange Coupling.

    Science.gov (United States)

    Vignesh, Kuduva R; Langley, Stuart K; Murray, Keith S; Rajaraman, Gopalan

    2017-01-31

    We report the synthesis, structural characterisation, magnetic properties and provide an ab initio analysis of the magnetic behaviour of two new heterometallic octanuclear coordination complexes containing Co(III) and Dy(III) ions. Single-crystal X-ray diffraction studies revealed molecular formulae of [Co(III)4 Dy(III)4 (μ-OH)4 (μ3 -OMe)4 {O2 CC(CH3 )3 }4 (tea)4 (H2 O)4 ]⋅4 H2 O (1) and [Co(III)4 Dy(III)4 (μ-F)4 (μ3 -OH)4 (o-tol)8 (mdea)4 ]⋅ 3 H2 O⋅EtOH⋅MeOH (2; tea(3-) =triply deprotonated triethanolamine; mdea(2-) =doubly deprotonated N-methyldiethanolamine; o-tol=o-toluate), and both complexes display an identical metallic core topology. Furthermore, the theoretical, magnetic and SMM properties of the isostructural complex, [Cr(III)4 Dy(III)4 (μ-F4 )(μ3 -OMe)1.25 (μ3 -OH)2.75 (O2 CPh)8 (mdea)4 ] (3), are discussed and compared with a structurally similar complex, [Cr(III)4 Dy(III)4 (μ3 -OH)4 (μ-N3 )4 (mdea)4 (O2 CC(CH3 )3 )4 ] (4). DC and AC magnetic susceptibility data revealed single-molecule magnet (SMM) behaviour for 1-4. Each complex displays dynamic behaviour, highlighting the effect of ligand and transition metal ion replacement on SMM properties. Complexes 2, 3 and 4 exhibited slow magnetic relaxation with barrier heights (Ueff ) of 39.0, 55.0 and 10.4 cm(-1) respectively. Complex 1, conversely, did not exhibit slow relaxation of magnetisation above 2 K. To probe the variance in the observed Ueff  values, calculations by using CASSCF, RASSI-SO and POLY_ANISO routine were performed on these complexes to estimate the nature of the magnetic coupling and elucidate the mechanism of magnetic relaxation. Calculations gave values of JDy-Dy as -1.6, 1.6 and 2.8 cm(-1) for complexes 1, 2 and 3, respectively, whereas the JDy-Cr interaction was estimated to be -1.8 cm(-1) for complex 3. The developed mechanism for magnetic relaxation revealed that replacement of the hydroxide ion by fluoride quenched the quantum tunnelling of

  4. Giant voltage manipulation of MgO-based magnetic tunnel junctions via localized anisotropic strain: A potential pathway to ultra-energy-efficient memory technology

    Science.gov (United States)

    Zhao, Zhengyang; Jamali, Mahdi; D'Souza, Noel; Zhang, Delin; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha; Wang, Jian-Ping

    2016-08-01

    Voltage control of magnetization via strain in piezoelectric/magnetostrictive systems is a promising mechanism to implement energy-efficient straintronic memory devices. Here, we demonstrate giant voltage manipulation of MgO magnetic tunnel junctions (MTJ) on a Pb(Mg1/3Nb2/3)0.7Ti0.3O3 piezoelectric substrate with (001) orientation. It is found that the magnetic easy axis, switching field, and the tunnel magnetoresistance (TMR) of the MTJ can be efficiently controlled by strain from the underlying piezoelectric layer upon the application of a gate voltage. Repeatable voltage controlled MTJ toggling between high/low-resistance states is demonstrated. More importantly, instead of relying on the intrinsic anisotropy of the piezoelectric substrate to generate the required strain, we utilize anisotropic strain produced using a local gating scheme, which is scalable and amenable to practical memory applications. Additionally, the adoption of crystalline MgO-based MTJ on piezoelectric layer lends itself to high TMR in the strain-mediated MRAM devices.

  5. Magnetic tunnel transistor with a perpendicular Co/Ni multilayer sputtered on a Si/Cu(1 0 0) Schottky diode

    Science.gov (United States)

    Vautrin, C.; Lu, Y.; Robert, S.; Sala, G.; Lenoble, O.; Petit-Watelot, S.; Devaux, X.; Montaigne, F.; Lacour, D.; Hehn, M.

    2016-09-01

    We have studied a magnetic tunnel transistor (MTT) structure based on a MgO tunnelling barrier emitter and a [Co/Ni]5/Cu multilayer base on a Si (0 0 1) substrate. Evident links between the Schottky barrier preparation techniques and the properties of perpendicular magnetic anisotropy (PMA) in the [Co/Ni] multilayer have been revealed by combined x-ray diffraction and magnetometry analyses. The Si surface treated by hydrofluoric acid (HF) is found to favour a Cu [1 0 0] texture growth which is detrimental to the [Co/Ni]5 PMA properties. However, a Ta layer insertion can restore the [1 1 1] texture required for the PMA appearance. By carefully engineering the base crystallographic texture structure, we obtain both a good quality of Schottky barrier and PMA property; a magneto-current ratio of 162% has been measured for MTTs with a spin-valve base composed of one magnetic layer having in-plane anisotropy and another one with out-of-plane anisotropy.

  6. Effect of coupling ability between a synthetic antiferromagnetic layer and pinned layer on a bridging layer of Ta, Ti, and Pt in perpendicular-magnetic tunnel junctions.

    Science.gov (United States)

    Lee, Du-Yeong; Shim, Tae-Hun; Park, Jea-Gun

    2016-07-22

    By fabricating CoFeB/MgO/CoFeB-based perpendicular-magnetic tunnel junction (p-MTJ) spin-valves stacked with a [Co/Pd] n -SyAF layer based on a TiN bottom electrode on a 12 inch Si wafer (001) substrate, we investigated how the bridging layers of Ta, Ti, and Pt and their thickness variation affected the tunneling magneto-resistance (TMR) ratio of Co2Fe6B2 pinned-layer behavior in magnetic-tunnel-junctions. TMR ratios for Ta, Ti, and Pt bridging layers were observed to be 64.1, 70.2, and 29.5%, respectively. It was confirmed by high resolution transmission electron microscopy (HR-TEM) that this difference resulted from CoFeB/MgO/CoFeB MTJ layers with Ta and Ti bridging layers being textured well with a bcc (100) structure, indicating that Ta and Ti bridging layers bridged SyAF fcc (111) and MTJ bcc (100). On the other hand, the MTJ layer with Pt bridging layer was incorrectly textured, indicating that a Pt bridging layer is unsuitable to bridge SyAF fcc (111) and MTJ bcc (100) due to Pt being diffused into the CoFeB pinned-layer. In addition, perpendicular magnetic anisotropy (PMA) behavior of the CoFeB pinned-layer was found to depend strongly on a bridging layer thickness; higher TMRs of Ta and Ti were observed at the optimal bridging layers' thickness, which enable the realization of PMAs of the pinned-layer and ferro-coupling of the pinned-layer with the lower-SyAF layer. Among the three bridging materials (Ta, Ti, and Pt), we observed that Ti showed the highest TMR ratio and widest thickness range for a high TMR ratio, indicating that a higher TMR ratio is needed to obtain the best deposition process margin.

  7. Effect of coupling ability between a synthetic antiferromagnetic layer and pinned layer on a bridging layer of Ta, Ti, and Pt in perpendicular-magnetic tunnel junctions

    Science.gov (United States)

    Lee, Du-Yeong; Shim, Tae-Hun; Park, Jea-Gun

    2016-07-01

    By fabricating CoFeB/MgO/CoFeB-based perpendicular-magnetic tunnel junction (p-MTJ) spin-valves stacked with a [Co/Pd] n -SyAF layer based on a TiN bottom electrode on a 12 inch Si wafer (001) substrate, we investigated how the bridging layers of Ta, Ti, and Pt and their thickness variation affected the tunneling magneto-resistance (TMR) ratio of Co2Fe6B2 pinned-layer behavior in magnetic-tunnel-junctions. TMR ratios for Ta, Ti, and Pt bridging layers were observed to be 64.1, 70.2, and 29.5%, respectively. It was confirmed by high resolution transmission electron microscopy (HR-TEM) that this difference resulted from CoFeB/MgO/CoFeB MTJ layers with Ta and Ti bridging layers being textured well with a bcc (100) structure, indicating that Ta and Ti bridging layers bridged SyAF fcc (111) and MTJ bcc (100). On the other hand, the MTJ layer with Pt bridging layer was incorrectly textured, indicating that a Pt bridging layer is unsuitable to bridge SyAF fcc (111) and MTJ bcc (100) due to Pt being diffused into the CoFeB pinned-layer. In addition, perpendicular magnetic anisotropy (PMA) behavior of the CoFeB pinned-layer was found to depend strongly on a bridging layer thickness; higher TMRs of Ta and Ti were observed at the optimal bridging layers’ thickness, which enable the realization of PMAs of the pinned-layer and ferro-coupling of the pinned-layer with the lower-SyAF layer. Among the three bridging materials (Ta, Ti, and Pt), we observed that Ti showed the highest TMR ratio and widest thickness range for a high TMR ratio, indicating that a higher TMR ratio is needed to obtain the best deposition process margin.

  8. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States)

    2014-04-15

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  9. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  10. Reliability enhancement due to in-situ post-oxidation of sputtered MgO barrier in double MgO barrier magnetic tunnel junction

    Science.gov (United States)

    Yoshida, Chikako; Noshiro, Hideyuki; Yamazaki, Yuichi; Sugii, Toshihiro

    2017-06-01

    We have investigated the effects of in-situ post-oxidation (PO) of a sputtered MgO barrier in a double-MgO-barrier magnetic tunnel junction (MTJ) and found that the short error rate was significantly reduced, the magnetoresistance (MR) ratio was increased approximately 18%, and the endurance lifetime was extend. In addition, we found that the distribution of breakdown number (a measure of endurance) exhibits trimodal characteristics, which indicates competition between extrinsic and intrinsic failures. This improvement in reliability might be related to the suppression of Fe and Co diffusion to the MgO barrier, as revealed by electron energy-loss spectroscopy (EELS) analysis.

  11. Magnetic tunneling junctions with the Heusler compound Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al

    Energy Technology Data Exchange (ETDEWEB)

    Conca Parra, A.

