WorldWideScience

Sample records for nanomagnetic tunnel junctions

  1. Spin nutation effects in molecular nanomagnet–superconductor tunnel junctions

    International Nuclear Information System (INIS)

    Abouie, J; Abdollahipour, B; Rostami, A A

    2013-01-01

    We study the spin nutation effects of a molecular nanomagnet on the Josephson current through a superconductor|molecular nanomagnet|superconductor tunnel junction. We explicitly demonstrate that, due to the spin nutation of the molecular nanomagnet, two oscillatory terms emerge in the ac Josephson current in addition to the conventional ac Josephson current. Some resonances occur in the junction due to the interactions of the transported quasiparticles with the bias voltage and molecular nanomagnet spin dynamics. Their appearance indicates that the energy exchanged during these interactions is in the range of the superconducting energy gap. We also show that the spin nutation is able to convert the ac Josephson current to a dc current, which is interesting for applications. (paper)

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

    International Nuclear Information System (INIS)

    Manipatruni, Sasikanth; Nikonov, Dmitri E.; Young, Ian A.

    2014-01-01

    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

  3. Integration of spintronic interface for nanomagnetic arrays

    Directory of Open Access Journals (Sweden)

    Andrew Lyle

    2011-12-01

    Full Text Available An experimental demonstration utilizing a spintronic input/output (I/O interface for arrays of closely spaced nanomagnets is presented. The free layers of magnetic tunnel junctions (MTJs form dipole coupled nanomagnet arrays which can be applied to different contexts including Magnetic Quantum Cellular Automata (MQCA for logic applications and self-biased devices for field sensing applications. Dipole coupled nanomagnet arrays demonstrate adaptability to a variety of contexts due to the ability for tuning of magnetic response. Spintronics allows individual nanomagnets to be manipulated with spin transfer torque and monitored with magnetoresistance. This facilitates measurement of the magnetic coupling which is important for (yet to be demonstrated data propagation reliability studies. In addition, the same magnetic coupling can be tuned to reduce coercivity for field sensing. Dipole coupled nanomagnet arrays have the potential to be thousands of times more energy efficient than CMOS technology for logic applications, and they also have the potential to form multi-axis field sensors.

  4. Magnetization-induced dynamics of a Josephson junction coupled to a nanomagnet

    Science.gov (United States)

    Ghosh, Roopayan; Maiti, Moitri; Shukrinov, Yury M.; Sengupta, K.

    2017-11-01

    We study the superconducting current of a Josephson junction (JJ) coupled to an external nanomagnet driven by a time-dependent magnetic field both without and in the presence of an external ac drive. We provide an analytic, albeit perturbative, solution for the Landau-Lifshitz (LL) equations governing the coupled JJ-nanomagnet system in the presence of a magnetic field with arbitrary time dependence oriented along the easy axis of the nanomagnet's magnetization and in the limit of weak dimensionless coupling ɛ0 between the JJ and the nanomagnet. We show the existence of Shapiro-type steps in the I -V characteristics of the JJ subjected to a voltage bias for a constant or periodically varying magnetic field and explore the effect of rotation of the magnetic field and the presence of an external ac drive on these steps. We support our analytic results with exact numerical solution of the LL equations. We also extend our results to dissipative nanomagnets by providing a perturbative solution to the Landau-Lifshitz-Gilbert (LLG) equations for weak dissipation. We study the fate of magnetization-induced Shapiro steps in the presence of dissipation both from our analytical results and via numerical solution of the coupled LLG equations. We discuss experiments which can test our theory.

  5. Scaling Projections on Spin-Transfer Torque Magnetic Tunnel Junctions

    Science.gov (United States)

    Das, Debasis; Tulapurkar, Ashwin; Muralidharan, Bhaskaran

    2018-02-01

    We investigate scaling of technologically relevant magnetic tunnel junction devices in the trilayer and pentalayer configurations by varying the cross-sectional area along the transverse direction using the non-equilibrium Green's function spin transport formalism. We study the geometry dependence by considering square and circular cross-sections. As the transverse dimension in each case reduces, we demonstrate that the transverse mode energy profile plays a major role in the resistance-area product. Both types of devices show constant tunnel magnetoresistance at larger cross-sectional areas but achieve ultra-high magnetoresistance at small cross-sectional areas, while maintaining low resistance-area products. We notice that although the critical switching voltage for switching the magnetization of the free layer nanomagnet in the trilayer case remains constant at larger areas, it needs more energy to switch at smaller areas. In the pentalayer case, we observe an oscillatory behavior at smaller areas as a result of double barrier tunneling. We also describe how switching characteristics of both kinds of devices are affected by the scaling.

  6. Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

    International Nuclear Information System (INIS)

    Cleland, A.N.

    1991-04-01

    Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q ∼ 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement

  7. Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Guenter; Muenzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

    2011-01-01

    Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: → Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. → Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. → Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. → Limitation indicates that Al-Ox layer is causing incoherent tunneling.

  8. Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

    International Nuclear Information System (INIS)

    Cleland, A.N.

    1991-01-01

    Experiments investigated the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very-small-capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson-phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters. The experiments on small-capacitance tunnel junctions extend the measurements on the large-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wave function has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias

  9. Electronic noise of superconducting tunnel junction detectors

    International Nuclear Information System (INIS)

    Jochum, J.; Kraus, H.; Gutsche, M.; Kemmather, B.; Feilitzsch, F. v.; Moessbauer, R.L.

    1994-01-01

    The optimal signal to noise ratio for detectors based on superconducting tunnel junctions is calculated and compared for the cases of a detector consisting of one single tunnel junction, as well as of series and of parallel connections of such tunnel junctions. The influence of 1 / f noise and its dependence on the dynamical resistance of tunnel junctions is discussed quantitatively. A single tunnel junction yields the minimum equivalent noise charge. Such a tunnel junction exhibits the best signal to noise ratio if the signal charge is independent of detector size. In case, signal charge increases with detector size, a parallel or a series connection of tunnel junctions would provide the optimum signal to noise ratio. The equivalent noise charge and the respective signal to noise ratio are deduced as functions of tunnel junction parameters such as tunneling time, quasiparticle lifetime, etc. (orig.)

  10. Molecular series-tunneling junctions.

    Science.gov (United States)

    Liao, Kung-Ching; Hsu, Liang-Yan; Bowers, Carleen M; Rabitz, Herschel; Whitesides, George M

    2015-05-13

    Charge transport through junctions consisting of insulating molecular units is a quantum phenomenon that cannot be described adequately by classical circuit laws. This paper explores tunneling current densities in self-assembled monolayer (SAM)-based junctions with the structure Ag(TS)/O2C-R1-R2-H//Ga2O3/EGaIn, where Ag(TS) is template-stripped silver and EGaIn is the eutectic alloy of gallium and indium; R1 and R2 refer to two classes of insulating molecular units-(CH2)n and (C6H4)m-that are connected in series and have different tunneling decay constants in the Simmons equation. These junctions can be analyzed as a form of series-tunneling junctions based on the observation that permuting the order of R1 and R2 in the junction does not alter the overall rate of charge transport. By using the Ag/O2C interface, this system decouples the highest occupied molecular orbital (HOMO, which is localized on the carboxylate group) from strong interactions with the R1 and R2 units. The differences in rates of tunneling are thus determined by the electronic structure of the groups R1 and R2; these differences are not influenced by the order of R1 and R2 in the SAM. In an electrical potential model that rationalizes this observation, R1 and R2 contribute independently to the height of the barrier. This model explicitly assumes that contributions to rates of tunneling from the Ag(TS)/O2C and H//Ga2O3 interfaces are constant across the series examined. The current density of these series-tunneling junctions can be described by J(V) = J0(V) exp(-β1d1 - β2d2), where J(V) is the current density (A/cm(2)) at applied voltage V and βi and di are the parameters describing the attenuation of the tunneling current through a rectangular tunneling barrier, with width d and a height related to the attenuation factor β.

  11. Electronic thermometry in tunable tunnel junction

    Science.gov (United States)

    Maksymovych, Petro

    2016-03-15

    A tunable tunnel junction thermometry circuit includes a variable width tunnel junction between a test object and a probe. The junction width is varied and a change in thermovoltage across the junction with respect to the change in distance across the junction is determined. Also, a change in biased current with respect to a change in distance across the junction is determined. A temperature gradient across the junction is determined based on a mathematical relationship between the temperature gradient, the change in thermovoltage with respect to distance and the change in biased current with respect to distance. Thermovoltage may be measured by nullifying a thermoelectric tunneling current with an applied voltage supply level. A piezoelectric actuator may modulate the probe, and thus the junction width, to vary thermovoltage and biased current across the junction. Lock-in amplifiers measure the derivatives of the thermovoltage and biased current modulated by varying junction width.

  12. Current noise in tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Frey, Moritz; Grabert, Hermann [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104, Freiburg (Germany)

    2017-06-15

    We study current fluctuations in tunnel junctions driven by a voltage source. The voltage is applied to the tunneling element via an impedance providing an electromagnetic environment of the junction. We use circuit theory to relate the fluctuations of the current flowing in the leads of the junction with the voltage fluctuations generated by the environmental impedance and the fluctuations of the tunneling current. The spectrum of current fluctuations is found to consist of three parts: a term arising from the environmental Johnson-Nyquist noise, a term due to the shot noise of the tunneling current and a third term describing the cross-correlation between these two noise sources. Our phenomenological theory reproduces previous results based on the Hamiltonian model for the dynamical Coulomb blockade and provides a simple understanding of the current fluctuation spectrum in terms of circuit theory and properties of the average current. Specific results are given for a tunnel junction driven through a resonator. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Supramolecular tunneling junctions

    NARCIS (Netherlands)

    Wimbush, K.S.

    2012-01-01

    In this study a variety of supramolecular tunneling junctions were created. The basis of these junctions was a self-assembled monolayer of heptathioether functionalized ß-cyclodextrin (ßCD) formed on an ultra-flat Au surface, i.e., the bottom electrode. This gave a well-defined hexagonally packed

  14. Particle detection with superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Jany, P.

    1990-08-01

    At the Institute of Experimental Nuclear Physics of the University of Karlsruhe (TH) and at the Institute for Nuclear Physics of the Kernforschungszentrum Karlsruhe we started to produce superconducting tunnel junctions and to investigate them for their suitability as particle detectors. The required facilities for the production of tunnel junctions and the experimental equipments to carry out experiments with them were erected. Experiments are presented in which radiations of different kinds of particles could successfully be measured with the tunnel junctions produced. At first we succeeded in detectioning light pulses of a laser. In experiments with alpha-particles of an energy of 4,6 MeV the alpha-particles were detected with an energy resolution of 1,1%, and it was shown in specific experiments that the phonons originating from the deposition of energy by an alpha-particle in the substrate can be detected with superconducting tunnel junctions at the surface. On that occasion it turned out that the signals could be separated with respect to their point of origin (tunnel junction, contact leads, substrate). Finally X-rays with an energy of 6 keV were detected with an energy resolution of 8% in a test arrangement that makes use of the so-called trapping effect to read out a larger absorber volume. (orig.) [de

  15. Scattering theory of superconductive tunneling in quantum junctions

    International Nuclear Information System (INIS)

    Shumeiko, V.S.; Bratus', E.N.

    1997-01-01

    A consistent theory of superconductive tunneling in single-mode junctions within a scattering formulation of Bogolyubov-de Gennes quantum mechanics is presented. The dc Josephson effect and dc quasiparticle transport in the voltage-biased junctions are considered. Elastic quasiparticle scattering by the junction determines the equilibrium Josephson current. The origin of Andreev bound states in tunnel junctions and their role in equilibrium Josephson transport are discussed. In contrast, quasiparticle tunneling in voltage-biased junctions is determined by inelastic scattering. A general expression for inelastic scattering amplitudes is derived and the quasiparticle current is calculated at all voltages with emphasis on a discussion of the properties of sub gap tunnel current and the nature of subharmonic gap structure

  16. Superconducting tunnel-junction refrigerator

    International Nuclear Information System (INIS)

    Melton, R.G.; Paterson, J.L.; Kaplan, S.B.

    1980-01-01

    The dc current through an S 1 -S 2 tunnel junction, with Δ 2 greater than Δ 1 , when biased with eV 1 +Δ 2 , will lower the energy in S 1 . This energy reduction will be shared by the phonons and electrons. This device is shown to be analogous to a thermoelectric refrigerator with an effective Peltier coefficient π* approx. Δ 1 /e. Tunneling calculations yield the cooling power P/sub c/, the electrical power P/sub e/ supplied by the bias supply, and the cooling efficiency eta=P/sub c//P/sub e/. The maximum cooling power is obtained for eV= +- (Δ 2 -Δ 1 ) and t 1 =T 1 /T/sub c/1 approx. 0.9. Estimates are made of the temperature difference T 2 -T 1 achievable in Al-Pb and Sn-Pb junctions with an Al 2 O 3 tunneling barrier. The performance of this device is shown to yield a maximum cooling efficiency eta approx. = Δ 1 /(Δ 2 -Δ 1 ) which can be compared with that available in an ideal Carnot refrigerator of eta=T 1 /(T 2 -T 1 ). The development of a useful tunnel-junction refrigerator requires a tunneling barrier with an effective thermal conductance per unit area several orders of magnitude less than that provided by the A1 2 O 3 barrier in the Al-Pb and Sn-Pb systems

  17. 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.

  18. Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation

    International Nuclear Information System (INIS)

    Nam, C.H.; Shim, Heejae; Kim, K.S.; Cho, B.K.

    2004-01-01

    Oxidation of an AlO x insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 A thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer

  19. Instabilities in thin tunnel junctions

    International Nuclear Information System (INIS)

    Konkin, M.K.; Adler, J.G.

    1978-01-01

    Tunnel junctions prepared for inelastic electron tunneling spectroscopy are often plagued by instabilities in the 0-500-meV range. This paper relates the bias at which the instability occurs to the barrier thickness

  20. Tunnel magnetoresistance in asymmetric double-barrier magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Useinov, N.Kh.; Petukhov, D.A.; Tagirov, L.R.

    2015-01-01

    The spin-polarized tunnel conductance and tunnel magnetoresistance (TMR) through a planar asymmetric double-barrier magnetic tunnel junction (DBMTJ) have been calculated using quasi-classical model. In DBMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. The transmission coefficients of an electron to pass through the barriers have been calculated in terms of quantum mechanics. The dependencies of tunnel conductance and TMR on the applied voltage have been calculated in case of non-resonant transmission. Estimated in the framework of our model, the difference between the spin-channels conductances at low voltages was found relatively large. This gives rise to very high magnitude of TMR. - Highlights: • The spin-polarized conductance through the junction is calculated. • Dependencies of the tunnel conductance vs applied bias are shown. • Bias voltage dependence of tunnel magnetoresistance for the structure is shown

  1. Spin-dependent quasiparticle tunneling in junction superconductor-isolator-ferromagnetic

    International Nuclear Information System (INIS)

    Shlapak, Yu.V.; Shaternik, V.E.; Rudenko, E.M.

    2001-01-01

    The influence of Andreev reflection of quasiparticles in transparent tunnel junctions of superconductor-isolator-ferromagnetic on electric-current transport is studied within the framework of the Blonder-Tinkham-Klapwijk (BTK) model. It's obtained that current and signal-to-noise ratio can be increased for the memory cell by using in it the double-barrier tunnel junction ferromagnetic-isolator-superconductor-isolator-ferromagnetic instead off the usual tunnel junction ferromagnetic-isolator-ferromagnetic. The evolution of non-linear (tunnel-type) current-voltage characteristics with increasing of the junction transparency is described. (orig.)

  2. Resonant tunnel magnetoresistance in a double magnetic tunnel junction

    KAUST Repository

    Useinov, Arthur; Useinov, Niazbeck Kh H; Tagirov, Lenar R.; Kosel, Jü rgen

    2011-01-01

    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

  3. Tunnel magnetoresistance in double spin filter junctions

    International Nuclear Information System (INIS)

    Saffarzadeh, Alireza

    2003-01-01

    We consider a new type of magnetic tunnel junction, which consists of two ferromagnetic tunnel barriers acting as spin filters (SFs), separated by a nonmagnetic metal (NM) layer. Using the transfer matrix method and the free-electron approximation, the dependence of the tunnel magnetoresistance (TMR) on the thickness of the central NM layer, bias voltage and temperature in the double SF junction are studied theoretically. It is shown that the TMR and electron-spin polarization in this structure can reach very large values under suitable conditions. The highest value of the TMR can reach 99%. By an appropriate choice of the thickness of the central NM layer, the degree of spin polarization in this structure will be higher than that of the single SF junctions. These results may be useful in designing future spin-polarized tunnelling devices

  4. Primary Tunnel Junction Thermometry

    International Nuclear Information System (INIS)

    Pekola, Jukka P.; Holmqvist, Tommy; Meschke, Matthias

    2008-01-01

    We describe the concept and experimental demonstration of primary thermometry based on a four-probe measurement of a single tunnel junction embedded within four arrays of junctions. We show that in this configuration random sample specific and environment-related errors can be avoided. This method relates temperature directly to Boltzmann constant, which will form the basis of the definition of temperature and realization of official temperature scales in the future

  5. A hysteresis phenomenon in NMR spectra of molecular nanomagnets Fe8: a resonant quantum tunneling system

    Science.gov (United States)

    Yamasaki, Tomoaki; Ueda, Miki; Maegawa, Satoru

    2003-05-01

    A molecular nanomagnet Fe8 with a total spin S=10 in the ground state attracts much attention as a substance which exhibits the quantum tunneling of magnetization below 300 mK. We performed 1H NMR measurements for a single crystal of Fe8 in temperature range between 20 and 800 mK. The spectra below 300 mK strongly depend on the sequence of the applied field and those in the positive and negative fields are not symmetric about zero field, while they are symmetric above 300 mK. We discuss the origin of this hysteresis phenomenon, relating to the initial spin state of molecules, the resonant quantum tunneling and the nuclear spin relaxation process.

  6. A hysteresis phenomenon in NMR spectra of molecular nanomagnets Fe8: a resonant quantum tunneling system

    International Nuclear Information System (INIS)

    Yamasaki, Tomoaki; Ueda, Miki; Maegawa, Satoru

    2003-01-01

    A molecular nanomagnet Fe8 with a total spin S=10 in the ground state attracts much attention as a substance which exhibits the quantum tunneling of magnetization below 300 mK. We performed 1 H NMR measurements for a single crystal of Fe8 in temperature range between 20 and 800 mK. The spectra below 300 mK strongly depend on the sequence of the applied field and those in the positive and negative fields are not symmetric about zero field, while they are symmetric above 300 mK. We discuss the origin of this hysteresis phenomenon, relating to the initial spin state of molecules, the resonant quantum tunneling and the nuclear spin relaxation process

  7. Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

    International Nuclear Information System (INIS)

    Gajewski, Krzysztof; Piasecki, Tomasz; Kopiec, Daniel; Gotszalk, Teodor

    2017-01-01

    Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown. (paper)

  8. 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.

  9. Capacitance measurement of Josephson tunnel junctions with microwave-induced dc quasiparticle tunneling currents

    International Nuclear Information System (INIS)

    Hamasaki, K.; Yoshida, K.; Irie, F.; Enpuku, K.

    1982-01-01

    The microwave response of the dc quasiparticle tunneling current in Josephson tunnel junctions, where the Josephson current is suppressed by an external magnetic field, has been studied quantitatively in order to clarify its characteristics as a probe for the measurement of the junction capacitance. Extensive experiments for both small and long junctions are carried out for distinguishing between microwave behaviors of lumped and distributed constant junctions. It is shown that the observed voltage dependence of the dc quasiparticle tunneling current modified by an applied rf field is in good agreement with a theoretical result which takes into account the influence of the microwave circuit connected to the junction. The comparison between theory and experiment gives the magnitude of the internal rf field in the junction. Together with the applied rf field, this internal rf field leads to the junction rf impedance which is dominated by the junction capacitance in our experimental condition. In the case of lumped junctions, this experimental rf impedance is in reasonable agreement with the theoretical one with the junction capacitance estimated from the Fiske step of the distributed junction fabricated on the same substrate; the obtained ratio of the experimental impedance to the theoretical one is approximately 0.6--1.7. In the case of distributed junctions, however, experimental values of their characteristic impedances are approximately 0.2--0.3 of theoretical values calculated by assuming the one-dimensional junction model and taking account of the standing-wave effect in the junction

  10. Robust spin transfer torque in antiferromagnetic tunnel junctions

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed

    2017-04-18

    We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque enabling electrical manipulation of the Néel antiferromagnetic order parameter is out of plane, ∼n×p, while the torque competing with the antiferromagnetic exchange is in plane, ∼n×(p×n). Here, p and n are the Néel order parameter direction of the reference and free layers, respectively. Their bias dependence shows behavior similar to that in ferromagnetic tunnel junctions, the in-plane torque being mostly linear in bias, while the out-of-plane torque is quadratic. Most importantly, we find that the spin transfer torque in antiferromagnetic tunnel junctions is much more robust against disorder than that in antiferromagnetic metallic spin valves due to the tunneling nature of spin transport.

  11. Tunneling junction as an open system. Normal tunneling

    International Nuclear Information System (INIS)

    Ono, Y.

    1978-01-01

    The method of the tunneling Hamiltonian is reformulated in the case of normal tunneling by introducing two independent particle baths. Due to the baths, it becomes possible to realize a final stationary state where the electron numbers of the two electrodes in the tunneling system are maintained constant and where there exists a stationary current. The effect of the bath-system couplings on the current-voltage characteristics of the junction is discussed in relation to the usual expression of the current as a function of voltage. (Auth.)

  12. Niobium nitride Josephson tunnel junctions with magnesium oxide barriers

    International Nuclear Information System (INIS)

    Shoji, A.; Aoyagi, M.; Kosaka, S.; Shinoki, F.; Hayakawa, H.

    1985-01-01

    Niobium nitride-niobium nitride Josephson tunnel junctions have been fabricated using amorphous magnesium oxide (a-MgO) films as barriers. These junctions have excellent tunneling characteristics. For example, a large gap voltage (V/sub g/ = 5.1 mV), a large product of the maximum critical current and the normal tunneling resistance (I/sub c/R/sub n/ = 3.25 mV), and a small subgap leakage current (V/sub m/ = 45 mV, measured at 3 mV) have been obtained for a NbN/a-MgO/NbN junction. The critical current of this junction remains finite up to 14.5 K

  13. 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...

  14. Planar Josephson tunnel junctions in a transverse magnetic field

    DEFF Research Database (Denmark)

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

    2007-01-01

    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......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...

  15. Spin-transfer torque in spin filter tunnel junctions

    KAUST Repository

    Ortiz Pauyac, Christian

    2014-12-08

    Spin-transfer torque in a class of magnetic tunnel junctions with noncollinear magnetizations, referred to as spin filter tunnel junctions, is studied within the tight-binding model using the nonequilibrium Green\\'s function technique within Keldysh formalism. These junctions consist of one ferromagnet (FM) adjacent to a magnetic insulator (MI) or two FM separated by a MI. We find that the presence of the magnetic insulator dramatically enhances the magnitude of the spin-torque components compared to conventional magnetic tunnel junctions. The fieldlike torque is driven by the spin-dependent reflection at the MI/FM interface, which results in a small reduction of its amplitude when an insulating spacer (S) is inserted to decouple MI and FM layers. Meanwhile, the dampinglike torque is dominated by the tunneling electrons that experience the lowest barrier height. We propose a device of the form FM/(S)/MI/(S)/FM that takes advantage of these characteristics and allows for tuning the spin-torque magnitudes over a wide range just by rotation of the magnetization of the insulating layer.

  16. Spin-transfer torque in spin filter tunnel junctions

    KAUST Repository

    Ortiz Pauyac, Christian; Kalitsov, Alan; Manchon, Aurelien; Chshiev, Mairbek

    2014-01-01

    Spin-transfer torque in a class of magnetic tunnel junctions with noncollinear magnetizations, referred to as spin filter tunnel junctions, is studied within the tight-binding model using the nonequilibrium Green's function technique within Keldysh formalism. These junctions consist of one ferromagnet (FM) adjacent to a magnetic insulator (MI) or two FM separated by a MI. We find that the presence of the magnetic insulator dramatically enhances the magnitude of the spin-torque components compared to conventional magnetic tunnel junctions. The fieldlike torque is driven by the spin-dependent reflection at the MI/FM interface, which results in a small reduction of its amplitude when an insulating spacer (S) is inserted to decouple MI and FM layers. Meanwhile, the dampinglike torque is dominated by the tunneling electrons that experience the lowest barrier height. We propose a device of the form FM/(S)/MI/(S)/FM that takes advantage of these characteristics and allows for tuning the spin-torque magnitudes over a wide range just by rotation of the magnetization of the insulating layer.

  17. 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...

  18. AlGaAs/InGaAlP tunnel junctions for multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    SHARPS,P.R.; LI,N.Y.; HILLS,J.S.; HOU,H.; CHANG,PING-CHIH; BACA,ALBERT G.

    2000-05-16

    Optimization of GaInP{sub 2}/GaAs dual and GaInP{sub 2}/GaAs/Ge triple junction cells, and development of future generation monolithic multi-junction cells will involve the development of suitable high bandgap tunnel junctions. There are three criteria that a tunnel junction must meet. First, the resistance of the junction must be kept low enough so that the series resistance of the overall device is not increased. For AMO, 1 sun operation, the tunnel junction resistance should be below 5 x 10{sup {minus}2} {Omega}-cm. Secondly, the peak current density for the tunnel junction must also be larger than the J{sub sc} of the cell so that the tunnel junction I-V curve does not have a deleterious effect on the I-V curve of the multi-junction device. Finally, the tunnel junction must be optically transparent, i.e., there must be a minimum of optical absorption of photons that will be collected by the underlying subcells. The paper reports the investigation of four high bandgap tunnel junctions grown by metal-organic chemical vapor deposition.

  19. Dependences of the Tunnel Magnetoresistance and Spin Transfer Torque on the Sizes and Concentration of Nanoparticles in Magnetic Tunnel Junctions

    Science.gov (United States)

    Esmaeili, A. M.; Useinov, A. N.; Useinov, N. Kh.

    2018-01-01

    Dependences of the tunnel magnetoresistance and in-plane component of the spin transfer torque on the applied voltage in a magnetic tunnel junction have been calculated in the approximation of ballistic transport of conduction electrons through an insulating layer with embedded magnetic or nonmagnetic nanoparticles. A single-barrier magnetic tunnel junction with a nanoparticle embedded in an insulator forms a double-barrier magnetic tunnel junction. It has been shown that the in-plane component of the spin transfer torque in the double-barrier magnetic tunnel junction can be higher than that in the single-barrier one at the same thickness of the insulating layer. The calculations show that nanoparticles embedded in the tunnel junction increase the probability of tunneling of electrons, create resonance conditions, and ensure the quantization of the conductance in contrast to the tunnel junction without nanoparticles. The calculated dependences of the tunnel magnetoresistance correspond to experimental data demonstrating peak anomalies and suppression of the maximum magnetoresistances at low voltages.

  20. The two Josephson junction flux qubit with large tunneling amplitude

    International Nuclear Information System (INIS)

    Shnurkov, V.I.; Soroka, A.A.; Mel'nik, S.I.

    2008-01-01

    In this paper we discuss solid-state nanoelectronic realizations of Josephson flux qubits with large tunneling amplitude between the two macroscopic states. The latter can be controlled via the height and form of the potential barrier, which is determined by quantum-state engineering of the flux qubit circuit. The simplest circuit of the flux qubit is a superconducting loop interrupted by a Josephson nanoscale tunnel junction. The tunneling amplitude between two macroscopically different states can be increased substantially by engineering of the qubit circuit if the tunnel junction is replaced by a ScS contact. However, only Josephson tunnel junctions are particularly suitable for large-scale integration circuits and quantum detectors with present-day technology. To overcome this difficulty we consider here a flux qubit with high energy-level separation between the 'ground' and 'excited' states, consisting of a superconducting loop with two low-capacitance Josephson tunnel junctions in series. We demonstrate that for real parameters of resonant superposition between the two macroscopic states the tunneling amplitude can reach values greater than 1 K. Analytical results for the tunneling amplitude obtained within the semiclassical approximation by the instanton technique show good correlation with a numerical solution

  1. Reactive tunnel junctions in electrically driven plasmonic nanorod metamaterials

    Science.gov (United States)

    Wang, Pan; Krasavin, Alexey V.; Nasir, Mazhar E.; Dickson, Wayne; Zayats, Anatoly V.

    2018-02-01

    Non-equilibrium hot carriers formed near the interfaces of semiconductors or metals play a crucial role in chemical catalysis and optoelectronic processes. In addition to optical illumination, an efficient way to generate hot carriers is by excitation with tunnelling electrons. Here, we show that the generation of hot electrons makes the nanoscale tunnel junctions highly reactive and facilitates strongly confined chemical reactions that can, in turn, modulate the tunnelling processes. We designed a device containing an array of electrically driven plasmonic nanorods with up to 1011 tunnel junctions per square centimetre, which demonstrates hot-electron activation of oxidation and reduction reactions in the junctions, induced by the presence of O2 and H2 molecules, respectively. The kinetics of the reactions can be monitored in situ following the radiative decay of tunnelling-induced surface plasmons. This electrically driven plasmonic nanorod metamaterial platform can be useful for the development of nanoscale chemical and optoelectronic devices based on electron tunnelling.

  2. delta-biased Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Koshelet, V.

    2010-01-01

    Abstract: The behavior of a long Josephson tunnel junction drastically depends on the distribution of the dc bias current. We investigate the case in which the bias current is fed in the central point of a one-dimensional junction. Such junction configuration has been recently used to detect...... the persistent currents circulating in a superconducting loop. Analytical and numerical results indicate that the presence of fractional vortices leads to remarkable differences from the conventional case of uniformly distributed dc bias current. The theoretical findings are supported by detailed measurements...

  3. Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

    NARCIS (Netherlands)

    Jansen, R.; Lodder, J.C.

    2000-01-01

    Resonant tunneling through states in the barrier of a magnetic tunnel junction has been analyzed theoretically for the case of a spin-polarized density of barrier states. It is shown that for highly spin-polarized barrier states, the magnetoresistance due to resonant tunneling is enhanced compared

  4. The critical current of point symmetric Josephson tunnel junctions

    International Nuclear Information System (INIS)

    Monaco, Roberto

    2016-01-01

    Highlights: • We disclose some geometrical properties of the critical current field dependence that apply to a large class of Josephson junctions characterized by a point symmetric shape. • The developed theory is valid for any orientation of the applied magnetic field, therefore it allows the determine the consequences of field misalignment in the experimental setups. • We also address that the threshold curves of Josephson tunnel junctions with complex shapes can be expressed as a linear combination of the threshold curves of junctions with simpler point symmetric shapes. - Abstract: The physics of Josephson tunnel junctions drastically depends on their geometrical configurations. The shape of the junction determines the specific form of the magnetic-field dependence of its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions in the presence of an in-plane magnetic field of arbitrary orientations. We focus on a wide ensemble of junctions whose shape is invariant under point reflection. We analyze the implications of this type of isometry and derive the threshold curves of junctions whose shape is the union or the relative complement of two point symmetric plane figures.

  5. Microscopic tunneling theory of long Josephson junctions

    DEFF Research Database (Denmark)

    Grønbech-Jensen, N.; Hattel, Søren A.; Samuelsen, Mogens Rugholm

    1992-01-01

    We present a numerical scheme for solving a nonlinear partial integro-differential equation with nonlocal time dependence. The equation describes the dynamics in a long Josephson junction modeled by use of the microscopic theory for tunneling between superconductors. We demonstrate that the detai......We present a numerical scheme for solving a nonlinear partial integro-differential equation with nonlocal time dependence. The equation describes the dynamics in a long Josephson junction modeled by use of the microscopic theory for tunneling between superconductors. We demonstrate...

  6. Single-electron tunnel junction array

    International Nuclear Information System (INIS)

    Likharev, K.K.; Bakhvalov, N.S.; Kazacha, G.S.; Serdyukova, S.I.

    1989-01-01

    The authors have carried out an analysis of statics and dynamics of uniform one-dimensional arrays of ultrasmall tunnel junctions. The correlated single-electron tunneling in the junctions of the array results in its behavior qualitatively similar to that of the Josephson transmission line. In particular, external electric fields applied to the array edges can inject single-electron-charged solitons into the array interior. Shape of such soliton and character of its interactions with other solitons and the array edges are very similar to those of the Josephson vortices (sine-Gordon solitons) in the Josephson transmission line. Under certain conditions, a coherent motion of the soliton train along the array is possible, resulting in generation of narrowband SET oscillations with frequency f/sub s/ = /e where is the dc current flowing along the array

  7. Highly doped layer for tunnel junctions in solar cells

    Science.gov (United States)

    Fetzer, Christopher M.

    2017-08-01

    A highly doped layer for interconnecting tunnel junctions in multijunction solar cells is presented. The highly doped layer is a delta doped layer in one or both layers of a tunnel diode junction used to connect two or more p-on-n or n-on-p solar cells in a multijunction solar cell. A delta doped layer is made by interrupting the epitaxial growth of one of the layers of the tunnel diode, depositing a delta dopant at a concentration substantially greater than the concentration used in growing the layer of the tunnel diode, and then continuing to epitaxially grow the remaining tunnel diode.

  8. 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.

  9. Spin transport in spin filtering magnetic tunneling junctions.

    Science.gov (United States)

    Li, Yun; Lee, Eok Kyun

    2007-11-01

    Taking into account spin-orbit coupling and s-d interaction, we investigate spin transport properties of the magnetic tunneling junctions with spin filtering barrier using Landauer-Büttiker formalism implemented with the recursive algorithm to calculate the real-space Green function. We predict completely different bias dependence of negative tunnel magnetoresistance (TMR) between the systems composed of nonmagnetic electrode (NM)/ferromagnetic barrier (FB)/ferromagnet (FM) and NM/FB/FM/NM spin filtering tunnel junctions (SFTJs). Analyses of the results provide us possible ways of designing the systems which modulate the TMR in the negative magnetoresistance regime.

  10. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

    Directory of Open Access Journals (Sweden)

    Takeo Ohno and Yutaka Oyama

    2012-01-01

    Full Text Available In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE, in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor.

  11. Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope.

    Science.gov (United States)

    Nazin, G V; Wu, S W; Ho, W

    2005-06-21

    The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.

  12. Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

    Energy Technology Data Exchange (ETDEWEB)

    Rashid, H., E-mail: hawal@chalmers.se; Desmaris, V.; Pavolotsky, A.; Belitsky, V. [Group for Advanced Receiver Development, Earth and Space Sciences Department, Chalmers University of Technology, Gothenburg, 412 96 (Sweden)

    2016-04-15

    In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.

  13. Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

    International Nuclear Information System (INIS)

    Rashid, H.; Desmaris, V.; Pavolotsky, A.; Belitsky, V.

    2016-01-01

    In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.

  14. Large resistance change on magnetic tunnel junction based molecular spintronics devices

    Science.gov (United States)

    Tyagi, Pawan; Friebe, Edward

    2018-05-01

    Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. This paper discusses the impact of molecule induced strong coupling on the spin transport. To study molecular coupling effect the octametallic molecular cluster (OMC) was bridged between two ferromagnetic electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the exposed side edges. OMCs induced strong inter-ferromagnetic electrode coupling to yield drastic changes in transport properties of the magnetic tunnel junction testbed at the room temperature. These OMCs also transformed the magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic resonance studies provided insightful data to explain transport studies on the magnetic tunnel junction based molecular spintronics devices.

  15. Hybrid tunnel junction contacts to III–nitride light-emitting diodes

    KAUST Repository

    Young, Erin C.; Yonkee, Benjamin P.; Wu, Feng; Oh, Sang Ho; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.

    2016-01-01

    In this work, we demonstrate highly doped GaN p–n tunnel junction (TJ) contacts on III–nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10−4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a ($20\\bar{2}\\bar{1}$) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

  16. Hybrid tunnel junction contacts to III–nitride light-emitting diodes

    KAUST Repository

    Young, Erin C.

    2016-01-26

    In this work, we demonstrate highly doped GaN p–n tunnel junction (TJ) contacts on III–nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10−4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a ($20\\\\bar{2}\\\\bar{1}$) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

  17. Nanomagnetism and spintronics

    CERN Document Server

    Shinjo, Teruya

    2014-01-01

    The concise and accessible chapters of Nanomagnetism and Spintronics, Second Edition, cover the most recent research in areas of spin-current generation, spin-calorimetric effect, voltage effects on magnetic properties, spin-injection phenomena, giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR). Spintronics is a cutting-edge area in the field of magnetism that studies the interplay of magnetism and transport phenomena, demonstrating how electrons not only have charge but also spin. This second edition provides the background to understand this novel physical phenomeno

  18. Atomically Thin Al2O3 Films for Tunnel Junctions

    Science.gov (United States)

    Wilt, Jamie; Gong, Youpin; Gong, Ming; Su, Feifan; Xu, Huikai; Sakidja, Ridwan; Elliot, Alan; Lu, Rongtao; Zhao, Shiping; Han, Siyuan; Wu, Judy Z.

    2017-06-01

    Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard AlOx tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin Al2O3 tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial H2O pulse hydroxylated the Al surface and enabled the creation of an atomically thin Al2O3 tunnel barrier with a high-quality M -I interface and a significantly enhanced barrier height compared to thermal AlOx . These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition Al2O3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions.

  19. Single-Molecule Nanomagnets

    Science.gov (United States)

    Friedman, Jonathan R.; Sarachik, Myriam P.

    2010-04-01

    Single-molecule magnets straddle the classical and quantum mechanical worlds, displaying many fascinating phenomena. They may have important technological applications in information storage and quantum computation. We review the physical properties of two prototypical molecular nanomagnets, Mn12-acetate and Fe8: Each behaves as a rigid, spin-10 object and exhibits tunneling between up and down directions. As temperature is lowered, the spin-reversal process evolves from thermal activation to pure quantum tunneling. At low temperatures, magnetic avalanches occur in which the magnetization of an entire sample rapidly reverses. We discuss the important role that symmetry-breaking fields play in driving tunneling and in producing Berry-phase interference. Recent experimental advances indicate that quantum coherence can be maintained on timescales sufficient to allow a meaningful number of quantum computing operations to be performed. Efforts are under way to create monolayers and to address and manipulate individual molecules.

  20. Magnetic reconstruction induced magnetoelectric coupling and spin-dependent tunneling in Ni/KNbO_3/Ni multiferroic tunnel junctions

    International Nuclear Information System (INIS)

    Zhang, Hu; Dai, Jian-Qing; Song, Yu-Min

    2016-01-01

    We investigate the magnetoelectric coupling and spin-polarized tunneling in Ni/KNbO_3/Ni multiferroic tunnel junctions with asymmetric interfaces based on density functional theory. The junctions have two stable polarization states. We predict a peculiar magnetoelectric effect in such junctions originating from the magnetic reconstruction of Ni near the KO-terminated interface. This reconstruction is induced by the reversal of the ferroelectric polarization of KNbO_3. Furthermore, the change in the magnetic ordering filters the spin-dependent current. This effect leads to a change in conductance by about two orders of magnitude. As a result we obtain a giant tunneling electroresistance effect. In addition, there exist sizable tunneling magnetoresistance effects for two polarization states. - Highlights: • We study the ME coupling and electron tunneling in Ni/KNbO_3/Ni junctions. • There is magnetic reconstruction of Ni atoms near the KO-terminated interface. • A peculiar magnetoelectric coupling effect is obtained. • Predicted giant tunneling electroresistance effects.

  1. 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.

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

    KAUST Repository

    Useinov, Arthur; Gooneratne, Chinthaka Pasan; Kosel, Jü rgen

    2012-01-01

    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.

  3. Robust spin transfer torque in antiferromagnetic tunnel junctions

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed; Waintal, Xavier; Manchon, Aurelien

    2017-01-01

    We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque

  4. Spin polarized electron tunneling and magnetoresistance in molecular junctions.

    Science.gov (United States)

    Szulczewski, Greg

    2012-01-01

    This chapter reviews tunneling of spin-polarized electrons through molecules positioned between ferromagnetic electrodes, which gives rise to tunneling magnetoresistance. Such measurements yield important insight into the factors governing spin-polarized electron injection into organic semiconductors, thereby offering the possibility to manipulate the quantum-mechanical spin degrees of freedom for charge carriers in optical/electrical devices. In the first section of the chapter a brief description of the Jullière model of spin-dependent electron tunneling is reviewed. Next, a brief description of device fabrication and characterization is presented. The bulk of the review highlights experimental studies on spin-polarized electron tunneling and magnetoresistance in molecular junctions. In addition, some experiments describing spin-polarized scanning tunneling microscopy/spectroscopy on single molecules are mentioned. Finally, some general conclusions and prospectus on the impact of spin-polarized tunneling in molecular junctions are offered.

  5. Spin-dependent tunnelling in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Tsymbal, Evgeny Y; Mryasov, Oleg N; LeClair, Patrick R

    2003-01-01

    The phenomenon of electron tunnelling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent tunnelling (SDT) in magnetic tunnel junctions (MTJs) has recently aroused enormous interest and has developed in a vigorous field of research. The large tunnelling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible applications in non-volatile random-access memories and next-generation magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of SDT. In this review article we present an overview of this field of research. We discuss various factors that control the spin polarization and magnetoresistance in MTJs. Starting from early experiments on SDT and their interpretation, we consider thereafter recent experiments and models which highlight the role of the electronic structure of the ferromagnets, the insulating layer, and the ferromagnet/insulator interfaces. We also discuss the role of disorder in the barrier and in the ferromagnetic electrodes and their influence on TMR. (topical review)

  6. Charge Transport in 2D DNA Tunnel Junction Diodes

    KAUST Repository

    Yoon, Minho

    2017-11-06

    Recently, deoxyribonucleic acid (DNA) is studied for electronics due to its intrinsic benefits such as its natural plenitude, biodegradability, biofunctionality, and low-cost. However, its applications are limited to passive components because of inherent insulating properties. In this report, a metal-insulator-metal tunnel diode with Au/DNA/NiOx junctions is presented. Through the self-aligning process of DNA molecules, a 2D DNA nanosheet is synthesized and used as a tunneling barrier, and semitransparent conducting oxide (NiOx ) is applied as a top electrode for resolving metal penetration issues. This molecular device successfully operates as a nonresonant tunneling diode, and temperature-variable current-voltage analysis proves that Fowler-Nordheim tunneling is a dominant conduction mechanism at the junctions. DNA-based tunneling devices appear to be promising prototypes for nanoelectronics using biomolecules.

  7. Charge Transport in 2D DNA Tunnel Junction Diodes

    KAUST Repository

    Yoon, Minho; Min, Sung-Wook; Dugasani, Sreekantha Reddy; Lee, Yong Uk; Oh, Min Suk; Anthopoulos, Thomas D.; Park, Sung Ha; Im, Seongil

    2017-01-01

    Recently, deoxyribonucleic acid (DNA) is studied for electronics due to its intrinsic benefits such as its natural plenitude, biodegradability, biofunctionality, and low-cost. However, its applications are limited to passive components because of inherent insulating properties. In this report, a metal-insulator-metal tunnel diode with Au/DNA/NiOx junctions is presented. Through the self-aligning process of DNA molecules, a 2D DNA nanosheet is synthesized and used as a tunneling barrier, and semitransparent conducting oxide (NiOx ) is applied as a top electrode for resolving metal penetration issues. This molecular device successfully operates as a nonresonant tunneling diode, and temperature-variable current-voltage analysis proves that Fowler-Nordheim tunneling is a dominant conduction mechanism at the junctions. DNA-based tunneling devices appear to be promising prototypes for nanoelectronics using biomolecules.

  8. Four-state non-volatile memory in a multiferroic spin filter tunnel junction

    Science.gov (United States)

    Ruan, Jieji; Li, Chen; Yuan, Zhoushen; Wang, Peng; Li, Aidong; Wu, Di

    2016-12-01

    We report a spin filter type multiferroic tunnel junction with a ferromagnetic/ferroelectric bilayer barrier. Memory functions of a spin filter magnetic tunnel junction and a ferroelectric tunnel junction are combined in this single device, producing four non-volatile resistive states that can be read out in a non-destructive manner. This concept is demonstrated in a LaNiO3/Pr0.8Ca0.2MnO3/BaTiO3/La0.7Sr0.3MnO3 all-oxide tunnel junction. The ferromagnetic insulator Pr0.8Ca0.2MnO3 serves as the spin filter and the ferromagnetic metal La0.7Sr0.3MnO3 is the spin analyzer. The ferroelectric polarization reversal in the BaTiO3 barrier switches the tunneling barrier height to produce a tunneling electroresistance. The ferroelectric switching also modulates the spin polarization and the spin filtering efficiency in Pr0.8Ca0.2MnO3.

  9. Magnetoresistance of galfenol-based magnetic tunnel junction

    International Nuclear Information System (INIS)

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

    2015-01-01

    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 (Fe 1-x Ga 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

  10. Macroscopic Refrigeration Using Superconducting Tunnel Junctions

    Science.gov (United States)

    Lowell, Peter; O'Neil, Galen; Underwood, Jason; Zhang, Xiaohang; Ullom, Joel

    2014-03-01

    Sub-kelvin temperatures are often a prerequisite for modern scientific experiments, such as quantum information processing, astrophysical missions looking for dark energy signatures and tabletop time resolved x-ray spectroscopy. Existing methods of reaching these temperatures, such as dilution refrigerators, are bulky and costly. In order to increase the accessibility of sub-Kelvin temperatures, we have developed a new method of refrigeration using normal-metal/insulator/superconductor (NIS) tunnel junctions. NIS junctions cool the electrons in the normal metal since the hottest electrons selectively tunnel from the normal metal into the superconductor. By extending the normal metal onto a thermally isolated membrane, the cold electrons can cool the phonons through the electron-phonon coupling. When these junctions are combined with a pumped 3He system, they provide a potentially inexpensive method of reaching these temperatures. Using only three devices, each with a junction area of approximately 3,500 μm2, we have cooled a 2 cm3 Cu plate from 290 mK to 256 mK. We will present these experimental results along with recent modeling predictions that strongly suggest that further refinements will allow cooling from 300 mK to 120 mK. This work is supported by the NASA APRA program.

  11. Performance analysis of AlGaAs/GaAs tunnel junctions for ultra-high concentration photovoltaics

    International Nuclear Information System (INIS)

    García, I; Rey-Stolle, I; Algora, C

    2012-01-01

    An n ++ -GaAs/p ++ -AlGaAs tunnel junction with a peak current density of 10 100 A cm -2 is developed. This device is a tunnel junction for multijunction solar cells, grown lattice-matched on standard GaAs or Ge substrates, with the highest peak current density ever reported. The voltage drop for a current density equivalent to the operation of the multijunction solar cell up to 10 000 suns is below 5 mV. Trap-assisted tunnelling is proposed to be behind this performance, which cannot be justified by simple band-to-band tunnelling. The metal-organic vapour-phase epitaxy growth conditions, which are in the limits of the transport-limited regime, and the heavy tellurium doping levels are the proposed origins of the defects enabling trap-assisted tunnelling. The hypothesis of trap-assisted tunnelling is supported by the observed annealing behaviour of the tunnel junctions, which cannot be explained in terms of dopant diffusion or passivation. For the integration of these tunnel junctions into a triple-junction solar cell, AlGaAs barrier layers are introduced to suppress the formation of parasitic junctions, but this is found to significantly degrade the performance of the tunnel junctions. However, the annealed tunnel junctions with barrier layers still exhibit a peak current density higher than 2500 A cm -2 and a voltage drop at 10 000 suns of around 20 mV, which are excellent properties for tunnel junctions and mean they can serve as low-loss interconnections in multijunction solar cells working at ultra-high concentrations. (paper)

  12. R.f.-induced steps in mutually coupled, two-dimensional distributed Josephson tunnel junctions

    International Nuclear Information System (INIS)

    Klein, U.; Dammschneider, P.

    1991-01-01

    This paper reports on the amplitudes of the current steps in the I-V characteristics of mutually coupled two-dimensional distributed Josephson tunnel junctions driven by microwaves. For this purpose we use a numerical computation algorithm based on a planar resonator model for the individual Josephson tunnel junctions to calculate the d.c. current density distribution. In addition to the fundamental microwave frequency, harmonic contents of the tunneling current are also considered. The lateral dimensions of the individual junctions are small compared to the microwave wavelength and the Josephson penetration depth, giving an almost constant current density distribution. Therefore, the coupled junctions can give much greater step amplitudes than a single junction with an equal tunneling area, because of their nonuniform current density distribution

  13. Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates

    International Nuclear Information System (INIS)

    Lumb, M. P.; Yakes, M. K.; Schmieder, K. J.; Affouda, C. A.; Walters, R. J.; González, M.; Bennett, M. F.; Herrera, M.; Delgado, F. J.; Molina, S. I.

    2016-01-01

    In this work, the electrical performance of strain-balanced quantum well tunnel junctions with varying designs is presented. Strain-balanced quantum well tunnel junctions comprising compressively strained InAlAs wells and tensile-strained InAlAs barriers were grown on InP substrates using solid-source molecular beam epitaxy. The use of InAlAs enables InP-based tunnel junction devices to be produced using wide bandgap layers, enabling high electrical performance with low absorption. The impact of well and barrier thickness on the electrical performance was investigated, in addition to the impact of Si and Be doping concentration. Finally, the impact of an InGaAs quantum well at the junction interface is presented, enabling a peak tunnel current density of 47.6 A/cm 2 to be realized.

