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Sample records for multi-quantum state magnetic

  1. Quantum transport through a multi-quantum-dot-pair chain side-coupled with Majorana bound states

    NASA Astrophysics Data System (ADS)

    Zhao-Tan, Jiang; Cheng-Cheng, Zhong

    2016-06-01

    We investigate the quantum transport properties through a special kind of quantum dot (QD) system composed of a serially coupled multi-QD-pair (multi-QDP) chain and side-coupled Majorana bound states (MBSs) by using the Green functions method, where the conductance can be classified into two kinds: the electron tunneling (ET) conductance and the Andreev reflection (AR) one. First we find that for the nonzero MBS-QDP coupling a sharp AR-induced zero-bias conductance peak with the height of e 2/h is present (or absent) when the MBS is coupled to the far left (or the other) QDP. Moreover, the MBS-QDP coupling can suppress the ET conductance and strengthen the AR one, and further split into two sub-peaks each of the total conductance peaks of the isolated multi-QDPs, indicating that the MBS will make obvious influences on the competition between the ET and AR processes. Then we find that the tunneling rate Γ L is able to affect the conductances of leads L and R in different ways, demonstrating that there exists a Γ L-related competition between the AR and ET processes. Finally we consider the effect of the inter-MBS coupling on the conductances of the multi-QDP chains and it is shown that the inter-MBS coupling will split the zero-bias conductance peak with the height of e 2/h into two sub-peaks. As the inter-MBS coupling becomes stronger, the two sub-peaks are pushed away from each other and simultaneously become lower, which is opposite to that of the single QDP chain where the two sub-peaks with the height of about e 2/2h become higher. Also, the decay of the conductance sub-peaks with the increase of the MBS-QDP coupling becomes slower as the number of the QDPs becomes larger. This research should be an important extension in studying the transport properties in the kind of QD systems coupled with the side MBSs, which is helpful for understanding the nature of the MBSs, as well as the MBS-related QD transport properties. Project supported by the National Natural

  2. GaAs/InAs Multi Quantum Well Solar Cell

    DTIC Science & Technology

    2012-12-01

    4. TITLE AND SUBTITLE GaAs /InAs MULTI QUANTUM WELL SOLAR CELL 5. FUNDING NUMBERS 6. AUTHOR(S) Evangelos Koletsios 7. PERFORMING ORGANIZATION NAME... GaAs /InAs MULTI QUANTUM WELL SOLAR CELL Evangelos Koletsios Lieutenant, Hellenic Navy B.S., Hellenic Naval Academy, 2001 Submitted in...similar, such as a GaAs crystal, which is mainly used in solar cells and it is described as a direct bandgap semiconductor. On the other hand, for

  3. Multi-quantum-well electroabsorption modulators

    NASA Astrophysics Data System (ADS)

    Piprek, Joachim; Chiu, Yijen; Bowers, John E.

    2002-06-01

    Electroabsorption modulators (EAMs) based on the quantum confined Stark effect have advantages in applications that require high speed, low drive voltage, and high extinction ratio. They are promising devices for external signal modulation in high-bandwidth optical communication systems. EAMs can be integrated with other devices like laser diodes, semiconductor optical amplifiers, and mode transformers. We have previously fabricated InGaAsP/InP multi-quantum well EAMs with a bandwidth of 25 GHz and a drive voltage of 1.2 V and 20 dB extinction ratio. Further optimization of our devices requires a detailed analysis of internal physical processes and their interaction. In this paper, we employ a two-dimensional electro-optic device model to analyze our EAMs. The model self-consistently combines kp bandstructure and absorption calculations with a carrier drift-diffusion model and optical waveguiding. The required low polarization sensitivity of EAMs leads to strong valence band mixing so that usual effective mass models cannot be applied. Optical transmission characteristics are calculated which are in good agreement with measurements. Modulation efficiency and linearity are analyzed in detail. Optimum operation voltages are identified.

  4. Energy band design for p-type tensile strained Si/SiGe multi-quantum well infrared photodetector

    NASA Astrophysics Data System (ADS)

    Li, Jin-tao; Chen, Song-yan; Qi, Dong-feng; Huang, Wei; Li, Cheng; Lai, Hong-kai

    2011-05-01

    The band structure of the confined states is calculated for Si/SiGe multi-quantum well infrared photodetector (M-QWIP). The influence of the Ge component in pseudosubstrate on the energy band structure of Si/Si{in0.54}Ge{in0.46} multi-quantum wells (MQWs) is investigated. It is found that the high energy levels in the MQWs move up while the low energy levels move down as the Ge component in pseudosubstrate increases. The influence of the barrier width on the energy band structure of MQWs is also studied based on the 6 × 6 k·p method. The results show that the Si barrier between 5 nm and 10 nm is optimized to enhance the intersubband absorption in the MQWs.

  5. Intersubband optical transients in multi-quantum-well structures

    NASA Astrophysics Data System (ADS)

    Luc, F.; Rosencher, E.; Bois, Ph.

    1993-05-01

    We show that optical transients due to the intersubband photoionization of the electrons from quantum wells may be observed by inserting a multi-quantum-well structure in the space-charge layer of a Schottky diode. This method provides a direct measurement of the photoionization cross section of a quantum well. The escape probability of the photoexcited electron from the quantum well can thus be unambiguously deduced. Its variation with the electric field may be described by a simple model based on the statistical fluctuation of the quantum-well width.

  6. Ferroelectric tunnel junctions with multi-quantum well structures

    SciTech Connect

    Ma, Zhijun; Zhang, Tianjin; Liang, Kun; Qi, Yajun; Wang, Duofa; Wang, Jinzhao; Jiang, Juan

    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.

  7. Dynamic control of spin states in interacting magnetic elements

    DOEpatents

    Jain, Shikha; Novosad, Valentyn

    2014-10-07

    A method for the control of the magnetic states of interacting magnetic elements comprising providing a magnetic structure with a plurality of interacting magnetic elements. The magnetic structure comprises a plurality of magnetic states based on the state of each interacting magnetic element. The desired magnetic state of the magnetic structure is determined. The active resonance frequency and amplitude curve of the desired magnetic state is determined. Each magnetic element of the magnetic structure is then subjected to an alternating magnetic field or electrical current having a frequency and amplitude below the active resonance frequency and amplitude curve of said desired magnetic state and above the active resonance frequency and amplitude curve of the current state of the magnetic structure until the magnetic state of the magnetic structure is at the desired magnetic state.

  8. Steady-state permanent magnet MPD thruster

    SciTech Connect

    Arakawa, Y.; Sasoh, A.

    1987-01-01

    A steady-state MPD arc thruster with permanent magnets has been made. The effect of the permanent magnets on thruster performance and the plasma acceleration mechanism was examined through measurements of thrust, chamber pressure, current densities, and plasma properties in the exhaust plume. Experimental results show that the use of the permanent magnets is desirable in steady-state MPD thrusters of the greater than 10 kW power range. 7 references.

  9. Magnetic bearings - State of the art

    NASA Astrophysics Data System (ADS)

    Fleming, David P.

    Magnetic bearings have existed for many years, at least in theory. Earnshaw's theorem, formulated in 1842, concerns stability of magnetic suspensions, and states that not all axes of a bearing can be stable without some means of active control. In Beam's widely referenced experiments, a tiny (1/64 in diameter) rotor was rotated to the astonishing speed of 800,000 rps while it was suspended in a magnetic field. Despite a long history, magnetic bearings have only begun to see practical application since about 1980. The development that finally made magnetic bearings practical was solid state electronics, enabling power supplies and controls to be reduced in size to where they are now comparable in volume to the bearings themselves. An attempt is made to document the current (1991) state of the art of magnetic bearings. The referenced papers are large drawn from two conferences publications published in 1988 and 1990 respectively.

  10. Magnetic bearings-state of the art

    NASA Technical Reports Server (NTRS)

    Fleming, David P.

    1991-01-01

    Magnetic bearings have existed for many years, at least in theory. Earnshaw's theorem, formulated in 1842, concerns stability of magnetic suspensions, and states that not all axes of a bearing can be stable without some means of active control. In Beam's widely referenced experiments, a tiny (1/64 in diameter) rotor was rotated to the astonishing speed of 800,000 rps while it was suspended in a magnetic field. Despite a long history, magnetic bearings have only begun to see practical application since about 1980. The development that finally made magnetic bearings practical was solid state electronics, enabling power supplies and controls to be reduced in size to where they are now comparable in volume to the bearings themselves. An attempt is made to document the current (1991) state of the art of magnetic bearings. The referenced papers are large drawn from two conferences publications published in 1988 and 1990 respectively.

  11. Magnetic bearings - State of the art

    NASA Technical Reports Server (NTRS)

    Fleming, David P.

    1993-01-01

    Magnetic bearings have existed for many years, at least in theory. Earnshaw's theorem, formulated in 1842, concerns stability of magnetic suspensions, and states that not all axes of a bearing can be stable without some means of active control. In Beam's widely referenced experiments, a tiny (1/64 in diameter) rotor was rotated to the astonishing speed of 800,000 rps while it was suspended in a magnetic field. Despite a long history, magnetic bearings have only begun to see practical application since about 1980. The development that finally made magnetic bearings practical was solid state electronics, enabling power supplies and controls to be reduced in size to where they are now comparable in volume to the bearings themselves. An attempt is made to document the current (1991) state of the art of magnetic bearings. The referenced papers are large drawn from two conferences publications published in 1988 and 1990 respectively.

  12. Study of dysprosium in different magnetic states

    SciTech Connect

    Lakhani, Archana Baidya, Arunmay; Jena, Rudra Parasad

    2016-05-23

    A magnetotrasnport and magnetization study has been performed in order to probe the changes in the magnetic states of the rare earth element Dysprosium. Primarily there are three magnetic states present in this element in different temperature regions; one changing at Neel temperature (T{sub N} ~ 180 K) via second order phase transition and another at Curie temperature (T{sub C} ~ 90 K) via first order magnetic phase transition (FOMT). These two transitions merge at the magnetic field above 1.5 T. The first derivative of resistivity indicates the possibility of spin fluctuation above first order phase transition in the spiral antiferromagnetic phase. The magnetoresistance up to 8 T reveals distinct features in the para, antiferromagnetic spiral and ferromagnetic regions.

  13. Evidence for formation of multi-quantum dots in hydrogenated graphene

    PubMed Central

    2012-01-01

    We report the experimental evidence for the formation of multi-quantum dots in a hydrogenated single-layer graphene flake. The existence of multi-quantum dots is supported by the low-temperature measurements on a field effect transistor structure device. The resulting Coulomb blockade diamonds shown in the color scale plot together with the number of Coulomb peaks exhibit the characteristics of the so-called ‘stochastic Coulomb blockade’. A possible explanation for the formation of the multi-quantum dots, which is not observed in pristine graphene to date, was attributed to the impurities and defects unintentionally decorated on a single-layer graphene flake which was not treated with the thermal annealing process. Graphene multi-quantum dots developed around impurities and defect sites during the hydrogen plasma exposure process. PMID:22898058

  14. Static spin susceptibility in magnetically ordered states

    NASA Astrophysics Data System (ADS)

    Kuboki, Kazuhiro; Yamase, Hiroyuki

    2017-08-01

    We report that special care is needed when longitudinal magnetic susceptibility is computed in a magnetically ordered phase, especially in metals. We demonstrate this by studying static susceptibility in both a ferromagnetic and an antiferromagnetic state in the random phase approximation to the two-dimensional Hubbard model on a square lattice. In contrast to the case in the disordered phase, a first derivative of the chemical potential (or the density) with respect to a magnetic field does not vanish in a magnetically ordered phase when the field is applied parallel to the magnetic moment. This effect is crucial and should be included when computing magnetic susceptibility in the ordered phase, otherwise an unphysical result would be obtained. In addition, consequently the magnetic susceptibility becomes different when computed at a fixed density and a fixed chemical potential in the ordered phase. In particular, we cannot employ magnetic susceptibility at a fixed chemical potential to describe a system with a fixed density even if the chemical potential is tuned to reproduce the correct density.

  15. Instability of Homogeneous State in Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Sinkkonen, J.; Kuivalainen, P.; Stubb, T.

    1982-06-01

    The instability of the homogeneous state in a ferromagnetic semiconductor is studied. The electronic part of the free energy is determined using Thomas-Fermi statistical model and the magnetic part is calculated by the molecular field approximation including the RKKY-interaction. The inhomogeneity consists of a small magnetically polarized region with a high electron density surrounded by a less polarized positively charged depletion layer. The inhomogeneous state is found to be stable in a relatively broad temperature range around the Curie temperature at low and intermediate doping densities. The stability range shrinks in an applied magnetic field. At fields exceeding about 3 T or at doping densities larger than 1021 cm-3 the inhomogeneous state is no more stable.

  16. Quantum Well States in Magnetic Nanostructures

    NASA Astrophysics Data System (ADS)

    Qiu, Z. Q.

    2000-03-01

    Quantum Well (QW) states in magnetic nanostructures play an important role in many phenomena such as the oscillatory interlayer coupling in giant magnetoresistance (GMR) multilayers. Photoemission provides the most direct measurement of QW states in k-space. In this talk, I will report our recent results on QW states obtained at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory. The high brightness and fine spot size of photon beam at beamline 7 of ALS allow the performance of photoemission experiment on double wedged samples. First, the nature of QW states in metallic thin films will be discussed. Using one monolayer Ni as a probe, we show that the amplitude of the QW wavefunction is described by an envelope function. Second, quantum interference between two QWs will be discussed. Finally, we demonstrate the interconnection between the QW states and the oscillatory interlayer coupling in magnetic multilayers.

  17. Magnetic ground state of FeSe

    PubMed Central

    Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K.; Iida, K.; Christianson, A. D.; Walker, H. C.; Adroja, D. T.; Abdel-Hafiez, M.; Chen, Xiaojia; Chareev, D. A.; Vasiliev, A. N.; Zhao, Jun

    2016-01-01

    Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986

  18. Magnetic ground state of FeSe.

    PubMed

    Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K; Iida, K; Christianson, A D; Walker, H C; Adroja, D T; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Zhao, Jun

    2016-07-19

    Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities.

  19. Magnetic Moments of States in 110Sn.

    NASA Astrophysics Data System (ADS)

    Kumbartzki, G. J.

    2016-06-01

    The semi-magic Sn isotopes with Z = 50 are the subject of extensive experimental and theoretical studies. The measured B(E2) values to the 21 + states for the neutron-deficient side of the isotope chain suggest enhanced collectivity when fewer particles are available if the proton shell is not broken. Magnetic moments which are sensitive to proton and neutron contributions to the wave functions of the states could provide critical and relevant information. Magnetic moments were previously measured only for the even stable and a few neutron-rich unstable Sn isotopes. A measurement of the g factors of excited states in 110Sn using the transient field technique was performed at the 88-Inch Cyclotron at the LBNL in Berkeley. The 110Sn nuclei were produced via an α-particle transfer to 106Cd.

  20. Bound states in a strong magnetic field

    SciTech Connect

    Machado, C. S.; Navarra, F. S.; Noronha, J.; Oliveira, E. G.; Ferreira Filho, L. G.

    2013-03-25

    We expect a strong magnetic field to be produced in the perpendicular direction to the reaction plane, in a noncentral heavy-ion collision . The strength of the magnetic field is estimated to be eB{approx}m{sup 2}{sub {pi}}{approx} 0.02 GeV{sup 2} at the RHIC and eB{approx} 15m{sup 2}{sub {pi}}{approx} 0.3 GeV{sup 2} at the LHC. We investigate the effects of the magnetic field on B{sup 0} and D{sup 0} mesons, focusing on the changes of the energy levels and of the mass of the bound states.

  1. Four states magnetic dots: a design selection by micromagnetic modeling

    NASA Astrophysics Data System (ADS)

    Louis, D.; Hauet, T.; Petit-Watelot, S.; Lacour, D.; Hehn, M.; Montaigne, F.

    2016-10-01

    In a context where sub-micrometric magnetic dots are foreseen to play an active role in various new breeds of electronics components such as magnetic memories, magnetic logics or bio-sensors, the use of micromagnetic simulations to optimize their shapes and spatial arrangement with respect to a chosen application has become unavoidable. Prior realizing experimentally magnetic dots presenting four stable magnetic states (4SMS), we performed a micromagnetic study to select a design providing not only four equivalent magnetic states in a single dot but also exhibiting mostly uniform magnetic states.

  2. Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

    SciTech Connect

    Mohanta, Antaryami; Wang, Shiang-Fu; Jang, Der-Jun; Young, Tai-Fa; Yeh, Ping-Hung; Ling, Dah-Chin; Lee, Meng-En

    2015-04-14

    Green emitting InGaN/GaN multi-quantum well samples were investigated using transmission electron microscopy, photoluminescence (PL), and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ∼12 meV due to an inhomogeneous distribution of In in the InGaN quantum (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τ{sub r}, extracted from the TRPL profile shows ∼T{sup 3/2} dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.

  3. Terahertz absorbing AlGaN/GaN multi-quantum-wells: Demonstration of a robust 4-layer design

    NASA Astrophysics Data System (ADS)

    Beeler, M.; Bougerol, C.; Bellet-Amalric, E.; Monroy, E.

    2013-08-01

    We report on AlGaN/GaN multi-quantum-well structures displaying intersubband absorption in the THz spectral range. First, we theoretically analyze the weaknesses of the state-of-the-art GaN-based step-quantum-well architecture from an optoelectronic standpoint. We then propose a modified geometry with improved structural robustness considering the uncertainties associated to the growth. This later structure, consisting of 4-layer quantum wells, has been grown by plasma-assisted molecular-beam epitaxy and characterized structurally and optically. Low temperature absorption of samples with different Si doping levels confirms intersubband transitions in the far-infrared, centred at 28 μm.

  4. Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

    NASA Astrophysics Data System (ADS)

    Chao, Wen-Ching; Mohanta, Antaryami; Yen, Tsu-Chiang; Chen, Wei-Sheng; Jang, Der-Jun

    Green emitting InGaN/GaN multi-quantum well samples were investigated using photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ~12 meV due to an inhomogeneous distribution of In in the InGaN quantum well (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum (FWHM) of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τr, extracted from the TRPL profile shows ~T 3 / 2 dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.

  5. Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

    NASA Astrophysics Data System (ADS)

    Mohanta, Antaryami; Wang, Shiang-Fu; Young, Tai-Fa; Yeh, Ping-Hung; Ling, Dah-Chin; Lee, Meng-En; Jang, Der-Jun

    2015-04-01

    Green emitting InGaN/GaN multi-quantum well samples were investigated using transmission electron microscopy, photoluminescence (PL), and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ˜12 meV due to an inhomogeneous distribution of In in the InGaN quantum (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τr, extracted from the TRPL profile shows ˜T3/2 dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.

  6. Magnetic states in multiply-connected flat nanoelements

    NASA Astrophysics Data System (ADS)

    Bogatyrev, Andrei B.; Metlov, Konstantin L.

    2015-10-01

    Flat magnetic nanoelements are an essential component of current and future spintronic devices. By shaping an element it is possible to select and stabilize chosen metastable magnetic states, control its magnetization dynamics. Here, using a recent significant development in mathematics of conformal mapping, complex variable based approach to the description of magnetic states in planar nanoelements is extended to the case when elements are multiply-connected (that is, contain holes or magnetic antidots). We show that presence of holes implies a certain restriction on the set of magnetic states of nanoelement.

  7. Magnetic Cluster States in Nanostructured Materials

    SciTech Connect

    Diandra Leslie-Pelecky

    2008-06-13

    The goal of this work is to fabricate model nanomaterials with different types of disorder and use atomic-scale characterization and macroscopic magnetization measurements to understand better how specific types of disorder affects macroscopic magnetic behavior. This information can be used to produce magnetic nanomaterials with specific properties for applications such as permanent magnets, soft magnetic material for motors and biomedical applications.

  8. Equilibrium magnetic states in individual hemispherical permalloy caps

    SciTech Connect

    Streubel, Robert; Schmidt, Oliver G.; Kravchuk, Volodymyr P.; Gaididei, Yuri; Sheka, Denis D.; Makarov, Denys; Kronast, Florian

    2012-09-24

    The magnetization distributions in individual soft magnetic permalloy caps on non-magnetic spherical particles with sizes ranging from 50 to 800 nm are investigated. We experimentally visualize the magnetic structures at the resolution limit of the x-ray magnetic circular dichroism photoelectron emission microscopy (XMCD-PEEM). By analyzing the so-called tail contrast in XMCD-PEEM, the spatial resolution is significantly enhanced, which allowed us to explore magnetic vortices and their displacement on curved surfaces. Furthermore, cap nanostructures are modeled as extruded hemispheres to determine theoretically the phase diagram of equilibrium magnetic states. The calculated phase diagram agrees well with the experimental observations.

  9. Tunable magnetic states in hexagonal boron nitride sheets

    NASA Astrophysics Data System (ADS)

    Machado-Charry, Eduardo; Boulanger, Paul; Genovese, Luigi; Mousseau, Normand; Pochet, Pascal

    2012-09-01

    Magnetism in two dimensional atomic sheets has attracted considerable interest as its existence could allow the development of electronic and spintronic devices. The existence of magnetism is not sufficient for devices, however, as states must be addressable and modifiable through the application of an external drive. We show that defects in hexagonal boron nitride present a strong interplay between the N-N distance in the edge and the magnetic moments of the defects. By stress-induced geometry modifications, we change the ground state magnetic moment of the defects. This control is made possible by the triangular shape of the defects as well as the strong spin localisation in the magnetic state.

  10. Vibrating sample magnetometer 2D and 3D magnetization effects associated with different initial magnetization states

    NASA Astrophysics Data System (ADS)

    Lukins, Ronald E.

    2017-05-01

    Differences in VSM magnetization vector rotation associated with various initial magnetization states were demonstrated. Procedures and criteria were developed to select sample orientation and initial magnetization states to allow for the combination of two different 2D measurements runs (with the same field profiles) to generate a dataset that can be representative of actual 3D magnetization rotation. Nickel, cast iron, and low moment magnetic tape media were used to demonstrate these effects using hysteresis and remanent magnetization test sequences. These results can be used to generate 2D and 3D magnetic properties to better characterize magnetic phenomena which are inherently three dimensional. Example applications are magnetic tape-head orientation sensitivity, reinterpretation of 3D coercivity and other standard magnetic properties, and multi-dimensional shielding effectiveness.

  11. Current density and state density in diluted magnetic semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Pérez Merchancano, S. T.; Paredes Gutiérrez, H.; Zuñiga, J. A.

    2016-02-01

    We study in this paper the spin-polarized current density components in diluted magnetic semiconductor tunnelling diodes with different sample geometries. We calculate the resonant JxV and the density of states. The differential conductance curves are analyzed as functions of the applied voltage and the magnetic potential strength induced by the magnetic ions.

  12. Smell sensing and visualizing based on multi-quantum wells spatial light modulator

    NASA Astrophysics Data System (ADS)

    Tian, Fengchun; Zhao, Zhenzhen; Jia, Pengfei; Liao, Hailin; Chen, Danyu; Liu, Shouqiong

    2014-09-01

    For the existing drawbacks of traditional detecting methods which use gratings or prisms to detect light intensity distribution at each wavelength of polychromatic light, a novel method based on multi-quantum wells spatial light modulator (MQWs-SLM) has been proposed in this paper. In the proposed method, MQWs-SLM serves as a distribution features detector of the signal light. It is on the basis of quantum-confine Stark effect (QCSE) that the vertical applied voltage can change the absorption features of exciton in multi-quantum wells, and further change the distribution features of the readout polychromatic light of MQWs-SLM. It can be not only an universal detecting method, but also especially recommended to use in the Electronic nose system for features detecting of signal light so as to realize smell sensing and visualizing. The feasibility of the proposed method has been confirmed by mathematical modeling and analysis, simulation experiments and research status analysis.

  13. Tracking protein function with sodium multi quantum spectroscopy in a 3D-tissue culture based on microcavity arrays.

    PubMed

    Neubauer, Andreas; Nies, Cordula; Schepkin, Victor D; Hu, Ruomin; Malzacher, Matthias; Chacón-Caldera, Jorge; Thiele, David; Gottwald, Eric; Schad, Lothar R

    2017-06-21

    The aim of this study was to observe the effects of strophanthin induced inhibition of the Na-/K-ATPase in liver cells using a magnetic resonance (MR) compatible bioreactor. A microcavity array with a high density three-dimensional cell culture served as a functional magnetic resonance imaging (MRI) phantom for sodium multi quantum (MQ) spectroscopy. Direct contrast enhanced (DCE) MRI revealed the homogenous distribution of biochemical substances inside the bioreactor. NMR experiments using advanced bioreactors have advantages with respect to having full control over a variety of physiological parameters such as temperature, gas composition and fluid flow. Simultaneous detection of single quantum (SQ) and triple quantum (TQ) MR signals improves accuracy and was achieved by application of a pulse sequence with a time proportional phase increment (TQTPPI). The time course of the Na-/K-ATPase inhibition in the cell culture was demonstrated by the corresponding alterations of sodium TQ/SQ MR signals.

  14. Decoherence in Superconducting Qubits from Surface Magnetic States

    NASA Astrophysics Data System (ADS)

    Hover, David; Sendelbach, Steven; Kittel, Achim; Mueck, Michael; McDermott, Robert

    2008-03-01

    Unpaired spins in amorphous surface oxides can act as a source of decoherence in superconducting and other solid-state qubits. A density of surface spins can give rise to low-frequency magnetic flux noise, which in turn leads to dephasing of the qubit state. In addition, magnetic surface states can couple to high-frequency resonant magnetic fields, and thereby contribute to energy relaxation of the qubit. We present the results of low-frequency measurements of the nonlinear and imaginary spin susceptibility of surface magnetic states in superconducting devices at millikelvin temperatures. In addition, we describe high-frequency magnetic resonance measurements that directly probe the surface spin density of states. We present calculations that connect the measurement results to qubit energy relaxation and dephasing times.

  15. Towards a six-state magnetic memory element

    NASA Astrophysics Data System (ADS)

    Telepinsky, Yevgeniy; Mor, Vladislav; Schultz, Moty; Hung, Yu-Ming; Kent, Andrew D.; Klein, Lior

    2016-05-01

    We pattern permalloy films into three crossing elongated ellipses with an angle of 60 ° between the major axes of any pair of ellipses. Planar Hall effect measurements show that the magnetization in the area of overlap of the ellipses has six stable magnetic orientations parallel to the major axes of the three ellipses. We determine the effective anisotropy field for small magnetic deviations from the easy axis and the switching field between the easy axes as a function of magnetic field orientation. We compare our results with micromagnetic simulations and present an effective Hamiltonian that captures the magnetic response. We show how such magnetic structures in a magnetic tunnel junction would result in a magnetic memory element with six distinct resistance states that could be written using spin-orbit torques.

  16. Exotic magnetic states in Pauli-limited superconductors

    NASA Astrophysics Data System (ADS)

    Kenzelmann, M.

    2017-03-01

    Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

  17. Exotic magnetic states in Pauli-limited superconductors.

    PubMed

    Kenzelmann, M

    2017-03-01

    Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

  18. Magnetic Möbius stripe without frustration: Noncollinear metastable states

    NASA Astrophysics Data System (ADS)

    Castillo-Sepúlveda, S.; Escobar, R. A.; Altbir, D.; Krizanac, M.; Vedmedenko, E. Y.

    2017-07-01

    The recently introduced area of topological magnetism searches for equilibrium structures stabilized by a combination of interactions and specific boundary conditions. Until now, the internal energy of open magnetic chains has been explored. Here, we study the energy landscape of closed magnetic chains with on-site anisotropy coupled with antiferromagnetic exchange and dipolar interactions analytically and numerically. We show that there are many stable stationary states in closed geometries. These states correspond to the noncollinear spin spirals for vanishing anisotropy or to kink solitons for high magnetic anisotropy. Particularly, the noncollinear Möbius magnetic state can be stabilized at finite temperatures in nonfrustrated rings or other closed shapes with an even number of sites without the Dzyaloshinskii-Moriya interaction. We identify the described configurations with the stable stationary states, which appear due to the finite length of a ring.

  19. Edge states and skyrmion dynamics in nanostripes of frustrated magnets

    PubMed Central

    Leonov, A. O.; Mostovoy, M.

    2017-01-01

    Magnetic skyrmions are particle-like topological excitations recently discovered in chiral magnets. Their small size, topological protection and the ease with which they can be manipulated by electric currents generated much interest in using skyrmions for information storage and processing. Recently, it was suggested that skyrmions with additional degrees of freedom can exist in magnetically frustrated materials. Here, we show that dynamics of skyrmions and antiskyrmions in nanostripes of frustrated magnets is strongly affected by complex spin states formed at the stripe edges. These states create multiple edge channels which guide the skyrmion motion. Non-trivial topology of edge states gives rise to complex current-induced dynamics, such as emission of skyrmion–antiskyrmion pairs. The edge-state topology can be controlled with an electric current through the exchange of skyrmions and antiskyrmions between the edges of a magnetic nanostructure. PMID:28240226

  20. Edge states and skyrmion dynamics in nanostripes of frustrated magnets.

    PubMed

    Leonov, A O; Mostovoy, M

    2017-02-27

    Magnetic skyrmions are particle-like topological excitations recently discovered in chiral magnets. Their small size, topological protection and the ease with which they can be manipulated by electric currents generated much interest in using skyrmions for information storage and processing. Recently, it was suggested that skyrmions with additional degrees of freedom can exist in magnetically frustrated materials. Here, we show that dynamics of skyrmions and antiskyrmions in nanostripes of frustrated magnets is strongly affected by complex spin states formed at the stripe edges. These states create multiple edge channels which guide the skyrmion motion. Non-trivial topology of edge states gives rise to complex current-induced dynamics, such as emission of skyrmion-antiskyrmion pairs. The edge-state topology can be controlled with an electric current through the exchange of skyrmions and antiskyrmions between the edges of a magnetic nanostructure.

  1. Magnetic force microscopy reveals meta-stable magnetic domain states that prevent reliable absolute palaeointensity experiments.

    PubMed

    de Groot, Lennart V; Fabian, Karl; Bakelaar, Iman A; Dekkers, Mark J

    2014-08-22

    Obtaining reliable estimates of the absolute palaeointensity of the Earth's magnetic field is notoriously difficult. The heating of samples in most methods induces magnetic alteration--a process that is still poorly understood, but prevents obtaining correct field values. Here we show induced changes in magnetic domain state directly by imaging the domain configurations of titanomagnetite particles in samples that systematically fail to produce truthful estimates. Magnetic force microscope images were taken before and after a heating step typically used in absolute palaeointensity experiments. For a critical temperature (250 °C), we observe major changes: distinct, blocky domains before heating change into curvier, wavy domains thereafter. These structures appeared unstable over time: after 1-year of storage in a magnetic-field-free environment, the domain states evolved into a viscous remanent magnetization state. Our observations qualitatively explain reported underestimates from otherwise (technically) successful experiments and therefore have major implications for all palaeointensity methods involving heating.

  2. Morphological and functional state of the heart during magnetic storm.

    PubMed

    Chibisov, S M; Breus, T K; Illarionova, T S

    2001-12-01

    Magnetic storm modulates morphological and functional state of the heart and the related systems. Changes in cardiomyocyte ultrastructure induced by changes in geomagnetic activity were studied in experiments on rabbits. We describe a possible mechanism underlying changes in cardiac activity in intact animals induced by geomagnetic perturbations. The most pronounced alterations of cardiomyocyte ultrastructure were observed during the major phase of magnetic storm.

  3. Demagnetization using a determined estimated magnetic state

    DOEpatents

    Denis, Ronald J; Makowski, Nathanael J

    2015-01-13

    A method for demagnetizing comprising positioning a core within the electromagnetic field generated by a first winding until the generated first electrical current is not substantially increasing, thereby determining a saturation current. A second voltage, having the opposite polarity, is then applied across the first winding until the generated second electrical current is approximately equal to the magnitude of the determined saturation current. The maximum magnetic flux within the core is then determined using the voltage across said first winding and the second current. A third voltage, having the opposite polarity, is then applied across the first winding until the core has a magnetic flux equal to approximately half of the determined maximum magnetic flux within the core.

  4. Chimera states and synchronization in magnetically driven SQUID metamaterials

    NASA Astrophysics Data System (ADS)

    Hizanidis, J.; Lazarides, N.; Neofotistos, G.; Tsironis, G. P.

    2016-09-01

    One-dimensional arrays of Superconducting QUantum Interference Devices (SQUIDs) form magnetic metamaterials exhibiting extraordinary properties, including tunability, dynamic multistability, negative magnetic permeability, and broadband transparency. The SQUIDs in a metamaterial interact through non-local, magnetic dipole-dipole forces, that makes it possible for multiheaded chimera states and coexisting patterns, including solitary states, to appear. The spontaneous emergence of chimera states and the role of multistability is demonstrated numerically for a SQUID metamaterial driven by an alternating magnetic field. The spatial synchronization and temporal complexity are discussed and the parameter space for the global synchronization reveals the areas of coherence-incoherence transition. Given that both one- and two-dimensional SQUID metamaterials have been already fabricated and investigated in the lab, the presence of a chimera state could in principle be detected with presently available experimental set-ups.

  5. Strain dependence of In incorporation in m-oriented GaInN/GaN multi quantum well structures

    SciTech Connect

    Horenburg, Philipp Buß, Ernst Ronald; Rossow, Uwe; Ketzer, Fedor Alexej; Bremers, Heiko; Hangleiter, Andreas

    2016-03-07

    We demonstrate a strong dependence of the indium incorporation efficiency on the strain state in m-oriented GaInN/GaN multi quantum well (MQW) structures. Insertion of a partially relaxed AlInN buffer layer opens up the opportunity to manipulate the strain situation in the MQW grown on top. By lattice-matching this AlInN layer to the c- or a-axis of the underlying GaN, relaxation towards larger a- or smaller c-lattice constants can be induced, respectively. This results in a modified template for the subsequent MQW growth. From X-ray diffraction and photoluminescence measurements, we derive significant effects on the In incorporation efficiency and In concentrations in the quantum well (QW) up to x = 38% without additional accumulation of strain energy in the QW region. This makes strain manipulation a very promising method for growth of high In-containing MQW structures for efficient, long wavelength light-emitting devices.

  6. Silicon-Germanium multi-quantum well photodetectors in the near infrared.

    PubMed

    Onaran, Efe; Onbasli, M Cengiz; Yesilyurt, Alper; Yu, Hyun Yong; Nayfeh, Ammar M; Okyay, Ali K

    2012-03-26

    Single crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ~10 mA/cm² and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage.

  7. Magnetized color flavor locked state and compact stars

    NASA Astrophysics Data System (ADS)

    González Felipe, R.; Manreza Paret, D.; Pérez Martınez, A.

    2011-01-01

    The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model, taking into account the variation of the strange quark mass, the baryon density, the magnetic field, as well as the bag and gap parameters. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The mass-radius relation for such stars is also studied.

  8. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W. (Principal Investigator); Starich, P. J.

    1984-01-01

    The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced to pole and derivative maps provide constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.

  9. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Starich, P. J.

    1985-01-01

    The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free-air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced-to-pole and derivative maps provide additional constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.

  10. Tunable magnetic textures: From Majorana bound states to braiding

    NASA Astrophysics Data System (ADS)

    Matos-Abiague, Alex; Shabani, Javad; Kent, Andrew D.; Fatin, Geoffrey L.; Scharf, Benedikt; Žutić, Igor

    2017-08-01

    A versatile control of magnetic systems, widely used to store information, can also enable manipulating Majorana bounds states (MBS) and implementing fault-tolerant quantum information processing. The proposed platform relies on the proximity-induced superconductivity in a two-dimensional electron gas placed next to an array of magnetic tunnel junctions (MTJs). A change in the magnetization configuration in the MTJ array creates tunable magnetic textures thereby removing several typical requirements for MBS: strong spin-orbit coupling, applied magnetic field, and confinement by one-dimensional structures which complicates demonstrating non-Abelian statistics through braiding. Recent advances in fabricating two-dimensional epitaxial superconductor/semiconductor heterostructures and designing tunable magnetic textures support the feasibility of this novel platform for MBS.

  11. Field-induced magnetic states in holmium tetraboride

    NASA Astrophysics Data System (ADS)

    Brunt, D.; Balakrishnan, G.; Wildes, A. R.; Ouladdiaf, B.; Qureshi, N.; Petrenko, O. A.

    2017-01-01

    A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at TN 1=7.1 K to an incommensurate state with a propagation vector (δ ,δ ,δ') , where δ =0.02 and δ'=0.43 and at TN 2=5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3 ) -type reflections between 18 and 24 kOe. This field range is marked by the previously reported M /Msat=1/3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M /Msat≈3/5 . Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H -T phase diagram of HoB4 for the H ∥c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.

  12. An equivalent layer magnetization model for the United States derived from satellite altitude magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.

    1982-01-01

    Long wavelength magnetic anomalies measured by the Pogo series satellites at altitudes 400-700 km over the United States and adjacent areas are inverted to an equivalent layer magnetization model based on an equal area dipole source array at the earth's surface. Minimum source spacing giving a stable solution and a physically meaningful magnetization distribution is 300 km, and a scheme is presented for effectively sampling the distribution on a grid twice as fine. The model expresses lateral variation in the vertical integral of magnetization and is a starting point for models of lateral variation in the form of the magnetization-depth curve in the magnetic crust. The magnetization model contours correlate with large-scale tectonic features, and in the western part of the country, probably reflect Curie isotherm undulations.

  13. Classifying magnetic and superfluid equilibrium states in magnets with the spin s = 1

    NASA Astrophysics Data System (ADS)

    Kovalevskii, M. Yu.

    2016-03-01

    Based on the method of quasiaverages, we classify magnetic and superfluid equilibrium states in magnets with the spin s = 1. Under certain simplifications, assumptions about the residual symmetry of degenerate states and the transformation properties of order parameter operators under transformations generated by additive integrals of motions lead to linear algebraic equations for a classification of the equilibrium means of the order parameters. We consider different cases of the magnetic SO(3) or SU(3) symmetry breaking and obtain solutions for the vector and tensor order parameters for particular forms of the parameters of the residual symmetry generators. We study the equilibriums of magnets with simultaneously broken phase and magnetic symmetries. We find solutions of the classification equations for superfluid equilibrium states and establish relations between the parameters of the residual symmetry generator that allow the thermodynamic coexistence of nonzero equilibrium means of the order parameters.

  14. New type of stable particlelike states in chiral magnets.

    PubMed

    Rybakov, Filipp N; Borisov, Aleksandr B; Blügel, Stefan; Kiselev, Nikolai S

    2015-09-11

    We present a new type of thermodynamically stable magnetic state at interfaces and surfaces of chiral magnets. The state is a soliton solution of micromagnetic equations localized in all three dimensions near a boundary, and it contains a singularity but nevertheless has finite energy. Both features combine to form a quasiparticle state for which we expect unusual transport and dynamical properties. It exhibits high thermal stability and thereby can be considered as a promising object for fundamental research and practical applications in spintronic devices. We identified the range of existence of such particlelike states in the thickness dependent magnetic phase diagram for helimagnet films and analyzed its stability in comparison with the isolated skyrmion within the conical phase. We provide arguments that such a state can be found in different B20-type alloys, e.g., Mn_{1-x}Fe_{x}Ge, Mn_{1-x}Fe_{x}Si, Fe_{1-x}Co_{x}Si.

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

    DOE PAGES

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

    2017-02-08

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

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

    PubMed

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

    2017-02-08

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed Central

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

    2017-01-01

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

  19. Wavy growth onset in strain-balanced InGaAs multi-quantum wells

    NASA Astrophysics Data System (ADS)

    Nasi, L.; Ferrari, C.; Lanzi, A.; Lazzarini, L.; Balboni, R.; Clarke, G.; Mazzer, M.; Rohr, C.; Abbott, P.; Barnham, K. W. J.

    2005-01-01

    Different strain-balanced InGaAs/InGaAs multi-quantum wells (MQWs) were grown on (0 0 1) InP to be used as active layers of thermophotovoltaic devices. Transmission electron microscopy (TEM) and high-resolution X-ray diffraction (HRXRD) were performed to correlate the evolution of the layer interfaces from planar to wavy and the consequent nucleation of extended defects with the well and barrier compositions and thicknesses and the growth temperature. The existence of a critical elastic energy density for the wavy growth onset has been experimentally confirmed by changing both the well and barrier misfit and the multi-quantum well layer thickness. A decrease of the growth temperature shifts the critical energy to higher values. An empirical model to predict the maximum number of layers that can be grown without modulations as a function of the strain energy stored in the MQW period and the growth temperature is presented and successfully applied for the growth of high quality 40 repetitions MQWs with a well misfit of about 1.5%.

  20. Ridge InGaAs/InP multi-quantum-well selective growth in nanoscale trenches on Si (001) substrate

    SciTech Connect

    Li, S.; Zhou, X.; Li, M.; Kong, X.; Mi, J.; Wang, M.; Wang, W.; Pan, J.

    2016-01-11

    Metal organic chemical vapor deposition of InGaAs/InP multi-quantum-well in nanoscale V-grooved trenches on Si (001) substrate was studied using the aspect ratio trapping method. A high quality GaAs/InP buffer layer with two convex (111) B facets was selectively grown to promote the highly uniform, single-crystal ridge InP/InGaAs multi-quantum-well structure growth. Material quality was confirmed by transmission electron microscopy and room temperature micro-photoluminescence measurements. This approach shows great promise for the fabrication of photonics devices and nanolasers on Si substrate.

  1. Magnetic ground states in nanocuboids of cubic magnetocrystalline anisotropy

    NASA Astrophysics Data System (ADS)

    Bonilla, F. J.; Lacroix, L.-M.; Blon, T.

    2017-04-01

    Flower and easy-axis vortex states are well-known magnetic configurations that can be stabilized in small particles. However, <111> vortex (V<111>), i.e. a vortex state with its core axis along the hard-axis direction, has been recently evidenced as a stable configuration in Fe nanocubes of intermediate sizes in the flower/vortex transition. In this context, we present here extensive micromagnetic simulations to determine the different magnetic ground states in ferromagnetic nanocuboids exhibiting cubic magnetocrystalline anisotropy (MCA). Focusing our study in the single-domain/multidomain size range (10-50 nm), we showed that V<111> is only stable in nanocuboids exhibiting peculiar features, such as a specific size, shape and magnetic environment, contrarily to the classical flower and easy-axis vortex states. Thus, to track experimentally these V<111> states, one should focused on (i) nanocuboids exhibiting a nearly perfect cubic shape (size distorsion <12%) made of (ii) a material which combines a zero or positive MCA and a high saturation magnetization, such as Fe or FeCo; and (iii) a low magnetic field environment, V<111> being only observed in virgin or remanent states.

  2. Lifetimes of long-lived states in inhomogeneous magnetic fields

    NASA Astrophysics Data System (ADS)

    Singh, Maninder; Chinthalapalli, Srinivas; Bodenhausen, Geoffrey

    2015-03-01

    Long-lived states (LLS), also known as singlet states, have been widely studied in the last decade. So far, LLS have only been observed in homogeneous magnetic fields, which preclude applications to many biological samples that are inherently inhomogeneous. We present a method to measure the lifetimes TLLS of long-lived states in inhomogeneous magnetic fields, which combines established sequences for the excitation of LLS with their conversion into long-lived coherences (LLC) that can be detected by windowed acquisition. The method is applied to a pair of diastereotopic scalar-coupled protons of glycine in the dipeptide Alanine-Glycine (Ala-Gly).

  3. Majorana bound states in magnetic skyrmions (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Stano, Peter

    2016-10-01

    Magnetic skyrmions are highly mobile nanoscale topological spin textures. We show, both analytically and numerically, that a magnetic skyrmion of an even azimuthal winding number placed in proximity to an s-wave superconductor hosts a zero-energy Majorana bound state in its core, when the exchange coupling between the itinerant electrons and the skyrmion is strong. This Majorana bound state is stabilized by the presence of a spin-orbit interaction. We propose the use of a superconducting tri-junction to realize non-Abelian statistics of such Majorana bound states. http://arxiv.org/abs/1602.00968

  4. High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic

    NASA Astrophysics Data System (ADS)

    Duran, I.; Entler, S.; Kohout, M.; Kočan, M.; Vayakis, G.

    2016-11-01

    Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."

  5. High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic.

    PubMed

    Ďuran, I; Entler, S; Kohout, M; Kočan, M; Vayakis, G

    2016-11-01

    Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique."

  6. Magnetic field induced lattice ground states from holography

    NASA Astrophysics Data System (ADS)

    Bu, Yan-Yan; Erdmenger, Johanna; Shock, Jonathan P.; Strydom, Migael

    2013-03-01

    We study the holographic field theory dual of a probe SU(2) Yang-Mills field in a background (4 + 1)-dimensional asymptotically Anti-de Sitter space. We find a new ground state when a magnetic component of the gauge field is larger than a critical value. The ground state forms a triangular Abrikosov lattice in the spatial directions perpendicular to the magnetic field. The lattice is composed of superconducting vortices induced by the condensation of a charged vector operator. We perform this calculation both at finite temperature and at zero temperature with a hard wall cutoff dual to a confining gauge theory. The study of this state may be of relevance to both holographic condensed matter models as well as to heavy ion physics. The results shown here provide support for the proposal that such a ground state may be found in the QCD vacuum when a large magnetic field is present.

  7. The magnetic charts of the United States for Epoch 1975

    USGS Publications Warehouse

    Fabiano, Eugene B.; Jones, W.J.; Peddie, Norman W.

    1979-01-01

    Approximately 24,000 measurements taken from 1900 to 1974 were analyzed by least-squares methods to produce a series of five magnetic charts of the United States for 1975. A feature of the analysis, differing from techniques used for previous editions of the national chart, is that analytic models define the regional magnetic field and are used to contour the magnetic charts. An overall rms (root mean square) fit of less than 235 nT was obtained for the horizontal and vertical intensities; for the chart of magnetic declination, the rms deviation was on the order of 0.5 degrees. The models of annual change, derived from data at repeat stations and observatories operated by the U.S. Geological Survey, yielded an rms deviation of approximately 6 nT/yr in the force components and 0.7 min/yr in magnetic declination.

  8. What is the magnetic field distribution for the equation of state of magnetized neutron stars?

    NASA Astrophysics Data System (ADS)

    Dexheimer, V.; Franzon, B.; Gomes, R. O.; Farias, R. L. S.; Avancini, S. S.; Schramm, S.

    2017-10-01

    In this Letter, we report a realistic calculation of the magnetic field profile for the equation of state inside strongly magnetized neutron stars. Unlike previous estimates, which are widely used in the literature, we find that magnetic fields increase relatively slowly with increasing baryon chemical potential (or baryon density) of magnetized matter. More precisely, the increase is polynomial instead of exponential, as previously assumed. Through the analysis of several different realistic models for the microscopic description of stellar matter (including hadronic, hybrid and quark models) combined with general relativistic solutions endowed with a poloidal magnetic field obtained by solving Einstein-Maxwell's field equations in a self-consistent way, we generate a phenomenological fit for the magnetic field distribution in the stellar polar direction to be used as input in microscopic calculations.

  9. Magnetic models for the United States for 1985

    USGS Publications Warehouse

    Peddie, Norman W.; Zunde, Audronis K.

    1990-01-01

    New models describing the magnetic field in the United States at the beginning of 1985 and the rate of change expected during the next few years have been developed. The models--which will serve as the basis for a new set of magnetic charts--were derived from several tens of thousands of original field measurements from land, marine, and aerial surveys; from values derived from the MAGSAT-based International Geomagnetic Reference Field; and from recent data from magnetic observatories and repeat stations. , They are in the form of spherical harmonic series that represent the scalar magnetic potential from which all the field components can be derived. The models for the conterminous States and Alaska are of maximum degree and order 4 (24 coefficients each) and the models for Hawaii are of maximum degree and order 2 (8 coefficients each).

  10. A novel model on time-resolved photoluminescence measurements of polar InGaN/GaN multi-quantum-well structures

    PubMed Central

    Xing, Yuchen; Wang, Lai; Yang, Di; Wang, Zilan; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yanjun; Wang, Jian; Li, Hongtao

    2017-01-01

    Based on carrier rate equation, a new model is proposed to explain the non-exponential nature of time-resolved photoluminescence (TRPL) decay curves in the polar InGaN/GaN multi-quantum-well structures. From the study of TRPL curves at different temperatures, it is found that both radiative and non-radiative recombination coefficients vary from low temperature to room temperature. The variation of the coefficients is compatible with the carrier density of states distribution as well as the carrier localization process. These results suggest that there is a novel method to calculate the internal quantum efficiency, which is a complement to the traditional one based on temperature dependent photoluminescence measurement. PMID:28327629

  11. A novel model on time-resolved photoluminescence measurements of polar InGaN/GaN multi-quantum-well structures

    NASA Astrophysics Data System (ADS)

    Xing, Yuchen; Wang, Lai; Yang, Di; Wang, Zilan; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yanjun; Wang, Jian; Li, Hongtao

    2017-03-01

    Based on carrier rate equation, a new model is proposed to explain the non-exponential nature of time-resolved photoluminescence (TRPL) decay curves in the polar InGaN/GaN multi-quantum-well structures. From the study of TRPL curves at different temperatures, it is found that both radiative and non-radiative recombination coefficients vary from low temperature to room temperature. The variation of the coefficients is compatible with the carrier density of states distribution as well as the carrier localization process. These results suggest that there is a novel method to calculate the internal quantum efficiency, which is a complement to the traditional one based on temperature dependent photoluminescence measurement.

  12. A novel model on time-resolved photoluminescence measurements of polar InGaN/GaN multi-quantum-well structures.

    PubMed

    Xing, Yuchen; Wang, Lai; Yang, Di; Wang, Zilan; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yanjun; Wang, Jian; Li, Hongtao

    2017-03-22

    Based on carrier rate equation, a new model is proposed to explain the non-exponential nature of time-resolved photoluminescence (TRPL) decay curves in the polar InGaN/GaN multi-quantum-well structures. From the study of TRPL curves at different temperatures, it is found that both radiative and non-radiative recombination coefficients vary from low temperature to room temperature. The variation of the coefficients is compatible with the carrier density of states distribution as well as the carrier localization process. These results suggest that there is a novel method to calculate the internal quantum efficiency, which is a complement to the traditional one based on temperature dependent photoluminescence measurement.

  13. Switching behavior and novel stable states of magnetic hexagonal nanorings

    NASA Astrophysics Data System (ADS)

    Yasir Rafique, M.; Pan, Liqing; Guo, Zhengang

    2017-06-01

    Micromagnetic simulations for Cobalt hexagonal shape nanorings show onion (O) and vortex state (V) along with new state named ;tri-domain state;. The tri-domain state is observed in sufficiently large width of ring. The magnetic reversible mechanism and transition of states are explained with help of vector field display. The transitions from one state to other occur by propagation of domain wall. The vertical parts of hexagonal rings play important role in developing the new ;tri-domain; state. The behaviors of switching fields from onion to tri-domain (HO-Tr), tri-domain to vortex state (HTr-V) and vortex to onion state and ;states size; are discussed in term of geometrical parameter of ring.

  14. Steady state magnetic field configurations for the earth's magnetotail

    NASA Technical Reports Server (NTRS)

    Hau, L.-N.; Wolf, R. A.; Voigt, G.-H.; Wu, C. C.

    1989-01-01

    A two-dimensional, force-balance magnetic field model is presented. The theoretical existence of a steady state magnetic field configuration that is force-balanced and consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD is demonstrated. A numerical solution is obtained for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The results are consistent with the convection time sequences reported by Erickson (1985).

  15. Magnetic field sensors using 13-spin cat states

    SciTech Connect

    Simmons, Stephanie; Karlen, Steven D.; Jones, Jonathan A.; Ardavan, Arzhang; Morton, John J. L.

    2010-08-15

    Measurement devices could benefit from entangled correlations to yield a measurement sensitivity approaching the physical Heisenberg limit. Building upon previous magnetometric work using pseudoentangled spin states in solution-state NMR, we present two conceptual advancements to better prepare and interpret the pseudoentanglement resource. We apply these to a 13-spin cat state to measure the local magnetic field with a 12.2 sensitivity increase over an equivalent number of isolated spins.

  16. Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers

    SciTech Connect

    Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; Okamoto, Satoshi; Xiao, Di

    2015-06-16

    Layered transition-metal trichalcogenides with the chemical formula ABX3 have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides.We show that the second and third nearest-neighbor exchange interactions (J2 and J3) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe3 is an antiferromagnet with a zigzag spin texture due to significant contribution from J3, whereas CrGeTe3 is a ferromagnet with a Curie temperature of 106 K. Monolayers of Mn compounds (MnPS3 and MnPSe3) always show antiferromagnetic N eel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. In conclusion, our study suggests that ABX3 can be a promising platform to explore two-dimensional magnetic phenomena.

  17. Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers

    DOE PAGES

    Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; ...

    2015-06-16

    Layered transition-metal trichalcogenides with the chemical formula ABX3 have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides.We show that the second and third nearest-neighbor exchange interactions (J2 and J3) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe3 is an antiferromagnet with a zigzag spin texture due to significant contribution from J3, whereas CrGeTe3 is a ferromagnet with a Curie temperaturemore » of 106 K. Monolayers of Mn compounds (MnPS3 and MnPSe3) always show antiferromagnetic N eel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. In conclusion, our study suggests that ABX3 can be a promising platform to explore two-dimensional magnetic phenomena.« less

  18. Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; Okamoto, Satoshi; Xiao, Di

    2015-06-01

    Layered transition-metal trichalcogenides with the chemical formula A B X3 have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides. We show that the second and third nearest-neighbor exchange interactions (J2 and J3) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe3 is an antiferromagnet with a zigzag spin texture due to significant contribution from J3, whereas CrGeTe3 is a ferromagnet with a Curie temperature of 106 K. Monolayers of Mn compounds (MnPS3 and MnPSe3) always show antiferromagnetic Néel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. Our study suggests that A B X3 can be a promising platform to explore two-dimensional magnetic phenomena.

  19. Ground state magnetic response of two coupled dodecahedra

    NASA Astrophysics Data System (ADS)

    Konstantinidis, N. P.

    2016-01-01

    The antiferromagnetic Heisenberg model on the dodecahedron possesses a number of ground state magnetization discontinuities in a field at the classical and quantum level, even though it lacks magnetic anisotropy. Here the model is considered for two dodecahedra coupled antiferromagnetically along one of their faces, as a first step to determine the magnetic response of collections of fullerene molecules. The magnetic response is determined from the competition among the intra-, interdodecahedral exchange and magnetic field energies. At the classical level the discontinuities of the isolated dodecahedron are renormalized by the interdodecahedral coupling, while new ones show up, with the maximum number of ground state discontinuities being six for a specific range of the coupling. In the full quantum limit where the individual spin magnitude s=\\frac{1}{2} , there are two ground state discontinuities originating in the single discontinuity of the isolated dodecahedron, and another one due to the intermolecular coupling, generating a total of three discontinuities which come one right after the other. These results show that the magnetic response of more than one dodecahedra interacting together is quite richer than the one of a single dodecahedron.

  20. Ground state magnetic response of two coupled dodecahedra.

    PubMed

    Konstantinidis, N P

    2016-01-13

    The antiferromagnetic Heisenberg model on the dodecahedron possesses a number of ground state magnetization discontinuities in a field at the classical and quantum level, even though it lacks magnetic anisotropy. Here the model is considered for two dodecahedra coupled antiferromagnetically along one of their faces, as a first step to determine the magnetic response of collections of fullerene molecules. The magnetic response is determined from the competition among the intra-, interdodecahedral exchange and magnetic field energies. At the classical level the discontinuities of the isolated dodecahedron are renormalized by the interdodecahedral coupling, while new ones show up, with the maximum number of ground state discontinuities being six for a specific range of the coupling. In the full quantum limit where the individual spin magnitude [Formula: see text], there are two ground state discontinuities originating in the single discontinuity of the isolated dodecahedron, and another one due to the intermolecular coupling, generating a total of three discontinuities which come one right after the other. These results show that the magnetic response of more than one dodecahedra interacting together is quite richer than the one of a single dodecahedron.

  1. Stellar fibril magnetic systems. I - Reduced energy state

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1984-01-01

    The remarkable fibril structure of the magnetic fields at the surface of the sun (with fibrils compressed to 1,000-2,000 gauss) lies outside existing statistical theories of magnetohydrodynamic turbulence. The total energy of the fibril field is enhanced by a factor of more than 100 above the energy for the mean field in a continuum state. The magnetic energy density within a fibril is of the order of 100 times the local kinetic energy density, so that no simple application of equipartition principles is possible. It is pointed out that the total energy of the atmosphere (thermal + gravitational + magnetic) is reduced by the fibril state of the field by avoiding the magnetic inhibition of the convective overturning, suggesting that the formation of the observed intense fibril state may be in response to the associated energy reduction. Calculation of the minimum total energy of a polytropic atmosphere permeated by magnetic fibrils yields theoretical fibril fields of the order of 1-5 kilogauss when characteristics appropriate to the solar convective zone are introduced, in rough agreement with the actual fields of 1-2 kilogauss. The polytrope model, although crude, establishes that a large reduction in total energy is made possible by the fibril state.

  2. Remanent state studies of truncated conical magnetic particles

    SciTech Connect

    Hwang, M.; Redjdal, M.; Humphrey, F. B.; Ross, C. A.

    2001-06-01

    The remanent state of truncated conical particles is investigated as a function of their size, aspect ratio, and anisotropy, using a micromagnetic model based on the Landau{endash}Lifshitz{endash}Gilbert equation. Particles with a base diameter smaller than three times the exchange length show a {open_quotes}flower{close_quotes} state, while larger particles show a {open_quotes}vortex{close_quotes} magnetization state. The critical size for this transition increases with increasing anisotropy. Small flower-state particles show abrupt reorientation from out-of-plane to in-plane magnetization at a critical aspect ratio of 0.9. For vortex-state particles, the axial remanence gradually increases as the aspect ratio increases, and high aspect ratio particles have significant remanence even at larger diameters. {copyright} 2001 American Institute of Physics.

  3. Vortex State in Sub-100 nm Magnetic Nanodots.

    NASA Astrophysics Data System (ADS)

    Roshchin, Igor V.