    2007-07-20

    Materials with large spin polarization are required for applications in spintronics devices. For this reason, major research efforts are directed to study the properties of compounds which are expected to be half metals, i.e. materials with 100% spin polarization. Half metals are expected to have a gap in the density of states at the Fermi energy for one spin band while the other spin band is metallic leading to a completely spin polarized current. The ferromagnetic full Heusler alloy Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al (CCFA) has attracted great interest in the field of spintronics. The high Tc (800 K) and the expected half metallicity make CCFA a good candidate for applications in spintronic devices such as magnetic tunneling junctions (MTJs). This thesis presents the results of the study of the electronic and structural properties of CCFA thin films. The films were implemented in magnetic tunneling junctions and the tunneling magnetoresistance effect (TMR) was investigated. The main objectives were the measurement of the spin polarisation of the CCFA alloy and to obtain information about its electronic structure. The influence of the deposition conditions on the thin film properties and on the surface crystalline order and their respective influence on the TMR ratio was investigated. Epitaxial CCFA thin films with two alternative growth orientations were deposited on different substrates and buffer layers. An annealing step was used to improve the crystalline properties of the thin films. In the tunneling junctions, Al{sub 2}O{sub 3} was used as a barrier material and Co was chosen as counter electrode. The multilayer systems were patterned in Mesa structures using lithographic techniques. In the framework of the Julliere model, a maximum spin polarisation of 54% at 4K was measured in tunneling junctions with epitaxial CCFA electrodes. A strong influence of the annealing temperature on the TMR ratio was determined. The increase of the TMR ratio could be correlated

  12. Temperature increase due to Joule heating in a nanostructured MgO-based magnetic tunnel junction over a wide current-pulse range.

    Science.gov (United States)

    Jeong, Boram; Lim, Sang Ho

    2011-07-01

    The temperature increase due to Joule heating in a nanopillar of a magnetic tunnel junction sandwiched by top and bottom electrodes was calculated by the finite element method. The results for the critical condition for the current-induced magnetization switching measured over a wide current-pulse range were taken from the literature. At long pulse widths, the temperature increase was solely dependent on the magnitude of the critical current density. However, no saturation in the temperature increase occurred for short pulse widths. In this case, the temperature increase additionally depended on the pulse width, so that a broad maximum occurred in the pulse width (or the critical current density) dependence of the temperature increase. The original results for the critical condition were corrected by accounting for the temperature increase and these corrected results, together with the Slonczewski equation, were used to extract an accurate value for the thermal stability factor.

  13. Nanosecond-Timescale Low Energy Switching of In-Plane Magnetic Tunnel Junctions through Dynamic Oersted-Field-Assisted Spin Hall Effect.

    Science.gov (United States)

    Aradhya, S V; Rowlands, G E; Oh, J; Ralph, D C; Buhrman, R A

    2016-10-12

    We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel junctions (MTJs) within 3-terminal devices in which spin-transfer torque is applied to the MTJ by the giant spin Hall effect. We measure reliable switching, with write error rates down to 10(-5), using current pulses as short as just 2 ns in duration. This represents the fastest reliable switching reported to date for any spin-torque-driven magnetic memory geometry and corresponds to a characteristic time scale that is significantly shorter than predicted possible within a macrospin model for in-plane MTJs subject to thermal fluctuations at room temperature. Using micromagnetic simulations, we show that in the three-terminal spin-Hall devices the Oersted magnetic field generated by the pulse current strongly modifies the magnetic dynamics excited by the spin-Hall torque, enabling this unanticipated performance improvement. Our results suggest that in-plane MTJs controlled by Oersted-field-assisted spin-Hall torque are a promising candidate for both cache memory applications requiring high speed and for cryogenic memories requiring low write energies.

  14. Inhomogeneous free layer in perpendicular magnetic tunnel junctions and its impact on the effective anisotropies and spin transfer torque switching efficiency

    Science.gov (United States)

    Timopheev, A. A.; Teixeira, B. M. S.; Sousa, R. C.; Aufret, S.; Nguyen, T. N.; Buda-Prejbeanu, L. D.; Chshiev, M.; Sobolev, N. A.; Dieny, B.

    2017-07-01

    Magnetoresistive and magnetoresonance measurements carried out on patterned perpendicular magnetic tunnel junction pillars and full-sheet films reveal magnetic inhomogeneities of FeCoB free layer grown on MgO and coated with Ta. At low FeCoB thicknesses, the layer behaves as an ensemble of weakly coupled grains resulting in a decrease of the free-layer thermal stability. In contrast, for thicker layers, the grains become more strongly coupled but strong magnetic inhomogeneities remain, yielding the emergence and further increase of a second-order magnetic anisotropy term (˜K2 effco s4θ ), eventually resulting in an easy-cone anisotropy. We show that the static and dynamic magnetic properties of such a free layer can be successfully described by a granular model with three thickness-dependent parameters: mean perpendicular anisotropy of the grains, grain-to-grain anisotropy distribution, and intergrain exchangelike coupling strength. Easy-cone anisotropy may help reduce the stochasticity of the spin transfer torque switching. However, it arises at intermediate values of the intergrain exchange coupling where the spin transfer torque (STT) switching efficiency is degraded, as shown by multimacrospin modeling. This is due to the excitation of exchange modes contributing weakly to the STT switching process while dissipating part of the STT energy.

  15. Short tunnels.

    NARCIS (Netherlands)

    Schreuder, D.A.

    1965-01-01

    Before dealing with the question of lighting short tunnels, it is necessary define what is meant by a tunnel and when it should be called 'short'. Confined to motorized road traffic the following is the most apt definition of a tunnel: every form of roofing-over a road section, irrespective of it le

  16. Fast neutron tolerance of the perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with junction diameters between 46 and 64 nm

    Science.gov (United States)

    Narita, Yuzuru; Takahashi, Yutaka; Harada, Masahide; Oikawa, Kenichi; Kobayashi, Daisuke; Hirose, Kazuyuki; Sato, Hideo; Ikeda, Shoji; Endoh, Tetsuo; Ohno, Hideo

    2017-08-01

    This work represents the first-ever investigation of the effects of fast neutron exposure on the perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions (p-MTJs) with practical junction diameters (D) between 46 and 64 nm. In this study, 461 p-MTJs, each with a tunnel magnetoresistance (TMR) ratio above 90%, were irradiated with fast neutrons at a total 1 MeV equivalent fluence of 3.79 × 1012 cm-2, corresponding to 1.90 × 1011 h irradiation with fast atmospheric neutrons (20 cm-2 h-1), without applying a bias voltage. Following irradiation, there were no changes in the properties of these devices, such as their resistance versus magnetic field curves, resistance values in the parallel and anti-parallel states, or TMR ratios, regardless of the neutron fluence. On the basis of these data, the nuclear reactions that occur under the specific experimental neutron irradiation conditions employed in this work are discussed.

  17. Influence of the buffer-layer on the tunnel barrier quality in CoFeB/MgO/CoFeB magnetic tunnel junctions on the tunnel magneto resistance (TMR)

    Energy Technology Data Exchange (ETDEWEB)

    Zbarsky, Vladyslav; Walter, Marvin; Eilers, Gerrit; Leutenantsmeyer, Johannes Christian; Muenzenberg, Markus [I. Physikalisches Institut, Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Peretzki, Patrick; Seibt, Michael [IV. Physikalisches Institut, Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany)

    2011-07-01

    The optimization of MTJs is necessary for increasing of TMR and therefore is very important for the production of MRAM devices. The quality of the tunnel barrier of our CoFeB/MgO/CoFeB MTJs is essential for getting high TMR. For this reason we investigate the influence of roughness of the MgO layer on the TMR. Another important parameter which we could optimize is the choice and preparation of the buffer-layer. For example we compared two sorts of Ta buffer-layers: prepared via magnetron sputtering and via e-beam evaporation. Already by optimizing these two parameters we increase the TMR from 80% to above 200%. In addition we show the investigations of the influence of the annealing temperatures and annealing duration on the TMR. Fast annealing time prevents diffusion, however for short annealing time no full crystallization is observed.

  18. Testing epitaxial Co{sub 1.5}Fe{sub 1.5}Ge(001) electrodes in MgO-based magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Neggache, A. [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre lès Nancy (France); Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin BP48, 91192 Gif-sur-Yvette (France); Hauet, T.; Petit-Watelot, S.; Boulet, P.; Andrieu, S., E-mail: stephane.andrieu@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre lès Nancy (France); Bertran, F.; Le Fèvre, P.; Ohresser, P. [Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin BP48, 91192 Gif-sur-Yvette (France); Devolder, T. [Institut d' Electronique Fondamentale, CNRS, UMR 8622, 91405 Orsay (France); Mewes, C. [Department of Physics and Astronomy/Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Maat, S.; Childress, J. R. [San Jose Research Center, HGST, a Western Digital company, San Jose, California 95135 (United States)

    2014-06-23

    The ability of the full Heusler alloy Co{sub 1.5}Fe{sub 1.5}Ge(001) (CFG) to be a Half-Metallic Magnetic (HMM) material is investigated. Epitaxial CFG(001) layers were grown by molecular beam epitaxy. The results obtained using electron diffraction, X-ray diffraction, and X-ray magnetic circular dichroism are consistent with the full Heusler structure. The pseudo-gap in the minority spin density of state typical in HMM is examined using spin-resolved photoemission. Interestingly, the spin polarization found to be negative at E{sub F} in equimolar CoFe(001) is observed to shift to positive values when inserting Ge in CoFe. However, no pseudo-gap is found at the Fermi level, even if moderate magnetization and low Gilbert damping are observed as expected in HMM materials. Magneto-transport properties in MgO-based magnetic tunnel junctions using CFG electrodes are investigated via spin and symmetry resolved photoemission.

  19. Effect of f-f interactions on quantum tunnelling of the magnetization: mono- and dinuclear Dy(III) phthalocyaninato triple-decker single-molecule magnets with the same octacoordination environment.

    Science.gov (United States)

    Katoh, Keiichi; Asano, Rina; Miura, Akira; Horii, Yoji; Morita, Takaumi; Breedlove, Brian K; Yamashita, Masahiro

    2014-06-07

    The single-molecule magnet (SMM) behaviour of dinuclear Ln(III)-Pc triple-decker complexes (Dy(III)-Y(III): 1 and Dy(III)-Dy(III): 2) with the same octacoordination environment and slow magnetic relaxation behaviour were explained using X-ray crystallography and static and dynamic susceptibility measurements. In particular, interactions among the 4f electrons of dinuclear Dy(III)-Pc triple-decker type SMMs have never been discussed on the basis of the same octacoordination environment. Our results clearly show that the Dy(III) ion sites of 1 and 2 are equivalent, consistent with the crystal structure. 2 Exhibited ferromagnetic interaction between Dy(III) ions. This is clear evidence that the magnetic relaxation mechanism depends heavily on the dipole-dipole (f-f) interactions between the Dy(III) ions in the dinuclear systems. For both 1 and 2, quantum tunnelling of the magnetization (QTM) was observed. However, the magnetic relaxation time (τ) for 2 was one order of magnitude greater than that for 1, and single-component magnetic relaxation behaviour was explained. In other words, it is possible to use f-f interactions to increase τ by one order of magnitude.