  14. Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates

    Energy Technology Data Exchange (ETDEWEB)

    Lumb, M. P. [The George Washington University, Washington, DC 20037 (United States); US Naval Research Laboratory, Washington, DC 20375 (United States); Yakes, M. K.; Schmieder, K. J.; Affouda, C. A.; Walters, R. J. [US Naval Research Laboratory, Washington, DC 20375 (United States); González, M.; Bennett, M. F. [Sotera Defense Solutions, Annapolis Junction, Maryland 20701 (United States); US Naval Research Laboratory, Washington, DC 20375 (United States); Herrera, M.; Delgado, F. J.; Molina, S. I. [University of Cádiz, 11510, Puerto Real, Cádiz (Spain)

    2016-05-21

    In this work, the electrical performance of strain-balanced quantum well tunnel junctions with varying designs is presented. Strain-balanced quantum well tunnel junctions comprising compressively strained InAlAs wells and tensile-strained InAlAs barriers were grown on InP substrates using solid-source molecular beam epitaxy. The use of InAlAs enables InP-based tunnel junction devices to be produced using wide bandgap layers, enabling high electrical performance with low absorption. The impact of well and barrier thickness on the electrical performance was investigated, in addition to the impact of Si and Be doping concentration. Finally, the impact of an InGaAs quantum well at the junction interface is presented, enabling a peak tunnel current density of 47.6 A/cm{sup 2} to be realized.

  15. Josephson tunnel junctions with ferromagnetic interlayer

    International Nuclear Information System (INIS)

    Weides, M.P.

    2006-01-01

    Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al 2 O 3 tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or π coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, π) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-π Josephson junction. At a certain temperature this 0-π junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum Φ 0 . Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T → 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)

  16. Josephson tunnel junctions with ferromagnetic interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Weides, M.P.

    2006-07-01

    Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al{sub 2}O{sub 3} tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or {pi} coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, {pi}) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-{pi} Josephson junction. At a certain temperature this 0-{pi} junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum {phi}{sub 0}. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T {yields} 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)

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

    International Nuclear Information System (INIS)

    Rehman, Mushtaq; Park, Junghwan; Song, Woon; Chong, Yonuk; Lee, Yeonsub; Min, Byoungchul; Shin, Kyungho; Ryu, Sangwan; Khim, Zheong

    2010-01-01

    We measured the noise power of a magnetic tunnel junction in the frequency range of 710 ∼ 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 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.

  18. Tunneling explains efficient electron transport via protein junctions.

    Science.gov (United States)

    Fereiro, Jerry A; Yu, Xi; Pecht, Israel; Sheves, Mordechai; Cuevas, Juan Carlos; Cahen, David

    2018-05-15

    Metalloproteins, proteins containing a transition metal ion cofactor, are electron transfer agents that perform key functions in cells. Inspired by this fact, electron transport across these proteins has been widely studied in solid-state settings, triggering the interest in examining potential use of proteins as building blocks in bioelectronic devices. Here, we report results of low-temperature (10 K) electron transport measurements via monolayer junctions based on the blue copper protein azurin (Az), which strongly suggest quantum tunneling of electrons as the dominant charge transport mechanism. Specifically, we show that, weakening the protein-electrode coupling by introducing a spacer, one can switch the electron transport from off-resonant to resonant tunneling. This is a consequence of reducing the electrode's perturbation of the Cu(II)-localized electronic state, a pattern that has not been observed before in protein-based junctions. Moreover, we identify vibronic features of the Cu(II) coordination sphere in transport characteristics that show directly the active role of the metal ion in resonance tunneling. Our results illustrate how quantum mechanical effects may dominate electron transport via protein-based junctions.

  19. Giant electroresistance of super-tetragonal BiFeO3-based ferroelectric tunnel junctions.

    Science.gov (United States)

    Yamada, Hiroyuki; Garcia, Vincent; Fusil, Stéphane; Boyn, Sören; Marinova, Maya; Gloter, Alexandre; Xavier, Stéphane; Grollier, Julie; Jacquet, Eric; Carrétéro, Cécile; Deranlot, Cyrile; Bibes, Manuel; Barthélémy, Agnès

    2013-06-25

    Ferroelectric tunnel junctions enable a nondestructive readout of the ferroelectric state via a change of resistance induced by switching the ferroelectric polarization. We fabricated submicrometer solid-state ferroelectric tunnel junctions based on a recently discovered polymorph of BiFeO3 with giant axial ratio ("T-phase"). Applying voltage pulses to the junctions leads to the highest resistance changes (OFF/ON ratio >10,000) ever reported with ferroelectric tunnel junctions. Along with the good retention properties, this giant effect reinforces the interest in nonvolatile memories based on ferroelectric tunnel junctions. We also show that the changes in resistance scale with the nucleation and growth of ferroelectric domains in the ultrathin BiFeO3 (imaged by piezoresponse force microscopy), thereby suggesting potential as multilevel memory cells and memristors.

  20. 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.

  1. Analysis of different tunneling mechanisms of InxGa1−xAs/AlGaAs tunnel junction light-emitting transistors

    International Nuclear Information System (INIS)

    Wu, Cheng-Han; Wu, Chao-Hsin

    2014-01-01

    The electrical and optical characteristics of tunnel junction light-emitting transistors (TJLETs) with different indium mole fractions (x = 5% and 2.5%) of the In x Ga 1−x As base-collector tunnel junctions have been investigated. Two electron tunneling mechanisms (photon-assisted or direct tunneling) provide additional currents to electrical output and resupply holes back to the base region, resulting in the upward slope of I-V curves and enhanced optical output under forward-active operation. The larger direct tunneling probability and stronger Franz-Keldysh absorption for 5% TJLET lead to higher collector current slope and less optical intensity enhancement when base-collector junction is under reverse-biased.

  2. Spin-dependent transport in metal/semiconductor tunnel junctions

    NARCIS (Netherlands)

    Prins, M.W.J.; Kempen, van H.; Leuken, Van H.; Groot, de R.A.; Roy, van W.; De Boeck, J.

    1995-01-01

    This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to

  3. Magnetic tunnel junction device having an intermediate layer

    NARCIS (Netherlands)

    2001-01-01

    A magnetic tunnel junction device has a multi-layer structure including a pair of electrode layers of a ferromagnetic material and a tunnel barrier layer of an insulating material between the electrode layers. In order to realize a low resistance, the multi-layer structure also includes an

  4. Optical photon detection in Al superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Brammertz, G.; Peacock, A.; Verhoeve, P.; Martin, D.; Venn, R.

    2004-01-01

    We report on the successful fabrication of low leakage aluminium superconducting tunnel junctions with very homogeneous and transparent insulating barriers. The junctions were tested in an adiabatic demagnetisation refrigerator with a base temperature of 35 mK. The normal resistance of the junctions is equal to ∼7 μΩ cm 2 with leakage currents in the bias voltage domain as low as 100 fA/μm 2 . Optical single photon counting experiments show a very high responsivity with charge amplification factors in excess of 100. The total resolving power λ/Δλ (including electronic noise) for 500 nm photons is equal to 13 compared to a theoretical tunnel limited value of 34. The current devices are found to be limited spectroscopically by spatial inhomogeneities in the detectors response

  5. Tunneling magnetoresistance and electroresistance in Fe/PbTiO3/Fe multiferroic tunnel junctions

    International Nuclear Information System (INIS)

    Dai, Jian-Qing

    2016-01-01

    We perform first-principles electronic structure and spin-dependent transport calculations for a Fe/PbTiO 3 /Fe multiferroic tunnel junction with asymmetric TiO 2 - and PbO-terminated interfaces. We demonstrate that the interfacial electronic reconstruction driven by the in situ screening of ferroelectric polarization, in conjunction with the intricate complex band structure of barrier, play a decisive role in controlling the spin-dependent tunneling. Reversal of ferroelectric polarization results in a transition from insulating to half-metal-like conducting state for the interfacial Pb 6p z orbitals, which acts as an atomic-scale spin-valve by releasing the tunneling current in antiparallel magnetization configuration as the ferroelectric polarization pointing to the PbO-terminated interface. This effect produces large change in tunneling conductance. Our results open an attractive avenue in designing multiferroic tunnel junctions with excellent performance by exploiting the interfacial electronic reconstruction originated from the in situ screening of ferroelectric polarization.

  6. Tunneling anisotropic magnetoresistance in Co/AIOx/Al tunnel junctions with fcc Co (111) electrodes

    NARCIS (Netherlands)

    Wang, Kai; Tran, T. Lan Ahn; Brinks, Peter; Brinks, P.; Sanderink, Johannes G.M.; Bolhuis, Thijs; van der Wiel, Wilfred Gerard; de Jong, Machiel Pieter

    2013-01-01

    Tunneling anisotropic magnetoresistance (TAMR) has been characterized in junctions comprised of face-centered cubic (fcc) Co (111) ferromagnetic electrodes grown epitaxially on sapphire substrates, amorphous AlOx tunnel barriers, and nonmagnetic Al counterelectrodes. Large TAMR ratios have been

  7. Tunneling conductance in superconductor-hybrid double quantum dots Josephson junction

    Science.gov (United States)

    Chamoli, Tanuj; Ajay

    2018-05-01

    The present work deals with the theoretical model study to analyse the tunneling conductance across a superconductor hybrid double quantum dots tunnel junction (S-DQD-S). Recently, there are many experimental works where the Josephson current across such nanoscopic junction is found to be dependent on nature of the superconducting electrodes, coupling of the hybrid double quantum dot's electronic states with the electronic states of the superconductors and nature of electronic structure of the coupled dots. For this, we have attempted a theoretical model containing contributions of BCS superconducting leads, magnetic coupled quantum dot states and coupling of superconducting leads with QDs. In order to include magnetic coupled QDs the contributions of competitive Kondo and Ruderman-Kittel- Kasuya-Yosida (RKKY) interaction terms are also introduced through many body effects in the model Hamiltonian at low temperatures (where Kondo temperature TK tunnel junctions. Tunneling conductance is proportional to DOS, hence we can analyse it's behaviour with the help of DOS.

  8. Interfacial density of states in magnetic tunnel junctions

    NARCIS (Netherlands)

    LeClair, P.R.; Kohlhepp, J.T.; Swagten, H.J.M.; Jonge, de W.J.M.

    2001-01-01

    Large zero-bias resistance anomalies as well as a collapse of magnetoresistance were observed in Co/Al2O3/Co magnetic tunnel junctions with thin Cr interfacial layers. The tunnel magnetoresistance decays exponentially with nominal Cr interlayer thickness with a length scale of ~1 Å more than twice

  9. Coherent Cooper pair tunneling in systems of Josephson junctions: effects of quasiparticle tunneling and of the electromagnetic environment

    NARCIS (Netherlands)

    Maassen van den Brink, A.; Odintsov, A.A.; Bobbert, P.A.; Schön, G.

    1991-01-01

    Small capacitance tunnel junctions show single electron effects and, in the superconducting state, the coherent tunneling of Cooper pairs. We study these effects in a system of two Josephson junctions, driven by a voltage source with a finite impedance. Novel features show up in theI–V

  10. Josephson tunnel junctions in niobium films

    International Nuclear Information System (INIS)

    Wiik, Tapio.

    1976-12-01

    A method of fabricating stable Josephson tunnel junctions with reproducible characteristics is described. The junctions have a sandwich structure consisting of a vacuum evaporated niobium film, a niobium oxide layer produced by the glow discharge method and a lead film deposited by vacuum evaporation. Difficulties in producing thin-film Josephson junctions are discussed. Experimental results suggest that the lower critical field of the niobium film is the most essential parameter when evaluating the quality of these junctions. The dependence of the lower critical field on the film thickness and on the Ginzburg-Landau parameter of the film is studied analytically. Comparison with the properties of the evaporated films and with the previous calculations for bulk specimens shows that the presented model is applicable for most of the prepared samples. (author)

  11. Recent Trends in Spintronics-Based Nanomagnetic Logic

    Science.gov (United States)

    Das, Jayita; Alam, Syed M.; Bhanja, Sanjukta

    2014-09-01

    With the growing concerns of standby power in sub-100-nm CMOS technologies, alternative computing techniques and memory technologies are explored. Spin transfer torque magnetoresistive RAM (STT-MRAM) is one such nonvolatile memory relying on magnetic tunnel junctions (MTJs) to store information. It uses spin transfer torque to write information and magnetoresistance to read information. In 2012, Everspin Technologies, Inc. commercialized the first 64Mbit Spin Torque MRAM. On the computing end, nanomagnetic logic (NML) is a promising technique with zero leakage and high data retention. In 2000, Cowburn and Welland first demonstrated its potential in logic and information propagation through magnetostatic interaction in a chain of single domain circular nanomagnetic dots of Supermalloy (Ni80Fe14Mo5X1, X is other metals). In 2006, Imre et al. demonstrated wires and majority gates followed by coplanar cross wire systems demonstration in 2010 by Pulecio et al. Since 2004 researchers have also investigated the potential of MTJs in logic. More recently with dipolar coupling between MTJs demonstrated in 2012, logic-in-memory architecture with STT-MRAM have been investigated. The architecture borrows the computing concept from NML and read and write style from MRAM. The architecture can switch its operation between logic and memory modes with clock as classifier. Further through logic partitioning between MTJ and CMOS plane, a significant performance boost has been observed in basic computing blocks within the architecture. In this work, we have explored the developments in NML, in MTJs and more recent developments in hybrid MTJ/CMOS logic-in-memory architecture and its unique logic partitioning capability.

  12. Quantum-limited detection of millimeter waves using superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Mears, C.A.

    1991-09-01

    The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 ± 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker's theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs

  13. Magnetic tunnel junctions with AlN and AlNxOy barriers

    International Nuclear Information System (INIS)

    Schwickert, M. M.; Childress, J. R.; Fontana, R. E.; Kellock, A. J.; Rice, P. M.; Ho, M. K.; Thompson, T. J.; Gurney, B. A.

    2001-01-01

    Nonoxide tunnel barriers such as AlN are of interest for magnetic tunnel junctions to avoid the oxidation of the magnetic electrodes. We have investigated the fabrication and properties of thin AlN-based barriers for use in low resistance magnetic tunnel junctions. Electronic, magnetic and structural data of tunnel valves of the form Ta (100 Aa)/PtMn (300 Aa)/CoFe 20 (20 Aa - 25 Aa)/barrier/CoFe 20 (10 - 20 Aa)/NiFe 16 (35 - 40 Aa)/Ta (100 Aa) are presented, where the barrier consists of AlN, AlN x O y or AlN/AlO x with total thicknesses between 8 and 15 Aa. The tunnel junctions were sputter deposited and then lithographically patterned down to 2 x 2μm 2 devices. AlN was deposited by reactive sputtering from an Al target with 20% - 35% N 2 in the Ar sputter gas at room temperature, resulting in stoichiometric growth of AlN x (x=0.50±0.05), as determined by RBS. TEM analysis shows that the as-deposited AlN barrier is crystalline. For AlN barriers and AlN followed by natural O 2 oxidation, we obtain tunnel magnetoresistance >10% with specific junction resistance R j down to 60Ωμm 2 . [copyright] 2001 American Institute of Physics

  14. Thermopower in double planar tunnel junctions with ferromagnetic barriers and nonmagnetic electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Wilczyński, M., E-mail: wilczyns@if.pw.edu.pl

    2017-01-01

    The Seebeck effect is investigated in double planar tunnel junctions consisting of nonmagnetic electrodes and the central layer separated by ferromagnetic barriers. Calculations are performed in the linear response theory using the free-electron model. The thermopower is analyzed as a function of the thickness of the central layer, temperature of the junctions and the relative orientation of magnetic moments of the barriers. It has been found that the thermopower can be significantly enhanced in the junction with special central layer thickness due to electron tunneling by resonant states. The thickness of the central layer for which the thermopower is enhanced depends not only on the temperature of the junction but also on the orientation of magnetic moments in the barriers. - Highlights: • Thermopower in the double planar junctions with magnetic barriers is analyzed. • Thermopower can be enhanced due to the resonant tunneling. • Thermopower depends on the magnetic configuration of the junction.

  15. Temperature dependence of shot noise in double barrier magnetic tunnel junctions

    Science.gov (United States)

    Niu, Jiasen; Liu, Liang; Feng, J. F.; Han, X. F.; Coey, J. M. D.; Zhang, X.-G.; Wei, Jian

    2018-03-01

    Shot noise reveals spin dependent transport properties in a magnetic tunnel junction. We report measurement of shot noise in CoFeB/MgO/CoFeB/MgO/CoFeB double barrier magnetic tunnel junctions, which shows a strong temperature dependence. The Fano factor used to characterize shot noise increases with decreasing temperature. A sequential tunneling model can be used to account for these results, in which a larger Fano factor results from larger spin relaxation length at lower temperatures.

  16. Properties on niobium-based Josephson tunneling elements in junction microstructures

    International Nuclear Information System (INIS)

    Albrecht, G.; Richter, J.; Weber, P.

    1982-01-01

    We describe the fabrication and electrical characteristics of niobium oxide-barrier tunnel junctions with counterelectrodes of lead/lead alloy. Primary attention is directed to the experimental conditions necessary to obtain high-quality tunnel barriers as well as studies on characterizing the atomic structure of the barrier region. In order to study the tunnel barrier homogeneity in the tunneling region the magnetic field dependence of the critical Josephson current is investigated. The I--V characteristics and dependence of the critical Josephson current on temperature are analyzed quantitatively by using a proximity effect model. Finally, we discuss experimental results on the improvement of junction quality by including traces of carbon in the rf argon plasma during the sputter cleaning of niobium base electrodes

  17. Giant electrode effect on tunnelling electroresistance in ferroelectric tunnel junctions.

    Science.gov (United States)

    Soni, Rohit; Petraru, Adrian; Meuffels, Paul; Vavra, Ondrej; Ziegler, Martin; Kim, Seong Keun; Jeong, Doo Seok; Pertsev, Nikolay A; Kohlstedt, Hermann

    2014-11-17

    Among recently discovered ferroelectricity-related phenomena, the tunnelling electroresistance (TER) effect in ferroelectric tunnel junctions (FTJs) has been attracting rapidly increasing attention owing to the emerging possibilities of non-volatile memory, logic and neuromorphic computing applications of these quantum nanostructures. Despite recent advances in experimental and theoretical studies of FTJs, many questions concerning their electrical behaviour still remain open. In particular, the role of ferroelectric/electrode interfaces and the separation of the ferroelectric-driven TER effect from electrochemical ('redox'-based) resistance-switching effects have to be clarified. Here we report the results of a comprehensive study of epitaxial junctions comprising BaTiO(3) barrier, La(0.7)Sr(0.3)MnO(3) bottom electrode and Au or Cu top electrodes. Our results demonstrate a giant electrode effect on the TER of these asymmetric FTJs. The revealed phenomena are attributed to the microscopic interfacial effect of ferroelectric origin, which is supported by the observation of redox-based resistance switching at much higher voltages.

  18. 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.

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

    KAUST Repository

    Useinov, A. N.; Kosel, Jü rgen; Useinov, N. Kh.; Tagirov, L. R.

    2011-01-01

    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.

  20. Humidity dependence of molecular tunnel junctions with an AlOx/COOH- interface

    Science.gov (United States)

    Zhang, Xiaohang; McGill, Stephen; Xiong, Peng

    2006-03-01

    We have studied the electron transport in planar tunneling junctions with aluminum oxide and an organic self-assembled monolayer (SAM) as the tunnel barrier. The structure of the junctions is Al/AlOx/SAM/(Au, Pb) with a junction area of ˜ 0.4mm^2. The organic molecules investigated include mercaptohexadecanoic acid (MHA), hexadecanoic acid (HDA), and octadecyltrichlorosilane (OTS); all of which form ordered SAMs on top of aluminum oxide. The use of a superconducting electrode (Al) enables us to determine unambiguously that these are high-quality tunnel junctions. For junctions incorporating MHA, the transport behavior is found to be strongly humidity dependent. The resistance of these junctions drops more than 50% when placed in dry nitrogen and recovers when returned into the ambient. The same drop also occurs when the sample is placed into a vacuum, and backfilling the vacuum with either dry N2 or O2 has negligible effect on the resistance. For comparison, junctions with HDA show the same humidity dependence, while OTS samples do not. Since both MHA and HDA have carboxylic groups and OTS does not, the results suggest that water molecules at the AlOx/COOH- interface play the central role in the observed behavior. Inelastic tunneling spectroscopy (IETS) has also been performed to understand the role of water. This work was supported by a FSU Research Foundation PEG grant.

  1. Tunneling magnetoresistance and electroresistance in Fe/PbTiO{sub 3}/Fe multiferroic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Jian-Qing, E-mail: djqkust@sina.com [School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

    2016-08-21

    We perform first-principles electronic structure and spin-dependent transport calculations for a Fe/PbTiO{sub 3}/Fe multiferroic tunnel junction with asymmetric TiO{sub 2}- and PbO-terminated interfaces. We demonstrate that the interfacial electronic reconstruction driven by the in situ screening of ferroelectric polarization, in conjunction with the intricate complex band structure of barrier, play a decisive role in controlling the spin-dependent tunneling. Reversal of ferroelectric polarization results in a transition from insulating to half-metal-like conducting state for the interfacial Pb 6p{sub z} orbitals, which acts as an atomic-scale spin-valve by releasing the tunneling current in antiparallel magnetization configuration as the ferroelectric polarization pointing to the PbO-terminated interface. This effect produces large change in tunneling conductance. Our results open an attractive avenue in designing multiferroic tunnel junctions with excellent performance by exploiting the interfacial electronic reconstruction originated from the in situ screening of ferroelectric polarization.

  2. A review on all-perovskite multiferroic tunnel junctions

    Directory of Open Access Journals (Sweden)

    Yuewei Yin

    2017-12-01

    Full Text Available Although the basic concept was proposed only about 10 years ago, multiferroic tunnel junctions (MFTJs with a ferroelectric barrier sandwiched between two ferromagnetic electrodes have already drawn considerable interests, driven mainly by its potential applications in multi-level memories and electric field controlled spintronics. The purpose of this article is to review the recent progress of all-perovskite MFTJs. Starting from the key functional properties of the tunneling magnetoresistance, tunneling electroresistance, and tunneling electromagnetoresistance effects, we discuss the main origins of the tunneling electroresistance effect, recent progress in achieving multilevel resistance states in a single device, and the electrical control of spin polarization and transport through the ferroelectric polarization reversal of the tunneling barrier.

  3. Study of the geometrical resonances of superconducting tunnel junctions

    DEFF Research Database (Denmark)

    Sørensen, O. Hoffmann; Finnegan, T.F.; Pedersen, Niels Falsig

    1973-01-01

    The resonant cavity structure of superconducting Sn-Sn-oxide-Sn tunnel junctions has been investigated via photon-assisted quasiparticle tunneling. We find that the temperature-dependent losses at 35 GHz are determined by the surface resistance of the Sn films for reduced temperatures between 0...

  4. 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.

  5. Spin-frustrated V3 and Cu3 nanomagnets with Dzialoshinsky-Moriya exchange. 2. Spin structure, spin chirality and tunneling gaps

    International Nuclear Information System (INIS)

    Belinsky, Moisey I.

    2009-01-01

    The spin chirality and spin structure of the Cu 3 and V 3 nanomagnets with the Dzialoshinsky-Moriya (DM) exchange interaction are analyzed. The correlations between the vector κ and the scalar χ chirality are obtained. The DM interaction forms the spin chirality which is equal to zero in the Heisenberg clusters. The dependences of the spin chirality on magnetic field and deformations are calculated. The cluster distortions reduce the spin chirality. The vector chirality is reduced partially and the scalar chirality vanishes in the transverse magnetic field. In the isosceles clusters, the DM exchange and distortions determine the sign and degree of the spin chirality κ. The correlations between the chirality parameters κ n and the intensities of the EPR and INS transitions are obtained. The vector chirality κ n describes the spin chirality of the Cu 3 and V 3 nanomagnets, the scalar chirality describes the pseudoorbital moment of the DM cluster. It is shown that in the consideration of the DM exchange, the spin states DM mixing and tunneling gaps at level crossing fields depend on the coordinate system of the DM model. The calculations in the DM exchange models in the right-handed and left-handed frame show opposite magnetic behavior at the level crossing field and allow to explain the opposite schemes of the tunneling gaps and levels crossing, which have been obtained in different treatments. The results of the DM model in the right-handed frame are consistent with the results of the group-theoretical analysis, whereas the results in the left-handed frame are inconsistent with that. The correlations between the spin chirality of the ground state and tunneling gaps at the level crossing field are obtained for the equilateral and isosceles nanoclusters.

  6. Photon-assisted Tunneling In Double-barrier Superconducting Tunnel-junctions

    NARCIS (Netherlands)

    Dierichs, M. M. T. M.; Dieleman, P.; Wezelman, J. J.; Honingh, C. E.; Klapwijk, T. M.

    1994-01-01

    Double-barrier Nb/Al2O3/Al/Al2O3/Nb tunnel junctions are used as mixing elements in a 345 GHz waveguide mixer. Noise temperatures (double side band) down to 720 K at 3.0 K are obtained without the need to apply a magnetic field to suppress the Josephson current. It is shown that the composite

  7. A15 Nb-Sn tunnel junction fabrication and properties

    International Nuclear Information System (INIS)

    Rudman, D.A.; Hellman, F.; Hammond, R.H.; Beasley, M.R.

    1984-01-01

    We have investigated the deposition conditions necessary to produce optimized films of A15 Nb-Sn (19--26 at. % Sn) by electron-beam codeposition. Reliable high-quality superconducting tunnel junctions can be made on this material by using an oxidized-amorphous silicon overlayer as the tunneling barrier and lead as the counter-electrode. These junctions have been used both as a tool for materials diagnosis and as a probe of the superconducting properties (critical temperature and gap) of the films. Careful control of the substrate temperature during the growth of the films has proved critical to obtain homogeneous samples. When the substrate temperature is properly stabilized, stoichiometric Nb 3 Sn is found to be relatively insensitive to the deposition temperature and conditions. In contrast, the properties of the off-stoichiometry (Sn-poor) material depend strongly on the deposition temperature. For this Sn-poor material the ratio 2Δ/kT/sub c/ at a given composition increases with increasing deposition temperature. This change appears to be due to an increase in the gap at the surface of the material (as measured by tunneling) relative to the critical temperature of the bulk. All the tunnel junctions exhibit some persistent nonidealities in their current-voltage characteristics that are qualitatively insensitive to composition or deposition conditions. In particular, the junctions show excess conduction below the sum of the energy gaps (with onset at the counter-electrode gap) and a broadened current rise at the sum gap. The detailed origins of these problems are not yet understood

  8. Fluctuations of the peak current of tunnel diodes in multi-junction solar cells

    International Nuclear Information System (INIS)

    Jandieri, K; Baranovskii, S D; Stolz, W; Gebhard, F; Guter, W; Hermle, M; Bett, A W

    2009-01-01

    Interband tunnel diodes are widely used to electrically interconnect the individual subcells in multi-junction solar cells. Tunnel diodes have to operate at high current densities and low voltages, especially when used in concentrator solar cells. They represent one of the most critical elements of multi-junction solar cells and the fluctuations of the peak current in the diodes have an essential impact on the performance and reliability of the devices. Recently we have found that GaAs tunnel diodes exhibit extremely high peak currents that can be explained by resonant tunnelling through defects homogeneously distributed in the junction. Experiments evidence rather large fluctuations of the peak current in the diodes fabricated from the same wafer. It is a challenging task to clarify the reason for such large fluctuations in order to improve the performance of the multi-junction solar cells. In this work we show that the large fluctuations of the peak current in tunnel diodes can be caused by relatively small fluctuations of the dopant concentration. We also show that the fluctuations of the peak current become smaller for deeper energy levels of the defects responsible for the resonant tunnelling.

  9. Theoretical consideration of spin-polarized resonant tunneling in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Mu Haifeng; Zhu Zhengang; Zheng Qingrong; Jin Biao; Wang Zhengchuan; Su Gang

    2004-01-01

    A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations

  10. Proximity effect and hot-electron diffusion in Ag/Al2O3/Al tunnel junctions

    International Nuclear Information System (INIS)

    Netel, H.; Jochum, J.; Labov, S.E.; Mears, C.A.; Frank, M.; Chow, D.; Lindeman, M.A.; Hiller, L.J.

    1997-01-01

    We have fabricated Ag/Al 2 O 3 /Al tunnel junctions on Si substrates using a new process. This process was developed to fabricate superconducting tunnel junctions (STJs) on the surface of a superconductor. These junctions allow us to study the proximity effect of a superconducting Al film on a normal metal trapping layer. In addition, these devices allow us to measure the hot-electron diffusion constant using a single junction. Lastly these devices will help us optimize the design and fabrication of tunnel junctions on the surface of high-Z, ultra-pure superconducting crystals. 5 refs., 8 figs

  11. Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

    Science.gov (United States)

    Althammer, Matthias; Mishra, Rohan; Borisevich, Albina J.; Singh, Amit Vikam; Keshavarz, Sahar; Yurtisigi, Mehmet Kenan; Leclair, Patrick; Gupta, Arunava

    We experimentally investigate the structural, magnetic and electrical transport properties of La0.67Sr0.33MnO3 based magnetic tunnel junctions with a SrSnO3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier the observed tunnel magnetoresistance is comparable to tunnel junctions with a better lattice matched SrTiO3 barrier, reaching values of up to 350 % at T = 5 K . Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease of the TMR with increasing bias voltage. Our results suggest that by reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future. We gratefully acknowledge financial support via NSF-ECCS Grant No. 1509875.

  12. Fabrication of tunnel junction-based molecular electronics and spintronics devices

    International Nuclear Information System (INIS)

    Tyagi, Pawan

    2012-01-01

    Tunnel junction-based molecular devices (TJMDs) are highly promising for realizing futuristic electronics and spintronics devices for advanced logic and memory operations. Under this approach, ∼2.5 nm molecular device elements bridge across the ∼2-nm thick insulator of a tunnel junction along the exposed side edge(s). This paper details the efforts and insights for producing a variety of TJMDs by resolving multiple device fabrication and characterization issues. This study specifically discusses (i) compatibility between tunnel junction test bed and molecular solutions, (ii) optimization of the exposed side edge profile and insulator thickness for enhancing the probability of molecular bridging, (iii) effect of fabrication process-induced mechanical stresses, and (iv) minimizing electrical bias-induced instability after the device fabrication. This research will benefit other researchers interested in producing TJMDs efficiently. TJMD approach offers an open platform to test virtually any combination of magnetic and nonmagnetic electrodes, and promising molecules such as single molecular magnets, porphyrin, DNA, and molecular complexes.

  13. Creation of stable molecular junctions with a custom-designed scanning tunneling microscope.

    Science.gov (United States)

    Lee, Woochul; Reddy, Pramod

    2011-12-02

    The scanning tunneling microscope break junction (STMBJ) technique is a powerful approach for creating single-molecule junctions and studying electrical transport in them. However, junctions created using the STMBJ technique are usually mechanically stable for relatively short times (scanning tunneling microscope that enables the creation of metal-single molecule-metal junctions that are mechanically stable for more than 1 minute at room temperature. This stability is achieved by a design that minimizes thermal drift as well as the effect of environmental perturbations. The utility of this instrument is demonstrated by performing transition voltage spectroscopy-at the single-molecule level-on Au-hexanedithiol-Au, Au-octanedithiol-Au and Au-decanedithiol-Au junctions.

  14. Tunneling magnetoresistance in junctions composed of ferromagnets and time-reversal invariant topological superconductors

    International Nuclear Information System (INIS)

    Yan, Zhongbo; Wan, Shaolong

    2016-01-01

    Tunneling magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of an injected electron from the ferromagnet lies in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with other spin-polarization directions will be partially Andreev reflected and partially normal reflected, which consequently has a lower conductance, and therefore, the magnetoresistance effect emerges. Compared to conventional magnetic tunnel junctions, an unprecedented advantage of the junctions studied here is that arbitrary high tunneling magnetoresistance can be obtained even when the magnetization of the ferromagnets are weak and the insulating tunneling barriers are featureless. Our findings provide a new fascinating mechanism to obtain high tunneling magnetoresistance. (paper)

  15. Soliton excitations in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Lomdahl, P. S.; Sørensen, O. H.; Christiansen, Peter Leth

    1982-01-01

    A detailed numerical study of a sine-Gordon model of the Josephson tunnel junction is compared with experimental measurements on junctions with different L / λJ ratios. The soliton picture is found to apply well on both relatively long (L / λJ=6) and intermediate (L / λJ=2) junctions. We find good...... agreement for the current-voltage characteristics, power output, and for the shape and height of the zero-field steps (ZFS). Two distinct modes of soliton oscillations are observed: (i) a bunched or congealed mode giving rise to the fundamental frequency f1 on all ZFS's and (ii) a "symmetric" mode which...... on the Nth ZFS yields the frequency Nf1 Coexistence of two adjacent frequencies is found on the third ZFS of the longer junction (L / λJ=6) in a narrow range of bias current as also found in the experiments. Small asymmetries in the experimental environment, a weak magnetic field, e.g., is introduced via...

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

    Energy Technology Data Exchange (ETDEWEB)

    Dartora, C.A., E-mail: cadartora@eletrica.ufpr.br [Electrical Engineering Department, Federal University of Parana (UFPR), C.P. 19011 Curitiba, 81.531-970 PR (Brazil); Nobrega, K.Z., E-mail: bzuza1@yahoo.com.br [Federal Institute of Education, Science and Technolgy of Maranhão (IFMA), Av. Marechal Castelo Branco, 789, São Luís, 65.076-091 MA (Brazil); Cabrera, G.G., E-mail: cabrera@ifi.unicamp.br [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas (UNICAMP), C.P. 6165, Campinas 13.083-970 SP (Brazil)

    2016-08-15

    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.

  17. Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance.

    Science.gov (United States)

    Wang, Mengxing; Cai, Wenlong; Cao, Kaihua; Zhou, Jiaqi; Wrona, Jerzy; Peng, Shouzhong; Yang, Huaiwen; Wei, Jiaqi; Kang, Wang; Zhang, Youguang; Langer, Jürgen; Ocker, Berthold; Fert, Albert; Zhao, Weisheng

    2018-02-14

    Perpendicular magnetic tunnel junctions based on MgO/CoFeB structures are of particular interest for magnetic random-access memories because of their excellent thermal stability, scaling potential, and power dissipation. However, the major challenge of current-induced switching in the nanopillars with both a large tunnel magnetoresistance ratio and a low junction resistance is still to be met. Here, we report spin transfer torque switching in nano-scale perpendicular magnetic tunnel junctions with a magnetoresistance ratio up to 249% and a resistance area product as low as 7.0 Ω µm 2 , which consists of atom-thick W layers and double MgO/CoFeB interfaces. The efficient resonant tunnelling transmission induced by the atom-thick W layers could contribute to the larger magnetoresistance ratio than conventional structures with Ta layers, in addition to the robustness of W layers against high-temperature diffusion during annealing. The critical switching current density could be lower than 3.0 MA cm -2 for devices with a 45-nm radius.

  18. Fine structures on zero-field steps in low-loss Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Monaco, Roberto; Barbara, Paola; Mygind, Jesper

    1993-01-01

    The first zero-field step in the current-voltage characteristic of intermediate-length, high-quality, low-loss Nb/Al-AlOx/Nb Josephson tunnel junctions has been carefully investigated as a function of temperature. When decreasing the temperature, a number of structures develop in the form...... of regular and slightly hysteretic steps whose voltage position depends on the junction temperature and length. This phenomenon is interesting for the study of nonlinear dynamics and for application of long Josephson tunnel junctions as microwave and millimeter-wavelength oscillators....

  19. Ferroelectric tunnel junctions with multi-quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Zhijun; Zhang, Tianjin, E-mail: zhangtj@hubu.edu.cn [Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062 (China); Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei University, Wuhan 430062 (China); Liang, Kun; Qi, Yajun; Wang, Duofa; Wang, Jinzhao; Jiang, Juan [Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei University, Wuhan 430062 (China)

    2014-06-02

    Ferroelectric tunnel junctions (FTJs) with multi-quantum well structures are proposed and the tunneling electroresistance (TER) effect is investigated theoretically. Compared with conventional FTJs with monolayer ferroelectric barriers, FTJs with single-well structures provide TER ratio improvements of one order of magnitude, while FTJs with optimized multi-well structures can enhance this improvement by another order of magnitude. It is believed that the increased resonant tunneling strength combined with appropriate asymmetry in these FTJs contributes to the improvement. These studies may help to fabricate FTJs with large TER ratio experimentally and put them into practice.

  20. Dynamic Tunneling Junctions at the Atomic Intersection of Two Twisted Graphene Edges.

    Science.gov (United States)

    Bellunato, Amedeo; Vrbica, Sasha D; Sabater, Carlos; de Vos, Erik W; Fermin, Remko; Kanneworff, Kirsten N; Galli, Federica; van Ruitenbeek, Jan M; Schneider, Grégory F

    2018-04-11

    The investigation of the transport properties of single molecules by flowing tunneling currents across extremely narrow gaps is relevant for challenges as diverse as the development of molecular electronics and sequencing of DNA. The achievement of well-defined electrode architectures remains a technical challenge, especially due to the necessity of high precision fabrication processes and the chemical instability of most bulk metals. Here, we illustrate a continuously adjustable tunneling junction between the edges of two twisted graphene sheets. The unique property of the graphene electrodes is that the sheets are rigidly supported all the way to the atomic edge. By analyzing the tunneling current characteristics, we also demonstrate that the spacing across the gap junction can be controllably adjusted. Finally, we demonstrate the transition from the tunneling regime to contact and the formation of an atomic-sized junction between the two edges of graphene.

  1. Creation of stable molecular junctions with a custom-designed scanning tunneling microscope

    International Nuclear Information System (INIS)

    Lee, Woochul; Reddy, Pramod

    2011-01-01

    The scanning tunneling microscope break junction (STMBJ) technique is a powerful approach for creating single-molecule junctions and studying electrical transport in them. However, junctions created using the STMBJ technique are usually mechanically stable for relatively short times (<1 s), impeding detailed studies of their charge transport characteristics. Here, we report a custom-designed scanning tunneling microscope that enables the creation of metal–single molecule–metal junctions that are mechanically stable for more than 1 minute at room temperature. This stability is achieved by a design that minimizes thermal drift as well as the effect of environmental perturbations. The utility of this instrument is demonstrated by performing transition voltage spectroscopy—at the single-molecule level—on Au–hexanedithiol–Au, Au–octanedithiol–Au and Au–decanedithiol–Au junctions.

  2. First-principles investigation of quantum transport in GeP3 nanoribbon-based tunneling junctions

    Science.gov (United States)

    Wang, Qiang; Li, Jian-Wei; Wang, Bin; Nie, Yi-Hang

    2018-06-01

    Two-dimensional (2D) GeP3 has recently been theoretically proposed as a new low-dimensional material [ Nano Lett. 17(3), 1833 (2017)]. In this manuscript, we propose a first-principles calculation to investigate the quantum transport properties of several GeP3 nanoribbon-based atomic tunneling junctions. Numerical results indicate that monolayer GeP3 nanoribbons show semiconducting behavior, whereas trilayer GeP3 nanoribbons express metallic behavior owing to the strong interaction between each of the layers. This behavior is in accordance with that proposed in two-dimensional GeP3 layers. The transmission coefficient T( E) of tunneling junctions is sensitive to the connecting formation between the central monolayer GeP3 nanoribbon and the trilayer GeP3 nanoribbon at both ends. The T( E) value of the bottom-connecting tunneling junction is considerably larger than those of the middle-connecting and top-connecting ones. With increases in gate voltage, the conductances increase for the bottom-connecting and middle-connecting tunneling junctions, but decrease for the top-connecting tunneling junctions. In addition, the conductance decreases exponentially with respect to the length of the central monolayer GeP3 nanoribbon for all the tunneling junctions. I-V curves show approximately linear behavior for the bottom-connecting and middle-connecting structures, but exhibit negative differential resistance for the top-connecting structures. The physics of each phenomenon is analyzed in detail.

  3. Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

    Energy Technology Data Exchange (ETDEWEB)

    Arai, Miho; Moriya, Rai, E-mail: moriyar@iis.u-tokyo.ac.jp; Yabuki, Naoto; Masubuchi, Satoru [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Ueno, Keiji [Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570 (Japan); Machida, Tomoki, E-mail: tmachida@iis.u-tokyo.ac.jp [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan)

    2015-09-07

    We investigate the micromechanical exfoliation and van der Waals (vdW) assembly of ferromagnetic layered dichalcogenide Fe{sub 0.25}TaS{sub 2}. The vdW interlayer coupling at the Fe-intercalated plane of Fe{sub 0.25}TaS{sub 2} allows exfoliation of flakes. A vdW junction between the cleaved crystal surfaces is constructed by dry transfer method. We observe tunnel magnetoresistance in the resulting junction under an external magnetic field applied perpendicular to the plane, demonstrating spin-polarized tunneling between the ferromagnetic layered material and the vdW junction.

  4. Electrical resistivity of monolayers and bilayers of alkanethiols in tunnel junction with gate electrode

    International Nuclear Information System (INIS)

    York, Roger L.; Nacionales, David; Slowinski, Krzysztof

    2005-01-01

    The tunneling resistances of monolayers and bilayers of n-alkanethiols in macroscopic Hg-Hg junctions with an electrochemical gate are reported. The resistances near zero bias calculated per 1 hydrocarbon chain vary from (5 ± 4) x 10 12 Ω for n-nonanethiol to (4 ± 2) x 10 16 Ω for n-octadecanethiol. These values indicate that monolayers of hydrocarbons in Hg-Hg junctions are substantially more resistive as compared to measurements employing microscopic tunnel junctions. The tunneling resistances of monolayer junctions are approximately 1 order of magnitude larger than those of bilayer junctions containing the same number of atoms indicating inefficient electronic coupling across the non-bonded -CH 3 |Hg interface. The symmetric current-voltage curves observed for the asymmetric junctions of Hg-S-(CH 2 ) n -CH 3 |Hg type suggest that these junctions do not behave as molecular diodes. Additional experimental evidence for the nature of the -CH 3 |Hg interface in the Hg-S-(CH 2 ) n -CH 3 |Hg junction is also presented

  5. Performance comparison between p–i–n and p–n junction tunneling field-effect transistors

    Science.gov (United States)

    Yoon, Young Jun; Seo, Jae Hwa; Kang, In Man

    2018-06-01

    In this study, we investigated the direct-current (DC) and radio-frequency (RF) performances of p–i–n and p–n junction tunneling field-effect transistors (TFETs). Compared to the p–i–n junction TFET, the p–n junction TFET exhibited higher on-state current (I on) because the channel formation mechanism of the p–n junction TFET resulted in a narrower tunneling barrier and an expanded tunneling area. Further, the reduction of I on of the p–n junction TFET by the interface trap was smaller. Moreover, the p–n junction TFET exhibited lower gate-to-drain capacitance (C gd) because a depletion capacitance (C gd,dep) was formed by the depletion region under gate dielectric. Consequently, the p–n junction TFET achieved an improvement of cut-off frequency (f T) and intrinsic delay time (τ), which are related to the current performance and total gate capacitance (C gg). We confirmed the enhancement of device performances in terms of I on, f T, and τ by the conduction mechanism of the p–n junction TFET.

  6. Flicker (1/f) noise in tunnel junction DC SQUIDS

    International Nuclear Information System (INIS)

    Koch, R.H.; Clarke, J.; Goubau, W.M.; Martinis, J.M.; Pegrum, C.M.; Van Harlingen, D.J.

    1983-01-01

    We have measured the spectral density of the 1/f voltage noise in current-biased resistively shunted Josephson tunnel junctions and dc SQUIDs. A theory in which fluctuations in the temperature give rise to fluctuations in the critical current and hence in the voltage predicts the magnitude of the noise quite accurately for junctions with areas of about 2 x 10 4 μm 2 , but significantly overestimates the noise for junctions with areas of about 6 μm 2 . DC SQUIDs fabricated from these two types of junctions exhibit substantially more 1/f voltage noise than would be predicted from a model in which the noise arises from critical current fluctuations in the junctions. This result was confirmed by an experiment involving two different bias current and flux modulation schemes, which demonstrated that the predominant 1/f voltage noise arises not from critical current fluctuations, but from some unknown source that can be regarded as an apparent 1/f flux noise. Measurements on five different configurations of dc SQUIDs fabricated with thin-film tunnel junctions and with widely varying areas, inductances, and junction capacitances show that the spectral density of the 1/f equivalent flux noise is roughtly constant, within a factor of three of (10 -10 /f)phi 2 0 Hz -1 . It is emphasized that 1/f flux noise may not be the predominant source of 1/f noise in SQUIDS fabricated with other technologies

  7. 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.

  8. Normal-state conductance used to probe superconducting tunnel junctions for quantum computing

    Energy Technology Data Exchange (ETDEWEB)

    Chaparro, Carlos; Bavier, Richard; Kim, Yong-Seung; Kim, Eunyoung; Oh, Seongshik [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Kline, Jeffrey S; Pappas, David P, E-mail: carlosch@physics.rutgers.ed, E-mail: ohsean@physics.rutgers.ed [National Institute of Standards and Technology, Boulder, CO 80305 (United States)

    2010-04-15

    Here we report normal-state conductance measurements of three different types of superconducting tunnel junctions that are being used or proposed for quantum computing applications: p-Al/a-AlO/p-Al, e-Re/e-AlO/p-Al, and e-V/e-MgO/p-V, where p stands for polycrystalline, e for epitaxial, and a for amorphous. All three junctions exhibited significant deviations from the parabolic behavior predicted by the WKB approximation models. In the p-Al/a-AlO/p-Al junction, we observed enhancement of tunneling conductances at voltages matching harmonics of Al-O stretching modes. On the other hand, such Al-O vibration modes were missing in the epitaxial e-Re/e-AlO/p-Al junction. This suggests that absence or existence of the Al-O stretching mode might be related to the crystallinity of the AlO tunnel barrier and the interface between the electrode and the barrier. In the e-V/e-MgO/p-V junction, which is one of the candidate systems for future superconducting qubits, we observed suppression of the density of states at zero bias. This implies that the interface is electronically disordered, presumably due to oxidation of the vanadium surface underneath the MgO barrier, even if the interface was structurally well ordered, suggesting that the e-V/e-MgO/p-V junction will not be suitable for qubit applications in its present form. This also demonstrates that the normal-state conductance measurement can be effectively used to screen out low quality samples in the search for better superconducting tunnel junctions.

  9. Effect of single Abrikosov vortices on the properties of Josephson tunnel junctions

    International Nuclear Information System (INIS)

    Golubov, A.A.; Kupriyanov, M.Yu.

    1987-01-01

    The effect of single Abrikosov vortices, trapped in the electrodes of a Josephson tunnel junction perpendicularly to the junction surface, on the tunnel current through the junction is studied within the framework of the microscopic theory. The current-voltage characteristic and the critical junction current I c are calculated for temperatures 0 c . It is shown that if the vortices at the junction are misaligned, singularities on the current-voltage characteristic appear at eV Δ (T), and in some cases the magnitude of suppression of I c may be of the order of magnitude of I c itself. The temperature dependence of the critical current is calculated for the case of one of the electrodes being a two-dimensional superconducting film in which the creation of opposite sign vortex pairs is significant

  10. Instantons and magnetization tunneling: Beyond the giant-spin approximation

    International Nuclear Information System (INIS)

    Florez, J.M.; Vargas, P.; Nunez, Alvaro S.

    2009-01-01

    In this work we show that commonly neglected fluctuations of the net total spin of a molecular nanomagnet strongly modified its tunneling properties and provide a scenario to explain some discrepancies between theory and experiment. Starting off from an effective spin Hamiltonian, we study the quantum tunneling of the magnetization of molecular nanomagnets in the regime where the giant-spin approximation is breaking down. This study is done using an instanton description of the tunneling path. The instanton is calculated considering its coupling to quantum fluctuations.

  11. Magnetic tunnel junction thermocouple for thermoelectric power harvesting

    Science.gov (United States)

    Böhnert, T.; Paz, E.; Ferreira, R.; Freitas, P. P.

    2018-05-01

    The thermoelectric power generated in magnetic tunnel junctions (MTJs) is determined as a function of the tunnel barrier thickness for a matched electric circuit. This study suggests that lower resistance area product and higher tunnel magnetoresistance will maximize the thermoelectric power output of the MTJ structures. Further, the thermoelectric behavior of a series of two MTJs, a MTJ thermocouple, is investigated as a function of its magnetic configurations. In an alternating magnetic configurations the thermovoltages cancel each other, while the magnetic contribution remains. A large array of MTJ thermocouples could amplify the magnetic thermovoltage signal significantly.

  12. Advanced Metrology for Characterization of Magnetic Tunnel Junctions

    DEFF Research Database (Denmark)

    Kjær, Daniel

    -plane tunneling (CIPT) for characterization of magnetic tunnel junctions (MTJs), which constitutes the key component not only in MRAM but also the read-heads of modern hard disk drives. MTJs are described by their tunnel magnetoresistance (TMR), which is the relative difference of the resistance area products (RA...... of this project has been to provide cheaper, faster and more precise metrology for MTJs. This goal has been achieved in part by the demonstration of a static field CIPT method, which allows us to reduce the measurement time by a factor of 5, by measuring only RA thus excluding TMR. This enhancement is obtained...

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    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 2 O 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.

  14. 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.

  15. Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions.