    2006-03-01

    Magnetism of nanostructured magnets, which size is comparable to or smaller than ferromagnetic domain size, offers a great potential for new physics. Detailed knowledge of magnetization reversal and possible magnetic configurations in magnetic nanostructures is essential for high-density magnetic memory. Many theoretical and experimental studies are focused on a magnetic vortex which in addition to a circular in-plane configuration of spins has a core, - the region with out-of-plane magnetization. We present a quantitative study of the magnetic vortex state and the vortex core in sub-100 nm magnetic dots. Arrays of single-layer and bilayer nanodots covering over 1 cm^2 are fabricated using self-assembled nanopores in anodized alumina. This method allows good control over the dot size and periodicity. Magnetization measurements performed using SQUID, VSM, and MOKE indicate a transition from a vortex to a single domain state for the Fe dots. This transition is studied as a function of the magnetic field and dots size. Micromagnetic and Monte Carlo simulations confirm the experimental observations. Thermal activation and exchange bias strongly affect the vortex nucleation field and have a much weaker effect on the vortex annihilation field. Direct imaging of magnetic moments in sub-100 nm dots is extremely difficult and has not been reported yet. Polarized grazing incidence small angle neutron scattering measurements allow dot imaging in reciprocal space. Quantitative analysis of such measurements performed on 65 nm Fe dots yields the vortex core size of ˜15 nm, in good agreement with the 14 nm obtained from the simulations. This work is done in collaboration with Chang-Peng Li, Zhi-Pan Li, S. Roy, S. K. Sinha, (UCSD), Xavier Batlle (U. Barcelona), R. K. Dumas, Kai Liu, (UC Davis), S. Park, R. Pynn, M. R. Fitzsimmons (LANL), J. Mejia Lopez (Pontificia U. Catolica de Chile), D. Altbir, (U. de Santiago de Chile), A. H. Romero (Cinvestav-Unidad Queretaro), and Ivan K

  4. Understanding and controlling complex states arising from magnetic frustration

    SciTech Connect

    Zapf, Vivien

    2012-06-01

    Much of our national security relies on capabilities made possible by magnetism, in particular the ability to compute and store huge bodies of information as well as to move things and sense the world. Most of these technologies exploit ferromagnetism, i.e. the global parallel alignment of magnetic spins as seen in a bar magnet. Recent advances in computing technologies, such as spintronics and MRAM, take advantage of antiferromagnetism where the magnetic spins alternate from one to the next. In certain crystal structures, however, the spins take on even more complex arrangements. These are often created by frustration, where the interactions between spins cannot be satisfied locally or globally within the material resulting in complex and often non-coplanar spin textures. Frustration also leads to the close proximity of many different magnetic states, which can be selected by small perturbations in parameters like magnetic fields, temperature and pressure. It is this tunability that makes frustrated systems fundamentally interesting and highly desirable for applications. We move beyond frustration in insulators to itinerant systems where the interaction between mobile electrons and the non-coplanar magnetic states lead to quantum magneto-electric amplification. Here a small external field is amplified by many orders of magnitude by non-coplanar frustrated states. This greatly enhances their sensitivity and opens broader fields for applications. Our objective is to pioneer a new direction for condensed matter science at the Laboratory as well as for international community by discovering, understanding and controlling states that emerge from the coupling of itinerant charges to frustrated spin textures.

  5. Collective magnetic excitations of C4-symmetric magnetic states in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Scherer, Daniel D.; Eremin, Ilya; Andersen, Brian M.

    2016-11-01

    We study the collective magnetic excitations of the recently discovered C4-symmetric spin-density-wave states of iron-based superconductors with particular emphasis on their orbital character based on an itinerant multiorbital approach. This is important since the C4-symmetric spin-density-wave states exist only at moderate interaction strengths where damping effects from a coupling to the continuum of particle-hole excitations strongly modify the shape of the excitation spectra compared to predictions based on a local moment picture. We uncover a distinct orbital polarization inherent to magnetic excitations in C4-symmetric states, which provide a route to identify the different commensurate magnetic states appearing in the continuously updated phase diagram of the iron-pnictide family.

  6. Experimental evidence of hot carriers solar cell operation in multi-quantum wells heterostructures

    SciTech Connect

    Rodière, Jean; Lombez, Laurent; Le Corre, Alain; Durand, Olivier; Guillemoles, Jean-François

    2015-05-04

    We investigated a semiconductor heterostructure based on InGaAsP multi quantum wells (QWs) using optical characterizations and demonstrate its potential to work as a hot carrier cell absorber. By analyzing photoluminescence spectra, the quasi Fermi level splitting Δμ and the carrier temperature are quantitatively measured as a function of the excitation power. Moreover, both thermodynamics values are measured at the QWs and the barrier emission energy. High values of Δμ are found for both transition, and high carrier temperature values in the QWs. Remarkably, the quasi Fermi level splitting measured at the barrier energy exceeds the absorption threshold of the QWs. This indicates a working condition beyond the classical Shockley-Queisser limit.

  7. Nonlinear processes in multi-quantum-well plasmonic metasurfaces: Electromagnetic response, saturation effects, limits, and potentials

    NASA Astrophysics Data System (ADS)

    Gomez-Diaz, J. S.; Tymchenko, M.; Lee, J.; Belkin, M. A.; Alà, Andrea

    2015-09-01

    Nonlinear metasurfaces based on coupling a locally enhanced plasmonic response to intersubband transitions of n -doped multi-quantum-wells (MQWs) can provide second-order susceptibilities orders of magnitude larger than any other nonlinear flat structure measured so far. Here we present a comprehensive theory to characterize the electromagnetic response of nonlinear processes occurring in ultrathin MQW-based plasmonic metasurfaces, providing a homogeneous model that takes phase matching at the unit-cell level and the influence of saturation and losses into account. In addition, the limits imposed by saturation of the MQW transitions on the nonlinear response of these metasurfaces are analytically derived, revealing useful guidelines to design devices with enhanced performance. Our approach is first validated using experimental data and then applied to theoretically investigate novel designs able to achieve significant second-harmonic generation efficiency in the infrared frequency band.

  8. LOW-STATE MAGNETIC STRUCTURES IN POLARS: NATURE OR NURTURE?

    SciTech Connect

    Kafka, S.; Tappert, C.; Ribeiro, T.; Honeycutt, R. K.; Hoard, D. W.

    2010-10-01

    We present an orbit-resolved study of the magnetic cataclysmic variable (MCV) BL Hyi in its low state, and we explore the origin of its H{alpha} emission line components, their properties, and their possible formation mechanism. We tentatively associate one of the line components with a high-velocity component also seen in the high state. We propose a scenario in which streaming prominence-like magnetic loops (super-prominences) are kept in place by magnetic field interactions between the white dwarf and the donor star and are responsible for the high-velocity line components in the Balmer lines. We also discuss how this is in accord with the standard scenario of the secular evolution for MCVs. Finally, we offer an observational test of our ideas and present challenges for future theoretical studies.

  9. Low-state Magnetic Structures in Polars: Nature or Nurture?

    NASA Astrophysics Data System (ADS)

    Kafka, S.; Tappert, C.; Ribeiro, T.; Honeycutt, R. K.; Hoard, D. W.; Saar, S.

    2010-10-01

    We present an orbit-resolved study of the magnetic cataclysmic variable (MCV) BL Hyi in its low state, and we explore the origin of its Hα emission line components, their properties, and their possible formation mechanism. We tentatively associate one of the line components with a high-velocity component also seen in the high state. We propose a scenario in which streaming prominence-like magnetic loops (super-prominences) are kept in place by magnetic field interactions between the white dwarf and the donor star and are responsible for the high-velocity line components in the Balmer lines. We also discuss how this is in accord with the standard scenario of the secular evolution for MCVs. Finally, we offer an observational test of our ideas and present challenges for future theoretical studies.

  10. Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states

    PubMed Central

    Heo, Changhoon; Kiselev, Nikolai S.; Nandy, Ashis Kumar; Blügel, Stefan; Rasing, Theo

    2016-01-01

    Magnetic chiral skyrmions are vortex like spin structures that appear as stable or meta-stable states in magnetic materials due to the interplay between the symmetric and antisymmetric exchange interactions, applied magnetic field and/or uniaxial anisotropy. Their small size and internal stability make them prospective objects for data storage but for this, the controlled switching between skyrmion states of opposite polarity and topological charge is essential. Here we present a study of magnetic skyrmion switching by an applied magnetic field pulse based on a discrete model of classical spins and atomistic spin dynamics. We found a finite range of coupling parameters corresponding to the coexistence of two degenerate isolated skyrmions characterized by mutually inverted spin structures with opposite polarity and topological charge. We demonstrate how for a wide range of material parameters a short inclined magnetic field pulse can initiate the reliable switching between these states at GHz rates. Detailed analysis of the switching mechanism revealed the complex path of the system accompanied with the excitation of a chiral-achiral meron pair and the formation of an achiral skyrmion. PMID:27273157

  11. Transition states of magnetization reversal in ferromagnetic nanorings

    NASA Astrophysics Data System (ADS)

    Chaves-O'Flynn, Gabriel; Kent, Andrew; Stein, Daniel

    2008-03-01

    Thin ferromagnetic rings are of interest for fundamental studies of magnetization reversal, in part, because they are a rare example of a geometry for which an analytical solution for the rate of thermally induced switching has been determined [1]. The theoretical model predicts the transition state to be either a global magnetization rotation of constant azimuthal angle or a localized fluctuation, denoted the instanton saddle. Numerically we have confirmed that for a range of values of external magnetic field and ring size the instanton saddle is energetically favored [2]. The model takes the annular width to be small compared to the mean radius of the annulus; in which case the main contribution to the magnetization energy comes from the surface magnetostatic energy. We present numerical micromagnetic calculations of the activation energy for thermally induced magnetization reversal for the two different transition states for the case when the annular width is equal in magnitude to the mean radius of the ring. Results of the total and surface magnetostatic energies are compared for different ring sizes. [1] K. Martens, D.L. Stein, A.D. Kent, PRB 73, 054413 (2006) [2] G.D. Chaves-O'Flynn, K. Xiao, D.L. Stein, A. D. Kent, arXiv:0710.2546 (2007)

  12. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Starich, P. J.; Hinze, W. J.; Braile, L. W.

    1985-01-01

    A positive magnetic anomaly, which dominates the MAGSAT scalar field over the south-central United States, results from the superposition of magnetic effects from several geologic sources and tectonic structures in the crust. The highly magnetic basement rocks of this region show good correlation with increased crustal thickness, above average crustal velocity and predominantly negative free-air gravity anomalies, all of which are useful constraints for modeling the magnetic sources. The positive anomaly is composed of two primary elements. The western-most segment is related to middle Proterozoic granite intrusions, rhyolite flows and interspersed metamorphic basement rocks in the Texas panhandle and eastern New Mexico. The anomaly and the magnetic crust are bounded to the west by the north-south striking Rio Grande Rift. The anomaly extends eastward over the Grenville age basement rocks of central Texas, and is terminated to the south and east by the buried extension of the Ouachita System. The northern segment of the anomaly extends eastward across Oklahoma and Arkansas to the Mississippi Embayment. It corresponds to a general positive magnetic region associated with the Wichita Mountains igneous complex in south-central Oklahoma and 1.2 to 1.5 Ga. felsic terrane to the north.

  13. Magnetic monopole interactions: shell structure of meson and baryon states

    SciTech Connect

    Akers, D.

    1986-12-01

    It is suggested that a low-mass magnetic monopole of Dirac charge g = (137/2)e may be interacting with a c-quark's magnetic dipole moment to produce Zeeman splitting of meson states. The mass M/sub 0/ = 2397 MeV of the monopole is in contrast to the 10/sup 16/-GeV monopoles of grand unification theories (GUT). It is shown that shell structure of energy E/sub n/ = M/sub 0/ + 1/4nM/sub 0/... exists for meson states. The presence of symmetric meson states leads to the identification of the shell structure. The possible existence of the 2397-MeV magnetic monopole is shown to quantize quark masses in agreement with calculations of quantum chromodynamics (QCD). From the shell structure of meson states, the existence of two new mesons is predicted: eta(1814 +/- 50 MeV) with I/sup G/(J/sup PC/) = 0/sup +/(0/sup - +/) and eta/sub c/ (3907 +/- 100 MeV) with J/sup PC/ = 0/sup - +/. The presence of shell structure for baryon states is shown.

  14. Magnetic edge-state excitons in zigzag graphene nanoribbons.

    PubMed

    Yang, Li; Cohen, Marvin L; Louie, Steven G

    2008-10-31

    We present first-principles calculations of the optical properties of zigzag-edged graphene nanoribbons (ZGNRs) employing the GW-Bethe-Salpeter equation approach with the spin interaction included. Optical response of the ZGNRs is found to be dominated by magnetic edge-state-derived excitons with large binding energy. The absorption spectrum is composed of a characteristic series of exciton states, providing a possible signature for identifying the ZGNRs. The edge-state excitons are charge-transfer excitations with the excited electron and hole located on opposite edges; they moreover induce a spin transfer across the ribbon, resulting in a photoreduction of the magnetic ordering. These novel characteristics are potentially useful in the applications.

  15. Theory of Magnetic Edge States in Chiral Graphene Nanoribbons

    NASA Astrophysics Data System (ADS)

    Capaz, Rodrigo; Yazyev, Oleg; Louie, Steven

    2011-03-01

    Using a model Hamiltonian approach including electron Coulomb interactions, we systematically investigate the electronic structure and magnetic properties of chiral graphene nanoribbons. We show that the presence of magnetic edge states is an intrinsic feature of any smooth graphene nanoribbons with chiral edges, and discover a number of structure-property relations. Specifically, we describe how the edge-state energy gap, zone-boundary edge-state energy splitting, and magnetic moment per edge length depend on the nanoribbon width and chiral angle. The role of environmental screening effects is also studied. Our results address a recent experimental observation of signatures of magnetic ordering at smooth edges of chiral graphene nanoribbons and provide an avenue towards tuning their properties via the structural and environmental degrees of freedom. This work was supported by National Science Foundation Grant No. DMR10-1006184, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and the ONR MURI program. RBC acknowledges financial support from Brazilian agencies CNPq, FAPERJ and INCT-Nanomateriais de Carbono.

  16. Exploring Magnetic Elastocaloric Materials for Solid-State Cooling

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Zhao, Dewei; Li, Yang

    2017-08-01

    In the past decade, there has been an increased surge in the research on elastocaloric materials for solid-state refrigerators. The strong coupling between structure and magnetism inspires the discovery of new multi-field driven elastocaloric alloys. This work is devoted to magnetic shape memory alloys suitable for mechanical cooling applications. Some novel characteristics in magnetostructural transition materials other than conventional shape memory alloys are overviewed. From the physical and engineering points of view, we have put forward general strategies to maximize elastocaloric temperature change to increase performance reversibility and to improve mechanical properties. The barocaloric effect as a sister-cooling alternative is also discussed.

  17. Algorithmic cooling in liquid-state nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Atia, Yosi; Elias, Yuval; Mor, Tal; Weinstein, Yossi

    2016-01-01

    Algorithmic cooling is a method that employs thermalization to increase qubit purification level; namely, it reduces the qubit system's entropy. We utilized gradient ascent pulse engineering, an optimal control algorithm, to implement algorithmic cooling in liquid-state nuclear magnetic resonance. Various cooling algorithms were applied onto the three qubits of C132-trichloroethylene, cooling the system beyond Shannon's entropy bound in several different ways. In particular, in one experiment a carbon qubit was cooled by a factor of 4.61. This work is a step towards potentially integrating tools of NMR quantum computing into in vivo magnetic-resonance spectroscopy.

  18. Cycloidal versus skyrmionic states in mesoscopic chiral magnets

    NASA Astrophysics Data System (ADS)

    Mulkers, Jeroen; Milošević, Milorad V.; Van Waeyenberge, Bartel

    2016-06-01

    When subjected to the interfacially induced Dzyaloshinskii-Moriya interaction, the ground state in thin ferromagnetic films with high perpendicular anisotropy is cycloidal. The period of this cycloidal state depends on the strength of the Dzyaloshinskii-Moriya interaction. In this work, we have studied the effect of confinement on the magnetic ground state and excited states, and we determined the phase diagram of thin strips and thin square platelets by means of micromagnetic calculations. We show that multiple cycloidal states with different periods can be stable in laterally confined films, where the period of the cycloids does not depend solely on the Dzyaloshinskii-Moriya interaction strength but also on the dimensions of the film. The more complex states comprising skyrmions are also found to be stable, though with higher energy.

  19. A novel experiment using rotating magnetic fields to study the pumping spin states in molecular magnets

    NASA Astrophysics Data System (ADS)

    Hernandez-Minguez, Alberto; Macia, Ferran; Hernandez, Joan Manel; Carbonell, Carla; Amigó, Roger; Tejada, Javier

    2008-03-01

    We report here a new experimental technique to monitor spin population dynamics in molecular magnets. This deals with a huge rotating magnetic field initially applied along the easy magnetization direction, z--axis, that rotates with components parallel and perpendicular to the z axis. This technique allows us to probe spin relaxation on reasonably fast time scales detecting the inversion of the whole spin states. The population of spin levels depends on the frequency of the rotating magnetic field. This very new technique could help to carry out new experiments in a number of different fields, broadening substantially the scope of their use until now. A Hern'andez-M'inguez et al., Appl. Phys. Lett. 91, 202502 (2007)

  20. Multi-Quantum Well Structures to Improve the Performance of Multijunction Solar Cells

    NASA Astrophysics Data System (ADS)

    Samberg, Joshua Paul

    Current, lattice matched triple junction solar cell efficiency is approximately 44% at a solar concentration of 942x. Higher efficiency for such cells can be realized with the development of a 1eV bandgap material lattice matched to Ge. One of the more promising materials for this application is that of the InGaAs/GaAsP multi-quantum well (MQW) structure. By inserting a stress/strain-balanced InGaAs/GaAsP MQW structure into the iregion of a GaAs p-i-n diode, the absorption edge of the p-i-n diode can be red shifted with respect to that of a standard GaAs p-n diode. Compressive stress in the InGaAs wells are balanced via GaAsP barriers subjected to tensile stress. Individually, the InGaAs and GaAsP layers are grown below their critical layer thickness to prevent the formation of misfit and threading dislocations. Until recently InGaAs/GaAsP MQWs have been somewhat hindered by their usage of low phosphorus-GaAsP barriers. Presented within is the development of a high-P composition GaAsP and the merits for using such a high composition of phosphorus are discussed. It is believed that these barriers represent the highest phosphorus content to date in such a structure. By using high composition GaAsP the carriers are collected via tunneling (for barriers .30A) as opposed to thermionic emission. Thus, by utilizing thin, high content GaAsP barriers one can increase the percentage of the intrinsic region in a p-i-n structure that is comprised of the InGaAs well in addition to increasing the number of periods that can be grown for a given depletion width. However, standard MQWs of this type inherently possess undesirable compressive strain and quantum size effects (QSE) that cause the optical absorption of the InGaAs wells to blue shift. To circumvent these deleterious QSEs stress balanced, pseudomorphic InGaAs/GaAsP staggered MQWs were developed. Tunneling is still a viable mode for carrier transport in the staggered MQW structures. GaAs interfacial layers within the multi-quantum

  1. Coherent states for a 2-sphere with a magnetic field

    NASA Astrophysics Data System (ADS)

    Hall, Brian C.; Mitchell, Jeffrey J.

    2012-06-01

    We consider a particle moving on a 2-sphere in the presence of a constant magnetic field. Building on our earlier work in the nonmagnetic case we construct coherent states for this system. The coherent states are labeled by points in the associated phase space, the (co)tangent bundle of S2. They are constructed as eigenvectors for certain annihilation operators and expressed in terms of a certain heat kernel. These coherent states are not of Perelomov type but rather are constructed according to the ‘complexifier’ approach of Thiemann. We describe the Segal-Bargmann representation associated with the coherent states which is equivalent to a resolution of the identity. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Coherent states: mathematical and physical aspects’.

  2. Superconducting plate in a transverse magnetic field: New state

    NASA Astrophysics Data System (ADS)

    Batyev, E. G.

    2012-07-01

    A model is proposed for describing Cooper pairs near the transition (in temperature and magnetic field) point when their spacing is larger than their size. The essence of the model is as follows: the Ginzburg-Landau functional is written in operator form in terms of field operators of the Bose type so that the average value of the density operator gives the concentration of Cooper pairs, and the same Ginzburg-Landau expression is obtained for the Bose condensate. The model is applied to a superconducting plate with a thickness smaller than the size of a pair in a transverse magnetic field near its upper critical value H c2. A new state is discovered that is energetically more advantageous in a certain interval in the vicinity of the transition point as compared to the Abrikosov vortex state. The wavefunction of the system in this state is of the type of the Laughlin function used in the fractional quantum Hall effect (naturally, as applied to Cooper pairs as Bose particles in our case) and corresponds to a homogeneous incompressible fluid. The energy of this state is proportional to the first power of quantity (1 - H/ H c2) in contrast to the energy of the vortex state containing the square of this quantity. The interval of the existence of the new state is the larger, the dirtier the sample.

  3. Superconducting plate in a transverse magnetic field: New state

    SciTech Connect

    Batyev, E. G.

    2012-07-15

    A model is proposed for describing Cooper pairs near the transition (in temperature and magnetic field) point when their spacing is larger than their size. The essence of the model is as follows: the Ginzburg-Landau functional is written in operator form in terms of field operators of the Bose type so that the average value of the density operator gives the concentration of Cooper pairs, and the same Ginzburg-Landau expression is obtained for the Bose condensate. The model is applied to a superconducting plate with a thickness smaller than the size of a pair in a transverse magnetic field near its upper critical value H{sub c2}. A new state is discovered that is energetically more advantageous in a certain interval in the vicinity of the transition point as compared to the Abrikosov vortex state. The wavefunction of the system in this state is of the type of the Laughlin function used in the fractional quantum Hall effect (naturally, as applied to Cooper pairs as Bose particles in our case) and corresponds to a homogeneous incompressible fluid. The energy of this state is proportional to the first power of quantity (1 - H/H{sub c2}) in contrast to the energy of the vortex state containing the square of this quantity. The interval of the existence of the new state is the larger, the dirtier the sample.

  4. Magnetic transitions and Fe(II) spin state in mackinawite

    NASA Astrophysics Data System (ADS)

    Schroeder, C.; Wan, M.; Peiffer, S.

    2012-12-01

    (S=1) state, but not high spin (S=2). Paramagnetic substances which become magnetically ordered below a certain temperature must have unpaired electrons (S≠0). Fe(II) in mackinawite is tetrahedrally coordinated to S, and frontier molecular orbital theory modeling suggests Fe to be either in intermediate spin (S=1) or high spin (S=2) state [7]. Combined with Mössbauer isomer shifts, Fe(II) in mackinawite must therefore be in the intermediate spin (S=1) state. The absence of magnetic ordering in the freshly precipitated and filtered mackinawite sample can be explained by either extremely small particle size resulting in superparamagnetic behavior, or Fe(II) is in a low spin (S=0) state and therefore diamagnetic. In the latter case this phase cannot be mackinawite but may be cubic FeSc, the Fe equivalent of sphalerite (cubic ZnS). References: [1] Wan et al., Mineral. Mag. 75(3) (2011) 2112. [2] Wan et al., Geophysical Research Abstracts 14, EGU2012-4724-3. [3] Hellige et al., Geochim. Cosmochim. Ac. 81 (2012) 69-81. [4] Morice et al., J. inorg. nucl. Chem. 31 (1969) 3797-3802. [5] Vaughan and Ridout, J. inorg. nucl. Chem. 33 (1971) 741-746. [6] Mullet et al., Geochim. Cosmochim. Ac. 66 (2002) 829-836. [7] Luther III, personal communication.

  5. Dynamic control of metastable remanent states in mesoscale magnetic elements

    SciTech Connect

    Ding, J.; Jain, S.; Pearson, J. E.; Lendinez, S.; Khovaylo, V.; Novosad, V.

    2015-05-07

    The formation of the vortex-antivortex-vortex (v-av-v) metastable remanent states in elongated magnetic elements have been systematically investigated using micromagnetic modeling. It is demonstrated that the v-av-v magnetization pattern can be effectively stabilized by exciting the single vortex state with an external RF field. Furthermore, we show that a set of different polarity combinations of the vortex cores can be achieved by adjusting the frequency and amplitude of the excitation field. The corresponding dynamic response in time- and frequency-domain has also been presented. Owing to the diversity of the collective modes with different vortex-antivortex combinations, this system may open promising perspectives in the area of spin transfer torque oscillators.

  6. Tunable Magnetization Dynamics through Solid-State Ligand Substitution Reaction.

    PubMed

    Wang, Long-Fei; Qiu, Jiang-Zhen; Hong, Jun-Yu; Chen, Yan-Cong; Li, Quan-Wen; Jia, Jian-Hua; Jover, Jesús; Ruiz, Eliseo; Liu, Jun-Liang; Tong, Ming-Liang

    2017-08-07

    The dimeric molecule [Dy2(acac)6(MeOH)2(bpe)]·bpe·2MeOH (1, acac = acetylacetonate, bpe = 1,2-bis(4-pyridyl)ethylene) undergoes a solid-state ligand substitution reaction upon heating, leading to the one-dimensional chain [Dy(acac)3(bpe)]n (2). This structural transformation takes advantage of the potential coordination of the guest bpe molecules present in 1. In both complexes the Dy(III) ions adopt similar octacoordinated D4d geometries. However, the different arrangement of the negatively charged and neutral ligands alters the direction of magnetic anisotropy axis and the energy states, thus resulting in largely distinct magnetization dynamics, as revealed by the CASSCF/RASSI calculations.

  7. Observation of Excited State Spin Ordering under Pulsed Magnetic Field

    NASA Astrophysics Data System (ADS)

    Amaya, Kiichi; Karaki, Yoshitomo; Yamada, Norikatsu; Haseda, Taiichiro

    1981-10-01

    Spin ordering among excited levels in NaNi Acac3\\cdotbenzene is observed in the course of pulsed adiabatic magnetization with sweep rate of 105 T/sec. For initial temperatures below 1 K, dM/dt signals give the characteristic double peaks around the field of 2.11 T where the excited singlet and the upper state of the ground doublet crosses.

  8. Thermal Stability of Magnetic States in Circular Thin-Film Nanomagnets with Large Perpendicular Magnetic Anisotropy

    NASA Astrophysics Data System (ADS)

    Chaves-O'Flynn, Gabriel

    The scaling of the energy barrier to magnetization reversal in thin-film nanomagnets with perpendicular magnetization as a function of their lateral size is of great interest and importance for high-density magnetic random access memory devices. Experimental studies of such elements show either a quadratic or linear dependence of the energy barrier on element diameter. I will discuss a theoretical model we developed to determine the micromagnetic configurations that set the energy barrier for thermally activated reversal of a thin disk with perpendicular magnetic anisotropy as a function of disk diameter. We find a critical length in the problem that is set by the exchange and effective perpendicular magnetic anisotropy energies, with the latter including the size dependence of the demagnetization energy. For diameters smaller than this critical length, the reversal occurs by nearly coherent magnetization rotation and the energy barrier scales with the square of the diameter normalized to the critical length (for fixed film thickness), while for larger diameters, the transition state has a domain wall, and the energy barrier depends linearly on the normalized diameter. Simple analytic expressions are derived for these two limiting cases and verified using full micromagnetic simulations with the string method. Further, the effect of an applied field is considered and shown to lead to a plateau in the energy barrier versus diameter dependence at large diameters. Based on these finding I discuss the prospects and material challenges in the scaling of magnetic memory devices based on thin films with strong perpendicular magnetic anisotropy. In collaboration with G. Wolf, J. Z. Sun and A. D. Kent. Supported by NSF-DMR-1309202 and in part by Spin Transfer Technologies Inc. and the Nanoelectronics Research Initiative through the Institute for Nanoelectronics Discovery and Exploration.

  9. Relativistic Killingbeck energy states under external magnetic fields

    NASA Astrophysics Data System (ADS)

    Eshghi, M.; Mehraban, H.; Ikhdair, S. M.

    2016-07-01

    We address the behavior of the Dirac equation with the Killingbeck radial potential including the external magnetic and Aharonov-Bohm (AB) flux fields. The spin and pseudo-spin symmetries are considered. The correct bound state spectra and their corresponding wave functions are obtained. We seek such a solution using the biconfluent Heun's differential equation method. Further, we give some of our results at the end of this study. Our final results can be reduced to their non-relativistic forms by simply using some appropriate transformations. The spectra, in the spin and pseudo-spin symmetries, are very similar with a slight difference in energy spacing between different states.

  10. Quantum well intermixing and radiation effects in InGaN/GaN multi quantum wells

    NASA Astrophysics Data System (ADS)

    Lorenz, K.; Redondo-Cubero, A.; Lourenço, M. B.; Sequeira, M. C.; Peres, M.; Freitas, A.; Alves, L. C.; Alves, E.; Leitão, M. P.; Rodrigues, J.; Ben Sedrine, N.; Correia, M. R.; Monteiro, T.

    2016-02-01

    Compositional grading of InGaN/GaN multi quantum wells (QWs) was proposed to mitigate polarization effects and Auger losses in InGaN-based light emitting diodes [K. P. O'Donnell et al., Phys. Status Solidi RRL 6 (2012) 49]. In this paper we are reviewing our recent attempts on achieving such gradient via quantum well intermixing. Annealing up to 1250 °C resulted in negligible interdiffusion of QWs and barriers revealing a surprising thermal stability well above the typical MOCVD growth temperatures. For annealing at 1400 °C results suggest a decomposition of the QWs in regions with high and low InN content. The defect formation upon nitrogen implantation was studied in detail. Despite strong dynamic annealing effects, which keep structural damage low, the created defects strongly quench the QW luminescence even for low implantation fluences. This degradation could not be reversed during thermal annealing and is hampering the use of implantation induced quantum well intermixing in InGaN/GaN structures.

  11. Investigation of temperature-dependent photoluminescence in multi-quantum wells

    PubMed Central

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-01-01

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells. PMID:26228734

  12. Investigation of temperature-dependent photoluminescence in multi-quantum wells.

    PubMed

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-07-31

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

  13. Investigation of carrier collection in multi-quantum well solar cells by luminescence spectra analysis

    NASA Astrophysics Data System (ADS)

    Delamarre, Amaury; Fujii, Hiromasa; Watanabe, Kentaroh; Guillemoles, Jean-François; Nakano, Yoshiaki; Sugiyama, Masakazu

    2015-03-01

    Multi-Quantum well solar cells (MQWSC) have been shown to present several advantages, among which are low dark currents and tunable bandgaps. They are especially suited for implementation in multi-junction cells, and are highly promising for absorbers in Hot Carrier Solar Cells (HCSC). Such applications require high concentration ratio, which arises the issue of collection efficiency. Whereas it is usually considered that collection in MQW is very close to unity at one sun, it has been shown to not be the case under high concentration at the maximum power point. We propose in this work to take advantage of the luminescence spectral variation to investigate the depth collection efficiency. In order to validate the model, a series of strain compensated InGaAs/GaAsP MQW solar cells with intentional variation of the MQW doping concentration are grown. This has the effect of switching the space charge region position and width as well as the electric field intensity. Recording the luminescence spectra at various illumination intensities and applied voltages, we show that the in-depth quasi-Fermi level splitting and thus collection properties can be probed. Other measurements (EQE, luminescence intensity variation) are shown to be consistent with these results. Regarding their use as HCSC, the luminescence of MQW solar cells has been mainly used so far for investigating the quasi-Fermi level splitting and the temperature. Our results improve our understanding by adding information on carrier transport.

  14. Radiation response of multi-quantum well solar cells: Electron-beam-induced current analysis

    NASA Astrophysics Data System (ADS)

    Maximenko, S. I.; Lumb, M. P.; Hoheisel, R.; Gonzalez, M.; Scheiman, D. A.; Messenger, S. R.; Tibbits, T. N. D.; Imaizumi, M.; Ohshima, T.; Sato, S. I.; Jenkins, P. P.; Walters, R. J.

    2015-12-01

    Solar cells utilizing multi-quantum well (MQW) structures are considered promising candidate materials for space applications. An open question is how well these structures can resist the impact of particle irradiation. The aim of this work is to provide feedback about the radiation response of In0.01Ga0.99As solar cells grown on Ge with MQWs incorporated within the i-region of the device. In particular, the local electronic transport properties of the MQW i-regions of solar cells subjected to electron and proton irradiation were evaluated experimentally using the electron beam induced current (EBIC) technique. The change in carrier collection distribution across the MQW i-region was analyzed using a 2D EBIC diffusion model in conjunction with numerical modeling of the electrical field distribution. Both experimental and simulated findings show carrier removal and type conversion from n- to p-type in MQW i-region at a displacement damage dose as low as ˜6.06-9.88 × 109 MeV/g. This leads to a redistribution of the electric field and significant degradation in charge carrier collection.

  15. Radiation response of multi-quantum well solar cells: Electron-beam-induced current analysis

    SciTech Connect

    Maximenko, S. I. Scheiman, D. A.; Jenkins, P. P.; Walters, R. J.; Lumb, M. P.; Hoheisel, R.; Gonzalez, M.; Messenger, S. R.; Tibbits, T. N. D.; Imaizumi, M.; Ohshima, T.; Sato, S. I.

    2015-12-28

    Solar cells utilizing multi-quantum well (MQW) structures are considered promising candidate materials for space applications. An open question is how well these structures can resist the impact of particle irradiation. The aim of this work is to provide feedback about the radiation response of In{sub 0.01}Ga{sub 0.99}As solar cells grown on Ge with MQWs incorporated within the i-region of the device. In particular, the local electronic transport properties of the MQW i-regions of solar cells subjected to electron and proton irradiation were evaluated experimentally using the electron beam induced current (EBIC) technique. The change in carrier collection distribution across the MQW i-region was analyzed using a 2D EBIC diffusion model in conjunction with numerical modeling of the electrical field distribution. Both experimental and simulated findings show carrier removal and type conversion from n- to p-type in MQW i-region at a displacement damage dose as low as ∼6.06–9.88 × 10{sup 9} MeV/g. This leads to a redistribution of the electric field and significant degradation in charge carrier collection.

  16. Nuclear Magnetic Moment of the {sup 57}Cu Ground State

    SciTech Connect

    Minamisono, K.; Mertzimekis, T.J.; Pereira, J.; Mantica, P.F.; Pinter, J.S.; Stoker, J.B.; Tomlin, B.E.; Weerasiri, R.R.; Davies, A.D.; Hass, M.; Rogers, W.F.

    2006-03-17

    The nuclear magnetic moment of the ground state of {sup 57}Cu(I{sup {pi}}=3/2{sup -},T{sub 1/2}=196.3 ms) has been measured to be vertical bar {mu}({sup 57}Cu) vertical bar =(2.00{+-}0.05){mu}{sub N} using the {beta}-NMR technique. Together with the known magnetic moment of the mirror partner {sup 57}Ni, the spin expectation value was extracted as <{sigma}{sigma}{sub z}>=-0.78{+-}0.13. This is the heaviest isospin T=1/2 mirror pair above the {sup 40}Ca region for which both ground state magnetic moments have been determined. The discrepancy between the present results and shell-model calculations in the full fp shell giving {mu}({sup 57}Cu){approx}2.4{mu}{sub N} and <{sigma}{sigma}{sub z}>{approx}0.5 implies significant shell breaking at {sup 56}Ni with the neutron number N=28.

  17. Vortex states in a non-Abelian magnetic field

    NASA Astrophysics Data System (ADS)

    Nikolić, Predrag

    2016-08-01

    A type-II superconductor survives in an external magnetic field by admitting an Abrikosov lattice of quantized vortices. This is an imprint of the Aharonov-Bohm effect created by the Abelian U(1) gauge field. The simplest non-Abelian analog of such a gauge field, which belongs to the SU(2) symmetry group, can be found in topological insulators. Here we discover a superconducting ground state with a lattice of SU(2) vortices in a simple two-dimensional model that presents an SU(2) "magnetic" field (invariant under time reversal) to attractively interacting fermions. The model directly captures the correlated topological insulator quantum well, and approximates one channel for instabilities on the Kondo topological insulator surface. Due to its simplicity, the model might become amenable to cold atom simulations in the foreseeable future. The vitality of low-energy vortex states born out of SU(2) magnetic fields is promising for the creation of incompressible vortex liquids with non-Abelian fractional excitations.

  18. Magnetic resonance force microscopy and a solid state quantum computer.

    SciTech Connect

    Pelekhov, D. V.; Martin, I.; Suter, A.; Reagor, D. W.; Hammel, P. C.

    2001-01-01

    A Quantum Computer (QC) is a device that utilizes the principles of Quantum Mechanics to perform computations. Such a machine would be capable of accomplishing tasks not achievable by means of any conventional digital computer, for instance factoring large numbers. Currently it appears that the QC architecture based on an array of spin quantum bits (qubits) embedded in a solid-state matrix is one of the most promising approaches to fabrication of a scalable QC. However, the fabrication and operation of a Solid State Quantum Computer (SSQC) presents very formidable challenges; primary amongst these are: (1) the characterization and control of the fabrication process of the device during its construction and (2) the readout of the computational result. Magnetic Resonance Force Microscopy (MRFM)--a novel scanning probe technique based on mechanical detection of magnetic resonance-provides an attractive means of addressing these requirements. The sensitivity of the MRFM significantly exceeds that of conventional magnetic resonance measurement methods, and it has the potential for single electron spin detection. Moreover, the MRFM is capable of true 3D subsurface imaging. These features will make MRFM an invaluable tool for the implementation of a spin-based QC. Here we present the general principles of MRFM operation, the current status of its development and indicate future directions for its improvement.

  19. Tuning the magnetic ground state of a triangular lattice system

    SciTech Connect

    Garlea, Vasile O; Savici, Andrei T; Jin, Rongying

    2011-01-01

    The anisotropic triangular lattice of the crednerite system Cu(Mn$_{1-x}$Cu$_{x}$)O$_{2}$ is used as a basic model for studying the influence of spin disorder on the ground state properties of a two-dimensional frustrated antiferromagnet. Neutron diffraction measurements show that the undoped phase (x=0) undergoes a transition to antiferromagnetic long-range order that is stabilized by a frustration-relieving structural distortion. Small deviation from the stoichiometric composition alters the magnetoelastic characteristics and reduces the effective dimensionality of the magnetic lattice. Upon increasing the doping level, the interlayer coupling changes from antiferromagnetic to ferromagnetic, while the structural distortion is fully suppressed. Concomitantly, the long-range magnetic order is gradually transformed into a two-dimensional order.

  20. Magnetic edge states in Aharonov-Bohm graphene quantum rings

    SciTech Connect

    Farghadan, R. Heidari Semiromi, E.; Saffarzadeh, A.

    2013-12-07

    The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zero and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.

  1. Solid-state dewetting of magnetic binary multilayer thin films

    NASA Astrophysics Data System (ADS)

    Esterina, Ria; Liu, X. M.; Adeyeye, A. O.; Ross, C. A.; Choi, W. K.

    2015-10-01

    We examined solid-state dewetting behavior of magnetic multilayer thin film in both miscible (CoPd) and immiscible (CoAu) systems and found that CoPd and CoAu dewetting stages follow that of elemental materials. We established that CoPd alloy morphology and dewetting rate lie in between that of the elemental materials. Johnson-Mehl-Avrami analysis was utilized to extract the dewetting activation energy of CoPd. For CoAu, Au-rich particles and Co-rich particles are distinguishable and we are able to predict the interparticle spacings and particle densities for the particles that agree well with the experimental results. We also characterized the magnetic properties of CoPd and CoAu nanoparticles.

  2. Electrical determination of vortex state in submicron magnetic elements

    NASA Astrophysics Data System (ADS)

    Gangwar, Ajay; Bauer, Hans G.; Chauleau, Jean-Yves; Noske, Matthias; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Back, Christian H.

    2015-03-01

    We have studied vortex dynamics excited by the spin-transfer-torque effect and find that the direction of the vortex state can be detected electrically using the homodyne voltage signal generated due to the anisotropic magnetoresistance (AMR) effect. An external in-plane dc magnetic field is required to break the cylindrical symmetry in order to obtain a dc response of the homodyne signal. The sign of this rectified voltage changes with the handedness of the vortex state, which makes it a promising method to detect the vortex state electrically. Vortex dynamics is also observed by direct imaging in a scanning transmission x-ray microscope, allowing verification of the measured AMR signal in the correct power and frequency range. The results of micromagnetic simulations are in good agreement with the experimental data.

  3. Adiabatic state preparation of stripe phases with strongly magnetic atoms

    NASA Astrophysics Data System (ADS)

    Mazloom, Azadeh; Vermersch, Benoît; Baranov, Mikhail A.; Dalmonte, Marcello

    2017-09-01

    We propose a protocol for realizing the stripe phase in two spin models on a two-dimensional square lattice, which can be implemented with strongly magnetic atoms (Cr, Dy, Er, etc.) in optical lattices by encoding spin states into Zeeman sublevels of the ground-state manifold. The protocol is tested with cluster-mean-field time-dependent variational Ansätze, validated by comparison with exact results for small systems, which enable us to simulate the dynamics of systems with up to 64 sites during the state-preparation protocol. This allows us, in particular, to estimate the time required for preparation of the stripe phase with high fidelity under real experimental conditions.

  4. The effect of magnetic and non-magnetic ion damage on the surface state in SmB6

    DOE PAGES

    Wakeham, N.; Wen, J.; Wang, Y. Q.; ...

    2015-07-14

    SmB6 is a Kondo insulator with a band structure that is topologically distinct from the vacuum. We theoretically predict this in order to produce metallic topological surface states that are robust to perturbations that do not break time reversal symmetry, such as non-magnetic defects. But, the surface state may be destroyed by an impurity with a sufficiently large magnetic moment. In order to test this prediction we show measurements of the resistance of the surface state of single crystals of SmB6 with varying levels of damage induced by magnetic and non-magnetic ion irradiation. Finally, we find that at a sufficientlymore » high concentration of damage the surface state reconstructs below an amorphous damaged layer, whether the damage was caused by a magnetic or non-magnetic ion.« less

  5. Magnetic switching behaviors of orbital states with different magnetic quantum numbers in Au/Fe/MgO multilayer system

    SciTech Connect

    Suzuki, Kosuke Takubo, Shota; Kato, Tadashi; Yamazoe, Masatoshi; Hoshi, Kazushi; Sakurai, Hiroshi; Homma, Yoshiya; Itou, Masayoshi; Sakurai, Yoshiharu

    2014-08-18

    A spin specific magnetic hysteresis (SSMH) curve and an orbital specific magnetic hysteresis (OSMH) curve are obtained for Fe/Au/Fe/MgO multilayers by magnetic Compton scattering and SQUID magnetometer measurements. The SSMH curve with each contribution of magnetic quantum number |m| = 0, 1, and 2 states is obtained by decomposition analyses of magnetic Compton profiles. Residual magnetization is observed for the SSMH curve with magnetic quantum number |m| = 0, 2 and the OSMH curve. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the present Fe/Au/Fe/MgO multilayer film, the SSMH curve with magnetic quantum number |m| = 0, 2 and OSMH curve show switching behaviors of PMA.

  6. Magnetic switching behaviors of orbital states with different magnetic quantum numbers in Au/Fe/MgO multilayer system

    NASA Astrophysics Data System (ADS)

    Suzuki, Kosuke; Takubo, Shota; Kato, Tadashi; Yamazoe, Masatoshi; Hoshi, Kazushi; Homma, Yoshiya; Itou, Masayoshi; Sakurai, Yoshiharu; Sakurai, Hiroshi

    2014-08-01

    A spin specific magnetic hysteresis (SSMH) curve and an orbital specific magnetic hysteresis (OSMH) curve are obtained for Fe/Au/Fe/MgO multilayers by magnetic Compton scattering and SQUID magnetometer measurements. The SSMH curve with each contribution of magnetic quantum number |m| = 0, 1, and 2 states is obtained by decomposition analyses of magnetic Compton profiles. Residual magnetization is observed for the SSMH curve with magnetic quantum number |m| = 0, 2 and the OSMH curve. Although the SQUID magnetometer measurements do not show perpendicular magnetic anisotropy (PMA) in the present Fe/Au/Fe/MgO multilayer film, the SSMH curve with magnetic quantum number |m| = 0, 2 and OSMH curve show switching behaviors of PMA.

  7. Novel states of matter with ultracold magnetic lanthanides

    NASA Astrophysics Data System (ADS)

    Kotochigova, Svetlana

    2016-05-01

    Ultracold atomic physics is now poised to enter a new regime, where far-more complex atomic species can be cooled and studied. Magnetic lanthanide atoms with their large magnetic moment and large orbital momentum are extreme examples of such species. In fact, ultracold gases of magnetic lanthanides provide the opportunity to examine strongly correlated matter, creating a platform to explore exotic many-body phases such as quantum ferrofluids, quantum liquid crystals, and supersolids. Experimental advances in trapping and cooling magnetic Dy and Er atoms are paving the way towards these goals. Over the last few years we have developed a framework for understanding the complex anisotropic interactions between magnetic lanthanide atoms. Our theoretical model uses novel tools and advanced numerical treatments to describe the underlying mechanism that generates correlations and chaos in dipolar scattering and bridges the enormous conceptual gap between simple atoms and complex molecules. This allows us to explain the origin of the dense spectra and statistics of the observed Er and Dy collisional resonances due to the anisotropy of the short- and long-range interactions between the atoms. We also study the distribution of the values of the molecular wave functions to isolate Anderson-type localized states within chaotic structures and confirm the existence of an intermediate chaotic regime. In addition, our model for the three-body recombination via the formation of a resonant trimer has identified the origin of the temperature-sensitive resonance density observed in both Er and Dy collisions as due to d-wave entrance channel collisions. This work is supported by AFOSR (No. FA9550-14-1-0321) and NSF (No. PHY-1308573) grants.

  8. Progressive Transformation between Two Magnetic Ground States for One Crystal Structure of a Chiral Molecular Magnet.

    PubMed

    Li, Li; Nishihara, Sadafumi; Inoue, Katsuya; Kurmoo, Mohamedally

    2016-03-21

    We report the exceptional observation of two different magnetic ground states (MGS), spin glass (SG, T(B) = 7 K) and ferrimagnet (FI, T(C) = 18 K), for one crystal structure of [{Mn(II)(D/L-NH2ala)}3{Mn(III)(CN)6}]·3H2O obtained from [Mn(CN)6](3-) and D/L-aminoalanine, in contrast to one MGS for [{Mn(II)(L-NH2ala)}3{Cr(III)(CN)6}]·3H2O. They consist of three Mn(NH2ala) helical chains bridged by M(III)(CN)6 to give the framework with disordered water molecules in channels and between the M(III)(CN)6. Both MGS are characterized by a negative Weiss constant, bifurcation in ZFC-FC magnetizations, blocking of the moments, both components of the ac susceptibilities, and hysteresis. They differ in the critical temperatures, absolute magnetization for 5 Oe FC (lack of spontaneous magnetization for the SG), and the shapes of the hysteresis and coercive fields. While isotropic pressure increases both T(crit) and the magnetizations linearly and reversibly in each case, dehydration progressively transforms the FI into the SG as followed by concerted in situ magnetic measurements and single-crystal diffraction. The relative strengths of the two moderate Mn(III)-CN-Mn(II) antiferromagnetic (J1 and J2), the weak Mn(II)-OCO-Mn(II) (J3), and Dzyaloshinkii-Moriya antisymmetric (DM) interactions generate the two sets of characters. Examination of the bond lengths and angles for several crystals and their corresponding magnetic properties reveals a correlation between the distortion of Mn(III)(CN)6 and the MGS. SG is favored by higher magnetic anisotropy by less distorted Mn(III)(CN)6 in good accordance with the Mn-Cr system. This conclusion is also born out of the magnetization measurements on orientated single crystals with fields parallel and perpendicular to the unique c axis of the hexagonal space group.

  9. Majorana edge states in superconductor-noncollinear magnet interfaces

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Schnyder, Andreas P.

    2015-12-01

    Through s -d coupling, a superconducting thin film interfaced to a noncollinear magnetic insulator inherits its magnetic order, which may induce unconventional superconductivity that hosts Majorana edge states. We present a unified formalism that covers the cycloidal, helical, and tilted conical order discovered in multiferroics, as well as Bloch and Neel domain walls of ferromagnetic insulators, and show that they induce (px+py )-wave pairing that supports Majorana edge modes. The advantages over one-dimensional proposals are that the Majorana states can exist without fine tuning of the chemical potential, can be stabilized in a much larger parameter space, and can be separated over the distance of long-range noncollinear order that is known to reach a macroscopic scale. A skyrmion spin texture, on the other hand, induces a nonuniform (pr+i pφ )-wave-like pairing under the influence of an emergent electromagnetic field, yielding a vortex state that displays both a bulk persistent current and a topological edge current.

  10. Raman transitions between hyperfine clock states in a magnetic trap

    NASA Astrophysics Data System (ADS)

    Naber, J. B.; Torralbo-Campo, L.; Hubert, T.; Spreeuw, R. J. C.

    2016-07-01

    We present our experimental investigation of an optical Raman transition between the magnetic clock states of 87Rb in an atom chip magnetic trap. The transfer of atomic population is induced by a pair of diode lasers which couple the two clock states off-resonantly to an intermediate state manifold. This transition is subject to destructive interference of two excitation paths, which leads to a reduction of the effective two-photon Rabi frequency. Furthermore, we find that the transition frequency is highly sensitive to the intensity ratio of the diode lasers. Our results are well described in terms of light shifts in the multilevel structure of 87Rb. The differential light shifts vanish at an optimal intensity ratio, which we observe as a narrowing of the transition linewidth. We also observe the temporal dynamics of the population transfer and find good agreement with a model based on the system's master equation and a Gaussian laser beam profile. Finally, we identify several sources of decoherence in our system, and discuss possible improvements.

  11. Muon-fluorine entangled states in molecular magnets.

    PubMed

    Lancaster, T; Blundell, S J; Baker, P J; Brooks, M L; Hayes, W; Pratt, F L; Manson, J L; Conner, M M; Schlueter, J A

    2007-12-31

    The information accessible from a muon-spin relaxation experiment can be limited due to a lack of knowledge of the precise muon stopping site. We demonstrate here the possibility of localizing a spin polarized muon in a known stopping state in a molecular material containing fluorine. The muon-spin precession that results from the entangled nature of the muon spin and surrounding nuclear spins is sensitive to the nature of the stopping site. We use this property to identify three classes of sites that occur in molecular magnets and describe the extent to which the muon distorts its surroundings.

  12. Manipulation of Magnetization States of Permalloy Nanorings by an External Azimuthal Field

    NASA Astrophysics Data System (ADS)

    Yang, Tianyu; Pradhan, Nihar; Goldman, Abby; Kemei, Moureen; Licht, Abbey; Li, Yihan; Tuominen, Mark; Aidala, Katherine

    2011-03-01

    This experimental research investigates a new method of manipulating the magnetic states of ferromagnetic nanorings using a circular magnetic field directed along the ring circumference. This type of azimuthal field can naturally select a vortex magnetization of desired chirality. The understanding of the magnetization switching behavior in an azimuthal field could lead to new designs of practical magnetic data storage devices. Symmetric and asymmetric nanorings made of permalloy are fabricated by a standard technique using electron-beam lithography and e-beam evaporation. Azimuthal fields are generated by passing current through an atomic force microscope tip, which is positioned at the center of the ring. The magnetic field direction and magnitude are controlled by the current. We demonstrate control over switching from an onion state to a vortex state, and also between two vortex states, using magnetic force microscopy to image the resulting magnetic states. This work was supported by NSF grants DMR-0907201 CMMI-0531171.

  13. Nuclear magnetic resonance of iron and copper disease states

    SciTech Connect

    Runge, V.M.; Clanton, J.A.; Smith, F.W.; Hutchison, J.; Mallard, J.; Partain, C.L.; James, A.E. Jr.

    1983-11-01

    The tissue levels of paramagnetic ions are an important factor in the determination of T/sub 1/ values as observed by nuclear magnetic resonance (NMR) imaging. The increased levels of iron present in human disease states such as hemochromatosis lead to decreased T/sub 1/ values. The mean liver T/sub 1/ of three patients with iron storage disease was determined to be 130 msec, significantly different from the value of 154 msec, the mean for 14 normal controls. Whether NMR will be able to detect the increased copper levels in liver and brain in Wilson disease remains for further clinical trials to evaluate. NMR imaging, however, does serve as a noninvasive method for the diagnosis of states of iron overload and as a technique to follow progression of disease or response to medical therapy.

  14. Inhomogeneities in spin states and magnetization reversal of geometrically identical elongated Co rings

    NASA Astrophysics Data System (ADS)

    Gao, X. S.; Adeyeye, A. O.; Goolaup, S.; Singh, N.; Jung, W.; Castaño, F. J.; Ross, C. A.

    2007-05-01

    The magnetic configurations and magnetic reversal processes in arrays of geometrically identical rounded rectangular Co rings have been investigated. Magnetic imaging reveals a range of configurations, including diagonal onion, horseshoe onion, and vortex states. Reversal from the onion to the vortex state can occur via different routes involving domain wall motion within the rings, and the mechanism depends on the applied field orientation.

  15. Resistive states of the composite superconductors at magnetic flux creep

    NASA Astrophysics Data System (ADS)

    Romanovskii, V. R.

    2017-04-01

    The effect of magnetic flux creep on the formation of resistive states of the composite superconductors has been studied taking into account their self-heating. The obtained results have been compared with the calculations carried out using the existing thermal stabilization theory, which is based on the model of a stepwise transition from the superconducting to normal state. It has been shown that, over a wide range of the superconductor temperature, this model leads to overrated effective electric resistances of the composite. As a result of its stable self-heating, the notions on the critical current, which determine the maximum transport current and on the resistive transition temperature, the higher of which in the transport current begins dividing between the superconductor and matrix, a loss a physical sense at magnetic flux creep, are used in the existing thermal stabilization theory. As a result, the limits of the theory of thermal stabilization of the composite superconductors can be extended if the theory has been used to describe stable sates at currents, which are higher than the conditionally defined critical current of the composite.

  16. Gravitational Steady States of Coronal Loops as Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Sugiyama, L.; Asgari-Targhi, M.

    2016-12-01

    Many coronal loops observed on the surface of the sun appear to bemagnetic flux ropes containing plasma, with ends tied in the photosphere. Different types of loops contribute to important solar processes, but relatively little is known about their configuration.Like all toroidal confined, curved plasmas carrying current,they are intrinsically unstable to expansion in major radius.Consistent 3D MHD steady states are derived for the coronal partof the loop, including non-negligible effects due to the plasma pressure and solar gravity. Most loops have relativelyslender inverse aspect ratios ɛ =a/R≤ 1.For predominantly simple, non-helical loops, three gravitationally stabilized asymptotic solutions can be foundthat can be related to toroidal magnetically confined plasams.Comparison to observations shows thattwo solutions bracket the observed heights R<108m of the common thin coronal loops (ɛ ˜ 0.02) in solar active regions.The third solution better describes the fatter loops (ɛ ˜ 0.1)that sometimes appear along the magnetic neutral line in an active regionand grow to produce solar flares or coronal mass ejections.Since radial expansion is higher order than the basic flux ropeconfinement, the states also approximately describe radially unstable loops over similar heights.The solutions can also be generalized to other stabilizing mechanismsand may provide a useful basis for studies of loop dynamics.

  17. X-ray diffraction simulation of GeSn/Ge multi-quantum wells with kinematic approach

    NASA Astrophysics Data System (ADS)

    Li, Hui; Chang, Chiao; Cheng, Hung-Hsiang

    2017-06-01

    We report an investigation on X-ray diffraction simulation of GeSn/Ge Multi-quantum wells (MQWs) with kinematic approach. X-ray diffraction in (004) ω-2θ scan and (224) reciprocal space mapping are performed for characterization of the MQWs. However, simulation of the diffraction process is imperative for further structural analysis of the MQWs. The compressive strain not only affects the calculation of Sn composition in GeSn wells, but also dramatically affects the symmetry of satellite peaks.

  18. Design of monocrystalline Si/SiGe multi-quantum well microbolometer detector for infrared imaging systems

    NASA Astrophysics Data System (ADS)

    Shafique, Atia; Durmaz, Emre C.; Cetindogan, Barbaros; Yazici, Melik; Kaynak, Mehmet; Kaynak, Canan B.; Gurbuz, Yasar

    2016-05-01

    This paper presents the design, modelling and simulation results of silicon/silicon-germanium (Si/SiGe) multi-quantum well based bolometer detector for uncooled infrared imaging system. The microbolometer is designed to detect light in the long wave length infrared (LWIR) range from 8 to 14 μm with pixel size of 25 x 25 μm. The design optimization strategy leads to achieve the temperature coefficient of resistance (TCR) 4.5%/K with maximum germanium (Ge) concentration of 50%. The design of microbolometer entirely relies on standard CMOS and MEMS processes which makes it suitable candidate for commercial infrared imaging systems.

  19. Stress state evaluation in low carbon and TRIP steels by magnetic permeability

    NASA Astrophysics Data System (ADS)

    Kouli, M.-E.; Giannakis, M.

    2016-03-01

    Magnetic permeability is an indicative factor for the steel health monitoring. The measurements of magnetic permeability lead to the evaluation of the stress state of any ferromagnetic steel. The magnetic permeability measurements were conducted on low carbon and TRIP steel samples, which were subjected to both tensile and compressive stresses. The results indicated a direct correlation of the magnetic permeability with the mechanical properties, the stress state and the microstructural features of the examined samples.

  20. Solid-State Molecular Nanomagnet Inclusion into a Magnetic Metal-Organic Framework: Interplay of the Magnetic Properties.

    PubMed

    Mon, Marta; Pascual-Álvarez, Alejandro; Grancha, Thais; Cano, Joan; Ferrando-Soria, Jesús; Lloret, Francesc; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

    2016-01-11

    Single-ion magnets (SIMs) are the smallest possible magnetic devices and are a controllable, bottom-up approach to nanoscale magnetism with potential applications in quantum computing and high-density information storage. In this work, we take advantage of the promising, but yet insufficiently explored, solid-state chemistry of metal-organic frameworks (MOFs) to report the single-crystal to single-crystal inclusion of such molecular nanomagnets within the pores of a magnetic MOF. The resulting host-guest supramolecular aggregate is used as a playground in the first in-depth study on the interplay between the internal magnetic field created by the long-range magnetic ordering of the structured MOF and the slow magnetic relaxation of the SIM. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Spin polarized photoemission studies of magnetic quantum well states

    SciTech Connect

    Johnson, P.D.