  20. Quantum molecular dynamics and molecular interactions studied by NMR and INS Nuclear magnetic resonance; Proton tunnelling; Hydrogen bond

    CERN Document Server

    Jones, N

    2002-01-01

    The wavefunction of a particle extends into the classically forbidden barrier region of the potential energy surface. The consequence of this partial delocalisation is the phenomenon of quantum tunnelling, an effect which enables a particle to penetrate a potential barrier of magnitude greater than the energy of the particle. The tunnelling probability is an exponential function of the particle mass. The effect is therefore an important contribution to the behaviour of light atoms, in particular the proton. The hydrogen bond has long been appreciated to be an essential component of many biological and chemical systems, and the proton transfer reaction in the hydrogen bond is fundamental to many of these processes. The proton behaviour in the hydrogen bonds of benzoic acid, acetylacetone and calix-4-arene has been studied. A variety of techniques, both experimental and computational, were adopted for the study of the three hydrogen bonded systems. The complementary spectroscopic techniques of inelastic neutron...

  1. First-principles study of spin transport in BN doped CrO{sub 2}–graphene–CrO{sub 2} magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Choudhary, Sudhanshu, E-mail: sudhanshu@nitkkr.ac.in; Mishra, Pradeep, E-mail: pradeepmshr26@gmail.com; Goyal, Rohit, E-mail: rohit91.goyal@gmail.com

    2016-03-06

    We investigate the spin-dependent electronic transport properties of Magnetic tunnel junction (MTJ) consisting of Boron (B) and Nitrogen (N) doped graphene nanosheet sandwiched between two CrO{sub 2} half-metallic–ferromagnet (HMF) electrodes. A large value of tunnel magnetoresistance (TMR) and perfect spin filtration was obtained as compared to un-doped graphene MTJ structures reported in past. The use of HMF electrodes further raises the TMR and improves the spin filtration in comparison to MTJs with metallic and ferromagnetic (FM) electrodes, which suggest HMF electrodes as a suitable candidate over metallic and FM electrodes for implementing graphene sheet based MTJs. A high value of TMR ∼100% is obtained at zero bias voltage, which remains constantly high at higher bias voltages in the range of 0 V to 1 V. The higher value of TMR and better (near perfect) spin filtration abilities suggest its usefulness in spin-valves and other spintronics based applications. The spin-dependent non-equilibrium transport is also investigated by analyzing the bias dependent transmission coefficients. - Highlights: • Higher TMR was observed in BN doped graphene based MTJ in comparison with undoped structure. • Perfect Spin Filtration Effect was observed in doped structure in comparison with undoped structure. • Use of HMF electrodes further raises TMR and Spin Filtration Effect.

  2. 86% TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers

    Institute of Scientific and Technical Information of China (English)

    Feifei LI; Xiufeng HAN; Lixian JIANG; Jing ZHAO; Lei WANG; Rehana Sharif

    2005-01-01

    Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21 (5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20, 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity HC of ≤4Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MT Js.

  3. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

    CERN Document Server

    Misra, Shashank; Drozdov, Ilya K; Seo, Jungpil; Gyenis, Andras; Kingsley, Simon C J; Jones, Howard; Yazdani, Ali

    2013-01-01

    We describe the construction and performance of a scanning tunneling microscope (STM) capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically-resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of perform...

  4. Spin dependent transport properties of Mn-Ga/MgO/Mn-Ga magnetic tunnel junctions with metal(Mg, Co, Cr) insertion layer

    Energy Technology Data Exchange (ETDEWEB)

    Liang, S. H.; Tao, L. L.; Liu, D. P., E-mail: dpliu@iphy.ac.cn; Han, X. F., E-mail: xfhan@iphy.ac.cn [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Lu, Y. [Institut Jean Lamour, UMR 7198, CNRS-Nancy Université, BP 239, 54506 Vandoeuvre (France)

    2014-04-07

    We report a first principles theoretical investigation of spin polarized quantum transport in Mn{sub 2}Ga/MgO/Mn{sub 2}Ga and Mn{sub 3}Ga/MgO/Mn{sub 3}Ga magnetic tunneling junctions (MTJs) with the consideration of metal(Mg, Co, Cr) insertion layer effect. By changing the concentration of Mn, our calculation shows a considerable disparity in transport properties: A tunneling magnetoresistance (TMR) ratio of 852% was obtained for Mn{sub 2}Ga-based MTJs, however, only a 5% TMR ratio for Mn{sub 3}Ga-based MTJs. In addition, the influence of insertion layer has been considered in our calculation. We found the Co insertion layer can increase the TMR of Mn{sub 2}Ga-based MTJ to 904%; however, the Cr insertion layer can decrease the TMR by 668%; A negative TMR ratio can be obtained with Mg insertion layer. Our work gives a comprehensive understanding of the influence of different insertion layer in Mn-Ga based MTJs. It is proved that, due to the transmission can be modulated by the interfacial electronic structure of insertion, the magnetoresistance ratio of Mn{sub 2}Ga/MgO/Mn{sub 2}Ga MTJ can be improved by inserting Co layer.

  5. Long distance tunneling

    CERN Document Server

    Ivlev, B I

    2005-01-01

    Quantum tunneling between two potential wells in a magnetic field can be strongly increased when the potential barrier varies in the direction perpendicular to the line connecting the two wells and remains constant along this line. A periodic structure of the wave function is formed in the direction joining the wells. The resulting motion can be coherent like motion in a conventional narrow band periodic structure. A particle penetrates the barrier over a long distance which strongly contrasts to WKB-like tunneling. The whole problem is stationary. The coherent process can be influenced by dissipation.

  6. The manufacture and testing of magnetic tunnel junctions and a study of their switching characteristics Cobalt; Aluminium oxide; Permalloy; Sputtering; Thin films

    CERN Document Server

    Hughes, N D

    2002-01-01

    This thesis investigates the manufacture and switching characteristics of a series of cobalt/aluminium oxide/permalloy magnetic tunnel junctions. It describes the assembly and commissioning of the sputtering, magnetometry and electron transport measurement equipment required to manufacture and test the junctions. The junctions are made by sputtering thin films of the ferromagnetic materials and an ultra thin film of aluminium, which is oxidised by means of a DC glow discharge. The optimum oxidation conditions for the barrier are investigated and its characteristics determined by current-voltage modelling. The barrier thickness identified by the modelling is compared with that found by x-ray reflectometry. A simple single domain model is shown to give a reasonable fit to hysteresis and magneto-resistive data from the junctions and to provide a means to quantify the interlayer coupling. A comparative study of the magneto-resistive characteristics of junctions with ferromagnetic layers of 10nm and 100nm finds th...

  7. Ultra-low switching energy and scaling in electric-field-controlled nanoscale magnetic tunnel junctions with high resistance-area product

    Energy Technology Data Exchange (ETDEWEB)

    Grezes, C.; Alzate, J. G.; Cai, X.; Wang, K. L. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Ebrahimi, F.; Khalili Amiri, P. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Inston, Inc., Los Angeles, California 90024 (United States); Katine, J. A. [HGST, Inc., San Jose, California 95135 (United States); Langer, J.; Ocker, B. [Singulus Technologies AG, Kahl am Main 63796 (Germany)

    2016-01-04

    We report electric-field-induced switching with write energies down to 6 fJ/bit for switching times of 0.5 ns, in nanoscale perpendicular magnetic tunnel junctions (MTJs) with high resistance-area product and diameters down to 50 nm. The ultra-low switching energy is made possible by a thick MgO barrier that ensures negligible spin-transfer torque contributions, along with a reduction of the Ohmic dissipation. We find that the switching voltage and time are insensitive to the junction diameter for high-resistance MTJs, a result accounted for by a macrospin model of purely voltage-induced switching. The measured performance enables integration with same-size CMOS transistors in compact memory and logic integrated circuits.

  8. Design and fabrication of a perpendicular magnetic tunnel junction based nonvolatile programmable switch achieving 40% less area using shared-control transistor structure.

    Science.gov (United States)

    Suzuki, D; Natsui, M; Mochizuki, A; Miura, S; Honjo, H; Kinoshita, K; Fukami, S; Sato, H; Ikeda, S; Endoh, T; Ohno, H; Hanyu, T

    2014-05-07

    A compact nonvolatile programmable switch (NVPS) using 90 nm CMOS technology together with perpendicular magnetic tunnel junction (p-MTJ) devices is fabricated for zero-standby-power field-programmable gate array. Because routing information does not change once it is programmed into an NVPS, high-speed read and write accesses are not required and a write-control transistor can be shared among all the NVPSs, which greatly simplifies structure of the NVPS. In fact, the effective area of the proposed NVPS is reduced by 40% compared to that of a conventional MTJ-based NVPS. The instant on/off behavior without external nonvolatile memory access is also demonstrated using the fabricated test chip.

  9. Reliability enhancement due to in-situ post-oxidation of sputtered MgO barrier in double MgO barrier magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Chikako Yoshida

    2017-06-01

    Full Text Available We have investigated the effects of in-situ post-oxidation (PO of a sputtered MgO barrier in a double-MgO-barrier magnetic tunnel junction (MTJ and found that the short error rate was significantly reduced, the magnetoresistance (MR ratio was increased approximately 18%, and the endurance lifetime was extend. In addition, we found that the distribution of breakdown number (a measure of endurance exhibits trimodal characteristics, which indicates competition between extrinsic and intrinsic failures. This improvement in reliability might be related to the suppression of Fe and Co diffusion to the MgO barrier, as revealed by electron energy-loss spectroscopy (EELS analysis.

  10. Electric field control of spin re-orientation in perpendicular magnetic tunnel junctions—CoFeB and MgO thickness dependence

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Hao; Naik, Vinayak Bharat; Liu, Ruisheng; Han, Guchang, E-mail: han-guchang@dsi.a-star.edu.sg [Data Storage Institute, A*STAR (Agency for Science Technology and Research), 5 Engineering Drive 1, DSI Building, Singapore 117608 (Singapore)

    2014-07-28

    We report an investigation of electric-field (EF) control of spin re-orientation as functions of the thicknesses of CoFeB free layer (FL) and MgO layer in synthetic-antiferromagnetic pinned magnetic tunnel junctions with perpendicular magnetic anisotropy. It is found that the EF modulates the coercivity (Hc) of the FL almost linearly for all FL thicknesses, while the EF efficiency, i.e., the slope of the linearity, increases as the FL thickness increases. This linear variation in Hc is also observed for larger MgO thicknesses (≥1.5 nm), while the EF efficiency increases only slightly from 370 to 410 Oe nm/V when MgO thickness increases from 1.5 to 1.76 nm. We have further observed the absence of quasi-DC unipolar switching. We discuss its origin and highlight the underlying challenges to implement the EF controlled switching in a practical magnetic memory.

  11. Sign change in the tunnel magnetoresistance of Fe3O4/MgO/Co-Fe-B magnetic tunnel junctions depending on the annealing temperature and the interface treatment

    Directory of Open Access Journals (Sweden)

    L. Marnitz

    2015-04-01

    Full Text Available Magnetite (Fe3O4 is an eligible candidate for magnetic tunnel junctions (MTJs since it shows a high spin polarization at the Fermi level as well as a high Curie temperature of 585°C. In this study, Fe3O4/MgO/Co-Fe-B MTJs were manufactured. A sign change in the TMR is observed after annealing the MTJs at temperatures between 200°C and 280°C. Our findings suggest an Mg interdiffusion from the MgO barrier into the Fe3O4 as the reason for the change of the TMR. Additionally, different treatments of the magnetite interface (argon bombardment, annealing at 200°C in oxygen atmosphere during the preparation of the MTJs have been studied regarding their effect on the performance of the MTJs. A maximum TMR of up to -12% could be observed using both argon bombardment and annealing in oxygen atmosphere, despite exposing the magnetite surface to atmospheric conditions before the deposition of the MgO barrier.