    Science.gov (United States)

    Zhang, Peng

    2015-05-19

    When two conductors are separated by a sufficiently thin insulator, electrical current can flow between them by quantum tunneling. This paper presents a self-consistent model of tunneling current in a nano- and subnano-meter metal-insulator-metal plasmonic junction, by including the effects of space charge and exchange correlation potential. It is found that the J-V curve of the junction may be divided into three regimes: direct tunneling, field emission, and space-charge-limited regime. In general, the space charge inside the insulator reduces current transfer across the junction, whereas the exchange-correlation potential promotes current transfer. It is shown that these effects may modify the current density by orders of magnitude from the widely used Simmons' formula, which is only accurate for a limited parameter space (insulator thickness > 1 nm and barrier height > 3 eV) in the direct tunneling regime. The proposed self-consistent model may provide a more accurate evaluation of the tunneling current in the other regimes. The effects of anode emission and material properties (i.e. work function of the electrodes, electron affinity and permittivity of the insulator) are examined in detail in various regimes. Our simple model and the general scaling for tunneling current may provide insights to new regimes of quantum plasmonics.

  16. Fabrication of TiN/AlN/TiN tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Nakayama, Takeru; Naruse, Masato; Myoren, Hiroaki; Taino, Tohru, E-mail: taino@mail.saitama-u.ac.jp

    2016-11-15

    Highlights: • We have fabricated TiN/AlN/TiN tunnel junctions with an epitaxial layer. • TiN and AlN films were deposited by dc and rf magnetron sputtering at ambient substrate temperatures. • The junctions have a V{sub g} = 1.1 mV, J{sub c} = 0.24 A/cm{sup 2}, R{sub sg}/R{sub n} of 7.2, and low subgap leakage current of 180 nA. - Abstract: We have fabricated TiN/AlN/TiN tunnel junctions with an epitaxial layer. The critical temperature of TiN can be changed in the range from 0.5 to 5.0 K. Therefore, it is easy to set 5.0 K as the target critical temperature. When a Superconducting Tunnel Junction (STJ) is operated as a photon detector, it is necessary to cool it to within 0.1 K of the critical temperature in consideration of the noise of the thermally stimulated currents. Because 0.3 K was desirable, as for the manufacture of general purpose photon detectors, the critical temperature 5.0 K. TiN and AlN films were deposited by dc and rf magnetron sputtering in a load-lock sputtering system at ambient substrate temperatures. The junctions have a gap voltage of V{sub g} = 1.1 mV, and critical current density of J{sub c} = 0.24 A/cm{sup 2}, and R{sub sg}/R{sub n} of 7.2, and low subgap leakage current (I{sub sub}@ 500 µV = 180 nA). We report our experiment system, the manufacture method and the junction properties in this paper.

  17. Thermal stability analysis of thin film Ni-NiOx-Cr tunnel junctions

    International Nuclear Information System (INIS)

    Krishnan, S.; Emirov, Y.; Bhansali, S.; Stefanakos, E.; Goswami, Y.

    2010-01-01

    This research reports on the thermal stability of Ni-NiO x -Cr based Metal-Insulator-Metal (MIM) junction. Effect of annealing (250 to 400 o C) on the electrical and physical transport properties of this MIM stack was understood to determine the thermal budget allowable when using these diodes. MIM tunnel junctions were fabricated by sputtering and the NiO x was formed through reactive sputtering. The performance of the tunnel junctions after exposure to elevated temperatures was investigated using current-voltage measurements. This was correlated to the structural properties of the interfaces at different temperatures, characterized by Atomic Force Microscopy, X-ray Diffraction and Transmission Electron Microscopy (TEM). MIM tunnel junctions annealed up to 350 o C demonstrated satisfactory current-voltage characteristics and sensitivity. MIM junctions exhibited improved electrical performance as they were heated to 250 o C (sensitivity of 42 V -1 and a zero-bias resistance of ∼300 Ω) due to improved crystallization of the layers within the stack. At temperatures over 350 o C, TEM and Energy Dispersive Spectra confirmed a breakdown of the MIM structure due to interdiffusion.

  18. Rectified tunneling current response of bio-functionalized metal-bridge-metal junctions.

    Science.gov (United States)

    Liu, Yaqing; Offenhäusser, Andreas; Mayer, Dirk

    2010-01-15

    Biomolecular bridged nanostructures allow direct electrical addressing of electroactive biomolecules, which is of interest for the development of bioelectronic and biosensing hybrid junctions. In the present paper, the electroactive biomolecule microperoxidase-11 (MP-11) was integrated into metal-bridge-metal (MBM) junctions assembled from a scanning tunneling microscope (STM) setup. Before immobilization of MP-11, the Au working electrode was first modified by a self-assembled monolayer of 1-undecanethiol (UDT). A symmetric and potential independent response of current-bias voltage (I(t)/V(b)) was observed for the Au (substrate)/UDT/Au (tip) junction. However, the I(t)/V(b) characteristics became potential dependent and asymmetrical after binding of MP-11 between the electrodes of the junction. The rectification ratio of the asymmetric current response varies with gate electrode modulation. A resonant tunneling process between metal electrode and MP-11 enhances the tunneling current and is responsible for the observed rectification. Our investigations demonstrated that functional building blocks of proteins can be reassembled into new conceptual devices with operation modes deviating from their native function, which could prove highly useful in the design of future biosensors and bioelectronic devices. Copyright 2009 Elsevier B.V. All rights reserved.

  19. Phonon spectroscopy with superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Grimshaw, J.M.

    1984-02-01

    Superconducting tunnel junctions can be used as generators and detectors of monochromatic phonons of frequency larger than 80 GHz, as was first devised by Eisenmenger and Dayem (1967) and Kinder (1972a, 1973). In this report, we intend to give a general outline of this type of spectroscopy and to present the results obtained so far. The basic physics underlying phonon generation and detection are described in chapter I, a wider approach being given in the references therein. In chapter II, the different types of junctions are considered with respect to their use. Chapter III deals with the evaporation technique for the superconducting junctions. The last part of this report is devoted to the results that we have obtained on γ-irradiated LiF, pure Si and Phosphorous implanted Si. In these chapters, the limitations of the spectrometer are brought out and suggestions for further work are given [fr

  20. Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions.

    Science.gov (United States)

    Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S; Saeys, Mark; Yang, Hyunsoo

    2014-09-30

    While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical strain, achieving an enhancement factor of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further correlate this strain-enhanced TMR with coherent spin tunneling through the MgO barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium Green's function (NEGF) quantum transport calculations. Our results help elucidate the TMR mechanism at the atomic level and can provide a new way to enhance, as well as tune, the quantum properties in nanoscale materials and devices.

  1. Q factor and resonance amplitude of Josephson tunnel junctions

    International Nuclear Information System (INIS)

    Broom, R.F.; Wolf, P.

    1977-01-01

    The surface impedance of the superconducting films comprising the electrodes of Josephson tunnel junctions has been derived from the BCS theory in the extreme London limit. Expressions have been obtained for (i) the dependence of the penetration depth lambda on frequency and temperature, and (ii) the quality factor Q of the junction cavity, attributable to surface absorption in the electrodes. The effect of thin electrodes (t 9 or approx. = lambda) is also included in the calculations. Comparison of the calculated frequency dependence of lambda with resonance measurements on Pb-alloy and all-Nb tunnel junctions yields quite good agreement, indicating that the assumptions made in the theory are reasonable. Measurements of the (current) amplitude of the resonance peaks of the junctions have been compared with the values obtained from inclusion of the calculated Q in the theory by Kulik. In common with observations on microwave cavities by other workers, we find that a small residual conductivity must be added to the real part of the BCS value. With its inclusion, good agreement is found between calculation and experiment, within the range determined by the simplifying assumptions of Kulik's theory. From the results, we believe the calculation of Q to be reasonably accurate for the materials investigated. It is shown that the resonance amplitude of Josephson junctions can be calculated directly from the material constants and a knowledge of the residual conductivity

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

    KAUST Repository

    Zhang, Kun; Cao, Yan-ling; Fang, Yue-wen; Li, Qiang; Zhang, Jie; Duan, Chun-gang; Yan, Shi-shen; Tian, Yu-feng; Huang, Rong; Zheng, Rong-kun; Kang, Shi-shou; Chen, Yan-xue; Liu, Guo-lei; Mei, Liang-mo

    2015-01-01

    , 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/Co

  3. Nb/NiCu bilayers in single and stacked superconductive tunnel junctions: preliminary results

    International Nuclear Information System (INIS)

    Pepe, G.P.; Ruotolo, A.; Parlato, L.; Peluso, G.; Ausanio, G.; Carapella, G.; Latempa, R.

    2004-01-01

    We present preliminary experimental results concerning both single and stacked tunnel junctions in which one of the electrodes was formed by a superconductor/ferromagnet (S/F) bi-layer. In particular, in the stacked configuration a Nb/NiCu bi-layer was used as the intermediate electrode, and it was probed by tunneling on both sides. Tunnel junctions have been characterized in terms of current-voltage characteristics (IVC), and differential conductance. Preliminary steady-state injection-detection measurements performed in the stacked devices at T=4.2 K are also presented and discussed

  4. Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions

    OpenAIRE

    Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S.; Saeys, Mark; Yang, Hyunsoo

    2014-01-01

    While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical...

  5. 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...

  6. Large positive spin polarization and giant inverse tunneling magnetoresistance in Fe/PbTiO3/Fe multiferroic tunnel junction

    International Nuclear Information System (INIS)

    Dai, Jian-Qing; Zhang, Hu; Song, Yu-Min

    2014-01-01

    We perform first-principles electronic structure and spin-dependent transport calculations of a multiferroic tunnel junction (MFTJ) with an epitaxial Fe/PbTiO 3 /Fe heterostructure. We predict a large positive spin-polarization (SP) and an intriguing giant inverse tunneling magnetoresistance (TMR) ratio in this tunnel junction. We demonstrate that the tunneling properties are determined by ferroelectric (FE) polarization screening and electronic reconstruction at the interface with lower electrostatic potential. The intricate complex band structure of PbTiO 3 , in particular the lowest decay rates concerning Pb 6p z and Ti 3d z2 states near the Γ ¯ point, gives rise to the large positive SP of the tunneling current in the parallel magnetic configuration. However, the giant inverse TMR ratio is attributed to the minority-spin electrons of the interfacial Ti 3d xz +3d yz orbitals which have considerably weight in the extended area around the Γ ¯ point at the Fermi energy and causes remarkable contributions to the conductance in the antiparallel magnetic configuration. - Highlights: • We study spin-dependent tunneling in Fe/PbTiO 3 /Fe multiferroic tunnel junction. • We find a large positive spin polarization in the parallel magnetic configuration. • An intriguing giant inverse TMR ratio (about −2000%) is predicted. • Complex band structure of PbTiO 3 causes the large positive spin polarization. • Negative TMR is due to minority-spin electrons of interfacial Ti d xz +d yz orbitals

  7. InAs/Si Hetero-Junction Nanotube Tunnel Transistors

    KAUST Repository

    Hanna, Amir; Fahad, Hossain M.; Hussain, Muhammad Mustafa

    2015-01-01

    Hetero-structure tunnel junctions in non-planar gate-all-around nanowire (GAA NW) tunnel FETs (TFETs) have shown significant enhancement in ‘ON’ state tunnel current over their all-silicon counterpart. Here we show the unique concept of nanotube TFET in a hetero-structure configuration that is capable of much higher drive current as opposed to that of GAA NW TFETs.Through the use of inner/outer core-shell gates, a single III-V hetero-structured nanotube TFET leverages physically larger tunneling area while achieving higher driver current (ION) and saving real estates by eliminating arraying requirement. Numerical simulations has shown that a 10 nm thin nanotube TFET with a 100 nm core gate has a 5×normalized output current compared to a 10 nm diameter GAA NW TFET.

  8. InAs/Si Hetero-Junction Nanotube Tunnel Transistors

    KAUST Repository

    Hanna, Amir

    2015-04-29

    Hetero-structure tunnel junctions in non-planar gate-all-around nanowire (GAA NW) tunnel FETs (TFETs) have shown significant enhancement in ‘ON’ state tunnel current over their all-silicon counterpart. Here we show the unique concept of nanotube TFET in a hetero-structure configuration that is capable of much higher drive current as opposed to that of GAA NW TFETs.Through the use of inner/outer core-shell gates, a single III-V hetero-structured nanotube TFET leverages physically larger tunneling area while achieving higher driver current (ION) and saving real estates by eliminating arraying requirement. Numerical simulations has shown that a 10 nm thin nanotube TFET with a 100 nm core gate has a 5×normalized output current compared to a 10 nm diameter GAA NW TFET.

  9. Electrically tunable tunneling rectification magnetoresistance in magnetic tunneling junctions with asymmetric barriers.

    Science.gov (United States)

    Wang, Jing; Huang, Qikun; Shi, Peng; Zhang, Kun; Tian, Yufeng; Yan, Shishen; Chen, Yanxue; Liu, Guolei; Kang, Shishou; Mei, Liangmo

    2017-10-26

    The development of multifunctional spintronic devices requires simultaneous control of multiple degrees of freedom of electrons, such as charge, spin and orbit, and especially a new physical functionality can be realized by combining two or more different physical mechanisms in one specific device. Here, we report the realization of novel tunneling rectification magnetoresistance (TRMR), where the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated in Co/CoO-ZnO/Co magnetic tunneling junctions with asymmetric tunneling barriers. Moreover, by simultaneously applying direct current and alternating current to the devices, the TRMR has been remarkably tuned in the range from -300% to 2200% at low temperature. This proof-of-concept investigation provides an unexplored avenue towards electrical and magnetic control of charge and spin, which may apply to other heterojunctions to give rise to more fascinating emergent functionalities for future spintronics applications.

  10. Comparison of band-to-band tunneling models in Si and Si—Ge junctions

    International Nuclear Information System (INIS)

    Jiao Yipeng; Wang Taihuan; Wei Kangliang; Du Gang; Liu Xiaoyan

    2013-01-01

    We compared several different band-to-band tunneling (BTBT) models with both Sentaurus and the two-dimensional full-band Monte Carlo simulator in Si homo-junctions and Si—Ge hetero-junctions. It was shown that in Si homo-junctions, different models could achieve similar results. However, in the Si—Ge hetero-junctions, there were significant differences among these models at high reverse biases (over 2 V). Compared to the nonlocal model, the local models in Sentaurus underrated the BTBT rate distinctly, and the Monte Carlo method was shown to give a better approximation. Additionally, it was found that in the Si region near the interface of the Si—Ge hetero-junctions, the direct tunneling rates increased largely due to the interaction of the band structures of Si and Ge. (semiconductor physics)

  11. Fabrication of sub-micron whole waffer SIS tunnel junctions for millimeter wave mixers

    International Nuclear Information System (INIS)

    Huq, S.E.; Blamire, M.G.; Evetts, J.E.; Hasko, D.G.; Ahmed, H.

    1991-01-01

    As a part of a programme for the development of a space-qualified sub-mm-wave mixer operating in the region of one terahertz we have been developing the processes required for the fabrication of submicron whole wafer tunnel junctions. Using the self-aligned whole-wafer process (SAWW) with electron beam lithography we have been able to reliably fabricate high quality (V m > 20 mV) submicron tunnel junctions from whole wafer Nb/AlO x /Nb structures. In particular we show that the junction quality is independent of size down to 0.3 μm 2 junction area. The problems of film stress, anodization, registration for electron beam lithography and lift-off, which limit the yield of good quality sub-micron scale junctions are addressed in this paper

  12. Terahertz Mixing Characteristics of NbN Superconducting Tunnel Junctions and Related Astronomical Observations

    Science.gov (United States)

    Li, J.

    2010-01-01

    High-sensitivity superconducting SIS (superconductor-insulator-superconductor) mixers are playing an increasingly important role in the terahertz (THz) astronomical observation, which is an emerging research frontier in modern astrophysics. Superconducting SIS mixers with niobium (Nb) tunnel junctions have reached a sensitivity close to the quantum limit, but have a frequency limit about 0.7 THz (i.e., gap frequency of Nb tunnel junctions). Beyond this frequency Nb superconducting films will absorb energetic photons (i.e., energy loss) to break Cooper pairs, thereby resulting in significant degradation of the mixer performance. Therefore, it is of particular interest to develop THz superconducting SIS mixers incorporating tunnel junctions with a larger energy gap. Niobium-nitride (NbN) superconducting tunnel junctions have been long known for their large energy gap, almost double that of Nb ones. With the introduction of epitaxially grown NbN films, the fabrication technology of NbN superconducting tunnel junctions has been considerably improved in the recent years. Nevertheless, their performances are still not as good as Nb ones, and furthermore they are not yet demonstrated in real astronomical applications. Given the facts mentioned above, in this paper we systematically study the quantum mixing behaviors of NbN superconducting tunnel junctions in the THz regime and demonstrate an astronomical testing observation with a 0.5 THz superconducting SIS mixer developed with NbN tunnel junctions. The main results of this study include: (1) successful design and fabrication of a 0.4˜0.6 THz waveguide mixing circuit with the high-dielectric-constant MgO substrate; (2) successful fabrication of NbN superconducting tunnel junctions with the gap voltage reaching 5.6 mV and the quality factor as high as 15; (3) demonstration of a 0.5 THz waveguide NbN superconducting SIS mixer with a measured receiver noise temperature (no correction) as low as five times the quantum limit

  13. Impact of semiconducting electrodes on the electroresistance of ferroelectric tunnel junctions

    Science.gov (United States)

    Asa, M.; Bertacco, R.

    2018-02-01

    Ferroelectric tunnel junctions are promising candidates for the realization of energy-efficient digital memories and analog memcomputing devices. In this work, we investigate the impact of a semiconducting layer in series to the junction on the sign of electroresistance. To this scope, we compare tunnel junctions fabricated out of Pt/BaTiO3/La1/3Sr2/3MnO3 (LSMO) and Pt/BaTiO3/Nb:SrTiO3 (Nb:STO) heterostructures, displaying an opposite sign of the electroresistance. By capacitance-voltage profiling, we observe a behavior typical of Metal-Oxide-Semiconductor tunnel devices in both cases but compatible with the opposite sign of charge carriers in the semiconducting layer. While Nb:STO displays the expected n-type semiconducting character, metallic LSMO develops an interfacial p-type semiconducting layer. The different types of carriers at the semiconducting interfaces and the modulation of the depleted region by the ferroelectric charge have a deep impact on electroresistance, possibly accounting for the different sign observed in the two systems.

  14. Quantum decrease of capacitance in a nanometer-sized tunnel junction

    Science.gov (United States)

    Untiedt, C.; Saenz, G.; Olivera, B.; Corso, M.; Sabater, C.; Pascual, J. I.

    2013-03-01

    We have studied the capacitance of the tunnel junction defined by the tip and sample of a Scanning Tunnelling Microscope through the measurement of the electrostatic forces and impedance of the junction. A decrease of the capacitance when a tunnel current is present has shown to be a more general phenomenon as previously reported in other systems. On another hand, an unexpected reduction of the capacitance is also observed when increasing the applied voltage above the work function energy of the electrodes to the Field Emission (FE) regime, and the decrease of capacitance due to a single FE-Resonance has been characterized. All these effects should be considered when doing measurements of the electronic characteristics of nanometer-sized electronic devices and have been neglected up to date. Spanish government (FIS2010-21883-C02-01, CONSOLIDER CSD2007-0010), Comunidad Valenciana (ACOMP/2012/127 and PROMETEO/2012/011)

  15. 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.

  16. Fabrication of magnetic tunnel junctions with a single-crystalline LiF tunnel barrier

    Science.gov (United States)

    Krishna Narayananellore, Sai; Doko, Naoki; Matsuo, Norihiro; Saito, Hidekazu; Yuasa, Shinji

    2018-04-01

    We fabricated Fe/LiF/Fe magnetic tunnel junctions (MTJs) by molecular beam epitaxy on a MgO(001) substrate, where LiF is an insulating tunnel barrier with the same crystal structure as MgO (rock-salt type). Crystallographical studies such as transmission electron microscopy and nanobeam electron diffraction observations revealed that the LiF tunnel barrier is single-crystalline and has a LiF(001)[100] ∥ bottom Fe(001)[110] crystal orientation, which is constructed in the same manner as MgO(001) on Fe(001). Also, the in-plane lattice mismatch between the LiF tunnel barrier and the Fe bottom electrode was estimated to be small (about 0.5%). Despite such advantages for the tunnel barrier of the MTJ, the observed tunnel magnetoresistance (MR) ratio was low (˜6% at 20 K) and showed a significant decrease with increasing temperature (˜1% at room temperature). The results imply that indirect tunneling and/or thermally excited carriers in the LiF tunnel barrier, in which the current basically is not spin-polarized, play a major role in electrical transport in the MTJ.

  17. Josephson tunnel junction microwave attenuator

    DEFF Research Database (Denmark)

    Koshelets, V. P.; Shitov, S. V.; Shchukin, A. V.

    1993-01-01

    A new element for superconducting electronic circuitry-a variable attenuator-has been proposed, designed, and successfully tested. The principle of operation is based on the change in the microwave impedance of a superconductor-insulator-superconductor (SIS) Josephson tunnel junction when dc biased...... at different points in the current-voltage characteristic. Both numerical calculations based on the Tien-Gordon theory and 70-GHz microwave experiments have confirmed the wide dynamic range (more than 15-dB attenuation for one stage) and the low insertion loss in the ''open'' state. The performance of a fully...

  18. Microscopic theory of the Coulomb based exchange coupling in magnetic tunnel junctions.

    Science.gov (United States)

    Udalov, O G; Beloborodov, I S

    2017-05-04

    We study interlayer exchange coupling based on the many-body Coulomb interaction between conduction electrons in magnetic tunnel junction. This mechanism complements the known interaction between magnetic layers based on virtual electron hopping (or spin currents). We find that these two mechanisms have different behavior on system parameters. The Coulomb based coupling may exceed the hopping based exchange. We show that the Coulomb based exchange interaction, in contrast to the hopping based coupling, depends strongly on the dielectric constant of the insulating layer. The dependence of the interlayer exchange interaction on the dielectric properties of the insulating layer in magnetic tunnel junction is similar to magneto-electric effect where electric and magnetic degrees of freedom are coupled. We calculate the interlayer coupling as a function of temperature and electric field for magnetic tunnel junction with ferroelectric layer and show that the exchange interaction between magnetic leads has a sharp decrease in the vicinity of the ferroelectric phase transition and varies strongly with external electric field.

  19. InP tunnel junctions for InP/InGaAs tandem solar cells

    Science.gov (United States)

    Vilela, Mauro F.; Freundlich, Alex; Renaud, P.; Medelci, N.; Bensaoula, A.

    1996-01-01

    We report, for the first time, an epitaxially grown InP p(+)/n(++) tunnel junction. A diode with peak current densities up to 1600 A/cm and maximum specific resistivities (Vp/Ip - peak voltage to peak current ratio) in the range of 10(exp -4)Omega cm(exp 2) is obtained. This peak current density is comparable to the highest results previously reported for lattice matched In(0.53)Ga(0.47)As tunnel junctions. Both results were obtained using chemical beam epitaxy (CBE). In this paper we discuss the electrical characteristics of these tunnel diodes and how the growth conditions influence them.

  20. Josephson Junction as a Magnetic Switch

    Science.gov (United States)

    Cai, Liufei; Chudnovsky, Eugene

    2011-03-01

    We study electromagnetic interaction of a nanomagnet with a weak superconducting link. Equations that govern coupled dynamics of the two systems are derived and investigated numerically. We show that despite very weak magnetic field generated by the weak link, a time-dependent bias voltage applied to the link can initiate a non-linear dynamics of the nanomagnet that leads to the reversal of its magnetic moment. We also consider quantum problem in which a nanomagnet interacting with a weak link is treated as a two-state spin system due to quantum tunneling between spin-up and spin-down states. L. Cai and E. M. Chudnovsky, Phys. Rev B 82, 104429 (2010).

  1. Superconducting Tunnel Junction Arrays for UV Photon Detection, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — An innovative method is described for the fabrication of superconducting tunnel junction (STJ) detector arrays offering true "three dimensional" imaging throughout...

  2. Inter-band phase fluctuations in macroscopic quantum tunneling of multi-gap superconducting Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Asai, Hidehiro, E-mail: hd-asai@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ota, Yukihiro [CCSE, Japan Atomic Energy Agency, Kashiwa, Chiba 277-8587 (Japan); Kawabata, Shiro [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Nori, Franco [CEMS, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 (United States)

    2014-09-15

    Highlights: • We study MQT in Josephson junctions composed of multi-gap superconductors. • We derive a formula of the MQT escape rate for multiple phase differences. • We investigate the effect of inter-band phase fluctuation on MQT. • The MQT escape rate is significantly enhanced by the inter-band phase fluctuation. - Abstract: We theoretically investigate macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multi-gap superconductor. In such Josephson junctions, phase differences for each tunneling channel are defined, and the fluctuation of the relative phase differences appear which is referred to as Josephson–Leggett’s mode. We take into account the effect of the fluctuation in the tunneling process and calculate the MQT escape rate for various junction parameters. We show that the fluctuation of relative phase differences drastically enhances the escape rate.

  3. Inter-band phase fluctuations in macroscopic quantum tunneling of multi-gap superconducting Josephson junctions

    International Nuclear Information System (INIS)

    Asai, Hidehiro; Ota, Yukihiro; Kawabata, Shiro; Nori, Franco

    2014-01-01

    Highlights: • We study MQT in Josephson junctions composed of multi-gap superconductors. • We derive a formula of the MQT escape rate for multiple phase differences. • We investigate the effect of inter-band phase fluctuation on MQT. • The MQT escape rate is significantly enhanced by the inter-band phase fluctuation. - Abstract: We theoretically investigate macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multi-gap superconductor. In such Josephson junctions, phase differences for each tunneling channel are defined, and the fluctuation of the relative phase differences appear which is referred to as Josephson–Leggett’s mode. We take into account the effect of the fluctuation in the tunneling process and calculate the MQT escape rate for various junction parameters. We show that the fluctuation of relative phase differences drastically enhances the escape rate

  4. Theory of spin-dependent tunnelling in magnetic junctions

    International Nuclear Information System (INIS)

    Mathon, J.

    2002-01-01

    Rigorous theory of the tunnelling magnetoresistance (TMR) based on the real-space Kubo formula and fully realistic tight-binding bands fitted to an ab initio band structure is described. It is first applied to calculate the TMR of two Co electrodes separated by a vacuum gap. The calculated TMR ratio reaches ∼65% in the tunnelling regime but can be as high as 280% in the metallic regime when the vacuum gap is of the order of the Co interatomic distance (abrupt domain wall). It is also shown that the spin polarization P of the tunnelling current is negative in the metallic regime but becomes positive P∼35% in the tunnelling regime. Calculation of the TMR of an epitaxial Fe/MgO/Fe(001) junction is also described. The calculated optimistic TMR ratio is in excess of 1000% for an MgO barrier of ∼20 atomic planes and the spin polarization of the tunnelling current is positive for all MgO thicknesses. It is also found that spin-dependent tunnelling in an Fe/MgO/Fe(001) junction is not entirely determined by states at the Γ point (k parallel = 0) even for MgO thicknesses as large as ∼20 atomic planes. Finally, it is demonstrated that the TMR ratio calculated from the Kubo formula remains non-zero when one of the Co electrodes is covered with a copper layer. It is shown that non-zero TMR is due to quantum well states in the Cu layer which do not participate in transport. Since these only occur in the down-spin channel, their loss from transport creates a spin asymmetry of electrons tunnelling from a Cu interlayer, i.e. non-zero TMR. Numerical modelling is used to show that diffuse scattering from a random distribution of impurities in the barrier may cause quantum well states to evolve into propagating states, in which case the spin asymmetry of the non-magnetic layer is lost and with it the TMR. (author)

  5. Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope

    OpenAIRE

    Nazin, G. V.; Wu, S. W.; Ho, W.

    2005-01-01

    The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks correspondi...

  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. Fabrication and dc characteristics of small-area tantalum and niobium superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Face, D.W.; Prober, D.E.

    1987-01-01

    We discuss the fabrication and dc electrical characteristics of small-area (1--6 μm 2 ) superconducting tunnel junctions with Ta or Nb base electrodes and Pb or Pb/sub 0.9/Bi/sub 0.1/ counterelectrodes. These junctions have very small subgap leakage currents, a ''sharp'' current rise at the sum-gap voltage, and show strong quantum effects when used as microwave mixers. The use of a low-energy (--150 eV) ion cleaning process and a novel step-defined fabrication process that eliminates photoresist processing after base electrode deposition are discussed. Tunnel barriers formed by dc glow discharge oxidation were the most successful. Tunnel barrier formation by thermal oxidation and ion-beam oxidation is also discussed. An oxidized Ta overlayer (--7 nm thick) was found to improve the characteristics of Nb-based junctions. The electrical characteristics of junctions with different electrode and barrier materials are presented and discussed in terms of the physical mechanisms that lead to excess subgap current and to a width of the current rise at the sum-gap voltage

  8. Influence of quasiparticle multi-tunneling on the energy flow through the superconducting tunnel junction

    International Nuclear Information System (INIS)

    Samedov, V. V.; Tulinov, B. M.

    2011-01-01

    Superconducting tunnel junction (STJ) detector consists of two layers of superconducting material separated by thin insulating barrier. An incident particle produces in superconductor excess nonequilibrium quasiparticles. Each quasiparticle in superconductor should be considered as quantum superposition of electron-like and hole-like excitations. This duality nature of quasiparticle leads to the effect of multi-tunneling. Quasiparticle starts to tunnel back and forth through the insulating barrier. After tunneling from biased electrode quasiparticle loses its energy via phonon emission. Eventually, the energy that equals to the difference in quasiparticle energy between two electrodes is deposited in the signal electrode. Because of the process of multi-tunneling, one quasiparticle can deposit energy more than once. In this work, the theory of branching cascade processes was applied to the process of energy deposition caused by the quasiparticle multi-tunneling. The formulae for the mean value and variance of the energy transferred by one quasiparticle into heat were derived. (authors)

  9. NIS tunnel junction as an x-ray photon sensor

    Science.gov (United States)

    Azgui, Fatma; Mears, Carl A.; Labov, Simon E.; Frank, Matthias A.; Sadoulet, Bernard; Brunet, E.; Hiller, Lawrence J.; Lindeman, Mark A.; Netel, Harrie

    1995-09-01

    This work presents the first results of our development of normal-insulating-superconducting tunnel junctions used as energy dispersive detectors for low energy particles. The device described here is a Ag/Al(subscript 2)O(subscript 3)/Al tunnel junction of area 1.5 multiplied by 10(superscript 4) micrometer squared with thicknesses of 200 nm for the normal Ag strip and 100 nm for the superconducting Al film. Two different high-speed SQUID systems manufactured by quantum magnetics and HYPRES, respectively, were used for the readout of this device. At 80 mK bath temperature we obtained an energy resolution DeltaE(subscript FWHM) equals 250 eV for 5.89 keV x rays absorbed directly in the normal metal. This energy resolution appears to be limited in large part by the observed strong position dependence of the device response.

  10. Cotunneling enhancement of magnetoresistance in double magnetic tunnel junctions with embedded superparamagnetic NiFe nanoparticles

    International Nuclear Information System (INIS)

    Dempsey, K.J.; Arena, D.; Hindmarch, A.T.; Wei, H.X.; Qin, Q.H.; Wen, Z.C.; Wang, W.X.; Vallejo-Fernandez, G.; Han, X.F.; Marrows, C.H.

    2010-01-01

    Temperature and bias voltage-dependent transport characteristics are presented for double magnetic tunnel junctions (DMTJs) with self-assembled NiFe nanoparticles embedded between insulating alumina barriers. The junctions with embedded nanoparticles are compared to junctions with a single barrier of comparable size and growth conditions. The embedded particles are characterized using x-ray absorption spectroscopy, transmission electron microscopy, and magnetometry techniques, showing that they are unoxidized and remain superparamagnetic to liquid helium temperatures. The tunneling magnetoresistance (TMR) for the DMTJs is lower than the control samples, however, for the DMTJs an enhancement in TMR is seen in the Coulomb blockade region. Fitting the transport data in this region supports the theory that cotunneling is the dominant electron transport process within the Coulomb blockade region, sequential tunneling being suppressed. We therefore see an enhanced TMR attributed to the change in the tunneling process due to the interplay of the Coulomb blockade and spin-dependent tunneling through superparamagnetic nanoparticles, and develop a simple model to quantify the effect, based on the fact that our nanoparticles will appear blocked when measured on femtosecond tunneling time scales.

  11. Macroscopic quantum tunneling in 1 μm Nb junctions below 100mK

    International Nuclear Information System (INIS)

    Voss, R.F.; Webb, R.A.

    1981-01-01

    The transition probabilities out of the superconducting state of low current density 1 μm Nb Josephson junctions with capacitance < 0.15 pF have been measured as a function of temperature T down to 3 mK. Below 100 mK the distribution widths become independent of T. Junctions with critical currents that differ by an order of magnitude have the same dependence of relative width on T. The low T results are interpreted in terms of quantum tunneling of the (macroscopic) junction phase. The observed low temperature widths are smaller than expected indicating the necessity of corrections to the simple WKB tunneling rates. (orig.)

  12. 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.

  13. Tunneling conductance oscillations in spin-orbit coupled metal-insulator-superconductor junctions

    Science.gov (United States)

    Kapri, Priyadarshini; Basu, Saurabh

    2018-01-01

    The tunneling conductance for a device consisting of a metal-insulator-superconductor (MIS) junction is studied in presence of Rashba spin-orbit coupling (RSOC) via an extended Blonder-Tinkham-Klapwijk formalism. We find that the tunneling conductance as a function of an effective barrier potential that defines the insulating layer and lies intermediate to the metallic and superconducting electrodes, displays an oscillatory behavior. The tunneling conductance shows high sensitivity to the RSOC for certain ranges of this potential, while it is insensitive to the RSOC for others. Additionally, when the period of oscillations is an odd multiple of a certain value of the effective potential, the conductance spectrum as a function of the biasing energy demonstrates a contrasting trend with RSOC, compared to when it is not an odd multiple. The explanations for the observation can be found in terms of a competition between the normal and Andreev reflections. Similar oscillatory behavior of the conductance spectrum is also seen for other superconducting pairing symmetries, thereby emphasizing that the insulating layer plays a decisive role in the conductance oscillations of a MIS junction. For a tunable Rashba coupling, the current flowing through the junction can be controlled with precision.

  14. Ultrafast demagnetization enhancement in CoFeB/MgO/CoFeB magnetic tunneling junction driven by spin tunneling current.

    Science.gov (United States)

    He, Wei; Zhu, Tao; Zhang, Xiang-Qun; Yang, Hai-Tao; Cheng, Zhao-Hua

    2013-10-07

    The laser-induced ultrafast demagnetization of CoFeB/MgO/CoFeB magnetic tunneling junction is exploited by time-resolved magneto-optical Kerr effect (TRMOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electrons tunneling current. It opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions.

  15. Dynamics of a nanoscale Josephson junction probed by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ast, Christian R.; Jaeck, Berthold; Eltschka, Matthias; Etzkorn, Markus [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Kern, Klaus [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany); Institut de Physique de la Matiere Condensee, EPFL, Lausanne (Switzerland)

    2015-07-01

    The Josephson effect is an intriguing phenomenon as it presents an interplay of different energy scales, such as the Josephson energy ε{sub J} (critical current), charging energy ε{sub C}, and temperature T. Using a scanning tunneling microscope (STM) operating at a base temperature of 15 mK, we create a nanoscale superconductor-vacuum-superconductor tunnel junction in an extremely underdamped regime (Q>>10). We observe extremely small retrapping currents also owing to strongly reduced ohmic losses in the well-developed superconducting gaps. While formally operating in the zero temperature limit, i.e. the temperature T is smaller than the Josephson plasma frequency ω{sub J} (k{sub B}T<<ℎω{sub J}=√(8ε{sub J}ε{sub C})), experimentally other phenomena, such as stray photons, may perturb the Josephson junction, leading to an effectively higher temperature. The dynamics of the Josephson junction can be addressed experimentally by looking at characteristic parameters, such as the switching current and the retrapping current. We discuss the dynamics of the Josephson junction in the context of reaching the zero temperature limit.

  16. 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...

  17. Universal tunneling behavior in technologically relevant P/N junction diodes

    International Nuclear Information System (INIS)

    Solomon, Paul M.; Jopling, Jason; Frank, David J.; D'Emic, Chris; Dokumaci, O.; Ronsheim, P.; Haensch, W.E.

    2004-01-01

    Band-to-band tunneling was studied in ion-implanted P/N junction diodes with profiles representative of present and future silicon complementary metal-oxide-silicon (CMOS) field effect transistors. Measurements were done over a wide range of temperatures and implant parameters. Profile parameters were derived from analysis of capacitance versus voltage characteristics, and compared to secondary-ion mass spectroscopy analysis. When the tunneling current was plotted against the effective tunneling distance (tunneling distance corrected for band curvature) a quasi-universal exponential reduction of tunneling current versus, tunneling distance was found with an attenuation length of 0.38 nm, corresponding to a tunneling effective mass of 0.29 times the free electron mass (m 0 ), and an extrapolated tunneling current at zero tunnel distance of 5.3x10 7 A/cm 2 at 300 K. These results are directly applicable for predicting drain to substrate currents in CMOS transistors on bulk silicon, and body currents in CMOS transistors in silicon-on-insulator

  18. Magnetoresistance in Co/AlO sub x /Co tunnel junction arrays

    CERN Document Server

    Urech, M; Haviland, D B

    2002-01-01

    Lateral arrays of Co/AlO sub x /Co junctions with dimensions down to 60 nm and inter-junction separations approx 60-100 nm have been fabricated and analyzed for possible coherent tunneling effects. Extra attention is paid to avoid uncertainties due to inconsistencies in switching and/or resistance of successive barriers. We observe approx 10% magnetoresistance enhancement at moderate bias in double junctions that cannot be accounted for by a simple model of two resistsors in series.

  19. Long Josephson tunnel junctions with doubly connected electrodes

    DEFF Research Database (Denmark)

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

    2012-01-01

    of such experiments, the number of magnetic flux quanta spontaneously trapped in a superconducting loop was measured by means of a long Josephson tunnel junction built on top of the loop itself. We have analyzed this system and found a number of interesting features not occurring in the conventional case with simply...... connected electrodes. In particular, the fluxoid quantization results in a frustration of the Josephson phase, which, in turn, reduces the junction critical current. Further, the possible stable states of the system are obtained by a self-consistent application of the principle of minimum energy...

  20. 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.

  1. 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.

  2. Coherence in a transmon qubit with epitaxial tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Weides, Martin [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Karlsruhe Institute of Technology (Germany); Kline, Jeffrey; Vissers, Michael; Sandberg, Martin; Pappas, David [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Wisbey, David [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Saint Louis University, St. Louis, Missouri 63103 (United States); Johnson, Blake; Ohki, Thomas [Raytheon BBN Technologies, Cambridge, Massachusetts 02138 (United States)

    2012-07-01

    Transmon qubits based on epitaxial tunnel junctions and interdigitated capacitors were developed. This multileveled qubit, patterned by use of all-optical lithography, is a step towards scalable qubits with a high integration density. The relaxation time T{sub 1} is.72-.86 {mu} sec and the ensemble dephasing time T{sub 2}{sup *} is slightly larger than T{sub 1}. The dephasing time T{sub 2} (1.36 {mu} sec) is nearly energy-relaxation-limited. Qubit spectroscopy yields weaker level splitting than observed in qubits with amorphous barriers in equivalent-size junctions. The qubit's inferred microwave loss closely matches the weighted losses of the individual elements (junction, wiring dielectric, and interdigitated capacitor), determined by independent resonator measurements.

  3. Measured Temperature Dependence of the cos-phi Conductance in Josephson Tunnel Junctions

    DEFF Research Database (Denmark)

    Sørensen, O. H.; Mygind, Jesper; Pedersen, Niels Falsig

    1977-01-01

    The temperature dependence of the cosϕ conductance in Sn-O-Sn Josephson tunnel junctions has been measured just below the critical temperature, Tc. From the resonant microwave response at the junction plasma frequency as the temperature is decreased from Tc it is deduced that the amplitude of the...

  4. 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

    2015-01-01

    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. PMID:26681336

  5. Current-voltage characteristics of a tunnel junction with resonant centers

    International Nuclear Information System (INIS)

    Ivanov, T.; Valtchinov, V.

    1994-05-01

    We calculated the I-V characteristics of a tunnel junction containing impurities in the barrier. We consider the indirect resonant tunneling involving the impurities. The Coulomb repulsion energy E c between two electrons with opposite spins simultaneously residing on the impurity is introduced by an Anderson Hamiltonian. At low temperatures T is much less than E c the I-V characteristics is linear in V both for V c and for V>E c and changes slope at V=E c . This behaviour reflects the energy spectrum of the impurity electrons - the finite value of the charging energy E c . At T ∼ E c the junction reveals an ohmic-like behaviour as a result of the smearing out of the charging effects by the thermal fluctuations. (author). 10 refs, 2 figs

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

    KAUST Repository

    Useinov, Arthur; Mryasov, Oleg; Kosel, Jü rgen

    2011-01-01

    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

  7. Observation of gap inhomogeneity in superconducting aluminum tunnel junctions

    International Nuclear Information System (INIS)

    Gilmartin, H.R.

    1982-01-01

    Experiments using a novel technique to investigate spatial variations in the superconducting gap parameter of aluminum films driven out of equilibrium by intense tunnel injection are described. The technique features fine spatial and energy resolution of the gap parameter. The experiments employed a finely focused laser spot scanned across the surface of a double tunnel junction sandwich to produce a very weak electrical signal that was analyzed to determine the gap parameter as a function of position in the plane of the device. Technical aspects of the problem are emphasized, since a new technique is presented. An elaborate explanation of the origin and analysis of the laser induced signal is given, as well as a detailed description of the experimental apparatus. Very briefly, the principle of operation is that a large flux of quasiparticles is injected through the lower junction of the sandwich into the middle aluminum film, and the upper junction serves to detect the effects of that injection. The middle film takes on two or more values of the gap parameter under injection, presumably indicating spatial variation. The presence of a small laser spot on a given point on the device perturbs the potential on the detector junction very slightly. That perturbation is measured as a function of bias current to determine the gap parameter of the middle film at that point. The spot is scanned in a raster pattern to produce a picture of the space dependence of the gap parameter

  8. Optically induced bistable states in metal/tunnel-oxide/semiconductor /MTOS/ junctions

    Science.gov (United States)

    Lai, S. K.; Dressendorfer, P. V.; Ma, T. P.; Barker, R. C.

    1981-01-01

    A new switching phenomenon in metal-oxide semiconductor tunnel junction has been discovered. With a sufficiently large negative bias applied to the electrode, incident visible light of intensity greater than about 1 microW/sq cm causes the reverse-biased junction to switch from a low-current to a high-current state. It is believed that hot-electron-induced impact ionization provides the positive feedback necessary for switching, and causes the junction to remain in its high-current state after the optical excitation is removed. The junction may be switched back to the low-current state electrically. The basic junction characteristics have been measured, and a simple model for the switching phenomenon has been developed.

  9. 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.

  10. Multiband model for tunneling in MgB2 junctions

    NARCIS (Netherlands)

    Brinkman, Alexander; Golubov, Alexandre Avraamovitch; Rogalla, Horst; Dolgov, O.V.; Kortus, J.; Kong, Y.; Jepsen, O.; Andersen, O.K.

    2002-01-01

    A theoretical model for quasiparticle and Josephson tunneling in multiband superconductors is developed and applied to MgB2-based junctions. The gap functions in different bands in MgB2 are obtained from an extended Eliashberg formalism, using the results of band structure calculations. The

  11. High-Performance Flexible Magnetic Tunnel Junctions for Smart Miniaturized Instruments

    KAUST Repository

    Amara, Selma.; Sevilla, Gallo. A. Torres; Hawsawi, Mayyada.; Mashraei, Yousof.; Mohammed, Hanan .; Cruz, Melvin E.; Ivanov, Yurii. P.; Jaiswal, Samridh.; Jakob, Gerhard.; Klä ui, Mathias.; Hussain, Muhammad.; Kosel, Jurgen.

    2018-01-01

    , where size and weight are critical parameters. Given their prevalence on the sensors market, flexible magnetic sensors play a major role in this progress. For many high-performance applications, magnetic tunnel junctions (MTJs) have become the first

  12. 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

  13. Interconnected magnetic tunnel junctions for spin-logic applications

    Science.gov (United States)

    Manfrini, Mauricio; Vaysset, Adrien; Wan, Danny; Raymenants, Eline; Swerts, Johan; Rao, Siddharth; Zografos, Odysseas; Souriau, Laurent; Gavan, Khashayar Babaei; Rassoul, Nouredine; Radisic, Dunja; Cupak, Miroslav; Dehan, Morin; Sayan, Safak; Nikonov, Dmitri E.; Manipatruni, Sasikanth; Young, Ian A.; Mocuta, Dan; Radu, Iuliana P.

    2018-05-01

    With the rapid progress of spintronic devices, spin-logic concepts hold promises of energy-delay conscious computation for efficient logic gate operations. We report on the electrical characterization of domain walls in interconnected magnetic tunnel junctions. By means of spin-transfer torque effect, domains walls are produced at the common free layer and its propagation towards the output pillar sensed by tunneling magneto-resistance. Domain pinning conditions are studied quasi-statically showing a strong dependence on pillar size, ferromagnetic free layer width and inter-pillar distance. Addressing pinning conditions are detrimental for cascading and fan-out of domain walls across nodes, enabling the realization of domain-wall-based logic technology.

  14. Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions

    International Nuclear Information System (INIS)

    Zou Jianfei; Jin Guojun; Ma Yuqiang

    2009-01-01

    We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.

  15. Negative tunnel magnetoresistance and spin transport in ferromagnetic graphene junctions.

    Science.gov (United States)

    Zou, Jianfei; Jin, Guojun; Ma, Yu-Qiang

    2009-03-25

    We study the tunnel magnetoresistance (TMR) and spin transport in ferromagnetic graphene junctions composed of ferromagnetic graphene (FG) and normal graphene (NG) layers. It is found that the TMR in the FG/NG/FG junction oscillates from positive to negative values with respect to the chemical potential adjusted by the gate voltage in the barrier region when the Fermi level is low enough. Particularly, the conventionally defined TMR in the FG/FG/FG junction oscillates periodically from a positive to negative value with increasing the barrier height at any Fermi level. The spin polarization of the current through the FG/FG/FG junction also has an oscillating behavior with increasing barrier height, whose oscillating amplitude can be modulated by the exchange splitting in the ferromagnetic graphene.

  16. Voltage-driven versus current-driven spin torque in anisotropic tunneling junctions

    KAUST Repository

    Manchon, Aurelien

    2011-01-01

    Nonequilibrium spin transport in a magnetic tunnel junction comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is studied theoretically. The interfacial SOI generates a spin torque of the form T=T∥ M×(z× M)+T⊥ z× M, even in the absence of an external spin polarizer. For thick and large tunnel barriers, the torque reduces to the perpendicular component T⊥, which can be electrically tuned by applying a voltage across the insulator. In the limit of thin and low tunnel barriers, the in-plane torque T∥ emerges, proportional to the tunneling current density. Experimental implications on magnetic devices are discussed. © 2011 IEEE.

  17. Voltage-driven versus current-driven spin torque in anisotropic tunneling junctions

    KAUST Repository

    Manchon, Aurelien

    2011-10-01

    Nonequilibrium spin transport in a magnetic tunnel junction comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is studied theoretically. The interfacial SOI generates a spin torque of the form T=T∥ M×(z× M)+T⊥ z× M, even in the absence of an external spin polarizer. For thick and large tunnel barriers, the torque reduces to the perpendicular component T⊥, which can be electrically tuned by applying a voltage across the insulator. In the limit of thin and low tunnel barriers, the in-plane torque T∥ emerges, proportional to the tunneling current density. Experimental implications on magnetic devices are discussed. © 2011 IEEE.

  18. GaN-based vertical-cavity laser performance improvements using tunnel-junction-cascaded active regions

    International Nuclear Information System (INIS)

    Piprek, Joachim

    2014-01-01

    This Letter investigates the output power enhancement achieved by tunnel junction insertion into the InGaN multi-quantum well (MQW) active region of a 410 nm vertical-cavity surface-emitting laser which enables the repeated use of carriers for light generation (carrier recycling). While the number of quantum wells remains unchanged, the tunnel junction eliminates absorption caused by the non-uniform MQW carrier distribution. The thermal resistance drops and the excess bias lead to a surprisingly small rise in self-heating.

  19. The anisotropic tunneling behavior of spin transport in graphene-based magnetic tunneling junction

    Science.gov (United States)

    Pan, Mengchun; Li, Peisen; Qiu, Weicheng; Zhao, Jianqiang; Peng, Junping; Hu, Jiafei; Hu, Jinghua; Tian, Wugang; Hu, Yueguo; Chen, Dixiang; Wu, Xuezhong; Xu, Zhongjie; Yuan, Xuefeng

    2018-05-01

    Due to the theoretical prediction of large tunneling magnetoresistance (TMR), graphene-based magnetic tunneling junction (MTJ) has become an important branch of high-performance spintronics device. In this paper, the non-collinear spin filtering and transport properties of MTJ with the Ni/tri-layer graphene/Ni structure were studied in detail by utilizing the non-equilibrium Green's formalism combined with spin polarized density functional theory. The band structure of Ni-C bonding interface shows that Ni-C atomic hybridization facilitates the electronic structure consistency of graphene and nickel, which results in a perfect spin filtering effect for tri-layer graphene-based MTJ. Furthermore, our theoretical results show that the value of tunneling resistance changes with the relative magnetization angle of two ferromagnetic layers, displaying the anisotropic tunneling behavior of graphene-based MTJ. This originates from the resonant conduction states which are strongly adjusted by the relative magnetization angles. In addition, the perfect spin filtering effect is demonstrated by fitting the anisotropic conductance with the Julliere's model. Our work may serve as guidance for researches and applications of graphene-based spintronics device.