    1994-12-01

    There is currently considerable technological interest in the properties of transition metal multilayers. In these multilayers, which include Fe/Cr(001) and Cu/Co(001), it is possible to achieve either ferromagnetic or antiferromagnetic coupling of the adjacent ferromagnetic layers depending on the thickness of the intervening layer. The related giant magnetoresistance properties and the large enhancement of the Kerr rotation in these systems make them particularly interesting. In this paper, quantum well states with discrete binding energies dependent on the thickness of the film are observed in copper films deposited on a Co(001) substrate. They are found to be spin polarized, preferentially with minority spin. These states pass up to and through the Fermi level with a frequency identical to the long period of oscillation in the associated magnetic multilayers. In the pre-asymptotic limit the dispersion of these states away from the center of the zone is described by enhanced effective masses. This has implications for theories of the oscillatory exchange coupling that invoke the bulk Fermi surface.

  2. Prediction of magnetic substorms using a state space model

    NASA Astrophysics Data System (ADS)

    Unnikrishnan, K.

    2012-02-01

    Nonlinear dynamical models of the magnetosphere derived from observational time series data using phase space reconstruction techniques have yielded new advances in the understanding of its dynamics. Considering the solar wind-magnetosphere interaction to be a natural input-output system its dynamical features can be reconstructed on the storm time scale by using the method of time delay embedding. Here, fourteen magnetic storm intervals belonging to low/moderate and high solar activity periods are considered and a suitable state space model has designed by performing training and validation tests, for which dawn to dusk electric field (VBz) is chosen as the input, and the AL time series as the output. The percentage of the output variations that is reproduced by the model is termed as fit_model and a higher number of fit_model means a better model. The number of components m used in the state space model is varied from 1-9 and the best prediction is obtained when m=4. The fit_model values of time series used for validation are 67.96, 67.2, 72.44, and 70.89, with m=4. In the present study most of the storms considered are having Dstmax in between -100 and -300 nT, and they can be predicted well with this procedure. To reveal the prediction capability of the proposed state space model the 30 steps ahead outputs for the storm events are generated, which reasonably reproduce the observed values.

  3. Electronic structure and magnetic state of transuranium metals under pressure.

    PubMed

    Lukoyanov, A V; Shorikov, A O; Bystrushkin, V B; Dyachenko, A A; Kabirova, L R; Tsiovkin, Yu Yu; Povzner, A A; Dremov, V V; Korotin, M A; Anisimov, V I

    2010-12-15

    The electronic structures of bcc Np, fcc Pu, Am, and Cm pure metals under pressure have been investigated employing the LDA + U method with spin-orbit coupling (LDA + U + SO). The magnetic state of the actinide ions was analyzed in both LS and jj coupling schemes to reveal the applicability of corresponding coupling bases. It was demonstrated that whereas Pu and Am are well described within the jj coupling scheme, Np and Cm can be described appropriately neither in a {mσ}, nor in a {jmj} basis, due to intermediate coupling scheme realization in these metals that requires some finer treatment. The LDA + U + SO results for the considered transuranium metals reveal band broadening and gradual 5f electron delocalization under pressure.

  4. State interrogation in nuclear magnetic resonance quantum-information processing

    SciTech Connect

    Leskowitz, Garett M.; Mueller, Leonard J.

    2004-05-01

    Reconstruction of a reduced density operator for weakly coupled systems of spins (1/2) from fits to nuclear magnetic resonance spectra is described in detail. Particular emphasis is placed on data treatment procedures that specify fewer than the 3{sup n} complete spectra that are implicitly prescribed in published references to state tomography on n-spin systems. It is shown that if the density operator is expanded in the so-called product-operator basis, it is always possible to estimate a desired coefficient in the expansion by measuring a single spectral multiplet. This simple observation can substantially reduce the experimental effort required for either complete density-matrix reconstruction or estimation of subsets of the coefficients in the product-operator expansion. A simple iterative algorithm can be used to produce reduced measurement procedures for experiments involving small numbers of qubits.

  5. Dependence of device performance on carrier escape sequence in multi-quantum-well p-i-n solar cells

    NASA Astrophysics Data System (ADS)

    Alemu, A.; Coaquira, J. A. H.; Freundlich, A.

    2006-04-01

    This work is a study relating device performance and carrier escape sequence in a large set of InAsP/InP p-i-n multi-quantum-well solar cells. The devices encompass nearly identical i-region thickness and built-in electric field and present similar absorption threshold energies. The escape sequence of the first confined electron-to-conduction band continuum and heavy/light holes-to-valence band continuum is extracted from the photoluminescence versus temperature analysis and by comparing the measured activation energies to calculated hole/electron well depths and thermionic escape times. Light holes, as expected for most III-V nanostructure systems, are found to be the fastest escaping carriers in all samples. The escape of electrons prior to heavy holes is shown to be a prerequisite to prevent severe open circuit voltage degradation. A possible explanation of the origin of this effect is offered. InP/InAsP multi-quantum-well solar cells with high built-in electric field and fast electronic escape time display better open circuit voltage and performance.

  6. Role of Fe magnetic subsystems to form a magnetic spin glass state in RFeTi2O7

    NASA Astrophysics Data System (ADS)

    Drokina, T. V.; Petrakovskii, G. A.; Bayukov, O. A.; Molokeev, M. S.; Bartolomé, J.; Arauzo, A.

    2017-10-01

    The experimental studies on R3+Fe3+Ti2O7 (R=Sm, Gd, Tb, Tm, Dy) magnetic properties evidence the low temperature spin glass state in all compounds. The possibility of rare-earth cation substitution allows the investigation of the role of magnetic iron Fe3+ ions and rare earth R3+ ions subsystems in a ground state formation in these oxide compounds.

  7. Advances in Theory of Solid-State Nuclear Magnetic Resonance

    PubMed Central

    Mananga, Eugene S.; Moghaddasi, Jalil; Sana, Ajaz; Akinmoladun, Andrew; Sadoqi, Mostafa

    2015-01-01

    Recent advances in theory of solid state nuclear magnetic resonance (NMR) such as Floquet-Magnus expansion and Fer expansion, address alternative methods for solving a time-dependent linear differential equation which is a central problem in quantum physics in general and solid-state NMR in particular. The power and the salient features of these theoretical approaches that are helpful to describe the time evolution of the spin system at all times are presented. This review article presents a broad view of manipulations of spin systems in solid-state NMR, based on milestones theories including the average Hamiltonian theory and the Floquet theory, and the approaches currently developing such as the Floquet-Magnus expansion and the Fer expansion. All these approaches provide procedures to control and describe the spin dynamics in solid-state NMR. Applications of these theoretical methods to stroboscopic and synchronized manipulations, non-synchronized experiments, multiple incommensurated frequencies, magic-angle spinning samples, are illustrated. We also reviewed the propagators of these theories and discussed their convergences. Note that the FME is an extension of the popular Magnus Expansion and Average Hamiltonian Theory. It aims is to bridge the AHT to the Floquet Theorem but in a more concise and efficient formalism. Calculations can then be performed in a finite-dimensional Hilbert space instead of an infinite dimensional space within the so-called Floquet theory. We expected that the FME will provide means for more accurate and efficient spin dynamics simulation and for devising new RF pulse sequence. PMID:26878063

  8. Advances in Theory of Solid-State Nuclear Magnetic Resonance.

    PubMed

    Mananga, Eugene S; Moghaddasi, Jalil; Sana, Ajaz; Akinmoladun, Andrew; Sadoqi, Mostafa

    Recent advances in theory of solid state nuclear magnetic resonance (NMR) such as Floquet-Magnus expansion and Fer expansion, address alternative methods for solving a time-dependent linear differential equation which is a central problem in quantum physics in general and solid-state NMR in particular. The power and the salient features of these theoretical approaches that are helpful to describe the time evolution of the spin system at all times are presented. This review article presents a broad view of manipulations of spin systems in solid-state NMR, based on milestones theories including the average Hamiltonian theory and the Floquet theory, and the approaches currently developing such as the Floquet-Magnus expansion and the Fer expansion. All these approaches provide procedures to control and describe the spin dynamics in solid-state NMR. Applications of these theoretical methods to stroboscopic and synchronized manipulations, non-synchronized experiments, multiple incommensurated frequencies, magic-angle spinning samples, are illustrated. We also reviewed the propagators of these theories and discussed their convergences. Note that the FME is an extension of the popular Magnus Expansion and Average Hamiltonian Theory. It aims is to bridge the AHT to the Floquet Theorem but in a more concise and efficient formalism. Calculations can then be performed in a finite-dimensional Hilbert space instead of an infinite dimensional space within the so-called Floquet theory. We expected that the FME will provide means for more accurate and efficient spin dynamics simulation and for devising new RF pulse sequence.

  9. Quantum Hall states stabilized in semi-magnetic bilayers of topological insulators

    NASA Astrophysics Data System (ADS)

    Yoshimi, R.; Yasuda, K.; Tsukazaki, A.; Takahashi, K. S.; Nagaosa, N.; Kawasaki, M.; Tokura, Y.

    2015-10-01

    By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. Further breaking of inversion symmetry is possible by employing magnetic topological insulator heterostructures that host non-degenerate top and bottom surface states. Here we demonstrate the tailored-material approach for the realization of robust quantum Hall states in the bilayer system, in which the cooperative or cancelling combination of the anomalous and ordinary Hall responses from the respective magnetic and non-magnetic layers is exemplified. The appearance of quantum Hall states at filling factor 0 and +1 can be understood by the relationship of energy band diagrams for the two independent surface states. The designable heterostructures of magnetic topological insulator may explore a new arena for intriguing topological transport and functionality.

  10. Quantum Hall states stabilized in semi-magnetic bilayers of topological insulators

    PubMed Central

    Yoshimi, R.; Yasuda, K.; Tsukazaki, A.; Takahashi, K. S.; Nagaosa, N.; Kawasaki, M.; Tokura, Y.

    2015-01-01

    By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. Further breaking of inversion symmetry is possible by employing magnetic topological insulator heterostructures that host non-degenerate top and bottom surface states. Here we demonstrate the tailored-material approach for the realization of robust quantum Hall states in the bilayer system, in which the cooperative or cancelling combination of the anomalous and ordinary Hall responses from the respective magnetic and non-magnetic layers is exemplified. The appearance of quantum Hall states at filling factor 0 and +1 can be understood by the relationship of energy band diagrams for the two independent surface states. The designable heterostructures of magnetic topological insulator may explore a new arena for intriguing topological transport and functionality. PMID:26497065

  11. Quantum Hall states stabilized in semi-magnetic bilayers of topological insulators.

    PubMed

    Yoshimi, R; Yasuda, K; Tsukazaki, A; Takahashi, K S; Nagaosa, N; Kawasaki, M; Tokura, Y

    2015-10-26

    By breaking the time-reversal symmetry in three-dimensional topological insulators with the introduction of spontaneous magnetization or application of magnetic field, the surface states become gapped, leading to quantum anomalous Hall effect or quantum Hall effect, when the chemical potential locates inside the gap. Further breaking of inversion symmetry is possible by employing magnetic topological insulator heterostructures that host non-degenerate top and bottom surface states. Here we demonstrate the tailored-material approach for the realization of robust quantum Hall states in the bilayer system, in which the cooperative or cancelling combination of the anomalous and ordinary Hall responses from the respective magnetic and non-magnetic layers is exemplified. The appearance of quantum Hall states at filling factor 0 and +1 can be understood by the relationship of energy band diagrams for the two independent surface states. The designable heterostructures of magnetic topological insulator may explore a new arena for intriguing topological transport and functionality.

  12. New models for fast steady state magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1986-01-01

    A new unified family of models for incompressible, steady-state magnetic reconnection in a finite region is presented. The models are obtained by expanding in powers of the Alfven Mach number and may be used to elucidate some of the puzzling properties of numerical experiments on reconnection which are not present in the classical models. The conditions imposed on the inflow boundary of the finite region determine which member of the family occurs. Petscheklien and Sonnerup like solutions are particular members. The Sonneruplike regime is a special case of a weak slow mode expansion in the inflow region, and it separates two classes of members with reversed currents. The Petscheklike regime is a singular case of a weak fast mode expansion, and it separates the hybrid regime from a regime of slow mode compressions. Care should be taken in deciding which type of reconnection is operating in a numerical experiment. Indeed, no experiment to date has used boundary conditions appropriate for demonstrating steady state Petschek reconnection.

  13. Explosive generation of high magnetic fields in large volumes and solid state applications

    SciTech Connect

    Fowler, C.M.; Caird, R.S.; Erickson, D.J.; Freeman, B.L.; Garn, W.B.

    1980-01-01

    Various methods of producing ultra-high magnetic fields by explosive flux compression are described. A survey is made of the kinds of high magnetic field solid state data obtained in such fields by various groups. Preliminary results are given for the magnetic phase boundary that separates the spin-flop and paramagnetic regions of MnF/sub 2/.

  14. Magnetic glass state and magnetoresistance in SrLaFeCoO6 double perovskite.

    PubMed

    Pradheesh, R; Nair, Harikrishnan S; Haripriya, G R; Senyshyn, Anatoliy; Chatterji, Tapan; Sankaranarayanan, V; Sethupathi, K

    2017-03-08

    Unusual features in magnetization resembling the kinetic arrest of a magnetic glass state are observed in the La-doped double perovskite, SrLaFeCoO6. Neutron powder diffraction experiments confirm the presence of antisite disorder as well as a lack of long-range magnetic order down to 4 K in this double perovskite which displays spin glass-like features in dc and ac susceptibilities. Magnetic relaxation observed through cooling and heating under unequal fields (CHUF) point towards unusual domain dynamics which is supported by a broad memory effect. Among the two anomalies that are observed at [Formula: see text] 75 K and at [Formula: see text] 250 K in the magnetic measurements, the former is associated with a spin-freezing temperature below which the magnetic glass state is experimentally verified. The magnetometric experiments detailed in the paper bring out the non-equilibrium metastable magnetic states in this disordered magnetic system. The magnetic glass state described above manifests in the electrical resistivity [Formula: see text] through the formation of a 'hard gap' because of the spin-exchange energy following the formation of magnetic glass. It is observed that the combination of disorder and magnetic glass state leads to a large, negative magnetoresistance (MR) of  ≈47[Formula: see text] at 5 K in 8 T.

  15. Magnetic glass state and magnetoresistance in SrLaFeCoO6 double perovskite

    NASA Astrophysics Data System (ADS)

    Pradheesh, R.; Nair, Harikrishnan S.; Haripriya, G. R.; Senyshyn, Anatoliy; Chatterji, Tapan; Sankaranarayanan, V.; Sethupathi, K.

    2017-03-01

    Unusual features in magnetization resembling the kinetic arrest of a magnetic glass state are observed in the La-doped double perovskite, SrLaFeCoO6. Neutron powder diffraction experiments confirm the presence of antisite disorder as well as a lack of long-range magnetic order down to 4 K in this double perovskite which displays spin glass-like features in dc and ac susceptibilities. Magnetic relaxation observed through cooling and heating under unequal fields (CHUF) point towards unusual domain dynamics which is supported by a broad memory effect. Among the two anomalies that are observed at {{T}\\text{a1}}≈ 75 K and at {{T}\\text{a2}}≈ 250 K in the magnetic measurements, the former is associated with a spin-freezing temperature below which the magnetic glass state is experimentally verified. The magnetometric experiments detailed in the paper bring out the non-equilibrium metastable magnetic states in this disordered magnetic system. The magnetic glass state described above manifests in the electrical resistivity ρ (T) through the formation of a ‘hard gap’ because of the spin-exchange energy following the formation of magnetic glass. It is observed that the combination of disorder and magnetic glass state leads to a large, negative magnetoresistance (MR) of  ≈47 % at 5 K in 8 T.

  16. Pulsed field magnets at the United States National High Magnetic Field Laboratory

    SciTech Connect

    Campbell, L.J.; Parkin, D.M.; Crow, J.E.; Schneider-Muntau, H.J.; Sullivan, N.S.

    1993-11-01

    The pulsed field facility of the National High Magnetic Field Laboratory (NHMFL) consists of four components. Now available are (1) explosive driven flux compression, (2) capacitor-driven magnets, and (3) a 20 T superconducting magnet. The fourth component, a 60 T quasi-continuous magnet, has been designed and is scheduled for installation in early 1995. All magnets have He-4 cryostats giving temperatures from room temperature (RT) to 2.2--1.5 K. Dilution refrigerators for the superconducting 20 T magnet and the 50 T pulsed magnet will be installed by early 1994. A wide range of experiments has been completed within the past year.

  17. Magnetic states of multilayer Fe /Cr structures with ultrathin iron layers

    NASA Astrophysics Data System (ADS)

    Drovosekov, A. B.; Kreines, N. M.; Kholin, D. I.

    2010-08-01

    The evolution of the magnetic properties of Fe /Cr superlattices is studied as the nominal thickness of the iron layers is reduced to atomic values, when these layers are no longer continuous. The studies were done on multilayer samples with Fe thicknesses of 2-6Å and chromium spacer thicknesses of 10 and 20Å. The samples were prepared by molecular beam epitaxy. The static magnetization and complex magnetic susceptibility were measured and FMR spectra taken. It was found that, depending on the thickness of the Fe layers and temperature, different magnetic phases are realized in the system: supermagnetism, magnetic ordering, and a nonergodic state characterized by a dependence of the magnetization of a sample on its magnetic prehistory. The observed nonergodic phase is found to exhibit spin glass properties. A qualitative phase diagram of the magnetic states of this system is constructed.

  18. Multiply periodic states and isolated skyrmions in an anisotropic frustrated magnet

    PubMed Central

    Leonov, A. O.; Mostovoy, M.

    2015-01-01

    Multiply periodic states appear in a wide variety of physical contexts, such as the Rayleigh–Bénard convection, Faraday waves, liquid crystals and skyrmion crystals recently observed in chiral magnets. Here we study the phase diagram of an anisotropic frustrated magnet which contains five different multiply periodic states including the skyrmion crystal. We clarify the mechanism for stabilization of these states and discuss how they can be observed in magnetic resonance and electric polarization measurements. We also find stable isolated skyrmions with topological charge 1 and 2. Their spin structure, interactions and dynamics are more complex than those in chiral magnets. In particular, magnetic resonance in the skyrmion crystal should be accompanied by oscillations of the electric polarization with a frequency depending on the amplitude of the a.c. magnetic field. These results show that skyrmion materials with rich physical properties can be found among frustrated magnets. We formulate rules to help the search. PMID:26394924

  19. Multiply periodic states and isolated skyrmions in an anisotropic frustrated magnet.

    PubMed

    Leonov, A O; Mostovoy, M

    2015-09-23

    Multiply periodic states appear in a wide variety of physical contexts, such as the Rayleigh-Bénard convection, Faraday waves, liquid crystals and skyrmion crystals recently observed in chiral magnets. Here we study the phase diagram of an anisotropic frustrated magnet which contains five different multiply periodic states including the skyrmion crystal. We clarify the mechanism for stabilization of these states and discuss how they can be observed in magnetic resonance and electric polarization measurements. We also find stable isolated skyrmions with topological charge 1 and 2. Their spin structure, interactions and dynamics are more complex than those in chiral magnets. In particular, magnetic resonance in the skyrmion crystal should be accompanied by oscillations of the electric polarization with a frequency depending on the amplitude of the a.c. magnetic field. These results show that skyrmion materials with rich physical properties can be found among frustrated magnets. We formulate rules to help the search.

  20. Single molecule magnet behavior of a pentanuclear Mn-based metallacrown complex: solid state and solution magnetic studies.

    PubMed

    Zaleski, Curtis M; Tricard, Simon; Depperman, Ezra C; Wernsdorfer, Wolfgang; Mallah, Talal; Kirk, Martin L; Pecoraro, Vincent L

    2011-11-21

    The magnetic behavior of the pentanuclear complex of formula Mn(II)(O(2)CCH(3))(2)[12-MC(Mn(III)(N)shi)-4](DMF)(6), 1, was investigated using magnetization and magnetic susceptibility measurements both in the solid state and in solution. Complex 1 has a nearly planar structure, made of a central Mn(II) ion surrounded by four peripheral Mn(III) ions. Solid state variable-field dc magnetic susceptibility experiments demonstrate that 1 possesses a low value for the total spin in the ground state; fitting appropriate expressions to the data results in antiferromangetic coupling both between the peripheral Mn(III) ions (J = -6.3 cm(-1)) and between the central Mn(II) ion and the Mn(III) ones (J' = -4.2 cm(-1)). In order to obtain a reasonable fit, a relatively large single ion magnetic anisotropy (D) value of 1 cm(-1) was necessary for the central Mn(II) ion. The single crystal magnetization measurements using a microsquid array display a very slight opening of the hysteresis loop but only at a very low temperature (0.04 K), which is in line with the ac susceptibility data where a slow relaxation of the magnetization occurs just around 2 K. In frozen solution, complex 1 displays a frequency dependent ac magnetic susceptibility signal with an energy barrier to magnetization reorientation (E) and relaxation time at an infinite temperature (τ(o)) of 14.7 cm(-1) and 1.4 × 10(-7) s, respectively, demonstrating the single molecule magnetic behavior in solution.

  1. Perfusion information extracted from resting state functional magnetic resonance imaging.

    PubMed

    Tong, Yunjie; Lindsey, Kimberly P; Hocke, Lia M; Vitaliano, Gordana; Mintzopoulos, Dionyssios; Frederick, Blaise deB

    2017-02-01

    It is widely known that blood oxygenation level dependent (BOLD) contrast in functional magnetic resonance imaging (fMRI) is an indirect measure for neuronal activations through neurovascular coupling. The BOLD signal is also influenced by many non-neuronal physiological fluctuations. In previous resting state (RS) fMRI studies, we have identified a moving systemic low frequency oscillation (sLFO) in BOLD signal and were able to track its passage through the brain. We hypothesized that this seemingly intrinsic signal moves with the blood, and therefore, its dynamic patterns represent cerebral blood flow. In this study, we tested this hypothesis by performing Dynamic Susceptibility Contrast (DSC) MRI scans (i.e. bolus tracking) following the RS scans on eight healthy subjects. The dynamic patterns of sLFO derived from RS data were compared with the bolus flow visually and quantitatively. We found that the flow of sLFO derived from RS fMRI does to a large extent represent the blood flow measured with DSC. The small differences, we hypothesize, are largely due to the difference between the methods in their sensitivity to different vessel types. We conclude that the flow of sLFO in RS visualized by our time delay method represents the blood flow in the capillaries and veins in the brain.

  2. Steady State Turbulent Transport in Magnetic Fusion Plasmas

    SciTech Connect

    Lee, W. W.; Ethier, S.; Kolesnikov, R.; Wang, W. X.; Tang, W. M.

    2007-12-20

    For more than a decade, the study of microturbulence, driven by ion temperature gradient (ITG) drift instabilities in tokamak devices, has been an active area of research in magnetic fusion science for both experimentalists and theorists alike. One of the important impetus for this avenue of research was the discovery of the radial streamers associated the ITG modes in the early nineties using a Particle-In-Cell (PIC) code. Since then, ITG simulations based on the codes with increasing realism have become possible with the dramatic increase in computing power. The notable examples were the demonstration of the importance of nonlinearly generated zonal flows in regulating ion thermal transport and the transition from Bohm to GyroBoham scaling with increased device size. In this paper, we will describe another interesting nonlinear physical process associated with the parallel acceleration of the ions, that is found to play an important role for the steady state turbulent transport. Its discovery is again through the use of the modern massively parallel supercomputers.

  3. Effect of potential barrier height on the carrier transport in InGaAs/GaAsP multi-quantum wells and photoelectric properties of laser diode.

    PubMed

    Dong, Hailiang; Sun, Jing; Ma, Shufang; Liang, Jian; Lu, Taiping; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

    2016-03-07

    The growth and strain-compensation behaviour of InGaAs/GaAsP multi-quantum wells, which were fabricated by metal-organic chemical vapor deposition, have been studied towards the application of these quantum wells in high-power laser diodes. The effect of the height of the potential barrier on the confined level of carrier transport was studied by incorporating different levels of phosphorus content into the GaAsP barrier. The crystal quality and interface roughness of the InGaAs/GaAsP multi-quantum wells with different phosphorus contents were evaluated by high resolution X-ray diffraction and in situ optical surface reflectivity measurements during the growth. The surface morphology and roughness were characterized by atomic force microscopy, which indicates the variation law of surface roughness, terrace width and uniformity with increasing phosphorus content, owing to strain accumulation. Moreover, the defect generation and structural disorder of the multi-quantum wells were investigated by Raman spectroscopy. The optical properties of the multi-quantum wells were characterized by photoluminescence, which shows that the spectral intensity increases as the phosphorus content increases. The results suggest that more electrons are well bound in InGaAs because of the high potential barrier. Finally, the mechanism of the effect of the height of the potential barrier on laser performance was proposed on the basis of simulation calculations and experimental results.

  4. Steady State Chaotic Magnetic Fields and Particle Dynamics Cross-field Transport of Particles in Chaotic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Dasgupta, B.; Ram, A.

    2009-12-01

    The observed propagation of cosmic rays in the interplanetary space cannot be explained unless there is diffusion of the energetic particles across the interplanetary magnetic field. The cross-field diffusion of cosmic rays is assumed to be due to the chaotic nature of the interplanetary/intergalactic magnetic fields. Among the classic works on this subject have been those of Parker [1] and Jokipii [2]. Parker considered the passage of cosmic ray particles and energetic solar particles in a large scale magnetic field containing small scale irregularities. In the context of cosmic ray propagation, Jokipii considered a small fluctuating component, added on to a uniform magnetic field, to study the spatial transport of particles. We consider asymmetric, steady-state magnetic fields, in three spatial dimensions, generated by currents flowing in circular loops and straight lines [3]. We find that under very special circumstances can one generate large scale coherent magnetic fields. In general, even simple asymmetric current configurations generate spatially chaotic magnetic fields in three-dimensions. The motion of charged particles in these chaotic magnetic fields is quite coherent. This is a surprising result as one generally assumes that spatially chaotic magnetic fields will give rise to chaotic particle motion. So chaotic magnetic fields by themselves do not lead to cross-field transport. However, if we consider a current system, e.g., a current loop, embedded in a uniform magnetic field then a particle can undergo cross-field transport. For cross-field diffusion of charged particles it is necessary that the magnetic field lines be three dimensional. [1] E.N. Parker, Planet. Space Sci. 13, 9, (1965) [2] J.R. Jokipii, Astrophys. J. 146, 480, (1966). [3] A.K. Ram and B. Dasgupta, in 35th EPS Conference on Plasma Phys. Hersonissos, ECA Vol.32D, O-4.059 (2008); and Eos Trans. AGU 88 (52), Fall Meet. Suppl. Abstract NG21B-0522 (2007).

  5. Magnetization distribution in a soft magnetic amorphous alloy ribbon in as-quenched state and efficiency of heat treatment

    NASA Astrophysics Data System (ADS)

    Skulkina, N. A.; Ivanov, O. A.; Shubina, L. N.; Blinova, O. V.

    2016-11-01

    The effect of heat treatment in air on the formation of magnetic properties has been studied based on the example of soft magnetic Fe77Ni1Si9B13 and Fe81B13Si4C2 amorphous ribbons characterized by positive magneto-striction. The magnetization distribution in the ribbons in the as-quenched state was shown to affect the efficiency of annealing. Under certain conditions, heat treatment, which results in the formation of mainly amorphous state of ribbon surface, is more efficient for samples characterized by high volume of orthogonally magnetized domains. This can be related to high in-plane tensile stresses, which are induced by hydrogen and oxygen atoms introduced into the ribbon surface upon its interaction with atmospheric water vapor.

  6. Carrier dynamics in Ga(NAsP)/Si multi-quantum well heterostructures with varying well thickness

    NASA Astrophysics Data System (ADS)

    Shakfa, M. K.; Woscholski, R.; Gies, S.; Wegele, T.; Wiemer, M.; Ludewig, P.; Jandieri, K.; Baranovskii, S. D.; Stolz, W.; Volz, K.; Heimbrodt, W.; Koch, M.

    2016-05-01

    Time-resolved photoluminescence (TR-PL) measurements have been performed in Ga(NAsP)/(BGa)(AsP) multi-quantum well heterostructures (MQWHs) with different well thicknesses. The studied structures have been pseudomorphically grown on Si substrates by metal organic vapor phase epitaxy (MOVPE) with an N content of about 7%. Experimental results reveal a shortening in the PL decay time with increasing QW thickness, meanwhile, accompanied by a decrease in the PL intensity. We attribute this behavior to an increasing non-radiative recombination rate for broader QWs which arises from an increasing number of defects in the QW material. The emission-energy distribution of the PL decay time is studied at various temperatures. The PL decay time strongly depends on the emission energy at low temperatures and becomes emission-energy-independent close to room temperature. This is discussed in terms of the carrier localization in the studied structures.

  7. Room temperature mid-infrared InAsSbN multi-quantum well photodiodes grown by MBE

    NASA Astrophysics Data System (ADS)

    Kesaria, M.; de la Mare, M.; Krier, A.

    2016-11-01

    Room temperature photoresponse in the mid-infrared spectral region is demonstrated from InAsSbN/InAs multi-quantum well photodiodes grown by nitrogen plasma assisted molecular beam epitaxy. The structural quality of the InAsSbN MQWs was ascertained in situ by reflection high energy electron diffraction and ex situ by high resolution x-ray diffraction and photoluminescence measurements. The extended long wavelength photoresponse is identified to originate from the electron-heavy hole (e1-hh1) and electron-light hole (e1-lh1) transitions in the InAsSbN MQW, with a cut off wavelength ~4.20 µm and peak detectivity D *  =  1.25  ×  109 cm Hz1/2 W-1.

  8. Stress influenced trapping processes in Si based multi-quantum well structures and heavy ions implanted Si

    SciTech Connect

    Ciurea, Magdalena Lidia Lazanu, Sorina

    2014-10-06

    Multi-quantum well structures and Si wafers implanted with heavy iodine and bismuth ions are studied in order to evaluate the influence of stress on the parameters of trapping centers. The experimental method of thermostimullatedcurrents without applied bias is used, and the trapping centers are filled by illumination. By modeling the discharge curves, we found in multilayered structures the parameters of both 'normal' traps and 'stress-induced' ones, the last having a Gaussian-shaped temperature dependence of the cross section. The stress field due to the presence of stopped heavy ions implanted into Si was modeled by a permanent electric field. The increase of the strain from the neighborhood of I ions to the neighborhood of Bi ions produces the broadening of some energy levels and also a temperature dependence of the cross sections for all levels.

  9. Magnetic-field dependence of the impurity states in a dome-shaped quantum dot

    NASA Astrophysics Data System (ADS)

    Niculescu, E. C.; Stan, C.; Cristea, M.; Truscă, C.

    2017-08-01

    Using the finite element method, the effect of magnetic fields on the donor states and transition energies in a InAs/GaAs quantum dot coupled to its wetting layers is investigated. Results are obtained for different impurity locations. We found that the diamagnetic shift of the ground state energy increases monotonously with the applied field and can be described by a simple function which interpolates between the low and high magnetic-field behavior. Frequencies associated to the transitions between the S-like ground state and P- (P+) excited states range in terahertz region and show a magnetic field-induced red (blue) shift, irrespectively of the impurity position.

  10. Magnetization due to localized states on graphene grain boundary

    PubMed Central

    Dutta, Sudipta; Wakabayashi, Katsunori

    2015-01-01

    Magnetism in graphene has been found to originate from various defects, e.g., vacancy, edge formation, add-atoms etc. Here, we discuss about an alternate route of achieving magnetism in graphene via grain boundary. During chemical vapor deposition of graphene, several graphene nucleation centers grow independently and face themselves with unusual bonding environment, giving rise to the formation of grain boundaries. We investigate the origin of magnetism in such grain boundaries within first-principles calculations, by letting two nucleation centers interact with each other at their interface. We observe formation of unprecedented point defect, consisting of fused three-membered and larger carbon rings, which induces net magnetization to graphene quantum dots. In case of periodic lattices, the appearance of array of point defects leads to the formation of magnetic grain boundaries. The net magnetization on these defects arises due to the deviation from bipartite characteristics of pristine graphene. We observe magnetic grain boundary induced dispersion less flat bands near Fermi energy, showing higher localization of electrons. These flat bands can be accessed via small doping, leading to enhanced magnetism. Moreover, the grain boundaries can induce asymmetric spin conduction behavior along the cross boundary direction. These properties can be exploited for sensor and spin-filtering applications. PMID:26145161

  11. High pressure and time resolved studies of optical properties of n-type doped GaN/AlN multi-quantum wells: Experimental and theoretical analysis

    SciTech Connect

    Kaminska, A.; Jankowski, D.; Sobczak, K.; Beeler, M.; Monroy, E.; Borysiuk, J.

    2016-09-07

    High-pressure and time-resolved studies of the optical emission from n-type doped GaN/AlN multi-quantum-wells (MQWs) with various well thicknesses are analysed in comparison with ab initio calculations of the electronic (band structure, density of states) and optical (emission energies and their pressure derivatives, oscillator strength) properties. The optical properties of GaN/AlN MQWs are strongly affected by quantum confinement and polarization-induced electric fields. Thus, the photoluminescence (PL) peak energy decreases by over 1 eV with quantum well (QW) thicknesses increasing from 1 to 6 nm. Furthermore, the respective PL decay times increased from about 1 ns up to 10 μs, due to the strong built-in electric field. It was also shown that the band gap pressure coefficients are significantly reduced in MQWs as compared to bulk AlN and GaN crystals. Such coefficients are strongly dependent on the geometric factors such as the thickness of the wells and barriers. The transition energies, their oscillator strength, and pressure dependence are modeled for tetragonally strained structures of the same geometry using a full tensorial representation of the strain in the MQWs under external pressure. These MQWs were simulated directly using density functional theory calculations, taking into account two different systems: the semi-insulating QWs and the n-doped QWs with the same charge density as in the experimental samples. Such an approach allowed an assessment of the impact of n-type doping on optical properties of GaN/AlN MQWs. We find a good agreement between these two approaches and between theory and experimental results. We can therefore confirm that the nonlinear effects induced by the tetragonal strain related to the lattice mismatch between the substrates and the polar MQWs are responsible for the drastic decrease of the pressure coefficients observed experimentally.

  12. Levitation force on a permanent magnet over a superconducting plane: Modified critical-state model

    SciTech Connect

    Yang, Z.J.

    1997-08-01

    The authors consider a model system of a permanent magnet above a semi-infinite superconductor. They introduce a modified critical-state model, and carry out derivations of the levitation force acting on the magnet. A key feature of the modification allows the current density to be less than the critical value. The theoretical results show an exponential relationship between the force and the distance. Analytical expressions are developed for permanent magnets in the form of a point dipole, a tip of a magnetic force microscope, and a cylindrical magnet. In the latter case, the exponential relationship has been observed in numerous experiments but without previous interpretation.

  13. A novel method for the injection and manipulation of magnetic charge states in nanostructures

    PubMed Central

    Gartside, J. C.; Burn, D. M.; Cohen, L. F.; Branford, W. R.

    2016-01-01

    Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360° domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics. Here, we demonstrate a straightforward and powerful process whereby a moving magnetic charge, provided experimentally by a magnetic force microscope tip, can write and manipulate magnetic charge states in ferromagnetic nanowires. The method is applicable to a wide range of nanowire architectures with considerable benefits over existing techniques. We confirm the method’s efficacy via the injection and spatial manipulation of 360° domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction. PMID:27615372

  14. Zero-energy states of graphene triangular quantum dots in a magnetic field

    NASA Astrophysics Data System (ADS)

    Güçlü, A. D.; Potasz, P.; Hawrylak, P.

    2013-10-01

    We present a tight-binding theory of triangular graphene quantum dots (TGQD) with zigzag edge and broken sublattice symmetry in an external magnetic field. The lateral size quantization opens an energy gap, and broken sublattice symmetry results in a shell of degenerate states at the Fermi level. We derive a semianalytical form for zero-energy states in a magnetic field and show that the shell remains degenerate in a magnetic field, in analogy to the zeroth Landau level of bulk graphene. The magnetic field closes the energy gap and leads to the crossing of valence and conduction states with the zero-energy states, modulating the degeneracy of the shell. The closing of the gap with increasing magnetic field is present in all graphene quantum dot structures investigated irrespective of shape and edge termination.

  15. Magnetic field dependence of a charge-frustrated state in a triangular triple quantum dot

    NASA Astrophysics Data System (ADS)

    Seo, M.; Chung, Y.

    2013-11-01

    We studied the magnetic field dependence of a charge-frustrated state formed in a triangular triple quantum dot. Stability diagrams at various magnetic fields were measured by using two-terminal and three-terminal conductance measurement schemes. We found that the frustrated state broke down at an external magnetic field of around 0.1 T. This result is due to the confinement energy shifts in quantum dots under external magnetic fields. A similar breakdown of the frustrated state was observed when the confinement energy of a quantum dot was intentionally shifted by the plunger gate of the dot, which confirm the reason for the breakdown of the frustrated state under on applied magnetic field. Our measured stability diagrams differed depending on the measurement schemes, which could not be explained by the capacitive interaction model based on an independent particle picture. We believe that the discrepancy is related to the closed electron and hole trajectories inside a triple quantum dot.

  16. A novel method for the injection and manipulation of magnetic charge states in nanostructures

    NASA Astrophysics Data System (ADS)

    Gartside, J. C.; Burn, D. M.; Cohen, L. F.; Branford, W. R.

    2016-09-01

    Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360° domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics. Here, we demonstrate a straightforward and powerful process whereby a moving magnetic charge, provided experimentally by a magnetic force microscope tip, can write and manipulate magnetic charge states in ferromagnetic nanowires. The method is applicable to a wide range of nanowire architectures with considerable benefits over existing techniques. We confirm the method’s efficacy via the injection and spatial manipulation of 360° domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction.

  17. Experimental observation of multiple-Q states for the magnetic skyrmion lattice and skyrmion excitations under a zero magnetic field

    NASA Astrophysics Data System (ADS)

    Nagao, Masahiro; So, Yeong-Gi; Yoshida, Hiroyuki; Yamaura, Kazunari; Nagai, Takuro; Hara, Toru; Yamazaki, Atsushi; Kimoto, Koji

    2015-10-01

    Model calculations indicate that the magnetic skyrmion lattice (SkL) is represented by a superposition of three spin helices at an angle of 120∘ to each other, the so-called triple-Q state. Using Lorentz transmission electron microscopy, we investigated the relationship between the SkL and the helix in FeGe thin films. After the magnetic field is removed, the ordered skyrmions are trapped inside helimagnetic domain walls (HDWs) where the different helical Q vectors are encountered. In situ observation revealed an unexpected topological excitation under such a zero-field state: skyrmions are spontaneously formed at HDWs.

  18. In Situ control and modification of the probe magnetization state for accurate magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Angeloni, Livia; Passeri, Daniele; Natali, Marco; Reggente, Melania; Anelli, Emanuele; Bettucci, Andrea; Mantovani, Diego; Rossi, Marco

    2017-08-01

    Electrostatic tip-sample interactions currently represent the main limitation to accurate quantitative analysis of magnetic force microscopy (MFM) data. Controlled magnetization MFM (CM-MFM) represents a smart solution to overcome this limitation as it allows one to identify electrostatic artifacts and to subtract them from standard MFM images, thus enabling the quantitative investigation of magnetic properties of materials at the nanometer scale. CM-MFM, however, requires not only the magnetization, but also the in situ accurate demagnetization of the MFM probe. In particular, the latter represents a crucial step for the complete removal of electrostatic artifacts. In this work, we describe two different methods to depolarize the MFM tip, based on the application of the coercive remanent magnetic field of the tip and on a damped alternating magnetic field, respectively. The two techniques are escribed and compared to emphasize their specific advantages and limitations.

  19. Resting-state functional magnetic resonance imaging: review of neurosurgical applications.

    PubMed

    Lang, Stefan; Duncan, Niall; Northoff, Georg

    2014-05-01

    Recent research in brain imaging has highlighted the role of different neural networks in the resting state (ie, no task) in which the brain displays spontaneous low-frequency neuronal oscillations. These can be indirectly measured with resting-state functional magnetic resonance imaging, and functional connectivity can be inferred as the spatiotemporal correlations of this signal. This technique has proliferated in recent years and has allowed the noninvasive investigation of large-scale, distributed functional networks. In this review, we give a brief overview of resting-state networks and examine the use of resting-state functional magnetic resonance imaging in neurosurgical contexts, specifically with respect to neurooncology, epilepsy surgery, and deep brain stimulation. We discuss the advantages and disadvantages compared with task-based functional magnetic resonance imaging, the limitations of resting-state functional magnetic resonance imaging, and the emerging directions of this relatively new technology.

  20. Solid state nuclear magnetic resonance investigations of advanced energy materials

    NASA Astrophysics Data System (ADS)

    Bennett, George D.

    In order to better understand the physical electrochemical changes that take place in lithium ion batteries and asymmetric hybrid supercapacitors solid state nuclear magnetic resonance (NMR) spectroscopy has been useful to probe and identify changes on the atomic and molecular level. NMR is used to characterize the local environment and investigate the dynamical properties of materials used in electrochemical storage devices (ESD). NMR investigations was used to better understand the chemical composition of the solid electrolyte interphase which form on the negative and positive electrodes of lithium batteries as well as identify the breakdown products that occur in the operation of the asymmetric hybrid supercapacitors. The use of nano-structured particles in the development of new materials causes changes in the electrical, structural and other material properties. NMR was used to investigate the affects of fluorinated and non fluorinated single wall nanotubes (SWNT). In this thesis three experiments were performed using solid state NMR samples to better characterize them. The electrochemical reactions of a lithium ion battery determine its operational profile. Numerous means have been employed to enhance battery cycle life and operating temperature range. One primary means is the choice and makeup of the electrolyte. This study focuses on the characteristics of the solid electrolyte interphase (SEI) that is formed on the electrodes surface during the charge discharge cycle. The electrolyte in this study was altered with several additives in order to determine the influence of the additives on SEI formation as well as the intercalation and de-intercalation of lithium ions in the electrodes. 7Li NMR studies where used to characterize the SEI and its composition. Solid state NMR studies of the carbon enriched acetonitrile electrolyte in a nonaqueous asymmetric hybrid supercapacitor were performed. Magic angle spinning (MAS) coupled with cross polarization NMR

  1. Magnetization reversal assisted by half antivortex states in nanostructured circular cobalt disks

    SciTech Connect

    Lara, A.; Aliev, F. G.; Dobrovolskiy, O. V.; Prieto, J. L.; Huth, M.

    2014-11-03

    The half antivortex, a fundamental topological structure which determines magnetization reversal of submicron magnetic devices with domain walls, has been suggested also to play a crucial role in spin torque induced vortex core reversal in circular disks. Here, we report on magnetization reversal in circular disks with nanoholes through consecutive metastable states with half antivortices. In-plane anisotropic magnetoresistance and broadband susceptibility measurements accompanied by micromagnetic simulations reveal that cobalt (Co) disks with two and three linearly arranged nanoholes directed at 45° and 135° with respect to the external magnetic field show reproducible step-like changes in the anisotropic magnetoresistance and magnetic permeability due to transitions between different intermediate states mediated by vortices and half antivortices confined to the dot nanoholes and edges, respectively. Our findings are relevant for the development of multi-hole based spintronic and magnetic memory devices.

  2. Reentrant superspin glass state and magnetization steps in the oxyborate Co 2AlBO5

    NASA Astrophysics Data System (ADS)

    Kumar, Jitender; Panja, Soumendra Nath; John, Deepak; Bhattacharyya, Arpan; Nigam, A. K.; Nair, Sunil

    2017-04-01

    An oxyborate Co 2AlBO5 belonging to the ludwigite family is investigated using structural, thermodynamic, dielectric, and magnetic measurements. Magnetic measurements indicate that this system is seen to exhibit long-range magnetic ordering at T N=42 K , signatures of which are also seen in the specific heat, dielectric susceptibility, and lattice parameters. The absence of a structural phase transition down to the lowest measured temperatures distinguishes it from the more extensively investigated Fe-based ludwigites. At low temperatures, the system is seen to stabilize in a reentrant superspin glass phase at T G=10.6 K from within the magnetically ordered state. This ground state is also characterized by magnetic-field-induced metamagnetic transitions, which at the lowest measured temperatures exhibit a number of sharp magnetization steps, reminiscent of that observed in the mixed valent manganites.

  3. Low temperature magnetically-inhomogeneous states of Sr2FeMoO6-δ compounds

    NASA Astrophysics Data System (ADS)

    Kalanda, N. A.; Demyanov, S. E.; Kovalev, L. V.

    2011-10-01

    The present paper shows that inhomogeneity in magnetic structure of Sr2FeMoO6-δ metal oxide compounds, that essentially depends on synthesis conditions, leads to different degrees of superstructural ordering of Fe3+ and Mo5+ cations. According to the temperature dependence of magnetization measured in the absence of a magnetic field, the sharp jump in the low temperature region (2.3-23 K) indicates the existence of magnetic fields with low coercivity, where the superparamagnetic state is realized. It has been established that magnetic inhomogeneity of antiferromagnetic-ferromagnetic materials promotes a frustration of the exchange coupling and facilitates a realization of the spin glass state in the material. A decrease of magnetic inhomogeneity and the corresponding increase in the degree of superstructural ordering of cations cause the negative magnetoresistivity effect to increase up to 14%, and to be unchanged at temperatures below 15 K.

  4. Magnetic state selection in atomic frequency and time standards. [hydrogen masers

    NASA Technical Reports Server (NTRS)

    Peters, H. E.

    1982-01-01

    Atomic standards such as those based upon cesium and hydrogen rely upon magnetic state selection to obtain population inversion in the hyperfine transition levels. Use of new design approaches and improved magnetic materials has made it possible to fabricate improved state selectors of small size, and thus the efficiency of utilization of beam flux is greatly improved and the size and weight of the standard is reduced. The sensitivity to magnetic perturbations is also decreased, so that the accuracy and stability of the standard is improved. Several new state selector designs are illustrated and the application to standards utilizing different atomic species is analyzed.

  5. An NCN-pincer ligand dysprosium single-ion magnet showing magnetic relaxation via the second excited state

    PubMed Central

    Guo, Yun-Nan; Ungur, Liviu; Granroth, Garrett E.; Powell, Annie K.; Wu, Chunji; Nagler, Stephen E.; Tang, Jinkui; Chibotaru, Liviu F.; Cui, Dongmei

    2014-01-01

    Single-molecule magnets are compounds that exhibit magnetic bistability purely of molecular origin. The control of anisotropy and suppression of quantum tunneling to obtain a comprehensive picture of the relaxation pathway manifold, is of utmost importance with the ultimate goal of slowing the relaxation dynamics within single-molecule magnets to facilitate their potential applications. Combined ab initio calculations and detailed magnetization dynamics studies reveal the unprecedented relaxation mediated via the second excited state within a new DyNCN system comprising a valence-localized carbon coordinated to a single dysprosium(III) ion. The essentially C2v symmetry of the DyIII ion results in a new relaxation mechanism, hitherto unknown for mononuclear DyIII complexes, opening new perspectives for means of enhancing the anisotropy contribution to the spin-relaxation barrier. PMID:24969218

  6. Influence of magnetic field on electric-field-induced local polar states in manganites

    SciTech Connect

    Mamin, R. F.; Strle, J.; Kabanov, V. V.; Kranjec, A.; Borovsak, M.; Mihailovic, D.; Bizyaev, D. A.; Yusupov, R. V.; Bukharaev, A. A.

    2015-11-09

    It is shown that creation of local charged states at the surface of the lanthanum-strontium manganite single crystals by means of bias application via a conducting atomic force microscope tip is strongly affected by magnetic field. Both a charge and a size of created structures increase significantly on application of the magnetic field during the induction. We argue that the observed phenomenon originates from a known tendency of manganites toward charge segregation and its intimate relation to magnetic ordering.

  7. Contribution of Eu 4f states to the magnetic anisotropy of EuO

    SciTech Connect

    Arenholz, E.; Schmehl, A.; Schlom, D.G.; van der Laan, G.

    2008-09-11

    Anisotropic x-ray magnetic linear dichroism (AXMLD) provides a novel element-, site-, shell-, and symmetry-selective techniques to study the magnetic anisotropy induced by a crystalline electric field. The weak Eu2+ M4,5 AXMLD observed in EuO(001) indicates that the Eu 4f states are not rotationally invariant and hence contribute weakly to the magnetic anisotropy of EuO. The results are contrasted with those obtained for 3d transition metal oxides.

  8. An equivalent layer magnetization model for the United States derived from MAGSAT data

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.; Galliher, S. C. (Principal Investigator)

    1982-01-01

    Long wavelength anomalies in the total magnetic field measured field measured by MAGSAT over the United States and adjacent areas are inverted to an equivalent layer crustal magnetization distribution. The model is based on an equal area dipole grid at the Earth's surface. Model resolution having physical significance, is about 220 km for MAGSAT data in the elevation range 300-500 km. The magnetization contours correlate well with large-scale tectonic provinces.

  9. A Magnetic Solid-State Storage Technology: Vertical Bloch Line Storage

    NASA Technical Reports Server (NTRS)

    Katti, R. R.

    1993-01-01

    No storage technology is known to exist today which simultaneously offers high-storage density, nonvolatility, and a solid-state form factor. For example, common random access memories are solid-state, but are volatile and typically offer modest density. Alternatively, mainstream magnetic disk and magnetic tape systems offer high storage density and nonvolatility, but are fundamentally not solid-state. A number of applications exist which would be suited well with high performance solid- state technology. NASA, for example, is beginning baseline solid-state recorders for upcoming space missions, such as the Cassini mission to Saturn.

  10. A geometrical crossover in excited states of two-electron quantum dots in a magnetic field

    NASA Astrophysics Data System (ADS)

    Nazmitdinov, R. G.; Simonović, N. S.; Plastino, A. R.; Chizhov, A. V.

    2012-11-01

    We use the entanglement measure to study the evolution of quantum correlations in two-electron axially-symmetric parabolic quantum dots under a perpendicular magnetic field. We found that the entanglement indicates on the shape transition in the density distribution of two electrons in the lowest state with zero angular momentum projection at the specific value of the applied magnetic field.

  11. Magnetic order and magnon coherent state in double exchange s=1/2 lattices

    SciTech Connect

    Lopez-Aguilar, F.

    2010-02-15

    Starting from trial wave functions and by minimizing the total energy, we obtain the ground state (GS) of a magnetic system in which there is competition between two exchange interactions: one of them between localized and unlocalized spins and another one among the spins of a Heisenberg s=1/2 lattice. This analysis allows us to analyze directly a particular case of a magnetic ground state: a magnon gas whose collective wave function presents similarities with the coherent state of the electromagnetic field which is the basis for the laser. The Kondo coupling becomes concomitant with the external magnetic field which can control the number of magnons. The corresponding Zeeman effect provoked by the magnetic external field plus the Kondo interaction energy compete with the spin-spin Heisenberg exchange of the localized magnetic lattices. The fruit of the competition of these three interactions is the existence of a collective state which can be represented with an oscillation with one only frequency which has a minimum uncertainty and therefore it is a most similar quantum state to a classical wave. This collective state for determined crystal conditions, values of Kondo coupling strength, external B values and Heisenberg J{sub ij}-parameters tends to be a minimal energy state, and then, this coherent state, can transit to a magnon Bose-Einstein condensate (BEC). The passing from the minimal coherent state towards the BEC condensation is thermodynamically analyzed and we have deduced the critical temperature of this phase transition.

  12. Coronary magnetic resonance imaging: current state-of-the-art.

    PubMed

    Appelbaum, Evan; Botnar, René M; Yeon, Susan B; Manning, Warren J

    2005-09-01

    Over the past decade, coronary magnetic resonance imaging has been transformed from a scientific curiosity to a clinically useful imaging tool for patients with known or suspected anomalous coronary arteries or coronary artery aneurysms and for assessment of coronary artery bypass graft patency. Coronary magnetic resonance imaging also appears to be of clinical value for assessment of native vessel integrity in selected patients, especially those patients with suspected left main/multivessel disease. Among patients referred for X-ray angiography, a normal coronary magnetic resonance imaging strongly suggests the absence of severe multivessel disease. Technical and methodological advances in motion suppression, along with increasing clinical experience will no doubt facilitate improved visualization of the distal and branch vessel.

  13. Surveying techniques with a solid-state magnetic multishot device

    SciTech Connect

    Thorogood, J.L. ); Knott, D.R. )

    1990-09-01

    An electronic magnetic multishot instrument was introduced in 1985 to overcome accuracy and reliability limitations associated with conventional photomechanical multishot systems. This paper describes the survey system and the instrument's performance capabilities. Our aim is to develop a tool-performance model for general application to the management of surveying operations. Accuracy is considered in two parts: sensor errors are considered in detail, and external effects on accuracy- e.g., axial misalignment, bottom-hole-assembly (BHA) deflection, geomagnetic influences, and drillstring-induced interference- are analyzed and quantified. The authors found that geomagnetic influences and drillstring-induced interference dominate the ultimate performance of all magnetic tools, particularly this electronic multishot instrument. This paper also describes in-hole referencing, a method of eliminating these errors that involves surveying the first part of an openhole section with a high-accuracy gyroscope and aligning data derived from subsequent magnetic surveys with it.

  14. Neutrons in strong magnetic fields and equation of state of neutron matter

    NASA Astrophysics Data System (ADS)

    Bigdeli, Mohsen

    2017-02-01

    In the present work, I investigate the influence of neutron mass reduction due to magnetic field on the equation of state of neutron matter using the lowest-order constraint variational (LOCV) method with the A V18 potential.

  15. Modified magnetic ground state in NiMn2O4 thin films

    SciTech Connect

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

    2010-08-03

    We demonstrate the stabilization of a magnetic ground state in epitaxial NiMn2O4 (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral Mn{sup 4+}:Mn{sup 3+} concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low temperature. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn{sup 4+} while the canted moment ferrimagnetic ordering is preserved below 60 K.

  16. Modified Magnetic Ground State in Nimn (2) O (4) Thin Films

    SciTech Connect

    Nelson-Cheeseman, B.B.; Chopdekar, R.V.; Iwata, J.M.; Toney, M.F.; Arenholz, E.; Suzuki, Y.; /SLAC

    2012-08-23

    The authors demonstrate the stabilization of a magnetic ground state in epitaxial NiMn{sub 2}O{sub 4} (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral Mn{sup 4+}:Mn{sup 3+} concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low T. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn{sup 4+}, while the canted moment ferrimagnetic ordering is preserved below 60 K.

  17. Realization of quantum state privacy amplification in a nuclear magnetic resonance quantum system

    NASA Astrophysics Data System (ADS)

    Hao, Liang; Wang, Chuan; Long, Gui Lu

    2010-06-01

    Quantum state privacy amplification (QSPA) is the quantum analogue of classical privacy amplification. If the state information of a series of single-particle states has some leakage, QSPA reduces this leakage by condensing the state information of two particles into the state of one particle. Recursive applications of the operations will eliminate the quantum state information leakage to a required minimum level. In this paper, we report the experimental implementation of a quantum state privacy amplification protocol in a nuclear magnetic resonance system. The density matrices of the states are constructed in the experiment, and the experimental results agree well with theory.

  18. Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

    SciTech Connect

    Woolley, R.D.

    1996-12-31

    A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.

  19. Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

    DOEpatents

    Woolley, Robert D.

    1998-01-01

    A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.

  20. Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

    DOEpatents

    Woolley, R.D.

    1998-09-08

    A method and apparatus are disclosed for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators. 6 figs.

  1. Interlayer coupling through a dimensionality-induced magnetic state.

    PubMed

    Gibert, M; Viret, M; Zubko, P; Jaouen, N; Tonnerre, J-M; Torres-Pardo, A; Catalano, S; Gloter, A; Stéphan, O; Triscone, J-M

    2016-04-15

    Dimensionality is known to play an important role in many compounds for which ultrathin layers can behave very differently from the bulk. This is especially true for the paramagnetic metal LaNiO3, which can become insulating and magnetic when only a few monolayers thick. We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers. For 7-monolayer-thick LaNiO3/LaMnO3 superlattices, negative and positive exchange bias, as well as antiferromagnetic interlayer coupling are observed in different temperature windows. All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3. This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices.

  2. Interlayer coupling through a dimensionality-induced magnetic state

    PubMed Central

    Gibert, M.; Viret, M.; Zubko, P.; Jaouen, N.; Tonnerre, J.-M.; Torres-Pardo, A.; Catalano, S.; Gloter, A.; Stéphan, O.; Triscone, J.-M.

    2016-01-01

    Dimensionality is known to play an important role in many compounds for which ultrathin layers can behave very differently from the bulk. This is especially true for the paramagnetic metal LaNiO3, which can become insulating and magnetic when only a few monolayers thick. We show here that an induced antiferromagnetic order can be stabilized in the [111] direction by interfacial coupling to the insulating ferromagnet LaMnO3, and used to generate interlayer magnetic coupling of a nature that depends on the exact number of LaNiO3 monolayers. For 7-monolayer-thick LaNiO3/LaMnO3 superlattices, negative and positive exchange bias, as well as antiferromagnetic interlayer coupling are observed in different temperature windows. All three behaviours are explained based on the emergence of a (¼,¼,¼)-wavevector antiferromagnetic structure in LaNiO3 and the presence of interface asymmetry with LaMnO3. This dimensionality-induced magnetic order can be used to tailor a broad range of magnetic properties in well-designed superlattice-based devices. PMID:27079668

  3. Bound and Scattering States of Itinerant Charge Carriers in Complex Magnetic Materials

    NASA Astrophysics Data System (ADS)

    Kuzemsky, A. L.

    The concept of magnetic polaron is analyzed and developed to elucidate the nature of itinerant charge carrier states in magnetic semiconductors and similar complex magnetic materials. By contrasting the scattering and bound states of carriers within the s-d exchange model, the nature of bound states at finite temperatures is clarified. The free magnetic polaron at certain conditions is realized as a bound state of the carrier (electron or hole) with the spin wave. Quite generally, a self-consistent theory of a magnetic polaron is formulated within a nonperturbative many-body approach, the Irreducible Green Functions (IGF) method which is used to describe the quasiparticle many-body dynamics at finite temperatures. Within the above many-body approach we elaborate a self-consistent picture of dynamic behavior of two interacting subsystems, the localized spins and the itinerant charge carriers. In particular, we show that the relevant generalized mean fields emerges naturally within our formalism. At the same time, the correct separation of elastic scattering corrections permits one to consider the damping effects (inelastic scattering corrections) in the unified and coherent fashion. The damping of magnetic polaron state, which is quite different from the damping of the scattering states, finds a natural interpretation within the present self-consistent scheme.