  12. Spin tunnelling in mesoscopic systems

    Indian Academy of Sciences (India)

    Anupam Garg

    2001-02-01

    We study spin tunnelling in molecular magnets as an instance of a mesoscopic phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel splitting between various pairs of Zeeman levels in this molecule oscillates as a function of applied magnetic field, vanishing completely at special points in the space of magnetic fields, known as diabolical points. This phenomena is explained in terms of two approaches, one based on spin-coherent-state path integrals, and the other on a generalization of the phase integral (or WKB) method to difference equations. Explicit formulas for the diabolical points are obtained for a model Hamiltonian.

  13. Time scales of bias voltage effects in FE/MgO-based magnetic tunnel junctions with voltage-dependent perpendicular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Lytvynenko, Ia.M. [Sumy State University, 2, Rimskogo-Korsakova Str., 40007 Sumy (Ukraine); Hauet, T., E-mail: thomas.hauet@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre les Nancy (France); Montaigne, F. [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre les Nancy (France); Bibyk, V.V. [Sumy State University, 2, Rimskogo-Korsakova Str., 40007 Sumy (Ukraine); Andrieu, S. [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre les Nancy (France)

    2015-12-15

    Interplay between voltage-induced magnetic anisotropy transition and voltage-induced atomic diffusion is studied in epitaxial V/Fe (0.7 nm)/ MgO/ Fe(5 nm)/Co/Au magnetic tunnel junction where thin Fe soft electrode has in-plane or out-of-plane anisotropy depending on the sign of the bias voltage. We investigate the origin of the slow resistance variation occurring when switching bias voltage in opposite polarity. We demonstrate that the time to reach resistance stability after voltage switching is reduced when increasing the voltage amplitude or the temperature. A single energy barrier of about 0.2 eV height is deduced from temperature dependence. Finally, we demonstrate that the resistance change is not correlated to a change in soft electrode anisotropy. This conclusion contrasts with observations recently reported on analogous systems. - Highlights: • Voltage-induced time dependence of resistance is studied in epitaxial Fe/MgO/Fe. • Resistance change is not related to the bottom Fe/MgO interface. • The effect is thermally activated with an energy barrier of the order of 0.2 eV height.

  14. A linearly controlled direct-current power source for high-current inductive loads in a magnetic suspension wind tunnel

    Science.gov (United States)

    Tripp, John S.; Daniels, Taumi S.

    1990-01-01

    The NASA Langley 6 inch magnetic suspension and balance system (MSBS) requires an independently controlled bidirectional DC power source for each of six positioning electromagnets. These electromagnets provide five-degree-of-freedom control over a suspended aerodynamic test model. Existing power equipment, which employs resistance coupled thyratron controlled rectifiers as well as AC to DC motor generator converters, is obsolete, inefficient, and unreliable. A replacement six phase bidirectional controlled bridge rectifier is proposed, which employs power MOSFET switches sequenced by hybrid analog/digital circuits. Full load efficiency is 80 percent compared to 25 percent for the resistance coupled thyratron system. Current feedback provides high control linearity, adjustable current limiting, and current overload protection. A quenching circuit suppresses inductive voltage impulses. It is shown that 20 kHz interference from positioning magnet power into MSBS electromagnetic model position sensors results predominantly from capacitively coupled electric fields. Hence, proper shielding and grounding techniques are necessary. Inductively coupled magnetic interference is negligible.

  15. A linearly controlled direct-current power source for high-current inductive loads in a magnetic suspension wind tunnel

    Science.gov (United States)

    Tripp, John S.; Daniels, Taumi S.

    1990-08-01

    The NASA Langley 6 inch magnetic suspension and balance system (MSBS) requires an independently controlled bidirectional DC power source for each of six positioning electromagnets. These electromagnets provide five-degree-of-freedom control over a suspended aerodynamic test model. Existing power equipment, which employs resistance coupled thyratron controlled rectifiers as well as AC to DC motor generator converters, is obsolete, inefficient, and unreliable. A replacement six phase bidirectional controlled bridge rectifier is proposed, which employs power MOSFET switches sequenced by hybrid analog/digital circuits. Full load efficiency is 80 percent compared to 25 percent for the resistance coupled thyratron system. Current feedback provides high control linearity, adjustable current limiting, and current overload protection. A quenching circuit suppresses inductive voltage impulses. It is shown that 20 kHz interference from positioning magnet power into MSBS electromagnetic model position sensors results predominantly from capacitively coupled electric fields. Hence, proper shielding and grounding techniques are necessary. Inductively coupled magnetic interference is negligible.

  16. Interface properties of magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3 superlattices studied by standing-wave excited photoemission spectroscopy

    NARCIS (Netherlands)

    Gray, A.X.; Papp, C.; Balke, B.; Yang, S.-H.; Huijben, M.; Rotenberg, E.; Bostwick, A.; Ueda, S.; Yamashita, Y.; Kobayashi, K.; Gullikson, E.M.; Kortright, J.B.; Groot, de F.M.F.; Rijnders, G.; Blank, D.H.A.; Ramesh, R.; Fadley, C.S.

    2010-01-01

    The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical

  17. Impact of sub-volume excitation on improving overdrive delay product of sub-40 nm perpendicular magnetic tunnel junctions in adiabatic regime and its beyond

    Science.gov (United States)

    Ohuchida, Satoshi; Ito, Kenchi; Endoh, Tetsuo

    2015-04-01

    In this paper, we introduced a new figure of merit, overdrive delay product Pod which is defined as the product of overdrive factor (I/Ic0 - 1) and delay of transit time, to evaluate power consumption and switching delay from the viewpoint of perpendicular magnetic tunnel junctions (p-MTJs) switching. The impact of sub-volume excitation on the dependence of overdrive delay product on the junction size and material parameters of p-MTJs in adiabatic regime were clarified. Two strategies to decrease the Pod were proposed. The first strategy is scaling down the junction size free from sub-volume effect. A reduction more than 86% of Pod of p-MTJ with exchange stiffness Aij = 19 pJ/m was realized by scaling down the junction size from 70 to 10 nm when I/Ic0 - 1 = 0.5. The second strategy is to increase Aij to suppress the effect of sub-volume excitation. A 26% reduction of the overdrive delay product was realized by enlarging Aij from 10 to 31 pJ/m with annealing process in the p-MTJ with the diameter of 40 nm. These results indicate that p-MTJs of embedded magnetoresistive random access memory (MRAM) should be scaled down under 30 nm where no sub-volume effect occurs for high speed programing.

  18. Nonequilibrium green function approach to elastic and inelastic spin-charge transport in topological insulator-based heterostructures and magnetic tunnel junctions

    Science.gov (United States)

    Mahfouzi, Farzad

    Current and future technological needs increasingly motivate the intensive scientific research of the properties of materials at the nano-scale. One of the most important domains in this respect at present concerns nano-electronics and its diverse applications. The great interest in this domain arises from the potential reduction of the size of the circuit components, maintaining their quality and functionality, and aiming at greater efficiency, economy, and storage characteristics for the corresponding physical devices. The aim of this thesis is to present a contribution to the analysis of the electronic charge and spin transport phenomena that occur at the quantum level in nano-structures. This thesis spans the areas of quantum transport theory through time-dependent systems, electron-boson interacting systems and systems of interest to spintronics. A common thread in the thesis is to develop the theoretical foundations and computational algorithms to numerically simulate such systems. In order to optimize the numerical calculations I resort to different techniques (such as graph theory in finding inverse of a sparse matrix, adaptive grids for integrations and programming languages (e.g., MATLAB and C++) and distributed computing tools (MPI, CUDA). Outline of the Thesis: After giving an introduction to the topics covered in this thesis in Chapter 1, I present the theoretical foundations to the field of non-equilibrium quantum statistics in Chapter 2. The applications of this formalism and the results are covered in the subsequent chapters as follows: Spin and charge quantum pumping in time-dependent systems: Covered in Chapters 3, 4 and 5, this topics was initially motivated by experiments on measuring voltage signal from a magnetic tunnel junction (MTJ) exposed to a microwave radiation in ferromagnetic resonance (FMR) condition. In Chapter 3 we found a possible explanation for the finite voltage signal measured from a tunnel junction consisting of only a single

  19. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    Science.gov (United States)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-01-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses. PMID:27405788

  20. Design of a low-power nonvolatile flip-flop using three-terminal magnetic-tunnel-junction-based self-terminated mechanism

    Science.gov (United States)

    Suzuki, Daisuke; Hanyu, Takahiro

    2017-04-01

    A nonvolatile flip-flop (NV-FF) using a three-terminal magnetic tunnel junction (3T-MTJ)-based self-terminated mechanism is proposed for a low-power logic LSI while maintaining almost the same performance as a conventional CMOS-based logic LSI. The use of a self-terminated mechanism, which continuously monitors the change in MTJ resistance, makes it possible not only to minimize the write energy consumption for the 3T-MTJ device but also to ensure a reliable write. Moreover, since the write current path is separated from the read current path in the 3T-MTJ device, the sensing circuit and the write driver are individually optimized, which makes it possible to minimize the performance overhead due to additional components. As a result, the write energy of the proposed NV-FF is reduced by 69% with a small performance overhead compared with that of a conventional NV-FF using a worst-case-oriented writing scheme.

  1. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    Science.gov (United States)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-07-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses.

  2. Effect of Mo capping layers thickness on the perpendicular magnetic anisotropy in MgO/CoFeB based top magnetic tunnel junction structure

    Science.gov (United States)

    Liu, Yi; Zhu, Kai-Gui; Zhong, Hui-Cai; Zhu, Zheng-Yong; Yu, Tao; Ma, Su-De

    2016-11-01

    A detailed study of the magnetic characterizations of the top structure MgO/CoFeB/Mo is presented. The samples show strong perpendicular magnetic anisotropy (PMA) when the thickness of CoFeB is 0.9 nm and 1.1 nm. The saturation magnetic moment and interface anisotropy constant are 1566 emu/cm3 and 3.75 erg/cm2, respectively. The magnetic dead layer (MDL) is about 0.23 nm in this system. Furthermore, strong capping layer thickness dependence is also observed. The strong PMA of 1.1 nm CoFeB only exists in a Mo cap layer thickness window of 1.2-2 nm. To maintain PMA, the metal layer could not be too thin or thick in these multilayers. The oxidation and diffusion of the metal capping layer should be respectively responsibility for the degradation of PMA in these thin or thick metal capping layer samples. Project supported by the National Fundamental Research Program of China (Grant No. 2011CB921804) and Beijing Key Subject Foundation of Condensed Matter Physics, China (Grant No. 0114023).