  20. Terahertz time domain interferometry of a SIS tunnel junction and a quantum point contact

    Energy Technology Data Exchange (ETDEWEB)

    Karadi, Chandu [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1995-09-01

    The author has applied the Terahertz Time Domain Interferometric (THz-TDI) technique to probe the ultrafast dynamic response of a Superconducting-Insulating-Superconducting (SIS) tunnel junction and a Quantum Point Contact (QPC). The THz-TDI technique involves monitoring changes in the dc current induced by interfering two picosecond electrical pulses on the junction as a function of time delay between them. Measurements of the response of the Nb/AlOxNb SIS tunnel junction from 75--200 GHz are in full agreement with the linear theory for photon-assisted tunneling. Likewise, measurements of the induced current in a QPC as a function of source-drain voltage, gate voltage, frequency, and magnetic field also show strong evidence for photon-assisted transport. These experiments together demonstrate the general applicability of the THz-TDI technique to the characterization of the dynamic response of any micron or nanometer scale device that exhibits a non-linear I-V characteristic.

  1. Terahertz time domain interferometry of a SIS tunnel junction and a quantum point contact

    International Nuclear Information System (INIS)

    Karadi, C.; Lawrence Berkeley Lab., CA

    1995-09-01

    The author has applied the Terahertz Time Domain Interferometric (THz-TDI) technique to probe the ultrafast dynamic response of a Superconducting-Insulating-Superconducting (SIS) tunnel junction and a Quantum Point Contact (QPC). The THz-TDI technique involves monitoring changes in the dc current induced by interfering two picosecond electrical pulses on the junction as a function of time delay between them. Measurements of the response of the Nb/AlO x /Nb SIS tunnel junction from 75--200 GHz are in full agreement with the linear theory for photon-assisted tunneling. Likewise, measurements of the induced current in a QPC as a function of source-drain voltage, gate voltage, frequency, and magnetic field also show strong evidence for photon-assisted transport. These experiments together demonstrate the general applicability of the THz-TDI technique to the characterization of the dynamic response of any micron or nanometer scale device that exhibits a non-linear I-V characteristic. 133 refs., 49 figs

  2. 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.

  3. Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

    Science.gov (United States)

    Louarn, K.; Claveau, Y.; Marigo-Lombart, L.; Fontaine, C.; Arnoult, A.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

    2018-04-01

    In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm‑2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

  4. Large Magnetoresistance at Room Temperature in Organic Molecular Tunnel Junctions with Nonmagnetic Electrodes.

    Science.gov (United States)

    Xie, Zuoti; Shi, Sha; Liu, Feilong; Smith, Darryl L; Ruden, P Paul; Frisbie, C Daniel

    2016-09-27

    We report room-temperature resistance changes of up to 30% under weak magnetic fields (0.1 T) for molecular tunnel junctions composed of oligophenylene thiol molecules, 1-2 nm in length, sandwiched between gold contacts. The magnetoresistance (MR) is independent of field orientation and the length of the molecule; it appears to be an interface effect. Theoretical analysis suggests that the source of the MR is a two-carrier (two-hole) interaction at the interface, resulting in spin coupling between the tunneling hole and a localized hole at the Au/molecule contact. Such coupling leads to significantly different singlet and triplet transmission barriers at the interface. Even weak magnetic fields impede spin relaxation processes and thus modify the ratio of holes tunneling via the singlet state versus the triplet state, which leads to the large MR. Overall, the experiments and analysis suggest significant opportunities to explore large MR effects in molecular tunnel junctions based on widely available molecules.

  5. Quasiparticle losses at the surface of superconducting tunnel junction detectors

    NARCIS (Netherlands)

    Panteleit, F.; Schroeder, T.; Martin, J.; Huebener, R.P.; Kiewiet, F.B.; Berg, van den M.L.; Korte, P.A.J.

    1999-01-01

    Superconducting tunnel junctions (STJs) are promising as high energy resolution x-ray detectors. However, the theoretical limit of the energy resolution of STJs has not yet been reached for several reasons. In many cases quasiparticle losses limit the energy resolution. We have investigated STJs

  6. 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.

  7. Molecular nanomagnets

    CERN Document Server

    Gatteschi, Dante; Villain, Jacques

    2006-01-01

    Nanomagnetism is a rapidly expanding area of research which appears to be able to provide novel applications. Magnetic molecules are at the very bottom of the possible size of nanomagnets and they provide a unique opportunity to observe the coexistence of classical and quantum properties. The discovery in the early 90's that a cluster comprising twelve manganese ions shows hysteresis of molecular origin, and later proved evidence of quantum effects, opened a new research area whichis still flourishing through the collaboration of chemists and physicists. This book is the first attempt to cover

  8. Exploring the Tilt-Angle Dependence of electron tunneling across Molecular junction of Self-Assembled Alkanethiols

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Munuera, C.; Ocal, C.

    2009-01-01

    Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current−voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions...... for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect....

  9. Coherent tunnelling conductance in normal-metal/d-wave superconductor/normal-metal double tunnel junctions

    International Nuclear Information System (INIS)

    Dong, Z C; Zheng, Z M; Xing, D Y

    2004-01-01

    Taking simultaneously into account the electron-injected current from one normal-metal (N) electrode and the hole-injected current from the other N electrode, we study the coherent tunnelling conductance and quantum interference effects in N/d-wave superconductor (S)/N double tunnel junctions. It is found that oscillations of all quasiparticle transport coefficients and the conductance spectrum with quasiparticle energy and thickness of the d-wave S depend to a great extent on the crystal orientation of the d-wave S. The zero-bias conductance peak is gradually lowered with increasing barrier strength and/or temperature, its magnitude exhibiting damped oscillatory behaviour with thickness of S

  10. An x-ray detector using superconducting aluminum tunnel junctions

    International Nuclear Information System (INIS)

    Barber, W.C.; Bland, R.W.; Carpenter, J.W.; Johnson, R.T.; Laws, K.E.; Lockhart, J.; Lee, J.S.; Watson, R.M.

    1992-01-01

    We report on tests of a prototype detector for 6-keV X-rays, using series arrays of tunnel junction. Tests with higher-energy particles indicate an energy resolution of 4 keV, at 0.3K and with a warm pre-amp. At lower temperatures and with a cooled FET, the resolution should approach 100 eV

  11. Multiband corrections for the semi-classical simulation of interband tunneling in GaAs tunnel junctions

    Science.gov (United States)

    Louarn, K.; Claveau, Y.; Hapiuk, D.; Fontaine, C.; Arnoult, A.; Taliercio, T.; Licitra, C.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

    2017-09-01

    The aim of this study is to investigate the impact of multiband corrections on the current density in GaAs tunnel junctions (TJs) calculated with a refined yet simple semi-classical interband tunneling model (SCITM). The non-parabolicity of the considered bands and the spin-orbit effects are considered by using a recently revisited SCITM available in the literature. The model is confronted to experimental results from a series of molecular beam epitaxy grown GaAs TJs and to numerical results obtained with a full quantum model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We emphasize the importance of considering the non-parabolicity of the conduction band by two different measurements of the energy-dependent electron effective mass in N-doped GaAs. We also propose an innovative method to compute the non-uniform electric field in the TJ for the SCITM simulations, which is of prime importance for a successful operation of the model. We demonstrate that, when considering the multiband corrections and this new computation of the non-uniform electric field, the SCITM succeeds in predicting the electrical characteristics of GaAs TJs, and are also in agreement with the quantum model. Besides the fundamental study of the tunneling phenomenon in TJs, the main benefit of this SCITM is that it can be easily embedded into drift-diffusion software, which are the most widely-used simulation tools for electronic and opto-electronic devices such as multi-junction solar cells, tunnel field-effect transistors, or vertical-cavity surface-emitting lasers.

  12. Integrating atomic layer deposition and ultra-high vacuum physical vapor deposition for in situ fabrication of tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Elliot, Alan J., E-mail: alane@ku.edu, E-mail: jwu@ku.edu; Malek, Gary A.; Lu, Rongtao; Han, Siyuan; Wu, Judy Z., E-mail: alane@ku.edu, E-mail: jwu@ku.edu [Department of Physics and Astronomy, The University of Kansas, Lawrence, Kansas 66045 (United States); Yu, Haifeng; Zhao, Shiping [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2014-07-15

    Atomic Layer Deposition (ALD) is a promising technique for growing ultrathin, pristine dielectrics on metal substrates, which is essential to many electronic devices. Tunnel junctions are an excellent example which require a leak-free, ultrathin dielectric tunnel barrier of typical thickness around 1 nm between two metal electrodes. A challenge in the development of ultrathin dielectric tunnel barriers using ALD is controlling the nucleation of dielectrics on metals with minimal formation of native oxides at the metal surface for high-quality interfaces between the tunnel barrier and metal electrodes. This poses a critical need for integrating ALD with ultra-high vacuum (UHV) physical vapor deposition. In order to address these challenges, a viscous-flow ALD chamber was designed and interfaced to an UHV magnetron sputtering chamber via a load lock. A sample transportation system was implemented for in situ sample transfer between the ALD, load lock, and sputtering chambers. Using this integrated ALD-UHV sputtering system, superconductor-insulator-superconductor (SIS) Nb-Al/Al{sub 2}O{sub 2}/Nb Josephson tunnel junctions were fabricated with tunnel barriers of thickness varied from sub-nm to ∼1 nm. The suitability of using an Al wetting layer for initiation of the ALD Al{sub 2}O{sub 3} tunnel barrier was investigated with ellipsometry, atomic force microscopy, and electrical transport measurements. With optimized processing conditions, leak-free SIS tunnel junctions were obtained, demonstrating the viability of this integrated ALD-UHV sputtering system for the fabrication of tunnel junctions and devices comprised of metal-dielectric-metal multilayers.

  13. Tuning the tunneling magnetoresistance by using fluorinated graphene in graphene based magnetic junctions

    Directory of Open Access Journals (Sweden)

    Shweta Meena

    2017-12-01

    Full Text Available Spin polarized properties of fluorinated graphene as tunnel barrier with CrO2 as two HMF electrodes are studied using first principle methods based on density functional theory. Fluorinated graphene with different fluorine coverages is explored as tunnel barriers in magnetic tunnel junctions. Density functional computation for different fluorine coverages imply that with increase in fluorine coverages, there is increase in band gap (Eg of graphene, Eg ∼ 3.466 e V was observed when graphene sheet is fluorine adsorbed on both-side with 100% coverage (CF. The results of CF graphene are compared with C4F (fluorination on one-side of graphene sheet with 25% coverage and out-of-plane graphene based magnetic tunnel junctions. On comparison of the results it is observed that CF graphene based structure offers high TMR ∼100%, and the transport of carrier is through tunneling as there are no transmission states near Fermi level. This suggests that graphene sheet with both-side fluorination with 100% coverages acts as a perfect insulator and hence a better barrier to the carriers which is due to negligible spin down current (I↓ in both Parallel Configuration (PC and Antiparallel Configuration (APC.

  14. Spin Tunneling in a Rotating Nanomagnet

    Science.gov (United States)

    O'Keeffe, Michael; Chudnovsky, Eugene; Lehman College Theoretical Condensed Matter Physics Team

    2011-03-01

    We study spin tunneling in a magnetic nanoparticle with biaxial anisotropy that is free to rotate about its anisotropy axis. Exact instanton of the coupled equations of motion is found that connects degenerate classical energy minima. We show that mechanical freedom of the particle renormalizes magnetic anisotropy and increases the tunnel splitting. M. F. O'Keeffe and E. M. Chudnovsky, cond-mat, arXiv:1011.3134.

  15. Experimental observation of the transition from weak link to tunnel junction

    International Nuclear Information System (INIS)

    Muller, C.J.; Ruitenbeek, J.M. van; Jongh, L.J. de

    1992-01-01

    An extension to Morelands break junction technique is developed in order to obtain a clean and stable, mechanically adjustable junction. As a function of an externally applied force the coupling of two electrodes can be varied in vacuum. Experiments are described of a junction with niobium electrodes at 4.2 K which undergo a continuous change in normal resistance R N , from 1 to 10 9 Ω upon applying an increasing force. In this resistance range we discern a transition from a weak link regime to a tunnel regime. The current voltage (I-V) curves are reproducible upon adjustment changes in the whole resistance range. In the weak link regime the two electrodes of the junction are in physical contact with each other. The product of the critical current and normal resistance is compared with predictions of Ambegaokar-Baratoff and Kulik-Omelyanchuk. The product of the excess current and normal resistance shows a logarithmic increase for low R N values and decreases for the highest R N values in the weak link regime. Subharmonic gap structure, originating from multiple Andreev reflections is observed over a wide range of R N . In the transition regime the two electrodes are not in contact but there is still a large overlap of the superconducting and quasiparticle wave functions. In this regime a finite slope in the ''critical current part'' in the current voltage curve is observed. The I-V curves show features characteristic for both a weak link and a tunnel junction. In the tunnel regime there exists a vacuum gap between the electrodes and the Josephson coupling is suppressed. A considerable subgap current is observed, where the product of the subgap current and normal resistance is constant over almost four orders of magnitude of R N . A decreasing conductance near zero bias shows up in this regime. The normal resistance exhibits an exponential behaviour upon variations in the vacuum gap. (orig./WL)

  16. Nanomagnetic Logic

    Science.gov (United States)

    Carlton, David Bryan

    The exponential improvements in speed, energy efficiency, and cost that the computer industry has relied on for growth during the last 50 years are in danger of ending within the decade. These improvements all have relied on scaling the size of the silicon-based transistor that is at the heart of every modern CPU down to smaller and smaller length scales. However, as the size of the transistor reaches scales that are measured in the number of atoms that make it up, it is clear that this scaling cannot continue forever. As a result of this, there has been a great deal of research effort directed at the search for the next device that will continue to power the growth of the computer industry. However, due to the billions of dollars of investment that conventional silicon transistors have received over the years, it is unlikely that a technology will emerge that will be able to beat it outright in every performance category. More likely, different devices will possess advantages over conventional transistors for certain applications and uses. One of these emerging computing platforms is nanomagnetic logic (NML). NML-based circuits process information by manipulating the magnetization states of single-domain nanomagnets coupled to their nearest neighbors through magnetic dipole interactions. The state variable is magnetization direction and computations can take place without passing an electric current. This makes them extremely attractive as a replacement for conventional transistor-based computing architectures for certain ultra-low power applications. In most work to date, nanomagnetic logic circuits have used an external magnetic clocking field to reset the system between computations. The clocking field is then subsequently removed very slowly relative to the magnetization dynamics, guiding the nanomagnetic logic circuit adiabatically into its magnetic ground state. In this dissertation, I will discuss the dynamics behind this process and show that it is greatly

  17. Electron transport and noise spectroscopy in organic magnetic tunnel junctions with PTCDA and Alq3 barriers

    Science.gov (United States)

    Martinez, Isidoro; Cascales, Juan Pedro; Hong, Jhen-Yong; Lin, Minn-Tsong; Prezioso, Mirko; Riminucci, Alberto; Dediu, Valentin A.; Aliev, Farkhad G.

    2016-10-01

    The possible influence of internal barrier dynamics on spin, charge transport and their fluctuations in organic spintronics remains poorly understood. Here we present investigation of the electron transport and low frequency noise at temperatures down to 0.3K in magnetic tunnel junctions with an organic PTCDA barriers with thickness up to 5 nm in the tunneling regime and with 200 nm thick Alq3 barrier in the hopping regime. We observed high tunneling magneto-resistance at low temperatures (15-40%) and spin dependent super-poissonian shot noise in organic magnetic tunnel junctions (OMTJs) with PTCDA. The Fano factor exceeds 1.5-2 values which could be caused by interfacial states controlled by spin dependent bunching in the tunneling events through the molecules.1 The bias dependence of the low frequency noise in OMTJs with PTCDA barriers which includes both 1/f and random telegraph noise activated at specific biases will also be discussed. On the other hand, the organic junctions with ferromagnetic electrodes and thick Alq3 barriers present sub-poissonian shot noise which depends on the temperature, indicative of variable range hopping.

  18. A passive on-chip, superconducting circulator using rings of tunnel junctions

    OpenAIRE

    Müller, Clemens; Guan, Shengwei; Vogt, Nicolas; Cole, Jared H.; Stace, Thomas M.

    2017-01-01

    We present the design of a passive, on-chip microwave circulator based on a ring of superconducting tunnel junctions. We investigate two distinct physical realisations, based on either Josephson junctions (JJ) or quantum phase slip elements (QPS), with microwave ports coupled either capacitively (JJ) or inductively (QPS) to the ring structure. A constant bias applied to the center of the ring provides the symmetry breaking (effective) magnetic field, and no microwave or rf bias is required. W...

  19. 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

    We have investigated the static properties of one-dimensional planar Josephson tunnel junctions (JTJs) in the most general case of elliptic annuli. We have analyzed the dependence of the critical current in the presence of an external magnetic field applied either in the junction plane...... 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...

  20. NbN/AlN/NbN tunnel junctions with high current density up to 54 kA/cm2

    International Nuclear Information System (INIS)

    Wang, Z.; Kawakami, A.; Uzawa, Y.

    1997-01-01

    We report on progress in the development of high current density NbN/AlN/NbN tunnel junctions for applications as submillimeter wave superconductor-insulator-superconductor mixers. A very high current density up to 54 kA/cm 2 , roughly an order of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions with about 1 nm thick AlN barriers. The magnetic field and temperature dependence of critical supercurrents were measured to investigate the Josephson tunneling behavior of critical supercurrents in the high-J c junctions. The junctions showed high-quality junction characteristics with a large gap voltage of 5 mV and sharp quasiparticle current rise (ΔV g =0.1 mV). The R sg /R N ratio was about 5 with a V m value of 14 mV measured at 4.2 K. copyright 1997 American Institute of Physics

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

    DEFF Research Database (Denmark)

    Cagliani, Alberto; Kjær, Daniel; Østerberg, Frederik Westergaard

    2017-01-01

    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...... 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....

  2. Direct detection of the parametrically generated half-harmonic voltage in a Josephson tunnel junction

    DEFF Research Database (Denmark)

    Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.

    1976-01-01

    The first direct observation of the parametrically generated half-harmonic voltage in a Josephson tunnel junction is reported. A microwave signal at f=17.25 GHz is applied to the junction dc current biased at zero voltage such that the Josephson plasma resonance fp=f/2. Under these conditions...

  3. A Monolithic Interconnected module with a tunnel Junction for Enhanced Electrical and Optical Performance

    Energy Technology Data Exchange (ETDEWEB)

    Murray, Christopher Sean; Wilt, David Morgan

    1999-06-30

    An improved thermophotovoltaic (TPV) n/p/n device is provided. Monolithic Interconnected Modules (MIMs), semiconductor devices converting infrared radiation to electricity, have been developed with improved electrical and optical performance. The structure is an n-type emitter on a p-type base with an n-type lateral conduction layer. The incorporation of a tunnel junction and the reduction in the amount of p-type material used results in negligible parasitic absorption, decreased series resistance, increased voltage and increased active area. The novel use of a tunnel junction results in the potential for a TPV device with efficiency greater than 24%.

  4. Bias voltage effect on electron tunneling across a junction with a ferroelectric–ferromagnetic two-phase composite barrier

    International Nuclear Information System (INIS)

    Wang Jian; Ju Sheng; Li, Z.Y.

    2012-01-01

    The effect of bias voltage on electron tunneling across a junction with a ferroelectric–ferromagnetic composite barrier is investigated theoretically. Because of the inversion symmetry breaking of the spontaneous ferroelectric polarization, bias voltage dependence of the electron tunneling shows significant differences between the positive bias and the negative one. The differences of spin filtering or tunnel magnetoresistance increase with the increasing absolute value of bias voltage. Such direction preferred electron tunneling is found intimately related with the unusual asymmetry of the electrical potential profile in two-phase composite barrier and provides a unique change to realize rectifying functions in spintronics. - Highlights: ► Electron tunneling across a ferroelectric–ferromagnetic composite barrier junction. ► TMR effect is different under the same value but opposite direction bias voltage. ► This directionality of the electron tunneling enhances with increasing bias voltage.

  5. Simulations of fine structures on the zero field steps of Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Scheuermann, M.; Chi, C. C.; Pedersen, Niels Falsig

    1986-01-01

    Fine structures on the zero field steps of long Josephson tunnel junctions are simulated for junctions with the bias current injected into the junction at the edges. These structures are due to the coupling between self-generated plasma oscillations and the traveling fluxon. The plasma oscillations...... are generated by the interaction of the bias current with the fluxon at the junction edges. On the first zero field step, the voltages of successive fine structures are given by Vn=[h-bar]/2e(2omegap/n), where n is an even integer. Applied Physics Letters is copyrighted by The American Institute of Physics....

  6. Evaluation of the Kinetic Property of Single-Molecule Junctions by Tunneling Current Measurements.

    Science.gov (United States)

    Harashima, Takanori; Hasegawa, Yusuke; Kiguchi, Manabu; Nishino, Tomoaki

    2018-01-01

    We investigated the formation and breaking of single-molecule junctions of two kinds of dithiol molecules by time-resolved tunneling current measurements in a metal nanogap. The resulting current trajectory was statistically analyzed to determine the single-molecule conductance and, more importantly, to reveal the kinetic property of the single-molecular junction. These results suggested that combining a measurement of the single-molecule conductance and statistical analysis is a promising method to uncover the kinetic properties of the single-molecule junction.

  7. Encoding, training and retrieval in ferroelectric tunnel junctions

    Science.gov (United States)

    Xu, Hanni; Xia, Yidong; Xu, Bo; Yin, Jiang; Yuan, Guoliang; Liu, Zhiguo

    2016-05-01

    Ferroelectric tunnel junctions (FTJs) are quantum nanostructures that have great potential in the hardware basis for future neuromorphic applications. Among recently proposed possibilities, the artificial cognition has high hopes, where encoding, training, memory solidification and retrieval constitute a whole chain that is inseparable. However, it is yet envisioned but experimentally unconfirmed. The poor retention or short-term store of tunneling electroresistance, in particular the intermediate states, is still a key challenge in FTJs. Here we report the encoding, training and retrieval in BaTiO3 FTJs, emulating the key features of information processing in terms of cognitive neuroscience. This is implemented and exemplified through processing characters. Using training inputs that are validated by the evolution of both barrier profile and domain configuration, accurate recalling of encoded characters in the retrieval stage is demonstrated.

  8. Optically controlled electroresistance and electrically controlled photovoltage in ferroelectric tunnel junctions

    KAUST Repository

    Jin Hu, Wei; Wang, Zhihong; Yu, Weili; Wu, Tao

    2016-01-01

    Ferroelectric tunnel junctions (FTJs) have recently attracted considerable interest as a promising candidate for applications in the next-generation non-volatile memory technology. In this work, using an ultrathin (3 nm) ferroelectric Sm0.1Bi0.9FeO3 layer as the tunnelling barrier and a semiconducting Nb-doped SrTiO3 single crystal as the bottom electrode, we achieve a tunnelling electroresistance as large as 105. Furthermore, the FTJ memory states could be modulated by light illumination, which is accompanied by a hysteretic photovoltaic effect. These complimentary effects are attributed to the bias- and light-induced modulation of the tunnel barrier, both in height and width, at the semiconductor/ferroelectric interface. Overall, the highly tunable tunnelling electroresistance and the correlated photovoltaic functionalities provide a new route for producing and non-destructively sensing multiple non-volatile electronic states in such FTJs.

  9. Optically controlled electroresistance and electrically controlled photovoltage in ferroelectric tunnel junctions

    KAUST Repository

    Jin Hu, Wei

    2016-02-29

    Ferroelectric tunnel junctions (FTJs) have recently attracted considerable interest as a promising candidate for applications in the next-generation non-volatile memory technology. In this work, using an ultrathin (3 nm) ferroelectric Sm0.1Bi0.9FeO3 layer as the tunnelling barrier and a semiconducting Nb-doped SrTiO3 single crystal as the bottom electrode, we achieve a tunnelling electroresistance as large as 105. Furthermore, the FTJ memory states could be modulated by light illumination, which is accompanied by a hysteretic photovoltaic effect. These complimentary effects are attributed to the bias- and light-induced modulation of the tunnel barrier, both in height and width, at the semiconductor/ferroelectric interface. Overall, the highly tunable tunnelling electroresistance and the correlated photovoltaic functionalities provide a new route for producing and non-destructively sensing multiple non-volatile electronic states in such FTJs.

  10. 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.

  11. 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; Saeed, Yasir; Schwingenschlö gl, Udo; Singh, Nirpendra; Useinov, N.

    2013-01-01

    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.

  12. Radiation detection with Nb/Al-AlOx/Al/Nb superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Matsumura, Atsuki; Takahashi, Toru; Kurakado, Masahiko

    1992-01-01

    Superconductor radiation detectors have the possibility of 20-30 times better energy resolution than that of a high resolution Si detector. We fabricated Nb/Al-AlOx/Al/Nb superconducting tunnel junctions with low leakage current. X rays were detected with large area junctions of 178x178 μm 2 . High energy resolution of 160 eV for 5.9 keV was obtained. We also fabricated series connected junctions which covers a rather large area of 4x4 mm 2 . α particles injected into the rear substrate were detected using nonthermal phonons induced by the radiations in the substrate. (author)

  13. Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOX barriers

    Science.gov (United States)

    Newhouse-Illige, T.; Xu, Y. H.; Liu, Y. H.; Huang, S.; Kato, H.; Bi, C.; Xu, M.; LeRoy, B. J.; Wang, W. G.

    2018-02-01

    Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here, we investigate the quality of the GdOX barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlOX and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence including sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.

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

    KAUST Repository

    Chshiev, M.; Manchon, Aurelien; Kalitsov, A.; Ryzhanova, N.; Vedyayev, A.; Strelkov, N.; Butler, W. H.; Dieny, B.

    2015-01-01

    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

  15. Electron-spin polarization in tunnel junctions with ferromagnetic EuS barriers

    International Nuclear Information System (INIS)

    Hao, X.; Moodera, J.S.; Meservey, R.

    1989-01-01

    The authors report here spin-polarized tunneling experiments using non-ferromagnetic electrodes and ferromagnetic EuS barriers. Because of the conduction band in EuS splits into spin-up and spin-down subbands when the temperature is below 16.7 K, the Curie temperature of EuS, the tunnel barrier for electrons with different spin directions is different, therefore giving rise to tunnel current polarization. The spin-filter effect, as it may be called, was observed earlier, directly or indirectly, by several groups: Esaki et al. made a tunneling study on junctions having EuS and EuSe barriers; Thompson et al. studied Schottky barrier tunneling between In and doped EuS; Muller et al. and Kisker et al. performed electron field emission experiments on EuS-coated tungsten tips. The field emission experiments gave a maximum polarization of (89 + 7)% for the emitted electrons. Although the previous tunneling studies did not directly show electron polarization, their results were explained by the same spin- filter effect. This work uses the spin-polarized tunneling technique to show directly that tunnel current is indeed polarized and polarization can be as high as 85%

  16. Preparation and properties of Ni80Fe20/Al2O3/Co magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Chen Jing; Du Jun; Wu Xiaoshan; Pan Minghu; Long Jianguo; Zhang Wei; Lu Mu; Hu An; Zhai Hongru

    2000-01-01

    With plasma oxidisation to create an insulating layer of Al 2 O 3 , the authors have repeatedly fabricated Ni 80 Fe 20 /Al 2 O 3 /Co magnetic tunnel junctions which show obvious tunneling magnetoresistance (TMR) effect. At room temperature, the maximum TMR ratio reaches 6.0%. The switch field can be less than 800 A/m with a relative step width of about 2400 A/m. The junction resistance changes from hundreds of ohms to hundreds of kilo-ohms

  17. High performance as-grown and annealed high band gap tunnel junctions: Te behavior at the interface

    Energy Technology Data Exchange (ETDEWEB)

    Bedair, S. M., E-mail: bedair@ncsu.edu; Harmon, Jeffrey L.; Carlin, C. Zachary; Hashem Sayed, Islam E.; Colter, P. C. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2016-05-16

    The performance of n{sup +}-InGaP(Te)/p{sup +}-AlGaAs(C) high band gap tunnel junctions (TJ) is critical for achieving high efficiency in multijunction photovoltaics. Several limitations for as grown and annealed TJ can be attributed to the Te doping of InGaP and its behavior at the junction interface. Te atoms in InGaP tend to get attached at step edges, resulting in a Te memory effect. In this work, we use the peak tunneling current (J{sub pk}) in this TJ as a diagnostic tool to study the behavior of the Te dopant at the TJ interface. Additionally, we used our understanding of Te behavior at the interface, guided by device modeling, to modify the Te source shut-off procedure and the growth rate. These modifications lead to a record performance for both the as-grown (2000 A/cm{sup 2}) and annealed (1000 A/cm{sup 2}) high band gap tunnel junction.

  18. Device-quality tunnel junctions on the high Tc superconductor HgBa2CuO4+δ

    International Nuclear Information System (INIS)

    Zasadzinski, J.; Chen, J.; Romano, P.; Gray, K.E.; Wagner, J.L.; Hinks, D.G.

    1995-01-01

    SIN and SIS tunnel junction devices (e.g. photon detectors, logic elements) require quasiparticle characteristics that exhibit sharp current onsets at the gap voltage and very low sub-gap conductances. Progress is reported on the development of such junctions on High Tc cuprates using mechanical point contacts. In general, these contacts display the optimum characteristics that can be obtained from HTS native-surface tunnel barriers. Most cuprates display a sub-gap conductance which monotonically increases with voltage about the minimum value at zero bias. However, tunneling data of unusually high quality have been obtained for the recently discovered Hg-based cuprate, HgBa 2 CuO 4 (T c =96K). SIS' tunneling data using a Nb tip are presented which exhibit very low and flat sub-gap conductances and sharp conductance peaks as expected from a BCS density of states. These results are slightly improved over earlier published results with SIN junctions. Use of the experimental data to simulate the performance of a quasiparticle mixer demonstrates that noise temperatures approaching the quantum limit are possible for SIS and SIN mixers in the range 1-5 THz

  19. MgO magnetic tunnel junctions of enduring F-type upon annealing

    International Nuclear Information System (INIS)

    Schleicher, F; Halisdemir, U; Urbain, E; Gallart, M; Boukari, S; Beaurepaire, E; Gilliot, P; Bowen, M; Lacour, D; Montaigne, F; Hehn, M

    2015-01-01

    The authors performed magnetotransport experiments to determine whether annealing alters the oxygen vacancy-mediated tunnelling potential landscape of the central portion of a MgO ultrathin film within sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions. Using the Î rel method reveals a temperature-dependent tunnelling barrier height for a non-annealed barrier that arises from single oxygen vacancies (F centres) and is qualitatively identical to that found for its partly and fully annealed counterparts. Thus these MTJs with F centres remain of F-type upon annealing. This explicitly confirms that the large tunnel-magnetoresistance (TMR) increase upon annealing results mainly from structural modifications of MgO and CoFeB and not from vacancy pairing within the barrier. Photoluminescence spectra performed on both annealed and non-annealed thin MgO films grown on CoFeB electrodes support this conclusion. This work should promote renewed scrutiny over the precise impact of annealing on tunnelling magnetotransport across MgO. (paper)

  20. Theory of the low-voltage impedance of superconductor-- p insulator--normal metal tunnel junctions

    International Nuclear Information System (INIS)

    Lemberger, T.R.

    1984-01-01

    A theory for the low-voltage impedance of a superconductor-- p insulator--normal metal tunnel junction is developed that includes the effects of charge imbalance and of quasiparticle fluctuations. A novel, inelastic, charge-imbalance relaxation process is identified that is associated with the junction itself. This new process leads to the surprising result that the charge-imbalance component of the dc resistance of a junction becomes independent of the electron-phonon scattering rate as the insulator resistance decreases

  1. Spin–transfer torque oscillator in magnetic tunneling junction with short–wavelength magnon excitation

    Directory of Open Access Journals (Sweden)

    Shizhu Qiao

    2018-05-01

    Full Text Available Bloch–Bloembergen–Slonczewski (BBS equation is established by extending Bloch–Bloembergen equation, and it is used to study magnetization oscillation in the free magnetic layer of a magnetic tunneling junction. Since both short–wavelength magnon excitation and spin–transfer torque are taken into account in the BBS equation, it is distinguished from Landau–Lifshitz–Gilbert–Slonczewski equation. The macro–spin BBS model predicts that the transverse relaxation time in free magnetic layer should be long enough, as compared with the longitudinal relaxation time, to achieve stable magnetization oscillation for spin–transfer torque oscillator application. Moreover, field–like torque favors the tolerance of fast transverse relaxation, which makes magnetic tunneling junction a better choice than spin valve for the spin–transfer torque oscillator application.

  2. Macroscopic Quantum Tunneling in Superconducting Junctions of β-Ag2Se Topological Insulator Nanowire.

    Science.gov (United States)

    Kim, Jihwan; Kim, Bum-Kyu; Kim, Hong-Seok; Hwang, Ahreum; Kim, Bongsoo; Doh, Yong-Joo

    2017-11-08

    We report on the fabrication and electrical transport properties of superconducting junctions made of β-Ag 2 Se topological insulator (TI) nanowires in contact with Al superconducting electrodes. The temperature dependence of the critical current indicates that the superconducting junction belongs to a short and diffusive junction regime. As a characteristic feature of the narrow junction, the critical current decreases monotonously with increasing magnetic field. The stochastic distribution of the switching current exhibits the macroscopic quantum tunneling behavior, which is robust up to T = 0.8 K. Our observations indicate that the TI nanowire-based Josephson junctions can be a promising building block for the development of nanohybrid superconducting quantum bits.

  3. Magnetic-field-controlled negative differential conductance in scanning tunneling spectroscopy of graphene npn junction resonators

    Science.gov (United States)

    Li, Si-Yu; Liu, Haiwen; Qiao, Jia-Bin; Jiang, Hua; He, Lin

    2018-03-01

    Negative differential conductance (NDC), characterized by the decreasing current with increasing voltage, has attracted continuous attention for its various novel applications. The NDC typically exists in a certain range of bias voltages for a selected system and controlling the regions of NDC in curves of current versus voltage (I -V ) is experimentally challenging. Here, we demonstrate a magnetic-field-controlled NDC in scanning tunneling spectroscopy of graphene npn junction resonators. The magnetic field not only can switch on and off the NDC, but also can continuously tune the regions of the NDC in the I -V curves. In the graphene npn junction resonators, magnetic fields generate sharp and pronounced Landau-level peaks with the help of the Klein tunneling of massless Dirac fermions. A tip of scanning tunneling microscope induces a relatively shift of the Landau levels in graphene beneath the tip. Tunneling between the misaligned Landau levels results in the magnetic-field-controlled NDC.

  4. Tunneling Negative Magnetoresistance via δ Doping in a Graphene-Based Magnetic Tunnel Junction

    International Nuclear Information System (INIS)

    Yuan Jian-Hui; Chen Ni; Mo Hua; Zhang Yan; Zhang Zhi-Hai

    2016-01-01

    We investigate the tunneling magnetoresistance via δ doping in a graphene-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and the aptitude of the δ doping. Also, both the transmission probability and the conductance at the parallel configuration are suppressed by the magnetic field more obviously than that at the antiparallel configuration, which implies a large negative magnetoresistance for this device. The results show that the negative magnetoresistance of over 300% at B = 1.0 T is observed by choosing suitable doped parameters, and the temperature plays an important role in the magnetoresistance. Thus it is possible to open a way to effectively manipulate the magnetoresistance devices, and to make a type of magnetoresistance device by controlling the structural parameter of the δ doping. (paper)

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

    Science.gov (United States)

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

    2011-04-01

    A single-molecule magnet (SMM) coupled to two normal metallic electrodes can both switch spin-up and spin-down 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.

  6. Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions

    International Nuclear Information System (INIS)

    Asai, Hidehiro; Kawabata, Shiro; Ota, Yukihiro; Machida, Masahiko

    2014-01-01

    Low-temperature characters of superconducting devices yield definite probes for different superconducting phenomena. We study the macroscopic quantum tunneling (MQT) in a Josephson junction, composed of a single-gap superconductor and a two-gap superconductor. Since this junction has two kinds to the superconducting phase differences, calculating the MQT escape rate requires the analysis of quantum tunneling in a multi-dimensional configuration space. Our approach is the semi-classical approximation along a 1D curve in a 2D potential- energy landscape, connecting two adjacent potential (local) minimums through a saddle point. We find that this system has two plausible tunneling paths; an in-phase path and an out-of-phase path. The former is characterized by the Josephson-plasma frequency, whereas the latter is by the frequency of the characteristic collective mode in a two-band superconductor, Josephson- Leggett mode. Depending on external bias current and inter-band Josephson-coupling energy, one of them mainly contributes to the MQT. Our numerical calculations show that the difference between the in-phase path and the out-of-phase path is manifest, with respect to the bias- current-dependence of the MQT escape rate. This result suggests that our MQT setting be an indicator of the Josephson-Leggett mode

  7. Computational logic with square rings of nanomagnets

    Science.gov (United States)

    Arava, Hanu; Derlet, Peter M.; Vijayakumar, Jaianth; Cui, Jizhai; Bingham, Nicholas S.; Kleibert, Armin; Heyderman, Laura J.

    2018-06-01

    Nanomagnets are a promising low-power alternative to traditional computing. However, the successful implementation of nanomagnets in logic gates has been hindered so far by a lack of reliability. Here, we present a novel design with dipolar-coupled nanomagnets arranged on a square lattice to (i) support transfer of information and (ii) perform logic operations. We introduce a thermal protocol, using thermally active nanomagnets as a means to perform computation. Within this scheme, the nanomagnets are initialized by a global magnetic field and thermally relax on raising the temperature with a resistive heater. We demonstrate error-free transfer of information in chains of up to 19 square rings and we show a high level of reliability with successful gate operations of ∼94% across more than 2000 logic gates. Finally, we present a functionally complete prototype NAND/NOR logic gate that could be implemented for advanced logic operations. Here we support our experiments with simulations of the thermally averaged output and determine the optimal gate parameters. Our approach provides a new pathway to a long standing problem concerning reliability in the use of nanomagnets for computation.

  8. Magnetic and transport properties of single and double perpendicular magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Cuchet, Lea

    2015-01-01

    Due to their advantageous properties in terms of data retention, storage density and critical current density for Spin Transfer Torque (STT) switching, the magnetic tunnel junctions with perpendicular anisotropy have become predominant in the developments for MRAM applications. The aim of this thesis is to improve the anisotropy and transport properties of such structures and to realize even more complex stacks such as perpendicular double junctions. Studies on the magnetic properties and Tunnel Magnetoresistance (TMR) measurements showed that to optimize the performances of the junctions, all the thicknesses of the different layers constituting the stack have to be adapted. To guaranty both a large TMR as well a strong perpendicular anisotropy, compromises are most of the time needed. Studies as a function of magnetic thickness enabled to extract the saturation magnetization, the critical thickness and the magnetic dead layer thickness both in the bottom reference and the top storage layer in structures capped with Ta. This type of junction could be tested electrically after patterning the sample into nano-pillars. Knowing that perpendicular anisotropy mostly arises at the metal/oxide interface, the Ta capping layer was replaced by a MgO one, leading to a huge increase in the anisotropy of the free layer. A second top reference was then added on such a stack to create functional perpendicular double junctions. CoFeB/insertion/CoFeB synthetic antiferromagnetic storage layers could be developed and were proved to be stable enough to replace the standard Co/Pt-based reference layers. (author) [fr

  9. Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

    DEFF Research Database (Denmark)

    Pedersen, Niels Falsig; Sørensen, O. H.; Mygind, Jesper

    1978-01-01

    The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature Tc of the Sn films. The temperature dependence of the cosφ conductance is determined from the resonant response at the junction plasma frequency fp...

  10. Liquid phase epitaxy of abrupt junctions in InAs and studies of injection radiative tunneling processes

    International Nuclear Information System (INIS)

    Bull, D.J.

    1977-01-01

    The p-n junction in a InAs crystal, by liquid phase epitaxy is obtained. The processes of injection and tunneling radiative recombination by emitted radiation from active region of p-n junction for low injection current are studied. (M.C.K.) [pt

  11. Influence of chemical composition of CoFeB on tunneling magnetoresistance and microstructure in polycrystalline CoFeB/MgO/CoFeB magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Tsunekawa, Koji; Choi, Young-Suk; Nagamine, Yoshinori; Djayaprawira, David D.; Takeuchi, Takashi; Kitamoto, Yoshitaka

    2006-01-01

    We report, for the first time, the correlation between tunneling magnetoresistance (TMR) and the microstructure of polycrystalline CoFeB/MgO/CoFeB magnetic tunnel junctions with various Co/Fe ratios in the (CoFe) 81 B 19 reference and free layers. It is found that the Co/Fe ratio in the (CoFe) 81 B 19 reference layer strongly affects the (001) out-of-plane texture of the MgO tunnel barrier, resulting in the variation in TMR ratio. Further microstructure characterization of the magnetic tunnel junction with a higher TMR ratio and a stronger (001) out-of-plane texture in the MgO tunnel barrier reveals a grain-to-grain lattice match between the crystallized bcc CoFeB reference layer and MgO with a 45deg rotational epitaxial relationship, that is, CoFeB(001)[110]//MgO(001)[100]. (author)

  12. Oxidation process of AlOx-based magnetic tunnel junctions studied by photoconductance

    NARCIS (Netherlands)

    Koller, P.H.P.; Vanhelmont, F.W.M.; Boeve, H.; Lumens, P.G.E.; Jonge, de W.J.M.

    2003-01-01

    The oxidation process of Co/AlOx/Co magnetic tunnel junctions has been investigated by photoconductance, in addition to traditional transport measurements. The shape of the photoconductance curves is explained within the framework of a simple qualitative model, assuming an oxidation time dependent

  13. 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.

  14. Resonant TMR inversion in LiF/EuS based spin-filter tunnel junctions

    Directory of Open Access Journals (Sweden)

    Fen Liu

    2016-08-01

    Full Text Available Resonant tunneling can lead to inverse tunnel magnetoresistance when impurity levels rather than direct tunneling dominate the transport process. We fabricated hybrid magnetic tunnel junctions of CoFe/LiF/EuS/Ti, with an epitaxial LiF energy barrier joined with a polycrystalline EuS spin-filter barrier. Due to the water solubility of LiF, the devices were fully packaged in situ. The devices showed sizeable positive TMR up to 16% at low bias voltages but clearly inverted TMR at higher bias voltages. The TMR inversion depends sensitively on the thickness of LiF, and the tendency of inversion disappears when LiF gets thick enough and recovers its intrinsic properties.

  15. Current-driven thermo-magnetic switching in magnetic tunnel junctions

    Science.gov (United States)

    Kravets, A. F.; Polishchuk, D. M.; Pashchenko, V. A.; Tovstolytkin, A. I.; Korenivski, V.

    2017-12-01

    We investigate switching of magnetic tunnel junctions (MTJs) driven by the thermal effect of the transport current through the junctions. The switching occurs in a specially designed composite free layer, which acts as one of the MTJ electrodes, and is due to a current-driven ferro-to-paramagnetic Curie transition with the associated exchange decoupling within the free layer leading to magnetic reversal. We simulate the current and heat propagation through the device and show how heat focusing can be used to improve the power efficiency. The Curie-switch MTJ demonstrated in this work has the advantage of being highly tunable in terms of its operating temperature range, conveniently to or just above room temperature, which can be of technological significance and competitive with the known switching methods using spin-transfer torques.

  16. Fluxon dynamics in long annular Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Martucciello, N.; Mygind, Jesper; Koshelets, V.P.

    1998-01-01

    Single-fluxon dynamics has been experimentally investigated in high-quality Nb/Al-AlOx/Nb annular Josephson tunnel junctions having a radius much larger than the Josephson penetration depth. Strong evidence of self-field effects is observed. An external magnetic field in the barrier plane acts...... on the fluxon as a periodic potential and lowers its average speed. Further, the results of perturbative calculations do not fit the experimental current-voltage profile and, provided the temperature is low enough, this profile systematically shows pronounced deviations from the smooth predicted form...

  17. Size dependence of spin-torque induced magnetic switching in CoFeB-based perpendicular magnetization tunnel junctions (invited)

    Science.gov (United States)

    Sun, J. Z.; Trouilloud, P. L.; Gajek, M. J.; Nowak, J.; Robertazzi, R. P.; Hu, G.; Abraham, D. W.; Gaidis, M. C.; Brown, S. L.; O'Sullivan, E. J.; Gallagher, W. J.; Worledge, D. C.

    2012-04-01

    CoFeB-based magnetic tunnel junctions with perpendicular magnetic anisotropy are used as a model system for studies of size dependence in spin-torque-induced magnetic switching. For integrated solid-state memory applications, it is important to understand the magnetic and electrical characteristics of these magnetic tunnel junctions as they scale with tunnel junction size. Size-dependent magnetic anisotropy energy, switching voltage, apparent damping, and anisotropy field are systematically compared for devices with different materials and fabrication treatments. Results reveal the presence of sub-volume thermal fluctuation and reversal, with a characteristic length-scale of the order of approximately 40 nm, depending on the strength of the perpendicular magnetic anisotropy and exchange stiffness. To have the best spin-torque switching efficiency and best stability against thermal activation, it is desirable to optimize the perpendicular anisotropy strength with the junction size for intended use. It also is important to ensure strong exchange-stiffness across the magnetic thin film. These combine to give an exchange length that is comparable or larger than the lateral device size for efficient spin-torque switching.

  18. Multiple frequency generation by bunched solitons in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Lomdahl, P. S.; Sørensen, O. H.; Christiansen, Peter Leth

    1981-01-01

    A detailed numerical study of a long Josephson tunnel junction modeled by a perturbed sine-Gordon equation demonstrates the existence of a variety of bunched soliton configurations. Thus, on the third zero-field step of the V-I characteristic, two simultaneous adjacent frequencies are generated...... in a narrow bias current range. The analysis of the soliton modes provides an explanation of recent experimental observations....

  19. Rapid prototyping of magnetic tunnel junctions with focused ion beam processes

    International Nuclear Information System (INIS)

    Persson, Anders; Thornell, Greger; Nguyen, Hugo

    2010-01-01

    Submicron-sized magnetic tunnel junctions (MTJs) are most often fabricated by time-consuming and expensive e-beam lithography. From a research and development perspective, a short lead time is one of the major concerns. Here, a rapid process scheme for fabrication of micrometre size MTJs with focused ion beam processes is presented. The magnetic properties of the fabricated junctions are investigated in terms of magnetic domain structure, tunnelling magnetoresistance (TMR) and coercivity, with extra attention given to the effect of Ga implantation from the ion beam. In particular, the effect of the implantation on the minimum junction size and the magnetization of the sensing layer are studied. In the latter case, magnetic force microscopy and micromagnetic simulations, with the object-oriented micromagnetic framework (OOMMF), are used to study the magnetization reversal. The fabricated junctions show considerable coercivity both along their hard and easy axes. Interestingly, the sensing layer exhibits two remanent states: one with a single and one with a double domain. The hard axis TMR loop has kinks at about ±20 mT which is attributed to a non-uniform lateral coercivity, where the rim of the junctions, which is subjected to Ga implantation from the flank of the ion beam, is more coercive than the unirradiated centre. The width of the coercive rim is estimated to be 160 nm from the hard axis TMR loop. The easy axis TMR loop shows more coercivity than an unirradiated junction and, this too, is found to stem from the coercive rim, as seen from the simulations. It is concluded that the process scheme has three major advantages. Firstly, it has a high lateral and depth resolution—the depth resolution is enhanced by end point detection—and is capable of making junctions of sizes down towards the limit set by the width of the irradiated rim. Secondly, the most delicate process steps are performed in the unbroken vacuum enabling the use of materials prone to

  20. Perpendicular magnetic tunnel junction with tunneling magnetoresistance ratio of 64% using MgO (100) barrier layer prepared at room temperature

    International Nuclear Information System (INIS)

    Ohmori, Hideto; Hatori, Tomoya; Nakagawa, Shigeki

    2008-01-01

    MgO (100) textured films can be prepared by reactive facing targets sputtering at room temperature without postdeposition annealing process when they were deposited on (100) oriented Fe buffer layers. This method allows fabrication of perpendicular magnetic tunnel junction (p-MTJ) with MgO (100) tunneling barrier layer and rare-earth transition metal (RE-TM) alloy thin films as perpendicularly magnetized free and pinned layers. The 3-nm-thick MgO tunneling barrier layer in p-MTJ multilayer prepared on glass substrate revealed (100) crystalline orientation. Extraordinary Hall effect measurement clarified that the perpendicular magnetic components of 3-nm-thick Fe buffer layers on the two ends of MgO tunneling barrier layer were increased by exchange coupling with RE-TM alloy layers. The RA of 35 kΩ μm 2 and tunneling magnetoresistance ratio of 64% was observed in the multilayered p-MTJ element by current-in-plane-tunneling

  1. Low-field Switching Four-state Nonvolatile Memory Based on Multiferroic Tunnel Junctions

    Science.gov (United States)

    Yau, H. M.; Yan, Z. B.; Chan, N. Y.; Au, K.; Wong, C. M.; Leung, C. W.; Zhang, F. Y.; Gao, X. S.; Dai, J. Y.