  4. FeCr2S4 in magnetic fields: possible evidence for a multiferroic ground state

    PubMed Central

    Bertinshaw, J.; Ulrich, C.; Günther, A.; Schrettle, F.; Wohlauer, M.; Krohns, S.; Reehuis, M.; Studer, A. J.; Avdeev, M.; Quach, D. V.; Groza, J. R.; Tsurkan, V.; Loidl, A.; Deisenhofer, J.

    2014-01-01

    We report on neutron diffraction, thermal expansion, magnetostriction, dielectric, and specific heat measurements on polycrystalline FeCr2S4 in external magnetic fields. The ferrimagnetic ordering temperatures TC ≈ 170 K and the transition at TOO ≈ 10 K, which has been associated with orbital ordering, are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the state below TOO. The magnetic moments of the Cr- and Fe-ions are reduced from the spin-only values throughout the magnetically ordered regime, but approach the spin-only values for fields >5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample below about 60 K. Below TOO this contraction is followed by a moderate expansion of the sample for fields larger than ~4.5 T. The transition at TOO is accompanied by an anomaly in the dielectric constant. The dielectric constant depends on both the strength and orientation of the external magnetic field with respect to the applied electric field for T < TOO. A linear correlation of the magnetic-field-induced change of the dielectric constant and the magnetic-field dependent magnetization is observed. This behaviour is consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10 K. PMID:25123960

  5. FeCr₂S₄ in magnetic fields: possible evidence for a multiferroic ground state.

    PubMed

    Bertinshaw, J; Ulrich, C; Günther, A; Schrettle, F; Wohlauer, M; Krohns, S; Reehuis, M; Studer, A J; Avdeev, M; Quach, D V; Groza, J R; Tsurkan, V; Loidl, A; Deisenhofer, J

    2014-08-15

    We report on neutron diffraction, thermal expansion, magnetostriction, dielectric, and specific heat measurements on polycrystalline FeCr2S4 in external magnetic fields. The ferrimagnetic ordering temperatures TC ≈ 170 K and the transition at TOO ≈ 10 K, which has been associated with orbital ordering, are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the state below TOO. The magnetic moments of the Cr- and Fe-ions are reduced from the spin-only values throughout the magnetically ordered regime, but approach the spin-only values for fields >5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample below about 60 K. Below TOO this contraction is followed by a moderate expansion of the sample for fields larger than ~4.5 T. The transition at TOO is accompanied by an anomaly in the dielectric constant. The dielectric constant depends on both the strength and orientation of the external magnetic field with respect to the applied electric field for T < TOO. A linear correlation of the magnetic-field-induced change of the dielectric constant and the magnetic-field dependent magnetization is observed. This behaviour is consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10 K.

  6. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

    PubMed Central

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-01-01

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications. PMID:28176869

  7. The quantum equations of state of plasma under the influence of a weak magnetic field

    SciTech Connect

    Hussein, N. A.; Eisa, D. A.; Eldin, M. G.

    2012-05-15

    The aim of this paper is to calculate the magnetic quantum equations of state of plasma, the calculation is based on the magnetic binary Slater sum in the case of low density. We consider only the thermal equilibrium plasma in the case of n{lambda}{sub ab}{sup 3} Much-Less-Than 1, where {lambda}{sub ab}{sup 2}=( Planck-Constant-Over-Two-Pi {sup 2}/m{sub ab}KT) is the thermal De Broglie wave length between two particles. The formulas contain the contributions of the magnetic field effects. Using these results we compute the magnetization and the magnetic susceptibility. Our equation of state is compared with others.

  8. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets.

    PubMed

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-02-08

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.

  9. Switchable Multiple Spin States in the Kondo description of Doped Molecular Magnets

    NASA Astrophysics Data System (ADS)

    Ray, Rajyavardhan; Kumar, Sanjeev

    2017-02-01

    We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications.

  10. Magnetic ground state and giant spontaneous exchange bias in Ni46Mn43In11 alloy

    NASA Astrophysics Data System (ADS)

    Ray, Mayukh K.; Maji, Bibekananda; Modak, M.; Banerjee, S.

    2017-05-01

    We report non-equilibrium dynamics and giant spontaneous exchange bias obtained in zero field cooled mode for Ni46Mn43In11 alloy. The dc magnetic measurements indicate a super spin glass type magnetic ground state in the system. This SSG state is formed when superparamagnetic domains are collectively frozen inside strong antiferromagnetic matrix at low temperature. The ZFCEB arises due to the development of strong superferromagnetic unidirectional anisotropy at the interface of SSG and AFM during the initial magnetization processes. The temperature variation of field cooled exchange bias and ZFCEB is almost similar whilst their field dependency is different. Possible reasons for observed behaviors are comprehensively discussed in this article.

  11. Defect induced electronic states and magnetism in ball-milled graphite.

    PubMed

    Milev, Adriyan; Dissanayake, D M A S; Kannangara, G S K; Kumarasinghe, A R

    2013-10-14

    The electronic structure and magnetism of nanocrystalline graphite prepared by ball milling of graphite in an inert atmosphere have been investigated using valence band spectroscopy (VB), core level near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and magnetic measurements as a function of the milling time. The NEXAFS spectroscopy of graphite milled for 30 hours shows simultaneous evolution of new states at ~284.0 eV and at ~290.5 eV superimposed upon the characteristic transitions at 285.4 eV and 291.6 eV, respectively. The modulation of the density of states is explained by evolution of discontinuities within the sheets and along the fracture lines in the milled graphite. The magnetic measurements in the temperature interval 2-300-2 K at constant magnetic field strength show a correlation between magnetic properties and evolution of the new electronic states. With the reduction of the crystallite sizes of the graphite fragments, the milled material progressively changes its magnetic properties from diamagnetic to paramagnetic with contributions from both Pauli and Curie paramagnetism due to the evolution of new states at ~284 and ~290.5 eV, respectively. These results indicate that the magnetic behaviour of ball-milled graphite can be manipulated by changing the milling conditions.

  12. Ground state selection under pressure in the quantum pyrochlore magnet Yb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Kermarrec, E.; Gaudet, J.; Fritsch, K.; Khasanov, R.; Guguchia, Z.; Ritter, C.; Ross, K. A.; Dabkowska, H. A.; Gaulin, B. D.

    2017-03-01

    A quantum spin liquid is a state of matter characterized by quantum entanglement and the absence of any broken symmetry. In condensed matter, the frustrated rare-earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7, so-called spin ices, exhibit a classical spin liquid state with fractionalized thermal excitations (magnetic monopoles). Evidence for a quantum spin ice, in which the magnetic monopoles become long range entangled and an emergent quantum electrodynamics arises, seems within reach. The magnetic properties of the quantum spin ice candidate Yb2Ti2O7 have eluded a global understanding and even the presence or absence of static magnetic order at low temperatures is controversial. Here we show that sensitivity to pressure is the missing key to the low temperature behaviour of Yb2Ti2O7. By combining neutron diffraction and muon spin relaxation on a stoichiometric sample under pressure, we evidence a magnetic transition from a disordered, non-magnetic, ground state to a splayed ferromagnetic ground state.

  13. Ground state selection under pressure in the quantum pyrochlore magnet Yb2Ti2O7.

    PubMed

    Kermarrec, E; Gaudet, J; Fritsch, K; Khasanov, R; Guguchia, Z; Ritter, C; Ross, K A; Dabkowska, H A; Gaulin, B D

    2017-03-15

    A quantum spin liquid is a state of matter characterized by quantum entanglement and the absence of any broken symmetry. In condensed matter, the frustrated rare-earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7, so-called spin ices, exhibit a classical spin liquid state with fractionalized thermal excitations (magnetic monopoles). Evidence for a quantum spin ice, in which the magnetic monopoles become long range entangled and an emergent quantum electrodynamics arises, seems within reach. The magnetic properties of the quantum spin ice candidate Yb2Ti2O7 have eluded a global understanding and even the presence or absence of static magnetic order at low temperatures is controversial. Here we show that sensitivity to pressure is the missing key to the low temperature behaviour of Yb2Ti2O7. By combining neutron diffraction and muon spin relaxation on a stoichiometric sample under pressure, we evidence a magnetic transition from a disordered, non-magnetic, ground state to a splayed ferromagnetic ground state.

  14. Probing the spinor nature of electronic states in nanosize non-collinear magnets

    PubMed Central

    Fischer, Jeison A.; Sandratskii, Leonid M.; Phark, Soo-Hyon; Ouazi, Safia; Pasa, André A.; Sander, Dirk; Parkin, Stuart S. P.

    2016-01-01

    Non-collinear magnetization textures provide a route to novel device concepts in spintronics. These applications require laterally confined non-collinear magnets (NCM). A crucial aspect for potential applications is how the spatial proximity between the NCM and vacuum or another material impacts the magnetization texture on the nanoscale. We focus on a prototypical exchange-driven NCM given by the helical spin order of bilayer Fe on Cu(111). Spin-polarized scanning tunnelling spectroscopy and density functional theory reveal a nanosize- and proximity-driven modification of the electronic and magnetic structure of the NCM in interfacial contact with a ferromagnet or with vacuum. An intriguing non-collinearity between the local magnetization in the sample and the electronic magnetization probed above its surface results. It is a direct consequence of the spinor nature of electronic states in NCM. Our findings provide a possible route for advanced control of nanoscale spin textures by confinement. PMID:27721384

  15. Magnetic states controlled by energetic ion irradiation in FeRh thin films

    SciTech Connect

    Fujita, Nao.; Kosugi, S.; Matsui, T.; Iwase, A.; Saitoh, Y.; Kaneta, Y.; Kume, K.; Batchuluun, T.; Ishikawa, N.

    2010-05-15

    Changes in magnetic properties and lattice structure of FeRh films by 180 keV-10 MeV ion (H, He, and I) irradiation are studied. In spite of the irradiation with different ion species and wide range of energies, the changes in magnetization are dominated by solely a single parameter; the density of energy which is deposited through elastic collision between the ions and the samples. For the low deposition energy density, the magnetization increases with increasing the deposition energy density, while the lattice structure remains unchanged. When the deposition energy density becomes larger, however, the magnetization decreases after reaching the maximum value. The decrease in the magnetization accompanies the crystal structure change from B2 to A1. The present results imply that the magnetic state of FeRh films can be designedly controlled by the energetic ion irradiations.

  16. Mapping Curie temperature depth in the western United States with a fractal model for crustal magnetization

    USGS Publications Warehouse

    Bouligand, C.; Glen, J.M.G.; Blakely, R.J.

    2009-01-01

    We have revisited the problem of mapping depth to the Curie temperature isotherm from magnetic anomalies in an attempt to provide a measure of crustal temperatures in the western United States. Such methods are based on the estimation of the depth to the bottom of magnetic sources, which is assumed to correspond to the temperature at which rocks lose their spontaneous magnetization. In this study, we test and apply a method based on the spectral analysis of magnetic anomalies. Early spectral analysis methods assumed that crustal magnetization is a completely uncorrelated function of position. Our method incorporates a more realistic representation where magnetization has a fractal distribution defined by three independent parameters: the depths to the top and bottom of magnetic sources and a fractal parameter related to the geology. The predictions of this model are compatible with radial power spectra obtained from aeromagnetic data in the western United States. Model parameters are mapped by estimating their value within a sliding window swept over the study area. The method works well on synthetic data sets when one of the three parameters is specified in advance. The application of this method to western United States magnetic compilations, assuming a constant fractal parameter, allowed us to detect robust long-wavelength variations in the depth to the bottom of magnetic sources. Depending on the geologic and geophysical context, these features may result from variations in depth to the Curie temperature isotherm, depth to the mantle, depth to the base of volcanic rocks, or geologic settings that affect the value of the fractal parameter. Depth to the bottom of magnetic sources shows several features correlated with prominent heat flow anomalies. It also shows some features absent in the map of heat flow. Independent geophysical and geologic data sets are examined to determine their origin, thereby providing new insights on the thermal and geologic crustal

  17. Analysis of electromagnetic propagation in the magnetic plasma state in spin-ice systems

    NASA Astrophysics Data System (ADS)

    López-Bara, F. I.; López-Aguilar, F.

    2017-05-01

    Low energy excitation states in magnetic structures of the so-called spin-ices are produced via spin flips among contiguous tetrahedrons of their crystal structure. When there are sufficient free positive and negative charges, the system behaves as a magnetic plasma, which could correspond to the highest temperature peak of the specific heat. The electromagnetic waves in both unconfined and confined systems (waveguides) filled with materials of magnetic charges can be able to transmit information and energy. The only problem is the low temperature for which these magnetic entities appear in the spin-ice materials. However, similar behaviour may be present in other compounds at higher temperatures. This analysis is addressed to study physical properties which should be present in those new materials. Therefore, in this paper, we obtain some magnetic linear responses, the effective masses of the magnetic charges from the precession movement of the monopoles which coincides with a strong electromagnetic absorption frequency, the plasmonic physical magnitude which is identified with the cut propagation frequency in a wave guide, and other properties of the electromagnetic propagation in these compounds with effective magnetic monopoles such as the modification of the electromagnetic fields of the wave in the presence of magnetic charges and currents. All these electromagnetic properties can serve as tests for detecting magnetic entities which mimic the behaviour of magnetic monopoles in other different new materials. Besides, these analyses can be illuminating for obtaining possible circuital applications of these materials that lead to "Magnetronic" devices.

  18. Topological repulsion between domain walls in magnetic nanowires leading to the formation of bound states.

    PubMed

    Thomas, Luc; Hayashi, Masamitsu; Moriya, Rai; Rettner, Charles; Parkin, Stuart

    2012-05-01

    Head-to-head and tail-to-tail magnetic domain walls in nanowires behave as free magnetic monopoles carrying a single magnetic charge. Since adjacent walls always carry opposite charges, they attract one another. In most cases this long-range attractive interaction leads to annihilation of the two domain walls. Here, we show that, in some cases, a short-range repulsive interaction suppresses annihilation of the walls, even though the lowest energy state is without any domain walls. This repulsive interaction is a consequence of topological edge defects that have the same winding number. We show that the competition between the attractive and repulsive interactions leads to the formation of metastable bound states made up of two or more domain walls. We have created bound states formed from up to eight domain walls, corresponding to the magnetization winding up over four complete 360° rotations.

  19. Impurity- and magnetic-field-induced quasiparticle states in chiral p-wave superconductors

    NASA Astrophysics Data System (ADS)

    Guo, Yao-Wu; Li, Wei; Chen, Yan

    2017-10-01

    Both impurity- and magnetic-field-induced quasiparticle states in chiral p-wave superconductors are investigated theoretically by solving the Bogoliubov-de Gennes equations self-consistently. At the strong scattering limit, we find that a universal state bound to the impurity can be induced for both a single nonmagnetic impurity and a single magnetic impurity. Furthermore, we find that different chiral order parameters and the corresponding supercurrents have uniform distributions around linear impurities. Calculations of the local density of states in the presence of an external magnetic field show that the intensity peak of the zero-energy Majorana mode in the vortex core can be enhanced dramatically by tuning the strength of the external magnetic field or pairing interaction.

  20. Functional magnetic resonance imaging in oncology: state of the art.

    PubMed

    Guimaraes, Marcos Duarte; Schuch, Alice; Hochhegger, Bruno; Gross, Jefferson Luiz; Chojniak, Rubens; Marchiori, Edson

    2014-01-01

    In the investigation of tumors with conventional magnetic resonance imaging, both quantitative characteristics, such as size, edema, necrosis, and presence of metastases, and qualitative characteristics, such as contrast enhancement degree, are taken into consideration. However, changes in cell metabolism and tissue physiology which precede morphological changes cannot be detected by the conventional technique. The development of new magnetic resonance imaging techniques has enabled the functional assessment of the structures in order to obtain information on the different physiological processes of the tumor microenvironment, such as oxygenation levels, cellularity and vascularity. The detailed morphological study in association with the new functional imaging techniques allows for an appropriate approach to cancer patients, including the phases of diagnosis, staging, response evaluation and follow-up, with a positive impact on their quality of life and survival rate.

  1. Functional magnetic resonance imaging in oncology: state of the art*

    PubMed Central

    Guimaraes, Marcos Duarte; Schuch, Alice; Hochhegger, Bruno; Gross, Jefferson Luiz; Chojniak, Rubens; Marchiori, Edson

    2014-01-01

    In the investigation of tumors with conventional magnetic resonance imaging, both quantitative characteristics, such as size, edema, necrosis, and presence of metastases, and qualitative characteristics, such as contrast enhancement degree, are taken into consideration. However, changes in cell metabolism and tissue physiology which precede morphological changes cannot be detected by the conventional technique. The development of new magnetic resonance imaging techniques has enabled the functional assessment of the structures in order to obtain information on the different physiological processes of the tumor microenvironment, such as oxygenation levels, cellularity and vascularity. The detailed morphological study in association with the new functional imaging techniques allows for an appropriate approach to cancer patients, including the phases of diagnosis, staging, response evaluation and follow-up, with a positive impact on their quality of life and survival rate. PMID:25741058

  2. Possible ground states and parallel magnetic-field-driven phase transitions of collinear antiferromagnets

    NASA Astrophysics Data System (ADS)

    Li, Hai-Feng

    2016-10-01

    Understanding the nature of all possible ground states and especially magnetic-field-driven phase transitions of antiferromagnets represents a major step towards unravelling the real nature of interesting phenomena such as superconductivity, multiferroicity or magnetoresistance in condensed-matter science. Here a consistent mean-field calculation endowed with antiferromagnetic (AFM) exchange interaction (J), easy axis anisotropy (γ), uniaxial single-ion anisotropy (D) and Zeeman coupling to a magnetic field parallel to the AFM easy axis consistently unifies the AFM state, spin-flop (SFO) and spin-flip transitions. We reveal some mathematically allowed exotic spin states and fluctuations depending on the relative coupling strength of (J, γ and D). We build the three-dimensional (J, γ and D) and two-dimensional (γ and D) phase diagrams clearly displaying the equilibrium phase conditions and discuss the origins of various magnetic states as well as their transitions in different couplings. Besides the traditional first-order type one, we unambiguously confirm an existence of a second-order type SFO transition. This study provides an integrated theoretical model for the magnetic states of collinear antiferromagnets with two interpenetrating sublattices and offers a practical approach as an alternative to the estimation of magnetic exchange parameters (J, γ and D), and the results may shed light on nontrivial magnetism-related properties of bulks, thin films and nanostructures of correlated electron systems.

  3. Enhanced Light Emission due to Formation of Semi-polar InGaN/GaN Multi-quantum Wells.

    PubMed

    Zhao, Wan-Ru; Weng, Guo-En; Wang, Jian-Yu; Zhang, Jiang-Yong; Liang, Hong-Wei; Sekiguchi, Takashi; Zhang, Bao-Ping

    2015-12-01

    InGaN/GaN multi-quantum wells (MQWs) are grown on (0001) sapphire substrates by metal organic chemical vapor deposition (MOCVD) with special growth parameters to form V-shaped pits simultaneously. Measurements by atomic force microscopy (AFM) and transmission electron microscopy (TEM) demonstrate the formation of MQWs on both (0001) and ([Formula: see text]) side surface of the V-shaped pits. The latter is known to be a semi-polar surface. Optical characterizations together with theoretical calculation enable us to identify the optical transitions from these MQWs. The layer thickness on ([Formula: see text]) surface is smaller than that on (0001) surface, and the energy level in the ([Formula: see text]) semi-polar quantum well (QW) is higher than in the (0001) QW. As the sample temperature is increased from 15 K, the integrated cathodoluminescence (CL) intensity of (0001) MQWs increases first and then decreases while that of the ([Formula: see text]) MQWs decreases monotonically. The integrated photoluminescence (PL) intensity of (0001) MQWs increases significantly from 15 to 70 K. These results are explained by carrier injection from ([Formula: see text]) to (0001) MQWs due to thermal excitation. It is therefore concluded that the emission efficiency of (0001) MQWs at high temperatures can be greatly improved due to the formation of semi-polar MQWs.

  4. Modeling of Metal-Insulator-Semiconductor Dualband Si/SiO2 Multi-Quantum Well UV Detectors

    NASA Astrophysics Data System (ADS)

    Rostami, A.; Leilaeioun, M.; Golmohammadi, S.; Rasooli Saghai, H.

    2012-11-01

    This article intends to propose a self-consistent theoretical model for Metal-Insulator-Semiconductor (MIS) dualband Si/SiO2 multi-quantum well (MQW) UV photodetector. Employing this model, general characteristics of MIS UV photodetectors such as dark and photocurrent density-voltage (J-V) curves are simulated. The results reveal that the proposed structure reduces dark current since first the resonant tunneling multi-barrier is designed such that the electron tunneling probability is unity at energies coincident with the peak detection wavelength, and secondly, tunneling significantly decreases at energies which are smaller than this optimum value and accordingly, transport of carriers contributing to the dark current, which have broad energy distribution at high temperatures, is inhibited. Moreover, the article demonstrates that the proposed structure can detect two individual x wavelengths in the UV range, simultaneously. The related absorption and responsivity curves are obtained and depicted. Defects in the SiO2 barriers are simulated indirectly by varying the electron effective tunneling mass in SiO2. Reductions in the SiO2 electron effective tunneling mass lead to an increase in dark current of the device.

  5. Dilute nitride multi-quantum well multi-junction design: a route to ultra-efficient photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Vijaya, Gopi Krishna; Alemu, Andenet; Freundlich, Alex

    2011-02-01

    The current high-efficiency triple junction (Al)InGaP (1.9eV)/GaAs(1.42eV)/ Ge(0.66eV) design for a solar cell can be improved upon by the use dilute nitrides to include a sub-cell in the 1eV range. Addition of a small percentage of nitrogen to III-V semiconductor alloys (such as GaAsN) enables us to achieve the required bandgap, however these bulk dilute nitride structures suffer from a reduced minority carrier lifetime, decreasing the overall current output. The route suggested herein is to include dilute nitride multi-quantum wells (with thicknesses much lesser than the minority carrier diffusion length) within the intrinsic region of a GaAs subcell. Modeling has been done for this structure to obtain the confined energies of the electrons and holes, as well as the absorption coefficient and thereby the spectral response of the 4-junction cell. The results show that it is possible to achieve with the appropriate current matching, a conversion efficiency of ~40% under AM0 (1 sun) with up to ~18 mAcm-2 short circuit current.

  6. Magnetic Fabrics of the Cabreuva Granite, São Paulo State, SE Brazil: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Abujamra, J. P.; Raposo, M. I. B.

    2015-12-01

    Magnetic fabric and rock magnetism studies were performed on the units of the 570 ± 3 Ma-old isotropic Cabreuva granite (NW of São Paulo State). This intrusion with 160 km2 is roughly elliptical in the oriental and occidental sectors whereas in the south sector it is circular. It is composed of quartz-monzodiorite, granodiorite, quartz-monzonite, monzogranite, diorite, quartz syenite and synogarnite. Magnetic fabrics were determined by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). The two fabrics are coaxial. The parallelism between AMS and AARM tensors excludes the presence of a single domain (SD) effect on the AMS fabric of the units. Several rock-magnetism experiments performed in one specimen from each sampled unit show that for all units the magnetic susceptibility and magnetic fabrics are carried by magnetite grains. Foliations and lineations in the units were successful determined by applying magnetic methods. Most of the magnetic foliations are horizontal or steeply dipping in all units, and are roughly parallel to the foliation of the rocks which surround the granite. The magnetic lineations present mostly low plunges for the whole pluton. Thin section analysis show that rocks from the Cabreuva granite were not affected by the regional strain during and after emplacement. This evidence allows us to interpret the observed magnetic fabrics as primary in origin (magmatic) acquired when the rocks were solidified as a result of magma flow, in which horizontally plunging magnetic lineation suggests that the feeder zone is far from this area.

  7. Statistical Behavior of Formation Process of Magnetic Vortex State in Ni80Fe20 Nanodisks

    SciTech Connect

    Im, Mi-Young; Fischer, Peter; Keisuke, Yamada; Kasai, Shinya

    2011-01-14

    Magnetic vortices in magnetic nanodots, which are characterized by an in-plane (chirality) and an out-of-plane (polarity) magnetizations, have been intensively attracted because of their high potential for technological application to data storage and memory scheme as well as their scientific interest for an understanding of fundamental physics in magnetic nanostructures. Complete understanding of the formation process of vortex state in magnetic vortex systems is very significant issue to achieve storage and memory technologies using magnetic vortices and understand intrinsic physical properties in magnetic nanostructures. In our work, we have statistically investigated the formation process of vortex state in permalloy (Py, Ni{sub 80}Fe{sub 20}) nanodisks through the direct observation of vortex structure utilizing a magnetic transmission soft X-ray microscopy (MTXM) with a high spatial resolution down to 20 nm. Magnetic imaging in Py nanodots was performed at the Fe L{sub 3} (707 eV) absorption edge. Figure 1 shows in-plane and out-of-plane magnetic components observed in 40 nm thick nanodot arrays with different dot radius of r = 500 and 400 nm, respectively. Vortex chirality, either clockwise (CW) or counter-clockwise (CCW), and polarity, either up or down, are clearly visible in both arrays. To investigate the statistical behavior in formation process of the vortex state, the observation of vortex structure at a remanant state after saturation of nanodots by an external magnetic field of 1 kOe has been repeatedly performed over 100 times for each array. The typical MTXM images of vortex chirality taken in two successive measurements together with their overlapped images in nanodot arrays of r = 500 and 400 nm are displayed in Fig. 2. Within the statistical measurement, the formation process of chirality of either CW or CCW is quite stochastic in each nanodot. Similar behavior is also witnessed in the formation of vortex polarity observed in consecutive

  8. An agglomeration induced glassy magnetic state in a carbon nanotube/NiO nanocomposite system.

    PubMed

    Chattopadhyay, S; Jana, S; Giri, S; Majumdar, S

    2012-10-31

    A series of nanocomposite materials were synthesized using multi-walled carbon nanotubes (MWCNTs) and NiO nanoparticles by varying the concentration of NiO in the MWCNT host matrix. Such an increment in the NiO particle density actually tunes the degree of isolation among the magnetic nanoparticles. Careful investigation by transmission electron microscopy shows that particle agglomeration increases substantially with NiO particle density. Field dependence of magnetization measurements depict a gradual enhancement of coercivity with increasing NiO concentration, signifying the enhancement of magnetic anisotropy in this nanocomposite system. Furthermore, field cooled and zero field cooled memory effect as well as magnetization relaxation measurements show that a glassy magnetic state gradually develops when the concentration increases. Analysis based on the result of high resolution transmission electron microscopy along with the magnetization data reveals that interparticle magnetic exchange interaction in the presence of interfacial disorders plays the major role in the emergence of the glassy magnetic state in this nanocomposite system.

  9. Exciton states in a circular graphene quantum dot: Magnetic field induced intravalley to intervalley transition

    NASA Astrophysics Data System (ADS)

    Li, L. L.; Zarenia, M.; Xu, W.; Dong, H. M.; Peeters, F. M.

    2017-01-01

    The magnetic-field dependence of the energy spectrum, wave function, binding energy, and oscillator strength of exciton states confined in a circular graphene quantum dot (CGQD) is obtained within the configuration interaction method. We predict that (i) excitonic effects are very significant in the CGQD as a consequence of a combination of geometric confinement, magnetic confinement, and reduced screening; (ii) two types of excitons (intravalley and intervalley) are present in the CGQD because of the valley degree of freedom in graphene; (iii) the intravalley and intervalley exciton states display different magnetic-field dependencies due to the different electron-hole symmetries of the single-particle energy spectra; (iv) with increasing magnetic field, the exciton ground state in the CGQD undergoes an intravalley to intervalley transition accompanied by a change of angular momentum; (v) the exciton binding energy does not increase monotonically with the magnetic field due to the competition between geometric and magnetic confinements; and (vi) the optical transitions of the intervalley and intravalley excitons can be tuned by the magnetic field, and valley-dependent excitonic transitions can be realized in a CGQD.

  10. Experimental manipulation of magnetic states of magnetostrictive nanomagnets using surface acoustic waves

    NASA Astrophysics Data System (ADS)

    Sampath, Vimal; Bhattacharya, Dhritiman; D'Souza, Noel; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

    The use of Surface Acoustic Waves (SAW) to assist magnetization switching in magnetostrictive nanomagnets has been theoretically studied and SAW-induced magnetization rotation in micron size magnets has been experimentally demonstrated. We report recent experiments on manipulation of magnetic states of Co nanoscale magnets shaped like elliptical disks (~300 nm major axis, 240 nm minor axis and 10 nm thickness) delineated on bulk 128 Y-cut lithium niobate using SAW. Specifically, isolated nanomagnets that are initially in single domain states with magnetization pointing along the major axis of the ellipse are driven into a vortex state by SAW waves. However, SAW waves can trigger complete magnetization reversal in nanomagnets of moderate shape anisotropy that are dipole coupled to a highly shape anisotropic neighboring nanomagnet. The authors acknowledge the use of high voltage and high frequency pulse generator from Prof. Umit Ozgur's lab and the help of Prof. Gary Atkinson in fabrication of the IDTs for generating the SAW. We acknowledge SHF-Small CCF-1216614 and CAREER CCF-1253370 grants; and use of CNST Nanofab facility at NIST, Gaithersburg.

  11. Magnetically Ordered State and Crystalline-Electric-Field Effects in SmBe13

    NASA Astrophysics Data System (ADS)

    Hidaka, Hiroyuki; Yamazaki, Seigo; Shimizu, Yusei; Miura, Naoyuki; Tabata, Chihiro; Yanagisawa, Tatsuya; Amitsuka, Hiroshi

    2017-07-01

    The physical properties of single-crystalline SmBe13 with a NaZn13-type cubic structure have been studied by electrical resistivity (ρ), specific heat (C), and magnetization (M) measurements in magnetic fields of up to 9 T. The temperature (T) dependence of ρ shows normal metallic behavior without showing the Kondo -ln T behavior, suggesting the weak hybridization effect in this system. Analyses of the temperature dependence of C suggest that the Sm ions of this compound are trivalent and that the crystalline-electric-field (CEF) ground state is a Γ8 quartet with a first-excited state of a Γ7 doublet located at the energy scale of ˜90 K. Mean-field calculations based on the suggested CEF level scheme can reasonably well reproduce the T dependence of magnetic susceptibility (χ) below ˜70 K. These results in the paramagnetic state strongly indicate that the 4f electrons are well localized with the Sm3+ configuration. At low temperatures, the 4f electrons undergo a magnetic order at TM ˜ 8.3 K, where χ(T) shows an antiferromagnetic-like cusp anomaly. From the positive Curie-Weiss temperature obtained from the mean-field calculations and from a constructed magnetic phase diagram with multiple regions, we discussed the magnetic structure of SmBe13 below TM, by comparing with other isostructural MBe13 compounds showing helical-magnetic ordering.

  12. Effect of hybrid state of surface plasmon-polaritons, magnetic defect mode and optical Tamm state on nonreciprocal propagation

    NASA Astrophysics Data System (ADS)

    Fang, Yun-tuan; Ni, Yue-xin; He, Hang-qing; Hu, Jian-xia

    2014-06-01

    A coupled system of semi-infinite one-dimensional photonic crystal coated with metal and magnetic films is proposed. The properties of hybrid states of surface plasmon-polaritons, magnetic defect mode and optical Tamm state from the system have been studied through the Bloch theorem of periodic structure and the transfer matrix method. In the hybrid states the magneto-optical effect is amplified due to the field resonance amplification at the interface between the metal and magneto-optical material. Tunable nonreciprocal propagation can be achieved from the hybrid states through changing the thickness of magneto-optical material layer. The nonreciprocity is found to be robust to the change of metal thickness.

  13. Zero-field NMR and NQR studies of magnetically ordered state in charge-ordered EuPtP

    NASA Astrophysics Data System (ADS)

    Koyama, T.; Maruyama, T.; Ueda, K.; Mito, T.; Mitsuda, A.; Umeda, M.; Sugishima, M.; Wada, H.

    2015-03-01

    EuPtP undergoes two valence transitions and has two kinds of valence states of Eu ions at low temperatures. In the charge-ordered state, this compound shows an antiferromagnetic order ascribed to magnetic divalent Eu ions. We investigated the antiferromagnetically ordered state of EuPtP by nuclear magnetic resonance (NMR) measurement and nuclear quadrupole resonance (NQR) measurement in a zero external magnetic field. The observed 153Eu NMR signals of a magnetic divalent state and Eu,153151 NQR signals of a nonmagnetic trivalent state clearly demonstrate that the spins order in the hexagonal basal plane and the internal magnetic field is not canceled out, even at the Eu3 + layers which are in the middle of magnetic Eu2 + layers. In addition, the observation of 31P and 195Pt NMR spectra allowed us to discuss a possible magnetic structure. We also evaluated the nuclear quadrupole frequencies for both Eu2 + and Eu3 + ion states.

  14. United States Research and Development effort on ITER magnet tasks

    DOE PAGES

    Martovetsky, Nicolai N.; Reierson, Wayne T.

    2011-01-22

    This study presents the status of research and development (R&D) magnet tasks that are being performed in support of the U.S. ITER Project Office (USIPO) commitment to provide a central solenoid assembly and toroidal field conductor for the ITER machine to be constructed in Cadarache, France. The following development tasks are presented: winding development, inlets and outlets development, internal and bus joints development and testing, insulation development and qualification, vacuum-pressure impregnation, bus supports, and intermodule structure and materials characterization.

  15. Model for QCD ground state with magnetic disorder

    NASA Astrophysics Data System (ADS)

    Szczepaniak, Adam P.; Matevosyan, Hrayr H.

    2010-05-01

    We explore an ansatz for the QCD vacuum in the Coulomb gauge that describes gauge field fluctuations in the presence of a weakly interacting gas of Abelian monopoles. Such magnetic disorder leads to long-range correlations which are manifested through the area law for the Wilson loop. In particular we focus on the role of the residual monopole-monopole interactions in providing the mechanism for suppression of the gluon propagator at low momenta which also leads to low-momentum enhancement in the ghost propagator.

  16. Diamond-nitrogen-vacancy electronic and nuclear spin-state anticrossings under weak transverse magnetic fields

    NASA Astrophysics Data System (ADS)

    Clevenson, Hannah; Chen, Edward H.; Dolde, Florian; Teale, Carson; Englund, Dirk; Braje, Danielle

    2016-08-01

    We report on detailed studies of electronic and nuclear spin states in the diamond-nitrogen-vacancy (NV) center under weak transverse magnetic fields. We numerically predict and experimentally verify a previously unobserved NV hyperfine level anticrossing (LAC) occurring at bias fields of tens of gauss—two orders of magnitude lower than previously reported LACs at ˜500 and ˜1000 G axial magnetic fields. We then discuss how the NV ground-state Hamiltonian can be manipulated in this regime to tailor the NV's sensitivity to environmental factors and to map into the nuclear spin state.

  17. Superconductivity in the non-magnetic state of iron under pressure.

    PubMed

    Shimizu, K; Kimura, T; Furomoto, S; Takeda, K; Kontani, K; Onuki, Y; Amaya, K

    2001-07-19

    Ferromagnetism and superconductivity are thought to compete in conventional superconductors, although in principle it is possible for any metal to become a superconductor in its non-magnetic state at a sufficiently low temperature. At pressures above 10 GPa, iron is known to transform to a non-magnetic structure and the possibility of superconductivity in this state has been predicted. Here we report that iron does indeed become superconducting at temperatures below 2 K at pressures between 15 and 30 GPa. The transition to the superconducting state is confirmed by both a drop in resistivity and observation of the Meissner effect.

  18. Competing magnetic orders in the superconducting state of heavy-fermion CeRhIn5

    DOE PAGES

    Rosa, P. F. S.; Kang, J.; Luo, Yongkang; ...

    2017-05-09

    Applied pressure drives the heavy-fermion antiferromagnet CeRhIn5 toward a quantum critical point that becomes hidden by a dome of unconventional superconductivity. Magnetic fields suppress this superconducting dome, unveiling the quantum phase transition of local character. Here in this paper, we show that 5% magnetic substitution at the Ce site in CeRhIn5, either by Nd or Gd, induces a zero-field magnetic instability inside the superconducting state. This magnetic state not only should have a different ordering vector than the high-field local-moment magnetic state, but it also competes with the latter, suggesting that a spin-density-wave phase is stabilized in zero field bymore » Nd and Gd impurities, similarly to the case of Ce0.95Nd0.05CoIn5. Supported by model calculations, we attribute this spin-density wave instability to a magnetic-impurity-driven condensation of the spin excitons that form inside the unconventional superconducting state.« less

  19. Competing magnetic orders in the superconducting state of heavy-fermion CeRhIn5

    NASA Astrophysics Data System (ADS)

    Rosa, P. F. S.; Kang, J.; Luo, Yongkang; Wakeham, N.; Bauer, E. D.; Ronning, F.; Fisk, Z.; Fernandes, R. M.; Thompson, J. D.

    2017-05-01

    Applied pressure drives the heavy-fermion antiferromagnet CeRhIn5 toward a quantum critical point that becomes hidden by a dome of unconventional superconductivity. Magnetic fields suppress this superconducting dome, unveiling the quantum phase transition of local character. Here, we show that 5%5% magnetic substitution at the Ce site in CeRhIn5, either by Nd or Gd, induces a zero-field magnetic instability inside the superconducting state. This magnetic state not only should have a different ordering vector than the high-field local-moment magnetic state, but it also competes with the latter, suggesting that a spin-density-wave phase is stabilized in zero field by Nd and Gd impurities, similarly to the case of Ce0.95Nd0.05CoIn5. Supported by model calculations, we attribute this spin-density wave instability to a magnetic-impurity-driven condensation of the spin excitons that form inside the unconventional superconducting state.

  20. Short-range correlations in the magnetic ground state of Na4 Ir3 O8

    NASA Astrophysics Data System (ADS)

    Dally, Rebecca; Hogan, Tom; Amato, Alex; Luetkens, Hubertus; Baines, Chris; Rodriguez-Rivera, Jose; Graf, Michael; Wilson, Stephen

    2015-03-01

    The magnetic ground state of the candidate three-dimensional quantum spin liquid Na4 Ir3O8 has been studied through bulk magnetization, muon spin relaxation and neutron scattering measurements. Na4 Ir3O8 possesses a unique hyper-Kagome lattice of Ir moments that is potentially accompanied by a novel realization of Heisenberg-Kitaev exchange. This fact combined with the absence of previously reported magnetic ordering has led to its candidacy as a three-dimensional quantum spin liquid. Our combined experimental data show that a short-range, frozen, ground state comprised of quasi-static moments develops in this material below a characteristic temperature TF = 6 K , persisting down until at least 20 mK. The expected dynamical ground state of a quantum spin liquid was not observed but rather an inhomogeneous quasi-static spin state that survives with persistent long timescale fluctuations.

  1. The effect of magnetic and non-magnetic ion damage on the surface state in SmB6

    SciTech Connect

    Wakeham, N.; Wen, J.; Wang, Y. Q.; Fisk, Z.; Ronning, F.; Thompson, J. D.

    2015-07-14

    SmB6 is a Kondo insulator with a band structure that is topologically distinct from the vacuum. We theoretically predict this in order to produce metallic topological surface states that are robust to perturbations that do not break time reversal symmetry, such as non-magnetic defects. But, the surface state may be destroyed by an impurity with a sufficiently large magnetic moment. In order to test this prediction we show measurements of the resistance of the surface state of single crystals of SmB6 with varying levels of damage induced by magnetic and non-magnetic ion irradiation. Finally, we find that at a sufficiently high concentration of damage the surface state reconstructs below an amorphous damaged layer, whether the damage was caused by a magnetic or non-magnetic ion.

  2. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Electronic States of Elliptical Quantum Rings Subjected to a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Li, Hai-Tao; Liu, Li-Zhe; Liu, Jian-Jun

    2008-11-01

    We calculate the energy states and Aharonov-Bohm oscillations of an electron in elliptical quantum rings in the presence of a uniform magnetic Geld by using an exact numerical diagonalization. The calculated results show that the elliptical quantum rings are flatter, larger amplitudes and periods of the Aharonov-Bohm oscillations are observed. In addition, in the limits of a circular quantum ring, the results of our approach are in good agreement with those of earlier theories.

  3. Strain engineering of nanowire multi-quantum well demonstrated by Raman spectroscopy.

    PubMed

    Wölz, Martin; Ramsteiner, Manfred; Kaganer, Vladimir M; Brandt, Oliver; Geelhaar, Lutz; Riechert, Henning

    2013-09-11

    An analysis of the strain in an axial nanowire superlattice shows that the dominating strain state can be defined arbitrarily between unstrained and maximum mismatch strain by choosing the segment height ratios. We give experimental evidence for a successful strain design in series of GaN nanowire ensembles with axial InxGa1-xN quantum wells. We vary the barrier thickness and determine the strain state of the quantum wells by Raman spectroscopy. A detailed calculation of the strain distribution and LO phonon frequency shift shows that a uniform in-plane lattice constant in the nanowire segments satisfactorily describes the resonant Raman spectra, although in reality the three-dimensional strain profile at the periphery of the quantum wells is complex. Our strain analysis is applicable beyond the InxGa1-xN/GaN system under study, and we derive universal rules for strain engineering in nanowire heterostructures.

  4. Dynamical skyrmion state in a spin current nano-oscillator with perpendicular magnetic anisotropy.

    PubMed

    Liu, R H; Lim, W L; Urazhdin, S

    2015-04-03

    We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films.

  5. Exact ground state properties of the classical Heisenberg model for giant magnetic molecules

    SciTech Connect

    Axenovich, Maria; Luban, Marshall

    2001-03-01

    We find the exact ground state energy and magnetic moment for an arbitrary magnetic field H of the classical Heisenberg model of spins on the vertices of an icosidodecahedron. This model provides an accurate description of the magnetic properties of the giant paramagnetic molecule {l_brace}Mo{sub 72}Fe{sub 30}{r_brace} in which 30 Fe{sup 3+} ions are coupled via antiferromagnetic exchange. The strong frustration of the magnetic interaction in the molecule is relaxed when the angle between nearest-neighbor spins is 120{sup o}. We predict that the magnetic moment is linear with H until saturating at a critical field H{sub c}, and this is consistent with the results of a recent experiment at 0.46 K. We derive our results using a graph-theoretical construction and a special property, three-colorability, of the icosidodecahedron. We also consider spins on the vertices of an octahedron, icosahedron, and dodecahedron.

  6. The transverse magnetic field effect on steady-state solutions of the Bursian diode

    SciTech Connect

    Pramanik, Sourav; Chakrabarti, Nikhil

    2015-04-15

    A study of steady-states of a planar vacuum diode driven by a cold electron beam (the Bursian diode) under an external transverse magnetic field is presented. The regime of no electrons turned around by a magnetic field only is under the consideration. The emitter electric field is evaluated as a characteristic function for the existence of solutions depending on the diode length, the applied voltage, and the magnetic field strength. At certain conditions, it is shown that a region of non-unique solutions exists in the Bursian diode when the magnetic field is absent. An expression for the maximum current transmitted through the diode is derived. The external magnetic field is put forth to control fast electronic switches based on the Bursian diode.

  7. Laboratory Observation of a Plasma-Flow-State Transition from Diverging to Stretching a Magnetic Nozzle.

    PubMed

    Takahashi, Kazunori; Ando, Akira

    2017-06-02

    An axial magnetic field induced by a plasma flow in a divergent magnetic nozzle is measured when injecting the plasma flow from a radio frequency (rf) plasma source located upstream of the nozzle. The source is operated with a pulsed rf power of 5 kW, and the high density plasma flow is sustained only for the initial ∼100  μsec of the discharge. The measurement shows a decrease in the axial magnetic field near the source exit, whereas an increase in the field is detected at the downstream side of the magnetic nozzle. These results demonstrate a spatial transition of the plasma-flow state from diverging to stretching the magnetic nozzle, where the importance of both the Alfvén and ion Mach numbers is shown.

  8. Kinetic control of structural and magnetic states in LuBaCo4O7.

    SciTech Connect

    Avci, S.; Chmaissem, O.; Zheng, H.; Huq, A.; Khalyavin, D.; Stephens, P.; Suchomel, M.; Manuel, P.; Mitchell, J.

    2012-01-01

    The RBaCo{sub 4}O{sub 7} (R = Ca, Y, Tb, Ho, Tm, Yb, Lu) compounds provide a novel topology for studying the competition between triangular geometry and magnetic order. Here, we report the structural and magnetic behavior of the Lu member of this series via neutron and synchrotron x-ray diffraction, magnetization, and resistivity measurements. We determined sequential phase transitions and a strong competition between a stable and a metastable low-temperature state that critically depends on controlled cooling rates and the associated heat removal kinetics. No evidence for long-range ordered magnetism was detected by neutron diffraction at any temperature. However, very slow spin dynamics are evidenced by time-dependent neutron diffraction measurements and can be explained by several competing magnetic phases with incommensurate short-range correlations coexisting in this material.

  9. Exchange coupling and noncollinear magnetic states in Ni/Fen/Ni(1 0 0) multilayers

    NASA Astrophysics Data System (ADS)

    Malonda-Boungou, B. R.; Stojić, N.; Binggeli, N.; M'Passi-Mabiala, B.

    2015-01-01

    The Ni interlayer exchange coupling (IEC) and the atomic-scale magnetic configurations in fcc Ni /Fen /Ni (1 0 0) multilayers, with ultrathin Fe spacers, are investigated using first-principles density-functional theory including the noncollinear spin formalism. The trends with changing Fe thickness (n) between 3 and 5 monolayers (MLs) are examined. For n = 3 and 4 MLs, we find the ground state to display antiferromagnetic IEC between the Ni films, while for the 5-ML Fe spacer, the IEC changes into ferromagnetic. Upon reversal of the magnetization alignment, from antiparallel to parallel, between the Ni films with 3- and 4-ML thick Fe spacer, we find noncollinear magnetic configurations in the Fe layer as the lowest-energy states, which are related to the magnetic instability towards noncollinear solutions in bulk γ -Fe.

  10. Vortex states of a superconducting film from a magnetic dot array.

    PubMed

    Priour, D J; Fertig, H A

    2004-07-30

    Using Ginzburg-Landau theory, we find novel configurations of vortices in superconducting thin films subject to the magnetic field of a magnetic dot array, with dipole moments oriented perpendicular to the film. Sufficiently strong magnets cause the formation of vortex-antivortex pairs. In most cases, the vortices are confined to dot regions, while the antivortices can form a rich variety of lattice states. We propose an experiment in which the perpendicular component of the dot dipole moments can be tuned using an in-plane magnetic field. We show that in such an experiment the vortex-antivortex pair density shows broad plateaus as a function of the dipole strength. Many of the plateaus correspond to vortex configurations that break dot lattice symmetries. In some of these states, the vortex cores are strongly distorted. Possible experimental consequences are mentioned.

  11. Effect of transverse magnetic field on the steady state properties of Plasma Diodes

    NASA Astrophysics Data System (ADS)

    Pramanik, Sourav; Kuznetsov, Victor; Chakrabarti, Nikhil

    2016-10-01

    A study of the steady-states of the Plasma Diodes (e.g., Bursian diode, Pierce diode etc.) driven by a cold electron beam is presented in presence of an external transverse magnetic field is presented. Both the regimes of no electron-reflection and electron-reflection are taken into account. Steady state solutions are evaluated using emitter electric field as a characteristic parameters, for fixed values of the diode length, applied voltage, and magnetic field strength. For our purpose, both the Eulerian and Lagrangian descriptions are employed. It is shown that transverse magnetic field has profound influences on the space charge limit, maximum diode current, aperiodic instability and other characteristic parameters. An external magnetic field can be used to design fast electronic switches based on its effects on the Plasma diode.

  12. Magnetic states of linear defects in graphene monolayers: Effects of strain and interaction

    NASA Astrophysics Data System (ADS)

    Alexandre, Simone S.; Nunes, R. W.

    2017-08-01

    The combined effects of defect-defect interaction and strains of up to 10% on the onset of magnetic states in the quasi-one-dimensional electronic states generated by the so-called 558 linear defect in graphene monolayers are investigated by means of ab initio calculations. Results are analyzed on the basis of the heuristics of the Stoner criterion. We find that conditions for the emergence of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel strains (along the defect direction) as well as by uniaxial compressive perpendicular strains, at both limits of isolated and interacting 558 defects. Parallel tensile strains and perpendicular compressive strains are shown to give rise to two cooperative effects that favor the emergence of itinerant magnetism on the 558 defect in graphene: enhancement of the density of states (DOS) of the resonant defect states in the region of the Fermi level and tuning of the Fermi level to the maximum of the related DOS peak. On the other hand, parallel compressive strains and perpendicular tensile strains are shown to be detrimental to the development of magnetic states in the 558 defect, because in these cases the Fermi level is found to shift away from the maximum of the DOS of the defect states. Effects of isotropic and unisotropic biaxial strains are also analyzed in terms of the conditions encoded in the Stoner criterion.

  13. Probing Electronic States of Magnetic Semiconductors Using Atomic Scale Microscopy & Spectroscopy

    DTIC Science & Technology

    2013-12-01

    magnetic atoms on the surface of a superconductor can be used as a versatile platform for creating a topological superconductor . These initial...topological superconductivity and Majorana fermions in a chain of magnetic atoms on the surface of a superconductor Students and postdocs supported...of this grant: 1. H. Beidenkopf, P . Roushan, and A. Yazdani, “Visualizing topological surface states and their novel properties using scanning

  14. Topological and unconventional magnetic states in transition metal oxides

    NASA Astrophysics Data System (ADS)

    Fiete, Gregory

    In this talk I describe some recent work on unusual correlated phases that may be found in bulk transition metal oxides with strong spin-orbit coupling. I will focus on model Hamiltonian studies that are motivated by the pyrocholore iridates, though the correlated topological phases described may appear in a much broader class of materials. I will describe a variety of fractionalized topological phases protected by time-reversal and crystalline symmetries: The weak topological Mott insulator (WTMI), the TI* phase, and the topological crystalline Mott insulator (TCMI). If time permits, I will also discuss closely related heterostructures of pyrochlore iridates in a bilayer and trilayer film geometry. These quasi-two dimensional systems may exhibit a number of interesting topological and magnetic phases. This work is generously funded by the ARO, DARPA, and the NSF.

  15. Melting of hexagonal skyrmion states in chiral magnets

    NASA Astrophysics Data System (ADS)

    Ambrose, M. C.; Stamps, R. L.

    2013-05-01

    Skyrmions are spiral structures observed in thin films of certain magnetic materials (Uchida et al 2006 Science 311 359-61). Of the phases allowed by the crystalline symmetries of these materials (Yi et al 2009 Phys. Rev. B 80 054416), only the hexagonally packed phases (SCh) have been observed. Here the melting of the SCh phase is investigated using Monte Carlo simulations. In addition to the usual measure of skyrmion density, chiral charge, a morphological measure is considered. In doing so it is shown that the low-temperature reduction in chiral charge is associated with a change in skyrmion profiles rather than skyrmion destruction. At higher temperatures, the loss of six-fold symmetry is associated with the appearance of elongated skyrmions that disrupt the hexagonal packing.

  16. Solving Quantum Ground-State Problems with Nuclear Magnetic Resonance

    PubMed Central

    Li, Zhaokai; Yung, Man-Hong; Chen, Hongwei; Lu, Dawei; Whitfield, James D.; Peng, Xinhua; Aspuru-Guzik, Alán; Du, Jiangfeng

    2011-01-01

    Quantum ground-state problems are computationally hard problems for general many-body Hamiltonians; there is no classical or quantum algorithm known to be able to solve them efficiently. Nevertheless, if a trial wavefunction approximating the ground state is available, as often happens for many problems in physics and chemistry, a quantum computer could employ this trial wavefunction to project the ground state by means of the phase estimation algorithm (PEA). We performed an experimental realization of this idea by implementing a variational-wavefunction approach to solve the ground-state problem of the Heisenberg spin model with an NMR quantum simulator. Our iterative phase estimation procedure yields a high accuracy for the eigenenergies (to the 10−5 decimal digit). The ground-state fidelity was distilled to be more than 80%, and the singlet-to-triplet switching near the critical field is reliably captured. This result shows that quantum simulators can better leverage classical trial wave functions than classical computers PMID:22355607

  17. Switchable quantum anomalous Hall state in a strongly frustrated lattice magnet.

    PubMed

    Venderbos, Jörn W F; Daghofer, Maria; van den Brink, Jeroen; Kumar, Sanjeev

    2012-10-19

    We establish that the interplay of itinerant fermions with localized magnetic moments on a checkerboard lattice leads to magnetic flux phases. For weak itineracy the flux phase is coplanar and the electronic dispersion takes the shape of graphenelike Dirac fermions. Stronger itineracy drives the formation of a noncoplanar, chiral flux phase, in which the Dirac fermions acquire a topological mass that is proportional to a ferromagnetic spin polarization. Consequently the system self-organizes into a ferromagnetic quantum anomalous Hall state in which the direction of its dissipationless edge currents can be switched by an applied magnetic field.

  18. Magnetic Polarization of the Americium J =0 Ground State in AmFe2

    NASA Astrophysics Data System (ADS)

    Magnani, N.; Caciuffo, R.; Wilhelm, F.; Colineau, E.; Eloirdi, R.; Griveau, J.-C.; Rusz, J.; Oppeneer, P. M.; Rogalev, A.; Lander, G. H.

    2015-03-01

    Trivalent americium has a nonmagnetic (J =0 ) ground state arising from the cancellation of the orbital and spin moments. However, magnetism can be induced by a large molecular field if Am3 + is embedded in a ferromagnetic matrix. Using the technique of x-ray magnetic circular dichroism, we show that this is the case in AmFe2 . Since ⟨Jz⟩=0 , the spin component is exactly twice as large as the orbital one, the total Am moment is opposite to that of Fe, and the magnetic dipole operator ⟨Tz⟩ can be determined directly; we discuss the progression of the latter across the actinide series.

  19. Shallow donor-like impurity states in magnetic field in n-type InP

    NASA Astrophysics Data System (ADS)

    Aulombard, R. L.; Kadri, A.; Zitouni, K.; Konczewicz, L.

    1987-02-01

    We present the evidence of hydrogenic behavior of shallow donor-like impurity states in n-type InP (8.5 × 10 15 cm -3 ≲ N d-N a ≲ 6.2 × 10 16 cm -3) from magnetic freeze out experiments at magnetic fields up to 18 T. This occurs at T ≳ 10 K and at a magnetic field sufficiently high to induce a metal-insulator transition. At high fields, the reduction of the binding energy with respect to the hydrogenic model of LARSEN can be well accounted for by the increasing overlap of the impurity wave functions as the donor concentration increases.

  20. Spherical, cylindrical and tetrahedral symmetries; hydrogenic states at high magnetic field in Si:P

    PubMed Central

    Lewis, R. A.; Bruno-Alfonso, A.; de Souza, G. V. B.; Vickers, R. E. M.; Colla, J. A.; Constable, E.

    2013-01-01

    Phosphorous donors in silicon have an electronic structure that mimics the hydrogen atom, albeit on a larger length, smaller energy and smaller magnetic field scale. While the hydrogen atom is spherically symmetric, an applied magnetic field imposes cylindrical symmetry, and the solid-state analogue involves, in addition, the symmetry of the Si crystal. For one magnetic field direction, all six conduction-band valleys of Si:P become equivalent. New experimental data to high laboratory fields (30 T), supported by new calculations, demonstrate that this high symmetry field orientation allows the most direct comparison with free hydrogen. PMID:24336145

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

    SciTech Connect

    Demin, G. D. Popkov, A. F.; Dyuzhev, N. A.

    2015-12-15

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

  2. Electronic and magnetic properties of spiral spin-density-wave states in transition-metal chains

    NASA Astrophysics Data System (ADS)

    Tanveer, M.; Ruiz-Díaz, P.; Pastor, G. M.

    2016-09-01

    The electronic and magnetic properties of one-dimensional (1D) 3 d transition-metal nanowires are investigated in the framework of density functional theory. The relative stability of collinear and noncollinear (NC) ground-state magnetic orders in V, Mn, and Fe monoatomic chains is quantified by computing the frozen-magnon dispersion relation Δ E (q ⃗) as a function of the spin-density-wave vector q ⃗. The dependence on the local environment of the atoms is analyzed by varying systematically the lattice parameter a of the chains. Electron correlation effects are explored by comparing local spin-density and generalized-gradient approximations to the exchange and correlation functional. Results are given for Δ E (q ⃗) , the local magnetic moments μ⃗i at atom i , the magnetization-vector density m ⃗(r ⃗) , and the local electronic density of states ρi σ(ɛ ) . The frozen-magnon dispersion relations are analyzed from a local perspective. Effective exchange interactions Ji j between the local magnetic moments μ⃗i and μ⃗j are derived by fitting the ab initio Δ E (q ⃗) to a classical 1D Heisenberg model. The dominant competing interactions Ji j at the origin of the NC magnetic order are identified. The interplay between the various Ji j is revealed as a function of a in the framework of the corresponding magnetic phase diagrams.

  3. Chemical disorder in topological insulators: A route to magnetism tolerant topological surface states

    DOE PAGES

    Martínez-Velarte, M. Carmen; Kretz, Bernhard; Moro-Lagares, Maria; ...