  3. A Supermagnetic Tunnel Full of Subatomic Action

    CERN Multimedia

    2008-01-01

    Last year, before the gigantic hadron supercollider at CERN research facility was installed underground, a photographer captured this picture of a 1,950 metric ton tunnel containing giant magnets that will be placed in a tunnel and kept at near-zero temperatures.

  4. Computer graphic of LHC in the tunnel

    CERN Multimedia

    1996-01-01

    A computer-generated image of the LHC particle accelerator at CERN in the tunnel originally built for the LEP accelerator that was closed in 2000. The cross-section of an LHC superconducting dipole magnet is also seen.

  5. Thermal creation of a spin current by Seebeck spin tunneling

    Science.gov (United States)

    Jansen, R.; Le Breton, J. C.; Deac, A. M.; Saito, H.; Yuasa, S.

    2013-09-01

    The thermoelectric analog of spin-polarized tunneling, namely Seebeck spin tunneling, is a recently discovered phenomenon that arises from the spin-dependent Seebeck coefficient of a magnetic tunnel contact. In a tunnel junction with one ferromagnetic electrode and one non-magnetic electrode, a temperature difference between the two electrodes creates a spin current across the contact. Here, the basic principle and the observation of Seebeck spin tunneling are described. It is shown how it can be used to create a spin accumulation in silicon driven by a heat flow across a magnetic tunnel contact, without a charge tunnel current. The sign of the spin current depends on the direction of the heat flow, whereas its magnitude is anisotropic, i.e., dependent on the absolute orientation of the magnetization of the ferromagnet. The connection between Seebeck spin tunneling and the tunnel magneto-Seebeck effect, observed in metal magnetic tunnel junctions, is also clarified. Seebeck spin tunneling may be used to convert waste heat into useful thermal spin currents that aid or replace electrical spin current, and thereby improve the energy efficiency of spintronic devices and technologies.

  6. Fused Perovskite Tunnel Structures in Ba5 Fe6+x S4+x O8 (0.44≤x≤0.55) with x-Dependent Two-Stage Magnetizations.

    Science.gov (United States)

    Wright, Taylor; Prots, Yurii; Valldor, Martin

    2016-08-01

    Ba5 Fe6+x S4+x O8 was synthesized through a solid-state reaction, and pure powders of nominal compositions x=0.44-0.55 were obtained after being rinsed with water. The crystal structures (P4/mmm, a=10.13, c=4.03 Å) and sample purities were investigated by powder synchrotron X-ray diffraction and were found to be composed of a tunnel lattice (Ba5 Fe6 S4 O8 ), built from fused perovskite units and the tunnel filling (Fex Sx ). The variable composition, that is, the tunnel filling (x), causes partially occupied sites as well as crystallographic split positions. Ba5 Fe6+x S4+x O8 (x=0.525) is semiconducting and all investigated compositions exhibit magnetic ground states that could be described as either semi-spin-glass-like (x>0.5) or canted antiferromagnetic (xx=0.525 exhibits magnetic relaxations that are affected by ageing.

  7. Perpendicular magnetic anisotropy in Ta|Co{sub 40}Fe{sub 40}B{sub 20}|MgAl{sub 2}O{sub 4} structures and perpendicular CoFeB|MgAl{sub 2}O{sub 4}|CoFeB magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Tao, B. S.; Li, D. L.; Yuan, Z. H.; Liu, H. F.; Ali, S. S.; Feng, J. F.; Wei, H. X.; Han, X. F., E-mail: xfhan@iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Liu, Y.; Zhao, Y. G. [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Zhang, Q.; Guo, Z. B. [Advanced Nanofabrication, Imaging and Characterization Core Laboratory, King Abdullah University of Science and Technology (KAUST), Thuwal 239955 (Saudi Arabia); Zhang, X. X. [Advanced Nanofabrication, Imaging and Characterization Core Laboratory, King Abdullah University of Science and Technology (KAUST), Thuwal 239955 (Saudi Arabia); Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 239955 (Saudi Arabia)

    2014-09-08

    Magnetic properties of Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) thin films sandwiched between Ta and MgAl{sub 2}O{sub 4} layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl{sub 2}O{sub 4} structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy K{sub i} = 1.22 erg/cm{sup 2}, which further increases to 1.30 erg/cm{sup 2} after annealing, while MgAl{sub 2}O{sub 4}/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0 nm, while that for top CoFeB layer is between 0.8 and 1.4 nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a core structure of CoFeB/MgAl{sub 2}O{sub 4}/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.

  8. Long-term reliable physically unclonable function based on oxide tunnel barrier breakdown on two-transistors two-magnetic-tunnel-junctions cell-based embedded spin transfer torque magnetoresistive random access memory

    Science.gov (United States)

    Takaya, Satoshi; Tanamoto, Tetsufumi; Noguchi, Hiroki; Ikegami, Kazutaka; Abe, Keiko; Fujita, Shinobu

    2017-04-01

    Among the diverse applications of spintronics, security for internet-of-things (IoT) devices is one of the most important. A physically unclonable function (PUF) with a spin device (spin transfer torque magnetoresistive random access memory, STT-MRAM) is presented. Oxide tunnel barrier breakdown is used to realize long-term stability for PUFs. A secure PUF has been confirmed by evaluating the Hamming distance of a 32-bit STT-MRAM-PUF fabricated using 65 nm CMOS technology.

  9. Subluxation of the peroneus long tendon in the cuboid tunnel: is it normal or pathologic? An ultrasound and magnetic resonance imaging study

    Energy Technology Data Exchange (ETDEWEB)

    Stone, Taylor J. [Charlotte Radiology, Charlotte, NC (United States); Rosenberg, Zehava S.; Ciavarra, Gina; Bencardino, Jenny T. [New York Langone Medical Center / Hospital for Joint Diseases, New York, NY (United States); Velez, Zoraida Restrepo [Cedimed-Dinamica, Medellin (Colombia); Prost, Roberto [Marino Hospital ASL Cagliari, Cagliari (Italy)

    2016-03-15

    To evaluate the position of the peroneus longus (PL) tendon relative to the cuboid tuberosity and cuboid tunnel during ankle dorsiflexion and plantarflexion using ultrasound and MRI. The study population included two groups: 20 feet of 10 asymptomatic volunteers who underwent prospective dynamic ultrasound and 55 ankles found through retrospective review of routine ankle MRI examinations. The location of the PL tendon at the cuboid tuberosity and cuboid tunnel was designated as completely within the tunnel, indeterminate, or subluxed with respect to ankle dorsiflexion and plantarflexion. On dynamic ultrasound, the PL tendon was perched plantar to the cuboid tuberosity in dorsiflexion, and glided to enter the cuboid tunnel distal to the tuberosity in plantarflexion in all 20 feet. On the MRI evaluation, there was a statistically significant difference (p = 0.0006) in the location of the PL tendon between the ankles scanned in dorsiflexion and plantarflexion. Based on our findings on ultrasound and MRI, the PL tendon can glide in and out of the cuboid tunnel along the cuboid tuberosity depending on ankle position. Thus, ''subluxation'' of the tendon as it curves to enter the cuboid tunnel, which to the best of our knowledge has not yet been described, should be recognized as a normal, position-dependent phenomenon and not be reported as pathology. (orig.)

  10. Carpal Tunnel Syndrome

    Science.gov (United States)

    ... arm. Just a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ligament and ... difficult. Often, the cause is having a smaller carpal tunnel than other people do. Other causes include ...

  11. Fabrication of a magnetic-tunnel-junction-based nonvolatile logic-in-memory LSI with content-aware write error masking scheme achieving 92% storage capacity and 79% power reduction

    Science.gov (United States)

    Natsui, Masanori; Tamakoshi, Akira; Endoh, Tetsuo; Ohno, Hideo; Hanyu, Takahiro

    2017-04-01

    A magnetic-tunnel-junction (MTJ)-based video coding hardware with an MTJ-write-error-rate relaxation scheme as well as a nonvolatile storage capacity reduction technique is designed and fabricated in a 90 nm MOS and 75 nm perpendicular MTJ process. The proposed MTJ-oriented dynamic error masking scheme suppresses the effect of write operation errors on the operation result of LSI, which results in the increase in an acceptable MTJ write error rate up to 7.8 times with less than 6% area overhead, while achieving 79% power reduction compared with that of the static-random-access-memory-based one.

  12. Predictive modelling of ferroelectric tunnel junctions

    Science.gov (United States)

    Velev, Julian P.; Burton, John D.; Zhuravlev, Mikhail Ye; Tsymbal, Evgeny Y.

    2016-05-01

    Ferroelectric tunnel junctions combine the phenomena of quantum-mechanical tunnelling and switchable spontaneous polarisation of a nanometre-thick ferroelectric film into novel device functionality. Switching the ferroelectric barrier polarisation direction produces a sizable change in resistance of the junction—a phenomenon known as the tunnelling electroresistance effect. From a fundamental perspective, ferroelectric tunnel junctions and their version with ferromagnetic electrodes, i.e., multiferroic tunnel junctions, are testbeds for studying the underlying mechanisms of tunnelling electroresistance as well as the interplay between electric and magnetic degrees of freedom and their effect on transport. From a practical perspective, ferroelectric tunnel junctions hold promise for disruptive device applications. In a very short time, they have traversed the path from basic model predictions to prototypes for novel non-volatile ferroelectric random access memories with non-destructive readout. This remarkable progress is to a large extent driven by a productive cycle of predictive modelling and innovative experimental effort. In this review article, we outline the development of the ferroelectric tunnel junction concept and the role of theoretical modelling in guiding experimental work. We discuss a wide range of physical phenomena that control the functional properties of ferroelectric tunnel junctions and summarise the state-of-the-art achievements in the field.

  13. Six-band k•p calculation of spin-dependent interband tunneling in strained broken-gap heterostructures under a quantizing magnetic field

    Science.gov (United States)

    Zakharova, A.; Nilsson, K.; Chao, K. A.; Yen, S. T.

    2005-09-01

    We investigate spin-dependent interband magnetotunneling processes in strained broken-gap resonant tunneling structures made from InAs, AlSb, and GaSb, which are promising materials for quantum devices. InAs/AlSb/GaSb/InAs/AlSb/GaSb double-barrier structures grown on both InAs and GaSb are considered. Transmission coefficients for interband tunneling processes from individual eigenstates in the InAs emitter as well as current-voltage characteristics were calculated using a six-band k•p model and the scattering matrix method. We predict that due to lattice-mismatch induced strain, the interband tunneling current density for the structure grown on InAs can be one or two orders of magnitude less than that for the structure grown on GaSb. Furthermore, as a consequence of interband magnetotunneling, structures grown on different substrates yield different spin polarization of the tunneling current. It is obtained that the current spin polarization can be greater than 90%. These resonant tunneling structures can be used as spin filters in the rapidly growing field of spintronics.