    2015-08-01

    Multiferroic tunneling junction based four-state non-volatile memories are very promising for future memory industry since this kind of memories hold the advantages of not only the higher density by scaling down memory cell but also the function of magnetically written and electrically reading. In this work, we demonstrate a success of this four-state memory in a material system of NiFe/BaTiO3/La0.7Sr0.3MnO3 with improved memory characteristics such as lower switching field and larger tunneling magnetoresistance (TMR). Ferroelectric switching induced resistive change memory with OFF/ON ratio of 16 and 0.3% TMR effect have been achieved in this multiferroic tunneling structure.

  2. 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.

  3. Ferroelectric switching of band alignments in LSMO/PZT/Co multiferroic tunnel junctions: an ab initio study.

    Science.gov (United States)

    Imam, M; Stojić, N; Binggeli, N

    2017-08-04

    Band alignments in ferroelectric tunnel junctions (FTJs) are expected to play a critical role in determining the charge transport across the tunneling barrier. In general, however, the interface band discontinuities and their polarization dependence are not well known in these systems. Using a first-principles density-functional-theory approach, we explore the ferroelectric (FE) polarization dependence of the band alignments in [Formula: see text] (LSMO/PZT/Co) multiferroic tunnel junctions, for which recent experiments indicated an ON/OFF conductivity behavior upon switching the PZT FE polarization. Our results on the pseudomorphic defect-free LSMO/PZT/Co FTJs evidence a major FE switching effect on the band discontinuities at both interfaces. Based on the changes in the band alignments, we provide a possible explanation for the observed trends in the resistive switching.

  4. Determination of the thickness of Al2O3 barriers in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Buchanan, J.D.R.; Hase, T.P.A.; Tanner, B.K.; Hughes, N.D.; Hicken, R.J.

    2002-01-01

    The barrier thickness in magnetic spin-dependent tunnel junctions with Al 2 O 3 barriers has been measured using grazing incidence x-ray reflectivity and by fitting the tunneling current to the Simmons model. We have studied the effect of glow discharge oxidation time on the barrier structure, revealing a substantial increase in Al 2 O 3 thickness with oxidation. The greater thickness of barrier measured using grazing incidence x-ray reflectivity compared with that obtained by fitting current density-voltage to the Simmons electron tunneling model suggests that electron tunneling is localized to specific regions across the barrier, where the thickness is reduced by fluctuations due to nonconformal roughness

  5. Ballistic current transport studies of ferromagnetic multilayer films and tunnel junctions (invited)

    International Nuclear Information System (INIS)

    Rippard, W. H.; Perrella, A. C.; Buhrman, R. A.

    2001-01-01

    Three applications of ballistic electron microscopy are used to study, with nanometer-scale resolution, the magnetic and electronic properties of magnetic multilayer thin films and tunnel junctions. First, the capabilities of ballistic electron magnetic microscopy are demonstrated through an investigation of the switching behavior of continuous Ni 80 Fe 20 /Cu/Co trilayer films in the presence of an applied magnetic field. Next, the ballistic, hot-electron transport properties of Co films and multilayers formed by thermal evaporation and magnetron sputtering are compared, a comparison which reveals significant differences in the ballistic transmissivity of thin film multilayers formed by the two techniques. Finally, the electronic properties of thin aluminum oxide tunnel junctions formed by thermal evaporation and sputter deposition are investigated. Here the ballistic electron microscopy studies yield a direct measurement of the barrier height of the aluminum oxide barriers, a result that is invariant over a wide range of oxidation conditions. [copyright] 2001 American Institute of Physics

  6. Nb-based superconducting tunnel junctions for X-ray spectroscopy: TaOx and AlOx tunnelbarriers

    International Nuclear Information System (INIS)

    Bruijn, M.P.; Kiewiet, F.; Luiten, O.J.; Michels, F.A.; De Korte, P.A.J.

    1996-01-01

    Results are presented of an optimization study of TaO x -tunnel barriers in superconducting tunnel junctions for X-ray spectroscopy. The properties did not satisfy the critical demands. A comparison is made with first results on AlO x -barriers made with the same processing setup. AFM and TEM were used in studies of interface roughness. (orig.)

  7. Light emission and finite-frequency shot noise in molecular junctions: from tunneling to contact

    DEFF Research Database (Denmark)

    Lu, Jing Tao; Christensen, Rasmus Bjerregaard; Brandbyge, Mads

    2013-01-01

    Scanning tunneling microscope induced light emission from an atomic or molecular junction has been probed from the tunneling to contact regime in recent experiments. There, the measured light emission yields suggest a strong correlation with the high-frequency current/charge fluctuations. We show...... that this is consistent with the established theory in the tunneling regime, by writing the finite-frequency shot noise as a sum of inelastic transitions between different electronic states. Based on this, we develop a practical scheme to perform calculations on realistic structures using nonequilibrium Green's functions...

  8. Quasiparticle dynamics in superconducting tunnel junctions

    International Nuclear Information System (INIS)

    Kozorezov, A.G.; Brammertz, G.; Hijmering, R.A.; Wigmore, J.K.; Peacock, A.; Martin, D.; Verhoeve, P.; Golubov, A.A.; Rogalla, H.

    2006-01-01

    Superconducting Tunnel Junctions (STJs) used as single photon detectors possess extreme sensitivity and excellent resolving power. However, like many other cryogenic detectors they operate under extremely non-equilibrium conditions. In order to understand the physics of the non-equilibrium, non-stationary state, to interpret experimental data adequately, and to optimize the STJs unique performance, it is necessary to use a fully kinetic approach. We have developed the detailed theory of interactions between quasiparticles (qps) and the two types of phonons, sub-gap and pair-breaking, in STJ photon detectors. We discuss the results of extensive sets of experiments to study the non-equilibrium state in Al-based STJs. For the first time we are capable of explaining all available data systematically using a single set of parameters determined from STJ diagnostics and independent experiments

  9. Fabrication of fully epitaxial magnetic tunnel junctions with a Co2MnSi thin film and a MgO tunnel barrier

    International Nuclear Information System (INIS)

    Kijima, H.; Ishikawa, T.; Marukame, T.; Matsuda, K.-I.; Uemura, T.; Yamamoto, M.

    2007-01-01

    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co 2 MnSi (CMS) thin film having the ordered L2 1 structure as a lower electrode, a MgO tunnel barrier, and a Co 50 Fe 50 upper electrode. Reflection high-energy electron diffraction patterns observed in situ for each layer in the MTJ layer structure during fabrication clearly indicated that all layers of the CMS lower electrode, MgO tunnel barrier, and Co 50 Fe 50 upper electrode grew epitaxially. The microfabricated fully epitaxial CMS/MgO/Co 50 Fe 50 MTJs demonstrated relatively high tunnel magnetoresistance ratios of 90% at room temperature and 192% at 4.2 K

  10. Tunnel junctions with multiferroic barriers

    Science.gov (United States)

    Gajek, Martin; Bibes, Manuel; Fusil, Stéphane; Bouzehouane, Karim; Fontcuberta, Josep; Barthélémy, Agnès; Fert, Albert

    2007-04-01

    Multiferroics are singular materials that can exhibit simultaneously electric and magnetic orders. Some are ferroelectric and ferromagnetic and provide the opportunity to encode information in electric polarization and magnetization to obtain four logic states. However, such materials are rare and schemes allowing a simple electrical readout of these states have not been demonstrated in the same device. Here, we show that films of La0.1Bi0.9MnO3 (LBMO) are ferromagnetic and ferroelectric, and retain both ferroic properties down to a thickness of 2nm. We have integrated such ultrathin multiferroic films as barriers in spin-filter-type tunnel junctions that exploit the magnetic and ferroelectric degrees of freedom of LBMO. Whereas ferromagnetism permits read operations reminiscent of magnetic random access memories (MRAM), the electrical switching evokes a ferroelectric RAM write operation. Significantly, our device does not require the destructive ferroelectric readout, and therefore represents an advance over the original four-state memory concept based on multiferroics.

  11. A scanning tunneling microscope break junction method with continuous bias modulation.

    Science.gov (United States)

    Beall, Edward; Yin, Xing; Waldeck, David H; Wierzbinski, Emil

    2015-09-28

    Single molecule conductance measurements on 1,8-octanedithiol were performed using the scanning tunneling microscope break junction method with an externally controlled modulation of the bias voltage. Application of an AC voltage is shown to improve the signal to noise ratio of low current (low conductance) measurements as compared to the DC bias method. The experimental results show that the current response of the molecule(s) trapped in the junction and the solvent media to the bias modulation can be qualitatively different. A model RC circuit which accommodates both the molecule and the solvent is proposed to analyze the data and extract a conductance for the molecule.

  12. Near-Field Enhanced Photochemistry of Single Molecules in a Scanning Tunneling Microscope Junction.

    Science.gov (United States)

    Böckmann, Hannes; Gawinkowski, Sylwester; Waluk, Jacek; Raschke, Markus B; Wolf, Martin; Kumagai, Takashi

    2018-01-10

    Optical near-field excitation of metallic nanostructures can be used to enhance photochemical reactions. The enhancement under visible light illumination is of particular interest because it can facilitate the use of sunlight to promote photocatalytic chemical and energy conversion. However, few studies have yet addressed optical near-field induced chemistry, in particular at the single-molecule level. In this Letter, we report the near-field enhanced tautomerization of porphycene on a Cu(111) surface in a scanning tunneling microscope (STM) junction. The light-induced tautomerization is mediated by photogenerated carriers in the Cu substrate. It is revealed that the reaction cross section is significantly enhanced in the presence of a Au tip compared to the far-field induced process. The strong enhancement occurs in the red and near-infrared spectral range for Au tips, whereas a W tip shows a much weaker enhancement, suggesting that excitation of the localized plasmon resonance contributes to the process. Additionally, using the precise tip-surface distance control of the STM, the near-field enhanced tautomerization is examined in and out of the tunneling regime. Our results suggest that the enhancement is attributed to the increased carrier generation rate via decay of the excited near-field in the STM junction. Additionally, optically excited tunneling electrons also contribute to the process in the tunneling regime.

  13. Shapiro like steps reveals molecular nanomagnets’ spin dynamics

    International Nuclear Information System (INIS)

    Abdollahipour, Babak; Abouie, Jahanfar; Ebrahimi, Navid

    2015-01-01

    We present an accurate way to detect spin dynamics of a nutating molecular nanomagnet by inserting it in a tunnel Josephson junction and studying the current voltage (I-V) characteristic. The spin nutation of the molecular nanomagnet is generated by applying two circularly polarized magnetic fields. We demonstrate that modulation of the Josephson current by the nutation of the molecular nanomagnet’s spin appears as a stepwise structure like Shapiro steps in the I-V characteristic of the junction. Width and heights of these Shapiro-like steps are determined by two parameters of the spin nutation, frequency and amplitude of the nutation, which are simply tuned by the applied magnetic fields

  14. Electronic band alignment and electron transport in Cr/BaTiO3/Pt ferroelectric tunnel junctions

    International Nuclear Information System (INIS)

    Zenkevich, A.; Minnekaev, M.; Matveyev, Yu.; Lebedinskii, Yu.; Bulakh, K.; Chouprik, A.; Baturin, A.; Maksimova, K.; Thiess, S.; Drube, W.

    2013-01-01

    Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO 3 (001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO 3 /Pt junctions with a sub-μm Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ∼30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO 3 /Pt (Cr/BaTiO 3 ) interface +0.42(−0.03) eV following downward to upward polarization reversal.

  15. An ARC less InGaP/GaAs DJ solar cell with hetero tunnel junction

    Science.gov (United States)

    Sahoo, G. S.; Nayak, P. P.; Mishra, G. P.

    2016-07-01

    Multi junction solar cell has not achieved an optimum performance yet. To acquire more conversion efficiency research on multi junction solar cell are in progress. In this work we have proposed a dual junction solar cell with conversion efficiency of 43.603%. Mainly the focus is given on the tunnel diode, window layer and back surface field (BSF) layer of the cell, as all of them plays important role on the cell performance. Here we have designed a hetero InGaP/GaAs tunnel diode which makes tunnel diode more transparent to the bottom cell as well as reduces the recombination at the interfaces. The thickness of the window and BSF layer are optimized to achieve higher conversion efficiency. The simulation is carried out using Silvaco ATLAS TCAD under 1000 sun of AM1.5G spectrum. Different performance parameters of the cell like short circuit current density (Jsc), open circuit voltage (Voc), external quantum efficiency (EQE), fill factor (FF), conversion efficiency (η), spectral response and photogeneration rate of the cell are examined and compared with previously reported literatures. For the proposed model a Voc of 2.7043 V, Jsc of 1898.52 mA/cm2, FF of 88.88% and η of 43.6% are obtained.

  16. 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.

  17. Development of superconducting tunnel junction radiation detectors

    Energy Technology Data Exchange (ETDEWEB)

    Katagiri, Masaki; Kishimoto, Maki; Ukibe, Masahiro; Nakamura, Tatsuya; Nakazawa, Masaharu [Japan Atomic Energy Research Inst., Tokyo (Japan); Kurakado, Masahiko; Ishibashi, Kenji; Maehata, Keisuke

    1998-07-01

    Study on development of high energy resolution X-ray detector using superconducting tunnel junction (STJ) for radiation detection was conducted for 5 years under cooperation of University of Tokyo group and Kyushu University group by Quantum measurement research group of Advanced fundamental research center of JAERI. As the energy resolution of STJ could be obtained better results than that of Si semiconductor detector told to be actually best at present, this study aimed to actualize an X-ray detector usable for the experimental field and to elucidate radiation detection mechanism due to STJ. The STJ element used for this study was the one developed by Kurakado group of Nippon Steel Corp. As a results, some technical problems were almost resolved, which made some trouble when using the STJ element to detection element of X-ray spectrometer. In order to make the X-ray detector better, it is essential to manufacture a STJ element and develop serial junction type STJ element on the base of optimization of the element structure and selection and single crystallization of new superconducting materials such as Ta and others, activating the research results. (G.K.)

  18. Pronounced Environmental Effects on Injection Currents in EGaIn Tunneling Junctions Comprising Self-Assembled Monolayers.

    Science.gov (United States)

    Carlotti, Marco; Degen, Maarten; Zhang, Yanxi; Chiechi, Ryan C

    2016-09-15

    Large-area tunneling junctions using eutectic Ga-In (EGaIn) as a top contact have proven to be a robust, reproducible, and technologically relevant platform for molecular electronics. Thus far, the majority of studies have focused on saturated molecules with backbones consisting mainly of alkanes in which the frontier orbitals are either highly localized or energetically inaccessible. We show that self-assembled monolayers of wire-like oligophenyleneethynylenes (OPEs), which are fully conjugated, only exhibit length-dependent tunneling behavior in a low-O 2 environment. We attribute this unexpected behavior to the sensitivity of injection current on environment. We conclude that, contrary to previous reports, the self-limiting layer of Ga 2 O 3 strongly influences transport properties and that the effect is related to the wetting behavior of the electrode. This result sheds light on the nature of the electrode-molecule interface and suggests that adhesive forces play a significant role in tunneling charge-transport in large-area molecular junctions.

  19. One-third (period three) harmonic generation in microwave-driven Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Hansen, Jørn Bindslev; Clarke, J.; Mygind, Jesper

    1986-01-01

    One-third harmonic signals have been generated in the zero voltage state of a Josephson tunnel junction driven with a microwave current in the frequency range 8–20 GHz. The signal was as much as 50 dB above the noise level of the detector with a linewidth of less than 100 Hz. The junction...... parameters and microwave current were measured in situ in separate experiments. The subharmonic generation occurred for ranges of microwave current and frequency that were in reasonable agreement with the results of digital computer simulations. Applied Physics Letters is copyrighted by The American...

  20. Observation of negative differential resistance and single-electron tunneling in electromigrated break junctions

    International Nuclear Information System (INIS)

    Noguchi, Yutaka; Ueda, Rieko; Kubota, Tohru; Kamikado, Toshiya; Yokoyama, Shiyoshi; Nagase, Takashi

    2008-01-01

    We observed a negative differential resistance (NDR) along with single-electron tunneling (SET) in the electron transport of electromigrated break junctions with metal-free tetraphenylporphyrin (H 2 BSTBPP) at a temperature of 11 K. The NDR strongly depended on the applied gate voltages, and appeared only in the electron tunneling region of the Coulomb diamond. We could explain the mechanism of this new type of electron transport by a model assuming a molecular Coulomb island and local density of states of the source and the drain electrodes

  1. Spin-transfer torque in tunnel junctions with ferromagnetic layer of finite thickness

    International Nuclear Information System (INIS)

    Wilczynski, M.

    2011-01-01

    Two components of the spin torque exerted on a free ferromagnetic layer of finite thickness and a half-infinite ferromagnetic electrode in single tunnel junctions have been calculated in the spin-polarized free-electron-like one-band model. It has been found that the torque oscillates with the thickness of ferromagnetic layer and can be enhanced in the junction with the special layer thickness. The bias dependence of torque components also significantly changes with layer thickness. It is non-symmetric for the normal torque, in contrast to the symmetric junctions with two identical half-infinite ferromagnetic electrodes. The asymmetry of the bias dependence of the normal component of the torque can be also observed in the junctions with different spin splitting of the electron bands in the ferromagnetic electrodes. - Research highlights: → The torque oscillates with the thickness of ferromagnetic layer. → Bias dependence of the torque changes with the layer thickness. → Bias dependence of the normal torque can be asymmetric.

  2. The tunneling magnetoresistance and spin-polarized optoelectronic properties of graphyne-based molecular magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Yang, Zhi; Ouyang, Bin; Lan, Guoqing; Xu, Li-Chun; Liu, Ruiping; Liu, Xuguang

    2017-01-01

    Using density functional theory and the non-equilibrium Green’s function method, we investigate the spin-dependent transport and optoelectronic properties of the graphyne-based molecular magnetic tunnel junctions (MMTJs). We find that these MMTJs exhibit an outstanding tunneling magnetoresistance (TMR) effect. The TMR value is as high as 10 6 %. When the magnetization directions of two electrodes are antiparallel under positive or negative bias voltages, two kinds of pure spin currents can be obtained in the systems. Furthermore, under the irradiation of infrared, visible or ultraviolet light, spin-polarized photocurrents can be generated in the MMTJs, but the corresponding microscopic mechanisms are different. More importantly, if the magnetization directions of two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents. (paper)

  3. Long Josephson tunnel junctions with doubly connected electrodes

    Science.gov (United States)

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

    2012-03-01

    In order to mimic the phase changes in the primordial Big Bang, several cosmological solid-state experiments have been conceived, during the last decade, to investigate the spontaneous symmetry breaking in superconductors and superfluids cooled through their transition temperature. In one of such experiments, the number of magnetic flux quanta spontaneously trapped in a superconducting loop was measured by means of a long Josephson tunnel junction built on top of the loop itself. We have analyzed this system and found a number of interesting features not occurring in the conventional case with simply connected electrodes. In particular, the fluxoid quantization results in a frustration of the Josephson phase, which, in turn, reduces the junction critical current. Further, the possible stable states of the system are obtained by a self-consistent application of the principle of minimum energy. The theoretical findings are supported by measurements on a number of samples having different geometrical configuration. The experiments demonstrate that a very large signal-to-noise ratio can be achieved in the flux quanta detection.

  4. Quantum Effects in Molecule-Based Nanomagnets

    Science.gov (United States)

    Hill, Stephen

    2005-11-01

    Research into molecule-based-magnets has made immense strides in recent years, with the discoveries of all organic molecular magnets, room temperature 3D ordered permanent magnets, and single-molecule magnets (SMMs), the latter exhibiting a host of spectacular quantum phenomena; for a review, see ref. [1]. SMMs represent a molecular approach to nanoscale and sub-nanoscale magnetic particles. They offer all of the advantages of molecular chemistry as well as displaying the superparamagnetic properties of mesoscale magnetic particles of much larger dimensions. They also straddle the interface between classical and quantum behavior; for example, they exhibit quantum tunneling of their magnetization. I will give a general introduction to this area of research, followed by an overview of recent results obtained using high-frequency (40-800 GHz) electron paramagnetic resonance techniques developed at the University of Florida. These results include: an elucidation of the role of molecular symmetry in the magnetic quantum tunneling phenomenon [2]; and the observation of quantum entanglement between pairs of nanomagnets within a supramolecular dimer [3]. 1. D. Gatteschi and R. Sessoli, Angew. Chem. 42, 268 (2003). 2. E. del Barco et al., J. Low Temp. Phys. 140, 119-174 (2005). 3. S. Hill et al., Science 302, 1015 (2003).

  5. Simulation of magnetic tunnel junction in ferromagnetic/insulator/semiconductor structure

    Science.gov (United States)

    Kostrov, Alexander I.; Stempitsky, Viktor R.; Kazimirchik, Vladimir N.

    2008-07-01

    In this work, we present a physical model and electrical macromodel for simulation of Magnetic Tunnel Junction (MTJ) effect based on Ferromagnetic/Insulator/Semiconductor (FIS) nanostructure. A modified Brinkman model has been proposed by including the voltage-dependent density of states of the ferromagnetic electrodes in order to explain the bias dependence magnitoresistance. The model takes into account injection of carriers in the semiconductor and Shottky barrier, electron tunneling through thin insulator and spin-transfer torque writing approach in memory cell. These very promising features should constitute the third generation of Magnetoresistive RAM (MRAM). Besides, the model can efficiently be used to design magnetic CMOS circuits. The behavioral macro-model has been developed by means of Verilog-AMS language and implemented on the Cadence Virtuoso platform with Spectre simulator.

  6. High-temperature magnetoresistance study of a magnetic tunnel junction

    International Nuclear Information System (INIS)

    Chen, D.C.; Yao, Y.D.; Chen, C.M.; Hung, James; Chen, Y.S.; Wang, W.H.; Chen, W.C.; Kao, M.J.

    2006-01-01

    The thermal stability and the spin transportation phenomenon at room temperature and 140 deg. C of a series of magnetic tunneling junctions with the structure of bottom electrode/PtMn/Pinned layer/ AlO x /CoFe/NiFe/top electrode have been investigated. The MR ratio decreases from 33.5% at room temperature to 29% at 140 deg. C. The MR ratio at room temperature increases roughly 0.8% after thermal treatment at temperatures above 60 deg. C. This is related to the thermal relaxation of the strains existing in the samples

  7. Spatial dependence of plasma oscillations in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Holst, Thorsten; Hansen, Jørn Bindslev

    1991-01-01

    of an applied magnetic field. Numerical simulations of the governing partial-differential sine-Gordon equation were performed and compared to the experimental results and a perturbation analysis. The theoretical results support the experiments and allow us to interpret the observed crossover as due...... field threading the tunneling barrier. We compare measurements where the plasma frequency was tuned either by applying a magnetic field or by raising the temperature. A crossover from short- to long-junction behavior of the functional dependence of the plasma oscillations was observed in the case...

  8. InP tunnel junction for InGaAs/InP tandem solar cells

    Science.gov (United States)

    Vilela, M. F.; Freundlich, A.; Bensaoula, A.; Medelci, N.; Renaud, P.

    1995-01-01

    Chemical beam epitaxy (CBE) has been shown to allow the growth of high quality materials with reproducible complex compositional and doping profiles. The main advantage of CBE compared to metalorganic chemical vapor deposition (MOCVD), the most popular technique for InP-based photovoltaic device fabrication, is the ability to grow high purity epilayers at much lower temperatures (450-530 C). We have previously shown that CBE is perfectly suited toward the fabrication of complex photovoltaic devices such as InP/InGaAs monolithically integrated tandem solar cells, because its low process temperature preserves the electrical characteristics of the InGaAs tunnel junction commonly used as an ohmic interconnect. In this work using CBE for the fabrication of optically transparent (with respect to the bottom cell) InP tunnel diodes is demonstrated. Epitaxial growth were performed in a Riber CBE 32 system using PH3 and TMIn as III and V precursors. Solid Be (p-type) and Si (n-type) have been used as doping sources, allowing doping levels up to 2 x 10(exp -19)/cu cm and 1 x 10(exp -19)/cu cm for n and p type respectively. The InP tunnel junction characteristics and the influence of the growth's conditions (temperature, growth rate) over its performance have been carefully investigated. InP p(++)/n(++) tunnel junction with peak current densities up to 1600 A/sq cm and maximum specific resistivities (V(sub p)/I(sub p) - peak voltage to peak current ratio) in the range of 10(exp -4) Omega-sq cm were obtained. The obtained peak current densities exceed the highest results previously reported for their lattice matched counterparts, In(0.53)Ga( 0.47)As and should allow the realization of improved minimal absorption losses in the interconnect InP/InGaAs tandem devices for Space applications. Owing to the low process temperature required for the top cell, these devices exhibit almost no degradation of its characteristics after the growth of subsequent thick InP layer suggesting

  9. Thermoelectric-induced spin currents in single-molecule magnet tunnel junctions

    Science.gov (United States)

    Zhang, Zhengzhong; Jiang, Liang; Wang, Ruiqiang; Wang, Baigeng; Xing, D. Y.

    2010-12-01

    A molecular spin-current generator is proposed, which consists of a single-molecule magnet (SMM) coupled to two normal metal electrodes with temperature gradient. It is shown that this tunneling junction can generate a highly spin-polarized current by thermoelectric effects, whose flowing direction and spin polarization can be changed by adjusting the gate voltage applied to the SMM. This device can be realized with current technologies and may have practical use in spintronics and quantum information.

  10. Spin-dependent electronic transport characteristics in Fe4N/BiFeO3/Fe4N perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Yin, Li; Wang, Xiaocha; Mi, Wenbo

    2018-01-01

    Perpendicular magnetic tunnel junctions (MTJs) have attracted increasing attention owing to the low energy consumption and wide application prospects. Herewith, against Julliere's formula, an inverse tunnel magnetoresistance (TMR) appears in tetragonal Fe4N/BiFeO3/Fe4N perpendicular MTJs, which is attributed to the binding between the interface resonant tunneling state and central (bordered) hot spots. Especially, antiferromagnetic BiFeO3 shows an extra spin-polarized resonant state in the barrier, which provides a magnetic-barrier factor to affect the tunneling transport in MTJs. Meanwhile, due to the spin-polarized transport in Fe4N/BiFeO3/Fe4N MTJs, the sign of TMR can be tuned by the applied bias. The tunable TMR and resonant magnetic barrier effect pave the way for clarifying the tunneling transport in other junctions and spintronic devices.

  11. Tunneling anisotropic magnetoresistance in single-molecule magnet junctions

    Science.gov (United States)

    Xie, Haiqing; Wang, Qiang; Jiao, Hujun; Liang, J.-Q.

    2012-08-01

    We theoretically investigate quantum transport through single-molecule magnet (SMM) junctions with ferromagnetic and normal-metal leads in the sequential regime. The current obtained by means of the rate-equation gives rise to the tunneling anisotropic magnetoresistance (TAMR), which varies with the angle between the magnetization direction of ferromagnetic lead and the easy axis of SMM. The angular dependence of TAMR can serve as a probe to determine experimentally the easy axis of SMM. Moreover, it is demonstrated that both the magnitude and the sign of TAMR are tunable by the bias voltage, suggesting a new spin-valve device with only one magnetic electrode in molecular spintronics.

  12. Low-leakage superconducting tunnel junctions with a single-crystal Al{sub 2}O{sub 3} barrier

    Energy Technology Data Exchange (ETDEWEB)

    Oh, S [National Institute of Standards and Technology, Boulder, CO 80305 (United States); Department of Physics, University of Illinois, Urbana, IL 61801 (United States); Cicak, K; Osborn, K D; Simmonds, R W; Pappas, D P [National Institute of Standards and Technology, Boulder, CO 80305 (United States); McDermott, R; Cooper, K B; Steffen, M; Martinis, J M [University of California, Santa Barbara, CA 93106 (United States)

    2005-10-01

    We have developed a two-step growth scheme for single-crystal Al{sub 2}O{sub 3} tunnel barriers. The barriers are epitaxially grown on single-crystal rhenium (Re) base electrodes that are grown epitaxially on a sapphire substrate, while polycrystalline Al is used as the top electrode. We show that by first growing an amorphous aluminium (Al) oxide layer at room temperature and crystallizing it at a high temperature in oxygen environment, a morphologically intact single-crystal Al{sub 2}O{sub 3} layer is obtained. Tunnel junctions fabricated from these trilayers show very low subgap leakage current. This single-crystal Al{sub 2}O{sub 3} junction may open a new venue for coherent quantum devices.

  13. Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

    Directory of Open Access Journals (Sweden)

    Rui Sun

    2016-06-01

    Full Text Available We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100 substrates with a TiN buffer layer. A 50-nm-thick (200-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large IcRN product of 3.8 mV, a sharp quasiparticle current rise with a ΔVg of 0.4 mV, and a small subgap leakage current. The junction quality factor Rsg/RN was about 23 for the junction with a Jc of 47 A/cm2 and was about 6 for the junction with a Jc of 3.0 kA/cm2. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200-orientated TiN buffer layer and had a highly crystalline structure with the (200 orientation.

  14. Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Rui [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Makise, Kazumasa; Terai, Hirotaka [Advanced ICT Research Institute, National Institute of Information and Communications Technology (Japan); Zhang, Lu [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); Wang, Zhen, E-mail: zwang@mail.sim.ac.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Shanghai Tech University, Shanghai 201210 (China)

    2016-06-15

    We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100) substrates with a TiN buffer layer. A 50-nm-thick (200)-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large I{sub c}R{sub N} product of 3.8 mV, a sharp quasiparticle current rise with a ΔV{sub g} of 0.4 mV, and a small subgap leakage current. The junction quality factor R{sub sg}/R{sub N} was about 23 for the junction with a J{sub c} of 47 A/cm{sup 2} and was about 6 for the junction with a J{sub c} of 3.0 kA/cm{sup 2}. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200)-orientated TiN buffer layer and had a highly crystalline structure with the (200) orientation.

  15. Electronic band alignment and electron transport in Cr/BaTiO{sub 3}/Pt ferroelectric tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Zenkevich, A. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Minnekaev, M.; Matveyev, Yu.; Lebedinskii, Yu. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Bulakh, K.; Chouprik, A.; Baturin, A. [Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Maksimova, K. [Immanuel Kant Baltic Federal University, 236041 Kaliningrad (Russian Federation); Thiess, S.; Drube, W. [Deutsches Elektronen-Synchrotron DESY, D-22603 Hamburg (Germany)

    2013-02-11

    Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO{sub 3}(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO{sub 3}/Pt junctions with a sub-{mu}m Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of {approx}30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO{sub 3}/Pt (Cr/BaTiO{sub 3}) interface +0.42(-0.03) eV following downward to upward polarization reversal.

  16. Ultrahigh Tunneling-Magnetoresistance Ratios in Nitride-Based Perpendicular Magnetic Tunnel Junctions from First Principles

    Science.gov (United States)

    Yang, Baishun; Tao, Lingling; Jiang, Leina; Chen, Weizhao; Tang, Ping; Yan, Yu; Han, Xiufeng

    2018-05-01

    We report a first-principles study of electronic structures, magnetic properties, and the tunneling-magnetoresistance (TMR) effect of a series of ferromagnetic nitride M4N (M =Fe , Co, Ni)-based magnetic tunnel junctions (MTJs). It is found that bulk Fe4 N reveals a half-metal nature in terms of the Δ1 state. A perpendicular magnetic anisotropy is observed in the periodic system Fe4 N /MgO . In particular, the ultrahigh TMR ratio of over 24 000% is predicted in the Fe4 N /MgO /Fe4N MTJ due to the interface resonance tunneling and relatively high transmission for states of other symmetry. Besides, the large TMR can be maintained with the change of atomic details at the interface, such as the order-disorder interface, the change of thickness of the MgO barrier, and different in-plane lattice constants of the MTJ. The physical origin of the TMR effect can be well understood by analyzing the band structure and transmission channel of bulk Fe4 N as well as the transmission in momentum space of Fe4 N /MgO /Fe4N . Our results suggest that the Fe4 N /MgO /Fe4N MTJ is a benefit for spintronic applications.

  17. Spin injection and magnetoresistance in MoS2-based tunnel junctions using Fe3Si Heusler alloy electrodes.

    Science.gov (United States)

    Rotjanapittayakul, Worasak; Pijitrojana, Wanchai; Archer, Thomas; Sanvito, Stefano; Prasongkit, Jariyanee

    2018-03-19

    Recently magnetic tunnel junctions using two-dimensional MoS 2 as nonmagnetic spacer have been fabricated, although their magnetoresistance has been reported to be quite low. This may be attributed to the use of permalloy electrodes, injecting current with a relatively small spin polarization. Here we evaluate the performance of MoS 2 -based tunnel junctions using Fe 3 Si Heusler alloy electrodes. Density functional theory and the non-equilibrium Green's function method are used to investigate the spin injection efficiency (SIE) and the magnetoresistance (MR) ratio as a function of the MoS 2 thickness. We find a maximum MR of ~300% with a SIE of about 80% for spacers comprising between 3 and 5 MoS 2 monolayers. Most importantly, both the SIE and the MR remain robust at finite bias, namely MR > 100% and SIE > 50% at 0.7 V. Our proposed materials stack thus demonstrates the possibility of developing a new generation of performing magnetic tunnel junctions with layered two-dimensional compounds as spacers.

  18. Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

    Science.gov (United States)

    Ellis, Matthew O. A.; Stamenova, Maria; Sanvito, Stefano

    2017-12-01

    There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for nonvolatile memory devices. With the aim of analyzing potential materials for efficient current-operated magnetic junctions, we have developed a multi-scale methodology combining ab initio calculations of spin-transfer torque with large-scale time-dependent simulations using atomistic spin dynamics. In this work we introduce our multiscale approach, including a discussion on a number of possible schemes for mapping the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate, and versatile framework for designing novel current-operated magnetic devices, where all the materials details are taken into account.

  19. 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.

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

    KAUST Repository

    Caffrey, Nuala Mai; Archer, Thomas; Rungger, Ivan; Sanvito, Stefano

    2012-01-01

    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.

  1. Experimental study of macroscopic quantum tunnelling in Bi2212 intrinsic Josephson junctions

    International Nuclear Information System (INIS)

    Matsumoto, Tetsuro; Kashiwaya, Hiromi; Shibata, Hajime; Kashiwaya, Satoshi; Kawabata, Shiro; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Tanaka, Yukio

    2007-01-01

    The quantum dynamics of Bi 2 Sr 2 CaCu 2 O 8+δ intrinsic Josephson junctions (IJJs) is studied based on escape rate measurements. The saturations observed in the escape temperature and in the width of the switching current below 0.5 K (= T * ) indicate the transition of the switching mechanism from thermal activation to macroscopic quantum tunnelling. It is shown that the switching properties are consistently explained in terms of the underdamped Josephson junction with a quality factor of 70 ± 20 in spite of possible damping due to the nodal quasiparticles of d-wave superconductivity. The present result gives the upper limit of the damping of IJJs

  2. Valley and spin resonant tunneling current in ferromagnetic/nonmagnetic/ferromagnetic silicene junction

    Directory of Open Access Journals (Sweden)

    Yaser Hajati

    2016-02-01

    Full Text Available We study the transport properties in a ferromagnetic/nonmagnetic/ferromagnetic (FNF silicene junction in which an electrostatic gate potential, U, is attached to the nonmagnetic region. We show that the electrostatic gate potential U is a useful probe to control the band structure, quasi-bound states in the nonmagnetic barrier as well as the transport properties of the FNF silicene junction. In particular, by introducing the electrostatic gate potential, both the spin and valley conductances of the junction show an oscillatory behavior. The amplitude and frequency of such oscillations can be controlled by U. As an important result, we found that by increasing U, the second characteristic of the Klein tunneling is satisfied as a result of the quasiparticles chirality which can penetrate through a potential barrier. Moreover, it is found that for special values of U, the junction shows a gap in the spin and valley-resolve conductance and the amplitude of this gap is only controlled by the on-site potential difference, Δz. Our findings of high controllability of the spin and valley transport in such a FNF silicene junction may improve the performance of nano-electronics and spintronics devices.

  3. A new spin-functional MOSFET based on magnetic tunnel junction technology: pseudo-spin-MOSFET

    OpenAIRE

    Shuto, Yusuke; Nakane, Ryosho; Wang, Wenhong; Sukegawa, Hiroaki; Yamamoto, Shuu'ichirou; Tanaka, Masaaki; Inomata, Koichiro; Sugahara, Satoshi

    2009-01-01

    We fabricated and characterized a new spin-functional MOSFET referred to as a pseudo-spin-MOSFET (PS-MOSFET). The PS-MOSFET is a circuit using an ordinary MOSFET and magnetic tunnel junction (MTJ) for reproducing functions of spin-transistors. Device integration techniques for a bottom gate MOSFET using a silicon-on-insulator (SOI) substrate and for an MTJ with a full-Heusler alloy electrode and MgO tunnel barrier were developed. The fabricated PS-MOSFET exhibited high and low transconductanc...

  4. Characteristics of magnetic tunnel junctions comprising ferromagnetic amorphous NiFeSiB layers

    International Nuclear Information System (INIS)

    Chun, B.S.; Kim, Y.K.; Hwang, J.Y.; Yim, H.I.; Rhee, J.R.; Kim, T.W.

    2007-01-01

    Magnetic tunnel junctions (MTJs), which consisted of amorphous ferromagnetic Ni 16 Fe 62 Si 8 B 14 free layers, were investigated. NiFeSiB has a lower saturation magnetization (M s : 800 emu/cm 3 ) than Co 90 Fe 10 and a higher anisotropy constant (K u : 2700 erg/cm 3 ) than Ni 80 Fe 20 . By increasing the free layer thickness, the tunnel magnetoresistance (TMR) ratio of up to 41% was achieved and it exhibited a much lower switching field (H sw ) than the conventionally used CoFe free layer MTJ. Furthermore, by inserting a thin CoFe layer (1 nm) at the tunnel barrier/NiFeSiB interface, the TMR ratio and switching squareness were enhanced

  5. Development of superconducting tunnel junction as photon counting detector in astronomy

    International Nuclear Information System (INIS)

    Jorel, C.

    2004-12-01

    This work describes the development of S/Al-AlOx-Al/S Superconducting Tunnel Junctions (STJ) to count photons for astronomical applications in the near-infrared. The incoming light energy is converted into excited charges in a superconducting layer (S, either Nb or Ta) with a population proportional to the deposited energy. The photon energy can thus be evaluated by integrating the tunnel current induced in a voltage biased junction at a very low temperature (100 mK). The performance of STJ for light detection is discussed in the first chapter and compared with the best performances obtained with other techniques based on either superconductors. At the beginning of the thesis, a previous manufacturing process made it possible to obtain good quality Nb based junctions and preliminary results for photon counting. The objective of the thesis was to replace Nb as absorber with Ta, an intrinsically more sensitive material, and secondly to develop a new and more efficient manufacturing process. We first focused on the optimization of the Tantalum thin film quality. Structural analysis showed that these films can be grown epitaxially by magnetron sputtering onto an R-plane sapphire substrate heated to 600 Celsius degrees and covered by a thin Nb buffer layer. Electrical transport measurement from room to low temperatures gave excellent Relative Resistive Ratios of about 50 corresponding to mean free path of the order of 100 nm. Then, we conceived an original manufacturing process batch on 3 inch diameter sapphire substrate with five mask levels. These masks made it possible to produce single pixel STJ of different sizes (from 25*25 to 50*50 square microns) and shapes. We also produced multiple junctions onto a common absorber as well as 9-pixel arrays. Thanks to the development of this process we obtained a very large percentage of quality junctions (>90%) with excellent measured normal resistances of a few micro-ohm cm 2 and low leakage currents of the order of one n

  6. Effect of gamma-ray irradiation on the surface states of MOS tunnel junctions

    Science.gov (United States)

    Ma, T. P.; Barker, R. C.

    1974-01-01

    Gamma-ray irradiation with doses up to 8 megarad produces no significant change on either the C(V) or the G(V) characteristics of MOS tunnel junctions with intermediate oxide thicknesses (40-60 A), whereas the expected flat-band shift toward negative electrode voltages occurs in control thick oxide capacitors. A simple tunneling model would explain the results if the radiation-generated hole traps are assumed to lie below the valence band of the silicon. The experiments also suggest that the observed radiation-generated interface states in conventional MOS devices are not due to the radiation damage of the silicon surface.

  7. Thermally activated magnetization reversal in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Guang-Hong, Zhou; Yin-Gang, Wang; Xian-Jin, Qi; Zi-Quan, Li; Jian-Kang, Chen

    2009-01-01

    In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO x /CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  8. Limitations in cooling electrons using normal-metal-superconductor tunnel junctions.

    Science.gov (United States)

    Pekola, J P; Heikkilä, T T; Savin, A M; Flyktman, J T; Giazotto, F; Hekking, F W J

    2004-02-06

    We demonstrate both theoretically and experimentally two limiting factors in cooling electrons using biased tunnel junctions to extract heat from a normal metal into a superconductor. First, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do not obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Second, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.

  9. Pronounced Environmental Effects on Injection Currents in EGaln Tunneling Junctions Comprising Self-Assembled Monolayers

    NARCIS (Netherlands)

    Carlotti, Marco; Degen, Maarten; Zhang, Yanxi; Chiechi, Ryan C.

    2016-01-01

    Large-area tunneling junctions using eutectic Ga-In (EGaIn) as a top contact have proven to be a robust, reproducible, and technologically relevant platform for molecular electronics. Thus far, the majority of studies have focused on saturated molecules with backbones consisting mainly of alkanes in

  10. Inelastic electron tunneling through degenerate and nondegenerate ground state polymeric junctions

    International Nuclear Information System (INIS)

    Golsanamlou, Z.; Bagheri Tagani, M.; Rahimpour Soleimani, H.

    2015-01-01

    Highlights: • Current–voltage characteristics of two polymeric junctions are studied. • Current is reduced in phonon assistant tunneling regime. • Behavior of current is independent of temperature. • Elastic energy changes current drastically. - Abstract: The inelastic electron transport properties through two polymeric (trans-polyacetylene and polythiophene) molecular junctions are studied using Keldysh nonequilibrium Green function formalism. The Hamiltonian of the polymers is described via Su–Schrieffer–Heeger model and the metallic electrodes are modeled by the wide-band approximation. Results show that the step-like behavior of the current–voltage characteristics is deformed in presence of strong electron–phonon interaction. Also, the magnitude of current is slightly decreased in the phonon assistant electron transport regime. In addition, it is observed that the I–V curves are independent of temperature

  11. State diagram of a perpendicular magnetic tunnel junction driven by spin transfer torque: A power dissipation approach

    Energy Technology Data Exchange (ETDEWEB)

    Lavanant, M. [Institut Jean Lamour, UMR CNRS 7198 – Université de Lorraine, Nancy (France); Department of Physics, New York University, New York, NY 10003 (United States); Petit-Watelot, S. [Institut Jean Lamour, UMR CNRS 7198 – Université de Lorraine, Nancy (France); Kent, A.D. [Department of Physics, New York University, New York, NY 10003 (United States); Mangin, S., E-mail: stephane.mangin@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198 – Université de Lorraine, Nancy (France)

    2017-04-15

    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. - Highlights: • Methods to compute state Diagram (Voltage Versus Field) for perpendicular Magnetic Tunnel Junctions. • Comparison between the conventional LLG model and a model based on Power dissipation to study magnetization reversal in magnetic tunnel junction.

  12. Effect of resistance feedback on spin torque-induced switching of nanomagnets

    International Nuclear Information System (INIS)

    Garzon, Samir; Webb, Richard A.; Covington, Mark; Kaka, Shehzaad; Crawford, Thomas M.

    2009-01-01

    In large magnetoresistance devices spin torque-induced changes in resistance can produce GHz current and voltage oscillations which can affect magnetization reversal. In addition, capacitive shunting in large resistance devices can further reduce the current, adversely affecting spin torque switching. Here, we simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and the transmission line telegrapher's equations to study the effects of resistance feedback and capacitance on magnetization reversal of both spin valves and magnetic tunnel junctions. While for spin valves parallel (P) to anti-parallel (AP) switching is adversely affected by the resistance feedback due to saturation of the spin torque, in low resistance magnetic tunnel junctions P-AP switching is enhanced. We study the effect of resistance feedback on the switching time of magnetic tunnel junctions, and show that magnetization switching is only affected by capacitive shunting in the pF range.

  13. Electronic transport through EuO spin-filter tunnel junctions

    KAUST Repository

    Jutong, Nuttachai

    2012-11-12

    Epitaxial spin-filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide (EuO) are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore, we also discuss the relation between the spin transport properties and the Cu-EuO interface geometry. The level alignment of the junction is sensitively affected by the interface spacing, since this determines the charge transfer between EuO and the Cu electrodes. Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect spin filter, with a spin polarization of the current close to 100%, and with both the Eu-5d conduction-band and the Eu-4f valence-band states contributing to the coherent transport. For epitaxial EuO on Cu, a symmetry filtering is observed, with the Δ1 states dominating the transmission. This leads to a transport gap larger than the fundamental EuO band gap. Importantly, the high spin polarization of the current is preserved up to large bias voltages.

  14. Piezo-tunnel effect in Al/Al2O3/Al junctions elaborated by atomic layer deposition

    Science.gov (United States)

    Rafael, R.; Puyoo, E.; Malhaire, C.

    2017-11-01

    In this work, the electrical transport in Al/Al2O3/Al junctions under mechanical stress is investigated in the perspective to use them as strain sensors. The metal/insulator/metal junctions are elaborated with a low temperature process (≤200 °C) fully compatible with CMOS back-end-of-line. The conduction mechanism in the structure is found to be Fowler-Nordheim tunneling, and efforts are made to extract the relevant physical parameters. Gauge factors up to -32.5 were found in the fabricated devices under tensile stress. Finally, theoretical mechanical considerations give strong evidence that strain sensitivity in Al/Al2O3/Al structures originates not only from geometrical deformations but also from the variation of interface barrier height and/or effective electronic mass in the tunneling oxide layer.

  15. Defining the value of injection current and effective electrical contact area for EGaIn-based molecular tunneling junctions.

    Science.gov (United States)

    Simeone, Felice C; Yoon, Hyo Jae; Thuo, Martin M; Barber, Jabulani R; Smith, Barbara; Whitesides, George M

    2013-12-04

    Analysis of rates of tunneling across self-assembled monolayers (SAMs) of n-alkanethiolates SCn (with n = number of carbon atoms) incorporated in junctions having structure Ag(TS)-SAM//Ga2O3/EGaIn leads to a value for the injection tunnel current density J0 (i.e., the current flowing through an ideal junction with n = 0) of 10(3.6±0.3) A·cm(-2) (V = +0.5 V). This estimation of J0 does not involve an extrapolation in length, because it was possible to measure current densities across SAMs over the range of lengths n = 1-18. This value of J0 is estimated under the assumption that values of the geometrical contact area equal the values of the effective electrical contact area. Detailed experimental analysis, however, indicates that the roughness of the Ga2O3 layer, and that of the Ag(TS)-SAM, determine values of the effective electrical contact area that are ~10(-4) the corresponding values of the geometrical contact area. Conversion of the values of geometrical contact area into the corresponding values of effective electrical contact area results in J0(+0.5 V) = 10(7.6±0.8) A·cm(-2), which is compatible with values reported for junctions using top-electrodes of evaporated Au, and graphene, and also comparable with values of J0 estimated from tunneling through single molecules. For these EGaIn-based junctions, the value of the tunneling decay factor β (β = 0.75 ± 0.02 Å(-1); β = 0.92 ± 0.02 nC(-1)) falls within the consensus range across different types of junctions (β = 0.73-0.89 Å(-1); β = 0.9-1.1 nC(-1)). A comparison of the characteristics of conical Ga2O3/EGaIn tips with the characteristics of other top-electrodes suggests that the EGaIn-based electrodes provide a particularly attractive technology for physical-organic studies of charge transport across SAMs.

  16. The switching characteristics of free layer of patterned magnetic tunnel junction device

    International Nuclear Information System (INIS)

    Chen, C.C.; Wang, Y.R.; Kuo, C.Y.; Wu, J.C.; Horng, Lance; Wu, Teho; Yoshimura, S.; Tsunoda, M.; Takahashi, M.

    2006-01-01

    The free layer switching properties of microstructured magnetic tunnel junctions have been investigated. The M-H loop of nonpatterned film shows ferromagnetic coupling with 10 Oe shifting associated with the interlayer roughness coupling. The MR curve of the patterned element shows stepped minor loop, less loop shifting, and larger coercive field due to shape anisotropy and stray field effects. MFM images of the element show nonuniform domain structures during reversal process

  17. Retraction: Graphene-SnO2 nanocomposites decorated with quantum tunneling junctions: preparation strategies, microstructures and formation mechanism.

    Science.gov (United States)

    Simpson, Anna

    2017-09-20

    Retraction of 'Graphene-SnO 2 nanocomposites decorated with quantum tunneling junctions: preparation strategies, microstructures and formation mechanism' by Qingxiu Wang et al., Phys. Chem. Chem. Phys., 2014, 16, 19351-19357.

  18. Towards nanoscale magnetic memory elements : fabrication and properties of sub - 100 nm magnetic tunnel junctions

    NARCIS (Netherlands)

    Fabrie, C.G.C.H.M.

    2008-01-01

    The rapidly growing field of spintronics has recently attracted much attention. Spintronics is electronics in which the spin degree of freedom has been added to conventional chargebased electronic devices. A magnetic tunnel junction (MTJ) is an example of a spintronic device. MTJs consist of two

  19. 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...

  20. 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.