    2017-06-13

    Here, we show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronicmore » devices based on the coupling between magnetic materials and topological surface states. We demonstrate that the magnetization coming from individual Co atoms deposited on the surface can disrupt the spin coherence of the carriers in the archetypal topological insulator Bi2Te3, while in Bi2Se2Te the spin texture remains unperturbed. This is concluded from the observation of elastic backscattering events in quasiparticle interference patterns obtained by scanning tunneling spectroscopy. The mechanism responsible for the protection is investigated by energy resolved spectroscopy and ab initio calculations, and it is ascribed to the distorted adsorption geometry of localized magnetic moments due to Se–Te disorder, which suppresses the Co hybridization with the surface states.« less

  4. Chemical Disorder in Topological Insulators: A Route to Magnetism Tolerant Topological Surface States.

    PubMed

    Martínez-Velarte, M Carmen; Kretz, Bernhard; Moro-Lagares, María; Aguirre, Myriam H; Riedemann, Trevor M; Lograsso, Thomas A; Morellón, Luis; Ibarra, M Ricardo; Garcia-Lekue, Arán; Serrate, David

    2017-07-12

    We show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronic devices based on the coupling between magnetic materials and topological surface states. We demonstrate that the magnetization coming from individual Co atoms deposited on the surface can disrupt the spin coherence of the carriers in the archetypal topological insulator Bi2Te3, while in Bi2Se2Te the spin texture remains unperturbed. This is concluded from the observation of elastic backscattering events in quasiparticle interference patterns obtained by scanning tunneling spectroscopy. The mechanism responsible for the protection is investigated by energy resolved spectroscopy and ab initio calculations, and it is ascribed to the distorted adsorption geometry of localized magnetic moments due to Se-Te disorder, which suppresses the Co hybridization with the surface states.

  5. Attainable entanglement of unitary transformed thermal states in liquid-state nuclear magnetic resonance with the chemical shift

    NASA Astrophysics Data System (ADS)

    Ota, Yukihiro; Mikami, Shuji; Yoshida, Motoyuki; Ohba, Ichiro

    2007-11-01

    Yu, Brown and Chuang investigated the entanglement attainable from unitary transformed thermal states in liquid-state nuclear magnetic resonance (NMR). Their research gave insight into the role of entanglement in a liquid-state NMR quantum computer. However, they assumed that the Zeeman energy of each nuclear spin which corresponds to a qubit takes a common value for all; there is no chemical shift. In this paper, we research a model with chemical shifts and analytically derive the physical parameter region where unitary transformed thermal states are entangled, by employing the positive partial transposition (PPT) criterion with respect to any bipartition. The analysis taking account of the chemical shift reveals how the difference between quantum gates reflects on the physical parameter region where unitary transformed thermal states are entangled. In addition, we examine the distillability of unitary transformed thermal states and the effect of the chemical shifts on the boundary between the separability and the nonseparability.

  6. Towards a beyond 1 GHz solid-state nuclear magnetic resonance: External lock operation in an external current mode for a 500 MHz nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Takahashi, Masato; Ebisawa, Yusuke; Tennmei, Konosuke; Yanagisawa, Yoshinori; Hosono, Masami; Takasugi, Kenji; Hase, Takashi; Miyazaki, Takayoshi; Fujito, Teruaki; Nakagome, Hideki; Kiyoshi, Tsukasa; Yamazaki, Toshio; Maeda, Hideaki

    2012-10-01

    Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb3Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a 7Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm/3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.

  7. Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior

    NASA Astrophysics Data System (ADS)

    Friedman, S. A.; Feinberg, J. M.; Ferré, E. C.; Demory, F.; Martín-Hernández, F.; Conder, J. A.; Rochette, P.

    2014-06-01

    The interpretation of satellite magnetic information (Magsat, Oersted, CHAMP, Swarm) requires the understanding of the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and its magnetism is too weak to influence magnetic anomalies. Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single-component natural remanent magnetizations (NRMs), which, combined with optical and secondary electron microscopy support the lack of post-eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift is too hot and its magnetism is too weak to contribute to anomalies. The sulfide-dominated assemblage at Knippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm (craton) and abundance of magnetite formed at mantle depth. This cratonic mantle, metasomatized by fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies.

  8. Voltage control of magnetic anisotropy in Fe films with quantum well states

    NASA Astrophysics Data System (ADS)

    Bauer, Uwe; Przybylski, Marek; Beach, Geoffrey S. D.

    2014-05-01

    The influence of a gate voltage on magnetic anisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magnetic anisotropy due to quantum well states (QWS) confined in the Fe film are observed and shown to persist up to room temperature at low Fe thicknesses. By systematically examining the voltage and thickness dependence of the magnetic hysteresis loop characteristics, we identify two distinct effects by which an applied voltage modifies the magnetic anisotropy. The first effect is due to voltage-induced changes to interfacial perpendicular magnetic anisotropy which, due to the vicinal geometry, leads to changes in the effective in-plane uniaxial magnetic anisotropy. A second effect is observed at lower film thicknesses and shows nonmonotonic voltage-induced effects on magnetic anisotropy. This nonmonotonic behavior coincides with the onset of significant QWS-induced effects on magnetic anisotropy and suggests a link between QWS- and voltage-induced anisotropy changes.

  9. Using thermal boundary conditions to engineer the quantum state of a bulk magnet.

    PubMed

    Schmidt, M A; Silevitch, D M; Aeppli, G; Rosenbaum, T F

    2014-03-11

    The degree of contact between a system and the external environment can alter dramatically its proclivity to quantum mechanical modes of relaxation. We show that controlling the thermal coupling of cubic-centimeter-sized crystals of the Ising magnet LiHo(x)Y(1-x)F4 to a heat bath can be used to tune the system between a glassy state dominated by thermal excitations over energy barriers and a state with the hallmarks of a quantum spin liquid. Application of a magnetic field transverse to the Ising axis introduces both random magnetic fields and quantum fluctuations, which can retard and speed the annealing process, respectively, thereby providing a mechanism for continuous tuning between the destination states. The nonlinear response of the system explicitly demonstrates quantum interference between internal and external relaxation pathways.

  10. Using thermal boundary conditions to engineer the quantum state of a bulk magnet

    PubMed Central

    Schmidt, M. A.; Silevitch, D. M.; Aeppli, G.; Rosenbaum, T. F.

    2014-01-01

    The degree of contact between a system and the external environment can alter dramatically its proclivity to quantum mechanical modes of relaxation. We show that controlling the thermal coupling of cubic-centimeter–sized crystals of the Ising magnet LiHoxY1-xF4 to a heat bath can be used to tune the system between a glassy state dominated by thermal excitations over energy barriers and a state with the hallmarks of a quantum spin liquid. Application of a magnetic field transverse to the Ising axis introduces both random magnetic fields and quantum fluctuations, which can retard and speed the annealing process, respectively, thereby providing a mechanism for continuous tuning between the destination states. The nonlinear response of the system explicitly demonstrates quantum interference between internal and external relaxation pathways. PMID:24567389

  11. Acoustic-Wave-Induced Magnetization Switching of Magnetostrictive Nanomagnets from Single-Domain to Nonvolatile Vortex States.

    PubMed

    Sampath, Vimal; D'Souza, Noel; Bhattacharya, Dhritiman; Atkinson, Gary M; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

    2016-09-14

    We report experimental manipulation of the magnetic states of elliptical cobalt magnetostrictive nanomagnets (with nominal dimensions of ∼340 nm × 270 nm × 12 nm) delineated on bulk 128° Y-cut lithium niobate with acoustic waves (AWs) launched from interdigitated electrodes. Isolated nanomagnets (no dipole interaction with any other nanomagnet) that are initially magnetized with a magnetic field to a single-domain state with the magnetization aligned along the major axis of the ellipse are driven into a vortex state by acoustic waves that modulate the stress anisotropy of these nanomagnets. The nanomagnets remain in the vortex state until they are reset by a strong magnetic field to the initial single-domain state, making the vortex state nonvolatile. This phenomenon is modeled and explained using a micromagnetic framework and could lead to the development of extremely energy efficient magnetization switching methodologies for low-power computing applications.

  12. Coupled states of electromagnetic fields with magnetic-dipolar-mode vortices: Magnetic-dipolar-mode vortex polaritons

    NASA Astrophysics Data System (ADS)

    Kamenetskii, E. O.; Joffe, R.; Shavit, R.

    2011-08-01

    A coupled state of an electromagnetic field with an electric or magnetic dipole-carrying excitation is well known as a polariton. Such a state is the result of the mixing of a photon with the excitation of a material. The most discussed types of polaritons are phonon polaritons, exciton polaritons, and surface-plasmon polaritons. Recently, it was shown that, in microwaves, strong magnon-photon coupling can be achieved due to magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These coupled states can be specified as MDM-vortex polaritons. In this paper, we study the properties of MDM-vortex polaritons. We numerically analyze a variety of topological structures of MDM-vortex polaritons. Based on analytical studies of the MDM spectra, we give theoretical insight into a possible origin for the observed topological properties of the fields. We show that the MDM-vortex polaritons are characterized by helical-mode resonances. We demonstrate the PT-invariance properties of MDM oscillations in a quasi-two-dimensional ferrite disk and show that such properties play an essential role in the physics of the observed topologically distinctive states with the localization or cloaking of electromagnetic fields. We may suppose that one of the useful implementations of the MDM-vortex polaritons could be microwave metamaterial structures and microwave near-field sensors.

  13. Coupled states of electromagnetic fields with magnetic-dipolar-mode vortices: Magnetic-dipolar-mode vortex polaritons

    SciTech Connect

    Kamenetskii, E. O.; Joffe, R.; Shavit, R.

    2011-08-15

    A coupled state of an electromagnetic field with an electric or magnetic dipole-carrying excitation is well known as a polariton. Such a state is the result of the mixing of a photon with the excitation of a material. The most discussed types of polaritons are phonon polaritons, exciton polaritons, and surface-plasmon polaritons. Recently, it was shown that, in microwaves, strong magnon-photon coupling can be achieved due to magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These coupled states can be specified as MDM-vortex polaritons. In this paper, we study the properties of MDM-vortex polaritons. We numerically analyze a variety of topological structures of MDM-vortex polaritons. Based on analytical studies of the MDM spectra, we give theoretical insight into a possible origin for the observed topological properties of the fields. We show that the MDM-vortex polaritons are characterized by helical-mode resonances. We demonstrate the PT-invariance properties of MDM oscillations in a quasi-two-dimensional ferrite disk and show that such properties play an essential role in the physics of the observed topologically distinctive states with the localization or cloaking of electromagnetic fields. We may suppose that one of the useful implementations of the MDM-vortex polaritons could be microwave metamaterial structures and microwave near-field sensors.

  14. Dark state population determines magnetic sensitivity in radical pair magnetoreception model

    NASA Astrophysics Data System (ADS)

    Xu, Bao-Ming; Zou, Jian

    2016-03-01

    What is the real role of the quantum coherence and entanglement in the radical pair (RP) compass, and what determines the singlet yield have not been fully understood. In this paper, we find that the dark states of the two-electron Zeeman energy operator (TEZE) play an important role in the RP compass. We respectively calculate the singlet yields for two initial states in this dark state basis: the coherent state and the same state just removing the dark state coherence. For the later there is neither dark state coherence nor entanglement in the whole dynamical process. Surprisingly we find that in both cases the singlet yields are the same, and based on this result, we believe that the dark state population determines the singlet yield completely, and the dark state coherence and entanglement have little contribution to it. Finally, we also find that the dark state population as well as the singlet yield anisotropy is fragile to the vertical magnetic noise. However, the orientation is robust and is even enhanced by the parallel magnetic noise because the dark states expand a decoherence-free subspace. The dark state population as well as the orientation is more robust to the hyperfine coupling noise.

  15. Dark state population determines magnetic sensitivity in radical pair magnetoreception model.

    PubMed

    Xu, Bao-Ming; Zou, Jian

    2016-03-01

    What is the real role of the quantum coherence and entanglement in the radical pair (RP) compass, and what determines the singlet yield have not been fully understood. In this paper, we find that the dark states of the two-electron Zeeman energy operator (TEZE) play an important role in the RP compass. We respectively calculate the singlet yields for two initial states in this dark state basis: the coherent state and the same state just removing the dark state coherence. For the later there is neither dark state coherence nor entanglement in the whole dynamical process. Surprisingly we find that in both cases the singlet yields are the same, and based on this result, we believe that the dark state population determines the singlet yield completely, and the dark state coherence and entanglement have little contribution to it. Finally, we also find that the dark state population as well as the singlet yield anisotropy is fragile to the vertical magnetic noise. However, the orientation is robust and is even enhanced by the parallel magnetic noise because the dark states expand a decoherence-free subspace. The dark state population as well as the orientation is more robust to the hyperfine coupling noise.

  16. Dark state population determines magnetic sensitivity in radical pair magnetoreception model

    PubMed Central

    Xu, Bao-Ming; Zou, Jian

    2016-01-01

    What is the real role of the quantum coherence and entanglement in the radical pair (RP) compass, and what determines the singlet yield have not been fully understood. In this paper, we find that the dark states of the two-electron Zeeman energy operator (TEZE) play an important role in the RP compass. We respectively calculate the singlet yields for two initial states in this dark state basis: the coherent state and the same state just removing the dark state coherence. For the later there is neither dark state coherence nor entanglement in the whole dynamical process. Surprisingly we find that in both cases the singlet yields are the same, and based on this result, we believe that the dark state population determines the singlet yield completely, and the dark state coherence and entanglement have little contribution to it. Finally, we also find that the dark state population as well as the singlet yield anisotropy is fragile to the vertical magnetic noise. However, the orientation is robust and is even enhanced by the parallel magnetic noise because the dark states expand a decoherence-free subspace. The dark state population as well as the orientation is more robust to the hyperfine coupling noise. PMID:26926264

  17. Magnetic trapping of Yb in the metastable {sup 3}P{sub 2} state

    SciTech Connect

    Pandey, Kanhaiya; Rathod, K. D.; Pal, Sambit Bikas; Natarajan, Vasant

    2010-03-15

    We report magnetic trapping of Yb in the excited {sup 3}P{sub 2} state. This state, with a lifetime of 15 s, could play an important role in studies ranging from optical clocks and quantum computation to the search for a permanent electric dipole moment. Yb atoms are first cooled and trapped in the ground state in a 399-nm magneto-optic trap. The cold atoms are then pumped into the excited state by driving the {sup 1}S{sub 0{yields}}{sup 3}P{sub 1{yields}}{sup 3}S{sub 1} transition. Atoms in the {sup 3}P{sub 2} state are magnetically trapped in a spherical quadrupole field with an axial gradient of 110 G/cm. We trap up to 10{sup 6} atoms with a lifetime of 1.5 s.

  18. Permanent Magnet Synchronous Condenser with Solid State Excitation: Preprint

    SciTech Connect

    Hsu, P.; Muljadi, E.; Wu, Z.; Gao, W.

    2015-04-07

    A typical synchronous condenser (SC) consists of a free-spinning, wound-field synchronous generator and a field excitation controller. In this paper, we propose an SC that employs a permanent magnet synchronous generator (PMSG) instead of a wound-field machine. PMSGs have the advantages of higher efficiency and reliability. In the proposed configuration, the reactive power control is achieved by a voltage converter controller connected in series to the PMSG. The controller varies the phase voltage of the PMSG and creates the same effect on the reactive power flow as that of an over- or underexcited wound-field machine. The controller’s output voltage magnitude controls the amount of the reactive power produced by the SC. The phase of the controller’s output is kept within a small variation from the grid voltage phase. This small phase variation is introduced so that a small amount of power can be drawn from the grid into the controller to maintain its DC bus voltage. Because the output voltage of the controller is only a fraction of the line voltage, its VA rating is only a fraction of the rating of the PMSG. The proposed scheme is shown to be effective by computer simulations.

  19. Permanent Magnet Synchronous Condenser with Solid State Excitation

    SciTech Connect

    Hsu, Ping; Muljadi, Eduard; Wu, Ziping; Gao, Wenzhong

    2015-10-05

    A synchronous condenser consists of a free-spinning wound-field synchronous generator and a field excitation controller. In this paper, we propose a synchronous generator that employs a permanent magnet synchronous generator (PMSG) instead of a wound-field machine. PMSGs have the advantages of higher efficiency and reliability. In the proposed configuration, the reactive power control is achieved by a voltage source converter connected in series with the PMSG and the grid. The converter varies the phase voltage of the PMSG so as to create the same effect of over or under excitation in a wound-field machine. The converter output voltage level controls the amount and the direction of the produced reactive power and the voltage's phase is kept in-phase with the grid voltage except a slight phase can be introduced so that some power can be drawn from the grid for maintaining the DC bus voltage level of the converter. Since the output voltage of the converter is only a fraction of the line voltage, its VA rating is only a fraction of the rating of the PMSG. The proposed scheme is shown to be effective by computer simulation.

  20. Spin supercurrent, magnetization dynamics, and φ-state in spin-textured Josephson junctions

    NASA Astrophysics Data System (ADS)

    Kulagina, Iryna; Linder, Jacob

    2014-08-01

    The prospect of combining the dissipationless nature of superconducting currents with the spin polarization of magnetic materials is interesting with respect to exploring superconducting analogs of topics in spintronics. In order to accomplish this aim, it is pivotal to understand not only how such spin supercurrents can be created, but also how they interact dynamically with magnetization textures. In this paper, we investigate the appearance of a spin supercurrent and the resulting magnetization dynamics in a textured magnetic Josephson current by using three experimentally relevant models: (i) a superconductor∣ferromagnet∣superconductor (S∣F∣S) junction with spin-active interfaces, (ii) a S∣F1∣F2∣F3∣S Josephson junction with a ferromagnetic trilayer, and (iii) a Josephson junction containing a domain wall. In all of these cases, the supercurrent is spin polarized and exerts a spin-transfer torque on the ferromagnetic interlayers which causes magnetization dynamics. Using a scattering matrix formalism in the clean limit, we compute the Andreev bound states and resulting free energy of the system which in turn is used to solve the Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous magnetism influences the phase dependence of the charge supercurrent and the magnetization dynamics caused by the spin polarization of the supercurrent. Using a realistic experimental parameter set, we find that the spin supercurrent can induce magnetization switching that is controlled by the superconducting phase difference. Moreover, we demonstrate that the combined effect of chiral spin symmetry breaking of the system as a whole with interface scattering causes the systems above to act as phase batteries that may supply any superconducting phase difference φ in the ground state. Such a φ-junction is accompanied by an anomalous supercurrent appearing even at zero phase difference, and we demonstrate that the flow direction of this current is

  1. Tripartite entangled plaquette state in a cluster magnet

    NASA Astrophysics Data System (ADS)

    Carrasquilla, Juan; Chen, Gang; Melko, Roger G.

    2017-08-01

    Using large-scale quantum Monte Carlo simulations we show that a spin-1/2 X X Z model on a two-dimensional anisotropic kagome lattice exhibits a tripartite entangled plaquette state that preserves all of the Hamiltonian symmetries. It is connected via phase boundaries to a ferromagnet and a valence-bond solid that break U (1 ) and lattice translation symmetries, respectively. We study the phase diagram of the model in detail, in particular the transitions to the tripartite entangled plaquette state, which are consistent with conventional order-disorder transitions. Our results can be interpreted as a description of the charge sector dynamics of a Hubbard model applied to the spin liquid candidate LiZn2Mo3O8 , as well as a model of strongly correlated bosonic atoms loaded onto highly tunable trimerized optical kagome lattices.

  2. Fractional quantum Hall states at zero magnetic field.

    PubMed

    Neupert, Titus; Santos, Luiz; Chamon, Claudio; Mudry, Christopher

    2011-06-10

    We present a simple prescription to flatten isolated Bloch bands with a nonzero Chern number. We first show that approximate flattening of bands with a nonzero Chern number is possible by tuning ratios of nearest-neighbor and next-nearest-neighbor hoppings in the Haldane model and, similarly, in the chiral-π-flux square lattice model. Then we show that perfect flattening can be attained with further range hoppings that decrease exponentially with distance. Finally, we add interactions to the model and present exact diagonalization results for a small system at 1/3 filling that support (i) the existence of a spectral gap, (ii) that the ground state is a topological state, and (iii) that the Hall conductance is quantized.

  3. A 3-states magnetic model of binary decisions in sociophysics

    NASA Astrophysics Data System (ADS)

    Fernandez, Miguel A.; Korutcheva, Elka; de la Rubia, F. Javier

    2016-11-01

    We study a diluted Blume-Capel model of 3-states sites as an attempt to understand how some social processes as cooperation or organization happen. For this aim, we study the effect of the complex network topology on the equilibrium properties of the model, by focusing on three different substrates: random graph, Watts-Strogatz and Newman substrates. Our computer simulations are in good agreement with the corresponding analytical results.

  4. Influence of Temperature and Magnetic Field on the First Excited State of a Quantum Pseudodot

    NASA Astrophysics Data System (ADS)

    Cai, Chun-Yu; Zhao, Cui-Lan; Xiao, Jing-Lin

    2017-02-01

    Investigations on the properties of excited states of complex quantum systems can not only reveal the internal structure and properties of the system but also verify the accuracy of quantum theory. In the case of strong electron-longitudinal optical phonon coupling in a quantum pseudodot with an external magnetic field, the first excited state and transition frequency can be obtained by using the Pekar variational method and quantum statistics theory. Numerical calculations for CsI crystal show that (1) they are increasing functions of the magnetic field, and (2) they will first decrease and then increase as the temperature is increased from a low value.

  5. Experimental evidence of interface resonance states in single-crystal magnetic tunnel junctions

    SciTech Connect

    Zermatten, P.-J.; Gaudin, G.; Maris, G.; Miron, M.; Schuhl, A.; Tiusan, C.; Greullet, F.; Hehn, M.

    2008-07-15

    All solid-state tunnel spectroscopy experiments performed on single-crystal Fe/MgO/Fe magnetic tunnel junctions show sharp features at 0.2 and 1.1 V. These peaks are observed on the electrical differential conductivity only in the antiparallel magnetic configuration and only for the voltage sign corresponding to the injection of electrons toward the bottom electrode. They are attributed to the conductivity of two different resonant states of the Fe(001)/MgO bottom interface. The analysis of the attenuation of these peaks as a function of the insulator thickness provides information on their symmetry.

  6. Analysis of the stability of states of semiconductor superlattice in the presence of tilted magnetic field

    NASA Astrophysics Data System (ADS)

    Maksimenko, V. A.; Makarov, V. V.; Koronovskii, A. A.; Hramov, A. E.

    2016-03-01

    A method to calculate the spectrum of the Lyapunov exponents for a periodic semiconductor nanostructure (superlattice) described in the framework of a semiclassical approach is proposed. The analysis of the stability of a stationary state in such a system is performed for autonomous dynamics and in the presence of a tilted magnetic field. The method of the Lyapunov exponents is used to study the effect of the tilted magnetic field on the stability of the stationary state and the characteristics of subterahertz oscillation regimes.

  7. Comparison of nuclear electric resonance and nuclear magnetic resonance in integer and fractional quantum Hall states

    SciTech Connect

    Tomimatsu, Toru Shirai, Shota; Hashimoto, Katsushi Sato, Ken; Hirayama, Yoshiro

    2015-08-15

    Electric-field-induced nuclear resonance (NER: nuclear electric resonance) involving quantum Hall states (QHSs) was studied at various filling factors by exploiting changes in nuclear spins polarized at quantum Hall breakdown. Distinct from the magnetic dipole interaction in nuclear magnetic resonance, the interaction of the electric-field gradient with the electric quadrupole moment plays the dominant role in the NER mechanism. The magnitude of the NER signal strongly depends on whether electronic states are localized or extended. This indicates that NER is sensitive to the screening capability of the electric field associated with QHSs.

  8. Shape transitions in excited states of two-electron quantum dots in a magnetic field

    NASA Astrophysics Data System (ADS)

    Nazmitdinov, R. G.; Simonović, N. S.; Plastino, A. R.; Chizhov, A. V.

    2012-10-01

    We use entanglement to study shape transitions in two-electron axially symmetric parabolic quantum dots in a perpendicular magnetic field. At a specific magnetic field value the dot attains a spherical symmetry. The transition from the axial to the spherical symmetry manifests itself as a drastic change of the entanglement of the lowest state with zero angular momentum projection. While the electrons in such a state are always localized in the plane (x - y) before the transition point, after this point they become localized in the vertical direction.

  9. Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields

    SciTech Connect

    Reynolds, M.; Fallone, B. G.; Rathee, S.

    2014-09-15

    Purpose: MR-Linac devices under development worldwide will require standard calibration, commissioning, and quality assurance. Solid state radiation detectors are often used for dose profiles and percent depth dose measurements. The dose response of selected solid state detectors is therefore evaluated in varying transverse and longitudinal magnetic fields for this purpose. Methods: The Monte Carlo code PENELOPE was used to model irradiation of a PTW 60003 diamond detector and IBA PFD diode detector in the presence of a magnetic field. The field itself was varied in strength, and oriented both transversely and longitudinally with respect to the incident photon beam. The long axis of the detectors was oriented either parallel or perpendicular to the photon beam. The dose to the active volume of each detector in air was scored, and its ratio to dose with zero magnetic field strength was determined as the “dose response” in magnetic field. Measurements at low fields for both detectors in transverse magnetic fields were taken to evaluate the accuracy of the simulations. Additional simulations were performed in a water phantom to obtain few representative points for beam profile and percent depth dose measurements. Results: Simulations show significant dose response as a function of magnetic field in transverse field geometries. This response can be near 20% at 1.5 T, and it is highly dependent on the detectors’ relative orientation to the magnetic field, the energy of the photon beam, and detector composition. Measurements at low transverse magnetic fields verify the simulations for both detectors in their relative orientations to radiation beam. Longitudinal magnetic fields, in contrast, show little dose response, rising slowly with magnetic field, and reaching 0.5%–1% at 1.5 T regardless of detector orientation. Water tank and in air simulation results were the same within simulation uncertainty where lateral electronic equilibrium is present and expectedly

  10. Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields.

    PubMed

    Reynolds, M; Fallone, B G; Rathee, S

    2014-09-01

    MR-Linac devices under development worldwide will require standard calibration, commissioning, and quality assurance. Solid state radiation detectors are often used for dose profiles and percent depth dose measurements. The dose response of selected solid state detectors is therefore evaluated in varying transverse and longitudinal magnetic fields for this purpose. The Monte Carlo code PENELOPE was used to model irradiation of a PTW 60003 diamond detector and IBA PFD diode detector in the presence of a magnetic field. The field itself was varied in strength, and oriented both transversely and longitudinally with respect to the incident photon beam. The long axis of the detectors was oriented either parallel or perpendicular to the photon beam. The dose to the active volume of each detector in air was scored, and its ratio to dose with zero magnetic field strength was determined as the "dose response" in magnetic field. Measurements at low fields for both detectors in transverse magnetic fields were taken to evaluate the accuracy of the simulations. Additional simulations were performed in a water phantom to obtain few representative points for beam profile and percent depth dose measurements. Simulations show significant dose response as a function of magnetic field in transverse field geometries. This response can be near 20% at 1.5 T, and it is highly dependent on the detectors' relative orientation to the magnetic field, the energy of the photon beam, and detector composition. Measurements at low transverse magnetic fields verify the simulations for both detectors in their relative orientations to radiation beam. Longitudinal magnetic fields, in contrast, show little dose response, rising slowly with magnetic field, and reaching 0.5%-1% at 1.5 T regardless of detector orientation. Water tank and in air simulation results were the same within simulation uncertainty where lateral electronic equilibrium is present and expectedly differed at the beam edge in

  11. Magnetic character of the empty density of states in uranium compounds from X-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Dalmas de Réotier, P.; Yaouanc, A.

    2002-06-01

    We present a discussion of published X-ray magnetic circular dichroism (XMCD) measurements performed at the uranium M 4,5 edges of metallic uranium compounds, focusing on the shape of the dichroic signal at the M 5 edge. A well-resolved double-lobe structure, comprised of a positive and negative peak, is sometimes observed. Out of the 12 metallic uranium compounds so far investigated by XMCD, six exhibit an intense double-lobe structure at the M 5 edge. This line shape gives information on the empty 5f magnetic density of states with angular quantum number j=7/2. Conclusions about the difference between these two families of compounds are given regarding the splitting of the j=7/2 band and the occupation among the different m7/2 sublevels.

  12. Ground State Properties and Localized Excited States around a Magnetic Impurity Described by the Anisotropic s- d Interaction in Superconductivity

    NASA Astrophysics Data System (ADS)

    Yoshioka, Tomoki; Ohashi, Yoji

    1998-04-01

    We investigate the electronic state around a magnetic impurity in thesuperconductivity in order to clarify how the anisotropy of thes-d interaction works in the presence of the superconductingenergy gap. Using the numerical renormalization group method, weobtain regions induced by the anisotropy where two localizedexcited states with different energies appear at the same time; theycannot obtain as far as the isotropic interaction is considered. Thismeans that the anisotropy of the s-d interaction works relevantlyin some cases in the superconducting state. We also examine whether ornot the bound state energy for the anisotropic and antiferromagnetics-d interaction is scaled by T K/Δ (T K: Kondotemperature, Δ: superconducting order parameter), and find thatit does not hold in the regions with two bound states.

  13. Capped carbon nanotubes with a number of ground state magnetization discontinuities increasing with their size

    NASA Astrophysics Data System (ADS)

    Konstantinidis, N. P.

    2017-06-01

    The classical ground state magnetic response of fullerene molecules that resemble capped carbon nanotubes is calculated within the framework of the antiferromagnetic Heisenberg model. It is found that the magnetic response depends subtly on spatial symmetry and chirality. Clusters based on armchair carbon nanotubes which are capped with non-neighboring pentagons and have D 5d spatial symmetry have a number of magnetization discontinuities which increases with their size. This occurs even though the model completely lacks magnetic anisotropy, and even though the only source of frustration are the two groups of six pentagons located at the ends of the molecules, which become more strongly outnumbered as the clusters are filled in the middle with more unfrustrated hexagons with increasing size. For the cluster with 180 vertices there are already seven magnetization and one susceptibility discontinuities. Contrary to that, similar molecules which have D 5h spatial symmetry reach a limit of one magnetization and two susceptibility ground state discontinuities, while fullerene molecules based on zigzag carbon nanotubes and capped by neighboring pentagons also reach a fixed number of discontinuities with increasing size. Dedicated to the memory of Dr. Brahim Belhadji

  14. Scaling of the equilibrium magnetization in the mixed state of type-II superconductors

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Ott, H. R.

    2005-04-01

    We discuss the analysis of mixed-state magnetization data of type-II superconductors using a recently developed scaling procedure. It is based on the fact that, if the Ginzburg-Landau parameter κ does not depend on temperature, the magnetic susceptibility χ(H,T) is a universal function of H/Hc2(T), leading to a simple relation between magnetizations at different temperatures. Although this scaling procedure does not provide absolute values of the upper critical field Hc2(T), its temperature variation can be established rather accurately. This provides an opportunity to validate theoretical models that are usually employed for the evaluation of Hc2(T) from equilibrium magnetization data. In the second part of the paper we apply this scaling procedure for a discussion of the notorious first order phase transition in the mixed state of high-Tc superconductors. Our analysis, based on experimental magnetization data available in the literature, shows that the shift of the magnetization accross the transition may adopt either sign, depending on the particular chosen sample. We argue that this observation is inconsistent with the interpretation that this transition always represents the melting transition of the vortex lattice.

  15. Superconducting/magnetic Three-state Nanodevice for Memory and Reading Applications

    NASA Astrophysics Data System (ADS)

    Del Valle, J.; Gomez, A.; Gonzalez, E. M.; Osorio, M. R.; Granados, D.; Vicent, J. L.

    2015-10-01

    We present a simple nanodevice that can operate in two modes: i) non-volatile three-state memory and ii) reading device. The nanodevice can retain three well defined states -1, 0 and +1 and can operate in a second mode as a sensor for external magnetic fields. The nanodevice is fabricated with an array of ordered triangular-shaped nanomagnets embedded in a superconducting thin film gown on Si substrates. The device runs based on the combination of superconducting vortex ratchet effect (superconducting film) with the out of plane magnetization (nanomagnets). The input signals are ac currents and the output signal are dc voltages. The memory mode is realized without applying a magnetic field and the nanomagnet stray magnetic fields govern the effect. In the sensor mode an external magnetic field is applied. The main characteristic of this mode is that the output signal is null for a precise value of the external magnetic field that only depends on the fabrication characteristics of the nanodevice.

  16. Variable-State-Dimension Kalman-Based Filter for Orientation Determination Using Inertial and Magnetic Sensors

    PubMed Central

    Sabatini, Angelo Maria

    2012-01-01

    In this paper a quaternion-based Variable-State-Dimension Extended Kalman Filter (VSD-EKF) is developed for estimating the three-dimensional orientation of a rigid body using the measurements from an Inertial Measurement Unit (IMU) integrated with a triaxial magnetic sensor. Gyro bias and magnetic disturbances are modeled and compensated by including them in the filter state vector. The VSD-EKF switches between a quiescent EKF, where the magnetic disturbance is modeled as a first-order Gauss-Markov stochastic process (GM-1), and a higher-order EKF where extra state components are introduced to model the time-rate of change of the magnetic field as a GM-1 stochastic process, namely the magnetic disturbance is modeled as a second-order Gauss-Markov stochastic process (GM-2). Experimental validation tests show the effectiveness of the VSD-EKF, as compared to either the quiescent EKF or the higher-order EKF when they run separately. PMID:23012502

  17. Ground state magnetization of conduction electrons in graphene with Zeeman effect

    NASA Astrophysics Data System (ADS)

    Escudero, F.; Ardenghi, J. S.; Sourrouille, L.; Jasen, P.

    2017-05-01

    In this work we address the ground state magnetization in graphene, considering the Zeeman effect and taking into account the conduction electrons in the long wavelength approximation. We obtain analytical expressions for the magnetization at T=0 K, where the oscillations given by the de Haas van Alphen (dHvA) effect are present. We find that the Zeeman effect modifies the magnetization by introducing new peaks associated with the spin splitting of the Landau levels. These peaks are very small for typical carrier densities in graphene, but become more important for higher densities. The obtained results provide insight of the way in which the Zeeman effect modifies the magnetization, which can be useful to control and manipulate the spin degrees of freedom.

  18. Equation of State of the Strong Interaction Matter in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Liu, Yu-Xin

    2015-10-01

    We investigate the equation of state of the strong interaction matter in a background magnetic field via the two flavor Nambu-Jona-Lasinio model. Starting from the mean-field thermodynamical potential density Ω, we calculate the pressure density p, the entropy density s, the energy density ɛ, and the interaction measure (ɛ - 3p)/T4 of the strong interaction matter at finite temperature and finite magnetic field. The results manifest that the chiral phase transition is just a crossover but not a low order phase transition. Moreover there may exist magnetic catalysis effect, and its mechanism is just the effective dimension reduction induced by the magnetic field. Supported by the National Natural Science Foundation of China under Grant Nos. 10935001, 11175004 and 11435001, and the National Key Basic Research Program of China under Grant Nos. G2013CB834400 and 2015CB856900

  19. The effects of superhigh magnetic fields on the equations of state of neutron stars

    NASA Astrophysics Data System (ADS)

    Gao, Z. F.; Wang, N.; Xu, Y.; Shan, H.; Li, X.-D.

    2015-11-01

    By introducing Dirac's δ-function in superhigh magnetic fields, we deduce a general formula for the pressure of degenerate and relativistic electrons, Pe, which is suitable for superhigh magnetic fields, discuss the quantization of Landau levels of electrons, and consider the quantum electrodynamic(QED) effects on the equations of states (EOSs) for different matter systems. The main conclusions are as follows: the stronger the magnetic field strength, the higher the electron pressure becomes; compared with a common radio pulsar, a magnetar could be a more compact oblate spheroid-like deformed neutron star due to the anisotropic total pressure; and an increase in the maximum mass of a magnetar is expected because of the positive contribution of the magnetic field energy to the EoS of the star. Since this is an original work in which some uncertainties could exist, modifications and improvements of our theory should be considered in our future studies.

  20. Research Update: Utilizing magnetization dynamics in solid-state thermal energy conversion

    NASA Astrophysics Data System (ADS)

    Boona, Stephen R.; Watzman, Sarah J.; Heremans, Joseph P.

    2016-10-01

    We review the spin-Seebeck and magnon-electron drag effects in the context of solid-state energy conversion. These phenomena are driven by advective magnon-electron interactions. Heat flow through magnetic materials generates magnetization dynamics, which can strongly affect free electrons within or adjacent to the magnetic material, thereby producing magnetization-dependent (e.g., remnant) electric fields. The relative strength of spin-dependent interactions means that magnon-driven effects can generate significantly larger thermoelectric power factors as compared to classical thermoelectric phenomena. This is a surprising situation in which spin-based effects are larger than purely charge-based effects, potentially enabling new approaches to thermal energy conversion.

  1. Topological protection of electronic states against disorder probed by their magnetic moment

    NASA Astrophysics Data System (ADS)

    Tadjine, Athmane; Delerue, Christophe

    2017-06-01

    Magnetic moments (MMs) of electrons in topological insulator quantum dots (TI-QDs) are investigated using a model system, namely a multiorbital honeycomb lattice. Their nature and orientation with respect to the spin are studied. We show that large MMs are not specific to edge states in nontrivial gaps, as band states can host even larger MMs. However, we demonstrate that edge-state and band-state MMs have a totally different sensitivity to disorder. Measuring the MMs in TI-QDs is therefore a direct way to probe the nontrivial to trivial topological transition under increasing disorder.

  2. Fate of the cluster state on the square lattice in a magnetic field

    NASA Astrophysics Data System (ADS)

    Kalis, Henning; Klagges, Daniel; Orús, Román; Schmidt, Kai Phillip

    2012-08-01

    The cluster state represents a highly entangled state which is one central object for measurement-based quantum computing. Here we study the robustness of the cluster state on the two-dimensional square lattice at zero temperature in the presence of external magnetic fields by means of different types of high-order series expansions and variational techniques using infinite projected entangled pair states. The phase diagram displays a first-order phase transition line ending in two critical end points. Furthermore, it contains a characteristic self-dual line in parameter space allowing many precise statements. The self-duality is shown to exist on any lattice topology.

  3. The magnetic state of a single-crystal anion-excess manganite LaMnO3+δ

    NASA Astrophysics Data System (ADS)

    Galetich, I. K.; Eremenko, A. V.; Pashchenko, V. A.; Sirenko, V. A.; Brook, V. V.

    2012-06-01

    The magnetic moment of the LaMnO3+δ single crystal was measured in a wide range of temperatures and magnetic fields under different cooling and measuring conditions. As a result, the nature of the magnetic state of LaMnO3+δ was defined: spin glass clusters form in it.

  4. Ground state of the hydrogen molecule in a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Kravchenko, Yu. P.; Liberman, M. A.

    1997-10-01

    The ground state of a hydrogen molecule in magnetic fields is investigated using a fully numerical Hartree-Fock approach. We found that between 4.2×104 T and 3×106 T the ground state is 3Σ+u with very weak interaction between atoms. In this field region the hydrogen can form a superfluid phase, predicted earlier [Korolev and Liberman, Phys. Rev. Lett. 72, 270 (1994)]; the state 3Πu is metastable and may be responsible for the unknown excitonic line observed by Timofeev and Chernenko [JETP Lett. 61, 617 (1995)]. For magnetic fields stronger than 3×106 T the ground state is the tightly bound 3Πu.

  5. Oxidation and magnetic states of chalcopyrite CuFeS2: A first principles calculation

    NASA Astrophysics Data System (ADS)

    Klekovkina, V. V.; Gainov, R. R.; Vagizov, F. G.; Dooglav, A. V.; Golovanevskiy, V. A.; Pen'kov, I. N.

    2014-06-01

    The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu1+Fe3+S{2/2-}. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods.

  6. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    PubMed Central

    Nair, Sunil; Stockert, O.; Witte, U.; Nicklas, M.; Schedler, R.; Kiefer, K.; Thompson, J. D.; Bianchi, A. D.; Fisk, Z.; Wirth, S.; Steglich, F.

    2010-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity. PMID:20457945

  7. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    SciTech Connect

    Thompson, Joe E; Nair, S; Stockert, O; Witte, U; Nicklas, M; Schedler, R; Bianchi, A; Fisk, Z; Wirth, S; Steglich, K

    2009-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity.

  8. The first-principles investigations on magnetic ground-state in Sm-doped phenanthrene

    NASA Astrophysics Data System (ADS)

    Han, Jia-Xing; Zhong, Guo-Hua; Wang, Xiao-Hui; Chen, Xiao-Jia; Lin, Hai-Qing

    2017-05-01

    Based on the density functional theory plus the effective Coulomb repulsion U, we have investigated the crystal structure, electronic properties and magnetic characteristics in Sm-doped phenanthrene, recently characterized as a superconductor with Tc˜5 -6 Kelvin. Calculated total energies of different magnetic states indicate that Sm-doped phenanthrene is stable at the ferromagnetic ground-state. Considered the strong electronic correlations effect due to the intercalation of Sm-4f electrons, we found that the Sm-4f contributes to the Fermi surface together with C-2p, which is different from K-doped phenanthrene. Compared with alkali-metal-doped phenanthrene, Sm atom has larger local magnetic moment, which suppresses the superconductivity in conventional superconductors. Our results indicate that the electron-electron correlations play an important role in superconductivity of Sm-doped phenanthrene.

  9. Magnetic-field control of subradiance states of a system of two atoms

    NASA Astrophysics Data System (ADS)

    Makarov, A. A.; Yudson, V. I.

    2017-02-01

    A method is proposed for the creation of an entangled metastable (subradiance) excited state in a system of two closely spaced identical atoms. The system of unexcited atoms is first placed in a magnetic field that is directed at a magic angle of {α _0} = {{arccos}}( {1/√ 3 } ) ≈ 54.7° to the line connecting the atoms and has a transverse gradient. The gradient of the field results in the detuning of frequencies of an optical transition of the atoms. Then, the resonant laser excitation of an atom with a higher transition frequency is performed with the subsequent adiabatic switching-off of the gradient of the magnetic field. It is shown that the excited atomic system in this case transits with overwhelming probability to an entangled subradiance state. Requirements on the spectroscopic parameters of the transitions and on the rate of varying the gradient of the magnetic field necessary for the implementation of this effect are analyzed.

  10. Impurity-Induced Local Magnetism and Density of States in the Superconducting State of YBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Ouazi, S.; Bobroff, J.; Alloul, H.; Le Tacon, M.; Blanchard, N.; Collin, G.; Julien, M. H.; Horvatić, M.; Berthier, C.

    2006-03-01

    O17 NMR is used to probe the local influence of nonmagnetic Zn and magnetic Ni impurities in the superconducting state of optimally doped high TC YBa2Cu3O7. Zn and Ni induce a staggered paramagnetic polarization, similar to that evidenced above TC, with a typical extension ξ=3 cell units for Zn and ξ≥3 for Ni. In addition, Zn is observed to induce a local density of states near the Fermi energy in its neighborhood, which also decays over about 3 cell units. Its magnitude decreases sharply with increasing temperature. This allows direct comparison with the STM observations done in BiSCCO.

  11. Spatially Resolved Observation of Static Magnetic Flux States in YBa2Cu3O7-dgr Grain Boundary Josephson Junctions.

    PubMed

    Fischer, G M; Mayer, B; Gross, R; Nissel, T; Husemann, K D; Huebener, R P; Freltoft, T; Shen, Y; Vase, P

    1994-02-25

    With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with YBa(2)Cu(3)O(7-delta) thin-film grain boundary Josephson junctions fabricated on [001] tilt SrTiO(3) bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction. The spatial modulation of the Josephson current density by the external magnetic field is imaged directly with a spatial resolution of about 1 micrometer.

  12. LETTER TO THE EDITOR: Model of the mixed state of type-II superconductors in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Ott, H. R.

    2002-04-01

    In superconductors with large values of the Ginzburg-Landau parameter κ, exposed to magnetic fields close to the upper critical field Hc2, the magnetic field is practically homogeneous across the sample and the density of supercurrents is negligibly small. In this case, there is no obvious reason for the formation of Abrikosov vortices, characteristic for the well known mixed state. We consider an alternative model for describing the mixed state for κ>>1 and magnetic fields close to Hc2. We argue that with decreasing magnetic field the traditional vortex structure is adopted via a first-order phase transition, revealed by discontinuities in the magnetization as well as the resistivity.

  13. Formation properties of an InGaN active layer for high-efficiency InGaN/GaN multi-quantum-well-nanowire light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Hwang, Sung Won; Lee, Bongsoo; Choi, Suk-Ho

    2016-09-01

    Nitride-based nanowires (NWs) have several advantages, such as flexibility in choosing a substrate, easy fabrication, large light-emitting area, no internal electric field, enhanced light extraction, and reduced defects by strain relief, that are useful for enhancing the efficiency of light-emitting diodes (LEDs). Here, we report how crucial the formation properties of the InGaN active layer are for enhancing the efficiency of core-shell InGaN/GaN multi-quantum-well (MQW)-NW LEDs that are selectively grown on oxide templates with perfectly-circular hole patterns. The nanostructures are analyzed for two types of LEDs, one containing defect-free MQW active layer and the other containing MQW layer with defects by using high-resolution transmission electron microscopy. The I-V curve of the defect-free LED shows a rectifying behavior with an on/off ratio of ~109, typical of a diode, and the off-state leakage current of the LED with defects is much larger than that of the defect-free LED, resulting in brighter electroluminescence from the latter device. These results suggest that well-defined nonpolar InGaN/GaN MQW-NWs can be utilized for the realization of high-performance LEDs.

  14. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Wavelength Red-Shift of Long Wavelength InGaN/GaN Multi-Quantum Well by Using an InGaN Underlying Layer

    NASA Astrophysics Data System (ADS)

    Huang, Li-Rong; Wen, Feng; Tong, Liang-Zhu; Huang, De-Xiu

    2009-07-01

    Long-wavelength GaN based light-emitting diodes are of importance in full color displays, monolithic white light- emitting diodes and solid-state lighting, etc. However, their epitaxial growth faces great challenges because high indium (In) compositions of InGaN are difficult to grow. In order to enhance In incorporation and lengthen the emission wavelength of a InGaN/GaN multi-quantum well (MQW), we insert an InGaN underlying layer underneath the MQW. InGaN/GaN MQWs with various InGaN underlying layers, such as graded InyGa1-yN material with linearly increasing In content, or InyGa1-yN with fixed In content but different thicknesses, are grown by metal-organic chemical vapor deposition. Experimental results demonstrate the enhancement of In incorporation and the emission wavelength redshift by the insertion of an InGaN underlying layer.

  15. Evolution of localized states in Lieb lattices under time-dependent magnetic fields

    NASA Astrophysics Data System (ADS)

    Gouveia, J. D.; Maceira, I. A.; Dias, R. G.

    2016-11-01

    We study the slow time evolution of localized states of the open-boundary Lieb lattice when a magnetic flux is applied perpendicularly to the lattice and increased linearly in time. In this system, Dirac cones periodically disappear, reappear, and touch the flat band as the flux increases. We show that the slow time evolution of a localized state in this system is analogous to that of a zero-energy state in a three-level system whose energy levels intersect periodically and that this evolution can be mapped into a classical precession motion with a precession axis that rotates as times evolves. Beginning with a localized state of the Lieb lattice, as the magnetic flux is increased linearly and slowly, the evolving state precesses around a state with a small itinerant component and the amplitude of its localized component oscillates around a constant value (below but close to 1), except at multiples of the flux quantum where it may vary sharply. This behavior reflects the existence of an electric field (generated by the time-dependent magnetic field) which breaks the C4 symmetry of the constant flux Hamiltonian.

  16. Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces.

    PubMed

    Di Bernardo, A; Diesch, S; Gu, Y; Linder, J; Divitini, G; Ducati, C; Scheer, E; Blamire, M G; Robinson, J W A

    2015-09-02

    The theory of superconductivity developed by Bardeen, Cooper and Schrieffer (BCS) explains the stabilization of electron pairs into a spin-singlet, even frequency, state by the formation of an energy gap within which the density of states is zero. At a superconductor interface with an inhomogeneous ferromagnet, a gapless odd frequency superconducting state is predicted, in which the Cooper pairs are in a spin-triplet state. Although indirect evidence for such a state has been obtained, the gap structure and pairing symmetry have not so far been determined. Here we report scanning tunnelling spectroscopy of Nb superconducting films proximity coupled to epitaxial Ho. These measurements reveal pronounced changes to the Nb subgap superconducting density of states on driving the Ho through a metamagnetic transition from a helical antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap is recovered. The results prove odd frequency spin-triplet superconductivity at superconductor/inhomogeneous magnet interfaces.

  17. Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces

    PubMed Central

    Di Bernardo, A.; Diesch, S.; Gu, Y.; Linder, J.; Divitini, G.; Ducati, C.; Scheer, E.; Blamire, M.G.; Robinson, J.W.A.

    2015-01-01

    The theory of superconductivity developed by Bardeen, Cooper and Schrieffer (BCS) explains the stabilization of electron pairs into a spin-singlet, even frequency, state by the formation of an energy gap within which the density of states is zero. At a superconductor interface with an inhomogeneous ferromagnet, a gapless odd frequency superconducting state is predicted, in which the Cooper pairs are in a spin-triplet state. Although indirect evidence for such a state has been obtained, the gap structure and pairing symmetry have not so far been determined. Here we report scanning tunnelling spectroscopy of Nb superconducting films proximity coupled to epitaxial Ho. These measurements reveal pronounced changes to the Nb subgap superconducting density of states on driving the Ho through a metamagnetic transition from a helical antiferromagnetic to a homogeneous ferromagnetic state for which a BCS-like gap is recovered. The results prove odd frequency spin-triplet superconductivity at superconductor/inhomogeneous magnet interfaces. PMID:26329811

  18. Acoustic-Wave-Induced Magnetization Switching of Magnetostrictive Nanomagnets from Single-Domain to Nonvolatile Vortex States

    NASA Astrophysics Data System (ADS)

    Sampath, Vimal; D'Souza, Noel; Bhattacharya, Dhritiman; Atkinson, Gary M.; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

    2016-09-01

    We report manipulation of the magnetic states of elliptical cobalt magnetostrictive nanomagnets (of nominal dimensions ~ 340 nm x 270 nm x 12 nm) delineated on bulk 128{\\deg} Y-cut lithium niobate with Surface Acoustic Waves (SAWs) launched from interdigitated electrodes. Isolated nanomagnets that are initially magnetized to a single domain state with magnetization pointing along the major axis of the ellipse are driven into a vortex state by surface acoustic waves that modulate the stress anisotropy of these nanomagnets. The nanomagnets remain in the vortex state until they are reset by a strong magnetic field to the initial single domain state, making the vortex state non-volatile. This phenomenon is modeled and explained using a micromagnetic framework and could lead to the development of extremely energy efficient magnetization switching methodologies.

  19. Magnetic single-domain state of the monochiral helimagnet MnSi in the zero-field limit: Magnetic properties study

    NASA Astrophysics Data System (ADS)

    Narozhnyi, V. N.; Krasnorussky, V. N.

    2015-04-01

    Attention is drawn to the possibility of obtaining the monochiral helimagnet MnSi in the magnetic single-domain state (SDS) in a zero magnetic field limit. It is shown that this metastable zero-field magnetic SDS can be achieved by a gradual decrease of the field down to zero after an initial transformation of MnSi to a spin-polarized state in a high field H . This can be achieved only for H ∥[111 ] . Investigations of MnSi in the magnetic SDS give us the possibility of determining the two components of the low field magnetic susceptibility of this compound, χ⊥(T ) and χ∥(T ) [χ⊥ and χ∥ correspond to H ⊥(111 ) and H ∥(111 ) planes containing magnetic moments in a helically ordered state]. These results are compared with the macroscopic magnetic susceptibility of MnSi that was determined earlier for this compound, but only in a magnetic multidomain state. In addition, our results are compared with the data reported for some nonmonochiral helimagnets. The characteristic features of monochiral helimagnets are elucidated.

  20. Nonlocally sensing the magnetic states of nanoscale antiferromagnets with an atomic spin sensor

    PubMed Central

    Yan, Shichao; Malavolti, Luigi; Burgess, Jacob A. J.; Droghetti, Andrea; Rubio, Angel; Loth, Sebastian

    2017-01-01

    The ability to sense the magnetic state of individual magnetic nano-objects is a key capability for powerful applications ranging from readout of ultradense magnetic memory to the measurement of spins in complex structures with nanometer precision. Magnetic nano-objects require extremely sensitive sensors and detection methods. We create an atomic spin sensor consisting of three Fe atoms and show that it can detect nanoscale antiferromagnets through minute, surface-mediated magnetic interaction. Coupling, even to an object with no net spin and having vanishing dipolar stray field, modifies the transition matrix element between two spin states of the Fe atom–based spin sensor that changes the sensor’s spin relaxation time. The sensor can detect nanoscale antiferromagnets at up to a 3-nm distance and achieves an energy resolution of 10 μeV, surpassing the thermal limit of conventional scanning probe spectroscopy. This scheme permits simultaneous sensing of multiple antiferromagnets with a single-spin sensor integrated onto the surface. PMID:28560346

  1. Nonlocally sensing the magnetic states of nanoscale antiferromagnets with an atomic spin sensor.

    PubMed

    Yan, Shichao; Malavolti, Luigi; Burgess, Jacob A J; Droghetti, Andrea; Rubio, Angel; Loth, Sebastian

    2017-05-01

    The ability to sense the magnetic state of individual magnetic nano-objects is a key capability for powerful applications ranging from readout of ultradense magnetic memory to the measurement of spins in complex structures with nanometer precision. Magnetic nano-objects require extremely sensitive sensors and detection methods. We create an atomic spin sensor consisting of three Fe atoms and show that it can detect nanoscale antiferromagnets through minute, surface-mediated magnetic interaction. Coupling, even to an object with no net spin and having vanishing dipolar stray field, modifies the transition matrix element between two spin states of the Fe atom-based spin sensor that changes the sensor's spin relaxation time. The sensor can detect nanoscale antiferromagnets at up to a 3-nm distance and achieves an energy resolution of 10 μeV, surpassing the thermal limit of conventional scanning probe spectroscopy. This scheme permits simultaneous sensing of multiple antiferromagnets with a single-spin sensor integrated onto the surface.

  2. Magnetic resonance anisotropy in CeB6: an entangled state of the art

    NASA Astrophysics Data System (ADS)

    Semeno, A. V.; Gilmanov, M. I.; Bogach, A. V.; Krasnorussky, V. N.; Samarin, A. N.; Samarin, N. A.; Sluchanko, N. E.; Shitsevalova, N. Yu.; Filipov, V. B.; Glushkov, V. V.; Demishev, S. V.

    2016-12-01

    Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the detection limit. In this respect, ESR observation in CeB6 provides a unique chance to inspect Ce3+ magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of g-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ8 ground state of Ce3+ ion completely fails to predict both the g-factor magnitude and its angular dependence. Alignment of the external magnetic field along [100] axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the g-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at T* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB6 may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in [100] direction.

  3. Magnetic resonance anisotropy in CeB6: an entangled state of the art

    PubMed Central

    Semeno, A. V.; Gilmanov, M. I.; Bogach, A. V.; Krasnorussky, V. N.; Samarin, A. N.; Samarin, N. A.; Sluchanko, N. E.; Shitsevalova, N. Yu.; Filipov, V. B.; Glushkov, V. V.; Demishev, S. V.

    2016-01-01

    Electron spin resonance (ESR) in strongly correlated metals is an exciting phenomenon, as strong spin fluctuations in this class of materials broaden extremely the absorption line below the detection limit. In this respect, ESR observation in CeB6 provides a unique chance to inspect Ce3+ magnetic state in the antiferroquadrupole (AFQ) phase. We apply the original high frequency (60 GHz) experimental technique to extract the temperature and angular dependences of g-factor, line width and oscillating magnetization. Experimental data show unambiguously that the modern ESR theory in the AFQ phase considering the Γ8 ground state of Ce3+ ion completely fails to predict both the g-factor magnitude and its angular dependence. Alignment of the external magnetic field along [100] axis induces a strong (more than twofold) broadening of ESR line width with respect to the other crystallographic directions and results also in the anomalous temperature dependences of the g-factor and oscillating magnetization. In this experimental geometry the latter parameter surprisingly exceeds total static magnetization by 20% at T* ~ 2.5 K. We argue that the unusual physical picture of ESR in CeB6 may be strongly affected by spin fluctuations and dynamic collective effects predominantly pronounced in [100] direction. PMID:27982072

  4. Tunable magnetic states on the zigzag edges of hydrogenated and halogenated group-IV nanoribbons

    NASA Astrophysics Data System (ADS)

    Wang, Tzu-Cheng; Hsu, Chia-Hsiu; Huang, Zhi-Quan; Chuang, Feng-Chuan; Su, Wan-Sheng; Guo, Guang-Yu

    2016-12-01

    The magnetic and electronic properties of hydrogenated and halogenated group-IV zigzag nanoribbons (ZNRs) are investigated by first-principles density functional calculations. Fascinatingly, we find that all the ZNRs have magnetic edges with a rich variety of electronic and magnetic properties tunable by selecting the parent and passivating elements as well as controlling the magnetization direction and external strain. In particular, the electric property of the edge band structure can be tuned from the conducting to insulating with a band gap up to 0.7 eV. The last controllability would allow us to develop magnetic on-off nano-switches. Furthermore, ZNRs such as SiI, Ge, GeI and SnH, have fully spin-polarized metallic edge states and thus are promising materials for spintronics. The calculated magnetocrystalline anisotropy energy can be as large as ~9 meV/edge-site, being 2×103 time greater than that of bulk Ni and Fe (~5 μeV/atom), and thus has great potential for high density magneto-electric data-storage devices. Finally, the calculated exchange coupling strength and thus magnetic transition temperature increases as the applied strain goes from -5% to 5%. Our findings thus show that these ZNRs would have exciting applications in next-generation electronic and spintronic nano-devices.

  5. Tunable magnetic states on the zigzag edges of hydrogenated and halogenated group-IV nanoribbons

    PubMed Central

    Wang, Tzu-Cheng; Hsu, Chia-Hsiu; Huang, Zhi-Quan; Chuang, Feng-Chuan; Su, Wan-Sheng; Guo, Guang-Yu

    2016-01-01

    The magnetic and electronic properties of hydrogenated and halogenated group-IV zigzag nanoribbons (ZNRs) are investigated by first-principles density functional calculations. Fascinatingly, we find that all the ZNRs have magnetic edges with a rich variety of electronic and magnetic properties tunable by selecting the parent and passivating elements as well as controlling the magnetization direction and external strain. In particular, the electric property of the edge band structure can be tuned from the conducting to insulating with a band gap up to 0.7 eV. The last controllability would allow us to develop magnetic on-off nano-switches. Furthermore, ZNRs such as SiI, Ge, GeI and SnH, have fully spin-polarized metallic edge states and thus are promising materials for spintronics. The calculated magnetocrystalline anisotropy energy can be as large as ~9 meV/edge-site, being 2×103 time greater than that of bulk Ni and Fe (~5 μeV/atom), and thus has great potential for high density magneto-electric data-storage devices. Finally, the calculated exchange coupling strength and thus magnetic transition temperature increases as the applied strain goes from −5% to 5%. Our findings thus show that these ZNRs would have exciting applications in next-generation electronic and spintronic nano-devices. PMID:27982055

  6. Magnetic states, correlation effects and metal-insulator transition in FCC lattice

    NASA Astrophysics Data System (ADS)

    Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

    2016-12-01

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  7. Realizing artificial spin ice states for magnetic colloids on optical trap arrays

    NASA Astrophysics Data System (ADS)

    Libál, A.; Reichhardt, C. M.; Olson Reichhardt, C. J.