  14. Pulsed magnetic field versus ultrasound in the treatment of postnatal carpal tunnel syndrome: A randomized controlled trial in the women of an Egyptian population

    Directory of Open Access Journals (Sweden)

    Dalia M. Kamel

    2017-01-01

    Full Text Available The aim of this study was to compare the effects of pulsed electromagnetic field versus pulsed ultrasound in treating patients with postnatal carpal tunnel syndrome. The study was a randomized, double-blinded trial. Forty postnatal female patients with idiopathic carpal tunnel syndrome were divided randomly into two equal groups. One group received pulsed electromagnetic field, with nerve and tendon gliding exercises for the wrist, three times per week for four weeks. The other group received pulsed ultrasound and the same wrist exercises. Pain level, sensory and motor distal latencies and conduction velocities of the median nerve, functional status scale and hand grip strength were assessed pre- and post-treatment. There was a significant decrease (P  0.05. In conclusion, while the symptoms were alleviated in both groups, pulsed electromagnetic field was more effective than pulsed ultrasound in treating postnatal carpal tunnel syndrome.

  15. The role of Mg interface layer in MgO magnetic tunnel junctions with CoFe and CoFeB electrodes

    Directory of Open Access Journals (Sweden)

    Hyunsoo Yang

    2012-03-01

    Full Text Available The tunneling spin polarization (TSP is directly measured from reactively sputter deposited crystalline MgO tunnel barriers with various CoFe(B compositions using superconducting tunneling spectroscopy. We find that the Mg interface layer thickness dependence of TSP values for CoFeB/Mg/MgO junctions is substantially different from those for CoFe/Mg/MgO especially in the pre-annealed samples due to the formation of boron oxide at the CoFeB/MgO interface. Annealing depletes boron at the interface thus requiring a finite Mg interface layer to prevent CoFeOx formation at the CoFeB/MgO interface so that the TSP values can be optimized by controlling Mg thickness.

  16. Area and shape changes of the carpal tunnel in response to tunnel pressure.

    Science.gov (United States)

    Li, Zong-Ming; Masters, Tamara L; Mondello, Tracy A

    2011-12-01

    Carpal tunnel mechanics is relevant to our understanding of median nerve compression in the tunnel. The compliant characteristics of the tunnel strongly influence its mechanical environment. We investigated the distensibility of the carpal tunnel in response to tunnel pressure. A custom balloon device was designed to apply controlled pressure. Tunnel cross sections were obtained using magnetic resonance imaging to derive the relationship between carpal tunnel pressure and morphological parameters at the hook of hamate. The results showed that the cross-sectional area (CSA) at the level of the hook of hamate increased, on average, by 9.2% and 14.8% at 100 and 200 mmHg, respectively. The increased CSA was attained by a shape change of the cross section, displaying increased circularity. The increase in CSA was mainly attributable to the increase of area in the carpal arch region formed by the transverse carpal ligament. The narrowing of the carpal arch width was associated with an increase in the carpal arch. We concluded that the carpal tunnel is compliant to accommodate physiological variations of the carpal tunnel pressure, and that the increase in tunnel CSA is achieved by increasing the circularity of the cross section.

  17. Delayed ulnar neuropathy at the wrist following open carpal tunnel release.

    Science.gov (United States)

    Pingree, Matthew J; Bosch, E Peter; Liu, Patrick; Smith, Benn E

    2005-03-01

    Open carpal tunnel release is a common and successful treatment of median neuropathy at the wrist (carpal tunnel syndrome). We report a case of delayed ulnar neuropathy at the wrist with onset 2 months after open carpal tunnel release. Clinical findings, electrophysiological studies, magnetic resonance imaging, and surgical exploration demonstrated ulnar nerve compression at Guyon's canal resulting from translocation of the carpal tunnel contents. To our knowledge, this is an unreported complication of open carpal tunnel release that merits wide appreciation.

  18. Electron tunnel sensor technology

    Science.gov (United States)

    Waltman, S. B.; Kaiser, W. J.

    1989-01-01

    The recent development of Scanning Tunneling Microscopy technology allows the application of electron tunneling to position detectors for the first time. The vacuum tunnel junction is one of the most sensitive position detection mechanisms available. It is also compact, simple, and requires little power. A prototype accelerometer based on electron tunneling, and other sensor applications of this promising new technology are described.

  19. Electro-Magnetic Quadrupole Magnets in the LCLS FEL Undulator

    Energy Technology Data Exchange (ETDEWEB)

    Emma, P.

    2005-01-31

    We discuss various aspects of electro-magnetic quadrupole (EMQ) magnets for the LCLS FEL undulator, including their utility in beam-based alignment (BBA), magnet design issues, and impact on tunnel environment, reliability, and cost.

  20. In-situ grazing incidence X-ray diffraction measurements of relaxation in Fe/MgO/Fe epitaxial magnetic tunnel junctions during annealing

    Science.gov (United States)

    Eastwood, D. S.; Ali, M.; Hickey, B. J.; Tanner, B. K.

    2013-12-01

    The relaxation of Fe/MgO/Fe tunnel junctions grown epitaxially on (001) MgO substrates has been measured by in-situ grazing incidence in-plane X-ray diffraction during the thermal annealing cycle. We find that the Fe layers are fully relaxed and that there are no irreversible changes during annealing. The MgO tunnel barrier is initially strained towards the Fe but on annealing, relaxes and expands towards the bulk MgO value. The strain dispersion is reduced in the MgO by about 40% above 480 K post-annealing. There is no significant change in the "twist" mosaic. Our results indicate that the final annealing stage of device fabrication, crucial to attainment of high TMR, induces substantial strain relaxation at the MgO barrier/lower Fe electrode interface.

  1. Tunnel effect wave energy detection

    Science.gov (United States)

    Kaiser, William J. (Inventor); Waltman, Steven B. (Inventor); Kenny, Thomas W. (Inventor)

    1995-01-01

    Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.

  2. Simulations of Resonant Intraband and Interband Tunneling Spin Filters

    Science.gov (United States)

    Ting, David; Cartoixa-Soler, Xavier; McGill, T. C.; Smith, Darryl L.; Schulman, Joel N.

    2001-01-01

    This viewgraph presentation reviews resonant intraband and interband tunneling spin filters It explores the possibility of building a zero-magnetic-field spin polarizer using nonmagnetic III-V semiconductor heterostructures. It reviews the extensive simulations of quantum transport in asymmetric InAs/GaSb/AlSb resonant tunneling structures with Rashba spin splitting and proposes a. new device concept: side-gated asymmetric Resonant Interband Tunneling Diode (a-RITD).

  3. 18 January 2011 - Ing. Vittorio Malacalza, ASG Superconductors S.p.A, Italy in the LHC superconducting magnet test hall with Deputy Department Head L. Rossi, in the LHC tunnel at Point 5 and CMS experimental area with Spokesperson G. Tonelli.

    CERN Multimedia

    Maximilien Brice

    2011-01-01

    18 January 2011 - Ing. Vittorio Malacalza, ASG Superconductors S.p.A, Italy in the LHC superconducting magnet test hall with Deputy Department Head L. Rossi, in the LHC tunnel at Point 5 and CMS experimental area with Spokesperson G. Tonelli.

  4. 18 January 2011 - The British Royal Academy of Engineering in the LHC tunnel with CMS Collaboration Spokesperson G. Tonelli and Beams Department Head P. Collier; in the CERN Control Centre with P. Collier and LHC superconducting magnet test hall with Technology Department Head F. Bordry.

    CERN Multimedia

    Jean-Claude Gadmer

    2011-01-01

    18 January 2011 - The British Royal Academy of Engineering in the LHC tunnel with CMS Collaboration Spokesperson G. Tonelli and Beams Department Head P. Collier; in the CERN Control Centre with P. Collier and LHC superconducting magnet test hall with Technology Department Head F. Bordry.

  5. Dephasing of quantum tunnelling in molecular nanomagnets

    Institute of Scientific and Technical Information of China (English)

    Zhang Shu-Qun; Chen Zhi-De

    2008-01-01

    Dephasing mechanism of quantum tunnelling in molecular magnets has been studied by means of the spin-coherentstate path integral in a mean field approximation. It is found that the fluctuating uncompensated transverse field from the dipolar-dipolar interaction between molecular magnets contributes a random phase to the quantum interference phase. The resulting transition rate is determined by the average tunnel splitting over the random phase. Such a dephasing process leads to the suppression of quenching due to the quantum phase interference, and to the steps due to odd resonances in hysteresis loop survived, which is in good agreement with experimental observations in molecular nanomagnets Fee and Mn12.

  6. Effect of an interface Mg insertion layer on the reliability of a magnetic tunnel junction based on a Co{sub 2}FeAl full-Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jungmin; Kil, Gyuhyun; Lee, Gaehun; Choi, Chulmin; Song, Yunheub [Hanyang University, Seoul (Korea, Republic of); Sukegawa, Hiroaki; Mitani, Seiji [National Institute for Materials Science, Ibaraki (Japan)

    2014-04-15

    The reliability of a magnetic tunnel junction (MTJ) based on a Co{sub 2}FeAl (CFA) full-Heusler alloy with a MgO tunnel barrier was evaluated. In particular, the effect of a Mg insertion layer under the MgO was investigated in view of resistance drift by using various voltage stress tests. We compared the resistance change during constant voltage stress (CVS) and confirmed a trap/detrap phenomenon during the interval stress test for samples with and without a Mg insertion layer. The MTJ with a Mg insertion layer showed a relatively small resistance change for the CVS test and a reduced trap/detrap phenomenon for the interval stress test compared to the sample without a Mg insertion layer. This is understood to be caused by the improved crystallinity at the bottom of the CFA/MgO interface due to the Mg insertion layer, which provides a smaller number of trap site during the stress test. As a result, the interface condition of the MgO layer is very important for the reliability of a MTJ using a full-Heusler alloy, and the the insert of a Mg layer at the MgO interface is expected to be an effective method for enhancing the reliability of a MTJ.

  7. Hypersonic Tunnel Facility (HTF)

    Data.gov (United States)

    Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...

  8. Transonic Dynamics Tunnel (TDT)

    Data.gov (United States)

    Federal Laboratory Consortium — The Transonic Dynamics Tunnel (TDT) is a continuous flow wind-tunnel facility capable of speeds up to Mach 1.2 at stagnation pressures up to one atmosphere. The TDT...

  9. Road and Railroad Tunnels

    Data.gov (United States)

    Department of Homeland Security — Tunnels in the United States According to the HSIP Tiger Team Report, a tunnel is defined as a linear underground passageway open at both ends. This dataset is based...

  10. Quantum theory of tunneling

    CERN Document Server

    Razavy, Mohsen

    2014-01-01

    In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

  11. Hypersonic Tunnel Facility (HTF)

    Data.gov (United States)

    Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...

  12. Theory of electrically controlled resonant tunneling spin devices

    Science.gov (United States)

    Ting, David Z. -Y.; Cartoixa, Xavier

    2004-01-01

    We report device concepts that exploit spin-orbit coupling for creating spin polarized current sources using nonmagnetic semiconductor resonant tunneling heterostructures, without external magnetic fields. The resonant interband tunneling psin filter exploits large valence band spin-orbit interaction to provide strong spin selectivity.