  1. Conductance enhancement due to interface magnons in electron-beam evaporated MgO magnetic tunnel junctions with CoFeB free layer deposited at different pressure

    Energy Technology Data Exchange (ETDEWEB)

    Guo, P.; Yu, G. Q.; Wei, H. X.; Han, X. F., E-mail: jiafengfeng@aphy.iphy.ac.cn, E-mail: xfhan@aphy.iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, D. L.; Feng, J. F., E-mail: jiafengfeng@aphy.iphy.ac.cn, E-mail: xfhan@aphy.iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Kurt, H. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Department of Engineering Physics, Istanbul Medeniyet University, 34720 Istanbul (Turkey); Chen, J. Y.; Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland)

    2014-10-21

    Electron-beam evaporated MgO-based magnetic tunnel junctions have been fabricated with the CoFeB free layer deposited at Ar pressure from 1 to 4 mTorr, and their tunneling process has been studied as a function of temperature and bias voltage. By changing the growth pressure, the junction dynamic conductance dI/dV, inelastic electron tunneling spectrum d²I/dV², and tunneling magnetoresistance vary with temperature. Moreover, the low-energy magnon cutoff energy E{sub C} derived from the conductance versus temperature curve agrees with interface magnon energy obtained directly from the inelastic electron tunneling spectrum, which demonstrates that interface magnons are involved in the electron tunneling process, opening an additional conductance channel and thus enhancing the total conductance.

  2. 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.

  3. Magnetic tunneling junctions with the Heusler compound Co2Cr0.6Fe0.4Al

    International Nuclear Information System (INIS)

    Conca Parra, A.

    2007-01-01

    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 2 Cr 0.6 Fe 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 2 O 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 to an improvement of

  4. 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.

  5. Study of switching behavior of exchange-coupled nanomagnets by transverse magnetization metrology

    Science.gov (United States)

    Dey, Himadri S.; Csaba, Gyorgy; Bernstein, Gary H.; Porod, Wolfgang

    2017-05-01

    We investigate the static switching modes of nanomagnets patterned from antiferromagnetically exchange-coupled magnetic multilayers, and compare them to nanomagnets having only dipole coupling between the ferromagnetic layers. Vibrating sample magnetometry experiments, supported by micromagnetic simulations, reveal two distinct switching mechanisms between the exchange-coupled and only dipole-coupled nanomagnets. The exchange-coupled nanomagnets exhibit gradual switching of the layers, dictated by the strong antiferromagnetic exchange coupling present between the layers. However, the layers of the only dipole-coupled nanomagnets show abrupt nucleation/growth type switching. A comprehensive understanding of the switching modes of such layered and patterned systems can add new insight into the reversal mechanisms of similar systems employed for spintronic and magneto-logic device applications.

  6. 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.

  7. Superparamagnetic perpendicular magnetic tunnel junctions for true random number generators

    Science.gov (United States)

    Parks, Bradley; Bapna, Mukund; Igbokwe, Julianne; Almasi, Hamid; Wang, Weigang; Majetich, Sara A.

    2018-05-01

    Superparamagnetic perpendicular magnetic tunnel junctions are fabricated and analyzed for use in random number generators. Time-resolved resistance measurements are used as streams of bits in statistical tests for randomness. Voltage control of the thermal stability enables tuning the average speed of random bit generation up to 70 kHz in a 60 nm diameter device. In its most efficient operating mode, the device generates random bits at an energy cost of 600 fJ/bit. A narrow range of magnetic field tunes the probability of a given state from 0 to 1, offering a means of probabilistic computing.

  8. Generation of constant-amplitude radio-frequency sweeps at a tunnel junction for spin resonance STM

    International Nuclear Information System (INIS)

    Paul, William; Lutz, Christopher P.; Heinrich, Andreas J.; Baumann, Susanne

    2016-01-01

    We describe the measurement and successful compensation of the radio-frequency transfer function of a scanning tunneling microscope over a wide frequency range (15.5–35.5 GHz) and with high dynamic range (>50 dB). The precise compensation of cabling resonances and attenuations is critical for the production of constant-voltage frequency sweeps for electric-field driven electron spin resonance (ESR) experiments. We also demonstrate that a well-calibrated tunnel junction voltage is necessary to avoid spurious ESR peaks that can arise due to a non-flat transfer function.

  9. Generation of constant-amplitude radio-frequency sweeps at a tunnel junction for spin resonance STM

    Energy Technology Data Exchange (ETDEWEB)

    Paul, William; Lutz, Christopher P.; Heinrich, Andreas J. [IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States); Baumann, Susanne [IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States); Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland)

    2016-07-15

    We describe the measurement and successful compensation of the radio-frequency transfer function of a scanning tunneling microscope over a wide frequency range (15.5–35.5 GHz) and with high dynamic range (>50 dB). The precise compensation of cabling resonances and attenuations is critical for the production of constant-voltage frequency sweeps for electric-field driven electron spin resonance (ESR) experiments. We also demonstrate that a well-calibrated tunnel junction voltage is necessary to avoid spurious ESR peaks that can arise due to a non-flat transfer function.

  10. Anisotropic Magnetoresistance and Anisotropic Tunneling Magnetoresistance due to Quantum Interference in Ferromagnetic Metal Break Junctions

    DEFF Research Database (Denmark)

    Bolotin, Kirill; Kuemmeth, Ferdinand; Ralph, D

    2006-01-01

    We measure the low-temperature resistance of permalloy break junctions as a function of contact size and the magnetic field angle in applied fields large enough to saturate the magnetization. For both nanometer-scale metallic contacts and tunneling devices we observe large changes in resistance w...... with the angle, as large as 25% in the tunneling regime. The pattern of magnetoresistance is sensitive to changes in bias on a scale of a few mV. We interpret the effect as a consequence of conductance fluctuations due to quantum interference....

  11. Supersymmetric phase transition in Josephson-tunnel-junction arrays

    Energy Technology Data Exchange (ETDEWEB)

    Foda, O.

    1988-08-31

    The fully frustrated XY model in two dimensions exhibits a vortex-unbinding as well as an Ising transition. If the Ising transition overlaps with the critical line that ends on the vortex transition: T/sub I/less than or equal toT/sub V/, then the model is equivalent, at the overlap temperature, to a free massless field theory of 1 boson and 1 Majorana fermion, which is a superconformal field theory, of central charge c=3/2. The model is experimentally realized in terms of an array of Josephson-tunnel junctions in a transverse magnetic field. The experiment reveals a phase transition consistent with T/sub I/=T/sub V/. Thus, at the critical temperature, the array provides a physical realization of a supersymmetric quantum field theory.

  12. Electron Tunneling in Junctions Doped with Semiconductors and Metals.

    Science.gov (United States)

    Bell, Lloyd Douglas, II

    In this study, tunnel junctions incorporating thin layers of semiconductors and metals have been analyzed. Inelastic electron tunneling spectroscopy (IETS) was employed to yield high-resolution vibrational spectra of surface species deposited at the oxide-M_2 interface of M_1-M_1O _{rm x}-M _2 tunneling samples. Analysis was also performed on the elastic component of the tunneling current, yielding information on the tunnel barrier shape. The samples in this research exhibit a wide range of behavior. The IETS for Si, SiO_2, and Ge doped samples show direct evidence of SiH _{rm x} and GeH_ {rm x} formation. The particular species formed is shown to depend on the form of the evaporated dopant. Samples were also made with organic dopants deposited over the evaporated dopants. Many such samples show marked effects of the evaporated dopants on the inelastic peak intensities of the organic dopants. These alterations are correlated with the changed reactivity of the oxide surface coupled with a change in the OH dipole layer density on the oxide. Thicker organic dopant layers cause large changes in the elastic tunneling barrier due to OH layer alterations or the low barrier attributes of the evaporated dopant. In the cases of the thicker layers an extra current-carrying mechanism is shown to be contributing. Electron ejection from charge traps is proposed as an explanation for this extra current. The trend of barrier shape with dopant thickness is examined. Many of these dopants also produce a voltage-induced shift in the barrier shape which is stable at low temperature but relaxes at high temperature. This effect is similar to that produced by certain organic dopants and is explained by metastable bond formation between the surface OH and dopant. Other dopants, such as Al, Mg, and Fe, produce different effects. These dopants cause large I-V nonlinearity at low voltages. This nonlinearity is modeled as a giant zero-bias anomaly (ZBA) and fits are presented which show good

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

    KAUST Repository

    Useinov, Arthur; Kosel, Jü rgen

    2011-01-01

    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

  14. Tunneling current in HfO2 and Hf0.5Zr0.5O2-based ferroelectric tunnel junction

    Science.gov (United States)

    Dong, Zhipeng; Cao, Xi; Wu, Tong; Guo, Jing

    2018-03-01

    Ferroelectric tunnel junctions (FTJs) have been intensively explored for future low power data storage and information processing applications. Among various ferroelectric (FE) materials studied, HfO2 and H0.5Zr0.5O2 (HZO) have the advantage of CMOS process compatibility. The validity of the simple effective mass approximation, for describing the tunneling process in these materials, is examined by computing the complex band structure from ab initio simulations. The results show that the simple effective mass approximation is insufficient to describe the tunneling current in HfO2 and HZO materials, and quantitative accurate descriptions of the complex band structures are indispensable for calculation of the tunneling current. A compact k . p Hamiltonian is parameterized to and validated by ab initio complex band structures, which provides a method for efficiently and accurately computing the tunneling current in HfO2 and HZO. The device characteristics of a metal/FE/metal structure and a metal/FE/semiconductor (M-F-S) structure are investigated by using the non-equilibrium Green's function formalism with the parameterized effective Hamiltonian. The result shows that the M-F-S structure offers a larger resistance window due to an extra barrier in the semiconductor region at off-state. A FTJ utilizing M-F-S structure is beneficial for memory design.

  15. Theory of superconducting tunneling without the tunneling Hamiltonian

    International Nuclear Information System (INIS)

    Arnold, G.B.

    1987-01-01

    When a tunneling barrier is nearly transparent, the standard tunneling (or transfer) Hamiltonian approximation fails. The author describes the theory which is necessary for calculating the tunneling current in these cases, and illustrate it by comparing theory and experiment on superconductor/insulator/superconductor (SIS) junctions have ultra-thin tunnel barriers. This theory accurately explains the subgap structure which appears in the dynamical resistance of such SIS junctions, including many observed details which no previous theory has reproduced. The expression for the current through an SIS junction with an ultrathin barrier is given by I(t) = Re{Sigma/sub n/ J/sub n/ (omega/sub o/)e/sup in omega/o/sup t/} where omega/sub o/ = 2eV/h is the Josephson frequency, V is the bias voltage, and the J/sub n/ are voltage dependent coefficients, one for each positive or negative integer, n, and n=0. The relative sign of the terms involving cos(n omega/sub o/t) and sin(n omega/sub o/t) agrees with experiment, in contrast to previous theories of Josephson tunneling

  16. Performance enhancement of Ge-on-Insulator tunneling FETs with source junctions formed by low-energy BF2 ion implantation

    Science.gov (United States)

    Katoh, Takumi; Matsumura, Ryo; Takaguchi, Ryotaro; Takenaka, Mitsuru; Takagi, Shinichi

    2018-04-01

    To clarify the process of formation of source regions of high-performance Ge n-channel tunneling field-effect transistors (TFETs), p+-n junctions formed by low-energy ion implantation (I/I) of BF2 atoms are characterized. Here, the formation of p+-n junctions with steep B profiles and low junction leakage is a key issue. The steepness of 5.7 nm/dec in profiles of B implanted into Ge is obtained for BF2 I/I at 3 keV with a dose of 4 × 1014 cm-2. Ge-on-insulator (GOI) n-TFETs with the source tunnel junctions formed by low-energy B and BF2 I/I are fabricated on GOI substrates and the device operation is confirmed. Although the performance at room temperature is significantly degraded by the source junction leakage current, an I on/I off ratio of 105 and the minimum sub-threshold swing (S.S.) of 130 mV/dec are obtained at 10 K. It is found that GOI n-TFETs with steeper B profiles formed by BF2 I/I have led to higher on current and a lower sub-threshold slope, demonstrating the effectiveness of steep B profiles in enhancing the GOI TFET performance.

  17. Operating modes of superconducting tunnel junction device

    Energy Technology Data Exchange (ETDEWEB)

    Maehata, Keisuke [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering

    1998-07-01

    In the Electrotechnical Laboratory, an Nb type superconducting tunnel junction (STJ) device with 200 x 200 sq. micron in area and super high quality was manufactured. By using 55-fe source, response of this large area STJ to X-ray was measured. In this measurement, two action modes with different output wave height from front amplifier were observed. Then, in this study, current-voltage feature of the element in each action mode was analyzed to elucidate a mechanism to form such two action modes. The feature was analyzed by using first order approximate solution on cavity resonance mode of Sine-Gordon equation. From the analytical results, it could be supposed that direction and magnitude of effective magnetic field penetrating into jointed area changed by an induction current effect owing to impressing speed of the magnetic field, which brings two different current-voltage features to make possible to observe two action modes with different pulse wave height. (G.K.)

  18. Zurek–Kibble Symmetry Breaking Process in Superconducting Rings; Spontaneous Fluxon Formation in Annular Josephson Tunnel Junctions

    DEFF Research Database (Denmark)

    Aarøe, Morten; Monaco, Roberto; Dmitriev, P

    2007-01-01

    We report on new investigations of spontaneous symmetry breaking in non-adiabatic phase transitions. This Zurek-Kibble (ZK) process is mimicked in solid state systems by trapping of magnetic flux quanta, fluxons, in a long annular Josephson tunnel junction quenched through the normal-superconducting...

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

    International Nuclear Information System (INIS)

    Soodchomshom, Bumned; Chantngarm, Peerasak

    2010-01-01

    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 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 χ ∼ md/hv F . With the barrier strength Z ∼ V G d/hv F , the number of peaks N is determined through the relation Z ∼ Nπ + σπ (with 0 < σ≤1 for χ < 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.

  20. Dynamical properties of three terminal magnetic tunnel junctions: Spintronics meets spin-orbitronics

    Energy Technology Data Exchange (ETDEWEB)

    Tomasello, R. [Department of Computer Science, Modeling, Electronics and System Science, University of Calabria, Rende (CS) (Italy); Carpentieri, M., E-mail: m.carpentieri@poliba.it [Department of Electrical and Information Engineering, Politecnico of Bari, via E. Orabona 4, I-70125 Bari (Italy); Finocchio, G. [Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, C.da di Dio, I-98166 Messina (Italy)

    2013-12-16

    This Letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed.

  1. Dynamical properties of three terminal magnetic tunnel junctions: Spintronics meets spin-orbitronics

    International Nuclear Information System (INIS)

    Tomasello, R.; Carpentieri, M.; Finocchio, G.

    2013-01-01

    This Letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed

  2. Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope

    International Nuclear Information System (INIS)

    Naaman, O.; Teizer, W.; Dynes, R. C.

    2001-01-01

    We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50--300 k Omega. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory

  3. A supersymmetric phase transition in Josephson-tunnel-junction arrays

    International Nuclear Information System (INIS)

    Foda, O.

    1988-01-01

    The fully frustrated XY model in two dimensions exhibits a vortex-unbinding as well as an Ising transition. If the Ising transition overlaps with the critical line that ends on the vortex transition: T I ≤T V , then the model is equivalent, at the overlap temperature, to a free massless field theory of 1 boson and 1 Majorana fermion, which is a superconformal field theory, of central charge c=3/2. The model is experimentally realized in terms of an array of Josephson-tunnel junctions in a transverse magnetic field. The experiment reveals a phase transition consistent with T I =T V . Thus, at the critical temperature, the array provides a physical realization of a supersymmetric quantum field theory. (orig.)

  4. Transport properties of La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/LaAlO{sub 3}/Pt tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Galceran, R.; Balcells, Ll.; Pomar, A.; Konstantinović, Z.; Sandiumenge, F.; Martínez, B. [Instituto de Ciencia de Materiales de Barcelona - CSIC, Campus UAB, Bellaterra 08193 (Spain)

    2015-03-14

    Magnetotransport properties of La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/LaAlO{sub 3}/Pt tunnel junctions have been thoroughly analyzed, as a function of temperature and magnetic field, to test the suitability of LaAlO{sub 3} for insulating barriers and spin injection processes. The insulating behavior of LaAlO{sub 3} maintained down to 1–2 nm (corresponding to 4–5 unit cells) renders this material useful as tunnel barrier. The temperature dependence of the junction resistance, R(T), down to 200 K confirms direct tunneling as the dominant conduction channel. The barrier parameters of the junctions, φ{sub 0} and s, are estimated using Simmons' model in the intermediate voltage range. The energy of the barrier was estimated to be φ{sub 0} ∼ 0.4 eV at room temperature. The dependence of R(T) and φ{sub 0} on the magnetic field shows an anisotropic tunneling magnetoresistance of ∼4% at low T when changing the direction of the magnetization with respect to the current flow.

  5. NbN tunnel junctions

    International Nuclear Information System (INIS)

    Villegier, J.C.; Vieux-Rochaz, L.; Goniche, M.; Renard, P.; Vabre, M.

    1984-09-01

    All-niobium nitride Josephon junctions have been prepared successfully using a new processing called SNOP: Selective Niobium (nitride) Overlap Process. Such a process involves the ''trilayer'' deposition on the whole wafer before selective patterning of the electrodes by optically controlled dry reactive ion etching. Only two photomask levels are need to define an ''overlap'' or a ''cross-type'' junction with a good accuracy. The properties of the niobium nitride films deposited by DC-magnetron sputtering and the surface oxide growth are analysed. The most critical point to obtain high quality and high gap value junctions resides in the early stage of the NbN counterelectrode growth. Some possibilities to overcome such a handicap exist even if the fabrication needs substrate temperatures below 250 0 C

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

    International Nuclear Information System (INIS)

    Gobaut, B.; Ciprian, R.; Salles, B.R.; Krizmancic, D.; Rossi, G.; Panaccione, G.; Eddrief, M.; Marangolo, M.; Torelli, P.

    2015-01-01

    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

  7. Superluminescence from an optically pumped molecular tunneling junction by injection of plasmon induced hot electrons

    Directory of Open Access Journals (Sweden)

    Kai Braun

    2015-05-01

    Full Text Available Here, we demonstrate a bias-driven superluminescent point light-source based on an optically pumped molecular junction (gold substrate/self-assembled molecular monolayer/gold tip of a scanning tunneling microscope, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. A positive, steadily increasing bias voltage induces a step-like rise of the Stokes shifted optical signal emitted from the junction. This emission is strongly attenuated by reversing the applied bias voltage. At high bias voltage, the emission intensity depends non-linearly on the optical pump power. The enhanced emission can be modelled by rate equations taking into account hole injection from the tip (anode into the highest occupied orbital of the closest substrate-bound molecule (lower level and radiative recombination with an electron from above the Fermi level (upper level, hence feeding photons back by stimulated emission resonant with the gap mode. The system reflects many essential features of a superluminescent light emitting diode.

  8. Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction

    Science.gov (United States)

    Liu, Shuyi; Shiotari, Akitoshi; Baugh, Delroy; Wolf, Martin; Kumagai, Takashi

    2018-05-01

    Molecular hydrogen in a scanning tunneling microscope (STM) junction has been found to enhance the lateral spatial resolution of the STM imaging, referred to as scanning tunneling hydrogen microscopy (STHM). Here we report atomic resolution imaging of 2- and 3-monolayer (ML) thick ZnO layers epitaxially grown on Ag(111) using STHM. The enhanced resolution can be obtained at a relatively large tip to surface distance and resolves a more defective structure exhibiting dislocation defects for 3-ML-thick ZnO than for 2 ML. In order to elucidate the enhanced imaging mechanism, the electric and mechanical properties of the hydrogen molecular junction (HMJ) are investigated by a combination of STM and atomic force microscopy. It is found that the HMJ shows multiple kinklike features in the tip to surface distance dependence of the conductance and frequency shift curves, which are absent in a hydrogen-free junction. Based on a simple modeling, we propose that the junction contains several hydrogen molecules and sequential squeezing of the molecules out of the junction results in the kinklike features in the conductance and frequency shift curves. The model also qualitatively reproduces the enhanced resolution image of the ZnO films.

  9. Experimental Observation of Non-'S-Wave' Superconducting Behavior in Bulk Superconducting Tunneling Junctions of Yba2Cu3O7-δ

    Directory of Open Access Journals (Sweden)

    Leandro Jose Guerra

    1998-06-01

    Full Text Available Evidence of non-s-wave superconductivity from normal tunneling experiments in bulk tunneling junctions of YBa2Cu3O7-δ is presented. The I-V and dI/dV characteristics of bulk superconducting tunneling junctions of YBa2Cu3O7-δ have been measured at 77.0K and clear deviation from s-wave superconducting behavior has been observed. The result agrees with d-wave symmetry, and interpreting the data in this way, the magnitude of the superconducting energy gap, 2Δ, is found to be (0.038 ± 0.002 eV. Comparing this energy gap with Tc (2Δ/kB Tc = 5.735, indicates that these high-Tc superconductors are strongly correlated materials, which in contrast with BCS-superconductors are believed to be weakly correlated.

  10. Gap anisotropy and tunneling currents. [MPS3

    DEFF Research Database (Denmark)

    Lazarides, N.; Sørensen, Mads Peter

    1996-01-01

    The tunneling Hamiltonian formalism is applied to calculate the tunnelingcurrents through a small superconducting tunnel junction. The formalism isextended to nonconstant tunneling matrix elements. The electrodes of thejunction are assumed to......The tunneling Hamiltonian formalism is applied to calculate the tunnelingcurrents through a small superconducting tunnel junction. The formalism isextended to nonconstant tunneling matrix elements. The electrodes of thejunction are assumed to...

  11. 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...... profile from which the dependence of the maximum Josephson current on the applied field amplitude is derived. The most common geometrical configurations are considered and, when possible, the theoretical findings are compared with the experimental data. ©2008 American Institute of Physics...

  12. Symmetric and Asymmetric Magnetic Tunnel Junctions with Embedded Nanoparticles: Effects of Size Distribution and Temperature on Tunneling Magnetoresistance and Spin Transfer Torque.

    Science.gov (United States)

    Useinov, Arthur; Lin, Hsiu-Hau; Lai, Chih-Huang

    2017-08-21

    The problem of the ballistic electron tunneling is considered in magnetic tunnel junction with embedded non-magnetic nanoparticles (NP-MTJ), which creates additional conducting middle layer. The strong temperature impact was found in the system with averaged NP diameter d av  tunneling magnetoresistance (TMR) voltage behaviors. The low temperature approach also predicts step-like TMR and quantized in-plane spin transfer torque (STT) effects. The robust asymmetric STT respond is found due to voltage sign inversion in NP-MTJs with barrier asymmetry. Furthermore, it is shown how size distribution of NPs as well as quantization rules modify the spin-current filtering properties of the nanoparticles in ballistic regime. Different quantization rules for the transverse component of the wave vector are considered to overpass the dimensional threshold (d av  ≈ 1.8 nm) between quantum well and bulk-assisted states of the middle layer.

  13. 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.

  14. 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.

  15. Interfacial Nb-substitution induced anomalous enhancement of polarization and conductivity in BaTiO3 ferroelectric tunnel junctions

    Directory of Open Access Journals (Sweden)

    H. F. Li

    2014-12-01

    Full Text Available Using density functional theory (DFT method combined with non-equilibrium Green’s function approach, we systematically investigated the structural, ferroelectric and electronic transport properties of Pt/BaTiO3/Pt ferroelectric tunnel junctions (FTJ with the interface atomic layers doped by charge neutral NbTi substitution. It is found that interfacial NbTi substitution will produce several anomalous effects such as the vanishing of ferroelectric critical thickness and the decrease of junction resistance against tunneling current. Consequently, the thickness of the ferroelectric thin film (FTF in the FTJ can be reduced, and both the electroresistance effect and sensitivity to external bias of the FTJ are enhanced. Our calculations indicate that the enhancements of conductivity and ferroelectric distortion can coexist in FTJs, which should be important for applications of functional electronic devices based on FTJs.

  16. Electron holography study on the microstructure of magnetic tunnelling junctions

    International Nuclear Information System (INIS)

    Xu, Q.Y.; Wang, Y.G.; You, B.; Du, J.; Hu, A.; Zhang, Z.

    2004-01-01

    Electron holography was applied to study the microstructure evolution of magnetic tunnelling junctions (MTJs) CoFe/AlO x /Co annealed at different temperatures. A mean inner potential barrier was observed in the as-deposited MTJ sample, while it was changed to a potential well after a 200 deg. C or a 400 deg. C annealing. It is suggested that the oxygen atoms were redistributed during the annealing, which left metallic atoms acting as acceptors to confine the electrons, leading to the decrease of the potential of the AlO x barrier layer. The results suggest that the electron holography may be a useful tool for the study of the microstructure of amorphous materials

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

    International Nuclear Information System (INIS)

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

    2017-01-01

    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 and 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. (paper)

  18. Theoretical investigation of GaAsBi/GaAsN tunneling field-effect transistors with type-II staggered tunneling junction

    Science.gov (United States)

    Wang, Yibo; Liu, Yan; Han, Genquan; Wang, Hongjuan; Zhang, Chunfu; Zhang, Jincheng; Hao, Yue

    2017-06-01

    We investigate GaAsBi/GaAsN system for the design of type-II staggered hetero tunneling field-effect transistor (hetero-TFET). Strain-symmetrized GaAsBi/GaAsN with effective lattice match to GaAs exhibits a type-II band lineup, and the effective bandgap EG,eff at interface is significantly reduced with the incorporation of Bi and N elements. The band-to-band tunneling (BTBT) rate and drive current of GaAsBi/GaAsN hetero-TFETs are boosted due to the utilizing of the type-II staggered tunneling junction with the reduced EG,eff. Numerical simulation shows that the drive current and subthreshold swing (SS) characteristics of GaAsBi/GaAsN hetero-TFETs are remarkably improved by increasing Bi and N compositions. The dilute content GaAs0.85Bi0.15/GaAs0.92N0.08 staggered hetero-nTFET achieves 7.8 and 550 times higher ION compared to InAs and In0.53Ga0.47As homo-TFETs, respectively, at the supply voltage of 0.3 V. GaAsBi/GaAsN heterostructure is a potential candidate for high performance TFET.

  19. Fe concentration dependence of tunneling magnetoresistance in magnetic tunnel junctions using group-IV ferromagnetic semiconductor GeFe

    Directory of Open Access Journals (Sweden)

    Kosuke Takiguchi

    2017-10-01

    Full Text Available Group-IV-based ferromagnetic semiconductor Ge1−xFex (GeFe is one of the most promising materials for spin injection/detection in Si and Ge. In this paper, we demonstrate a systematic study of tunneling magnetoresistance (TMR in magnetic tunnel junctions (MTJs composed of Fe/MgO/Ge1−xFex with various Fe concentrations (x = 0.065, 0.105, 0.140, and 0.175. With increasing x, the TMR ratio increases up to 1.5% when x≤ 0.105, and it decreases when x> 0.105. This is the first observation of the TMR ratio over 1% in MTJs containing a group-IV ferromagnetic semiconductor. With increasing x, while the Curie temperature of GeFe increases, the MgO surface becomes rougher, which is thought to be the cause of the upper limit of the TMR ratio. The quality of the MgO layer on GeFe is an important factor for further improvement of TMR in Fe/MgO/GeFe MTJs.

  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. Junction and circuit fabrication

    International Nuclear Information System (INIS)

    Jackel, L.D.

    1980-01-01

    Great strides have been made in Josephson junction fabrication in the four years since the first IC SQUID meeting. Advances in lithography have allowed the production of devices with planar dimensions as small as a few hundred angstroms. Improved technology has provided ultra-high sensitivity SQUIDS, high-efficiency low-noise mixers, and complex integrated circuits. This review highlights some of the new fabrication procedures. The review consists of three parts. Part 1 is a short summary of the requirements on junctions for various applications. Part 2 reviews intergrated circuit fabrication, including tunnel junction logic circuits made at IBM and Bell Labs, and microbridge radiation sources made at SUNY at Stony Brook. Part 3 describes new junction fabrication techniques, the major emphasis of this review. This part includes a discussion of small oxide-barrier tunnel junctions, semiconductor barrier junctions, and microbridge junctions. Part 3 concludes by considering very fine lithography and limitations to miniaturization. (orig.)

  2. Structural details of Al/Al 2O3 junctions and their role in the formation of electron tunnel barriers

    Science.gov (United States)

    Koberidze, M.; Puska, M. J.; Nieminen, R. M.

    2018-05-01

    We present a computational study of the adhesive and structural properties of the Al/Al 2O3 interfaces as building blocks of the metal-insulator-metal (MIM) tunnel devices, where electron transport is accomplished via tunneling mechanism through the sandwiched insulating barrier. The main goal of this paper is to understand, on the atomic scale, the role of the geometrical details in the formation of the tunnel barrier profiles. Initially, we concentrate on the adhesive properties of the interfaces. To provide reliable results, we carefully assess the accuracy of the traditional methods used to examine Al/Al 2O3 systems. These are the most widely employed exchange-correlation functionals—local-density approximation and two different generalized gradient approximations; the universal binding-energy relation for predicting equilibrium interfacial distances and adhesion energies; and the ideal work of separation as a measure of junction stability. In addition, we show that the established interpretation of the computed ideal work of separation might be misleading in predicting the optimal interface structures. Finally, we perform a detailed analysis of the atomic and interplanar relaxations in each junction, and identify their contributions to the tunnel barrier parameters. Our results imply that the structural irregularities on the surface of the Al film have a significant contribution to lowering the tunnel barrier height, while atomic relaxations at the interface and interplanar relaxations in Al2O3 may considerably change the width of the barrier and, thus, distort its uniformity. Both the effects may critically influence the performance of the MIM tunnel devices.

  3. Isotopic effect on the quantum tunneling of the magnetization of molecular nanomagnets

    International Nuclear Information System (INIS)

    Sessoli, Roberta; Caneschi, Andrea; Gatteschi, Dante; Sorace, Lorenzo; Cornia, Andrea; Wernsdorfer, Wolfgang

    2001-01-01

    The molecular cluster [Fe 8 (tacn) 6 O 2 (OH) 12 ]Br 8 ·9H 2 O, Fe 8 , characterized by S=10, with biaxial magnetic anisotropy is an ideal system to investigate quantum effects in the dynamics of the magnetization. Resonant quantum tunneling gives rise to stepped hysteresis cycles and below 0.35 K pure quantum tunneling of the magnetization has been observed. The role of hyperfine fields in promoting the tunneling as a source of dynamic broadening of the states involved in the tunnel transition is investigated by preparing and characterizing two isotopically enriched samples using 57 Fe and 2 H. The relaxation rate in the tunneling regime is proportional to the hyperfine field generated by the nuclei. Also, the intrinsic linewidth of the tunneling resonance scales with the hyperfine field as confirmed by calculations of the super (or transfer) and direct hyperfine interactions. Preliminary results on a novel cluster of formula [Fe 4 (OCH 3 ) 6 (dpm) 6 ], Fe 4 , suited for a more dramatic isotope effect on the tunneling rate are also reported

  4. Effect of nitrogen plasma treatment at the Al2O3/Fe interface in magnetic tunnel junction

    International Nuclear Information System (INIS)

    Shim, Heejae; Cho, B. K.; Kim, Jin-Tae; Kim, T. W.; Park, W. J.

    2003-01-01

    We investigated the effects of nitrogen plasma treatment on top surface of Fe pinned layer for short times (t ex =0, 10, 30, and 60 s) in magnetic tunnel junctions and annealing of the junctions. The nitrogen-treated junctions show much reduced magnetoresistance (MR) ratio and significantly lower resistance-area (RA) products compared with the untreated junction, i.e., MR≅3%, RA≅30 kΩ μm 2 for t ex =10 s and MR≅10%, RA≅60 kΩ μm 2 for t ex =0 s. The untreated junction showed enhanced MR ratio up to about 17% and higher RA (≅70 kΩ μm2) upon thermal annealing at T a =230 deg. C, as expected. For the nitrogen-treated junctions, while the MR ratio also increases up to about 16% upon annealing at T a =230 deg. C, which is almost the same value as the one of the optimal reference junction, the RA values of the annealed junctions still keep as low as their initial values. We believe that the redistribution of nitrogen during the annealing process is responsible for the change of properties of nitrogen-treated junction. The bias dependence of MR and the estimation of effective barrier height and thickness are studied and found to be consistent with the observed changes in nitrogen-treated junctions

  5. Anomalous spin-dependent tunneling statistics in Fe/MgO/Fe junctions induced by disorder at the interface

    Science.gov (United States)

    Yan, Jiawei; Wang, Shizhuo; Xia, Ke; Ke, Youqi

    2018-01-01

    We present first-principles analysis of interfacial disorder effects on spin-dependent tunneling statistics in thin Fe/MgO/Fe magnetic tunnel junctions. We find that interfacial disorder scattering can significantly modulate the tunneling statistics in the minority spin of the parallel configuration (PC) while all other spin channels remain dominated by the Poissonian process. For the minority-spin channel of PC, interfacial disorder scattering favors the formation of resonant tunneling channels by lifting the limitation of symmetry conservation at low concentration, presenting an important sub-Poissonian process in PC, but is destructive to the open channels at high concentration. We find that the important modulation of tunneling statistics is independent of the type of interfacial disorder. A bimodal distribution function of transmission with disorder dependence is introduced and fits very well our first-principles results. The increase of MgO thickness can quickly change the tunneling from a sub-Poissonian to Poissonian dominated process in the minority spin of PC with disorder. Our results provide a sensitive detection method of an ultralow concentration of interfacial defects.

  6. Quasiparticle lifetimes and tunneling times in a superconductor-insulator-superconductor tunnel junction with spatially inhomogeneous electrodes

    International Nuclear Information System (INIS)

    Golubov, A.A.; Houwman, E.P.; Gijsbertsen, J.G.; Flokstra, J.; Rogalla, H.; le Grand, J.B.; de Korte, P.A.J.

    1994-01-01

    The low-energy quasiparticle scattering and recombination lifetimes for a proximity sandwich of two superconductors S and S' with different bulk energy gaps, are calculated as a function of the spatial coordinate and temperature. The spatial dependence of the order parameter and density of states are calculated on the basis of a microscopic model of the proximity effect, based on the Usadel equations, for dirty superconductors in thermal equilibrium. A zero boundary resistance between S and S' and a Boltzmann-like energy distribution of the excess quasiparticles are assumed. In the case of a small diffusion time constant an effective quasiparticle relaxation rate into and excitation rate out of the reduced gap region in the SS' sandwich are obtained as a function of (finite, but low) temperature and strength of the proximity effect, determined by the parameter γ m , by averaging over the energies and positions of the quasiparticles. In the same way effective tunneling times for electrons and holes tunneling out of the trap in the SS' sandwich to the other electrode of an SS'IS''S junction are determined as a function of temperature, voltage, and γ m

  7. 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

    2016-12-01

    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 %.

  8. 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

    2016-12-01

    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.

  9. Identification of microorganisms using superconducting tunnel junctions and time-of-flight mass spectrometry

    Science.gov (United States)

    Ullom, J. N.; Frank, M.; Horn, J. M.; Labov, S. E.; Langry, K.; Benner, W. H.

    2000-04-01

    We present time-of-flight measurements of biological material ejected from bacterial spores following laser irradiation. Ion impacts are registered on a microchannel plate detector and on a Superconducting Tunnel Junction (STJ) detector. We compare mass spectra obtained with the two detectors. The STJ has better sensitivity to massive ions and also measures the energy of each ion. We show evidence that spores of different bacillus species produce distinctive mass spectra and associate the observed mass peaks with coat proteins.

  10. Identification of microorganisms using superconducting tunnel junctions and time-of-flight mass spectrometry

    International Nuclear Information System (INIS)

    Ullom, J.N.; Frank, M.; Horn, J.M.; Labov, S.E.; Langry, K.; Benner, W.H.

    2000-01-01

    We present time-of-flight measurements of biological material ejected from bacterial spores following laser irradiation. Ion impacts are registered on a microchannel plate detector and on a Superconducting Tunnel Junction (STJ) detector. We compare mass spectra obtained with the two detectors. The STJ has better sensitivity to massive ions and also measures the energy of each ion. We show evidence that spores of different bacillus species produce distinctive mass spectra and associate the observed mass peaks with coat proteins

  11. Tunneling anisotropic magnetoresistance driven by magnetic phase transition.

    Science.gov (United States)

    Chen, X Z; Feng, J F; Wang, Z C; Zhang, J; Zhong, X Y; Song, C; Jin, L; Zhang, B; Li, F; Jiang, M; Tan, Y Z; Zhou, X J; Shi, G Y; Zhou, X F; Han, X D; Mao, S C; Chen, Y H; Han, X F; Pan, F

    2017-09-06

    The independent control of two magnetic electrodes and spin-coherent transport in magnetic tunnel junctions are strictly required for tunneling magnetoresistance, while junctions with only one ferromagnetic electrode exhibit tunneling anisotropic magnetoresistance dependent on the anisotropic density of states with no room temperature performance so far. Here, we report an alternative approach to obtaining tunneling anisotropic magnetoresistance in α'-FeRh-based junctions driven by the magnetic phase transition of α'-FeRh and resultantly large variation of the density of states in the vicinity of MgO tunneling barrier, referred to as phase transition tunneling anisotropic magnetoresistance. The junctions with only one α'-FeRh magnetic electrode show a magnetoresistance ratio up to 20% at room temperature. Both the polarity and magnitude of the phase transition tunneling anisotropic magnetoresistance can be modulated by interfacial engineering at the α'-FeRh/MgO interface. Besides the fundamental significance, our finding might add a different dimension to magnetic random access memory and antiferromagnet spintronics.Tunneling anisotropic magnetoresistance is promising for next generation memory devices but limited by the low efficiency and functioning temperature. Here the authors achieved 20% tunneling anisotropic magnetoresistance at room temperature in magnetic tunnel junctions with one α'-FeRh magnetic electrode.

  12. Superconducting tunneling with the tunneling Hamiltonian. II. Subgap harmonic structure

    International Nuclear Information System (INIS)

    Arnold, G.B.

    1987-01-01

    The theory of superconducting tunneling without the tunneling Hamiltonian is extended to treat superconductor/insulator/superconductor junctions in which the transmission coefficient of the insulating barrier approaches unity. The solution for the current in such junctions is obtained by solving the problem of a particle hopping in a one-dimensional lattice of sites, with forward and reverse transfer integrals that depend on the site. The results are applied to the problem of subgap harmonic structure in superconducting tunneling. The time-dependent current at finite voltage through a junction exhibiting subgap structure is found to have terms that oscillate at all integer multiples of the Josephson frequency, n(2eV/h). The amplitudes of these new, and as yet unmeasured, ac current contributions as a function of voltage are predicted

  13. Manipulating the spin states in a double molecular magnets tunneling junction

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Liang; Liu, Xi [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Zhang, Zhengzhong, E-mail: zeikeezhang@126.com [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Nano Science and Technology Institute, University of Science and Technology of China, Suzhou 215123 (China); Wang, Ruiqiang [Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China)

    2014-01-17

    We theoretically explore the spin transport through nano-structures consisting of two serially coupled single-molecular magnets (SMM) sandwiched between two nonmagnetic electrodes. We find that the magnetization of SMM can be controlled by the spin transfer torque with respect to the bias voltage direction, and the electron current can be switched on/off in different magnetic structures. Such a manipulation is performed by full electrical manner, and needs neither external magnetic field nor ferromagnetic electrodes in the tunneling junction. The proposal device scheme can be realized with the use of the present technology and has potential applications in molecular spintronics or quantum information processing.

  14. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Mingsen [Department of Physics, Guizhou University, Guiyang, 550025 (China); Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Institute of Applied Physics, Guizhou Normal College, Guiyang, 550018 (China); Ye, Gui; Jiang, Jun, E-mail: jiangj1@ustc.edu.cn [Department of Chemical Physics, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, 230026 (China); Cai, Shaohong, E-mail: caish@mail.gufe.edu.cn [Department of Physics, Guizhou University, Guiyang, 550025 (China); Guizhou Key Laboratory of Economic System Simulation, Guizhou University of Finance and Economics, Guiyang, 550004 (China); Sun, Guangyu [Guizhou Provincial Key Laboratory of Computational Nano-Material Science, Institute of Applied Physics, Guizhou Normal College, Guiyang, 550018 (China)

    2015-01-15

    The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS). Based on a model molecule of Bis-(4-mercaptophenyl)-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  15. Manipulating the spin states in a double molecular magnets tunneling junction

    Science.gov (United States)

    Jiang, Liang; Liu, Xi; Zhang, Zhengzhong; Wang, Ruiqiang

    2014-01-01

    We theoretically explore the spin transport through nano-structures consisting of two serially coupled single-molecular magnets (SMM) sandwiched between two nonmagnetic electrodes. We find that the magnetization of SMM can be controlled by the spin transfer torque with respect to the bias voltage direction, and the electron current can be switched on/off in different magnetic structures. Such a manipulation is performed by full electrical manner, and needs neither external magnetic field nor ferromagnetic electrodes in the tunneling junction. The proposal device scheme can be realized with the use of the present technology [6] and has potential applications in molecular spintronics or quantum information processing.

  16. Size dependence of magnetization reversal of ring shaped magnetic tunnel junction

    International Nuclear Information System (INIS)

    Chen, C.C.; Kuo, C.Y.; Chang, Y.C.; Chang, C.C.; Horng, Lance; Wu, Teho; Chern, G.; Huang, C.Y.; Tsunoda, M.; Takahashi, M.; Wu, J.C.

    2007-01-01

    The size dependence of magnetization reversal of magnetic tunnel junction (MTJ) rings has been investigated. The MTJ rings, with outer diameter of 4, 2 and 1 μm and inner diameter of 1.5, 1 and 0.5 μm were fabricated by a top-down technique. The magnetoresistance curves manifest all of the magnetic domain configurations during magnetization reversal in different sized rings. Various transition processes were observed, such as four transition, three transition and two transition in the largest, middle and smallest MTJ ring, respectively. Furthermore, the biasing fields observed from major loops decrease with decreasing size, which may result from edge roughness produced in the ion-milling process

  17. Isotopic effect on the quantum tunneling of the magnetization of molecular nanomagnets

    Energy Technology Data Exchange (ETDEWEB)

    Sessoli, Roberta E-mail: sessoli@chim1.unifi.it; Caneschi, Andrea; Gatteschi, Dante; Sorace, Lorenzo; Cornia, Andrea; Wernsdorfer, Wolfgang

    2001-05-01

    The molecular cluster [Fe{sub 8}(tacn){sub 6}O{sub 2}(OH){sub 12}]Br{sub 8}{center_dot}9H{sub 2}O, Fe{sub 8}, characterized by S=10, with biaxial magnetic anisotropy is an ideal system to investigate quantum effects in the dynamics of the magnetization. Resonant quantum tunneling gives rise to stepped hysteresis cycles and below 0.35 K pure quantum tunneling of the magnetization has been observed. The role of hyperfine fields in promoting the tunneling as a source of dynamic broadening of the states involved in the tunnel transition is investigated by preparing and characterizing two isotopically enriched samples using {sup 57}Fe and {sup 2}H. The relaxation rate in the tunneling regime is proportional to the hyperfine field generated by the nuclei. Also, the intrinsic linewidth of the tunneling resonance scales with the hyperfine field as confirmed by calculations of the super (or transfer) and direct hyperfine interactions. Preliminary results on a novel cluster of formula [Fe{sub 4}(OCH{sub 3}){sub 6}(dpm){sub 6}], Fe{sub 4}, suited for a more dramatic isotope effect on the tunneling rate are also reported.

  18. TMR- and TAMR-effects of (Ga,Mn)As and GaAs tunnel junctions; TMR- und TAMR-Effekt an (Ga,Mn)As und GaAs Tunnelstrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Brinkmeier, Eva

    2009-07-30

    This thesis is concerned with the experimental investigation of the tunnel magnetoresistance (TMR) and tunnel anistropic magnetoresistance (TAMR) in GaAs and (Ga,Mn)As tunnel junction. A special emphasis was put on the study of the newly discovered TAMR effect, which consists in the variation of the TMR with the magnetization's angle. The tunnel junctions were fabricated by means of optical lithography and wet chemical etching. The dependence of the TAMR effect on the layer system, the barrier thickness, the bias voltage, the temperature and the applied magnetic field magnitude was subsequently examined. The conducted measurements on (Ga,Mn)As junctions showed a TMR effect as well as various anisotropic effects which are in good agreement with the experimental reports published so far. The observed dependences of the TAMR effect on the aforementioned parameters were discussed within the framework of two distinct preexisting theoretical models and the experimental data could be explained by the superimposition of two effects stemming in one case from the spin orbit coupling in the (Ga,Mn)As layer and in the other from the concurrent action of the Rashba and Dresselhaus spin orbit interaction within the barrier. (orig.)

  19. Ferroelectric capped magnetization in multiferroic PZT/LSMO tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Ashok, E-mail: ashok553@nplindia.org; Shukla, A. K. [National Physical Laboratory (CSIR), Dr. K. S. Krishnan Road, New Delhi-110012 (India); Barrionuevo, D.; Ortega, N.; Katiyar, Ram S. [Department of Physics and Institute of Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico 00931-3343 (United States); Shannigrahi, Santiranjan [Institute of Materials Research and Engineering - IMRE, Agency for Science Technology and Research (A-STAR), 3 Research Link, Singapore 117602 (Singapore); Scott, J. F. [Department of Chemistry and Department of Physics, University of St. Andrews, St. Andrews KY16 ST (United Kingdom)

    2015-03-30

    Self-poled ultra-thin ferroelectric PbZr{sub 0.52}Ti{sub 0.48}O{sub 3} (PZT) (5 and 7 nm) films have been grown by pulsed laser deposition technique on ferromagnetic La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO) (30 nm) to check the effect of polar capping on magnetization for ferroelectric tunnel junction devices. PZT/LSMO heterostructures with thick polar PZT (7 nm) capping show nearly 100% enhancement in magnetization compared with thin polar PZT (5 nm) films, probably due to excess hole transfer from the ferroelectric to the ferromagnetic layers. Core-level x-ray photoelectron spectroscopy studies revealed the presence of larger Mn 3s exchange splitting and higher Mn{sup 3+}/Mn{sup 4+} ion ratio in the LSMO with 7 nm polar capping.

  20. Theoretical calculation of performance enhancement in lattice-matched SiGeSn/GeSn p-channel tunneling field-effect transistor with type-II staggered tunneling junction

    Science.gov (United States)

    Wang, Hongjuan; Han, Genquan; Wang, Yibo; Peng, Yue; Liu, Yan; Zhang, Chunfu; Zhang, Jincheng; Hu, Shengdong; Hao, Yue

    2016-04-01

    In this work, a lattice-matched SiGeSn/GeSn heterostructure p-channel tunneling field-effect transistor (hetero-PTFET) with a type-II staggered tunneling junction (TJ) is investigated theoretically. Lattice matching and type-II band alignment at the Γ-point is obtained at the SiGeSn/GeSn interface by tuning Sn and Si compositions. A steeper subthreshold swing (SS) and a higher on state current (I ON) are demonstrated in SiGeSn/GeSn hetero-PTFET than in GeSn homo-PTFET. Si0.31Ge0.49Sn0.20/Ge0.88Sn0.12 hetero-PTFET achieves a 2.3-fold higher I ON than Ge0.88Sn0.12 homo-PTFET at V DD of 0.3 V. Hetero-PTFET achieves a more abrupt hole profile and a higher carrier density near TJ than the homo-PTFET, which contributes to the significantly enhanced band-to-band tunneling (BTBT) rate and tunneling current in hetero-PTFET.

  1. Tunnelling anisotropic magnetoresistance of Fe/GaAs/Ag(001) junctions from first principles: effect of hybridized interface resonances

    Czech Academy of Sciences Publication Activity Database

    Sýkora, R.; Turek, Ilja

    2012-01-01

    Roč. 24, č. 36 (2012), 365801/1-365801/10 ISSN 0953-8984 R&D Projects: GA ČR(CZ) GAP204/11/1228 Institutional support: RVO:68081723 Keywords : tunnel junctions * magnetoresistance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.355, year: 2012

  2. 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

  3. Magnetization switching of NiFeSiB free layers for magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Chun, B.S.; Ko, S.P.; Oh, B.S.; Hwang, J.Y.; Rhee, J.R.; Kim, T.W.; Saito, S.; Yoshimura, S.; Tsunoda, M.; Takahashi, M.; Kim, Y.K.

    2006-01-01

    Ferromagnetic amorphous Ni 16 Fe 62 Si 8 B 14 layer have been studied as free layers for magnetic tunnel junctions (MTJs) to enhance cell switching performance. Traditional MTJ free layer materials such as NiFe and CoFe were also prepared for switching comparison purposes. Both NiFeSiB and NiFe resulted in an order of magnitude smaller switching fields compared to the CoFe. The switching field was further reduced for the synthetic antiferromagnetic NiFeSiB free layered structure

  4. Work function and temperature dependence of electron tunneling through an N-type perylene diimide molecular junction with isocyanide surface linkers.