    2016-10-01

    Colloids interacting with periodic substrates such as those created with optical traps are an ideal system in which to study various types of phase transitions such as commensurate to incommensurate states and melting behaviors, and they can also be used to create new types of ordering that can be mapped to spin systems. Here we numerically demonstrate how magnetic colloids interacting with an array of elongated two-state traps can be used to realize square artificial spin ice. By tuning the magnetic field, it is possible to precisely control the interaction strength between the colloids, making it possible to observe a transition from a disordered state to an ordered state that obeys the two-in/two-out ice rules. We also examine the dynamics of excitations of the ground state, including pairs of monopoles, and show that the monopoles have emergent attractive interactions. The strength of the interaction can be modified by the magnetic field, permitting the monopole velocity to be tuned.

  8. Magnetic states, correlation effects and metal-insulator transition in FCC lattice.

    PubMed

    Timirgazin, M A; Igoshev, P A; Arzhnikov, A K; Yu Irkhin, V

    2016-12-21

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals [Formula: see text]. In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most [Formula: see text]. The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on [Formula: see text]. The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  9. Polarization memory in the nonpolar magnetic ground state of multiferroic CuFeO2

    NASA Astrophysics Data System (ADS)

    Beilsten-Edmands, J.; Magorrian, S. J.; Foronda, F. R.; Prabhakaran, D.; Radaelli, P. G.; Johnson, R. D.

    2016-10-01

    We investigate polarization memory effects in single-crystal CuFeO2, which has a magnetically induced ferroelectric phase at low temperatures and applied B fields between 7.5 and 13 T. Following electrical poling of the ferroelectric phase, we find that the nonpolar collinear antiferromagnetic ground state at B =0 T retains a strong memory of the polarization magnitude and direction, such that upon reentering the ferroelectric phase a net polarization of comparable magnitude to the initial polarization is recovered in the absence of external bias. This memory effect is very robust: in pulsed-magnetic-field measurements, several pulses into the ferroelectric phase with reverse bias are required to switch the polarization direction, with significant switching only seen after the system is driven out of the ferroelectric phase and ground state either magnetically (by application of B >13 T) or thermally. The memory effect is also largely insensitive to the magnetoelastic domain composition, since no change in the memory effect is observed for a sample driven into a single-domain state by application of stress in the [1 1 ¯0 ] direction. On the basis of Monte Carlo simulations of the ground-state spin configurations, we propose that the memory effect is due to the existence of helical domain walls within the nonpolar collinear antiferromagnetic ground state, which would retain the helicity of the polar phase for certain magnetothermal histories.

  10. Holes localized in nanostructures in an external magnetic field: g-factor and mixing of states

    SciTech Connect

    Semina, M. A.; Suris, R. A.

    2015-06-15

    The energy spectrum and wave functions of holes in the valence band in semiconductor nanosystems, including quantum wells, quantum wires, and quantum dots, in an external magnetic field are theoretically investigated. The dependence of Zeeman splitting of the hole ground state upon variation in the size-quantization parameters with regard to the complex structure of the valence band and magnetic field-induced mixing of hole states is traced. Analytical formulas for describing the Zeeman effect in the valence band in the limiting cases of a quantum disk, spherically symmetric quantum dot, and quantum wire are presented. It is demonstrated that the g-factor of a hole is extremely sensitive to the hole-state composition (heavy or light hole) and, consequently, to the geometry of the size-quantization potential.

  11. Finite-temperature decoherence of spin states in a {Cu3} single molecular magnet

    NASA Astrophysics Data System (ADS)

    Hao, Xiang; Wang, Xiaoqun; Liu, Chen; Zhu, Shiqun

    2013-01-01

    We investigate the quantum evolution of spin states of a single molecular magnet in a local electric field. The decoherence of a {Cu3} single molecular magnet weakly coupled to a thermal bosonic environment can be analysed by the spin-boson model. Using the finite-temperature time-convolutionless quantum master equation, we obtain the analytical expression of the reduced density matrix of the system in the secular approximation. The suppressed and revived dynamical behaviour of the spin states are presented by the oscillation of the chirality spin polarization on the time scale of the correlation time of the environment. The quantum decoherence can be effectively restrained with the help of the manipulation of a local electric field and the environment spectral density function. Under the influence of the dissipation, the pointer states measured by the von Neumann entropy are calculated to manifest the entanglement property of the system-environment model.

  12. Interference of spin states in resonant photoemission induced by circularly polarized light from magnetized Gd

    SciTech Connect

    Mueller, N.; Khalil, T.; Pohl, M.; Uphues, T.; Heinzmann, U.; Polcik, M.; Rader, O.; Heigl, F.; Starke, K.; Fritzsche, S.; Kabachnik, N. M.

    2006-10-15

    We have observed the spin-state interference by measuring the photoelectron spin polarization in the resonant preedge 4d{yields}4f photoemission from magnetized Gd. The photoemission is induced by circularly polarized light which determines one preferential direction of electron spin orientation due to polarization transfer and spin-orbit interaction. Another direction perpendicular to the first one is determined by the target electron spin orientation connected with the target magnetization. We have measured the component of spin polarization perpendicular to those two directions which can only appear due to spin-state interference which implies coherence of the spin states produced by the two mechanisms of the photoelectron spin polarization.

  13. Quantum states emerging from charged transformation-wave in a uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Lin, De-Hone

    2016-06-01

    It is the purpose of this paper to investigate the behavior of a charged transformation-wave in a uniform magnetic field. We first derive the equation which a transformation-wave needs to satisfy, and then, as the main application, the magnetic duality of the Hooke-Newton transmutation is performed by a conformal mapping which generates the novel states with the following characteristics: (a) bound or scattering states are classified by the signatures of the quantum number of the angular momentum and the charge of the particle; (b) the angular momentum satisfies the half-integer quantization rule; and (c) the mass parameter to reach the states is isotropic. Finally, as an alternative application, we report the construction of the fractional angular momentum and fractional Landau levels with the transformation design method.

  14. Magnetic phase transition and clustered state in Ca-doped lanthanum cobaltite and manganite with insulator ground states.

    PubMed

    Ryzhov, V A; Lazuta, A V; Khavronin, V P; Molkanov, P L; Mukovskii, Ya M

    2014-02-19

    The transport and magnetic properties (ac linear and nonlinear (second and third orders) susceptibilities) are presented for La0.8Ca0.2MnO3 and La0.8Ca0.2CoO3 single crystals with insulator ground states. The ferromagnetic (FM) clusters with similar magnetic characteristics originate in the paramagnetic phases of both compounds below some temperature T(∗). At high temperatures the FM clusters arise at the preferable sites that can be attributed to the chemical inhomogeneities, their density being weakly T-dependent. On cooling a homogeneous nucleation of the FM clusters develops below a definite temperature T(#) that is characterized by a fast growth of their density. These two stages are observed in both compounds. At the third stage a coalescence of the FM clusters starts in the doped cobaltite, whereas in the manganite the development of matrix FM ordering occurs which changes a cluster's behavior. The indicated features support the common nature of the cluster state in the doped cobaltite and manganite. The difference in their evolution is a consequence of the different magnetic properties of the matrices in the manganite and cobaltite.

  15. Structurally driven magnetic state transition of biatomic Fe chains on Ir(001)

    NASA Astrophysics Data System (ADS)

    Mokrousov, Yuriy; Thiess, Alexander; Heinze, Stefan

    2009-11-01

    Using first-principles calculations, we demonstrate that the magnetic exchange interaction and the magnetocrystalline anisotropy of biatomic Fe chains grown in the trenches of the (5×1) reconstructed Ir(001) surface depend sensitively on the atomic arrangement of the Fe atoms. Two structural configurations have been considered which are suggested from recent experiments. They differ by the local symmetry and the spacing between the two strands of the biatomic Fe chain. Since both configurations are very close in total energy they may coexist in experiment. We have investigated collinear ferro- and antiferromagnetic solutions as well as a collinear state with two moments in one direction and one in the opposite direction ( ↑↓↑ -state). For the structure with a small interchain spacing, there is a strong exchange interaction between the strands and the ferromagnetic state is energetically favorable. In the structure with larger spacing, the two strands are magnetically nearly decoupled and exhibit antiferromagnetic order along the chain. In both cases, due to hybridization with the Ir substrate the exchange interaction along the chain axis is relatively small compared to free-standing biatomic iron chains. The easy magnetization axis of the Fe chains also switches with the structural configuration and is out-of-plane for the ferromagnetic chains with small spacing and along the chain axis for the antiferromagnetic chains with large spacing between the two strands. Calculated scanning tunneling microscopy images and spectra suggest the possibility to experimentally distinguish between the two structural and magnetic configurations.

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

    SciTech Connect

    Chantis, Athanasios N

    2008-01-01

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

  17. A multi-state magnetic memory dependent on the permeability of Metglas

    NASA Astrophysics Data System (ADS)

    Petrie, J. R.; Wieland, K. A.; Timmerwilke, J. M.; Barron, S. C.; Burke, R. A.; Newburgh, G. A.; Burnette, J. E.; Fischer, G. A.; Edelstein, A. S.

    2015-04-01

    A three-state magnetic memory was developed based on differences in the magnetic permeability of a soft ferromagnetic media, Metglas 2826MB (Fe40Ni38Mo4B18). By heating bits of a 250 nm thick Metglas film with 70-100 mW of laser power, we were able to tune the local microstructure, and hence, the permeability. Ternary memory states were created by using lower laser power to enhance the initial permeability through localized atomic rearrangement and higher power to reduce the permeability through crystallization. The permeability of the bits was read by detecting variations in an external 32 Oe probe field within 10 μm of the media via a magnetic tunnel junction read head. Compared to data based on remanent magnetization, these multi-permeability bits have enhanced insensitivity to unexpected field and temperature changes. We found that data was not corrupted after exposure to fields of 1 T or temperatures of 423 K, indicating the effectiveness of this multi-state approach for safely storing large amounts of data.

  18. Spin counting in electrically detected magnetic resonance via low-field defect state mixing

    SciTech Connect

    Cochrane, Corey J.; Lenahan, Patrick M.

    2014-03-03

    The work herein describes a method that allows one to measure paramagnetic defect densities in semiconductor and insulator based devices with electrically detected magnetic resonance (EDMR). The method is based upon the mixing of defect states which results from the dipolar coupling of paramagnetic sites at low magnetic fields. We demonstrate the measurement method with spin dependent tunneling in thin film dielectrics; however, the method should be equally applicable to paramagnetic defect density measurements in semiconductors via the more commonly utilized EDMR technique called spin dependent recombination.

  19. Spin counting in electrically detected magnetic resonance via low-field defect state mixing

    NASA Astrophysics Data System (ADS)

    Cochrane, Corey J.; Lenahan, Patrick M.

    2014-03-01

    The work herein describes a method that allows one to measure paramagnetic defect densities in semiconductor and insulator based devices with electrically detected magnetic resonance (EDMR). The method is based upon the mixing of defect states which results from the dipolar coupling of paramagnetic sites at low magnetic fields. We demonstrate the measurement method with spin dependent tunneling in thin film dielectrics; however, the method should be equally applicable to paramagnetic defect density measurements in semiconductors via the more commonly utilized EDMR technique called spin dependent recombination.

  20. Ordered states in binary alloys with one magnetic component: A binomial description

    NASA Astrophysics Data System (ADS)

    Rodríguez-Alba, R.; Acosta Ortíz, S. E.; Morán-López, J. L.

    2015-09-01

    A description of chemically and magnetically ordered states, based on the binomial formalism, is presented. By this method, one can analyze all possible configurations that depend on the crystalline structure and the size of the basic cluster used for the description of the system. The procedure is outlined for a cluster of n sites and its application is illustrated for a 4-point cluster in fcc and bcc lattices. This cluster size is big enough to describe ordered alloys with magnetic atoms forming decorated ferromagnetic, antiferromagnetic, superantiferromagnetic and other more complex arrangements.

  1. Controlling the Magnetic Ground State in Cr1-xVx Films

    NASA Astrophysics Data System (ADS)

    Krupin, O.; Rotenberg, Eli; Kevan, S. D.

    2007-10-01

    We demonstrate the ability to control the magnetic phase diagram of Cr1-xVx(110) thin films grown on a W(110) substrate. Using angle-resolved photoemission, we have mapped paramagnetic and commensurate and incommensurate antiferromagnetic phases as a function of temperature, film thickness, and composition. We show that surface-localized electron states play a key role in the observed phase behaviors and suggest from this that it might be possible to control the magnetic phase by applying an external electric field.

  2. Electronic states in the pressure-induced magnetically ordered phase in SmB6

    NASA Astrophysics Data System (ADS)

    Mito, Takeshi; Emi, Naoya; Kawamura, Naomi; Mizumaki, Masaichiro; Koyama, Takehide; Ueda, Koichi; Ishimatsu, Naoki; Iga, Fumitoshi

    2017-06-01

    We have carried out the high-pressure measurement of X-ray absorption spectroscopy on the intermediate valence compound SmB6 which shows magnetic ordering as well as an insulator-metal transition at critical pressure Pc ∼ 10 GPa. The valence of Sm atom at room temperature increases with increasing pressure, however it is far below a trivalent state at Pc . In contrast to cases of pressure-induced nonmagnetic-magnetic transition in Yb compounds, which mostly occurs in the scheme of well localized 4f electrons, the present observation suggests that electronic system in SmB6 still possesses strong delocalized characters at Pc .

  3. On the equation of state for an electron gas in an intense magnetic field

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Tsiang, E.

    1976-01-01

    In this paper we derive the equation of state for a relativistic electron gas imbedded in a static homogeneous magnetic field of arbitrary strength. The derivation is based on the evaluation of the energy-momentum tensor and the use of Dirac's equation for such a problem. Contrary to a derivation presented several years ago, the present derivation is completely gauge-invariant. We also show how to recover, in an exact manner, the perfect gas law for the case of weak magnetic fields.

  4. The Ground State of Monolayer Graphene in a Strong Magnetic Field

    PubMed Central

    Wu, Lian-Ao; Guidry, Mike

    2016-01-01

    Experiments indicate that the ground state of graphene in a strong magnetic field exhibits spontaneous breaking of SU(4) symmetry. However, the nature of the corresponding emergent state is unclear because existing theoretical methods approximate the broken-symmetry solutions, yielding nearly-degenerate candidate ground states having different emergent orders. Resolving this ambiguity in the nature of the strong-field ground state is highly desirable, given the importance of graphene for both fundamental physics and technical applications. We have discovered a new SO(8) symmetry that recovers standard graphene SU(4) quantum Hall physics, but predicts two new broken-SU(4) phases and new properties for potential ground states. Our solutions are analytical; thus we capture the essential physics of spontaneously-broken SU(4) states in a powerful yet solvable model useful both in correlating existing data and in suggesting new experiments. PMID:26927477

  5. Long-range magnetic fields in the ground state of the Standard Model plasma.

    PubMed

    Boyarsky, Alexey; Ruchayskiy, Oleg; Shaposhnikov, Mikhail

    2012-09-14

    In thermal equilibrium the ground state of the plasma of Standard Model particles is determined by temperature and exactly conserved combinations of baryon and lepton numbers. We show that at nonzero values of the global charges a translation invariant and homogeneous state of the plasma becomes unstable and the system transits into a new equilibrium state, containing a large-scale magnetic field. The origin of this effect is the parity-breaking character of weak interactions and chiral anomaly. This situation could occur in the early Universe and may play an important role in its subsequent evolution.

  6. Long-Range Magnetic Fields in the Ground State of the Standard Model Plasma

    NASA Astrophysics Data System (ADS)

    Boyarsky, Alexey; Ruchayskiy, Oleg; Shaposhnikov, Mikhail

    2012-09-01

    In thermal equilibrium the ground state of the plasma of Standard Model particles is determined by temperature and exactly conserved combinations of baryon and lepton numbers. We show that at nonzero values of the global charges a translation invariant and homogeneous state of the plasma becomes unstable and the system transits into a new equilibrium state, containing a large-scale magnetic field. The origin of this effect is the parity-breaking character of weak interactions and chiral anomaly. This situation could occur in the early Universe and may play an important role in its subsequent evolution.

  7. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

    PubMed Central

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-01-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity κxy which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2⋅2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that κxy is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that κxy is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons. PMID:27439874

  8. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite.

    PubMed

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-02

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons.

  9. Ground state of Ho atoms on Pt(111) metal surfaces: Implications for magnetism

    NASA Astrophysics Data System (ADS)

    Karbowiak, M.; Rudowicz, C.

    2016-05-01

    We investigated the ground state of Ho atoms adsorbed on the Pt(111) surface, for which conflicting results exist. The density functional theory (DFT) calculations yielded the Ho ground state as | Jz=±8 > . Interpretation of x-ray absorption spectroscopy and x-ray magnetic circular dichroism spectra and the magnetization curves indicated the ground state as | Jz=±6 > . Superposition model is employed to predict the crystal-field (CF) parameters based on the structural data for the system Ho/Pt(111) obtained from the DFT modeling. Simultaneous diagonalization of the free-ion (HFI) and the trigonal CF Hamiltonian (HCF) within the whole configuration 4 f10 of H o3 + ion was performed. The role of the trigonal CF terms, neglected in the pure uniaxial CF model used previously for interpretation of experimental spectra, is found significant, whereas the sixth-rank CF terms may be neglected in agreement with the DFT predictions. The results provide substantial support for the experimental designation of the | Jz=±6 > ground state, albeit with subtle difference due to admixture of other | Jz> states, but run against the DFT-based designation of the | Jz=±8 > ground state. A subtle splitting of the ground energy level with the state (predominantly), | Jz=±6 > is predicted. This paper provides better insight into the single-ion magnetic behavior of the Ho/Pt(111) system by helping to resolve the controversy concerning the Ho ground state. Experimental techniques with greater resolution powers are suggested for direct confirmation of this splitting and C3 v symmetry experienced by the Ho atom.

  10. Generation of excited coherent states for a charged particle in a uniform magnetic field

    SciTech Connect

    Mojaveri, B.; Dehghani, A. E-mail: alireza.dehghani@gmail.com

    2015-04-15

    We introduce excited coherent states, |β,α;nгЂ‰≔a{sup †n}|β,αгЂ‰, where n is an integer and states |β,αгЂ‰ denote the coherent states of a charged particle in a uniform magnetic field. States |β,αгЂ‰ minimize the Schrödinger-Robertson uncertainty relation while having the nonclassical properties. It has been shown that the resolution of identity condition is realized with respect to an appropriate measure on the complex plane. Some of the nonclassical features such as sub-Poissonian statistics and quadrature squeezing of these states are investigated. Our results are compared with similar Agarwal’s type photon added coherent states (PACSs) and it is shown that, while photon-counting statistics of |β,α,nгЂ‰ are the same as PACSs, their squeezing properties are different. It is also shown that for large values of |β|, while they are squeezed, they minimize the uncertainty condition. Additionally, it has been demonstrated that by changing the magnitude of the external magnetic field, B{sub ext}, the squeezing effect is transferred from one component to another. Finally, a new scheme is proposed to generate states |β,α;nгЂ‰ in cavities. .

  11. Reverse DNA translocation through a solid-state nanopore by magnetic tweezers

    PubMed Central

    Peng, Hongbo; Ling, Xinsheng Sean

    2009-01-01

    Voltage-driven DNA translocation through nanopores has attracted wide interest for many potential applications in molecular biology and biotechnology. However, it is intrinsically difficult to control the DNA motion in standard DNA translocation processes in which a strong electric field is required in drawing DNA into the pore, but it also leads to uncontrollable fast DNA translocation. Here we explore a new type of DNA translocation. We dub it ‘reverse DNA translocation’, in which the DNA is pulled through a nanopore mechanically by a magnetic bead, driven by a magnetic-field gradient. This technique is compatible with simultaneous ionic current measurements and is suitable for multiple nanopores, paving the way for large scale applications. We report the first experiment of reverse DNA translocation through a solid-state nanopore using magnetic tweezers. PMID:19420602

  12. Noiseless manipulation of helical edge state transport by a quantum magnet

    NASA Astrophysics Data System (ADS)

    Silvestrov, P. G.; Recher, P.; Brouwer, P. W.

    2016-05-01

    The current through a helical edge state of a quantum spin Hall insulator may be fully transmitted through a magnetically gapped region due to a combination of spin-transfer torque and spin pumping [Meng et al., Phys. Rev. B 90, 205403 (2014), 10.1103/PhysRevB.90.205403]. Using a scattering approach, we here argue that in such a system the current is effectively carried by electrons with energies below the magnet-induced gap and well below the Fermi energy. This has striking consequences, such as the absence of shot noise, an exponential suppression of thermal noise, and an obstruction of thermal transport. For two helical edges covered by the same quantum magnet, the device can act as a robust noiseless current splitter.

  13. Spiral magnetic order, non-uniform states and electron correlations in the conducting transition metal systems

    NASA Astrophysics Data System (ADS)

    Igoshev, P. A.; Timirgazin, M. A.; Arzhnikov, A. K.; Antipin, T. V.; Irkhin, V. Yu.

    2017-10-01

    The ground-state magnetic phase diagram is calculated within the Hubbard and s-d exchange (Kondo) models for square and simple cubic lattices vs. band filling and interaction parameter. The difference of the results owing to the presence of localized moments in the latter model is discussed. We employ a generalized Hartree-Fock approximation (HFA) to treat commensurate ferromagnetic (FM), antiferromagnetic (AFM), and incommensurate (spiral) magnetic phases. The electron correlations are taken into account within the Hubbard model by using the Kotliar-Ruckenstein slave boson approximation (SBA). The main advantage of this approach is a correct qualitative description of the paramagnetic phase: its energy becomes considerably lower as compared with HFA, and the gain in the energy of magnetic phases is substantially reduced.

  14. Electric field control of nonvolatile four-state magnetization at room temperature

    NASA Astrophysics Data System (ADS)

    Chun, Sae Hwan; Chai, Yi Sheng; Jeon, Byung-Gu; Kim, Hyung Joon; Oh, Yoon Seok; Kim, Ingyu; Kim, Hanbit; Jeon, Byeong Jo; Haam, So Young; Park, Ju-Young; Lee, Suk Ho; Kim, Kee Hoon; Chung, Jae-Ho; Park, Jae-Hoon

    2012-02-01

    We find the realization of large converse magnetoelectric (ME) effects at room temperature in a multiferroic hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62 μB/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be described by an effective free energy with a distinct set of ME coefficients. *These authors contributed equally to this work.

  15. Electric Field Control of Nonvolatile Four-State Magnetization at Room Temperature

    NASA Astrophysics Data System (ADS)

    Chun, Sae Hwan; Chai, Yi Sheng; Jeon, Byung-Gu; Kim, Hyung Joon; Oh, Yoon Seok; Kim, Ingyu; Kim, Hanbit; Jeon, Byeong Jo; Haam, So Young; Park, Ju-Young; Lee, Suk Ho; Chung, Jae-Ho; Park, Jae-Hoon; Kim, Kee Hoon

    2012-04-01

    We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200ps/m. The modulation of magnetization then reaches up to 0.62μB/f.u. in an electric field of 1.14MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.

  16. Magnetic polarization of the americium J=0 ground state in AmFe(2).

    PubMed

    Magnani, N; Caciuffo, R; Wilhelm, F; Colineau, E; Eloirdi, R; Griveau, J-C; Rusz, J; Oppeneer, P M; Rogalev, A; Lander, G H

    2015-03-06

    Trivalent americium has a nonmagnetic (J=0) ground state arising from the cancellation of the orbital and spin moments. However, magnetism can be induced by a large molecular field if Am^{3+} is embedded in a ferromagnetic matrix. Using the technique of x-ray magnetic circular dichroism, we show that this is the case in AmFe_{2}. Since ⟨J_{z}⟩=0, the spin component is exactly twice as large as the orbital one, the total Am moment is opposite to that of Fe, and the magnetic dipole operator ⟨T_{z}⟩ can be determined directly; we discuss the progression of the latter across the actinide series.

  17. Magnetization measurement of a possible high-temperature superconducting state in amorphous carbon doped with sulfur

    NASA Astrophysics Data System (ADS)

    Felner, Israel; Kopelevich, Yakov

    2009-06-01

    Magnetization M(T,H) measurements performed on thoroughly characterized commercial amorphous carbon powder doped with sulfur (AC-S), revealed the occurrence of an inhomogeneous superconductivity (SC) below Tc=38K . The constructed magnetic field-temperature (H-T) phase diagram resembles that of type-II superconductors. However, AC-S demonstrates a number of anomalies, such as: (1) a nonmonotonic behavior of the lower critical-field Hc1(T) ; (2) a pronounced positive curvature of the apparent upper critical-field boundary Hc2(T) ; and (3) a spontaneous ferromagneticlike magnetization M0 coexisting with SC. Based on the analysis of experimental results we propose a nonstandard SC state in AC-S.

  18. Topologically stable magnetization states on a spherical shell: Curvature-stabilized skyrmions

    NASA Astrophysics Data System (ADS)

    Kravchuk, Volodymyr P.; Rößler, Ulrich K.; Volkov, Oleksii M.; Sheka, Denis D.; van den Brink, Jeroen; Makarov, Denys; Fuchs, Hagen; Fangohr, Hans; Gaididei, Yuri

    2016-10-01

    Topologically stable structures include vortices in a wide variety of matter, skyrmions in ferro- and antiferromagnets, and hedgehog point defects in liquid crystals and ferromagnets. These are characterized by integer-valued topological quantum numbers. In this context, closed surfaces are a prominent subject of study as they form a link between fundamental mathematical theorems and real physical systems. Here we perform an analysis on the topology and stability of equilibrium magnetization states for a thin spherical shell with easy-axis anisotropy in normal directions. Skyrmion solutions are found for a range of parameters. These magnetic skyrmions on a spherical shell have two distinct differences compared to their planar counterpart: (i) they are topologically trivial and (ii) can be stabilized by curvature effects, even when Dzyaloshinskii-Moriya interactions are absent. Due to its specific topological nature a skyrmion on a spherical shell can be simply induced by a uniform external magnetic field.

  19. Enhanced diffusion and anomalous transport of magnetic colloids driven above a two-state flashing potential

    NASA Astrophysics Data System (ADS)

    Tierno, Pietro; Shaebani, M. Reza

    We combine experiment and theory to investigate the diffusive and subdiffusive dynamics of paramagnetic colloids driven above a two-state flashing potential. The magnetic potential was realized by periodically modulating the stray field of a magnetic bubble lattice in a uniaxial ferrite garnet film. At large amplitudes of the driving field, the dynamics of particles resembles an ordinary random walk with a frequency-dependent diffusion coefficient. However, subdiffusive and oscillatory dynamics at short time scales is observed when decreasing the amplitude. We present a persistent random walk model to elucidate the underlying mechanism of motion, and perform numerical simulations to demonstrate that the anomalous motion originates from the dynamic disorder in the structure of the magnetic lattice, induced by slightly irregular shape of bubbles.

  20. Chiral ground-state currents of interacting photons in a synthetic magnetic field

    NASA Astrophysics Data System (ADS)

    Roushan, P.; Neill, C.; Megrant, A.; Chen, Y.; Babbush, R.; Barends, R.; Campbell, B.; Chen, Z.; Chiaro, B.; Dunsworth, A.; Fowler, A.; Jeffrey, E.; Kelly, J.; Lucero, E.; Mutus, J.; O’Malley, P. J. J.; Neeley, M.; Quintana, C.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Kapit, E.; Neven, H.; Martinis, J.

    2016-10-01

    The intriguing many-body phases of quantum matter arise from the interplay of particle interactions, spatial symmetries, and external fields. Generating these phases in an engineered system could provide deeper insight into their nature. Using superconducting qubits, we simultaneously realize synthetic magnetic fields and strong particle interactions, which are among the essential elements for studying quantum magnetism and fractional quantum Hall phenomena. The artificial magnetic fields are synthesized by sinusoidally modulating the qubit couplings. In a closed loop formed by the three qubits, we observe the directional circulation of photons, a signature of broken time-reversal symmetry. We demonstrate strong interactions through the creation of photon vacancies, or `holes’, which circulate in the opposite direction. The combination of these key elements results in chiral ground-state currents. Our work introduces an experimental platform for engineering quantum phases of strongly interacting photons.

  1. Electric field control of nonvolatile four-state magnetization at room temperature.

    PubMed

    Chun, Sae Hwan; Chai, Yi Sheng; Jeon, Byung-Gu; Kim, Hyung Joon; Oh, Yoon Seok; Kim, Ingyu; Kim, Hanbit; Jeon, Byeong Jo; Haam, So Young; Park, Ju-Young; Lee, Suk Ho; Chung, Jae-Ho; Park, Jae-Hoon; Kim, Kee Hoon

    2012-04-27

    We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.

  2. Switching of bistable magnetic states in (NdSmDy)(FeCo)B alloy in the vicinity of a spin-reorientation transition

    NASA Astrophysics Data System (ADS)

    Dmitriev, A. I.; Kostyuchenko, S. A.

    2017-07-01

    Bistable magnetic states with two equiprobable orientations of the magnetization vector (corresponding to opposite polarities of a permanent magnet) exist in (NdSmDy)(FeCo)B magnetic alloy in the vicinity of a spin-reorientation transition. A critical value of the magnetic field strength 1 kOe is determined, at which switching of these bistable magnetic states takes place. It is established that the polarity of polycrystalline sintered magnets of the Nd2Fe14B family in the vicinity of a spin-reorientation transition can be stabilized by a small external bias magnetic field, which opens up new possibilities for using these magnets in cryomagnetic systems.

  3. Influence of the biquadratic exchange interaction in the classical ground state magnetic response of the antiferromagnetic icosahedron

    NASA Astrophysics Data System (ADS)

    Konstantinidis, N. P.

    2016-11-01

    The icosahedron has a ground state magnetization discontinuity in an external magnetic field when classical spins mounted on its vertices are coupled according to the antiferromagnetic Heisenberg model. This is so even if there is no magnetic anisotropy in the Hamiltonian. The discontinuity is a consequence of the frustrated nature of the interactions, which originates in the topology of the cluster. Here it is found that the addition of the next order isotropic spin exchange interaction term in the Hamiltonian, the biquadratic exchange interaction, significantly enriches the classical ground state magnetic response. For relatively weak biquadratic interaction new discontinuities emerge, while for even stronger the number of discontinuities for this small molecule can go up to seven, accompanied by a susceptibility discontinuity. These results demonstrate the possibility of using a small entity like the icosahedron as a magnetic unit whose ground state spin configuration and magnetization can be tuned between many different non-overlapping regimes with the application of an external field.

  4. Exploring performance, coherence, and clocking of magnetization in multiferroic four-state nanomagnets

    NASA Astrophysics Data System (ADS)

    Salehi-Fashami, Mohammad; D'Souza, Noel

    2017-09-01

    Nanomagnetic memory and logic are currently seen as promising candidates to replace current digital computing architectures due to its superior energy-efficiency, non-volatility and propensity for highly dense and low-power applications. In this work, we investigate the use of shape engineering (concave and diamond shape) to introduce biaxial anisotropy in single domain nanomagnets, giving rise to multiple easy and hard axes. Such nanomagnets, with dimensions of ∼100 nm × 100 nm, double the logic density of conventional two-state nanomagnetic devices by encoding more information (four binary bits: ;00;, ;11;, ;10;, ;01;) per nanomagnet and can be used in memory and logic devices as well as in higher order information processing applications. We study reliability, magnetization switching coherence, and show, for the first time, the use of voltage-induced strain for the clocking of magnetization in these four-state nanomagnets. Critical parameters such as size, thickness, concavity, and geometry of two types of four-state nanomagnets are also investigated. This analytical study provides important insights into achieving reliable and coherent single domain nanomagnets and low-energy magnetization clocking in four-state nanomagnets, paving the way for potential applications in advanced technologies.

  5. Quantum Percolation and Magnetic Nanodroplet States in Electronically Phase-Separated Manganite Nanowires.

    PubMed

    Zhang, Kaixuan; Li, Lin; Li, Hui; Feng, Qiyuan; Zhang, Nan; Cheng, Long; Fan, Xiaodong; Hou, Yubin; Lu, Qingyou; Zhang, Zhenyu; Zeng, Changgan

    2017-03-08

    One-dimensional (1D) confinement has been revealed to effectively tune the properties of materials in homogeneous states. The 1D physics can be further enriched by electronic inhomogeneity, which unfortunately remains largely unknown. Here we demonstrate the ultrahigh sensitivity to magnetic fluctuations and the tunability of phase stability in the electronic transport properties of self-assembled electronically phase-separated manganite nanowires with extreme aspect ratio. The onset of magnetic nanodroplet state, a precursor to the ferromagnetic metallic state, is unambiguously revealed, which is attributed to the small lateral size of the nanowires that is comparable to the droplet size. Moreover, the quasi-1D anisotropy stabilizes thin insulating domains to form intrinsic tunneling junctions in the low temperature range, which is robust even under magnetic field up to 14 T and thus essentially modifies the classic 1D percolation picture to stabilize a novel quantum percolation state. A new phase diagram is therefore established for the manganite system under quasi-1D confinement for the first time. Our findings offer new insight into understanding and manipulating the colorful properties of the electronically phase-separated systems via dimensionality engineering.

  6. Rotating entangled states of an exchange-coupled dimer of single-molecule magnets

    SciTech Connect

    Owerre, S. A.

    2014-04-21

    An antiferromagnetically exchange-coupled dimer of single molecule magnets which possesses a large spin tunneling has been investigated. For this system, the ground and first excited states are entangled states, and the Hamiltonian is effectively similar to that of a two-state system at 2sth order in perturbation theory; thus this system can be mapped to an entangled pseudospin 1/2 particles. We study the effects of interaction and rotation of this system about its staggered easy-axis direction. The corresponding Hamiltonian of a rotated two-state entangled spin system is derived with its exact low-energy eigenstates and eigenvalues. We briefly discuss the effect of a dissipative environment on this rotated two-state system.

  7. Using magnetic moments to study the nuclear structure of I{>=} 2 states

    SciTech Connect

    Torres, D. A.

    2013-05-06

    The experimental study of magnetic moments for nuclear states near the ground state, I{>=} 2, provides a powerful tool to test nuclear structure models. Traditionally, the use of Coulomb excitation reactions have been utilized to study low spin states, mostly I= 2. The use of alternative reaction channels, such as {alpha} transfer, for the production of radioactive species that, otherwise, will be only produced in future radioactive beam facilities has proved to be an alternative to measure not only excited states with I > 2, but to populate and study long-live radioactive nuclei. This contribution will present the experimental tools and challenges for the use of the transient field technique for the measurement of g factors in nuclear states with I{>=} 2, using Coulomb excitation and {alpha}-transfer reactions. Recent examples of experimental results near the N= 50 shell closure, and the experimental challenges for future implementations with radioactive beams, will be discussed.

  8. Using magnetic moments to study the nuclear structure of I ≥ 2 states

    NASA Astrophysics Data System (ADS)

    Torres, D. A.

    2013-05-01

    The experimental study of magnetic moments for nuclear states near the ground state, I ≥ 2, provides a powerful tool to test nuclear structure models. Traditionally, the use of Coulomb excitation reactions have been utilized to study low spin states, mostly I = 2. The use of alternative reaction channels, such as α transfer, for the production of radioactive species that, otherwise, will be only produced in future radioactive beam facilities has proved to be an alternative to measure not only excited states with I > 2, but to populate and study long-live radioactive nuclei. This contribution will present the experimental tools and challenges for the use of the transient field technique for the measurement of g factors in nuclear states with I ≥ 2, using Coulomb excitation and α-transfer reactions. Recent examples of experimental results near the N = 50 shell closure, and the experimental challenges for future implementations with radioactive beams, will be discussed.

  9. Magnetization in two-dimensional electron gas in a perpendicular magnetic field: The roles of edge states and spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Wang, Zhigang; Zhang, Wei; Zhang, Ping

    2009-06-01

    We study the de Haas-van Alphen (dHvA) oscillations in the magnetization of a two-dimensional electron gas under the influence of the edge states and/or the Rashba spin-orbit interaction (SOI). The boundaries of the systems lift partially the degeneracies of Landau levels (LLs) and the resulting edge states lead to the changes in both the center and the amplitude of the sawtoothlike magnetization oscillation. The SOI mixes the spin-up and spin-down states of neighboring LLs into two unequally spaced energy branches. The inclusion of SOI changes the well-defined sawtooth pattern of the dHvA oscillations in the magnetization. The weaker the magnetic field is, the larger the change in the dHvA oscillations is due to the edge effect and/or the spin-orbit coupling. Some theoretical results are compared with the experimental data.

  10. The current status and future direction of high magnetic field science in the United States

    SciTech Connect

    Lancaster, James

    2013-11-01

    This grant provided partial support for the National Research Council (NRC) study that assesses the current status of high magnetic field research in the United States and provides recommendations to guide the future of research and technology development for this area given the needs of user communities and in the context of other programs worldwide. A pdf version of the report is available for download, for free, at http://www.nap.edu/catalog.php?record_id=18355. The science drivers fall into 4 broad areas—(1) condensed matter and materials physics; (2) chemistry, biochemistry, and biology; (3) medical and life science studies; and (4) other fields such as high-energy physics, plasma physics, and particle astrophysics. Among the topics covered in the report’s findings, conclusions, and recommendations are a recognition that there is a continuing need for a centralized facility but also that clear benefits will flow to research communities from decentralized facilities. According to the report, support agencies should evaluate whether to establish such facilities when 32 Tesla superconducting magnets become available. The report also recommends the provision of facilities that combine magnetic fields with scattering facilities and THz radiation sources, and sets out specific magnet goals for magnets needed in several areas of research.

  11. Selective addressing of solid-state spins at the nanoscale via magnetic resonance frequency encoding

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Arai, K.; Belthangady, C.; Jaskula, J.-C.; Walsworth, R. L.

    2017-08-01

    The nitrogen vacancy centre in diamond is a leading platform for nanoscale sensing and imaging, as well as quantum information processing in the solid state. To date, individual control of two nitrogen vacancy electronic spins at the nanoscale has been demonstrated. However, a key challenge is to scale up such control to arrays of nitrogen vacancy spins. Here, we apply nanoscale magnetic resonance frequency encoding to realize site-selective addressing and coherent control of a four-site array of nitrogen vacancy spins. Sites in the array are separated by 100 nm, with each site containing multiple nitrogen vacancies separated by 15 nm. Microcoils fabricated on the diamond chip provide electrically tuneable magnetic field gradients 0.1 G/nm. Tailored application of gradient fields and resonant microwaves allow site-selective nitrogen vacancy spin manipulation and sensing applications, including Rabi oscillations, imaging, and nuclear magnetic resonance spectroscopy with nanoscale resolution. Microcoil-based magnetic resonance of solid-state spins provides a practical platform for quantum-assisted sensing, quantum information processing, and the study of nanoscale spin networks.

  12. Magnetic properties of superconducting FeSe in the normal state.

    PubMed

    Grechnev, G E; Panfilov, A S; Desnenko, V A; Fedorchenko, A V; Gnatchenko, S L; Chareev, D A; Volkova, O S; Vasiliev, A N

    2013-01-30

    A detailed magnetization study for the novel FeSe superconductor is carried out to investigate the behavior of the intrinsic magnetic susceptibility χ in the normal state with temperature and under hydrostatic pressure. The temperature dependences of χ and its anisotropy Δχ = χ([parallel]) - χ([perpendicular]) are measured for FeSe single crystals in the temperature range 4.2-300 K, and a substantial growth of susceptibility with temperature is revealed. The observed anisotropy Δχ is very large and comparable to the averaged susceptibility at low temperatures. For a polycrystalline sample of FeSe, the significant pressure effect on χ is determined to be essentially dependent on temperature. Ab initio calculations of the pressure-dependent electronic structure and magnetic susceptibility indicate that FeSe is close to magnetic instability, with dominating enhanced spin paramagnetism. The calculated paramagnetic susceptibility exhibits a strong dependence on the unit cell volume and especially on the height Z of chalcogen species from the Fe plane. The change of Z under pressure determines a large positive pressure effect on χ, which is observed at low temperatures. It is shown that the literature experimental data on the strong and nonmonotonic pressure dependence of the superconducting transition temperature in FeSe correlate qualitatively with the calculated behavior of the density of electronic states at the Fermi level.

  13. Steady state reconnection at a single 3D magnetic null point

    NASA Astrophysics Data System (ADS)

    Galsgaard, K.; Pontin, D. I.

    2011-05-01

    Aims: We systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point, thereby forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics, which may provide scaling relations for various characteristic parameters of the system. Methods: The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. Results: It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state is unlikely to be realised because the current layer tends to grow until it is restricted by the geometry of the computational domain and the imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values, so that the evolution is quasi-steady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.

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

    NASA Astrophysics Data System (ADS)

    Jug, Giancarlo; Bonfanti, Silvia; Kob, Walter

    2016-03-01

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

  15. New Shell Structures and Their Ground Electronic States in Spherical Quantum Dots (II) under Magnetic Field

    NASA Astrophysics Data System (ADS)

    Asari, Yusuke; Takeda, Kyozaburo; Tamura, Hiroyuki

    2005-04-01

    We theoretically studied the electronic structure of the three-dimensional spherical parabolic quantum dot (3D-SPQD) under a magnetic field. We obtained the quantum dot orbitals (QDOs) and determined the ground state by using the extended UHF approach where the expectation values of the z component of the total orbital angular momentum <\\hat{L}z> are conserved during the scf-procedure. The single-electron treatment predicts that the applied magnetic field (B) creates k-th new shells at the magnetic field of Bk=k(k+2)/(k+1)ω0 with the shell-energy interval of \\hbarω0/(k+1), where ω0(=\\hbar/m*l02) is the characteristic frequency originating from the spherical parabolic confinement potential. These shells are formed by the level crossing among multiple QDOs. The interelectron interaction breaks the simple level crossing but causes complicated dependences among the total energy, the chemical potential and their differences (magic numbers) with the magnetic field or the number of confinement electrons. The ground state having a higher spin multiplicity is theoretically predicted on the basis of the \\textit{quasi}-degeneracies of the QDOs around these shells.

  16. Probing the spinor nature of electronic states in nanosize non-collinear magnets (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Fischer, Jeison A.; Sander, Dirk; Parkin, Stuart

    2016-10-01

    Non-collinear magnets (NCM) exhibit a spatial variation of the magnetization direction, where helical and skyrmionic spin orders in materials have lately attracted considerable interest. This interest is spurred by both, exploring the physical origin of nanoscale NCM and applications in spintronics. Our study advances the understanding of nanoscale NCM by revealing the effect of nanoscale lateral confinement on the physical properties of NCM. We combine spin-polarized scanning tunneling microscopy/spectroscopy (sp-STM/S) and first-principles calculations to study prototypical helical NCM of some nm extension in proximity to both ferromagnetic Co and vacuum regions. We report a non-uniform distortion of the spin helix in an Fe bilayer on Cu(111)[1], where the spin orientation deviates from that of an ideal helical structure. The proximity to either Co or vacuum leads to distortions of the spin orientation within nm range of the respective interface. The distortions give rise to a specific energy dependent phenomenon of non-collinearity between the local magnetization in the sample and the electronic magnetization probed above its surface. This phenomenon is a direct consequence of the spinor nature of the electronic states in NCM. The symmetry breaking due to lateral confinement makes the spinor nature of electronic states observable in sp-STM/S experiments. [1] Phark, S. H.; Fischer, J. A.; Corbetta, M.; Sander, D.; Nakamura, K. and Kirschner, J. Reduced-dimensionality-induced helimagnetism in iron nanoislands Nat. Commun. 5 (2014) 5183.

  17. Anomalous wave structure in magnetized materials described by non-convex equations of state

    SciTech Connect

    Serna, Susana; Marquina, Antonio

    2014-01-15

    We analyze the anomalous wave structure appearing in flow dynamics under the influence of magnetic field in materials described by non-ideal equations of state. We consider the system of magnetohydrodynamics equations closed by a general equation of state (EOS) and propose a complete spectral decomposition of the fluxes that allows us to derive an expression of the nonlinearity factor as the mathematical tool to determine the nature of the wave phenomena. We prove that the possible formation of non-classical wave structure is determined by both the thermodynamic properties of the material and the magnetic field as well as its possible rotation. We demonstrate that phase transitions induced by material properties do not necessarily imply the loss of genuine nonlinearity of the wavefields as is the case in classical hydrodynamics. The analytical expression of the nonlinearity factor allows us to determine the specific amount of magnetic field necessary to prevent formation of complex structure induced by phase transition in the material. We illustrate our analytical approach by considering two non-convex EOS that exhibit phase transitions and anomalous behavior in the evolution. We present numerical experiments validating the analysis performed through a set of one-dimensional Riemann problems. In the examples we show how to determine the appropriate amount of magnetic field in the initial conditions of the Riemann problem to transform a thermodynamic composite wave into a simple nonlinear wave.

  18. Enhanced magnetic flux density mapping using coherent steady state equilibrium signal in MREIT

    SciTech Connect

    Jeong, Woo Chul; Sajib, Saurav Z. K.; Kim, Hyung Joong; Woo, Eung Je; Lee, Mun Bae; Kwon, Oh In

    2016-03-15

    Measuring the z-component of magnetic flux density B = (B{sub x}, B{sub y}, B{sub z}) induced by transversally injected current, magnetic resonance electrical impedance tomography (MREIT) aims to visualize electrical property (current density and/or conductivity distribution) in a three-dimensional imaging object. For practical implementations of MREIT technique, it is critical to reduce injection of current pulse within safety requirements. With the goal of minimizing the noise level in measured B{sub z} data, we propose a new method to enhance the measure B{sub z} data using steady-state coherent gradient multi-echo (SSC-GME) MR pulse sequence combining with injection current nonlinear encoding (ICNE) method in MREIT, where the ICNE technique injects current during a readout gradient to maximize the signal intensity of phase signal including B{sub z}. The total phase offset in SSC-GME includes additional magnetic flux density due to the injected current, which is different from the phase signal for the conventional spoiled MR pulse sequence. We decompose the magnetization precession phase from the total phase offset including B{sub z} and optimize B{sub z} data using the steady-state equilibrium signal. Results from a real phantom experiment including different kinds of anomalies demonstrated that the proposed method enhanced B{sub z} comparing to a conventional spoiled pulse sequence.

  19. The spectroscopic signature of Co magnetic state in Co{sub x}NbSe{sub 2} superconducting single crystals.

    SciTech Connect

    Iavarone, M.; Karapetrov, G.; Fedor, J.; Rosenmann, D.; Materials Science Division; Temple Univ.; Slovak Academy of Sciences

    2011-01-19

    The magnetic state of Co in NbSe{sub 2} has been studied with low temperature scanning tunneling microscopy and spectroscopy. The local density of states (DOS) at the surface of Co{sub x}NbSe{sub 2}, for different dopings x, does not show bound states predicted in the case of superconductors with magnetic impurities. Only occasionally local asymmetries in the DOS are found at some impurity sites and they appear to be very local. These asymmetries, together with a very low magnetic moment obtained from susceptibility measurements, point towards a possible Kondo effect at play. Tunneling spectra recorded at the impurity site in the presence of a magnetic field of 7 T (i.e. when the sample is in the normal state) show a dip-like feature at the Fermi energy, reminiscent of the Fano resonance observed in magnetic adatoms on metallic surfaces.

  20. GAS-PHASE FLAME SYNTHESIS AND PROPERTIES OF MAGNETIC IRON OXIDE NANOPARTICLES WITH REDUCED OXIDATION STATE

    PubMed Central

    Kumfer, Benjamin M; Shinoda, Kozo; Jeyadevan, Balachandran; Kennedy, Ian M

    2010-01-01

    Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane. PMID:20228941

  1. Ion Species and Charge States of Vacuum Arc Plasma with Gas Feed and Longitudinal Magnetic Field

    SciTech Connect

    Oks, Efim; Anders, Andre

    2010-06-23

    The evolution of copper ion species and charge state distributions is measured for a long vacuum arc discharge plasma operated in the presence of a longitudinal magnetic field of several 10 mT and working gas (Ar). It was found that changing the cathode-anode distance within 20 cm as well as increasing the gas pressure did not affect the arc burning voltage and power dissipation by much. In contrast, burning voltage and power dissipation were greatly increased as the magnetic field was increased. The longer the discharge gap the greater was the fraction of gaseous ions and the lower the fraction of metal ions, while the mean ion charge state was reduced. It is argued that the results are affected by charge exchange collisions and electron impact ionization.

  2. Topological Superconducting State of Lead Nanowires in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Rodrigo, J. G.; Crespo, V.; Suderow, H.; Vieira, S.; Guinea, F.

    2012-12-01

    Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one-dimensional geometries. We propose here that repeated indentation of a Pb tip on a Pb substrate can lead to nanowires such that the resulting superconducting system has novel topological properties. We have analyzed a number of conductance curves obtained in different nanowires, and observe, in a few cases, very peculiar dependence of the critical current on magnetic field. In these cases, the form of multiple Andreev reflections observed at finite voltages are compatible with topological superconductivity. The nanowires give a low number of 1D channels, large spin orbit coupling, and a sizable Zeeman energy, provided that the applied magnetic field is higher than the Pb bulk critical field.

  3. Topological superconducting state of lead nanowires in an external magnetic field.

    PubMed

    Rodrigo, J G; Crespo, V; Suderow, H; Vieira, S; Guinea, F

    2012-12-07

    Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one-dimensional geometries. We propose here that repeated indentation of a Pb tip on a Pb substrate can lead to nanowires such that the resulting superconducting system has novel topological properties. We have analyzed a number of conductance curves obtained in different nanowires, and observe, in a few cases, very peculiar dependence of the critical current on magnetic field. In these cases, the form of multiple Andreev reflections observed at finite voltages are compatible with topological superconductivity. The nanowires give a low number of 1D channels, large spin orbit coupling, and a sizable Zeeman energy, provided that the applied magnetic field is higher than the Pb bulk critical field.

  4. Pulsed CO2 laser pumped by an all solid-state magnetic exciter

    NASA Astrophysics Data System (ADS)

    Shimada, T.; Noda, K.; Obara, M.; Midorikawa, K.

    1985-11-01

    An all solid-state exciter, which consists of a Silicon Controlled Rectifier (SCR) switched pulse transformer and a three stage magnetic pulse compressor, has been successfully used for pulsed CO2 laser excitation. Using the exciter, output laser energy of 240 mJ has been obtained at 1 pps under sealed-off conditions. Since this laser has no discharge switch, long lifetime operation with high repetition rate (HRR) is anticipated.

  5. Solid state nuclear magnetic resonance studies of prion peptides and proteins

    SciTech Connect

    Heller, Jonathan

    1997-08-01

    High-resolution structural studies using x-ray diffraction and solution nuclear magnetic resonance (NMR) are not feasible for proteins of low volubility and high tendency to aggregate. Solid state NMR (SSNMR) is in principle capable of providing structural information in such systems, however to do this efficiently and accurately, further SSNMR tools must be developed This dissertation describes the development of three new methods and their application to a biological system of interest, the priori protein (PrP).

  6. Dzyaloshinskii-Morija interaction and local magnetic anisotropies in U2Pd2In : Ground state and metamagnetic transition

    NASA Astrophysics Data System (ADS)

    Sandratskii, L. M.

    2016-11-01

    U2Pd2In is the material where the elements of the geometrical frustration of the lattice coexist with strong spin-orbit coupling (SOC). The ground state of the system is a noncollinear planar magnetic structure with orthogonal atomic magnetic moments. There are three possible physical mechanisms that can lead to this nontrivial magnetic structure: frustrated isotropic exchange interaction, Dzyaloshinskii-Morija interaction (DMI), and magnetic anisotropy. Our first-principles calculations show that in the case where the SOC is neglected, and therefore the DMI and magnetic anisotropy are absent, the ground state structure is the collinear ferromagnetic one. The leading contribution to the stabilization of the magnetically compensated configuration of orthogonal atomic moments is provided by the local magnetic anisotropy of the U moments. A weaker DMI leads to the lifting of the degeneracy between the magnetic states with different local chirality. The established hierarchy of the interactions allows us to explain the metamagnetic phase transition in the in-plane external magnetic field. The analysis of the noncollinearity of the spin and orbital moments of the same U atom appearing in the applied external field show that the trend to the antiparallel orientation of the two atomic moments following from the third Hund's rule is much stronger than the trend to the parallel orientation of the moments due to the applied external magnetic field.

  7. Magnetic investigations of phase transitions, exchange interactions, and magnetic ground state in nanosheets of β-Co(OH)2

    NASA Astrophysics Data System (ADS)

    Wang, Zhengjun; Seehra, Mohindar S.

    2017-06-01

    Detailed investigations of the magnetic properties of the layered system β-Co(OH)2 are presented. X-ray diffraction and scanning electron microscopy of the sample show it to consist of hexagonal nanosheets with thickness  ≈30 nm and width ~100 nm-200 nm. Analysis of its measured magnetization (M) as a function of temperature (T  =  2 K to 300 K) and magnetic field (H up to 90 kOe) yields a Neel temperature T N  =  9.2 K. This lower T N  =  9.2 K, compared to T N  =  11.6 K reported for bulk β-Co(OH)2, is due to finite-size effects. Analysis of the data for T  >  T N shows that the M versus T data does not quite fit the Curie-Weiss law since both the Curie constant C and Weiss temperature θ have noticeable temperature dependence. This temperature dependence is interpreted to be due to the effect of spin-orbit coupling, yielding a low-temperature effective spin S  =  1/2 ground state with magnetic moment µ  =  4.745 µ B and g  =  5.479. For T  <  T N , M versus H data show two transitions, first at H C1  ≃  15 kOe and second at H C2  ≃  32 kOe. The transition at H C1 is a spin-flop transition and H C2 is due to forced alignment of the spins yielding saturation magnetization M S  =  160 emu g-1 at 2 K, in agreement with the calculated M S  =  163 emu g-1 for the complete alignment of the spins at T  =  0 K for the spin S  =  1/2 ground state with g  =  5.479. The fitting of the M versus T data for T  >  T N to the high temperature series for S  =  1/2 XY model yields the in-plane ferromagnetic exchange constant J 1/k B  =  (1.8  ±  0.2) K for Co2+ ions, with the interplane exchange constant J 2/k B  ≃  -0.2 K determined from the magnitude of T N. The temperature dependence of H C1 and H C2 is presented and discussed.

  8. Valence and spin-state transition in cobaltates revisited by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Guillou, F.; Kummer, K.; Bréard, Y.; Hervé, L.; Hardy, V.

    2017-05-01

    The compounds ( Pr1 -ySmy)0.7Ca0.3CoO3 belong to a class of Pr-based cobaltates presenting a unique case of simultaneous valence (charge transfer between Pr and Co ions) and spin-state transition (of the Co3 + ions), hereafter referred to as VSST. The present study sheds light on the debated issues of the Co4 + and Co3 + spin states, by combining x-ray absorption spectroscopy (XAS) at Co and Pr edges and x-ray magnetic circular dichroism (XMCD) at Co L2 ,3 edges. XAS experiments at both L3 and M4 ,5 Pr edges attest to the appearance of Pr4 + below the VSST at T*=106 K , and allow a precise characterization of the evolution of the Co4 + content as a function of the temperature. XMCD at the Co L2 ,3 edges at 5 K, and in magnetic field up to 9 T, directly tackles the issue of the Co4 + spin state. It is found that the Co4 + ions are most likely in a low spin state, and experience ferromagnetic interactions at T ≪T* . On the basis of temperature dependent XMCD at 9 T, the fingerprint of the VSST on the Co moments is isolated, and found to be consistent with bulk magnetization data when accounting for the rare-earth contributions derived from reference samples. These temperature dependent XMCD data are used to characterize the evolutions of the various valence/spin state of the Co species involved in the VSST. It appears that the Co3 + moments above T* are not consistent with a pure intermediate spin state, whereas they can be well reproduced by considering a low/high spin mixture. Finally, these XMCD results are compared to those derived from fitting of the XAS spectra recorded in zero field at various temperatures.

  9. Rare Low State of DO Dra, the Magnetic Dwarf Nova=Outbursting Intermediate Polar

    NASA Astrophysics Data System (ADS)

    Breus, Vitalii V.; Andronov, Ivan L.; Yoon, Joh-Na; Dubovský, Pavol

    2017-06-01

    DO Dra is an exotic cataclysmic variable which shows properties either of the intermediate polars, or dwarf novae. It may represent a new subclass of "magnetic Dwarf Nova=outbursting intermediate polar". Very rare low luminosity state (of =16.095±0.007) was detected on June 8/9, 2017. The light curve shows a double-humped shape with a phase of the orbital period, with two unequal maxima, arguing not only for an ellipticity effect, but for a bright spot as well. Totally, we have detected 3 lows states.

  10. Pure quantum states of a neutrino with rotating spin in dense magnetized matter

    NASA Astrophysics Data System (ADS)

    Arbuzova, E. V.; Lobanov, A. E.; Murchikova, E. M.

    2010-02-01

    The problem of neutrino spin rotation in dense matter and in strong electromagnetic fields is solved in accordance with the basic principles of quantum mechanics. We obtain a complete system of wave functions for a massive Dirac neutrino with an anomalous magnetic moment which are the eigenfunctions of the kinetic momentum operator and have the form of nonspreading wave packets. These wave functions enable one to consider the states of neutrino with rotating spin as pure quantum states and can be used for calculating probabilities of various processes with the neutrino in the framework of the Furry picture.