  13. The Tunnels of Samos

    Science.gov (United States)

    Apostol, Tom M. (Editor)

    1995-01-01

    This 'Project Mathematics' series video from CalTech presents the tunnel of Samos, a famous underground aquaduct tunnel located near the capital of Pithagorion (named after the famed Greek mathematician, Pythagoras, who lived there), on one of the Greek islands. This tunnel was constructed around 600 BC by King Samos and was built under a nearby mountain. Through film footage and computer animation, the mathematical principles and concepts of why and how this aquaduct tunnel was built are explained.

  14. Electric field modulation of tunneling anisotropic magnetoresistance in tunnel junctions with antiferromagnetic electrodes

    Science.gov (United States)

    Goto, Minori; Nawaoka, Kohei; Miwa, Shinji; Hatanaka, Shohei; Mizuochi, Norikazu; Suzuki, Yoshishige

    2016-08-01

    We present electric field modulation of tunneling anisotropic magnetoresistance (TAMR) in MnIr|MgO|Ta tunnel junctions. TAMR enables direct observation of the antiferromagnetic spin direction at the MnIr|MgO interface. We found that the shape of magnetoresistance (MR) curve can be modulated by an electric field, which can be explained by electric field modulation of the interfacial magnetic anisotropy at MnIr|MgO.

  15. Tunnel Spin Polarization Versus Energy for Clean and Doped Al2O3 Barriers

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the

  16. Proton tunneling in solids

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, J.

    1998-10-01

    The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

  17. Li-substituted MgAl2O4 barriers for spin-dependent coherent tunneling

    Science.gov (United States)

    Scheike, Thomas; Sukegawa, Hiroaki; Mitani, Seiji

    2016-11-01

    Epitaxial magnetic tunnel junctions (MTJs) with a Li-substituted spinel MgAl2O4 barrier were prepared by sputtering and plasma oxidation of an Mg/LiAl bilayer. The formed MTJ with Fe(001) electrodes showed a relatively large tunnel magnetoresistance (TMR) ratio of 120% (174%) at room temperature (3 K) and two local minima in the tunneling conductance spectra (parallel magnetization), revealing the occurrence of the coherent tunneling effect through the Li-substituted spinel barrier. The results are likely to pave the way for a variety of quaternary spinel oxide barriers in which structural and transport properties of MTJs can be engineered in the coherent tunneling regime.

  18. Quantum transport modeling of the symmetric Fe/FeO0.5/MgO magnetic tunnel junction: the effects of correlations in the buffer layer.

    Science.gov (United States)

    Timoshevskii, Vladimir; Hu, Yibin; Marcotte, Étienne; Guo, Hong

    2014-01-08

    We report ab initio simulations of quantum transport properties of Fe/MgO/Fe trilayer structures with FeO0.5 buffer iron oxide layer, where on-site Coulomb interaction is explicitly taken into account by local density approximation + Hubbard U approach. We show that on-site Coulomb repulsion in the iron-oxygen layer can cause a dramatic drop of the tunnel magnetoresistance of the system. We present an understanding of microscopic details of this phenomenon, connecting it to localization of electronic states of particular symmetry, which takes place in the buffer Fe-O layer, when on-site Coulomb repulsion is introduced. We further study the possible influence of the symmetry reduction in the buffer Fe-O layer on the transport properties of the Fe/MgO/Fe interface.

  19. Tunneling Anisotropic Magnetoresistance in Co/AlOx/Au Tunnel Junctions

    CERN Document Server

    Liu, R S; Canali, C M; Samuelson, L; Pettersson, H

    2008-01-01

    We observe spin-valve-like effects in nano-scaled thermally evaporated Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and depends on the relative orientation of the magnetization direction of the Co electrode with respect to the current direction. We attribute this effect to a two-step magnetization reversal and an anisotropic density of states resulting from spin-orbit interaction. The results of this study points to future applications of novel spintronics devices involving only one ferromagnetic layer.

  20. Magnetic suspension - Today's marvel, tomorrow's tool

    Science.gov (United States)

    Lawing, Pierce L.

    1989-01-01

    NASA's Langley facility has through constant advocacy of magnetic suspension systems (MSSs) for wind-tunnel model positioning obtained a technology-development status for the requisite large magnets, computers, automatic control techniques, and apparatus configurations, to contemplate the construction of MSSs for large wind tunnels. Attention is presently given to the prospects for MSSs in wind tunnels employing superfluid helium atmospheres to obtain very high Reynolds numbers, where the MSS can yield substantial enhancements of wind tunnel productivity.

  1. Fermi-edge singularity at tunneling and anisotropic magneto-tunneling in low-dimensional semiconductor structures

    Energy Technology Data Exchange (ETDEWEB)

    Larkin, Ivan A [International Institute of Physics (IIP), Universidade Federal do Rio Grande do Norte, Departamento de Fisica, Campus Universitario Lagoa Nova, Natal, RN, 59078-970 (Brazil); Vdovin, E E; Khanin, Yu N [Institute of Microelectronics Technology RAS, 142432 Chernogolovka (Russian Federation); Ujevic, Sebastian [Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, Santo Andre, Sao Paulo 09210-170 (Brazil); Henini, M, E-mail: vaniala2000@yahoo.co.u [School of Physics and Astronomy, University of Nottingham, NG7 2RD (United Kingdom)

    2010-09-15

    We consider many-body enhanced electron tunneling through an InAs quantum dot in a magnetic field applied perpendicular to the tunneling direction. The critical exponent of the Fermi-edge singularity in the tunneling current is calculated as a function of the magnetic field. We use lowest Landau level approximation for the electrons in the emitter and perform scattering matrix calculations using the Born approximation. We examine in detail the anisotropic behavior of the amplitude and shape of the resonant peaks.

  2. Confocal Annular Josephson Tunnel Junctions

    Science.gov (United States)

    Monaco, Roberto

    2016-09-01

    The physics of Josephson tunnel junctions drastically depends on their geometrical configurations and here we show that also tiny geometrical details play a determinant role. More specifically, we develop the theory of short and long annular Josephson tunnel junctions delimited by two confocal ellipses. The behavior of a circular annular Josephson tunnel junction is then seen to be simply a special case of the above result. For junctions having a normalized perimeter less than one, the threshold curves in the presence of an in-plane magnetic field of arbitrary orientations are derived and computed even in the case with trapped Josephson vortices. For longer junctions, a numerical analysis is carried out after the derivation of the appropriate motion equation for the Josephson phase. We found that the system is modeled by a modified and perturbed sine-Gordon equation with a space-dependent effective Josephson penetration length inversely proportional to the local junction width. Both the fluxon statics and dynamics are deeply affected by the non-uniform annulus width. Static zero-field multiple-fluxon solutions exist even in the presence of a large bias current. The tangential velocity of a traveling fluxon is not determined by the balance between the driving and drag forces due to the dissipative losses. Furthermore, the fluxon motion is characterized by a strong radial inward acceleration which causes electromagnetic radiation concentrated at the ellipse equatorial points.

  3. Resonance Enhanced Tunneling

    CERN Document Server

    Matsumoto, S; Matsumoto, Sh.

    2000-01-01

    Time evolution of tunneling in thermal medium is examined using the real-time semiclassical formalism previously developed. Effect of anharmonic terms in the potential well is shown to give a new mechanism of resonance enhanced tunneling. If the friction from environment is small enough, this mechanism may give a very large enhancement for the tunneling rate. The case of the asymmetric wine bottle potential is worked out in detail.

  4. Spin-polarized tunneling currents through a ferromagnetic insulator between two metallic or superconducting leads

    OpenAIRE

    Sandschneider, N.; Nolting, W.

    2007-01-01

    Using the Keldysh formalism the tunneling current through a hybrid structure where a confined magnetic insulator (I) is sandwiched between two non-magnetic leads is calculated. The leads can be either normal metals (M) or superconductors (S). Each region is modelled as a single band in tight-binding approximation in order to understand the formation of the tunneling current as clearly as possible. The tunneling process itself is simulated by a hybridization between the lead and insulator cond...

  5. Transport dépendant du spin dans des doubles jonctions tunnel magnétiques

    OpenAIRE

    Rodary, Guillemin

    2004-01-01

    The purpose of this work is the detection of magnetocurrent in the magnetic tunnel transistor based on a double tunnel junction. This magnetocurrent come from the emission of a spin polarized hot electrons current. Samples have been made by sputtering. A new technique of lithography and etching allowed us to take an electrical contact on each three electrode. We showed the influence of etching on magnetic tunnel junction transport properties. Thanks to these three contacts, we compared the in...

  6. A new family of 1D exchange biased heterometal single-molecule magnets: observation of pronounced quantum tunneling steps in the hysteresis loops of quasi-linear {Mn2Ni3} clusters.

    Science.gov (United States)

    Das, Animesh; Gieb, Klaus; Krupskaya, Yulia; Demeshko, Serhiy; Dechert, Sebastian; Klingeler, Rüdiger; Kataev, Vladislav; Büchner, Bernd; Müller, Paul; Meyer, Franc

    2011-03-16

    First members of a new family of heterometallic Mn/Ni complexes [Mn(2)Ni(3)X(2)L(4)(LH)(2)(H(2)O)(2)] (X = Cl: 1; X = Br: 2) with the new ligand 2-{3-(2-hydroxyphenyl)-1H-pyrazol-1-yl}ethanol (H(2)L) have been synthesized, and single crystals obtained from CH(2)Cl(2) solutions have been characterized crystallographically. The molecular structures feature a quasi-linear Mn(III)-Ni(II)-Ni(II)-Ni(II)-Mn(III) core with six-coordinate metal ions, where elongated axes of all the distorted octahedral coordination polyhedra are aligned parallel and are fixed with respect to each other by intramolecular hydrogen bonds. 1 and 2 exhibit quite strong ferromagnetic exchange interactions throughout (J(Mn-Ni) ≈ 40 K (1) or 42 K (2); J(Ni-Ni) ≈ 22 K (1) or 18 K (2)) that lead to an S(tot) = 7 ground state, and a sizable uniaxial magnetoanisotropy with D(mol) values -0.55 K (1) and -0.45 K (2). These values are directly derived also from frequency- and temperature-dependent high-field EPR spectra. Slow relaxation of the magnetization at low temperatures and single-molecule magnet (SMM) behavior are evident from frequency-dependent peaks in the out-of-phase ac susceptibilities and magnetization versus dc field measurements, with significant energy barriers to spin reversal U(eff) = 27 K (1) and 22 K (2). Pronounced quantum tunnelling steps are observed in the hysteresis loops of the temperature- and scan rate-dependent magnetization data, but with the first relaxation step shifted above (1) or below (2) the zero crossing of the magnetic field, despite the very similar molecular structures. The different behavior of 1 and 2 is interpreted in terms of antiferromagnetic (1) or ferromagnetic (2) intermolecular interactions, which are discussed in view of the subtle differences of intermolecular contacts within the crystal lattice.