    Science.gov (United States)

    Smith, Christopher E; Xie, Zuoti; Bâldea, Ioan; Frisbie, C Daniel

    2018-01-18

    Conducting probe atomic force microscopy (CP-AFM) was employed to examine electron tunneling in self-assembled monolayer (SAM) junctions. A 2.3 nm long perylene tetracarboxylic acid diimide (PDI) acceptor molecule equipped with isocyanide linker groups was synthesized, adsorbed onto Ag, Au and Pt substrates, and the current-voltage (I-V) properties were measured by CP-AFM. The dependence of the low-bias resistance (R) on contact work function indicates that transport is LUMO-assisted ('n-type behavior'). A single-level tunneling model combined with transition voltage spectroscopy (TVS) was employed to analyze the experimental I-V curves and to extract the effective LUMO position ε l = E LUMO - E F and the effective electronic coupling (Γ) between the PDI redox core and the contacts. This analysis revealed a strong Fermi level (E F ) pinning effect in all the junctions, likely due to interface dipoles that significantly increased with increasing contact work function, as revealed by scanning Kelvin probe microscopy (SKPM). Furthermore, the temperature (T) dependence of R was found to be substantial. For Pt/Pt junctions, R varied more than two orders of magnitude in the range 248 K tunneling mechanism and allow independent determination of ε l , giving values compatible with estimates of ε l based on analysis of the full I-V data. Theoretical analysis revealed a general criterion to unambiguously rule out a two-step transport mechanism: namely, if measured resistance data exhibit a pronounced Arrhenius-type temperature dependence, a two-step electron transfer scenario should be excluded in cases where the activation energy depends on contact metallurgy. Overall, our results indicate (1) the generality of the Fermi level pinning phenomenon in molecular junctions, (2) the utility of employing the single level tunneling model for determining essential electronic structure parameters (ε l and Γ), and (3) the importance of changing the nature of the contacts to

  5. 2D scattering of unpolarized beams of electrons by charged nanomagnets

    Energy Technology Data Exchange (ETDEWEB)

    Senbeta, Teshome, E-mail: teshearada@yahoo.com [Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa (Ethiopia); Mal' nev, V.N., E-mail: vnmalnev@aau.edu.et [Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa (Ethiopia)

    2012-07-15

    2D spin-dependent scattering of slow unpolarized beams of electrons by charged nanomagnets is analyzed in the Born approximation. The obtained scattering lengths are larger than those from the neutral nanomagnets approximately by one order. It is shown that for particular parameters of the system it is possible to polarize completely the scattered electrons in a narrow range of scattering angles. The most suitable system for realization of these effects is 2D Si electron gas with immersed nanomagnets. - Highlights: Black-Right-Pointing-Pointer We study 2D spin dependent electron scattering by charged nanomagnets. Black-Right-Pointing-Pointer The applicability of the Born approximation to the problem is discussed. Black-Right-Pointing-Pointer Unpolarized incident beams used to obtain completely polarized scattered electrons. Black-Right-Pointing-Pointer The study shows peculiarities of 2D spin dependent scattering enhanced by Coulomb potential. Black-Right-Pointing-Pointer The result obtained can be used as one method of controlling spin currents.

  6. Bias voltage induced resistance switching effect in single-molecule magnets’ tunneling junction

    Science.gov (United States)

    Zhang, Zhengzhong; Jiang, Liang

    2014-09-01

    An electric-pulse-induced reversible resistance change effect in a molecular magnetic tunneling junction, consisting of a single-molecule magnet (SMM) sandwiched in one nonmagnetic and one ferromagnetic electrode, is theoretically investigated. By applying a time-varying bias voltage, the SMM's spin orientation can be manipulated with large bias voltage pulses. Moreover, the different magnetic configuration at high-resistance/low-resistance states can be ‘read out’ by utilizing relative low bias voltage. This device scheme can be implemented with current technologies (Khajetoorians et al 2013 Science 339 55) and has potential application in molecular spintronics and high-density nonvolatile memory devices.

  7. Coulomb blockade threshold in finite one-dimensional arrays of small tunnel junctions

    International Nuclear Information System (INIS)

    Lien, Nguyen V.; Dat, Nguyen T.; Nam, Nguyen H.

    2001-11-01

    The current-voltage characteristics of one-dimensional tunnel junction arrays are simulated using the semiclassical and full capacitance matrix description. The threshold voltage V th of the Coulomb blockade (CB) is evaluated and analyzed in detail as a function of the gate capacitance C 0 , the array length N, the temperature, and the degree of disorder. The disordered effect is found to be essential, while the long range interaction included in the full capacitance matrix calculations, when decreasing V th , weakly affects the qualitative behaviour of the CB for the V th (C 0 ) - and the V th (N)-dependences. (author)

  8. Bias voltage induced resistance switching effect in single-molecule magnets' tunneling junction.

    Science.gov (United States)

    Zhang, Zhengzhong; Jiang, Liang

    2014-09-12

    An electric-pulse-induced reversible resistance change effect in a molecular magnetic tunneling junction, consisting of a single-molecule magnet (SMM) sandwiched in one nonmagnetic and one ferromagnetic electrode, is theoretically investigated. By applying a time-varying bias voltage, the SMM's spin orientation can be manipulated with large bias voltage pulses. Moreover, the different magnetic configuration at high-resistance/low-resistance states can be 'read out' by utilizing relative low bias voltage. This device scheme can be implemented with current technologies (Khajetoorians et al 2013 Science 339 55) and has potential application in molecular spintronics and high-density nonvolatile memory devices.

  9. Spin torque switching of 20 nm magnetic tunnel junctions with perpendicular anisotropy

    Science.gov (United States)

    Gajek, M.; Nowak, J. J.; Sun, J. Z.; Trouilloud, P. L.; O'Sullivan, E. J.; Abraham, D. W.; Gaidis, M. C.; Hu, G.; Brown, S.; Zhu, Y.; Robertazzi, R. P.; Gallagher, W. J.; Worledge, D. C.

    2012-03-01

    Spin-transfer torque magnetic random access memory (STT-MRAM) is one of the most promising emerging non-volatile memory technologies. MRAM has so far been demonstrated with a unique combination of density, speed, and non-volatility in a single chip, however, without the capability to replace any single mainstream memory. In this paper, we demonstrate the basic physics of spin torque switching in 20 nm diameter magnetic tunnel junctions with perpendicular magnetic anisotropy materials. This deep scaling capability clearly indicates the STT MRAM device itself may be suitable for integration at much higher densities than previously proven.

  10. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    International Nuclear Information System (INIS)

    Daqiq, Reza; Ghobadi, Nader

    2016-01-01

    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. - 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.

  11. 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.

  12. Linker-dependent Junction Formation Probability in Single-Molecule Junctions

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Pil Sun; Kim, Taekyeong [HankukUniversity of Foreign Studies, Yongin (Korea, Republic of)

    2015-01-15

    We compare the junction formation probabilities of single-molecule junctions with different linker molecules by using a scanning tunneling microscope-based break-junction technique. We found that the junction formation probability varies as SH > SMe > NH2 for the benzene backbone molecule with different types of anchoring groups, through quantitative statistical analysis. These results are attributed to different bonding forces according to the linker groups formed with Au atoms in the electrodes, which is consistent with previous works. Our work allows a better understanding of the contact chemistry in the metal.molecule junction for future molecular electronic devices.

  13. Multi-band tight-binding calculation of electronic transport in Fe/trans-polyacetylene/Fe tunnel junctions

    International Nuclear Information System (INIS)

    Abedi Ravan, B

    2012-01-01

    In this paper, the electronic transport characteristics of Fe/trans-polyacetylene/Fe magnetic tunnel junctions (MTJs) are investigated using multi-band tight-binding calculations within the framework of nonequilibrium Green function theory. A CH 2 radical is added to different positions on the polymer chain and its effects on the tunnelling magnetoresistance of the MTJ are studied. The ferromagnetic electrodes are assumed to be single-band and their tight-binding parameters are chosen in such a way as to simulate the ab initio density functional calculations of the band structure of bcc-Fe along its [001] crystallographic direction. In building the Hamiltonian of the trans-polyacetylene (t-PA) chain, we have assumed an s orbital on the H atoms and one s and three p(p x ,p y ,p z ) orbitals on the C atoms, and the dimerization effects are taken into account. It is found that moving the radical out of the centre of the polymer chain enhances the tunnelling magnetoresistance of the MTJ.

  14. The influence of shape anisotropy on vortex nucleation in Pacman-like nanomagnets

    International Nuclear Information System (INIS)

    Cambel, V.; Tóbik, J.; Šoltýs, J.; Fedor, J.; Precner, M.; Gaži, Š.; Karapetrov, G.

    2013-01-01

    In this paper we explore magnetic properties of Permalloy Pacman-like (PL) nanomagnets in external in-plain magnetic field. PL nanomagnets represent unique magnetic systems with broken symmetry, which are perspective as non-volatile memory elements. In these nanomagnets both bits, chirality and polarity of a single vortex state, can be easily read and written by in-plane magnetic field only. In the experimental part of this work we show that namely chirality of the∼1-μm large PL nanomagnet can be red easily by magnetic force microscopy method. The easy bit reading is enabled due to coupling of the polarity magnetization vector to the magnetic charges located at the surface of the PL missing sector. Using micromagnetic simulations we show the influence of spatial anisotropy on vortex nucleation and annihilation fields in the PL nanomagnets. Angular dependence of the vortex nucleation field is analysed in detail for PL nanomagnets of different diameter, thickness, and missing-sector dimensions. Best control of the ground state can be achieved for diameters not exceeding 100 nm, thicknesses from 40 to 45 nm, and for the missing sector angles from 30 to 60°. - Highlights: ► We explore magnetization dynamics in mesoscopic magnets with broken symmetry. ► We explain how to read and write chirality and polarity into such systems. ► Angular dependence of the vortex nucleation field in the systems is analysed

  15. Superradiance from crystals of molecular nanomagnets.

    Science.gov (United States)

    Chudnovsky, E M; Garanin, D A

    2002-10-07

    We show that crystals of molecular nanomagnets can exhibit giant magnetic relaxation due to the Dicke superradiance of electromagnetic waves. Rigorous theory is presented that combines superradiance with the Landau-Zener effect.

  16. Feasibilty of a Multi-bit Cell Perpendicular Magnetic Tunnel Junction Device

    Science.gov (United States)

    Kim, Chang Soo

    The ultimate objective of this research project was to explore the feasibility of making a multi-bit cell perpendicular magnetic tunnel junction (PMTJ) device to increase the storage density of spin-transfer-torque random access memory (STT-RAM). As a first step toward demonstrating a multi-bit cell device, this dissertation contributed a systematic and detailed study of developing a single cell PMTJ device using L10 FePt films. In the beginning of this research, 13 up-and-coming non-volatile memory (NVM) technologies were investigated and evaluated to see whether one of them might outperform NAND flash memories and even HDDs on a cost-per-TB basis in 2020. This evaluation showed that STT-RAM appears to potentially offer superior power efficiency, among other advantages. It is predicted that STTRAM's density could make it a promising candidate for replacing NAND flash memories and possibly HDDs if STTRAM could be improved to store multiple bits per cell. Ta/Mg0 under-layers were used first in order to develop (001) L1 0 ordering of FePt at a low temperature of below 400 °C. It was found that the tradeoff between surface roughness and (001) L10 ordering of FePt makes it difficult to achieve low surface roughness and good perpendicular magnetic properties simultaneously when Ta/Mg0 under-layers are used. It was, therefore, decided to investigate MgO/CrRu under-layers to simultaneously achieve smooth films with good ordering below 400°C. A well ordered 4 nm L10 FePt film with RMS surface roughness close to 0.4 nm, perpendicular coercivity of about 5 kOe, and perpendicular squareness near 1 was obtained at a deposition temperature of 390 °C on a thermally oxidized Si substrate when MgO/CrRu under-layers are used. A PMTJ device was developed by depositing a thin MgO tunnel barrier layer and a top L10 FePt film and then being postannealed at 450 °C for 30 minutes. It was found that the sputtering power needs to be minimized during the thin MgO tunnel barrier

  17. Chaos and related nonlinear noise phenomena in Josephson tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Miracky, R.F.

    1984-07-01

    The nonlinear dynamics of Josephson tunnel junctions shunted by a resistance with substantial self-inductance have been thoroughly investigated. The current-voltage characteristics of these devices exhibit stable regions of negative differential resistance. Very large increases in the low-frequency voltage noise with equivalent noise temperatures of 10/sup 6/ K or more, observed in the vicinity of these regions, arise from switching, or hopping, between subharmonic modes. Moderate increases in the noise, with temperatures of about 10/sup 3/ K, arise from chaotic behavior. Analog and digital simulations indicate that under somewhat rarer circumstances the same junction system can sustain a purely deterministic hopping between two unstable subharmonic modes, accompanied by excess low-frequency noise. Unlike the noise-induced case, this chaotic process occurs over a much narrower range in bias current and is destroyed by the addition of thermal noise. The differential equation describing the junction system can be reduced to a one-dimensional mapping in the vicinity of one of the unstable modes. A general analytical calculation of switching processes for a class of mappings yields the frequency dependence of the noise spectrum in terms of the parameters of the mapping. Finally, the concepts of noise-induced hopping near bifurcation thresholds are applied to the problem of the three-photon Josephson parametric amplifier. Analog simulations indicate that the noise rise observed in experimental devices arises from occasional hopping between a mode at the pump frequency ..omega../sub p/ and a mode at the half harmonic ..omega../sub p//2. The hopping is induced by thermal noise associated with the shunt resistance. 71 references.

  18. Chaos and related nonlinear noise phenomena in Josephson tunnel junctions

    International Nuclear Information System (INIS)

    Miracky, R.F.

    1984-07-01

    The nonlinear dynamics of Josephson tunnel junctions shunted by a resistance with substantial self-inductance have been thoroughly investigated. The current-voltage characteristics of these devices exhibit stable regions of negative differential resistance. Very large increases in the low-frequency voltage noise with equivalent noise temperatures of 10 6 K or more, observed in the vicinity of these regions, arise from switching, or hopping, between subharmonic modes. Moderate increases in the noise, with temperatures of about 10 3 K, arise from chaotic behavior. Analog and digital simulations indicate that under somewhat rarer circumstances the same junction system can sustain a purely deterministic hopping between two unstable subharmonic modes, accompanied by excess low-frequency noise. Unlike the noise-induced case, this chaotic process occurs over a much narrower range in bias current and is destroyed by the addition of thermal noise. The differential equation describing the junction system can be reduced to a one-dimensional mapping in the vicinity of one of the unstable modes. A general analytical calculation of switching processes for a class of mappings yields the frequency dependence of the noise spectrum in terms of the parameters of the mapping. Finally, the concepts of noise-induced hopping near bifurcation thresholds are applied to the problem of the three-photon Josephson parametric amplifier. Analog simulations indicate that the noise rise observed in experimental devices arises from occasional hopping between a mode at the pump frequency ω/sub p/ and a mode at the half harmonic ω/sub p//2. The hopping is induced by thermal noise associated with the shunt resistance. 71 references

  19. FUNDAMENTAL TUNNELING PROCESSES IN MOSa SOLAR CELLS

    OpenAIRE

    Balberg , I.; Hanak , J.; Weakliem , H.; Gal , E.

    1981-01-01

    In previous studies of tunneling through a MOSa tunnel junction, where Sa was a-Si : H, it was shown that their characteristics resemble those of MOSc devices where Sc was crystalline silicon. In the present work we would like to report a demonstration of fundamental tunneling processes in such tunnel junctions. In particular, the transition from semiconductor controlled regime to tunneling controlled regime can be clearly distinguished. The present results represent one of the rare cases whe...

  20. Submucosal Tunneling Endoscopic Resection vs Thoracoscopic Enucleation for Large Submucosal Tumors in the Esophagus and the Esophagogastric Junction.

    Science.gov (United States)

    Chen, Tao; Lin, Zong-Wu; Zhang, Yi-Qun; Chen, Wei-Feng; Zhong, Yun-Shi; Wang, Qun; Yao, Li-Qing; Zhou, Ping-Hong; Xu, Mei-Dong

    2017-12-01

    Submucosal tunneling endoscopic resection (STER) is regarded as a promising method for resection of submucosal tumors (SMTs); however, little is known about a comprehensive comparison of STER and thoracoscopic enucleation (TE). The aim of this study was to compare the clinical outcomes of STER and TE for large symptomatic SMTs in the esophagus and esophagogastric junction, as well as to analyze the factors that affect the feasibility and safety of STER. We enrolled 166 patients with large symptomatic SMTs in the esophagus and esophagogastric junction from September 2011 to March 2016 in this retrospective study. The clinicopathologic features and treatment results were collected and analyzed. En bloc resection was achieved in 84.6% of the patients in the STER group and 86.7% of the patients in the TE group (p = 0.708). Notably, the procedure time and hospital stay in the STER group were considerably shorter than those in the TE group. Tumor transverse diameter is a significant risk factor for piecemeal resection, adverse events, and technical difficulties. No recurrence or metastasis was found during a mean follow-up period of more than 2 years. Submucosal tunneling endoscopic resection is effective and safe for large SMTs in the esophagus and esophagogastric junction. This procedure has the advantage of being more minimally invasive with a shorter procedure time and hospital stay compared with TE. Submucosal tunneling endoscopic resection for tumors with a transverse diameter ≥3.5 cm and an irregular shape is associated with relatively high risk for piecemeal resection, adverse events, and technical difficulties. Copyright © 2017 American College of Surgeons. Published by Elsevier Inc. All rights reserved.

  1. An array of cold-electron bolometers with SIN tunnel junctions and JFET readout for cosmology instruments

    International Nuclear Information System (INIS)

    Kuzmin, L

    2008-01-01

    A novel concept of the parallel/series array of Cold-Electron Bolometers (CEB) with Superconductor-Insulator-Normal (SIN) Tunnel Junctions has been proposed. The concept was developed specially for matching the CEB with JFET amplifier at conditions of high optical power load. The CEB is a planar antenna-coupled superconducting detector with high sensitivity. For combination of effective HF operation and low noise properties the current-biased CEBs are connected in series for DC and in parallel for HF signal. A signal is concentrated from an antenna to the absorber through the capacitance of the tunnel junctions and through additional capacitance for coupling of superconducting islands. Using array of CEBs the applications can be considerably extended to higher power load by distributing the power between N CEBs and decreasing the electron temperature. Due to increased responsivity the noise matching is so effective that photon NEP could be easily achieved at 300 mK with a room temperature JFET for wide range of optical power loads. The concept of the CEB array has been developed for the BOOMERanG balloon telescope and other Cosmology instruments

  2. Linear nanometric tunnel junction sensors with exchange pinned sensing layer

    International Nuclear Information System (INIS)

    Leitao, D. C.; Silva, A. V.; Cardoso, S.; Ferreira, R.; Paz, E.; Deepack, F. L.; Freitas, P. P.

    2014-01-01

    Highly sensitive nanosensors with high spatial resolution provide the necessary features for high accuracy imaging of isolated magnetic nanoparticles. In this work, we report the fabrication and characterization of MgO-barrier magnetic tunnel junction nanosensors, with two exchange-pinned electrodes. The perpendicular magnetization configuration for field sensing is set using a two-step annealing process, where the second annealing temperature was optimized to yield patterned sensors responses with improved linearity. The optimized circular nanosensors show sensitivities up to 0.1%/Oe, larger than previously reported for nanometric sensors and comparable to micrometric spin-valves. Our strategy avoids the use of external permanent biasing or demagnetizing fields (large for smaller structures) to achieve a linear response, enabling the control of the linear operation range using only the stack and thus providing a small footprint device

  3. Linear nanometric tunnel junction sensors with exchange pinned sensing layer

    Energy Technology Data Exchange (ETDEWEB)

    Leitao, D. C., E-mail: dleitao@inesc-mn.pt; Silva, A. V.; Cardoso, S. [INESC-MN and IN, Rua Alves Redol 9, 1000-029 Lisboa (Portugal); Instituto Superior Técnico (IST), Universidade de Lisboa, Av. Rovisco Pais, 1000-029 Lisboa (Portugal); Ferreira, R.; Paz, E.; Deepack, F. L. [INL, Av. Mestre Jose Veiga, 4715-31 Braga (Portugal); Freitas, P. P. [INESC-MN and IN, Rua Alves Redol 9, 1000-029 Lisboa (Portugal); INL, Av. Mestre Jose Veiga, 4715-31 Braga (Portugal)

    2014-05-07

    Highly sensitive nanosensors with high spatial resolution provide the necessary features for high accuracy imaging of isolated magnetic nanoparticles. In this work, we report the fabrication and characterization of MgO-barrier magnetic tunnel junction nanosensors, with two exchange-pinned electrodes. The perpendicular magnetization configuration for field sensing is set using a two-step annealing process, where the second annealing temperature was optimized to yield patterned sensors responses with improved linearity. The optimized circular nanosensors show sensitivities up to 0.1%/Oe, larger than previously reported for nanometric sensors and comparable to micrometric spin-valves. Our strategy avoids the use of external permanent biasing or demagnetizing fields (large for smaller structures) to achieve a linear response, enabling the control of the linear operation range using only the stack and thus providing a small footprint device.

  4. A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Genghong; Zhu, Jia; Jiang, Gelei; Sheng, Qiang; Zheng, Yue, E-mail: zhengy35@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Micro& Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Chen, Weijin [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Micro& Nano Physics and Mechanics Research Laboratory, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082 (China); Wang, Biao, E-mail: wangbiao@mail.sysu.edu.cn [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai 519082 (China)

    2016-06-15

    Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge) and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop) with positive and negative signs (negative and positive signs) emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field) pointing from right to left (from left to right) are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

  5. A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

    Directory of Open Access Journals (Sweden)

    Genghong Zhang

    2016-06-01

    Full Text Available Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop with positive and negative signs (negative and positive signs emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field pointing from right to left (from left to right are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

  6. Single-contact tunneling thermometry

    Science.gov (United States)

    Maksymovych, Petro

    2016-02-23

    A single-contact tunneling thermometry circuit includes a tunnel junction formed between two objects. Junction temperature gradient information is determined based on a mathematical relationship between a target alternating voltage applied across the junction and the junction temperature gradient. Total voltage measured across the junction indicates the magnitude of the target alternating voltage. A thermal gradient is induced across the junction. A reference thermovoltage is measured when zero alternating voltage is applied across the junction. An increasing alternating voltage is applied while measuring a thermovoltage component and a DC rectification voltage component created by the applied alternating voltage. The target alternating voltage is reached when the thermovoltage is nullified or doubled by the DC rectification voltage depending on the sign of the reference thermovoltage. Thermoelectric current and current measurements may be utilized in place of the thermovoltage and voltage measurements. The system may be automated with a feedback loop.

  7. Performance of single-junction and dual-junction InGaP/GaAs solar cells under low concentration ratios

    International Nuclear Information System (INIS)

    Khan, Aurangzeb; Yamaguchi, Masafumi; Takamoto, Tatsuya

    2004-01-01

    A study of the performance of single-junction InGaP/GaAs and dual-junction InGaP/GaAs tandem cells under low concentration ratios (up to 15 suns), before and after 1 MeV electron irradiation is presented. Analysis of the tunnel junction parameters under different concentrated light illuminations reveals that the peak current (J P ) and valley current (J V ) densities should be greater than the short-circuit current density (J sc ) for better performance. The tunnel junction behavior against light intensity improved after irradiation. This led to the suggestion that the peak current density (J P ) and valley current density (J V ) of the tunnel junction were enhanced after irradiation or the peak current was shifted to higher concentration. The recovery of the radiation damage under concentrated light illumination conditions suggests that the performance of the InGaP/GaAs tandem solar cell can be enhanced even under low concentration ratios

  8. NbCN Josephson junctions with AlN barriers

    International Nuclear Information System (INIS)

    Thomasson, S.L.; Murduck, J.M.; Chan, H.

    1991-01-01

    This paper reports on niobium carbonitride (NbCN) Josephson circuits which operate over a wider temperature range than either niobium or niobium nitride circuits. Higher operating temperature places NbCN technology more comfortably within the range of closed cycle refrigerators, a key factor in aerospace applications. We have fabricated tunnel junctions from NbCN films with transition temperatures up to 18 Kelvin. High quality NbCN tunnel junction fabrication generally requires low stress films with roughness less than the barrier thickness (∼20 Angstrom). We have developed scanning tunneling microscopy as a tool for measuring and optimizing film smoothness. Junctions formed in situ with AIN tunneling barriers show reproducible I-V characteristics

  9. Magnetic Reversal and Thermal Stability of CoFeB Perpendicular Magnetic Tunnel Junction Arrays Patterned by Block Copolymer Lithography

    KAUST Repository

    Tu, Kun-Hua; Fernandez Martin, Eduardo; almasi, hamid; Wang, Weigang; Navas Otero, David; Ntetsikas, Konstantinos; Moschovas, Dimitrios; Avgeropoulos, Apostolos; Ross, Caroline A

    2018-01-01

    Dense arrays of pillars, with diameters of 64 and 25 nm, were made from a perpendicular CoFeB magnetic tunnel junction thin film stack using block copolymer lithography. While the soft layer and hard layer in the 64 nm pillars reverse at different

  10. Molecular-Beam Epitaxially Grown MgB2 Thin Films and Superconducting Tunnel Junctions

    Directory of Open Access Journals (Sweden)

    Jean-Baptiste Laloë

    2011-01-01

    Full Text Available Since the discovery of its superconducting properties in 2001, magnesium diboride has generated terrific scientific and engineering research interest around the world. With a of 39 K and two superconducting gaps, MgB2 has great promise from the fundamental point of view, as well as immediate applications. Several techniques for thin film deposition and heterojunction formation have been established, each with its own advantages and drawbacks. Here, we will present a brief overview of research based on MgB2 thin films grown by molecular beam epitaxy coevaporation of Mg and B. The films are smooth and highly crystalline, and the technique allows for virtually any heterostructure to be formed, including all-MgB2 tunnel junctions. Such devices have been characterized, with both quasiparticle and Josephson tunneling reported. MgB2 remains a material of great potential for a multitude of further characterization and exploration research projects and applications.

  11. Controlling the switching field in nanomagnets by means of domain-engineered antiferromagnets

    Science.gov (United States)

    Folven, E.; Linder, J.; Gomonay, O. V.; Scholl, A.; Doran, A.; Young, A. T.; Retterer, S. T.; Malik, V. K.; Tybell, T.; Takamura, Y.; Grepstad, J. K.

    2015-09-01

    Using soft x-ray spectromicroscopy, we investigate the magnetic domain structure in embedded nanomagnets defined in L a0.7S r0.3Mn O3 thin films and LaFe O3/L a0.7S r0.3Mn O3 bilayers. We find that shape-controlled antiferromagnetic domain states give rise to a significant reduction of the switching field of the rectangular nanomagnets. This is discussed within the framework of competition between an intrinsic spin-flop coupling and shape anisotropy. The data demonstrates that shape effects in antiferromagnets may be used to control the magnetic properties in nanomagnets.

  12. Dynamic Control of Tunneling Conductance in Ferroelectric Tunnel Junctions

    International Nuclear Information System (INIS)

    Zou Ya-Yi; Zhou Yan; Chew Khian-Hooi

    2013-01-01

    We investigate the dynamic characteristics of electric polarization P(t) in a ferroelectric junction under ac applied voltage and stress, and calculate the frequency response and the cut-off frequency f 0 , which provides a reference for the upper limit of the working frequency. Our study might be significant for sensor and memory applications of nanodevices based on ferroelectric junctions

  13. Quantitative impedance characterization of sub-10 nm scale capacitors and tunnel junctions with an interferometric scanning microwave microscope

    International Nuclear Information System (INIS)

    Wang, Fei; Clément, Nicolas; Ducatteau, Damien; Troadec, David; Legrand, Bernard; Dambrine, Gilles; Théron, Didier; Tanbakuchi, Hassan

    2014-01-01

    We present a method to characterize sub-10 nm capacitors and tunnel junctions by interferometric scanning microwave microscopy (iSMM) at 7.8 GHz. At such device scaling, the small water meniscus surrounding the iSMM tip should be reduced by proper tip tuning. Quantitative impedance characterization of attofarad range capacitors is achieved using an ‘on-chip’ calibration kit facing thousands of nanodevices. Nanoscale capacitors and tunnel barriers were detected through variations in the amplitude and phase of the reflected microwave signal, respectively. This study promises quantitative impedance characterization of a wide range of emerging functional nanoscale devices. (paper)

  14. Graphene-SnO2 nanocomposites decorated with quantum tunneling junctions: preparation strategies, microstructures and formation mechanism.

    Science.gov (United States)

    Wang, Qingxiu; Wu, Xianzheng; Wang, Lijun; Chen, Zhiwen; Wang, Shilong

    2014-09-28

    Tin dioxide (SnO2) and graphene are versatile materials that are vitally important for creating new functional and smart materials. A facile, simple and efficient ultrasonic-assisted hydrothermal synthesis approach has been developed to prepare graphene-SnO2 nanocomposites (GSNCs), including three samples with graphene/Sn weight ratios = 1 : 2 (GSNC-2), 1 : 1 (GSNC-1), and graphene oxide/Sn weight ratio = 1 : 1 (GOSNC-1). Low-magnification electron microscopy analysis indicated that graphene was exfoliated and adorned with SnO2 nanoparticles, which were dispersed uniformly on both the sides of the graphene nanosheets. High-magnification electron microscopy analysis confirmed that the graphene-SnO2 nanocomposites presented network tunneling frameworks, which were decorated with the SnO2 quantum tunneling junctions. The size distribution of SnO2 nanoparticles was estimated to range from 3 to 5.5 nm. Comparing GSNC-2, GSNC-1, and GOSNC-1, GOSNC-1 was found to exhibit a significantly better the homogeneous distribution and a considerably smaller size distribution of SnO2 nanoparticles, which indicated that it was better to use graphene oxide as a supporting material and SnCl4·5H2O as a precursor to synthesize hybrid graphene-SnO2 nanocomposites. Experimental results suggest that the graphene-SnO2 nanocomposites with interesting SnO2 quantum tunneling junctions may be a promising material to facilitate the improvement of the future design of micro/nanodevices.

  15. Low-noise parametric amplification at 35 GHz in a single Josephson tunnel junction

    DEFF Research Database (Denmark)

    Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.

    1979-01-01

    Parametric amplification at 35 GHz has been obtained using a single Josephson tunnel junction as the active element. The amplifier was operated in the singly quasidegenerate mode with a pump frequency at 70 GHz. The noise temperature was measured and found correlated with the gain. At the highest...... gain achieved, 11.6 dB, the noise temperature was 400 K. The noise temperature was reduced considerably by decreasing the gain. At 8 and 4 dB we found 165±25 K and 50±30 K, respectively. Applied Physics Letters is copyrighted by The American Institute of Physics....

  16. Effect of film roughness in Fe/MgO/Fe magnetic tunnel junctions: model calculations

    Energy Technology Data Exchange (ETDEWEB)

    Edalati Boostan, Saeideh; Heiliger, Christian [I. Physikalisches Institut, Justus Liebig University Giessen, D-35392 (Germany); Moradi, Hosein [Department of Physics,Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

    2011-07-01

    We calculate how interface roughness affects the tunneling magnetoresistance (TMR) in Fe/MgO/Fe (100) junctions. The used method is based on a single-band tight-binding (SBTB) approximation employing the Green's function formalism. We investigate the influence of disorder at the TMR ratio. Thereby, the disorder is modeled by considering different occupation probabilities of Fe and MgO at interface sites. We calculate the current densities for parallel and anti-parallel configurations for different disorders. The results show that the roughness decreases the TMR that match well with experimental observations.

  17. Dry transfer of chemical-vapor-deposition-grown graphene onto liquid-sensitive surfaces for tunnel junction applications

    International Nuclear Information System (INIS)

    Feng, Ying; Chen, Ke

    2015-01-01

    We report a dry transfer method that can tranfer chemical vapor deposition (CVD) grown graphene onto liquid-sensitive surfaces. The graphene grown on copper (Cu) foil substrate was first transferred onto a freestanding 4 μm thick sputtered Cu film using the conventional wet transfer process, followed by a dry transfer process onto the target surface using a polydimethylsiloxane stamp. The dry-transferred graphene has similar properties to traditional wet-transferred graphene, characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and electrical transport measurements. It has a sheet resistance of 1.6 ∼ 3.4 kΩ/□, hole density of (4.1 ∼ 5.3) × 10 12 cm −2 , and hole mobility of 460 ∼ 760 cm 2 V −1 s −1 without doping at room temperature. The results suggest that large-scale CVD-grown graphene can be transferred with good quality and without contaminating the target surface by any liquid. Mg/MgO/graphene tunnel junctions were fabricated using this transfer method. The junctions show good tunneling characteristics, which demonstrates the transfer technique can also be used to fabricate graphene devices on liquid-sensitive surfaces. (paper)

  18. Hybrid High-Temperature-Superconductor–Semiconductor Tunnel Diode

    Directory of Open Access Journals (Sweden)

    Alex Hayat

    2012-12-01

    Full Text Available We report the demonstration of hybrid high-T_{c}-superconductor–semiconductor tunnel junctions, enabling new interdisciplinary directions in condensed matter research. The devices are fabricated by our newly developed mechanical-bonding technique, resulting in high-T_{c}-superconductor–semiconductor tunnel diodes. Tunneling-spectra characterization of the hybrid junctions of Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} combined with bulk GaAs, or a GaAs/AlGaAs quantum well, exhibits excess voltage and nonlinearity, similarly to spectra obtained in scanning-tunneling microscopy, and is in good agreement with theoretical predictions for a d-wave-superconductor–normal-material junction. Additional junctions are demonstrated using Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} combined with graphite or Bi_{2}Te_{3}. Our results pave the way for new methods in unconventional superconductivity studies, novel materials, and quantum technology applications.

  19. Quantum Interference in the Longitudinal Oscillations of the Total Spin of a Dimeric Molecular Nanomagnet

    Science.gov (United States)

    Ramsey, Christopher; Del Barco, Enrique; Hill, Stephen; Shah, Sonali; Beedle, Christopher; Hendrickson, David

    2008-03-01

    The synthetic flexibility of molecular magnets allows one to systematically produce samples with desirable properties such as those with entangled spin states for implementation in quantum logic gates. Here we report direct evidence of quantum oscillations of the total spin length of a dimeric molecular nanomagnet through the observation of quantum interference associated with tunneling trajectories between states having different spin quantum numbers. As we outline, this is a consequence of the unique characteristics of a molecular Mn12 wheel which behaves as a (weak) ferromagnetic exchange-coupled molecular dimer: each half of the molecule acts as a single-molecule magnet (SMM), while the weak coupling between the two halves gives rise to an additional internal spin degree of freedom within the molecule, namely that its total spin may fluctuate. This extra degree of freedom accounts for several magnetization tunneling resonances that cannot be explained within the usual giant spin approximation. More importantly, the observation of quantum interference provides unambiguous evidence for the quantum mechanical superposition involving entangled states of both halves of the wheel.

  20. Nanomanipulation and Lithography: The Building (and Modeling) of Carbon Nanotube Magnetic Tunnel Junctions

    Science.gov (United States)

    Louie, Richard Nam

    2002-12-01

    Aircraft fuselages suffer alternating stress during takeoffs and landings, and fatigue cracks begin to grow, usually at rivet holes. The detection of these fatigue cracks under installed fasteners in aging aircraft is a major goal of the nondestructive evaluation (NDE) community. The use of giant magnetoresistance (GMR) sensors in electromagnetic (EM) NDE has been increasing rapidly. For example, here at Langley Research Center, a Rotating Probe System (RPS) containing a GMR element has been incorporated into a product to detect deeply buried flaws in aerospace structures. In order to advance this eddy current probe application and many similar ones, research to create smaller, more sensitive and energy-efficient EM sensors has been aggressively pursued. Recent theoretical and experimental work on spin coherent transport supports the feasibility of carbon nanotube (CNT) based magnetic tunnel junctions. In this study, a spatial filtering scheme is presented that improves the signal to noise ratio of the RPS and does not significantly impact the number of false alarms. Signals due to buried flaws occur at higher frequencies than do signals due to rivet tilt or probe misalignment, and the strategy purposefully targets this fact. Furthermore, the spatial filtering scheme exploits decreases in the probe output that are observed immediately preceding and following the peak in output due to a fatigue crack. Using the new filters, an enhanced probability of flaw detection is expected. In the future, even tinier, more sensitive, low-power sensors are envisioned for the rotating probe and other nondestructive inspection systems. These may be comprised of single-walled carbon nanotubes (SWCNTs) that connect two ferromagnetic (FM) electrodes. Theoretical work has been done at Langley to model the electrical and magnetoconductance behavior of such junctions, for systems containing short "armchair" nanotubes. The present work facilitates the modeling of more realistic system

  1. Modeling and Implementation of HfO2-based Ferroelectric Tunnel Junctions

    Science.gov (United States)

    Pringle, Spencer Allen

    HfO2-based ferroelectric tunnel junctions (FTJs) represent a unique opportunity as both a next-generation digital non-volatile memory and as synapse devices in braininspired logic systems, owing to their higher reliability compared to filamentary resistive random-access memory (ReRAM) and higher speed and lower power consumption compared to competing devices, including phase-change memory (PCM) and state-of-the-art FTJ. Ferroelectrics are often easier to deposit and have simpler material structure than films for magnetic tunnel junctions (MTJs). Ferroelectric HfO2 also enables complementary metal-oxide-semiconductor (CMOS) compatibility, since lead zirconate titanate (PZT) and BaTiO3-based FTJs often are not. No other groups have yet demonstrated a HfO2-based FTJ (to best of the author's knowledge) or applied it to a suitable system. For such devices to be useful, system designers require models based on both theoretical physical analysis and experimental results of fabricated devices in order to confidently design control systems. Both the CMOS circuitry and FTJs must then be designed in layout and fabricated on the same die. This work includes modeling of proposed device structures using a custom python script, which calculates theoretical potential barrier heights as a function of material properties and corresponding current densities (ranging from 8x103 to 3x10-2 A/cm 2 with RHRS/RLRS ranging from 5x105 to 6, depending on ferroelectric thickness). These equations were then combined with polynomial fits of experimental timing data and implemented in a Verilog-A behavioral analog model in Cadence Virtuoso. The author proposes tristate CMOS control systems, and circuits, for implementation of FTJ devices as digital memory and presents simulated performance. Finally, a process flow for fabrication of FTJ devices with CMOS is presented. This work has therefore enabled the fabrication of FTJ devices at RIT and the continued investigation of them as applied to any

  2. Tunnel splitting for a high-spin molecule in an in-plane field

    Science.gov (United States)

    Zhu, Jia-Lin

    2000-08-01

    Direction and strength effects of a magnetic field on the ground-state tunnel splitting for a biaxial spin molecule with the model Hamiltonian H = k1Sz2 + k2Sy2- gµBHzSz- gµBHySy have been investigated within a continuous-spin approach including the Wess-Zumino-Berry term. The topological oscillation and the non-Kramers freezing indicated in the approach are in agreement with those observed in a recent experiment on Fe8 molecular nanomagnets. The behaviour of tunnel splitting with multiple orbits induced by strong fields has been revealed clearly.

  3. Ge-on-insulator tunneling FET with abrupt source junction formed by utilizing snowplow effect of NiGe

    Science.gov (United States)

    Matsumura, Ryo; Katoh, Takumi; Takaguchi, Ryotaro; Takenaka, Mitsuru; Takagi, Shinichi

    2018-04-01

    Tunneling field-effect transistors (TFETs) attract much attention for use in realizing next-generation low-power processors. In particular, Ge-on-insulator (GOI) TFETs are expected to realize low power operation with a high on-current/off-current (I on/I off) ratio, owing to their narrow bandgap. Here, to improve the performance of GOI-TFETs, a source junction with a high doping concentration and an abrupt impurity profile is essential. In this study, a snowplow effect of NiGe combined with low-energy BF2 + implantation has been investigated to realize an abrupt p+/n Ge junction for GOI n-channel TFETs. By optimizing the Ni thickness to form NiGe (thickness: 4 nm), an abrupt junction with a B profile abruptness of ˜5 nm/dec has been realized with a high doping concentration of around 1021 cm-3. The operation of GOI n-TFETs with this source junction having the abrupt B profile has been demonstrated, and the improvement of TFET properties such as the I on/I off ratio from 311 to 743 and the subthreshold slope from 368 to 239 mV/dec has been observed. This junction formation technology is attractive for enhancing the TFET performance.

  4. Effects of junction resistance and counterelectrode material on point-contact tunneling into single- and polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-y/

    Energy Technology Data Exchange (ETDEWEB)

    Moog, E.R.; Hawley, M.E.; Gray, K.E.; Liu, J.Z.; Hinks, D.G.; Capone, D.W. II; Downey, J.

    1988-06-01

    The effects of junction resistance and counterelectrode material on the results of point-contact tunneling studies into single- and polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-y/ are illustrated. Although reasonably symmetric I(V) curves predominantly indicate energy gap values /Delta/ /approx/ 20 meV, large asymmetries are often found for high-resistance junctions. Very low-resistance junctions show the expected behavior of pure metallic bridge and indicate /Delta/ /approx/ 25-30 meV.

  5. Development of superconducting tunnel junction as photon counting detector in astronomy; Developpement de jonctions supraconductrices a effet tunnel pour le comptage de photons en astronomie

    Energy Technology Data Exchange (ETDEWEB)

    Jorel, C

    2004-12-15

    This work describes the development of S/Al-AlOx-Al/S Superconducting Tunnel Junctions (STJ) to count photons for astronomical applications in the near-infrared. The incoming light energy is converted into excited charges in a superconducting layer (S, either Nb or Ta) with a population proportional to the deposited energy. The photon energy can thus be evaluated by integrating the tunnel current induced in a voltage biased junction at a very low temperature (100 mK). The performance of STJ for light detection is discussed in the first chapter and compared with the best performances obtained with other techniques based on either superconductors. At the beginning of the thesis, a previous manufacturing process made it possible to obtain good quality Nb based junctions and preliminary results for photon counting. The objective of the thesis was to replace Nb as absorber with Ta, an intrinsically more sensitive material, and secondly to develop a new and more efficient manufacturing process. We first focused on the optimization of the Tantalum thin film quality. Structural analysis showed that these films can be grown epitaxially by magnetron sputtering onto an R-plane sapphire substrate heated to 600 Celsius degrees and covered by a thin Nb buffer layer. Electrical transport measurement from room to low temperatures gave excellent Relative Resistive Ratios of about 50 corresponding to mean free path of the order of 100 nm. Then, we conceived an original manufacturing process batch on 3 inch diameter sapphire substrate with five mask levels. These masks made it possible to produce single pixel STJ of different sizes (from 25*25 to 50*50 square microns) and shapes. We also produced multiple junctions onto a common absorber as well as 9-pixel arrays. Thanks to the development of this process we obtained a very large percentage of quality junctions (>90%) with excellent measured normal resistances of a few micro-ohm cm{sup 2} and low leakage currents of the order of one

  6. 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.

  7. 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.

  8. Magnetic microstructure of candidates for epitaxial dual Heusler magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Kaiser, A.; Banerjee, D.; Rata, A.D.; Wiemann, C.; Cramm, S.; Schneider, C.M.

    2009-01-01

    Heusler alloys are considered as interesting ferromagnetic electrode materials for magnetic tunnel junctions, because of their high spin polarization. We, therefore, investigated the micromagnetic properties in a prototypical thin film system comprising two different Heusler phases Co 2 MnSi (CMS) and Co 2 FeSi (CFS) separated by a MgO barrier. The magnetic microstructure was investigated by X-ray photoemission electron microscopy (XPEEM). We find a strong influence of the Heusler phase formation process on the magnetic domain patterns. SiO 2 /V/CMS/MgO/CFS and SiO 2 /V/CFS/MgO/CMS trilayer structures exhibit a strikingly different magnetic behavior, which is due to pinhole coupling through the MgO barrier and a strong thickness dependence of the magnetic ordering in Co 2 MnSi

  9. Low-resistance magnetic tunnel junctions prepared by partial remote plasma oxidation of 0.9 nm Al barriers

    International Nuclear Information System (INIS)

    Ferreira, Ricardo; Freitas, Paulo P.; MacKenzie, Maureen; Chapman, John N.

    2005-01-01

    Current perpendicular to the plane read-head elements suitable for high-density magnetic storage require low resistance while maintaining a reasonable magnetoresistive (MR) signal (RxA 2 and MR>20% for areal densities >200 Gb/in 2 ). This letter shows that competitive low RxA junctions can be produced using underoxidized barriers starting from 0.9 nm thick Al layers. For as-deposited junctions, tunneling magnetoresistance (TMR) ∼20% for RxA∼2-15 Ω μm 2 is obtained, while in the RxA∼60-150 Ω μm 2 range, TMR values between 40% to 45% are achieved. A limited number of junctions exhibits considerably lower RxA values with respect to the average, while keeping a similar MR (down to 0.44 Ω μm 2 with TMR of 20% and down to 2.2 Ω μm 2 with TMR of 52%). Experimental data suggest that current confinement to small regions (barrier defects/hot spots) may explain these results

  10. Phase-dependent noise in Josephson junctions

    Science.gov (United States)

    Sheldon, Forrest; Peotta, Sebastiano; Di Ventra, Massimiliano

    2018-03-01

    In addition to the usual superconducting current, Josephson junctions (JJs) support a phase-dependent conductance related to the retardation effect of tunneling quasi-particles. This introduces a dissipative current with a memory-resistive (memristive) character that should also affect the current noise. By means of the microscopic theory of tunnel junctions we compute the complete current autocorrelation function of a Josephson tunnel junction and show that this memristive component gives rise to both a previously noted phase-dependent thermal noise, and an undescribed non-stationary, phase-dependent dynamic noise. As experiments are approaching ranges in which these effects may be observed, we examine the form and magnitude of these processes. Their phase dependence can be realized experimentally as a hysteresis effect and may be used to probe defects present in JJ based qubits and in other superconducting electronics applications.

  11. Crossing Over from Attractive to Repulsive Interactions in a Tunneling Bosonic Josephson Junction.

    Science.gov (United States)

    Spagnolli, G; Semeghini, G; Masi, L; Ferioli, G; Trenkwalder, A; Coop, S; Landini, M; Pezzè, L; Modugno, G; Inguscio, M; Smerzi, A; Fattori, M

    2017-06-09

    We explore the interplay between tunneling and interatomic interactions in the dynamics of a bosonic Josephson junction. We tune the scattering length of an atomic ^{39}K Bose-Einstein condensate confined in a double-well trap to investigate regimes inaccessible to other superconducting or superfluid systems. In the limit of small-amplitude oscillations, we study the transition from Rabi to plasma oscillations by crossing over from attractive to repulsive interatomic interactions. We observe a critical slowing down in the oscillation frequency by increasing the strength of an attractive interaction up to the point of a quantum phase transition. With sufficiently large initial oscillation amplitude and repulsive interactions, the system enters the macroscopic quantum self-trapping regime, where we observe coherent undamped oscillations with a self-sustained average imbalance of the relative well population. The exquisite agreement between theory and experiments enables the observation of a broad range of many body coherent dynamical regimes driven by tunable tunneling energy, interactions and external forces, with applications spanning from atomtronics to quantum metrology.

  12. Electric field control of magnetic states in isolated and dipole-coupled FeGa nanomagnets delineated on a PMN-PT substrate.

    Science.gov (United States)

    Ahmad, Hasnain; Atulasimha, Jayasimha; Bandyopadhyay, Supriyo

    2015-10-09

    We report observation of a 'non-volatile' converse magneto-electric effect in elliptical FeGa nanomagnets delineated on a piezoelectric PMN-PT substrate. The nanomagnets are first magnetized with a magnetic field directed along their nominal major axes. Subsequent application of a strong electric field across the piezoelectric substrate generates strain in the substrate, which is partially transferred to the nanomagnets and rotates the magnetizations of some of them away from their initial orientations. The rotated magnetizations remain in their new orientations after the field is removed, resulting in 'non-volatility'. In isolated nanomagnets, the magnetization rotates by <90° upon application of the electric field, but in a dipole-coupled pair consisting of one 'hard' and one 'soft' nanomagnet, which are both initially magnetized in the same direction by the magnetic field, the soft nanomagnet's magnetization rotates by [Formula: see text] upon application of the electric field because of the dipole influence of the hard nanomagnet. This effect can be utilized for a nanomagnetic NOT logic gate.

  13. Spin-filtering junctions with double ferroelectric barriers

    International Nuclear Information System (INIS)

    Yan, Ju; Ding-Yu, Xing

    2009-01-01

    An FS/FE/NS/FE/FS double tunnel junction is suggested to have the ability to inject, modulate and detect the spin-polarized current electrically in a single device, where FS is the ferromagnetic semiconductor electrode, NS is the nonmagnetic semiconductor, and FE the ferroelectric barrier. The spin polarization of the current injected into the NS region can be switched between a highly spin-polarized state and a spin unpolarized state. The high spin polarization may be detected by measuring the tunneling magnetoresistance ratio of the double tunnel junction

  14. Tunneling Conductance in Ferromagnetic Metal/Normal Metal/Spin-Singlet -Wave Ferromagnetic Superconductor Junctions

    Directory of Open Access Journals (Sweden)

    Hamidreza Emamipour

    2013-01-01

    Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.

  15. A novel macro-model for spin-transfer-torque based magnetic-tunnel-junction elements

    Science.gov (United States)

    Lee, Seungyeon; Lee, Hyunjoo; Kim, Sojeong; Lee, Seungjun; Shin, Hyungsoon

    2010-04-01

    Spin-transfer-torque (STT) switching in magnetic-tunnel-junction (MTJ) has important merits over the conventional field induced magnetic switching (FIMS) MRAM in avoiding half-select problem, and improving scalability and selectivity. Design of MRAM circuitry using STT-based MTJ elements requires an accurate circuit model which exactly emulates the characteristics of an MTJ in a circuit simulator such as HSPICE. This work presents a novel macro-model that fully emulates the important characteristics of STT-based MTJ. The macro-model is realized as a three terminal sub-circuit that reproduces asymmetric resistance versus current (R-I) characteristics and temperature dependence of R-I hysteresis of STT-based MTJ element.