  11. Zero-energy state in graphene in a high magnetic field.

    PubMed

    Checkelsky, Joseph G; Li, Lu; Ong, N P

    2008-05-23

    The fate of the charge-neutral Dirac point in graphene in a high magnetic field H has been investigated at low temperatures (T approximately 0.3 K). In samples with small gate-voltage offset V0, the resistance R0 at the Dirac point diverges steeply with H, signaling a crossover to a state with a very large R0. The approach to this state is highly unusual. Despite the steep divergence in R0, the profile of R0 vs T in fixed H saturates to a T-independent value below 2 K, consistent with gapless charge-carrying excitations.

  12. Path dependent magnetic states and evidence of kinetically arrested states in Nd doped LaFe11.5Al1.5

    NASA Astrophysics Data System (ADS)

    Bag, Pallab; Nath, R.

    2017-03-01

    First order antiferromagnetic to ferromagnetic transition and path dependent magnetic states in La1-xNdxFe11.5Al1.5 for x∼0.1 are studied at low temperatures via powder x-ray diffraction, magnetization, and specific heat measurements. X-ray diffraction measurements suggest that around 8% of high temperature antiferromagnetic phase is converted to ferromagnetic phase at low temperatures in zero field cooling. A systematic study of temperature and magnetic field dependent magnetization measurements show a non-monotonic variation of upper critical field and re-entrant antiferromagnetic-ferromagnetic-antiferromagnetic transition while warming at an applied magnetic field under zero-field-cooled condition. This has been interpreted in the framework of kinetic arrest model for first order magnetic transition. It is also found that the antiferromagnetic phase is in the non-equilibrium state and behaves as a glass-like magnetic state at low temperatures. The specific heat in field-temperature space is studied and found to have a lower electronic contribution for the non-equilibrium antiferromagnetic state, compared to the equilibrium ferromagnetic state in this compound.

  13. Microscopic description of ground state magnetic moment and low-lying magnetic dipole excitations in heavy odd-mass 181Ta nucleus

    NASA Astrophysics Data System (ADS)

    Tabar, Emre; Yakut, Hakan; Kuliev, Ali Akbar

    2016-07-01

    The ground state magnetic moments and the low-lying magnetic dipole (Ml) transitions from the ground to excited states in heavy deformed odd-mass 181Ta have been microscopically investigated on the basis of the quasiparticle-phonon nuclear model (QPNM). The problem of the spurious state mixing in M1 excitations is overcome by a restoration method allowing a self-consistent determination of the separable effective restoration forces. Due to the self-consistency of the method, these effective forces contain no arbitrary parameters. The results of calculations are compared with the available experimental data, the agreement being reasonably satisfactory.

  14. Magnetic and metallic state at intermediate Hubbard U coupling in multiorbital models for undoped iron pnictides

    SciTech Connect

    Yu, Rong; Trinh, Kien T.; Moreo, Adriana; Daghofer, Maria; Riera, J. A.; Haas, Stephan; Dagotto, Elbio R

    2009-01-01

    Multiorbital Hubbard model Hamiltonians for the undoped parent compounds of the Fe-pnictide superconductors are investigated here using mean-field techniques. For a realistic four-orbital model, our results show the existence of an intermediate Hubbard U coupling regime where the mean-field ground state has a ,0 antiferromagnetic order, as in neutron-scattering experiments, while remaining metallic due to the phenomenon of band overlaps. The angle-resolved photoemission intensity and Fermi surface of this magnetic and metallic state are discussed. Other models are also investigated, including a two-orbital model where not only the mean-field technique can be used but also the exact diagonalization in small clusters and the variational cluster approximation in the bulk. The combined results of the three techniques point toward the existence of an intermediate-coupling magnetic and metallic state in the two-orbital model, similar to the intermediatecoupling mean-field state of the four-orbital model. We conclude that the state discussed here is compatible with the experimentally known properties of the undoped Fe pnictides.

  15. Experimental observation of temperature and magnetic-field evolution of the 4 f states in CeFe2 revealed by soft x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Saitoh, Y.; Yasui, A.; Fuchimoto, H.; Nakatani, Y.; Fujiwara, H.; Imada, S.; Narumi, Y.; Kindo, K.; Takahashi, M.; Ebihara, T.; Sekiyama, A.

    2017-07-01

    We revisit the delocalized character of the 4 f states of CeFe2 in the ferromagnetically ordered phase by x-ray magnetic circular dichroism (XMCD) in x-ray absorption spectroscopy (XAS) with improved data quality using single crystals. Surprisingly, the Ce M4 ,5 XMCD spectral shape changes significantly as a function of temperature and applied magnetic field, with no concomitant changes in the spectral shape of the Ce M4 ,5 XAS as well as the Fe L2 ,3 XAS and XMCD. This unusual behavior is characterized by the J =7 /2 states in a 4 f1 configuration mixed into the J =5 /2 ground state. Such extreme sensitivity of the Ce 4 f states to the external perturbations can be related to the magnetic instability toward an antiferromagnetic phase in CeFe2. Our experimental data presented here provide valuable insights into the underlying physics in strongly hybridized ferromagnetic Ce compounds.

  16. Weakly chiral networks and two-dimensional delocalized states in a weak magnetic field

    NASA Astrophysics Data System (ADS)

    Mkhitaryan, V. V.; Kagalovsky, V.; Raikh, M. E.

    2010-04-01

    We study numerically the localization properties of two-dimensional electrons in a weak perpendicular magnetic field. For this purpose we construct weakly chiral network models on the square and triangular lattices. The prime idea is to separate in space the regions with phase action of magnetic field, where it affects interference in course of multiple disorder scattering, and the regions with orbital action of magnetic field, where it bends electron trajectories. In our models, the disorder mixes counterpropagating channels on the links, while scattering matrices at the nodes describe exclusively the bending of electron trajectories. By artificially introducing a strong spread in the scattering strengths on the links (but keeping the average strength constant), we eliminate the interference and reduce the electron propagation over a network to a classical percolation problem. In this limit we establish the form of the disorder-magnetic field phase diagram. This diagram contains the regions with and without edge states, i.e., the regions with zero and quantized Hall conductivities. Taking into account that, for a given disorder, the scattering strength scales as inverse electron energy, we find agreement of our phase diagram with levitation scenario: energy separating the Anderson and quantum-Hall insulating phases floats up to infinity upon decreasing magnetic field. From numerical study, based on the analysis of quantum transmission of the network with random phases on the links, we conclude that the positions of the weak-field quantum-Hall transitions on the phase diagram are very close to our classical-percolation results. We checked that, in accord with the Pruisken theory, presence or absence of time-reversal symmetry on the links has no effect on the line of delocalization transitions. We also find that floating up of delocalized states in energy is accompanied by doubling of the critical exponent of the localization radius. We establish the origin of this

  17. Diamond nitrogen vacancy electronic and nuclear spin-state anti-crossings under weak transverse magnetic fields

    NASA Astrophysics Data System (ADS)

    Clevenson, Hannah; Chen, Edward; Dolde, Florian; Teale, Carson; Englund, Dirk; Braje, Danielle

    2016-05-01

    We report on detailed studies of electronic and nuclear spin states in the diamond nitrogen vacancy (NV) center under moderate transverse magnetic fields. We numerically predict and experimentally verify a previously unobserved NV ground state hyperfine anti-crossing occurring at magnetic bias fields as low as tens of Gauss - two orders of magnitude lower than previously reported hyperfine anti-crossings at ~ 510 G and ~ 1000 G axial magnetic fields. We then discuss how this regime can be optimized for magnetometry and other sensing applications and propose a method for how the nitrogen-vacancy ground state Hamiltonian can be manipulated by small transverse magnetic fields to polarize the nuclear spin state. Acknowlegement: The Lincoln Laboratory portion of this work is sponsored by the Assistant Secretary of Defense for Research & Engineering under Air Force Contract #FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the United States Government.

  18. Sickle cell disease painful crisis and steady state differentiation by proton magnetic resonance.

    PubMed

    Fernández, Adolfo A; Cabal, Carlos A; Lores, Manuel A; Losada, Jorge; Pérez, Enrique R

    2009-01-01

    The delay time of the Hb S polymerization process was investigated in 63 patients with sickle cell disease during steady state and 10 during painful crisis starting from spin-spin proton magnetic resonance (PMR) time behavior measured at 36 degrees C and during spontaneous deoxygenation. We found a significant decrease of delay time as a result of the crisis (36 +/- 10%) and two well-differentiated ranges of values for each state: 273-354 min for steady state and 166-229 min for crisis with an uncertainty region of 15%. It is possible to use PMR as an objective and quantitative method in order to differentiate both clinical conditions of the sickle cell patient, but a more clear differentiation can be established comparing the delay time (td) value of one patient during crisis with his own td value during steady state.

  19. Current driven tri-stable resistance states in magnetic point contacts.

    PubMed

    Yanson, I K; Fisun, V V; Naidyuk, Yu G; Balkashin, O P; Triputen, L Yu; Konovalenko, A; Korenivski, V

    2009-09-02

    Point contacts between normal and ferromagnetic metals are investigated using magnetoresistance and transport spectroscopy measurements combined with micromagnetic simulations. Pronounced hysteresis in the point contact resistance versus both bias current and external magnetic field are observed. It is found that such hysteretic resistance can exhibit, in addition to bi-stable resistance states found in ordinary spin valves, tri-stable resistance states with a middle resistance level. We interpret these observations in terms of surface spin valve and spin vortex states, originating from a substantially modified spin structure at the ferromagnetic interface in the contact core. We argue that these surface spin states, subject to a weakened exchange interaction, dominate the effects of spin transfer torques on the nanometer scale.

  20. State diagram for spin current-induced magnetization dynamics using a perpendicular polarizer and a planar free layer

    NASA Astrophysics Data System (ADS)

    Firastrau, I.; Ebels, U.; Buda-Prejbeanu, L.; Toussaint, J.-C.; Thirion, C.; Dieny, B.

    2007-03-01

    The dynamic state diagram for spin current-induced magnetization dynamics is presented for an out-of-plane magnetized (perpendicular) polarizer and an in-plane magnetized (planar) free layer as obtained from macrospin simulations. The state boundaries are compared upon using a constant spin polarization factor with an angular-dependent spin polarization factor g( θMP) as introduced by Slonczewski. While two critical boundaries remain unaffected by the angular dependence of the polarization, the transition from precession to an out-of-plane stable state is drastically shifted and shows a strong asymmetry with respect to the sign of the spin-polarized current.

  1. Features of the magnetic state of the layered Fe-V nanostructure of the superconductor-ferromagnet type

    SciTech Connect

    Aksenov, V. L.; Nikitenko, Yu. V.; Petrenko, A. V.; Uzdin, V. M.; Khaidukov, Yu. N. Zabel, H.

    2007-05-15

    The magnetic state of the V(39 nm)/20 [V(3 nm)/Fe(3 nm)] nanostructure has been investigated by polarized neutron reflectometry in the temperature range from 1.6 to 30 K in magnetic fields from 0.2 to 15 kOe. The data obtained indicate that the superconductivity of vanadium layers may affect magnetic ordering both over the depth of the structure and in its plane.

  2. Angular momentum, g-value, and magnetic flux of gyration states

    SciTech Connect

    Arunasalam, V.

    1991-10-01

    Two of the world's leading (Nobel laureate) physicists disagree on the definition of the orbital angular momentum L of the Landau gyration states of a spinless charged particle in a uniform external magnetic field B = B i{sub Z}. According to Richard P. Feynman (and also Frank Wilczek) L = (rx{mu}v) = rx(p - qA/c), while Felix Bloch (and also Kerson Huang) defines it as L = rxp. We show here that Bloch's definition is the correct one since it satisfies the necessary and sufficient condition LxL = i{Dirac h} L, while Feynman's definition does not. However, as a consequence of the quantized Aharonov-Bohm magnetic flux, this canonical orbital angular momentum (surprisingly enough) takes half-odd-integral values with a zero-point gyration states of L{sub Z} = {Dirac h}/2. Further, since the diamagnetic and the paramagnetic contributions to the magnetic moment are interdependent, the g-value of these gyration states is two and not one, again a surprising result for a spinless case. The differences between the gauge invariance in classical and quantum mechanics, Onsager's suggestion that the flux quantization might be an intrinsic property of the electromagnetic field-charged particle interaction, the possibility that the experimentally measured fundamental unit of the flux quantum need not necessarily imply the existence of electron pairing'' of the Bardeen-Cooper-Schrieffer superconductivity theory, and the relationship to the Dirac's angular momentum quantization condition for the magnetic monopole-charged particle composites (i.e. Schwinger's dyons), are also briefly examined from a pedestrian viewpoint.

  3. Deterministic multi-step rotation of magnetic single-domain state in Nickel nanodisks using multiferroic magnetoelastic coupling

    NASA Astrophysics Data System (ADS)

    Sohn, Hyunmin; Liang, Cheng-yen; Nowakowski, Mark E.; Hwang, Yongha; Han, Seungoh; Bokor, Jeffrey; Carman, Gregory P.; Candler, Robert N.

    2017-10-01

    We demonstrate deterministic multi-step rotation of a magnetic single-domain (SD) state in Nickel nanodisks using the multiferroic magnetoelastic effect. Ferromagnetic Nickel nanodisks are fabricated on a piezoelectric Lead Zirconate Titanate (PZT) substrate, surrounded by patterned electrodes. With the application of a voltage between opposing electrode pairs, we generate anisotropic in-plane strains that reshape the magnetic energy landscape of the Nickel disks, reorienting magnetization toward a new easy axis. By applying a series of voltages sequentially to adjacent electrode pairs, circulating in-plane anisotropic strains are applied to the Nickel disks, deterministically rotating a SD state in the Nickel disks by increments of 45°. The rotation of the SD state is numerically predicted by a fully-coupled micromagnetic/elastodynamic finite element analysis (FEA) model, and the predictions are experimentally verified with magnetic force microscopy (MFM). This experimental result will provide a new pathway to develop energy efficient magnetic manipulation techniques at the nanoscale.

  4. Direct imaging of magnetic field-driven transitions of skyrmion cluster states in FeGe nanodisks

    PubMed Central

    Zhao, Xuebing; Jin, Chiming; Wang, Chao; Du, Haifeng; Zang, Jiadong; Tian, Mingliang; Che, Renchao; Zhang, Yuheng

    2016-01-01

    Magnetic skyrmion is a nanosized magnetic whirl with nontrivial topology, which is highly relevant for applications on future memory devices. To enable the applications, theoretical efforts have been made to understand the dynamics of individual skyrmions in magnetic nanostructures. However, directly imaging the evolution of highly geometrically confined individual skyrmions is challenging. Here, we report the magnetic field-driven dynamics of individual skyrmions in FeGe nanodisks with diameters on the order of several skyrmion sizes by using Lorentz transmission electron microscopy. In contrast to the conventional skyrmion lattice in bulk, a series of skyrmion cluster states with different geometrical configurations and the field-driven cascading phase transitions are identified at temperatures far below the magnetic transition temperature. Furthermore, a dynamics, namely the intermittent jumps between the neighboring skyrmion cluster states, is found at elevated temperatures, at which the thermal energy competes with the energy barrier between the skyrmion cluster states. PMID:27051067

  5. Pressure dependence of the magnetic ground states in MnP

    DOE PAGES

    Matsuda, Masaaki; Ye, Feng; Dissanayake, Sachith E.; ...

    2016-03-17

    MnP, a superconductor under pressure, exhibits a ferromagnetic order below TC~290 K followed by a helical order with the spins lying in the ab plane and the helical rotation propagating along the c axis below Ts~50 K at ambient pressure. We performed single-crystal neutron diffraction experiments to determine the magnetic ground states under pressure. Both TC and Ts are gradually suppressed with increasing pressure and the helical order disappears at ~1.2 GPa. At intermediate pressures of 1.8 and 2.0 GPa, the ferromagnetic order first develops and changes to a conical or two-phase (ferromagnetic and helical) structure with the propagation alongmore » the b axis below a characteristic temperature. At 3.8 GPa, a helical magnetic order appears below 208 K, which hosts the spins in the ac plane and the propagation along the b axis. The period of this b axis modulation is shorter than that at 1.8 GPa. Here, our results indicate that the magnetic phase in the vicinity of the superconducting phase may have a helical magnetic correlation along the b axis.« less

  6. Pressure dependence of the magnetic ground states in MnP

    SciTech Connect

    Matsuda, Masaaki; Ye, Feng; Dissanayake, Sachith E.; Cheng, J. -G.; Chi, Songxue; Ma, Jie; Zhou, H. D.; Yan, Jia -Qiang; Kasamatsu, S.; Sugino, O.; Kato, T.; Matsubayashi, Kazuyuki; Okada, T.; Uwatoko, Yoshiya

    2016-03-17

    MnP, a superconductor under pressure, exhibits a ferromagnetic order below TC~290 K followed by a helical order with the spins lying in the ab plane and the helical rotation propagating along the c axis below Ts~50 K at ambient pressure. We performed single-crystal neutron diffraction experiments to determine the magnetic ground states under pressure. Both TC and Ts are gradually suppressed with increasing pressure and the helical order disappears at ~1.2 GPa. At intermediate pressures of 1.8 and 2.0 GPa, the ferromagnetic order first develops and changes to a conical or two-phase (ferromagnetic and helical) structure with the propagation along the b axis below a characteristic temperature. At 3.8 GPa, a helical magnetic order appears below 208 K, which hosts the spins in the ac plane and the propagation along the b axis. The period of this b axis modulation is shorter than that at 1.8 GPa. Here, our results indicate that the magnetic phase in the vicinity of the superconducting phase may have a helical magnetic correlation along the b axis.

  7. Magnetic states of MnP: muon-spin rotation studies

    NASA Astrophysics Data System (ADS)

    Khasanov, R.; Amato, A.; Bonfà, P.; Guguchia, Z.; Luetkens, H.; Morenzoni, E.; De Renzi, R.; Zhigadlo, N. D.

    2017-04-01

    Muon-spin rotation data collected at ambient pressure (p) and at p  =  2.42 GPa in MnP were analyzed to check their consistency with various low- and high-pressure magnetic structures reported in the literature. Our analysis confirms that in MnP the low-temperature and low-pressure helimagnetic phase is characterised by an increased value of the average magnetic moment compared to the high-temperature ferromagnetic phase. An elliptical double-helical structure with a propagation vector \\mathbf{Q}=(0,0,0.117) , an a-axis moment elongated by approximately 18% and an additional tilt of the rotation plane towards c-direction by ≃ 4 –8° leads to a good agreement between the theory and the experiment. The analysis of the high-pressure μSR data reveals that the new magnetic order appearing for pressures exceeding 1.5 GPa can not be described by keeping the propagation vector \\mathbf{Q}\\parallel c . Even the extreme case—decoupling the double-helical structure into four individual helices—remains inconsistent with the experiment. It is shown that the high-pressure magnetic phase which is a precursor of superconductivity is an incommensurate helical state with \\mathbf{Q}\\parallel b .

  8. Broken symmetry states in bilayer graphene in electric and in-plane magnetic fields

    NASA Astrophysics Data System (ADS)

    Jia, Junji; Pyatkovskiy, P. K.; Gorbar, E. V.; Gusynin, V. P.

    2017-01-01

    Broken symmetry states in bilayer graphene in perpendicular electric E⊥ and in-plane magnetic B∥ fields are studied in the presence of the dynamically screened long-range Coulomb interaction and the symmetry-breaking contact four-fermion interactions. The integral gap equations are solved numerically, and it is shown that the momentum dependence of gaps is essential: It diminishes by an order of magnitude the gaps compared to the case of momentum-independent approximation, and the obtained gap magnitudes are found to agree well with existing experimental values. We derived a phase diagram of bilayer graphene at the neutrality point in the plane (B∥,E⊥) showing that the (canted) layer antiferromagnetic (LAF) state remains a stable ground state of the system at large B∥. On the other hand, while the LAF phase is realized at small values of E⊥, the quantum valley Hall (QVH) phase is the ground state of the system at values E⊥>Ec r(B∥) , where a critical value Ec r(B∥) increases with in-plane magnetic field B||.

  9. Imaging the equilibrium state and magnetization dynamics of partially built hard disk write heads

    SciTech Connect

    Valkass, R. A. J. Yu, W.; Shelford, L. R.; Keatley, P. S.; Loughran, T. H. J.; Hicken, R. J.; Cavill, S. A.; Laan, G. van der; Dhesi, S. S.; Bashir, M. A.; Gubbins, M. A.; Czoschke, P. J.; Lopusnik, R.

    2015-06-08

    Four different designs of partially built hard disk write heads with a yoke comprising four repeats of NiFe (1 nm)/CoFe (50 nm) were studied by both x-ray photoemission electron microscopy (XPEEM) and time-resolved scanning Kerr microscopy (TRSKM). These techniques were used to investigate the static equilibrium domain configuration and the magnetodynamic response across the entire structure, respectively. Simulations and previous TRSKM studies have made proposals for the equilibrium domain configuration of similar structures, but no direct observation of the equilibrium state of the writers has yet been made. In this study, static XPEEM images of the equilibrium state of writer structures were acquired using x-ray magnetic circular dichroism as the contrast mechanism. These images suggest that the crystalline anisotropy dominates the equilibrium state domain configuration, but competition with shape anisotropy ultimately determines the stability of the equilibrium state. Dynamic TRSKM images were acquired from nominally identical devices. These images suggest that a longer confluence region may hinder flux conduction from the yoke into the pole tip: the shorter confluence region exhibits clear flux beaming along the symmetry axis, whereas the longer confluence region causes flux to conduct along one edge of the writer. The observed variations in dynamic response agree well with the differences in the equilibrium magnetization configuration visible in the XPEEM images, confirming that minor variations in the geometric design of the writer structure can have significant effects on the process of flux beaming.

  10. Manipulating magnetism of MnO nano-clusters by tuning the stoichiometry and charge state.

    PubMed

    Ganguly, Shreemoyee; Kabir, Mukul; Autieri, Carmine; Sanyal, Biplab

    2015-02-11

    In this paper, we have studied the composition dependent evolution of geometric and magnetic structures of MnO clusters within density functional theory. The magnetic structures are determined by the competition between direct and superexchange interactions, which have been analyzed by the parameters obtained from maximally localized Wannier functions. The intrinsic electronic structures of the clusters have been thoroughly studied by looking into the hybridization (quantified using the Hybridization Index) and charge transfer scenario. Further, the importance of electron correlation in describing simple Mn-dimer and MnO clusters has been discussed within the Hubbard model and hybrid exchange-correlation functional. Our calculated vertical detachment energies of off-stoichiometric MnO clusters compare well with the recent experimental results. Interestingly, the charged state of the cluster strongly influences the geometry and the magnetic structure of the cluster, which are very different from the corresponding neutral counterpart. We have demonstrated that the exchange interaction between Mn atoms can be switched between ferromagnetic and anitiferromagnetic ones by changing the charge state and hence can be useful for spin-based information technology.

  11. Interconnections between magnetic state and transport currents in antiferromagnetic Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Tsoi, Maxim

    Interconnections between magnetic state and transport currents in ferromagnetic (F) heterostructures are the basis for spintronic applications, e.g. tunneling magnetoresistance and spin-transfer torque phenomena provide a means to read and write information in magnetic memory devices like STTRAM. Similar interconnections were proposed to occur in systems where F-components are replaced with antiferromagnets (AFM). We demonstrated experimentally the existence of such interconnections in antiferromagnetic Mott insulator Sr2IrO4: first, we found a very large anisotropic magnetoresistance (AMR) which can be used to monitor (read) the magnetic state of AFM; second, we demonstrated the feasibility of reversible resistive switching driven by high-density currents/high electric fields which can be used for writing in AFM memory applications. These results support the feasibility of AFM spintronics where antiferromagnets are used in place of ferromagnets. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, and by NSF grants DMR-1207577, DMR-1265162 and DMR-1122603.

  12. Dynamic micromagnetic simulation of the magnetic spectrum of permalloy nanodot array with vortex state

    NASA Astrophysics Data System (ADS)

    Peng, Y.; Zhao, G. P.; Morvan, F. J.; Wu, S. Q.; Yue, M.

    2017-01-01

    Due to its potential applications in high-density magnetic storage and spin electronic devices, the ferromagnetic resonance absorption phenomenon has recently drawn much attention. By studying the influence of different materials with various shapes on this phenomenon, the new understandings gained could lead to other applications in the future. In this paper, dynamic magnetic susceptibilities of the vortex state in permalloy nanodot arrays have been investigated using a three-dimensional object oriented micromagnetic framework (OOMMF) code with a two-dimensional periodic boundary condition (2D-PBC) extension and compared with those of a single dot carefully. The resonance mode is excited in the vortex state of nanodot arrays by the microwave magnetic field perpendicular to the dot plane. In this case only radially symmetric spin wave modes can be excited. The influence of the geometric parameters on the resonance frequency has been studied systemically, including the dot radius, the number of repeating elements, and the dot distance. One can see that the resonance peak of the dot array is higher than that of a single dot because of the induced stronger magnetostatic coupling. A critical dot distance exists at which the dot array may be treated as a single dot. There is only one resonance peak for both the dot array and the single dot, as the radius changes.

  13. Cold equation of state in a strong magnetic field - Effects of inverse beta-decay

    NASA Technical Reports Server (NTRS)

    Lai, Dong; Shapiro, Stuart L.

    1991-01-01

    The influence of a high magnetic field (B is greater than 10 exp 12 G) on the degenerate matter equation of state appropriate to a neutron star is studied. The regime dominated by relativistic electrons up to the neutron drip density is highlighted. The equilibrium matter composition and equation of state, allowing for inverse beta-decay. Two different equilibrium models are determined: an ideal neutron-proton-electron (npe) gas and the more realistic model of Baym, Pethick, and Sutherland (1971) consisting of a Coulomb lattice of heavy nuclei embedded in an electron gas. For a sufficiently high field strength, the magnetic field has an appreciable effect, changing the adiabatic index of the matter and the nuclear transition densities. The influence of a strong field on some simple nonequilibrium processes, including beta-decay and inverse beta-decay (electron capture) is also considered. The effects produced by the magnetic field are mainly due to the changes in the transverse electron quantum orbits and the allowed electron phase space induced by the field.

  14. Magnetic measurements of the transuranium elements and charge state characterization of actinides in monazite. Progress report

    SciTech Connect

    Huray, P. G.

    1980-01-01

    A micromagnetic susceptometer for the purpose of measuring extremely small sample quantities (on the microgram level) was designed, constructed, and calibrated in previous years. (The 1979 progress report gives details of its operation.) This device has operated without significant downtime in this funding period, and much progress has been made in the magnetic characterization of elements beyond Am in the periodic table. This program has roughly doubled man's knowledge of magnetism in Cm, Bk, and Cf, and includes the only Es magnetic measurements to date. The incorporation of an automatic data collection system in this period has made analysis much more accurate, and has allowed quicker turnaround of compounds and metals for study. Results obtained for the compounds and metals studied this year are summarized. The lanthanide orthophosphates are being investigated as an alternate means of primary containment for high-level actinide wastes. Researchers at the Oak Ridge National Laboratory are involved in preparation of actinide-doped compounds for all of the lanthanide transition series (La through Lu) for a study of leaching characteristics and E.S.R. classification. To aid this study the charge state of /sup 237/Np or /sup 57/Fe has been identified, either in the as-prepared compounds or following radioactive decay of /sup 241/Am via the Moessbauer Effect. The final charge state will be an influential variable in the immobilization characteristics of the waste products stored in this synthetic monazite form. 10 figures, 1 table. (RWR)

  15. Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically doped topological insulator

    NASA Astrophysics Data System (ADS)

    Zhang, Duming; Richardella, Anthony; Rench, David W.; Xu, Su-Yang; Kandala, Abhinav; Flanagan, Thomas C.; Beidenkopf, Haim; Yeats, Andrew L.; Buckley, Bob B.; Klimov, Paul V.; Awschalom, David D.; Yazdani, Ali; Schiffer, Peter; Hasan, M. Zahid; Samarth, Nitin

    2012-11-01

    The breaking of time-reversal symmetry by ferromagnetism is predicted to yield profound changes to the electronic surface states of a topological insulator. Here, we report on a concerted set of structural, magnetic, electrical, and spectroscopic measurements of Mn-Bi2Se3 thin films wherein photoemission and x-ray magnetic circular dichroism studies have recently shown surface ferromagnetism in the temperature range 15K≤T≤100 K, accompanied by a suppressed density of surface states at the Dirac point. Secondary-ion mass spectroscopy and scanning tunneling microscopy reveal an inhomogeneous distribution of Mn atoms, with a tendency to segregate towards the sample surface. Magnetometry and anisotropic magnetoresistance measurements are insensitive to the high-temperature ferromagnetism seen in surface studies, revealing instead a low-temperature ferromagnetic phase at T≲5 K. The absence of both a magneto-optical Kerr effect and an anomalous Hall effect suggests that this low-temperature ferromagnetism is unlikely to be a homogeneous bulk phase but likely originates in nanoscale near-surface regions of the bulk where magnetic atoms segregate during sample growth. Although the samples are not ideal, with both bulk and surface contributions to electron transport, we measure a magnetoconductance whose behavior is qualitatively consistent with predictions that the opening of a gap in the Dirac spectrum drives quantum corrections to the conductance in topological insulators from the symplectic to the orthogonal class.

  16. Manipulating magnetism of MnO nano-clusters by tuning the stoichiometry and charge state

    NASA Astrophysics Data System (ADS)

    Ganguly, Shreemoyee; Kabir, Mukul; Autieri, Carmine; Sanyal, Biplab

    2015-02-01

    In this paper, we have studied the composition dependent evolution of geometric and magnetic structures of MnO clusters within density functional theory. The magnetic structures are determined by the competition between direct and superexchange interactions, which have been analyzed by the parameters obtained from maximally localized Wannier functions. The intrinsic electronic structures of the clusters have been thoroughly studied by looking into the hybridization (quantified using the Hybridization Index) and charge transfer scenario. Further, the importance of electron correlation in describing simple Mn-dimer and MnO clusters has been discussed within the Hubbard model and hybrid exchange-correlation functional. Our calculated vertical detachment energies of off-stoichiometric MnO clusters compare well with the recent experimental results. Interestingly, the charged state of the cluster strongly influences the geometry and the magnetic structure of the cluster, which are very different from the corresponding neutral counterpart. We have demonstrated that the exchange interaction between Mn atoms can be switched between ferromagnetic and anitiferromagnetic ones by changing the charge state and hence can be useful for spin-based information technology.

  17. Mid-infrared electro-luminescence and absorption from AlGaN/GaN-based multi-quantum well inter-subband structures

    SciTech Connect

    Hofstetter, Daniel; Bour, David P.; Kirste, Lutz

    2014-06-16

    We present electro-modulated absorption and electro-luminescence measurements on chirped AlGaN/GaN-based multi-quantum well inter-subband structures grown by metal-organic vapour phase epitaxy. The absorption signal is a TM-polarized, 70 meV wide feature centred at 230 meV. At medium injection current, a 58 meV wide luminescence peak corresponding to an inter-subband transition at 1450 cm{sup −1} (180 meV) is observed. Under high injection current, we measured a 4 meV wide structure peaking at 92.5 meV in the luminescence spectrum. The energy location of this peak is exactly at the longitudinal optical phonon of GaN.

  18. Effect of selective area growth mask width on multi-quantum-well electroabsorption modulated lasers investigated by synchrotron radiation X-ray microprobe

    NASA Astrophysics Data System (ADS)

    Mino, Lorenzo; Agostino, Angelo; Codato, Simone; Martinez-Criado, Gema; Lamberti, Carlo

    2012-08-01

    High performance optoelectronic devices require monolithic integration of different functions at chip level. This is the case of multi-quantum well (MQW) electroabsorption modulated laser (EML), employed in long-distance, high-frequency optical fiber communication applications, which is realized exploiting the selective area growth (SAG) technique. Optimization of the growth parameters is carried out by empirical approaches since a direct characterization of the MQW is not possible with laboratory X-ray sources, owing to the micrometer-variation of composition and thickness inherent to the SAG technique. In this work we combined micrometer-resolved photoluminescence with synchrotron radiation micrometer-resolved X-ray fluorescence to study the effect of different SAG masks on the electronic properties and chemical composition of the SAG MQW EML device.

  19. A facile method for highly uniform GaN-based nanorod light-emitting diodes with InGaN/GaN multi-quantum-wells.

    PubMed

    Park, Hyunik; Baik, Kwang Hyeon; Kim, Jihyun; Ren, Fan; Pearton, Stephen J

    2013-05-20

    We report on a simple and reproducible method for fabricating InGaN/GaN multi-quantum-well (MQW) nanorod light-emitting diodes (LEDs), prepared by combining a SiO2 nanosphere lithography and dry-etch process. Focused-ion-beam (FIB)-deposited Pt was contacted to both ends of the nanorod LEDs, producing bright electroluminescence from the LEDs under forward bias conditions. The turn-on voltage in these nanorod LEDs was higher (13 V) than in companion thin film devices (3 V) and this can be attributed to the high contact resistance between the FIB-deposited Pt and nanorod LEDs and the damage induced by inductively-coupled plasma and Ga + -ions. Our method to obtain uniform MQW nanorod LEDs shows promise for improving the reproducibility of nano-optoelectronics.

  20. Characterization of the InGaN/GaN Multi-Quantum-Wells Light-Emitting Diode Grown on Patterned Sapphire Substrate with Wide Electroluminescence Spectrum

    NASA Astrophysics Data System (ADS)

    Lee, Ah Reum; Jeon, Hunsoo; Lee, Gang-Seok; Ok, Jin-Eun; Jo, Dong-Wan; Kim, Kyoung Hwa; Yi, Sam Nyung; Yang, Min; Ahn, Hyung Soo; Cho, Chae-Ryong; Kim, Suok-Whan; Lee, Jae-Hak; Ha, Hong-Ju

    2011-01-01

    We report the characterization of the InGaN/GaN multi-quantum-well (MQW) light-emitting diode (LED) grown on a patterned sapphire substrate by metal organic chemical vapor deposition (MOCVD) using the selective area growth (SAG) method. The SAG patterns were designed to be circular and their diameters were 700 and 200 μm. After the growth, the InGaN/GaN MQW LED of 200 μm diameter had various crystal facets and a shape similar to volcanic craters, which were not observed in the 700-μm-diameter sample. We obtained an active layer with compositional nonuniformity and superior optical properties. We found wide electroluminescence (EL) spectral peaks near 470, 570, and 600 nm. The distribution of the EL spectrum of the sample was similar to that of a conventional phosphor-converted white LED.

  1. Characterization of the InGaN/GaN Multi-Quantum-Wells Light-Emitting Diode Grown on Patterned Sapphire Substrate with Wide Electroluminescence Spectrum

    NASA Astrophysics Data System (ADS)

    Reum Lee, Ah; Jeon, Hunsoo; Lee, Gang-Seok; Ok, Jin-Eun; Jo, Dong-Wan; Kim, Kyoung Hwa; Yi, Sam Nyung; Yang, Min; Ahn, Hyung Soo; Cho, Chae-Ryong; Kim, Suok-Whan; Lee, Jae-Hak; Ha, Hong-Ju

    2011-01-01

    We report the characterization of the InGaN/GaN multi-quantum-well (MQW) light-emitting diode (LED) grown on a patterned sapphire substrate by metal organic chemical vapor deposition (MOCVD) using the selective area growth (SAG) method. The SAG patterns were designed to be circular and their diameters were 700 and 200 µm. After the growth, the InGaN/GaN MQW LED of 200 µm diameter had various crystal facets and a shape similar to volcanic craters, which were not observed in the 700-µm-diameter sample. We obtained an active layer with compositional nonuniformity and superior optical properties. We found wide electroluminescence (EL) spectral peaks near 470, 570, and 600 nm. The distribution of the EL spectrum of the sample was similar to that of a conventional phosphor-converted white LED.

  2. Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

    SciTech Connect

    Yang, J.; Zhao, D. G. Jiang, D. S.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Le, L. C.; Li, X. J.; He, X. G.; Liu, J. P.; Yang, H.; Zhang, Y. T.; Du, G. T.

    2015-02-07

    The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, and therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.

  3. Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN /GaN multi-quantum wells

    NASA Astrophysics Data System (ADS)

    Keller, S.; Schaake, C.; Fichtenbaum, N. A.; Neufeld, C. J.; Wu, Y.; McGroddy, K.; David, A.; DenBaars, S. P.; Weisbuch, C.; Speck, J. S.; Mishra, U. K.

    2006-09-01

    GaN nanopillar and nanostripe arrays with embedded InGaN /GaN multi-quantum wells (MQWs) were fabricated by holographic lithography and subsequent reactive ion etching. Etch related damage of the nanostructures was successfully healed through annealing in NH3/N2 mixtures under optimized conditions. The nanopatterned samples exhibited enhanced luminescence in comparison to the planar wafers. X-ray reciprocal space maps recorded around the asymmetric (101¯5) reflection revealed that the MQWs in both nanopillars and nanostripes relaxed after nanopatterning and adopted a larger in-plane lattice constant than the underlying GaN layer. The pillar relaxation process had no measurable effect on the Stokes shift typically observed in MQWs on c-plane GaN, as evaluated by excitation power dependent photoluminescence (PL) measurements. Angular-resolved PL measurements revealed the extraction of guided modes from the nanopillar arrays.

  4. Investigating the origin of efficiency droop by profiling the voltage across the multi-quantum well of an operating light-emitting diode

    SciTech Connect

    Kim, Taewoong; Seong, Tae-Yeon; Kwon, Ohmyoung

    2016-06-06

    Efficiency droop is a phenomenon in which the efficiency of a light-emitting diode (LED) decreases with the increase in current density. To analyze efficiency droop, direct experimental observations on the energy conversion occurring inside the LED is required. Here, we present the measured voltage profiles on the cross section of an operating LED and analyze them with the cross-sectional temperature profiles obtained in a previous study under the same operation conditions. The measured voltage profiles suggest that with increases in the injection current density, electron depletion shifts from the multi-quantum well through an electron blocking layer to the p-GaN region. This is because electron leakage increases with increases in current density.

  5. Magnetic hexadecapole order and magnetopiezoelectric metal state in Ba1 -xKxMn2As2

    NASA Astrophysics Data System (ADS)

    Watanabe, Hikaru; Yanase, Youichi

    2017-08-01

    We study an odd-parity magnetic multipole order in Ba1 -xKxMn2As2 and related materials. Although BaMn2As2 is a seemingly conventional Mott insulator with G -type antiferromagnetic order, we identify the ground state as a magnetic hexadecapole ordered state accompanied by simultaneous time-reversal and space-inversion symmetry breaking. A symmetry argument and microscopic calculations reveal the ferroic ordering of leading magnetic hexadecapole moment and admixed magnetic quadrupole moment. Furthermore, we clarify electromagnetic responses characterizing the magnetic hexadecapole state of semiconducting BaMn2As2 and doped metallic systems. A magnetoelectric effect and antiferromagnetic Edelstein effect are shown. Interestingly, a counterintuitive current-induced nematic order occurs in the metallic state. The electric current along the z axis induces the x y -plane nematicity in sharp contrast to the spontaneous nematic order in superconducting Fe-based 122 compounds. Thus, the magnetic hexadecapole state of doped BaMn2As2 is regarded as a magnetopiezoelectric metal. Other candidate materials for magnetic hexadecapole order are proposed.

  6. Strong single-ion anisotropy and anisotropic interactions of magnetic adatoms induced by topological surface states

    NASA Astrophysics Data System (ADS)

    Li, Zhenglu; Yang, Jihui; Chen, Guohong; Whangbo, M.-H.; Xiang, Hongjun; Gong, Xingao

    2013-03-01

    The nature of the magnetism brought about by Fe adatoms on the surface of the topological insulator Bi2Se3 was examined in terms of density functional calculations. The Fe adatoms exhibit strong easy-axis magnetic anisotropy in the dilute adsorption limit due to the topological surface states (TSS). The spin exchange J between the Fe adatoms follows a Ruderman-Kittel-Kasuya-Yosida behavior with substantial anisotropy, and the Dzyaloshinskii-Moriya interaction between them is quite strong with |D/J| ~ 0.3 under the mediation by the TSS, and can be further raised to 0.6 by an external electric field. The apparent single-ion anisotropy of a Fe adatom is indispensable in determining the spin orientation. NSFC, FANEDD, Pujiang Plan, Eastern Scholar

  7. Emergent Antiferromagnetism out of the "Hidden-Order" State in URu2Si2: High Magnetic Field Nuclear Magnetic Resonance to 40 T

    NASA Astrophysics Data System (ADS)

    Sakai, H.; Tokunaga, Y.; Kambe, S.; Urbano, R. R.; Suzuki, M.-T.; Kuhns, P. L.; Reyes, A. P.; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Thompson, J. D.

    2014-06-01

    Very high field Si29-NMR measurements using a fully Si29-enriched URu2Si2 single crystal were carried out in order to microscopically investigate the "hidden order" (HO) state and adjacent magnetic phases in the high field limit. At the lowest measured temperature of 0.4 K, a clear anomaly reflecting a Fermi surface instability near 22 T inside the HO state is detected by the Si29 shift, Kc29. Moreover, a strong enhancement of Kc29 develops near a critical field Hc≃35.6 T, and the Si29-NMR signal disappears suddenly at Hc, indicating the total suppression of the HO state. Nevertheless, a weak and shifted Si29-NMR signal reappears for fields higher than Hc at 4.2 K, providing evidence for a magnetic structure within the magnetic phase caused by the Ising-type anisotropy of the uranium ordered moments.

  8. An attempt to obtain a detailed declination chart from the United States magnetic anomaly map

    USGS Publications Warehouse

    Alldredge, L.R.

    1989-01-01

    Modern declination charts of the United States show almost no details. It was hoped that declination details could be derived from the information contained in the existing magnetic anomaly map of the United States. This could be realized only if all of the survey data were corrected to a common epoch, at which time a main-field vector model was known, before the anomaly values were computed. Because this was not done, accurate declination values cannot be determined. In spite of this conclusion, declination values were computed using a common main-field model for the entire United States to see how well they compared with observed values. The computed detailed declination values were found to compare less favourably with observed values of declination than declination values computed from the IGRF 1985 model itself. -from Author

  9. Magnetic intragap states and mixed parity pairing at the edge of spin-triplet superconductors.

    PubMed

    Romano, Alfonso; Gentile, Paola; Noce, Canio; Vekhter, Ilya; Cuoco, Mario

    2013-06-28

    We show that a spontaneous magnetic moment may appear at the edge of a spin-triplet superconductor if the system allows for pairing in a subdominant channel. To unveil the microscopic mechanism behind such an effect, we combine numerical solution of the Bogoliubov-de Gennes equations for a tight-binding model with nearest-neighbor attraction, and the symmetry based Ginzburg-Landau approach. We find that a potential barrier modulating the electronic density near the edge of the system leads to a nonunitary superconducting state close to the boundary where spin-singlet pairing coexists with the dominant triplet superconducting order. We demonstrate that the spin polarization at the edge appears due to the inhomogeneity of the nonunitary state and originates in the lifting of the spin degeneracy of the Andreev bound states.

  10. Spin-orbit driven magnetic insulating state with Jeff=1/2 character in a 4d oxide

    DOE PAGES

    Calder, S.; Li, Ling; Okamoto, Satoshi; ...

    2015-11-30

    The unusual magnetic and electronic ground states of 5d iridates has been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here we present experimental and theoretical results on Sr4RhO6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogous Jeff=1/2 Mottmore » iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy and find a magnetic insulating ground state with Jeff =1/2 character.The unusual magnetic and electronic ground states of 5d iridates have been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here, we present experimental and theoretical results on Sr4RhO6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogous Jeff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy, and find a magnetic insulating ground state with Jeff=12 character.« less

  11. Travancore's magnetic crusade: geomagnetism and the geography of scientific production in a princely state.

    PubMed

    Ratcliff, Jessica

    2016-09-01

    In 1840 the raja of Travancore, Swathi Thirunal, would offer his government's assistance to the British Association for the Advancement of Science and its plan for a global system of magnetic observations. Over the next thirty years, the two directors of this princely state's observatory, John Caldecott and John Allan Broun, would pursue fundamental terrestrial magnetic research. Their efforts would culminate in the Trivandrum [Trevandrum] Magnetical Observations (1874). In what follows, the history of this publication is used to shed light on how and why a semi-autonomous princely state such as Travancore would engage the scientific community in Europe at this time. The article focuses in particular on the work of turning observation data into a published report and on how that labour would be distributed between the Indian subcontinent and Europe. Because the production of such reports required dozens of hands and decades of labour, its history can reveal much about the concrete working relationship between informal colony and imperial metropole within the British Empire. The Trivandrum Magnetic Observations were produced within a global economy of science in which Travancore sometimes had the upper hand. At the same time, data and scientific productions tended to accumulate in Europe (at least for a time), where ultimately the consumers of scientific products and the arbiters of 'scientific value' also largely remained. Within the sprawling economic, political and cultural infrastructures that linked geomagnetic research in Travancore and Europe, the relative strengths and weaknesses of each region would cut in different directions. The history of the production of the Trivandrum Observations brings to light this robustly interconnected geography of scientific production within the British Empire. It also reveals some of the processes by which 'centres' and 'peripheries' in the sciences were then becoming differentiated.

  12. Natural-abundance solid-state 2H NMR spectroscopy at high magnetic field.

    PubMed

    Aliev, Abil E; Mann, Sam E; Iuga, Dinu; Hughes, Colan E; Harris, Kenneth D M

    2011-06-09

    High-resolution solid-state (2)H NMR spectroscopy provides a method for measuring (1)H NMR chemical shifts in solids and is advantageous over the direct measurement of high-resolution solid-state (1)H NMR spectra, as it requires only the application of routine magic angle sample spinning (MAS) and routine (1)H decoupling methods, in contrast to the requirement for complex pulse sequences for homonuclear (1)H decoupling and ultrafast MAS in the case of high-resolution solid-state (1)H NMR. However, a significant obstacle to the routine application of high-resolution solid-state (2)H NMR is the very low natural abundance of (2)H, with the consequent problem of inherently low sensitivity. Here, we explore the feasibility of measuring (2)H MAS NMR spectra of various solids with natural isotopic abundances at high magnetic field (850 MHz), focusing on samples of amino acids, peptides, collagen, and various organic solids. The results show that high-resolution solid-state (2)H NMR can be used successfully to measure isotropic (1)H chemical shifts in favorable cases, particularly for mobile functional groups, such as methyl and -N(+)H(3) groups, and in some cases phenyl groups. Furthermore, we demonstrate that routine (2)H MAS NMR measurements can be exploited for assessing the relative dynamics of different functional groups in a molecule and for assessing whole-molecule motions in the solid state. The magnitude and field-dependence of second-order shifts due to the (2)H quadrupole interaction are also investigated, on the basis of analysis of simulated and experimental (1)H and (2)H MAS NMR spectra of fully deuterated and selectively deuterated samples of the α polymorph of glycine at two different magnetic field strengths.

  13. Positronium decay from n =2 states in electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Alonso, A. M.; Cooper, B. S.; Deller, A.; Hogan, S. D.; Cassidy, D. B.

    2016-01-01

    We report measurements and the results of calculations demonstrating that the annihilation dynamics of positronium (Ps) atoms can be controlled by Stark and Zeeman mixing of optically excited states. In the experiments a trap-based pulsed positron beam was employed to generate a dilute Ps gas with a density of ˜107 cm -3 using a porous silica target. These atoms were excited via 1 3S1→2 3PJ transitions in parallel electric and magnetic fields using a nanosecond pulsed dye laser, and Ps annihilation was measured using single-shot lifetime spectroscopy. The composition of the excited n =2 sublevels was controlled by varying the polarization of the excitation laser radiation and the strength of the electric and magnetic fields in the excitation region. The overall decay rates of the excited states can vary by a large amount, owing to the enormous differences between the annihilation and florescence lifetimes of the accessible field-free states. The energy-level structure, spectral intensities, and florescence and annihilation lifetimes in the presence of the fields were determined from the eigenvalues and eigenvectors of the complete n =2 Hamiltonian matrix in an |n S ℓ J MJ> basis. Using these data as the input to a Monte Carlo model yielded calculated values which could be compared with experimentally measured quantities; qualitative agreement with the measurements was found. Varying the electric field in the presence of a weak parallel magnetic field provides control over the amount of level mixing that occurs, making it possible to increase or decrease the Ps lifetime. Field-controlled Ps decay can be used as an ionization-free detection method. Conversely, increasing the excited-state lifetime can potentially be exploited to optimize multistep excitation processes using mixed intermediate states. This will be useful either in minimizing losses through intermediate-state decay during excitation or by making it possible to separate excitation laser pulses in

  14. Spin-Triplet Pairing State of Sr2RuO4 in the c-Axis Magnetic Field

    NASA Astrophysics Data System (ADS)

    Takamatsu, Shuhei; Yanase, Youichi

    2013-06-01

    We investigate the spin-triplet superconducting state of Sr2RuO4 in the magnetic field along the c-axis on the basis of the four-component Ginzburg--Landau (GL) model with a weak spin--orbit coupling. We consider superconducting states described by the d-vector parallel to the ab-plane (\\mbi{d}\\parallel ab), and find that three spin-triplet pairing states are stabilized in the magnetic field--temperature (H--T) phase diagram. Although a helical state is stable at low magnetic fields, a chiral II state is stabilized at high magnetic fields. A non-unitary spin-triplet pairing state appears near the transition temperature owing to the coupling of magnetic field and chirality. We elucidate synergistic and/or competing roles of the magnetic field, chirality, and spin--orbit coupling. It is shown that a fractional vortex lattice is stabilized in the chiral II phase owing to the spin--orbit coupling.

  15. Ground-state structures in Ising magnets on the Shastry-Sutherland lattice with long-range interactions and fractional magnetization plateaus in TmB4

    NASA Astrophysics Data System (ADS)

    Dublenych, Yu. I.

    2014-11-01

    A method for the study of the ground states of lattice-gas models or equivalent spin models with extended-range interactions is proposed. It is shown that effect of longer-range interactions can be studied in terms of the solution of the ground-state problem for a model with short-range interactions. The method is applied to explain the emergence of fractional magnetization plateaus in TmB 4 regarded as a strong Ising magnet on the Shastry-Sutherland lattice with long-range interactions.

  16. Synergic on/off Photoswitching Spin State and Magnetic Coupling between Spin Crossover Centers.

    PubMed

    Wang, Jun-Li; Liu, Qiang; Meng, Yin-Shan; Zheng, Hui; Zhu, Hai-Lang; Shi, Quan; Liu, Tao

    2017-09-05

    The existence of a correlation between spin crossover and dielectric properties is a hot topic in the field of multiresponse materials, which has potential applications in the memory devices, switches, and sensors. One formidable challenge is the simultaneous and rapid on/off switching of spin states of the spin carriers and magnetic coupling between them, which is crucial for both reversible photomagnetic behavior and variations in dielectric properties. Here, we report a dinuclear Fe(II) spin crossover complex, wherein each Fe(II) center exhibits an interconversion between Fe(II)HS (HS = high-spin) and Fe(II)LS (LS = low-spin) achieved upon heating and cooling. Moreover, the spin state of respective Fe(II) ions and the antiferromagnetic interaction between them can be switched bidirectionally under alternating irradiation with 532 and 808 nm light, resulting in interconversion between paramagnetic and diamagnetic properties. Interestingly, the spin crossover can also induce variations in dielectric tensors. This result provides a strategy to simultaneously and bidirectionally switch spin state, magnetic coupling, and dielectric properties using external stimuli.

  17. Unconventional spin-Peierls state in the quantum magnet TiOBr

    NASA Astrophysics Data System (ADS)

    Castellan, J.-P.; Clancy, J. P.; Ruff, J. P. C.; Rosenkranz, S.; Osborn, R.; Gaulin, B. D.; Chou, F. C.; Huang, S. H.

    2012-02-01

    The discovery of spin-Peierls transitions in inorganic materials such as CuGeO3 with Tsp of 14K allowed for the growth of large single crystals. With the availability of large single crystals the opportunity arises to introduce both magnetic and nonmagnetic impurities and study the resulting perturbations from the ground state. Recently a new class of unconventional spin-Peierls materials were discovered TiOBr and TiOCl. TiOBr and TiOCl have been shown to exhibit dimerized singlet ground states and undergo not one but two successive phase transitions. We have performed x-ray scattering measurements on single crystals of TiOBr. These measurements reveal both commensurate and incommensurate spin-Peierls phases; below Tc2 ˜48K incommensurate super-lattice reflections arise at Q=[H±δ,K+1/2±ɛ,L] which persists down to the lock in transition at Tc1˜27K. We will report on the details of these successive transitions and the destruction of the long-range ordered spin-Peierls state with introduction of magnetic vacancies by doping with Sc.

  18. Magnetic edge states and mixed-parity pairing in spin-triplet superconductors

    NASA Astrophysics Data System (ADS)

    Cuoco, Mario; Gentile, Paola; Noce, Canio; Vekhter, Ilya; Romano, Alfonso

    2014-03-01

    We show that a spontaneous magnetic moment may appear at the edge of a spin-triplet superconductor if the system allows for pairing in a subdominant channel and non-uniform spatial profile. To unveil the microscopic mechanism behind such effect we combine numerical solution of the Bogoliubov-De Gennes equations for a tight-binding model with nearest-neighbor attraction, and the symmetry based Ginzburg-Landau approach. We find that a modulation of the electronic density near the edge of the system leads to a non-unitary superconducting state where spin-singlet pairing coexists with the dominant triplet superconducting order. We demonstrate that the spin polarization at the edge appears due to the inhomogeneity of the non-unitary state and originates in the lifting of the spin-degeneracy of the Andreev bound-states. For chiral spin-triplet superconductors spin current flows along the interface and surface charge currents exhibit anomalous dependence on the magnetization. - A. Romano, P. Gentile, C. Noce, I. Vekhter, M. Cuoco, Phys. Rev. Lett. 110, 267002 (2013). This research has received funding from the EU -FP7/2007-2013 under grant agreement N. 264098 - MAMA, and was supported in part by US NSF via Grant No. DMR-1105339

  19. Effect of a Static Magnetic Field (1.5T) on Brain Oscillatory Activities in Resting State Condition.

    PubMed

    Formaggio, E; Avesani, M; Storti, S F; Milanese, F; Gasparini, A; Acler, M; Cerini, R; Pozzi Mucelli, R; Fiaschi, A; Manganotti, P

    2008-12-17

    The aim of the present study was to compare the EEG signal recorded outside and inside a 1.5T magnetic resonance (MR) scanner. The EEG was recorded in eyes open and eyes closed conditions using a digital recording MR-compatible system. To characterize how a static magnetic field induces changes in EEG signal, EEG data were analyzed using FFT frequency analysis. No significant difference between the alpha powers recorded outside and inside the magnetic field was observed in eyes closed conditions. However, in eyes open condition there was a significant increase in alpha power inside the magnet in comparison to the outside position. The changes in alpha power according to the eyes open/closed conditions could be inversely correlated to a subject's state of wakefulness and due to some physiological changes, rather than an effect of the magnetic field. This experiment suggests that subjects' state of wakefulness is of prime concern when performing functional MRI.

  20. Minimal Magnetic States of the Sun and the Solar Wind: Implications for the Origin of the Slow Solar Wind

    NASA Astrophysics Data System (ADS)

    Cliver, E. W.; von Steiger, R.

    2017-09-01

    During the last decade it has been proposed that both the Sun and the solar wind have minimum magnetic states, lowest order levels of magnetism that underlie the 11-yr cycle as well as longer-term variability. Here we review the literature on basal magnetic states at the Sun and in the heliosphere and draw a connection between the two based on the recent deep 2008-2009 minimum between cycles 23 and 24. In particular, we consider the implications of the low solar activity during the recent minimum for the origin of the slow solar wind.

  1. Pretty good quantum state transfer in symmetric spin networks via magnetic field

    NASA Astrophysics Data System (ADS)

    Kempton, Mark; Lippner, Gabor; Yau, Shing-Tung

    2017-09-01

    We study pretty good single-excitation quantum state transfer (i.e., state transfer that becomes arbitrarily close to perfect) between particles in symmetric spin networks, in the presence of an energy potential induced by a magnetic field. In particular, we show that if a network admits an involution that fixes at least one node or at least one link, then there exists a choice of potential on the nodes of the network for which we get pretty good state transfer between symmetric pairs of nodes. We show further that in many cases, the potential can be chosen so that it is only nonzero at the nodes between which we want pretty good state transfer. As a special case of this, we show that such a potential can be chosen on the endpoints of a spin chain to induce pretty good state transfer in chains of any length. This is in contrast to the result of Kempton et al. (Quantum Inf Comput 17(3):303-327, 2017), in which the authors show that there cannot be perfect state transfer in chains of length 4 or more, no matter what potential is chosen.

  2. Screening and edge states in two-dimensional metals in a magnetic field

    SciTech Connect

    Shikin, V. B. Nazin, S. S.

    2011-08-15

    The length {lambda}{sub 0} at which the lateral electric-field component E{sub Up-Tack} perpendicular to the boundary is conserved near the boundary of two-dimensional (2D) samples, which is covered by 2D electrons, has been determined. The existence of the finite such length follows from the self-consistent process of the screening of the external fields forming the boundaries of real 2D systems by the electrons of the metal. The effect of E{sub Up-Tack} on the structure of magnetic edge states has been taken into account in the mean field approximation in a wide range of the external field from the semiclassical limit ({epsilon}{sub F} Much-Greater-Than h{omega}{sub c}), where {epsilon}{sub F} is the Fermi energy of the 2D system and h{omega}{sub c} is the cyclotron energy to the quantum Hall effect (QHE) region ({epsilon}{sub F} Much-Less-Than h{omega}{sub c}). The positions of the magnetic edge state peaks against the background of their ideal distribution along the perimeter of the 2D circle in the known problem of transverse magnetic focusing have been determined in the semiclassical limit. The systematic description of the structure of the skin layer with {lambda}{sub H} {>=} {lambda}{sub 0}, consisting of the set of the so-called integer strips (overlapping or independent), which are carriers of the universal quantum conductance, has been proposed in the QHE regime. A relatively large probability of the overlapping of the fields of adjacent strips, as well as the possibility of describing coupled integer cascades, is remarkable. The existing data on the tunneling current through integer strips in the {lambda}{sub H} layer providing suitable information on the actual state of the boundary of the 2D system have been commented. A natural analogy between the properties of magnetic edge states and a well-known problem of the details of the ballistic conductance {sigma}{sub Double-Vertical-Line }(H) of narrow electron channels in the magnetic field H has been

  3. Phase-separated magnetic ground state in Mn3Ga0.45Sn0.55C

    NASA Astrophysics Data System (ADS)

    Dias, E. T.; Priolkar, K. R.; Nigam, A. K.; Singh, R.; Das, A.; Aquilanti, G.