  7. Tunnelling in Dante's Inferno

    Science.gov (United States)

    Furuuchi, Kazuyuki; Sperling, Marcus

    2017-05-01

    We study quantum tunnelling in Dante's Inferno model of large field inflation. Such a tunnelling process, which will terminate inflation, becomes problematic if the tunnelling rate is rapid compared to the Hubble time scale at the time of inflation. Consequently, we constrain the parameter space of Dante's Inferno model by demanding a suppressed tunnelling rate during inflation. The constraints are derived and explicit numerical bounds are provided for representative examples. Our considerations are at the level of an effective field theory; hence, the presented constraints have to hold regardless of any UV completion.

  8. Microsystem Aeromechanics Wind Tunnel

    Data.gov (United States)

    Federal Laboratory Consortium — The Microsystem Aeromechanics Wind Tunnel advances the study of fundamental flow physics relevant to micro air vehicle (MAV) flight and assesses vehicle performance...

  9. Ulnar tunnel syndrome.

    Science.gov (United States)

    Bachoura, Abdo; Jacoby, Sidney M

    2012-10-01

    Ulnar tunnel syndrome could be broadly defined as a compressive neuropathy of the ulnar nerve at the level of the wrist. The ulnar tunnel, or Guyon's canal, has a complex and variable anatomy. Various factors may precipitate the onset of ulnar tunnel syndrome. Patient presentation depends on the anatomic zone of ulnar nerve compression: zone I compression, motor and sensory signs and symptoms; zone II compression, isolated motor deficits; and zone III compression; purely sensory deficits. Conservative treatment such as activity modification may be helpful, but often, surgical exploration of the ulnar tunnel with subsequent ulnar nerve decompression is indicated.

  10. MAGNET

    CERN Multimedia

    by B. Curé

    2011-01-01

    The magnet operation was very satisfactory till the technical stop at the end of the year 2010. The field was ramped down on 5th December 2010, following the successful regeneration test of the turbine filters at full field on 3rd December 2010. This will limit in the future the quantity of magnet cycles, as it is no longer necessary to ramp down the magnet for this type of intervention. This is made possible by the use of the spare liquid Helium volume to cool the magnet while turbines 1 and 2 are stopped, leaving only the third turbine in operation. This obviously requires full availability of the operators to supervise the operation, as it is not automated. The cryogenics was stopped on 6th December 2010 and the magnet was left without cooling until 18th January 2011, when the cryoplant operation resumed. The magnet temperature reached 93 K. The maintenance of the vacuum pumping was done immediately after the magnet stop, when the magnet was still at very low temperature. Only the vacuum pumping of the ma...

  11. Tunneling magnetoresistance of silicon chains

    Science.gov (United States)

    Matsuura, Yukihito

    2016-05-01

    The tunneling magnetoresistance (TMR) of a silicon chain sandwiched between nickel electrodes was examined by using first-principles density functional theory. The relative orientation of the magnetization in a parallel-alignment (PA) configuration of two nickel electrodes enhanced the current with a bias less than 0.4 V compared with that in an antiparallel-alignment configuration. Consequently, the silicon chain-nickel electrodes yielded good TMR characteristics. In addition, there was polarized spin current in the PA configuration. The spin polarization of sulfur atoms functioning as a linking bridge between the chain and nickel electrode played an important role in the magnetic effects of the electric current. Moreover, the hybridization of the sulfur 3p orbital and σ-conjugated silicon 3p orbital contributed to increasing the total current.

  12. FeGa based tunneling magnetoresistance junctions and strain sensors

    OpenAIRE

    Thajudin, Ahmed Fazir

    2012-01-01

    Tunnel magnetoresistance (TMR) and inverse magnetostriction based strain gauges have gained immense importance due to their high spatial resolution and extremely high gauge factors. A TMR junction comprises of two ferromagnetic electrodes separated by an insulating barrier layer. One of the ferromagnetic layer is soft magnetic which is free to rotate its magnetization under external magnetic field, the other ferromagnet is hard magnetic and is stable under the same external field. An intentio...

  13. Virtual photons in macroscopic tunneling

    CERN Document Server

    Aichmann, Horst; Bruney, Paul

    2015-01-01

    Tunnelling processes are thought to proceed via virtual waves due to observed superluminal (faster than light) signal speeds. Some assume such speeds must violate causality. These assumptions contradict, for instance, superluminally tunnelled music and optical tunnelling couplers applied in fiber communication. Recently tunnelling barriers were conjectured to be cavities, wherein the tunnelled output signal is not causally related with the input. The tests described here resolve that tunnelling waves are virtual, propagations are superluminal, and causality is preserved.

  14. Coupling quantum tunneling with cavity photons.

    Science.gov (United States)

    Cristofolini, Peter; Christmann, Gabriel; Tsintzos, Simeon I; Deligeorgis, George; Konstantinidis, George; Hatzopoulos, Zacharias; Savvidis, Pavlos G; Baumberg, Jeremy J

    2012-05-11

    Tunneling of electrons through a potential barrier is fundamental to chemical reactions, electronic transport in semiconductors and superconductors, magnetism, and devices such as terahertz oscillators. Whereas tunneling is typically controlled by electric fields, a completely different approach is to bind electrons into bosonic quasiparticles with a photonic component. Quasiparticles made of such light-matter microcavity polaritons have recently been demonstrated to Bose-condense into superfluids, whereas spatially separated Coulomb-bound electrons and holes possess strong dipole interactions. We use tunneling polaritons to connect these two realms, producing bosonic quasiparticles with static dipole moments. Our resulting three-state system yields dark polaritons analogous to those in atomic systems or optical waveguides, thereby offering new possibilities for electromagnetically induced transparency, room-temperature condensation, and adiabatic photon-to-electron transfer.

  15. A 600-µW ultra-low-power associative processor for image pattern recognition employing magnetic tunnel junction-based nonvolatile memories with autonomic intelligent power-gating scheme

    Science.gov (United States)

    Ma, Yitao; Miura, Sadahiko; Honjo, Hiroaki; Ikeda, Shoji; Hanyu, Takahiro; Ohno, Hideo; Endoh, Tetsuo

    2016-04-01

    A novel associative processor using magnetic tunnel junction (MTJ)-based nonvolatile memories has been proposed and fabricated under a 90 nm CMOS/70 nm perpendicular-MTJ (p-MTJ) hybrid process for achieving the exceptionally low-power performance of image pattern recognition. A four-transistor 2-MTJ (4T-2MTJ) spin transfer torque magnetoresistive random access memory was adopted to completely eliminate the standby power. A self-directed intelligent power-gating (IPG) scheme specialized for this associative processor is employed to optimize the operation power by only autonomously activating currently accessed memory cells. The operations of a prototype chip at 20 MHz are demonstrated by measurement. The proposed processor can successfully carry out single texture pattern matching within 6.5 µs using 128-dimension bag-of-feature patterns, and the measured average operation power of the entire processor core is only 600 µW. Compared with the twin chip designed with 6T static random access memory, 91.2% power reductions are achieved. More than 88.0% power reductions are obtained compared with the latest associative memories. The further power performance analysis is discussed in detail, which verifies the special superiority of the proposed processor in power consumption for large-capacity memory-based VLSI systems.

  16. Tunnel fire dynamics

    CERN Document Server

    Ingason, Haukur; Lönnermark, Anders

    2015-01-01

    This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.

  17. MAGNET

    CERN Multimedia

    B. Curé

    2012-01-01

      The magnet was energised at the beginning of March 2012 at a low current to check all the MSS safety chains. Then the magnet was ramped up to 3.8 T on 6 March 2012. Unfortunately two days later an unintentional switch OFF of the power converter caused a slow dump. This was due to a misunderstanding of the CCC (CERN Control Centre) concerning the procedure to apply for the CMS converter control according to the beam-mode status at that time. Following this event, the third one since 2009, a discussion was initiated to define possible improvement, not only on software and procedures in the CCC, but also to evaluate the possibility to upgrade the CMS hardware to prevent such discharge from occurring because of incorrect procedure implementations. The magnet operation itself was smooth, and no power cuts took place. As a result, the number of magnetic cycles was reduced to the minimum, with only two full magnetic cycles from 0 T to 3.8 T. Nevertheless the magnet suffered four stops of the cryogeni...

  18. MAGNET

    CERN Multimedia

    Benoit Curé

    2010-01-01

    Operation of the magnet has gone quite smoothly during the first half of this year. The magnet has been at 4.5K for the full period since January. There was an unplanned short stop due to the CERN-wide power outage on May 28th, which caused a slow dump of the magnet. Since this occurred just before a planned technical stop of the LHC, during which access in the experimental cavern was authorized, it was decided to leave the magnet OFF until 2nd June, when magnet was ramped up again to 3.8T. The magnet system experienced a fault also resulting in a slow dump on April 14th. This was triggered by a thermostat on a filter choke in the 20kA DC power converter. The threshold of this thermostat is 65°C. However, no variation in the water-cooling flow rate or temperature was observed. Vibration may have been the root cause of the fault. All the thermostats have been checked, together with the cables, connectors and the read out card. The tightening of the inductance fixations has also been checked. More tem...

  19. MAGNET

    CERN Multimedia

    B. Curé

    2012-01-01

      Following the unexpected magnet stops last August due to sequences of unfortunate events on the services and cryogenics [see CMS internal report], a few more events and initiatives again disrupted the magnet operation. All the magnet parameters stayed at their nominal values during this period without any fault or alarm on the magnet control and safety systems. The magnet was stopped for the September technical stop to allow interventions in the experimental cavern on the detector services. On 1 October, to prepare the transfer of the liquid nitrogen tank on its new location, several control cables had to be removed. One cable was cut mistakenly, causing a digital input card to switch off, resulting in a cold-box (CB) stop. This tank is used for the pre-cooling of the magnet from room temperature down to 80 K, and for this reason it is controlled through the cryogenics control system. Since the connection of the CB was only allowed for a field below 2 T to avoid the risk of triggering a fast d...

  20. Conclusion of the He Spill Simulations in the LHC Tunnel

    CERN Document Server

    Vadon, Marc

    2004-01-01

    The LHC, currently under construction at CERN, will make use of superconducting magnets operating in super-fluid helium below 2 K provided via a separate cryogenic distribution line. An accidental spill of part of the helium inventory (approx. 12 tons per octant of 3.3-km length each) in the 3.8-m diameter underground tunnel is a potential risk to personnel i.e. lack of visibility, cold, lack of oxygen. Using a finite volume model of a 100-m long typical tunnel section, several scenarios with different leak rates and temperatures were simulated. Further parameters considered were ventilation rate, slope of the tunnel, helium leak temperature, etc. in order to point out the most critical factors influencing temperature and helium concentration distribution in the tunnel. Finally, this analysis allowed us to determine a maximum mass flow that can be released in the tunnel without putting personnel at risk.