  16. Magnetization switching driven by spin-transfer-torque in high-TMR magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Aurelio, D.; Torres, L.; Finocchio, G.

    2009-01-01

    This paper presents a numerical study of magnetization switching driven by spin-polarized current in high-TMR magnetic tunnel junctions (TMR>100%). The current density distribution throughout the free-layer is computed dynamically, by modeling the ferromagnet/insulator/ferromagnet trilayer as a series of parallel resistances. The validity of the main hypothesis, which states that the current flows perpendicular to the sample plane, has been verified by numerically solving the Poisson equation. Our results show that the nonuniform current density distribution is a source of asymmetry to the switching process. Furthermore, we observe that the reversal mechanisms are characterized by well-defined localized pre-switching oscillation modes.

  17. Spectroscopy of bulk and few-layer superconducting NbSe2 with van der Waals tunnel junctions.

    Science.gov (United States)

    Dvir, T; Massee, F; Attias, L; Khodas, M; Aprili, M; Quay, C H L; Steinberg, H

    2018-02-09

    Tunnel junctions, an established platform for high resolution spectroscopy of superconductors, require defect-free insulating barriers; however, oxides, the most common barrier, can only grow on a limited selection of materials. We show that van der Waals tunnel barriers, fabricated by exfoliation and transfer of layered semiconductors, sustain stable currents with strong suppression of sub-gap tunneling. This allows us to measure the spectra of bulk (20 nm) and ultrathin (3- and 4-layer) NbSe 2 devices at 70 mK. These exhibit two distinct superconducting gaps, the larger of which decreases monotonically with thickness and critical temperature. The spectra are analyzed using a two-band model incorporating depairing. In the bulk, the smaller gap exhibits strong depairing in in-plane magnetic fields, consistent with high out-of-plane Fermi velocity. In the few-layer devices, the large gap exhibits negligible depairing, consistent with out-of-plane spin locking due to Ising spin-orbit coupling. In the 3-layer device, the large gap persists beyond the Pauli limit.

  18. 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.

  19. 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.

  20. A 36-pixel superconducting tunnel junction soft X-ray detector for environmental science applications

    International Nuclear Information System (INIS)

    Friedrich, Stephan; Drury, Owen B.; Cramer, Stephen P.; Green, Peter G.

    2006-01-01

    We are operating a superconducting tunnel junction detector for high-resolution soft X-ray spectroscopy at the Advanced Biological and Environmental X-ray Facility at the Advanced Light Source synchrotron. We have recently upgraded the instrument from 9 to 36 pixels for increased sensitivity. We have also acquired a new digital signal readout to increase the total count rate capabilities to ∼10 6 counts/s while maintaining a high peak-to-background ratio. We report on the performance of the spectrometer, and discuss speciation measurements of chromium in welding aerosols as a typical application of the instrument in environmental science

  1. A 36-pixel superconducting tunnel junction soft X-ray detector for environmental science applications

    Energy Technology Data Exchange (ETDEWEB)

    Friedrich, Stephan [Lawrence Livermore National Laboratory, Advanced Detector Group, 7000 East Avenue, L-270, Livermore, CA 94550 (United States) and Lawrence Berkeley National Laboratory, Advanced Biological and Environmental X-ray Facility, 1 Cyclotron Road, Berkeley, CA 94720 (United States)]. E-mail: friedrich1@llnl.gov; Drury, Owen B. [Lawrence Livermore National Laboratory, Advanced Detector Group, 7000 East Avenue, L-270, Livermore, CA 94550 (United States); Lawrence Berkeley National Laboratory, Advanced Biological and Environmental X-ray Facility, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Cramer, Stephen P. [Lawrence Berkeley National Laboratory, Advanced Biological and Environmental X-ray Facility, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Green, Peter G. [University of California Davis, Department of Civil and Environmental Engineering, 1 Shields Avenue, Davis, CA 95616 (United States)

    2006-04-15

    We are operating a superconducting tunnel junction detector for high-resolution soft X-ray spectroscopy at the Advanced Biological and Environmental X-ray Facility at the Advanced Light Source synchrotron. We have recently upgraded the instrument from 9 to 36 pixels for increased sensitivity. We have also acquired a new digital signal readout to increase the total count rate capabilities to {approx}10{sup 6} counts/s while maintaining a high peak-to-background ratio. We report on the performance of the spectrometer, and discuss speciation measurements of chromium in welding aerosols as a typical application of the instrument in environmental science.

  2. Electrical Resistance of Ag-TS-S(CH2)(n-1)CH3//Ga2O3/EGaln Tunneling Junctions

    NARCIS (Netherlands)

    Cademartiri, Ludovico; Thuo, Martin M.; Nijhuis, Christian A.; Reus, William F.; Tricard, Simon; Barber, Jabulani R.; Sodhi, Rana N. S.; Brodersen, Peter; Kim, Choongik; Chiechi, Ryan C.; Whitesides, George M.

    2012-01-01

    Tunneling junctions having the structure Ag-TS-S(CH2)(n-1)CH3//Ga2O3/EGaIn allow physical-organic studies of charge transport across self-assembled monolayers (SAMs). In ambient conditions, the surface of the liquid metal electrode (EGaIn, 75.5 wt % Ga, 24.5 wt % In, mp 15.7 degrees C) oxidizes and

  3. Josephson junctions with ferromagnetic interlayer

    International Nuclear Information System (INIS)

    Wild, Georg Hermann

    2012-01-01

    We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlO x /Pd 0.82 Ni 0.18 /Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to π-coupling is observed for a thickness d F =6 nm of the ferromagnetic Pd 0.82 Ni 0.18 interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd 0.82 Ni 0.18 has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.

  4. Josephson junctions with ferromagnetic interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Wild, Georg Hermann

    2012-03-04

    We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlO{sub x}/Pd{sub 0.82}Ni{sub 0.18}/Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to {pi}-coupling is observed for a thickness d{sub F}=6 nm of the ferromagnetic Pd{sub 0.82}Ni{sub 0.18} interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd{sub 0.82}Ni{sub 0.18} has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.

  5. Barrier breakdown mechanism in nano-scale perpendicular magnetic tunnel junctions with ultrathin MgO barrier

    Science.gov (United States)

    Lv, Hua; Leitao, Diana C.; Hou, Zhiwei; Freitas, Paulo P.; Cardoso, Susana; Kämpfe, Thomas; Müller, Johannes; Langer, Juergen; Wrona, Jerzy

    2018-05-01

    Recently, the perpendicular magnetic tunnel junctions (p-MTJs) arouse great interest because of its unique features in the application of spin-transfer-torque magnetoresistive random access memory (STT-MRAM), such as low switching current density, good thermal stability and high access speed. In this paper, we investigated current induced switching (CIS) in ultrathin MgO barrier p-MTJs with dimension down to 50 nm. We obtained a CIS perpendicular tunnel magnetoresistance (p-TMR) of 123.9% and 7.0 Ω.μm2 resistance area product (RA) with a critical switching density of 1.4×1010 A/m2 in a 300 nm diameter junction. We observe that the extrinsic breakdown mechanism dominates, since the resistance of our p-MTJs decreases gradually with the increasing current. From the statistical analysis of differently sized p-MTJs, we observe that the breakdown voltage (Vb) of 1.4 V is 2 times the switching voltage (Vs) of 0.7 V and the breakdown process exhibits two different breakdown states, unsteady and steady state. Using Simmons' model, we find that the steady state is related with the barrier height of the MgO layer. Furthermore, our study suggests a more efficient method to evaluate the MTJ stability under high bias rather than measuring Vb. In conclusion, we developed well performant p-MTJs for the use in STT-MRAM and demonstrate the mechanism and control of breakdown in nano-scale ultrathin MgO barrier p-MTJs.

  6. 2D Spin-Dependent Diffraction of Electrons From Periodical Chains of Nanomagnets

    Directory of Open Access Journals (Sweden)

    Teshome Senbeta

    2012-03-01

    Full Text Available The scattering of the unpolarized beams of electrons by nanomagnets in the vicinity of some scattering angles leads to complete spin polarized electrons. This result is obtained with the help of the perturbation theory. The dipole-dipole interaction between the magnetic moment of the nanomagnet and the magnetic moment of electron is treated as perturbation. This interaction is not spherically symmetric. Rather it depends on the electron spin variables. It in turn results in spinor character of the scattering amplitudes. Due to the smallness of the magnetic interactions, the scattering length of this process is very small to be proved experimentally. To enhance the relevant scattering lengths, we considered the diffraction of unpolarized beams of electrons by linear chains of nanomagnets. By tuning the distance between the scatterers it is possible to obtain the diffraction maximum of the scattered electrons at scattering angles which corresponds to complete spin polarization of electrons. It is shown that the total differential scattering length is proportional to N2 (N is a number of scatterers. Even small number of nanomagnets in the chain helps to obtain experimentally visible enhancement of spin polarization of the scattered electrons.

  7. Model of a tunneling current in a p-n junction based on armchair graphene nanoribbons - an Airy function approach and a transfer matrix method

    International Nuclear Information System (INIS)

    Suhendi, Endi; Syariati, Rifki; Noor, Fatimah A.; Khairurrijal; Kurniasih, Neny

    2014-01-01

    We modeled a tunneling current in a p-n junction based on armchair graphene nanoribbons (AGNRs) by using an Airy function approach (AFA) and a transfer matrix method (TMM). We used β-type AGNRs, in which its band gap energy and electron effective mass depends on its width as given by the extended Huckel theory. It was shown that the tunneling currents evaluated by employing the AFA are the same as those obtained under the TMM. Moreover, the calculated tunneling current was proportional to the voltage bias and inversely with temperature

  8. Parametric frequency conversion in long Josephson junctions

    International Nuclear Information System (INIS)

    Irie, F.; Ashihara, S.; Yoshida, K.

    1976-01-01

    Current steps at voltages corresponding to the parametric coupling between an applied r.f. field and junction resonant modes have been observed in long Josephson tunnel junctions in the flux-flow state. The observed periodic variations of the step height due to the applied magnetic field are explained quantitatively by a perturbational analysis using Josephson phase equations. The present study demonstrates that the moving vortex array can serve as a coherent pump wave for signal waves propagating in the barrier region, which indicates, as a result, the possibility of traveling-wave parametric devices with long Josephson tunnel junctions. (author)

  9. Fluoride barriers in Nb/Pb Josephson junctions

    Science.gov (United States)

    Asano, H.; Tanabe, K.; Michikami, O.; Igarashi, M.; Beasley, M. R.

    1985-03-01

    Josephson tunnel junctions are fabricated using a new class of artificial barriers, metal fluorides (Al fluoride and Zr fluoride). These fluoride barriers are deposited on the surface of a Nb base electrode, which are previously cleaned using a CF4 cleaning process, and covered by a Pb counterelectrode. The junctions with both Al fluoride and Zr fluoride barriers exhibit good tunneling characteristics and have low specific capacitance. In the case of Zr fluoride, it is observed that reasonable resistances are obtained even at thickness greater than 100 A. This phenomenon might be explained by tunneling via localized states in Zr fluoride.

  10. Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions.

    Science.gov (United States)

    Bonell, F; Hauet, T; Andrieu, S; Bertran, F; Le Fèvre, P; Calmels, L; Tejeda, A; Montaigne, F; Warot-Fonrose, B; Belhadji, B; Nicolaou, A; Taleb-Ibrahimi, A

    2012-04-27

    In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with Δ(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.

  11. In-situ grazing incidence X-ray diffraction measurements of relaxation in Fe/MgO/Fe epitaxial magnetic tunnel junctions during annealing

    Energy Technology Data Exchange (ETDEWEB)

    Eastwood, D.S. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Ali, M.; Hickey, B.J. [Department of Physics and Astronomy, University of Leeds, Leeds LS2 1JT (United Kingdom); Tanner, B.K., E-mail: b.k.tanner@dur.ac.uk [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)

    2013-12-15

    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. - Highlights: • Lattice relaxation of Fe/MgO/Fe epitaxial magnetic tunnel junctions measured. • In-plane lattice parameter of Fe equal to bulk value; totally relaxed. • MgO barrier initially strained towards the Fe but relaxes on annealing. • Reduction in strain dispersion in the MgO barrier by 40% above about 470 K. • No change in the in-plane “twist” mosaic throughout the annealing cycle.

  12. Tunneling-Electron-Induced Light Emission from Single Gold Nanoclusters.

    Science.gov (United States)

    Yu, Arthur; Li, Shaowei; Czap, Gregory; Ho, W

    2016-09-14

    The coupling of tunneling electrons with the tip-nanocluster-substrate junction plasmon was investigated by monitoring light emission in a scanning tunneling microscope (STM). Gold atoms were evaporated onto the ∼5 Å thick Al2O3 thin film grown on the NiAl (110) surface where they formed nanoclusters 3-7 nm wide. Scanning tunneling spectroscopy (STS) of these nanoclusters revealed quantum-confined electronic states. Spatially resolved photon imaging showed localized emission hot spots. Size dependent study and light emission from nanocluster dimers further support the viewpoint that coupling of tunneling electrons to the junction plasmon is the main radiative mechanism. These results showed the potential of the STM to reveal the electronic and optical properties of nanoscale metallic systems in the confined geometry of the tunnel junction.

  13. Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

    NARCIS (Netherlands)

    Prins, M.W.J.; Jansen, R.; Kempen, van H.

    1996-01-01

    We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate

  14. Electronic tunneling currents at optical frequencies

    Science.gov (United States)

    Faris, S. M.; Fan, B.; Gustafson, T. K.

    1975-01-01

    Rectification characteristics of nonsuperconducting metal-barrier-metal junctions as deduced from electronic tunneling theory have been observed experimentally for optical frequency irradiation of the junction.

  15. Current-induced spin transfer torque in ferromagnet-marginal Fermi liquid double tunnel junctions

    International Nuclear Information System (INIS)

    Mu Haifeng; Zheng Qingrong; Jin Biao; Su Gang

    2005-01-01

    Current-induced spin transfer torque through a marginal Fermi liquid (MFL) which is connected to two noncollinearly aligned ferromagnets via tunnel junctions is discussed in terms of the nonequilibrium Green function method. It is found that in the absence of the spin-flip scattering, the magnitude of the torque increases with the polarization and the coupling constant λ of the MFL, whose maximum increases with λ linearly, showing that the interactions between electrons tend to enhance the spin torque. When the spin-flip scattering is included, an additional spin torque is induced. It is found that the spin-flip scattering enhances the spin torque and gives rise to a nonlinear angular shift

  16. Reduced-droop green III-nitride light-emitting diodes utilizing GaN tunnel junction

    Science.gov (United States)

    Alhassan, Abdullah I.; Young, Erin C.; Alyamani, Ahmed Y.; Albadri, Abdulrahman; Nakamura, Shuji; DenBaars, Steven P.; Speck, James S.

    2018-04-01

    We report the fabrication of low-droop high-efficiency green c-plane light-emitting diodes (LEDs) utilizing GaN tunnel junction (TJ) contacts. The LED epitaxial layers with a top p-GaN layer were grown by metal organic chemical vapor deposition and an n++-GaN layer was deposited by molecular beam epitaxy to form a TJ. The TJ LEDs were then compared with equivalent LEDs having a tin-doped indium oxide (ITO) contact. The TJ LEDs exhibited a higher performance and a lower efficiency droop than did the ITO LEDs. At 35 A/cm2, the external quantum efficiencies for the TJ and ITO LEDs were 31.2 and 27%, respectively.

  17. Superconducting β-ZrNClx probed by scanning-tunnelling and break-junction spectroscopy

    International Nuclear Information System (INIS)

    Ekino, Toshikazu; Sugimoto, Akira; Gabovich, Alexander M.; Zheng, Zhanfeng; Yamanaka, Shoji

    2013-01-01

    Highlights: •STM/STS combined with break-junction tunnelling spectroscopy (BJTS) on β-ZrNCl. •STM image on the ab plane shows triangular atomic lattice spots with a period of 0.36 nm. •The gap peaks are widely distributed (Δ p–p = 9–28 meV)over the area of 100 nm 2 . •Average gap ratio 2Δ/k B T c ∼ 10 is confirmed by both STS and BJTS. -- Abstract: Superconducting layered compound β-ZrNCl x (x = 0.7) with the critical temperature T c = 13–14 K was investigated by means of scanning tunnelling microscopy/spectroscopy. The single-crystal domain facet of ∼100 μm 2 in the c-axis-oriented polycrystal was used as a probing surface. The STM image at 4.9 K shows triangular atomic lattice spots with the period of ∼0.36 nm, which agrees with the X-ray diffraction measurements. The STS measurements of the local conductance, dI/dV, exhibit broadened gap structures with a substantial distribution of the gap-edge values. Most frequently observed peak-to-peak value of ∼20 mV is remarkably similar to the superconducting gap edge of the isostructural β-HfNCl x with T c = 24 K. Temperature, T, dependence of the dI/dV shows that the gap structure disappears above T c ∼ 13 K. Fitting of the dI/dV curve by the broadened BCS density of states leads to the superconducting gap of 2Δ(4.9 K) = 11–13 meV. This is in accordance with our former break-junction data confirming the intrinsic character of the previously obtained extremely large gap to T c ratio 2Δ(0)/k B T c ≈ 10 (k B is the Boltzmann constant), thereby pointing to the unusual superconducting properties of this compound

  18. A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jäck, Berthold, E-mail: b.jaeck@fkf.mpg.de; Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Hardock, Andreas [Institut für Theoretische Elektrotechnik, Technische Universität Hamburg-Harburg, 21079 Hamburg (Germany); 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)

    2015-01-05

    Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 10{sup 20 }cm{sup −2} s{sup −1} is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.

  19. Polaron effects on the dc- and ac-tunneling characteristics of molecular Josephson junctions

    Science.gov (United States)

    Wu, B. H.; Cao, J. C.; Timm, C.

    2012-07-01

    We study the interplay of polaronic effect and superconductivity in transport through molecular Josephson junctions. The tunneling rates of electrons are dominated by vibronic replicas of the superconducting gap, which show up as prominent features in the differential conductance for the dc and ac current. For relatively large molecule-lead coupling, a features that appears when the Josephson frequency matches the vibron frequency can be identified with an over-the-gap structure observed by Marchenkov [Nat. Nanotech. 1748-338710.1038/nnano.2007.2182, 481 (2007)]. However, we are more concerned with the weak-coupling limit, where resonant tunneling through the molecular level dominates. We find that certain features involving both Andreev reflection and vibron emission show an unusual shift of the bias voltage V at their maximum with the gate voltage Vg as V˜(2/3)Vg. Moreover, due to the polaronic effect, the ac Josephson current shows a phase shift of π when the bias eV is increased by one vibronic energy quantum ℏωv. This distinctive even-odd effect is explained in terms of the different sign of the coupling to vibrons of electrons and of Andreev-reflected holes.

  20. Phase locked 270-440 GHz local oscillator based on flux flow in long Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Koshelets, V.P.; Shitov, S.V.; Filippenko, L.V.

    2000-01-01

    The combination of narrow linewidth and wide band tunability makes the Josephson flux flow oscillator (FFO) a perfect on-chip local oscillator for integrated sub-mm wave receivers for, e.g., spectral radio astronomy. The feasibility of phase locking the FFO to an external reference oscillator......-running tunnel junction. The results of residual FFO phase noise measurements are also presented. Finally, we propose a single-chip fully superconductive receiver with two superconductor–insulator–superconductor mixers and an integrated phase-locked loop. ©2000 American Institute of Physics....

  1. Resonant tunneling via a Ru–dye complex using a nanoparticle bridge junction

    Science.gov (United States)

    Nishijima, Satoshi; Otsuka, Yoichi; Ohoyama, Hiroshi; Kajimoto, Kentaro; Araki, Kento; Matsumoto, Takuya

    2018-06-01

    Nonlinear current–voltage (I–V) characteristics is an important property for the realization of information processing in molecular electronics. We studied the electrical conduction through a Ru–dye complex (N-719) on a 2-aminoethanethiol (2-AET) monolayer in a nanoparticle bridge junction system. The nonlinear I–V characteristics exhibited a threshold voltage at around 1.2 V and little temperature dependence. From the calculation of the molecular states using density functional theory and the energy alignment between the electrodes and molecules, the conduction mechanism in this system was considered to be resonant tunneling via the HOMO level of N-719. Our results indicate that the weak electronic coupling of electrodes and molecules is essential for obtaining nonlinear I–V characteristics with a clear threshold voltage that reflect the intrinsic molecular state.

  2. Analytic expression for the giant fieldlike spin torque in spin-filter magnetic tunnel junctions

    Science.gov (United States)

    Tang, Y.-H.; Huang, Z.-W.; Huang, B.-H.

    2017-08-01

    We propose analytic expressions for fieldlike, T⊥, and spin-transfer, T∥, spin torque components in the spin-filter-based magnetic tunnel junction (SFMTJ), by using the single-band tight-binding model with the nonequilibrium Keldysh formalism. In consideration of multireflection processes between noncollinear magnetization of the spin-filter (SF) barrier and the ferromagnetic (FM) electrode, the central spin-selective SF barrier plays an active role in the striking discovery T⊥≫T∥ , which can be further identified by the unusual barrier thickness dependence of giant T⊥. Our general expressions reveal the sinusoidal angular dependence of both spin torque components, even in the presence of the SF barrier.

  3. 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.

  4. Thermal stability of tunneling spin polarization

    International Nuclear Information System (INIS)

    Kant, C.H.; Kohlhepp, J.T.; Paluskar, P.V.; Swagten, H.J.M.; Jonge, W.J.M. de

    2005-01-01

    We present a study of the thermal stability of tunneling spin polarization in Al/AlOx/ferromagnet junctions based on the spin-polarized tunneling technique, in which the Zeeman-split superconducting density of states in the Al electrode is used as a detector for the spin polarization. Thermal robustness of the polarization, which is of key importance for the performance of magnetic tunnel junction devices, is demonstrated for post-deposition anneal temperatures up to 500 o C with Co and Co 90 Fe 10 top electrodes, independent of the presence of an FeMn layer on top of the ferromagnet

  5. Interfacial spin-orbit splitting and current-driven spin torque in anisotropic tunnel junctions

    KAUST Repository

    Manchon, Aurelien

    2011-05-17

    Spin transport in magnetic tunnel junctions comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is investigated theoretically. Due to the presence of interfacial SOI, a current-driven spin torque can be generated at the second order in SOI, even in the absence of an external spin polarizer. This torque possesses two components, one in plane and one perpendicular to the plane of rotation, that can induce either current-driven magnetization switching from an in-plane to out-of-plane configuration or magnetization precessions, similar to spin transfer torque in spin valves. Consequently, it appears that it is possible to control the magnetization steady state and dynamics by either varying the bias voltage or electrically modifying the SOI at the interface.

  6. Distribution of tunnelling times for quantum electron transport

    International Nuclear Information System (INIS)

    Rudge, Samuel L.; Kosov, Daniel S.

    2016-01-01

    In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.

  7. Polarization-engineered GaN/InGaN/GaN tunnel diodes

    International Nuclear Information System (INIS)

    Krishnamoorthy, Sriram; Nath, Digbijoy N.; Akyol, Fatih; Park, Pil Sung; Esposto, Michele; Rajan, Siddharth

    2010-01-01

    We report on the design and demonstration of polarization-engineered GaN/InGaN/GaN tunnel junction diodes with high current density and low tunneling turn-on voltage. Wentzel-Kramers-Brillouin calculations were used to model and design tunnel junctions with narrow band gap InGaN-based barrier layers. N-polar p-GaN/In 0.33 Ga 0.67 N/n-GaN heterostructure tunnel diodes were grown using molecular beam epitaxy. Efficient interband tunneling was achieved close to zero bias with a high current density of 118 A/cm 2 at a reverse bias of 1 V, reaching a maximum current density up to 9.2 kA/cm 2 . These results represent the highest current density reported in III-nitride tunnel junctions and demonstrate the potential of III-nitride tunnel devices for a broad range of optoelectronic and electronic applications.

  8. Observation of large low field magnetoresistance in ramp-edge tunneling junctions based on doped manganite ferromagnetic electrodes and a SrTiO{sub 3} insulator

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, C.; Jia, Q.X.; Fan, Y.; Hundley, M.F.; Reagor, D.W.; Hawley, M.E.; Peterson, D.E.

    1998-07-01

    The authors report the fabrication of ferromagnet-insulator-ferromagnet junction devices using a ramp-edge geometry based on (La{sub 0.7}Sr{sub 0.3})MnO{sub 3} ferromagnetic electrodes and a SrTiO{sub 3} insulator. The multilayer thin films were deposited using pulsed laser deposition and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance depends on the relative orientation of the magnetization in the electrodes. The maximum junction magnetoresistance (JMR) of 30% is observed below 300 Oe at low temperatures (T < 100 K).

  9. Separating read and write units in multiferroic devices.

    Science.gov (United States)

    Roy, Kuntal

    2015-06-18

    Strain-mediated multiferroic composites, i.e., piezoelectric-magnetostrictive heterostructures, hold profound promise for energy-efficient computing in beyond Moore's law era. While reading a bit of information stored in the magnetostrictive nanomagnets using a magnetic tunnel junction (MTJ), a material selection issue crops up since magnetostrictive materials in general cannot be utilized as the free layer of the MTJ. This is an important issue since we need to achieve a high magnetoresistance for technological applications. We show here that magnetically coupling the magnetostrictive nanomagnet and the free layer e.g., utilizing the magnetic dipole coupling between them can circumvent this issue. By solving stochastic Landau-Lifshitz-Gilbert equation of magnetization dynamics in the presence of room-temperature thermal fluctuations, we show that such design can eventually lead to a superior energy-delay product.

  10. Modulation of Quantum Tunneling via a Vertical Two-Dimensional Black Phosphorus and Molybdenum Disulfide p-n Junction.

    Science.gov (United States)

    Liu, Xiaochi; Qu, Deshun; Li, Hua-Min; Moon, Inyong; Ahmed, Faisal; Kim, Changsik; Lee, Myeongjin; Choi, Yongsuk; Cho, Jeong Ho; Hone, James C; Yoo, Won Jong

    2017-09-26

    Diverse diode characteristics were observed in two-dimensional (2D) black phosphorus (BP) and molybdenum disulfide (MoS 2 ) heterojunctions. The characteristics of a backward rectifying diode, a Zener diode, and a forward rectifying diode were obtained from the heterojunction through thickness modulation of the BP flake or back gate modulation. Moreover, a tunnel diode with a precursor to negative differential resistance can be realized by applying dual gating with a solid polymer electrolyte layer as a top gate dielectric material. Interestingly, a steep subthreshold swing of 55 mV/dec was achieved in a top-gated 2D BP-MoS 2 junction. Our simple device architecture and chemical doping-free processing guaranteed the device quality. This work helps us understand the fundamentals of tunneling in 2D semiconductor heterostructures and shows great potential in future applications in integrated low-power circuits.

  11. Dissipative current in SIFS Josephson junctions

    NARCIS (Netherlands)

    Vasenko, A.; Kawabata, S.; Golubov, Alexandre Avraamovitch; Kupriyanov, M. Yu; Hekking, F.W.J.

    2010-01-01

    We investigate superconductor/insulator/ferromagnet/superconductor (SIFS) tunnel Josephson junctions in the dirty limit, using the quasiclassical theory. We consider the case of a strong tunnel barrier such that the left S layer and the right FS bilayer are decoupled. We calculate quantitatively the

  12. 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.

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

    International Nuclear Information System (INIS)

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

    2015-01-01

    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

  14. Reversal time of jump-noise magnetization dynamics in nanomagnets via Monte Carlo simulations

    Science.gov (United States)

    Parthasarathy, Arun; Rakheja, Shaloo

    2018-06-01

    The jump-noise is a nonhomogeneous Poisson process which models thermal effects in magnetization dynamics, with special applications in low temperature escape rate phenomena. In this work, we develop improved numerical methods for Monte Carlo simulation of the jump-noise dynamics and validate the method by comparing the stationary distribution obtained empirically against the Boltzmann distribution. In accordance with the Néel-Brown theory, the jump-noise dynamics display an exponential relaxation toward equilibrium with a characteristic reversal time, which we extract for nanomagnets with uniaxial and cubic anisotropy. We relate the jump-noise dynamics to the equivalent Landau-Lifshitz dynamics up to second order correction for a general energy landscape and obtain the analogous Néel-Brown theory's solution of the reversal time. We find that the reversal time of jump-noise dynamics is characterized by Néel-Brown theory's solution at the energy saddle point for small noise. For large noise, the magnetization reversal due to jump-noise dynamics phenomenologically represents macroscopic tunneling of magnetization.

  15. 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.

  16. Voltage-controlled low-energy switching of nanomagnets through Ruderman-Kittel-Kasuya-Yosida interactions for magnetoelectric device applications

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Bahniman, E-mail: bghosh@utexas.edu; Dey, Rik; Register, Leonard F.; Banerjee, Sanjay K. [Microelectronics Research Center, University of Texas at Austin, 10100 Burnet Road, Bldg. 160, Austin, Texas 78758 (United States)

    2016-07-21

    In this article, we consider through simulation low-energy switching of nanomagnets via electrostatically gated inter-magnet Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions on the surface of three-dimensional topological insulators, for possible memory and nonvolatile logic applications. We model the possibility and dynamics of RKKY-based switching of one nanomagnet by coupling to one or more nanomagnets of set orientation. Potential applications to both memory and nonvolatile logic are illustrated. Sub-attojoule switching energies, far below conventional spin transfer torque (STT)-based memories and even below CMOS logic appear possible. Switching times on the order of a few nanoseconds, comparable to times for STT switching, are estimated for ferromagnetic nanomagnets, but the approach also appears compatible with the use of antiferromagnets which may allow for faster switching.

  17. Voltage-controlled low-energy switching of nanomagnets through Ruderman-Kittel-Kasuya-Yosida interactions for magnetoelectric device applications

    International Nuclear Information System (INIS)

    Ghosh, Bahniman; Dey, Rik; Register, Leonard F.; Banerjee, Sanjay K.

    2016-01-01

    In this article, we consider through simulation low-energy switching of nanomagnets via electrostatically gated inter-magnet Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions on the surface of three-dimensional topological insulators, for possible memory and nonvolatile logic applications. We model the possibility and dynamics of RKKY-based switching of one nanomagnet by coupling to one or more nanomagnets of set orientation. Potential applications to both memory and nonvolatile logic are illustrated. Sub-attojoule switching energies, far below conventional spin transfer torque (STT)-based memories and even below CMOS logic appear possible. Switching times on the order of a few nanoseconds, comparable to times for STT switching, are estimated for ferromagnetic nanomagnets, but the approach also appears compatible with the use of antiferromagnets which may allow for faster switching.

  18. Spin-flip scattering effect on the current-induced spin torque in ferromagnet-insulator-ferromagnet tunnel junctions

    International Nuclear Information System (INIS)

    Zhu Zhengang; Su Gang; Jin Biao; Zheng Qingrong

    2003-01-01

    We have investigated the current-induced spin transfer torque of a ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip scatterings into account. It is found that the spin-flip scattering can induce an additional spin torque, enhancing the maximum of the spin torque and giving rise to an angular shift compared to the case when the spin-flip scatterings are neglected. The effects of the molecular fields of the left and right ferromagnets on the spin torque are also studied. It is found that τ Rx /I e (τ Rx is the spin-transfer torque acting on the right ferromagnet and I e is the tunneling electrical current) does vary with the molecular fields. At two certain angles, τ Rx /I e is independent of the molecular field of the right ferromagnet, resulting in two crossing points in the curve of τ Rx /I e versus the relevant orientation for different molecular fields

  19. Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

    International Nuclear Information System (INIS)

    Pedersen, N.F.; Soerensen, O.H.; Mygind, J.

    1978-01-01

    The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature T/sub c/ of the Sn films. The temperature dependence of the cosphi conductance is determined from the resonant response at the junction plasma frequency f/sub p/ as the temperature is decreased from T/sub c/. We used three different schemes for observation of the plasma oscillations: (a) second-harmonic generation (excitation at approx. 4.5 GHz, f/sub p/ approx. 4.5 GHz); (b) mixing (excitations at approx. 9 and approx. 18 GHz, f/sub p/ approx. 9 GHz); (c) parametric half-harmonic oscillation (excitation at approx. 18 GHz, f/sub p/ approx. 9 GHz). Measurements were possible in two temperature intervals; 0.994 or = T/T/sub c/ > or = 0.930, with the result that as the temperature was decreased the cosphi amplitude first increased from about zero to positive values and then at lower temperatures decreased approaching -1 at the lowest temperatures of the experiment

  20. Bias voltage dependence of magnetic tunnel junctions comprising amorphous ferromagnetic CoFeSiB layer with double barriers

    International Nuclear Information System (INIS)

    Yim, H.I.; Lee, S.Y.; Hwang, J.Y.; Rhee, J.R.; Chun, B.S.; Wang, K.L.; Kim, Y.K.; Kim, T.W.; Lee, S.S.; Hwang, D.G.

    2008-01-01

    Double-barrier magnetic tunnel junctions (DMTJs) with and without an amorphous ferromagnetic material such as CoFeSiB 10, CoFe 5/CoFeSiB 5, and CoFe 10 (nm) were prepared and compared to investigate the bias voltage dependence of the tunneling magnetoresistance (TMR) ratio. Typical DMTJ structures were Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO x /free layer 10/AlO x /CoFe 7/IrMn 10/Ru 60 (in nanometers). The interlayer coupling field and the normalized TMR ratios at the applied voltages of +0.4 and -0.4 V of the amorphous CoFeSiB free-layer DMTJ offer lower and higher values than that of the polycrystalline CoFe free-layer DMTJ, respectively. An amorphous ferromagnetic CoFeSiB layer improves the interface roughness of the free layer/tunnel barrier and, as a result, the interlayer coupling field and bias voltage dependence of the TMR ratio are suppressed at a given voltage. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. 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.

  2. Phonon superradiance and phonon laser effect in nanomagnets.

    Science.gov (United States)

    Chudnovsky, E M; Garanin, D A

    2004-12-17

    We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.

  3. Superconducting tunnel junctions on MgB{sub 2} using MgO and CaF{sub 2} as a barrier

    Energy Technology Data Exchange (ETDEWEB)

    Sakoda, Masahito, E-mail: sakoda@cc.tuat.ac.jp [Department of Applied Physics, Tokyo University of Agriculture and Technology, 2-24-16, Koganei, Tokyo 184-8588 (Japan); Aibara, Masato; Mede, Kazuya; Kikuchi, Motoyuki; Naito, Michio [Department of Applied Physics, Tokyo University of Agriculture and Technology, 2-24-16, Koganei, Tokyo 184-8588 (Japan)

    2016-11-15

    Highlights: • We have revised the manuscript according to reviewer's comments. The details are in “Response to Reviewers”. • Superconducting junctions with MgO and CaF{sub 2} barrier were fabricated in order to improve the quality of junctions. • In SIN junctions with MgO barrier, clear superconducting gap was observed. (). • In SIS junctions with CaF2 barrier, Josephson current was observed over 30 K. (). • The compatibility of each barrier material at the upper and lower interfaces was clarified. (). - Abstract: We report the fabrication of superconducting tunnel junctions, both of superconductor–insulator-normal metal (SIN) and superconductor–insulator-superconductor (SIS), on MgB{sub 2} using MgO and CaF{sub 2} as a barrier. The SIN junctions fabricated using an MgO barrier showed excellent quasi-particle characteristics, including a large superconducting gap (Δ) of 2.5–3 meV and a low zero-bias conductance. We have also fabricated SIS junctions with an MgO barrier, but the quasi-particle characteristics of the SIS junctions are not as good as those of the SIN junctions, namely a reduced superconducting gap and a high zero-bias conductance. It appears that top MgB{sub 2} electrodes do not grow well on an MgO barrier, which is also suggested from in-situ RHEED observation. The SIN junctions fabricated using a CaF{sub 2} barrier showed less sharp quasi-particle characteristics than using an MgO barrier. However, the SIS junctions using a CaF{sub 2} barrier showed a fairly large I{sub c}R{sub N} value at 4.2 K over 1 mV and also exhibited finite Josephson current up to almost the film's T{sub c} (∼30 K). The RHEED observation revealed that top MgB{sub 2} electrodes grow well on a CaF{sub 2} barrier.

  4. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Xing, Huili; Jena, Debdeep, E-mail: djena@cornell.edu [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States)

    2015-10-19

    By the insertion of thin In{sub x}Ga{sub 1−x}N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors.

  5. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    International Nuclear Information System (INIS)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick; Xing, Huili; Jena, Debdeep

    2015-01-01

    By the insertion of thin In x Ga 1−x N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors

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

    International Nuclear Information System (INIS)

    Guo, Peng; Feng, Jiafeng; Wei, Hongxiang; Han, Xiufeng; Fang, Bin; Zhang, Baoshun; Zeng, Zhongming

    2015-01-01

    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

  7. Improved impedance transformation between microwave oscillator and Josephson junction series array

    International Nuclear Information System (INIS)

    Gutmann, P.; Vollmer, E.; Niemeyer, J.

    1993-01-01

    Superconducting microwave monolithic integrated circuits (S-MMIC), based on Josephson tunnel junctions, are a well-established tool to reproduce the volt at the highest level of accuracy. An external oscillator of a fixed frequency f supplies microwave energy through a waveguide to the S-MMIC. The wave changes its mode at a waveguide-antipodal finline-stripline taper before entering a series array stripline of up to 30 000 Josephson tunnel junctions and is dissipated as heat in a lossy stripline. Both striplines have a characteristic impedance Z of 2 to 5 Ω. An equivalent circuit is shown in figure 1. The oscillator is matched to the waveguide with a source resistance R G Z(waveguide) ∼ 550 Ω. The most critical part is the taper, which should work as a lossless impedance matching network at the frequency of the oscillator. Microwave energy is fed into the tunnel junctions by the surface current I HF of the travelling wave in the series array stripline producing an rf voltage amplitude U JHF across the capacitance C of each junction. The Josephson tunnel junctions work as self-oscillating parametric mixers producing steps of constant voltage V in the current-voltage characteristic whenever (nf - 2eV/h) = 0, with n denoting an integer and e and h denoting the elementary charge and Planck's constant, respectively. The equivalent circuit of a Josephson tunnel element used in a voltage standard for 1 V working at a frequency of f = 70 GHz is given by a lumped parallel resonant circuit with a nonlinear inductance on the order of L = φ 0 /2πI 0 ∼ 1 pH, flux quantum φ 0 = h/2e and a linear capacitance of C ∼ 40 pF. These tunnel junctions have a maximum zero voltage current of approximately I 0 ∼ 350 μA. (orig.)

  8. Investigating spin-transfer torques induced by thermal gradients in magnetic tunnel junctions by using micro-cavity ferromagnetic resonance

    Science.gov (United States)

    Cansever, H.; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.

    2018-06-01

    Similar to electrical currents flowing through magnetic multilayers, thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin-currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics in the free layer. In this study, we describe a novel experimental approach to observe spin-transfer torques induced by thermal gradients in magnetic multilayers by studying their ferromagnetic resonance response in microwave cavities. Utilizing this approach allows for measuring the magnetization dynamics on micron/nano-sized samples in open-circuit conditions, i.e. without the need of electrical contacts. We performed first experiments on magnetic tunnel junctions patterned into 6  ×  9 µm2 ellipses from Co2FeAl/MgO/CoFeB stacks. We conducted microresonator ferromagnetic resonance (FMR) under focused laser illumination to induce thermal gradients in the layer stack and compared them to measurements in which the sample was globally heated from the backside of the substrate. Moreover, we carried out broadband FMR measurements under global heating conditions on the same extended films the microstructures were later on prepared from. The results clearly demonstrate the effect of thermal spin-torque on the FMR response and thus show that the microresonator approach is well suited to investigate thermal spin-transfer-driven processes for small temperatures gradients, far below the gradients required for magnetic switching.

  9. Demonstration of forward inter-band tunneling in GaN by polarization engineering

    International Nuclear Information System (INIS)

    Krishnamoorthy, Sriram; Park, Pil Sung; Rajan, Siddharth

    2011-01-01

    We report on the design, fabrication, and characterization of GaN interband tunnel junction showing forward tunneling characteristics. We have achieved very high forward tunneling currents (153 mA/cm 2 at 10 mV, and 17.7 A/cm 2 peak current) in polarization-engineered GaN/InGaN/GaN heterojunction diodes grown by plasma assisted molecular beam epitaxy. We also report the observation of repeatable negative differential resistance in interband III-Nitride tunnel junctions, with peak-valley current ratio of 4 at room temperature. The forward current density achieved in this work meets the typical current drive requirements of a multi-junction solar cell.

  10. Nonlocal vibration of Y-shaped CNT conveying nano-magnetic viscous fluid under magnetic field

    Directory of Open Access Journals (Sweden)

    A. Ghorbanpour Arani

    2015-06-01

    Full Text Available This study deals with the vibration and stability analysis of a Y-shaped single-walled carbon nanotube (SWCNT embedded in visco-Pasternak foundation and conveying nano-magnetic viscous fluid (NMF based on nonlocal elasticity theory and Euler–Bernoulli beam model. The fluid is two-phases due to the existence of magnetic nanoparticles which its volume fraction is much little in comparison with the base fluid where the influence of 2D magnetic field is taken into account. Also, Knudsen number is used to correct the velocity profile of fluid. The Galerkin method is applied to solve the equation of motion which is obtained by employing Hamilton’s principle. The detail parametric study is conducted, focusing on the combined effects of carbon nanotube and Y-shaped junction fitted at the downstream end, fluid velocity, Knudsen number and elastic medium. The results indicate that increasing the angle between centerline of the CNT and the downstream elbows decreases stability of system.

  11. Analog Approach to Constraint Satisfaction Enabled by Spin Orbit Torque Magnetic Tunnel Junctions.

    Science.gov (United States)

    Wijesinghe, Parami; Liyanagedera, Chamika; Roy, Kaushik

    2018-05-02

    Boolean satisfiability (k-SAT) is an NP-complete (k ≥ 3) problem that constitute one of the hardest classes of constraint satisfaction problems. In this work, we provide a proof of concept hardware based analog k-SAT solver, that is built using Magnetic Tunnel Junctions (MTJs). The inherent physics of MTJs, enhanced by device level modifications, is harnessed here to emulate the intricate dynamics of an analog satisfiability (SAT) solver. In the presence of thermal noise, the MTJ based system can successfully solve Boolean satisfiability problems. Most importantly, our results exhibit that, the proposed MTJ based hardware SAT solver is capable of finding a solution to a significant fraction (at least 85%) of hard 3-SAT problems, within a time that has a polynomial relationship with the number of variables(<50).

  12. Differential conductance measurements of low-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Nishioka, S.; Hamada, Y.V.; Matsumoto, R.; Mizuguchi, M.; Shiraishi, M.; Fukushima, A.; Kubota, H.; Nagahama, T.; Yuasa, S.; Maehara, H.; Nagamine, Y.; Tsunekawa, K.; Djayaprawira, D.D.; Watanabe, N.; Suzuki, Y.

    2007-01-01

    We measured differential conductance spectra of magnetic tunnel junctions (MTJs) with thin MgO barrier and low-resistance area product. The spectra of MTJs with MgO barrier thicker than 1.05 nm were essentially the same except for slight decrease of contributions from low-energy excitations, such as magnons. The spectra of MTJ with 1.01 nm MgO barrier were thoroughly different from the MTJs with thicker barrier. The result reveals that an MTJ with very thin MgO barrier thickness has different conduction characteristics from those with thicker MgO barriers

  13. 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.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  15. Systematic study on the tunneling conductance in a normal-metal/px+y ± ipy-x-wave superconductor junction

    International Nuclear Information System (INIS)

    Jin Biao; Zhang Yinhan; Cheng Qiang

    2010-01-01

    The chiral p x+y ± ip y-x -wave state is currently considered to be a promising candidate state for Sr 2 RuO 4 in the light of microscopic theories. We theoretically investigate the tunneling conductance in a normal-metal/p x+y ± ip y-x -wave superconductor junction over a wide range of temperature and barrier strength. For a cylindrical Fermi surface with the magnitude of the radius R, the p x+y ± ip y-x -wave gap function exhibits two typical types of nodal structures when R = 1.0 and R=1/√2, respectively. It is found, in particular, that the line shapes of the conductance spectra for R∼1/√2 cases can qualitatively account for the existing in-plane tunneling experiments on Sr 2 RuO 4 .

  16. On the discrimination between nucleation and propagation in nanomagnetic logic devices

    Science.gov (United States)

    Ziemys, Grazvydas; Csaba, Gyorgy; Becherer, Markus

    2018-05-01

    In this paper we present the extensive nucleation and propagation characterization of fabricated nanomagnets by applying ns-range magnetic field pulses. For that, an artificial nucleation center (ANC) is created by focused ion beam irradiation (FIB) of a 50 x 50 nm area at the side of a Co/Pt island as typically used in Nanomagnetic Logic with perpendicular anisotropy (pNML). Laser-Kerr Microscope is applied for statistical evaluation of the switching probability of the whole magnet, while the wide-field-Kerr microscopy is employed to discriminate between the nucleation process (which takes place at the irradiated ANC area) and the domain wall propagation process along the magnet. We show that the nanomagnet can be treated as a single Stoner-Wolfhart particle above 100 ns field-pulse width, as the whole magnetization is switched during the field-pulse. By contrary, for field-pulse width below 100 ns, the domain wall (DW) motion is the limiting process hindering full magnetization reversal on that time-scale. However, the nucleation still follows the Arrhenius law. The results allow precise understanding of the reversal process and highlight the need for faster DW speed in pNML materials.

  17. On the discrimination between nucleation and propagation in nanomagnetic logic devices

    Directory of Open Access Journals (Sweden)

    Grazvydas Ziemys

    2018-05-01

    Full Text Available In this paper we present the extensive nucleation and propagation characterization of fabricated nanomagnets by applying ns-range magnetic field pulses. For that, an artificial nucleation center (ANC is created by focused ion beam irradiation (FIB of a 50 x 50 nm area at the side of a Co/Pt island as typically used in Nanomagnetic Logic with perpendicular anisotropy (pNML. Laser-Kerr Microscope is applied for statistical evaluation of the switching probability of the whole magnet, while the wide-field-Kerr microscopy is employed to discriminate between the nucleation process (which takes place at the irradiated ANC area and the domain wall propagation process along the magnet. We show that the nanomagnet can be treated as a single Stoner-Wolfhart particle above 100 ns field-pulse width, as the whole magnetization is switched during the field-pulse. By contrary, for field-pulse width below 100 ns, the domain wall (DW motion is the limiting process hindering full magnetization reversal on that time-scale. However, the nucleation still follows the Arrhenius law. The results allow precise understanding of the reversal process and highlight the need for faster DW speed in pNML materials.

  18. Effect of the subgap conductance on the metastable states in a Josephson tunnel junction

    International Nuclear Information System (INIS)

    Cristiano, R.; Pagano, S.; Silvestrini, P.; Gray, K.E.; Liengme, O.

    1987-09-01

    An investigation of the decay rate of metastable states in Josephson tunnel junctions in presence of thermal noise is presented. We have observed that, in the extremely underdamped regime, there is an exponential temperature dependence of the best fit value for the shunt conductance. Such a dependence shows a close relation with the temperature dependence of the subgap conductance, suggesting that the effective conductance for the escape from the metastable states obeys to a quasi-particle thermal activation mechanism. The introduction of this effective conductance into the lifetime expression for the zero-voltage states leads to significant changes in the width of the switching current distributions. A comparisons of the experimental data with the proposed model is reported. 7 refs., 2 figs

  19. Visualizing supercurrents in 0-{pi} ferromagnetic Josephson tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Goldobin, Edward; Guerlich, Christian; Gaber, Tobias; Koelle, Dieter; Kleiner, Reinhold [Physikalisches Institut and Center for Collective Quantum Phenomena, Universitaet Tuebingen (Germany); Weides, Martin; Kohlstedt, Hermann [Institute of Solid State Physics, Reserch Center Juelich (Germany)

    2009-07-01

    So-called 0 and {pi} Josephson junctions can be treated as having positive and negative critical currents. This implies that the same phase shift applied to a Josephson junction causes counterflow of supercurrents in 0 and in {pi} junctions connected in parallel provided they are short in comparison with Josephson penetration depth {lambda}{sub J}. We have fabricated several 0, {pi}, 0-{pi}, 0-{pi}-0 and 20 x (0-{pi}-) planar superconductor-insulator-ferromagnet-superconductor Josephson junctions and studied the spatial supercurrent density distribution j{sub s}(x,y) across the junction area using low temperature scanning electron microscopy. At zero magnetic field we clearly see counterflow of the supercurrents in 0 and {pi} regions. The picture also changes consistently in the applied magnetic field.

  20. Eight-logic memory cell based on multiferroic junctions

    International Nuclear Information System (INIS)

    Yang Feng; Zhou, Y C; Tang, M H; Liu Fen; Ma Ying; Zheng, X J; Zhao, W F; Xu, H Y; Sun, Z H

    2009-01-01

    A model is proposed for a device combining a multiferroic tunnel junction with a magnetoelectric (ME) film in which the magnetic configuration is controlled by the electric field. Calculations embodying the Green's function approach show that the magnetic polarization can be switched on and off by an electric field in the ME film due to the effect of elastic coupling interaction. Using a model including the spin-filter effect and screening of polarization charges, we have produced eight logic states of tunnelling resistance in the tunnel junction and have obtained corresponding laws that control them. The results provide some insights into the realization of an eight-logic memory cell. (fast track communication)