    2017-04-01

    The existence of nonergodic ground states is considered as a precursor to a first-order long-range magnetostructural transformation. Mn3Ga0.45Sn0.55C lies compositionally between two compounds, Mn3GaC and Mn3SnC , undergoing first-order magnetic transformation. However, Mn3Ga0.45Sn0.55C , which crystallizes in a single-phase cubic structure, exhibits more than one long-range magnetic transition. Using a combination of magnetization, ac susceptibility, neutron diffraction, and x-ray-absorption fine-structure techniques, it is shown that, although Mn3Ga0.45Sn0.55C exhibits long-range magnetic order, it presents a cluster glassy ground state due to formation of magnetically ordered Ga-rich and Sn-rich clusters. The clusters are big enough to present signatures of long-range magnetic order but are distributed in a way that limits interactions between two clusters of the same type, leading to a frozen magnetic state at low temperatures. The main reason for such a cluster-glass state is the difference in the local structure of Mn atoms that find themselves in Ga-rich and Sn-rich clusters.

  4. Ground states, magnetization plateaus and bipartite entanglement of frustrated spin-1/2 Ising-Heisenberg and Heisenberg triangular tubes

    NASA Astrophysics Data System (ADS)

    Alécio, Raphael C.; Lyra, Marcelo L.; Strečka, Jozef

    2016-11-01

    The ground-state phase diagram, magnetization process and bipartite entanglement of the frustrated spin-1/2 Ising-Heisenberg and Heisenberg triangular tube (three-leg ladder) are investigated in a non-zero external magnetic field. The exact ground-state phase diagram of the spin-1/2 Ising-Heisenberg tube with Heisenberg intra-rung and Ising inter-rung couplings consists of six distinct gapped phases, which manifest themselves in a magnetization curve as intermediate plateaus at zero, one-third and two-thirds of the saturation magnetization. Four out of six available ground states exhibit quantum entanglement between two spins from the same triangular unit evidenced by a non-zero concurrence. Density-matrix renormalization group calculations are used in order to construct the ground-state phase diagram of the analogous but purely quantum spin-1/2 Heisenberg tube with Heisenberg intra- and inter-rung couplings, which consists of four gapped and three gapless phases. The Heisenberg tube shows a continuous change of the magnetization instead of a plateau at zero magnetization, while the intermediate one-third and two-thirds plateaus may be present or not in the zero-temperature magnetization curve.

  5. Investigation of linearity of the ITER outer vessel steady-state magnetic field sensors at high temperature

    NASA Astrophysics Data System (ADS)

    Entler, S.; Duran, I.; Kocan, M.; Vayakis, G.

    2017-07-01

    Three vacuum vessel sectors in ITER will be instrumented by the outer vessel steady-state magnetic field sensors. Each sensor unit features a pair of metallic Hall sensors with a sensing layer made of bismuth to measure tangential and normal components of the local magnetic field. The influence of temperature and magnetic field on the Hall coefficient was tested for the temperature range from 25 to 250 oC and the magnetic field range from 0 to 0.5 T. A fit of the Hall coefficient normalized temperature function independent of magnetic field was found, and a model of the Hall coefficient functional dependence at a wide range of temperature and magnetic field was built with the purpose to simplify the calibration procedure.

  6. Tolosa–Hunt Syndrome Demonstrated by Constructive Interference Steady State Magnetic Resonance Imaging

    PubMed Central

    Wani, Nisar A.; Jehangir, Majid; Lone, Parveen A.

    2017-01-01

    Purpose: To highlight the role of constructive interference steady state (CISS) magnetic resonance imaging (MRI) in the diagnosis of Tolosa-Hunt Syndrome (THS). Case Report: We describe a case of THS in a 55-year-old woman presenting with left painful opthalmoplegia that was diagnosed by CISS MRI. Patient responded to steroid treatment and the lesion resolved. Conclusion: Imaging with MRI can help in making the diagnosis of THS by demonstrating an enhancing soft tissue lesion in the cavernous sinus and orbital apex resolving with steroids. CISS MRI is a sensitive sequence for diagnosis and follow-up imaging in THS. PMID:28299013

  7. Solid State Multinuclear Magnetic Resonance Investigation of Electrolyte Decomposition Products on Lithium Ion Electrodes

    NASA Technical Reports Server (NTRS)

    DeSilva, J .H. S. R.; Udinwe, V.; Sideris, P. J.; Smart, M. C.; Krause, F. C.; Hwang, C.; Smith, K. A.; Greenbaum, S. G.

    2012-01-01

    Solid electrolyte interphase (SEI) formation in lithium ion cells prepared with advanced electrolytes is investigated by solid state multinuclear (7Li, 19F, 31P) magnetic resonance (NMR) measurements of electrode materials harvested from cycled cells subjected to an accelerated aging protocol. The electrolyte composition is varied to include the addition of fluorinated carbonates and triphenyl phosphate (TPP, a flame retardant). In addition to species associated with LiPF6 decomposition, cathode NMR spectra are characterized by the presence of compounds originating from the TPP additive. Substantial amounts of LiF are observed in the anodes as well as compounds originating from the fluorinated carbonates.

  8. Steady-state solutions for atomic multipole moments in an arbitrarily oriented static magnetic field

    NASA Astrophysics Data System (ADS)

    Bevilacqua, G.; Breschi, E.; Weis, A.

    2014-03-01

    We derive algebraic expressions for the atomic multipole moments mk ,q(F) describing the steady-state polarization of an atomic ensemble with angular momentum F in a static magnetic field of arbitrary direction and general multipole relaxation rates Γq(k). The longitudinal moments mk ,0 are given in terms of truncated continued fractions, while the transverse moments mk ,q≠0, representing the ensemble coherence, are given by products of truncated continued fractions. The special case of isotropic relaxation leads to particularly simple and elegant expressions. Our results are relevant for all domains of physics that consider the evolution of a spin system interacting with vector-type perturbations.

  9. Solid State Multinuclear Magnetic Resonance Investigation of Electrolyte Decomposition Products on Lithium Ion Electrodes

    NASA Technical Reports Server (NTRS)

    DeSilva, J .H. S. R.; Udinwe, V.; Sideris, P. J.; Smart, M. C.; Krause, F. C.; Hwang, C.; Smith, K. A.; Greenbaum, S. G.

    2012-01-01

    Solid electrolyte interphase (SEI) formation in lithium ion cells prepared with advanced electrolytes is investigated by solid state multinuclear (7Li, 19F, 31P) magnetic resonance (NMR) measurements of electrode materials harvested from cycled cells subjected to an accelerated aging protocol. The electrolyte composition is varied to include the addition of fluorinated carbonates and triphenyl phosphate (TPP, a flame retardant). In addition to species associated with LiPF6 decomposition, cathode NMR spectra are characterized by the presence of compounds originating from the TPP additive. Substantial amounts of LiF are observed in the anodes as well as compounds originating from the fluorinated carbonates.

  10. Magnetic ground state of Sr2IrO4 and implications for second-harmonic generation

    DOE PAGES

    Di Matteo, S.; Norman, M. R.

    2016-08-24

    The currently accepted magnetic ground state of Sr2IrO4 (the -++- state) preserves inversion symmetry. This is at odds, though, with recent experiments that indicate a magnetoelectric ground state, leading to the speculation that orbital currents or more exotic magnetic multipoles might exist in this material. In this paper, we analyze various magnetic configurations and demonstrate that two of them, the magnetoelectric -+-+ state and the nonmagnetoelectric ++++ state, can explain these recent second-harmonic generation (SHG) experiments, obviating the need to invoke orbital currents. The SHG-probed magnetic order parameter has the symmetry of a parity-breaking multipole in the -+-+ state andmore » of a parity-preserving multipole in the ++++ state. We speculate that either might have been created by the laser pump used in the experiments. An alternative is that the observed magnetic SHG signal is a surface effect. Finally, we suggest experiments that could be performed to test these various possibilities and also address the important issue of the suppression of the RXS intensity at the L2 edge.« less

  11. Reversible control of magnetization of Fe3O4 by a solid-state film lithium battery

    NASA Astrophysics Data System (ADS)

    Wei, Guodong; Wei, Lin; Wang, Dong; Chen, Yanxue; Tian, Yufeng; Yan, Shishen; Mei, Liangmo; Jiao, Jun

    2017-02-01

    The LiCoO2/LISICON/Fe3O4 structured solid-state film lithium battery is designed to realize a reversible control of the magnetization in Fe3O4 film. LISICON (Li1.5Al0.5Ge1.5P3O12) is selected to serve as the solid-state electrolyte owing to its excellent Li ion transport property at room temperature. A reversible and non-volatile control of the saturation magnetization of Fe3O4 film between the charged and discharged states was obtained, and the modulation ratio can reach as high as 10%. The redox of Fe ions, caused by the intercalation/deintercalation of lithium ion in Fe3O4 film, is responsible for the observed magnetic variation. The battery consisting entirely of solid films provides a promising strategy to control the magnetic properties electrically, which will be a very hopeful candidate for many practical applications.

  12. Ground state properties of spinless extended Falicov-Kimball model on a triangular lattice with finite magnetic field

    NASA Astrophysics Data System (ADS)

    Yadav, Umesh K.

    2017-07-01

    Combined effects of correlated electron hopping, electron correlations and orbital magnetic field are studied on ground state properties of spinless Falicov-Kimball model (FKM). Results are obtained for finite size triangular lattice with periodic boundary conditions using numerical diagonalization and Monte-Carlo simulation techniques. It is found that the ground state configurations of electrons strongly depend on correlated electron hopping, onsite Coulomb interaction and orbital magnetic field. Several interesting configurations e.g. regular, segregated, axial and diagonal striped and hexagonal phases are found with change in correlated hopping and magnetic field. Study of density of states reveals that magnetic field induces a metal to insulator transition accompanied by segregated phase to an ordered phase. These results are applicable to the systems of recent interest like GdI2, NaTiO2 and MgV2O4 and can also be seen experimentally in cold atomic set up.

  13. Effective Control of the Charge and Magnetic States of Transition-Metal Atoms on Single-Layer Boron Nitride

    NASA Astrophysics Data System (ADS)

    Huang, Bing; Xiang, Hongjun; Yu, Jaejun; Wei, Su-Huai

    2012-05-01

    Developing approaches to effectively control the charge and magnetic states is critical to the use of magnetic nanostructures in quantum information devices but is still challenging. Here we suggest that the magnetic and charge states of transition-metal (TM) doped single-layer boron-nitride (SLBN) systems can be easily controlled by the (internal) defect engineering and (external) electric fields (Eext). The relative positions and symmetries of the in-gap levels induced by defect engineering and the TM d-orbital energy levels effectively determine the charge states and magnetic properties of the TM/SLBN system. Remarkably, the application of an Eext can easily control the size of the crystal field splitting of the TM d orbitals and thus, leading to the spin crossover in TM/SLBN, which could be used as Eext-driven nonvolatile memory devices. Our conclusion obtained from TM/SLBN is valid generally in other TM adsorbed layered semiconductors.

  14. Effect of MgO/Fe Interface Oxidation State on Electric-Field Modulation of Interfacial Magnetic Anisotropy

    NASA Astrophysics Data System (ADS)

    Guan, X. W.; Cheng, X. M.; Wang, S.; Huang, T.; Xue, K. H.; Miao, X. S.

    2016-06-01

    The impact of the MgO/Fe interface oxidation state on the electric-field-modified magnetic anisotropy in MgO/Fe has been revealed by density functional calculations. It is shown that the influence of the interface oxidation is strong enough to dominate the effect of the electric field on the magnetic anisotropy of MgO/Fe-based films. The magnetoelectric coefficients are calculated to be positive for the ideal and overoxidized MgO/Fe interface, but an abnormal negative value emerges in the underoxidized case. By analyzing the interface states based on density of states and band structures, we demonstrate that the considerably different electronic structures of the three oxidized MgO/Fe interfaces lead to the strong discrepancy in the electric-field modulation of the interfacial magnetic anisotropy. These results are of considerable interest in the area of electric-field-controlled magnetic anisotropy and switching.

  15. Solid state magnetic field sensors for micro unattended ground networks using spin dependent tunneling

    NASA Astrophysics Data System (ADS)

    Tondra, Mark; Nordman, Catherine A.; Lange, Erik H.; Reed, Daniel; Jander, Albrect; Akou, Seraphin; Daughton, James

    2001-09-01

    Micro Unattended Ground Sensor Networks will likely employ magnetic sensors, primarily for discrimination of objects as opposed to initial detection. These magnetic sensors, then, must fit within very small cost, size, and power budgets to be compatible with the envisioned sensor suites. Also, a high degree of sensitivity is required to minimize the number of sensor cells required to survey a given area in the field. Solid state magnetoresistive sensors, with their low cost, small size, and ease of integration, are excellent candidates for these applications assuming that their power and sensitivity performance are acceptable. SDT devices have been fabricated into prototype magnetic field sensors suitable for use in micro unattended ground sensor networks. They are housed in tiny SOIC 8-pin packages and mounted on a circuit board with required voltage regulation, signal amplification and conditioning, and sensor control and communications functions. The best sensitivity results to date are 289 pT/rt. Hz at 1 Hz, and and 7 pT/rt. Hz at f > 10 kHz. Expected near term improvements in performance would bring these levels to approximately 10 pT/rt Hz at 1 Hz and approximately 1 pT/rt. Hz at > 1 kHz.

  16. Excited states of two-dimensional hydrogen atom in tilted magnetic field: Quantum chaos

    NASA Astrophysics Data System (ADS)

    Koval, Eugene A.; Koval, Oksana A.

    2017-09-01

    The aim of the current work is the research of the influence of a tilted magnetic field direction on the spectrum and the energy level spacing distribution of a two-dimensional (2D) hydrogen atom and of an exciton in GaAs/Al0.33Ga0.67As quantum well. It was discovered that the quantum chaos (QC) is initiated with an increasing angle α between the magnetic field direction and the normal to the atomic plane. It is characterized by the repulsion of levels leading to the eliminating of the shell structure and by changing the spectrum statistical properties. The statement about the initiation of chaos and its dominance over regular motion with increasing angle α is confirmed by the results of our calculations of the classical dynamics presented in this paper. The evolution of the spatial distribution of the square of the absolute value of the wave function at an increasing angle α was observed. The differences of calculated dependencies of energies for various excited states on the tilt angle at a wide range of the magnetic field strength were described.

  17. Ground state and magnetic phase transitions of orthoferrite DyFeO3

    NASA Astrophysics Data System (ADS)

    Zhao, Z. Y.; Zhao, X.; Zhou, H. D.; Zhang, F. B.; Li, Q. J.; Fan, C.; Sun, X. F.; Li, X. G.

    2014-06-01

    Low-temperature thermal conductivity (κ), as well as magnetization (M) and electric polarization (P), of multiferroic orthoferrite DyFeO3 single crystals are studied with H ∥c. When the crystal is cooled in zero field, M, P, and κ all consistently exhibit irreversible magnetic-field dependencies. In particular, with 500 mK magnetic phase transitions of the Fe3+ spins. In particular, the ground state, obtained with cooling to sub-Kelvin temperatures in zero field, is found to be an unexplored phase.

  18. 3-D Modelling of Magnetic Data from an Archaeological Site in Northwestern Tlaxcala State, Mexico

    NASA Astrophysics Data System (ADS)

    Chavez, R. E.; Argote, D. L.; Cifuentes, G.; Tejero, A.; Camara, E.

    2009-05-01

    In Archaeology, geophysical methods had been applied usually in a qualitative form, limited only to the use of filters that enhance the data display. The main objective in this work is the implementation of a modeling technique that allows us to reconstruct the geometry of buried bodies and the determination of their depths. This is done by means of the estimation of the magnetic moments of archaeological objects using a three- dimensional mesh of individual magnetic dipoles using the least squares method and the singular value decomposition of a weighted matrix to solve the linear problem. The distribution and shape of the underlying archaeological remains can be inferred. This methodology was applied to an archaeological site called Los Teteles de Ocotitla, in the state of Tlaxcala, Mexico. A high-resolution magnetic prospection was carried out in three selected areas (terraces). The most important total field anomalies found on each area were inverted, obtaining results that were corroborated by archaeological excavations. This investigation demonstrates the potential of quantitative geophysical methods for the characterization of archaeological structures, in extension and in depth.

  19. A magnetic model for low/hard state of black hole binaries

    NASA Astrophysics Data System (ADS)

    Ye, Yong-Chun; Wang, Ding-Xiong; Huang, Chang-Yin; Cao, Xiao-Feng

    2016-03-01

    A magnetic model for the low/hard state (LHS) of two black hole X-ray binaries (BHXBs), H1743-322 and GX 339-4, is proposed based on transport of the magnetic field from a companion into an accretion disk around a black hole (BH). This model consists of a truncated thin disk with an inner advection-dominated accretion flow (ADAF). The spectral profiles of the sources are fitted in agreement with the data observed at four different dates corresponding to the rising phase of the LHS. In addition, the association of the LHS with a quasi-steady jet is modeled based on transport of magnetic field, where the Blandford-Znajek (BZ) and Blandford-Payne (BP) processes are invoked to drive the jets from BH and inner ADAF. It turns out that the steep radio/X-ray correlations observed in H1743-322 and GX 339-4 can be interpreted based on our model.

  20. Valence state and magnetism of Yb7Co4InGe12.

    NASA Astrophysics Data System (ADS)

    Rak, Zsolt; Chondroudi, Maria; Mahanti, S. D.; Kanatzidis, M. G.

    2007-03-01

    Ytterbium (Yb) compounds exhibit unusual physical properties due to the Yb f-electrons, which play an active role in bonding, giving rise to intermediate valence, heavy-fermion or Kondo behavior. Many physical characteristics of the Yb systems are related to the fact that Yb can have two valence states: nonmagnetic divalent Yb^2+ (f^14) and magnetic trivalent Yb^3+ (f^13). We have synthesized a new Yb containing quaternary Yb7Co4InGe12. XPS and magnetic susceptibility measurements indicate that all Yb are all trivalent. To understand the Yb valency in this compound, we have carried out ab initio electronic structure calculations within density functional theory using FP-LAPW method. The electronic structure is obtained using LSDA with on-site Coulomb correlation potential (LSDA+U) included for both 4f electrons of Yb and 3d electrons of Co. As a one ``f-hole'' analogue of many Ce compounds^1, 2, we find that all the Yb atoms are trivalent, in agreement with XPS and magnetic susceptibility measurements. ^1A. I. Liechtenstein, V. P. Antropov, and B. N Harmon, Phys. Rev. B 49, 10770 (1994). ^2E. Bauer, Adv. Phys. 40, 417 (1991).

  1. Carrier States in Ferromagnetic Semiconductors and Diluted Magnetic Semiconductors—Coherent Potential Approach—

    PubMed Central

    Takahashi, Masao

    2010-01-01

    The theoretical study of magnetic semiconductors using the dynamical coherent potential approximation (dynamical CPA) is briefly reviewed. First, we give the results for ferromagnetic semiconductors (FMSs) such as EuO and EuS by applying the dynamical CPA to the s-f model. Next, applying the dynamical CPA to a simple model for A1−xMnxB-type diluted magnetic semiconductors (DMSs), we show the results for three typical cases to clarify the nature and properties of the carrier states in DMSs. On the basis of this model, we discuss the difference in the optical band edges between II-V DMSs and III-V-based DMSs, and show that two types of ferromagnetism can occur in DMSs when carriers are introduced. The carrier-induced ferromagnetism of Ga1−xMnxAs is ascribed to a double-exchange (DE)-like mechanism realized in the magnetic impurity band/or in the band tail.

  2. Measuring and manipulating brain connectivity with resting state functional connectivity magnetic resonance imaging (fcMRI) and transcranial magnetic stimulation (TMS).

    PubMed

    Fox, Michael D; Halko, Mark A; Eldaief, Mark C; Pascual-Leone, Alvaro

    2012-10-01

    Both resting state functional magnetic resonance imaging (fcMRI) and transcranial magnetic stimulation (TMS) are increasingly popular techniques that can be used to non-invasively measure brain connectivity in human subjects. TMS shows additional promise as a method to manipulate brain connectivity. In this review we discuss how these two complimentary tools can be combined to optimally study brain connectivity and manipulate distributed brain networks. Important clinical applications include using resting state fcMRI to guide target selection for TMS and using TMS to modulate pathological network interactions identified with resting state fcMRI. The combination of TMS and resting state fcMRI has the potential to accelerate the translation of both techniques into the clinical realm and promises a new approach to the diagnosis and treatment of neurological and psychiatric diseases that demonstrate network pathology.

  3. Measuring and manipulating brain connectivity with resting state functional connectivity magnetic resonance imaging (fcMRI) and transcranial magnetic stimulation (TMS)

    PubMed Central

    Fox, Michael D.; Halko, Mark A.; Eldaief, Mark C.; Pascual-Leone, Alvaro

    2012-01-01

    Both resting state functional magnetic resonance imaging (fcMRI) and transcranial magnetic stimulation (TMS) are increasingly popular techniques that can be used to non-invasively measure brain connectivity in human subjects. TMS shows additional promise as a method to manipulate brain connectivity. In this review we discuss how these two complimentary tools can be combined to optimally study brain connectivity and manipulate distributed brain networks. Important clinical applications include using resting state fcMRI to guide target selection for TMS and using TMS to modulate pathological network interactions identified with resting state fcMRI. The combination of TMS and resting state fcMRI has the potential to accelerate the translation of both techniques into the clinical realm and promises a new approach to the diagnosis and treatment of neurological and psychiatric diseases that demonstrate network pathology. PMID:22465297

  4. Thermodynamics of the magnetic-field-induced "normal" state in an underdoped high Tc superconductor

    NASA Astrophysics Data System (ADS)

    Riggs, Scott Chandler

    High magnetic fields are used to kill superconductivity and probe what happens to system when it cannot reach the ideal ground state, i.e. what is the normal-state ground state? Early work in High-Tc, where the application of magnetic field destroyed the zero resistance state and recovered a resistivity value that connected continuously with the zero field curve, lead people to believe this magnetic-field-induced-state had fully driven the system normal, revealing the true underlying ground state, without any vestige of superconductivity. Many experiments done in this region of phase space have results interpreted as coming from the low energy ground state excitations. With the emergence of ultra-clean crystals in a unique family of hole doped high-Tc superconductors, YBa2Cu3O 7-delta, YBCO, a new and highly unexpected phenomena of quantum oscillations were discovered, and they followed the standard Liftshitz-Kosevich (LK) theory for a normal metal. The results suddenly made the problem of high-T c appear to be analogous to superconductivity in the organics, which is brought about by a wave-vector nesting and Fermi surface reconstruction. The only problem, it appeared, that needed to be reconciled was with Angle Resolved Photo-Emission Spectroscopy (ARPES) and Scanning Tunneling Microscopy (STM) data that claimed to see no such Fermi surface, instead only "arcs", a set of disconnected segments in the Brillouin zone which quasiparticle peaks are observed at the Fermi energy, which in a mean field description does not allow for a continuous Fermi surface contour. These two discrepancies led to the "arc vs pocket" debate, which is still unresolved. The other kink in the quantum oscillation armor is that, to this date, quantum oscillations in the hole-doped cuprates have only been seen in YBCO, the only cuprate structure to have CuO chains, which conduct and are located in between two CuO2 superconducting planes in the unit cell. In an attempt to reconcile the "arc vs

  5. Anxiety Modulates Insula Recruitment in Resting-State Functional Magnetic Resonance Imaging in Youth and Adults

    PubMed Central

    Gotlib, Ian H.; Thompson, Paul M.; Thomason, Moriah E.

    2011-01-01

    Abstract Research on resting-state functional connectivity reveals intrinsically connected networks in the brain that are largely consistent across the general population. However, there are individual differences in these networks that have not been elucidated. Here, we measured the influence of naturally occurring mood on functional connectivity. In particular, we examined the association between self-reported levels of anxiety and connectivity in the default mode network (DMN). Healthy youth (n=43; ages 10–18) and adult participants (n=24, ages 19–59) completed a 6-min resting-state functional magnetic resonance imaging scan, then immediately completed questionnaires assessing their mood and thoughts during the scan. Regression analyses conducted separately for the youth and adult samples revealed brain regions in which increases in connectivity differentially corresponded to higher anxiety in each group. In one area, the left insular cortex, both groups showed similar increased connectivity to the DMN (youth: -30, 26, 14; adults: -33, 12, 14) with increased anxiety. State anxiety assessed during scanning was not correlated with trait anxiety, so our results likely reflect state levels of anxiety. To our knowledge, this is the first study to relate naturally occurring mood to resting state connectivity. PMID:22433052

  6. Hydrogen atom in a strong magnetic field. II. Relativistic corrections for low-lying excited states

    NASA Astrophysics Data System (ADS)

    Poszwa, A.; Rutkowski, A.

    2004-02-01

    The highly accurate solution of the Schrödinger equation in the form of common Landau exponential factor multiplied by a power series in two variables, the sine of the cone angle and radial variable is completed by the first-order relativistic correction calculated within the framework of the relativistic direct perturbation theory (DPT). It is found that in contrast to behavior of relativistic corrections for the ground state and 2p-1(ms=-1/2) excited state, which change sign from negative to positive near B≈1011 G and B≈1010 G, respectively [Z. Chen and S. P. Goldman, Phys. Rev A 45, 1722 (1992)], the relativistic corrections for 2s0(ms=-1/2) and 2p0(ms=-1/2) excited states are negative for the magnetic field varying in range 0states the near-degenerate version of DPT is used. The avoided crossings of relativistic levels with μ=-1/2 and π=-1, evolving from field-free states with principal quantum numbers n=2,3,4 are presented.

  7. 31P nuclear magnetic resonance determination of changes in energy state in lung preservation.

    PubMed

    Hall, T S; Buescher, P C; Borkon, A M; Reitz, B A; Michael, J R; Baumgartner, W A

    1988-11-01

    The significance of dynamic changes in energy state during lung harvesting and preservation has not been extensively studied. Phosphorus 31 nuclear magnetic resonance spectra at 81 MHz were obtained from degassed rabbit lungs. Changes in the adenosine 5'-triphosphate-to-inorganic phosphate peak-intensity ratios were used to measure changes in energy state. Two groups of rabbit preparations were studied to evaluate the effect of hypothermia during the initial 120 minutes of harvesting (n = 8 at 36 degrees C and n = 5 at 4 degrees C). The significance of these changes was assessed in a second experiment in which lungs were reperfused in vitro at selected intervals of hypothermia (5, 12, and 24 hours) and assessed for injury. Hypothermic preservation sustained a significantly higher energy state. The depletion of energy state was correlated with injury, particularly as measured by lung edema (r2 = -0.715). Short periods of warm ischemia (30 minutes) result in a significant depletion of energy state, which may be a component of pulmonary injury during harvesting and preservation.

  8. Magnetic susceptibility data for some exposed bedrock in the western conterminous United States

    USGS Publications Warehouse

    Gettings, Mark E.; Bultman, Mark W.

    2014-01-01

    In-place rock magnetic susceptibility measurements for 746 sites in the western conterminous United States are reported in a database. Of these 746 sites, 408 sites are in the Silverton Caldera area of the San Juan Mountains of southwestern Colorado. Of the 408 sites in the Silverton Caldera area, 106 sites are underground. The remaining 338 sites outside the Silverton Caldera area were on outcropping rock, are distributed from southern Arizona to northwestern Wyoming, and include data from California, Nevada, Utah, Colorado, and New Mexico. Rock-density measurements are included for some sites. These data have been collected by various U.S. Geological Survey studies from 1991 through 2012 and are intended to help improve geophysical modeling of the Earth’s crust in the Western United States. A map-based graphical user interface is included to facilitate use of the data.

  9. Ambient-Pressure Bulk Superconductivity Deep in the Magnetic State of CeRhIn5

    SciTech Connect

    Paglione,J.; Ho, P.; Maple, M.; Tanatar, M.; Taillefer, L.; Lee, Y.; Petrovic, C.

    2008-01-01

    Specific heat, magnetic susceptibility and electrical transport measurements were performed at ambient pressure on high-quality single crystal specimens of CeRhIn5 down to ultra-low temperatures. We report signatures of an anomaly observed in all measured quantities consistent with a bulk phase transition to a superconducting state at T{sub c}=110 mK. Occurring far below the onset of antiferromagnetism at T{sub N}=3.8 K, this transition appears to involve a significant portion of the available low-temperature density of electronic states, exhibiting an entropy change in line with that found in other members of the 115 family of superconductors tuned away from quantum criticality.

  10. Solid state nuclear magnetic resonance studies of cross polarization from quadrupolar nuclei

    SciTech Connect

    De Paul, Susan M.

    1997-08-01

    The development of solid-state Nuclear Magnetic Resonance (NMR) has, to a large extent, focused on using spin-1/2 nuclei as probes to investigate molecular structure and dynamics. For such nuclei, the technique of cross polarization is well-established as a method for sensitivity enhancement. However, over two-thirds of the nuclei in the periodic table have a spin-quantum number greater than one-half and are known as quadrupolar nuclei. Such nuclei are fundamental constituents of many inorganic materials including minerals, zeolites, glasses, and gels. It is, therefore, of interest to explore the extent to which polarization can be transferred from quadrupolar nuclei. In this dissertation, solid-state NMR experiments involving cross polarization from quadrupolar nuclei to spin-1/2 nuclei under magic-angle spinning (MAS) conditions are investigated in detail.

  11. Phonon structures in the electronic density of states of graphene in magnetic field

    NASA Astrophysics Data System (ADS)

    Pound, Adam; Carbotte, J. P.; Nicol, E. J.

    2011-06-01

    Unlike in ordinary metals, in graphene, phonon structure can be seen in the quasiparticle electronic density of states, because the latter varies on the scale of the phonon energy. In a magnetic field, quantization into Landau levels creates even more significant variations. We calculate the density of states incorporating electron-phonon coupling in this case and find that the coupling has pronounced new effects: shifting and broadening of Landau levels, creation of new peaks, and splitting of any Landau levels falling near one of the new peaks. Comparing our calculations with a recent experiment, we find evidence for a phonon with energy similar to but somewhat greater than the optical E2g mode and a coupling corresponding to a mass enhancement parameter λsime0.07.

  12. Relaxation and decoherence of qubits encoded in collective states of engineered magnetic structures

    NASA Astrophysics Data System (ADS)

    Shakirov, Alexey M.; Rubtsov, Alexey N.; Lichtenstein, Alexander I.; Ribeiro, Pedro

    2017-09-01

    The quantum nature of a microscopic system can only be revealed when it is sufficiently decoupled from surroundings. Interactions with the environment induce relaxation and decoherence that turn the quantum state into a classical mixture. Here, we study the timescales of these processes for a qubit encoded in the collective state of a set of magnetic atoms deposited on a metallic surface. For that, we provide a generalization of the commonly used definitions of T1 and T2 characterizing relaxation and decoherence rates. We calculate these quantities for several atomic structures, including a collective spin, a setup implementing a decoherence-free subspace, and two examples of spin chains. Our work contributes to the comprehensive understanding of the relaxation and decoherence processes and shows the advantages of the implementation of a decoherence free subspace in these setups.

  13. Impeded growth of magnetic flux bubbles in the intermediate state pattern of type I superconductors.

    PubMed

    Jeudy, V; Gourdon, C; Okada, T

    2004-04-09

    Normal state bubble patterns in type I superconducting indium and lead slabs are studied by the high resolution magneto-optical imaging technique. The size of bubbles is found to be independent of the long-range interaction between the normal state domains. Under bubble diameter and slab thickness proper scaling, the results gather onto a single master curve. We calculate the equilibrium diameter of an isolated bubble resulting from the competition between the Biot-and-Savart interaction of the Meissner current encircling the bubble and the superconductor-normal interface energy. A good quantitative agreement with the master curve is found over two decades of the magnetic Bond number. The isolation of each bubble in the superconductor and the interface energy are shown to preclude any continuous size variation of the bubbles after their formation, contrary to the prediction of mean-field models.

  14. Magnetic-field-induced Fabry-Pérot resonances in helical edge states

    NASA Astrophysics Data System (ADS)

    Soori, Abhiram; Das, Sourin; Rao, Sumathi

    2012-09-01

    We study electronic transport across a helical edge state exposed to a uniform magnetic (B⃗) field over a finite length. We show that this system exhibits Fabry-Pérot-type resonances in electronic transport. The intrinsic spin anisotropy of the helical edge states allows us to tune these resonances by changing the direction of the B⃗ field while keeping its magnitude constant. This is in sharp contrast to the case of nonhelical one-dimensional electron gases with a parabolic dispersion, where similar resonances do appear in individual spin channels (↑ and ↓) separately which, however, cannot be tuned by merely changing the direction of the B⃗ field. These resonances provide a unique way to probe the helical nature of the theory. We study the robustness of these resonances against a possible static impurity in the channel.

  15. Geometric Effect on Quantum Anomalous Hall State in Magnetic Topological Insulator

    NASA Astrophysics Data System (ADS)

    Xing, Yanxia

    An intriguing observation on the quantum anomalous Hall (QAH) effect in a magnetic topological insulator (MTI) is the dissipative edge states. With the aid of non-equilibrium Green's functions,the QAH effect in an MTI with a three dimensional effective tight-binding model is studied.We predict that due to geometric structure in the third dimension z,the unideal contact between terminal leads and central scattering region induces the backscattering in the central Hall bar,as the function of split gates. Such backscattering leads to a nonzero longitudinal resistance and quantized Hall resistance, which would explain the dissipative edge states in experiments.A further numerical simulation prove above prediction as well.These results are rewarding on future experimental observations and transport calculations based on first principe.

  16. Non-Hermitian approach of edge states and quantum transport in a magnetic field

    NASA Astrophysics Data System (ADS)

    Ostahie, B.; Niţa, M.; Aldea, A.

    2016-11-01

    We develop a manifest non-Hermitian approach of spectral and transport properties of two-dimensional mesoscopic systems in a strong magnetic field. The finite system to which several terminals are attached constitutes an open system that can be described by an effective Hamiltonian. The lifetime of the quantum states expressed by the energy imaginary part depends specifically on the lead-system coupling and makes the difference among three regimes: resonant, integer quantum Hall effect, and superradiant. The discussion is carried on in terms of edge state lifetime in different gaps, channel formation, role of hybridization, and transmission coefficients quantization. A toy model helps in understanding non-Hermitian aspects in open systems.

  17. Resting state functional magnetic resonance imaging processing techniques in stroke studies.

    PubMed

    Mirzaei, Golrokh; Adeli, Hojjat

    2016-12-01

    In recent years, there has been considerable research interest in the study of brain connectivity using the resting state functional magnetic resonance imaging (rsfMRI). Studies have explored the brain networks and connection between different brain regions. These studies have revealed interesting new findings about the brain mapping as well as important new insights in the overall organization of functional communication in the brain network. In this paper, after a general discussion of brain networks and connectivity imaging, the brain connectivity and resting state networks are described with a focus on rsfMRI imaging in stroke studies. Then, techniques for preprocessing of the rsfMRI for stroke patients are reviewed, followed by brain connectivity processing techniques. Recent research on brain connectivity using rsfMRI is reviewed with an emphasis on stroke studies. The authors hope this paper generates further interest in this emerging area of computational neuroscience with potential applications in rehabilitation of stroke patients.

  18. Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances

    NASA Astrophysics Data System (ADS)

    Bedrosian, Paul A.; Love, Jeffrey J.

    2015-12-01

    Empirical impedance tensors obtained from EarthScope magnetotelluric data at sites distributed across the midwestern United States are used to examine the feasibility of mapping magnetic storm induction of geoelectric fields. With these tensors, in order to isolate the effects of Earth conductivity structure, we perform a synthetic analysis—calculating geoelectric field variations induced by a geomagnetic field that is geographically uniform but varying sinusoidally with a chosen set of oscillation frequencies that are characteristic of magnetic storm variations. For north-south oriented geomagnetic oscillations at a period of T0=100 s, induced geoelectric field vectors show substantial geographically distributed differences in amplitude (approximately a factor of 100), direction (up to 130∘), and phase (over a quarter wavelength). These differences are the result of three-dimensional Earth conductivity structure, and they highlight a shortcoming of one-dimensional conductivity models (and other synthetic models not derived from direct geophysical measurement) that are used in the evaluation of storm time geoelectric hazards for the electric power grid industry. A hypothetical extremely intense magnetic storm having 500 nT amplitude at T0=100 s would induce geoelectric fields with an average amplitude across the midwestern United States of about 2.71 V/km, but with a representative site-to-site range of 0.15 V/km to 16.77 V/km. Significant improvement in the evaluation of such hazards will require detailed knowledge of the Earth's interior three-dimensional conductivity structure.

  19. Single-shot dual-polarization holography: measurement of the polarization state of a magnetic sample

    NASA Astrophysics Data System (ADS)

    Khodadad, Davood; Amer, Eynas; Gren, Per; Melander, Emil; Hällstig, Emil; Sjödahl, Mikael

    2015-08-01

    In this paper a single-shot digital holographic set-up with two orthogonally polarized reference beams is proposed to achieve rapid acquisition of Magneto-Optical Kerr Effect images. Principles of the method and the background theory for dynamic state of polarization measurement by use of digital holography are presented. This system has no mechanically moving elements or active elements for polarization control and modulation. An object beam is combined with two reference beams at different off-axis angles and is guided to a detector. Then two complex fields (interference terms) representing two orthogonal polarizations are recorded in a single frame simultaneously. Thereafter the complex fields are numerically reconstructed and carrier frequency calibration is done to remove aberrations introduced in multiplexed digital holographic recordings. From the numerical values of amplitude and phase, a real time quantitative analysis of the polarization state is possible by use of Jones vectors. The technique is demonstrated on a magnetic sample that is a lithographically patterned magnetic microstructure consisting of thin permalloy parallel stripes.

  20. Theory of Stochastic Dipolar Recoupling in Solid State Nuclear Magnetic Resonance

    PubMed Central

    Tycko, Robert

    2008-01-01

    Dipolar recoupling techniques in solid state nuclear magnetic resonance (NMR) consist of radio-frequency (rf) pulse sequences applied in synchrony with magic-angle spinning (MAS) that create non-zero average magnetic dipole-dipole couplings under MAS. Stochastic dipolar recoupling (SDR) is a variant in which randomly chosen rf carrier frequency offsets are introduced to cause random phase modulations of individual pairwise couplings in the dipolar spin Hamiltonian. Several aspects of SDR are investigated through analytical theory and numerical simulations: (1) An analytical expression for the evolution of nuclear spin polarization under SDR in a two-spin system is derived and verified through simulations, which show a continuous evolution from coherent, oscillatory polarization exchange to incoherent, exponential approach to equilibrium as the range of random carrier offsets (controlled by a parameter fmax) increases; (2) In a many-spin system, polarization transfers under SDR are shown to be described accurately by a rate matrix in the limit of large fmax, with pairwise transfer rates that are proportional to the inverse sixth power of pairwise internuclear distances; (3) Quantum mechanical interferences among non-commuting pairwise dipole-dipole couplings, which are a complicating factor in solid state NMR studies of molecular structures by traditional dipolar recoupling methods, are shown to be absent from SDR data in the limit of large fmax, provided that coupled nuclei have distinct NMR chemical shifts. PMID:18085769

  1. Composite dipolar recoupling: anisotropy compensated coherence transfer in solid-state nuclear magnetic resonance.

    PubMed

    Khaneja, Navin; Kehlet, Cindie; Glaser, Steffen J; Nielsen, Niels Chr

    2006-03-21

    The efficiency of dipole-dipole coupling driven coherence transfer experiments in solid-state nuclear magnetic resonance (NMR) spectroscopy of powder samples is limited by dispersion of the orientation of the internuclear vectors relative to the external magnetic field. Here we introduce general design principles and resulting pulse sequences that approach full polarization transfer efficiency for all crystallite orientations in a powder in magic-angle-spinning experiments. The methods compensate for the defocusing of coherence due to orientation dependent dipolar coupling interactions and inhomogeneous radio-frequency fields. The compensation scheme is very simple to implement as a scaffold (comb) of compensating pulses in which the pulse sequence to be improved may be inserted. The degree of compensation can be adjusted and should be balanced as a compromise between efficiency and length of the overall pulse sequence. We show by numerical and experimental data that the presented compensation protocol significantly improves the efficiency of known dipolar recoupling solid-state NMR experiments.

  2. Spin-state-correlated optical properties of copper(ii)-nitroxide based molecular magnets.

    PubMed

    Barskaya, Irina Yu; Veber, Sergey L; Suturina, Elizaveta A; Sherin, Peter S; Maryunina, Kseniya Yu; Artiukhova, Natalia A; Tretyakov, Evgeny V; Sagdeev, Renad Z; Ovcharenko, Victor I; Gritsan, Nina P; Fedin, Matvey V

    2017-10-03

    Molecular magnets based on copper(ii) ions and stable nitroxide radicals exhibit promising switchable behavior triggered by a number of external stimuli; however, their spin-state-correlated optical properties vital for photoinduced switching have not been profoundly investigated to date. Herein, the electronic absorption spectra of single crystals of three representatives of this unique family are studied experimentally and theoretically in the visible and near-IR regions. We established that the color of the complexes is mainly determined by optical properties of the nitroxide radicals, whereas the Cu(hfac)2 fragment contributes to the near-IR range with the intensity smaller by an order of magnitude. The thermochromism of these complexes evident upon thermal spin state switching is mainly caused by a spectral shift of the absorption bands of the nitroxides. The vibrational progression observed in the visible range for single crystals as well as for solutions of pure nitroxides is well reproduced by DFT calculations, where the C-C stretching mode governs the observed progression. The analysis of the spectra of single crystals in the near-IR region reveals changes in the energy and in the intensity of the copper(ii) d-d transitions, which are well reproduced by SOC-NEVPT2 calculations and owe to the flip of the Jahn-Teller axis in the coordination environment of copper. Further strategies for designing bidirectional magnetic photoswitches using these appealing compounds are discussed.

  3. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

    NASA Astrophysics Data System (ADS)

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity κxyκxy which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2ṡ2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that κxyκxy is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that κxyκxy is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force

  4. Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy.

    PubMed

    Wang, Y F; Singh, Shashi B; Limaye, Mukta V; Shao, Y C; Hsieh, S H; Chen, L Y; Hsueh, H C; Wang, H T; Chiou, J W; Yeh, Y C; Chen, C W; Chen, C H; Ray, Sekhar C; Wang, J; Pong, W F; Takagi, Y; Ohigashi, T; Yokoyama, T; Kosugi, N

    2015-10-20

    This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

  5. Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy

    PubMed Central

    Wang, Y. F.; Singh, Shashi B.; Limaye, Mukta V.; Shao, Y. C.; Hsieh, S. H.; Chen, L. Y.; Hsueh, H. C.; Wang, H. T.; Chiou, J. W.; Yeh, Y. C.; Chen, C. W.; Chen, C. H.; Ray, Sekhar C.; Wang, J.; Pong, W. F.; Takagi, Y.; Ohigashi, T.; Yokoyama, T.; Kosugi, N.

    2015-01-01

    This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets. PMID:26481557

  6. A Charged Particle in a Magnetic Field: A Review of Two Formalisms of Coherent States and the Husimi Function

    ERIC Educational Resources Information Center

    Herrera, D.; Valencia, A. M.; Pennini, F.; Curilef, S.

    2008-01-01

    In this work, we review two formalisms of coherent states for the case of a particle in a magnetic field. We focus our revision on both pioneering (Feldman and Kahn 1970 "Phys. Rev." B 1 4584) and recent (Kowalski and Rembielinski 2005 "J. Phys. A: Math. Gen." 38 8247) formulations of coherent states for this problem. We introduce a general…

  7. A Charged Particle in a Magnetic Field: A Review of Two Formalisms of Coherent States and the Husimi Function

    ERIC Educational Resources Information Center

    Herrera, D.; Valencia, A. M.; Pennini, F.; Curilef, S.

    2008-01-01

    In this work, we review two formalisms of coherent states for the case of a particle in a magnetic field. We focus our revision on both pioneering (Feldman and Kahn 1970 "Phys. Rev." B 1 4584) and recent (Kowalski and Rembielinski 2005 "J. Phys. A: Math. Gen." 38 8247) formulations of coherent states for this problem. We introduce a general…

  8. Determination of the magnetic coupling in the Co/Cu/Co(100) system with momentum-resolved quantum well states

    SciTech Connect

    Kawakami, R.K.; Rotenberg, E.; Escorcia-Aparicio, E.J.; Choi, Hyuk J.; Wolfe, J.H.; Smith, N.V.; Qiu, Z.Q.

    1999-05-17

    The relation between the quantum well (QW) states and the oscillatory magnetic coupling in Co/Cu/Co grown on Cu(100) was investigated by angle-resolved photoemission spectroscopy, magnetic x-ray linear dichroism, and the surface magneto-optic Kerr effect. The QW states were explained quantitatively using the phase accumulation model, and the derived QW phases at the Cu/Co interface were used to calculate the interlayer coupling. The agreement between this calculation and the experimental result reveals that the phase relation between the long- and short-period couplings is determined by the phase relation of the QW states in k-space.

  9. The Operating Principle of a Fully Solid State Active Magnetic Regenerator

    SciTech Connect

    Abdelaziz, Omar

    2016-01-01

    As an alternative refrigeration technology, magnetocaloric refrigeration has the potential to be safer, quieter, more efficient, and more environmentally friendly than the conventional vapor compression refrigeration technology. Most of the reported active magnetic regenerator (AMR) systems that operate based on the magnetocaloric effect use heat transfer fluid to exchange heat, which results in complicated mechanical subsystems and components such as rotating valves and hydraulic pumps. This paper presents an operating principle of a fully solid state AMR, in which an alternative mechanism for heat transfer between the AMR and the heat source/sink is proposed. The operating principle of the fully solid state AMR is based on moving rods/sheets (e.g. copper, brass, iron or aluminum), which are employed to replace the heat transfer fluid. Such fully solid state AMR would provide a significantly higher heat transfer rate than a conventional AMR because the conductivity of moving solid rods/plates is high and it enables the increase in the machine operating frequency hence the cooling capacity. The details of operating principle are presented and discussed here. One of the key enabling features for this technology is the contact between the moving rods/sheets and magnetocaloric material, and heat exchange mechanism at the heat source/sink. This paper provides an overview of the design for a fully solid state magnetocaloric refrigeration system along with guidelines for their optimal design.

  10. Hubbard U calculations for gap states in dilute magnetic semiconductors.

    PubMed

    Fukushima, T; Katayama-Yoshida, H; Sato, K; Bihlmayer, G; Mavropoulos, P; Bauer, D S G; Zeller, R; Dederichs, P H

    2014-07-09

    On the basis of constrained density functional theory, we present ab initio calculations for the Hubbard U parameter of transition metal impurities in dilute magnetic semiconductors, choosing Mn in GaN as an example. The calculations are performed by two methods: (i) the Korringa-Kohn-Rostoker (KKR) Green function method for a single Mn impurity in GaN and (ii) the full-potential linearized augmented plane-wave (FLAPW) method for a large supercell of GaN with a single Mn impurity in each cell. By changing the occupancy of the majority t2 gap state of Mn, we determine the U parameter either from the total energy differences E(N + 1) and E(N - 1) of the (N ± 1)-electron excited states with respect to the ground state energy E(N), or by using the single-particle energies for n(0) ± 1/2 occupancies around the charge-neutral occupancy n0 (Janak's transition state model). The two methods give nearly identical results. Moreover the values calculated by the supercell method agree quite well with the Green function values. We point out an important difference between the 'global' U parameter calculated using Janak's theorem and the 'local' U of the Hubbard model.

  11. Magnetic ground state of an individual Fe2+ ion in strained semiconductor nanostructure

    NASA Astrophysics Data System (ADS)

    Smoleński, T.; Kazimierczuk, T.; Kobak, J.; Goryca, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

    2016-01-01

    Single impurities with nonzero spin and multiple ground states offer a degree of freedom that can be utilized to store the quantum information. However, Fe2+ dopant is known for having a single nondegenerate ground state in the bulk host semiconductors and thus is of little use for spintronic applications. Here we show that the well-established picture of Fe2+ spin configuration can be modified by subjecting the Fe2+ ion to high strain, for example, produced by lattice mismatched epitaxial nanostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in nearly doubly degenerate ground state with spin projection Sz=+/-2. We provide an experimental proof of this concept using a new system: a strained epitaxial quantum dot containing individual Fe2+ ion. Magnetic character of the Fe2+ ground state in a CdSe/ZnSe dot is revealed in photoluminescence experiments by exploiting a coupling between a confined exciton and the single-iron impurity. We also demonstrate that the Fe2+ spin can be oriented by spin-polarized excitons, which opens a possibility of using it as an optically controllable two-level system free of nuclear spin fluctuations.

  12. Magnetic ground state of an individual Fe2+ ion in strained semiconductor nanostructure

    PubMed Central

    Smoleński, T.; Kazimierczuk, T.; Kobak, J.; Goryca, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

    2016-01-01

    Single impurities with nonzero spin and multiple ground states offer a degree of freedom that can be utilized to store the quantum information. However, Fe2+ dopant is known for having a single nondegenerate ground state in the bulk host semiconductors and thus is of little use for spintronic applications. Here we show that the well-established picture of Fe2+ spin configuration can be modified by subjecting the Fe2+ ion to high strain, for example, produced by lattice mismatched epitaxial nanostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in nearly doubly degenerate ground state with spin projection Sz=±2. We provide an experimental proof of this concept using a new system: a strained epitaxial quantum dot containing individual Fe2+ ion. Magnetic character of the Fe2+ ground state in a CdSe/ZnSe dot is revealed in photoluminescence experiments by exploiting a coupling between a confined exciton and the single-iron impurity. We also demonstrate that the Fe2+ spin can be oriented by spin-polarized excitons, which opens a possibility of using it as an optically controllable two-level system free of nuclear spin fluctuations. PMID:26818580

  13. Computation of magnetic circular dichroism by sum-over-states summations.

    PubMed

    Štěpánek, Petr; Bouř, Petr

    2013-07-05

    Magnetic circular dichroism (MCD) spectroscopy has been established as a convenient method to study electronic structure, in particular for small symmetric organic molecules. Newer applications on more complex systems are additionally stimulated by the latest availability of precise quantum-chemical techniques for the spectral simulations. In this work, a sum over states (SOS) summation is reexamined as an alternative to the derivative techniques for the MCD modeling. Unlike in previous works, the excited electronic states are calculated by the time-dependent density functional theory (TDDFT). A gradient formulation of the MCD intensities is also proposed, less dependent on the origin choice than the standard expressions. The dependencies of the results on the basis set, number of electronic states, and coordinate origin are tested on model examples, including large symmetric molecules with degenerate electronic states. The results suggest that the SOS/TDDFT approach is a viable and accurate technique for spectral simulation. It may even considerably reduce the computational time, if compared with the traditional MCD computational procedures based on the response theory.

  14. MAGNETS

    DOEpatents

    Hofacker, H.B.

    1958-09-23

    This patent relates to nmgnets used in a calutron and more particularly to means fur clamping an assembly of magnet coils and coil spacers into tightly assembled relation in a fluid-tight vessel. The magnet comprises windings made up of an assembly of alternate pan-cake type coils and spacers disposed in a fluid-tight vessel. At one end of the tank a plurality of clamping strips are held firmly against the assembly by adjustable bolts extending through the adjacent wall. The foregoing arrangement permits taking up any looseness which may develop in the assembly of coils and spacers.

  15. Structural and magnetic properties of La–Co substituted Sr–Ca hexaferrites synthesized by the solid state reaction method

    SciTech Connect

    Yang, Yujie; Liu, Xiansong Jin, Dali; Ma, Yuqi

    2014-11-15

    Graphical abstract: The change of the remanence (B{sub r}) and intrinsic coercivity (H{sub cj}) with La content (x) and Co content (y) of hexagonal ferrite Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} magnets. - Highlights: • Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} hexaferrites were synthesized by the solid state reaction method. • B{sub r} continuously increases with increasing dopant contents. • H{sub cb}, H{sub cj} and (BH){sub max} for the magnets first increases and then decreases with an increase in the La–Co contents. - Abstract: Hexagonal ferrite Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} (x = 0.05–0.50; y = 0.04–0.40) magnetic powders and magnets were synthesized by the solid state reaction method. X-ray diffraction was employed to determine the phase compositions of the magnetic powders. There is a single magnetoplumbite phase in the magnetic powders with the substitution of La (0.05 ≤ x ≤ 0.15) and Co (0.04 ≤ y ≤ 0.12) contents. For the magnetic powders containing La (x ≥ 0.20) and Co (y ≥ 0.16), magnetic impurities begin to appear in the structure. A field emission scanning electron microscope was used to characterize the micrographs of the magnets. The magnets have formed hexagonal structures. Magnetic properties of the magnets were measured by a magnetic properties test instrument. The remanence continuously increases with increasing dopant contents. Whereas, the magnetic induction coercivity, intrinsic coercivity and maximum energy product for the magnets first increases and then decreases with an increase in the La–Co contents.

  16. Equation of state for the magnetic-color-flavor-locked phase and its implications for compact star models

    NASA Astrophysics Data System (ADS)

    Paulucci, L.; Ferrer, Efrain J.; de La Incera, Vivian; Horvath, J. E.

    2011-02-01

    Using the solutions of the gap equations of the magnetic-color-flavor-locked (MCFL) phase of paired quark matter in a magnetic field, and taking into consideration the separation between the longitudinal and transverse pressures due to the field-induced breaking of the spatial rotational symmetry, the equation of state of the MCFL phase is self-consistently determined. This result is then used to investigate the possibility of absolute stability, which turns out to require a field-dependent “bag constant” to hold. That is, only if the bag constant varies with the magnetic field, there exists a window in the magnetic field vs bag constant plane for absolute stability of strange matter. Implications for stellar models of magnetized (self-bound) strange stars and hybrid (MCFL core) stars are calculated and discussed.

  17. Network asymmetry of motor areas revealed by resting-state functional magnetic resonance imaging.

    PubMed

    Yan, Li-Rong; Wu, Yi-Bo; Hu, De-Wen; Qin, Shang-Zhen; Xu, Guo-Zheng; Zeng, Xiao-Hua; Song, Hua

    2012-02-01

    There are ample functional magnetic resonance imaging (fMRI) studies on functional brain asymmetries, and the asymmetry of cerebral network in the resting state may be crucial to brain function organization. In this paper, a unified schema of voxel-wise functional connectivity and asymmetry analysis was presented and the network asymmetry of motor areas was studied. Twelve healthy male subjects with mean age 29.8 ± 6.4 were studied. Functional network in the resting state was described by using functional connectivity magnetic resonance imaging (fcMRI) analysis. Motor areas were selected as regions of interest (ROIs). Network asymmetry, including intra- and inter-network asymmetries, was formulated and analyzed. The intra-network asymmetry was defined as the difference between the left and right part of a particular functional network. The inter-network asymmetry was defined as the difference between the networks for a specific ROI in the left hemisphere and its homotopic ROI in the right hemisphere. Primary motor area (M1), primary sensory area (S1) and premotor area (PMA) exhibited higher functional correlation with the right parietal-temporal-occipital circuit and the middle frontal gyrus than they did with the left hemisphere. Right S1 and right PMA exhibited higher functional correlation with the ipsilateral precentral and supramarginal areas. There exist the large-scale hierarchical network asymmetries of the motor areas in the resting state. These asymmetries imply the right hemisphere dominance for predictive motor coding based on spatial attention and higher sensory processing load for the motor performance of non-dominant hemisphere.

  18. Strong spin-orbit splitting and magnetism of point defect states in monolayer WS2

    NASA Astrophysics Data System (ADS)

    Li, Wun-Fan; Fang, Changming; van Huis, Marijn A.

    2016-11-01

    The spin-orbit coupling (SOC) effect has been known to be profound in monolayer pristine transition metal dichalcogenides (TMDs). Here we show that point defects, which are omnipresent in the TMD membranes, exhibit even stronger SOC effects and change the physics of the host materials drastically. In this article we chose the representative monolayer WS2 slabs from the TMD family together with seven typical types of point defects including monovacancies, interstitials, and antisites. We calculated the formation energies of these defects, and studied the effect of spin-orbit coupling (SOC) on the corresponding defect states. We found that the S monovacancy (VS) and S interstitial (adatom) have the lowest formation energies. In the case of VS and both of the WS and WS 2 antisites, the defect states exhibit strong splitting up to 296 meV when SOC is considered. Depending on the relative position of the defect state with respect to the conduction band minimum (CBM), the hybrid functional HSE will either increase the splitting by up to 60 meV (far from CBM), or decrease the splitting by up to 57 meV (close to CBM). Furthermore, we found that both the WS and WS 2 antisites possess a magnetic moment of 2 μB localized at the antisite W atom and the neighboring W atoms. The dependence of SOC on the orientation of the magnetic moment for the WS and WS 2 antisites is discussed. All these findings provide insights in the defect behavior under SOC and point to possibilities for spintronics applications for TMDs.

  19. Experimental implementation of heat-bath algorithmic cooling using solid-state nuclear magnetic resonance.

    PubMed

    Baugh, J; Moussa, O; Ryan, C A; Nayak, A; Laflamme, R

    2005-11-24

    The counter-intuitive properties of quantum mechanics have the potential to revolutionize information processing by enabling the development of efficient algorithms with no known classical counterparts. Harnessing this power requires the development of a set of building blocks, one of which is a method to initialize the set of quantum bits (qubits) to a known state. Additionally, fresh ancillary qubits must be available during the course of computation to achieve fault tolerance. In any physical system used to implement quantum computation, one must therefore be able to selectively and dynamically remove entropy from the part of the system that is to be mapped to qubits. One such method is an 'open-system' cooling protocol in which a subset of qubits can be brought into contact with an external system of large heat capacity. Theoretical efforts have led to an implementation-independent cooling procedure, namely heat-bath algorithmic cooling. These efforts have culminated with the proposal of an optimal algorithm, the partner-pairing algorithm, which was used to compute the physical limits of heat-bath algorithmic cooling. Here we report the experimental realization of multi-step cooling of a quantum system via heat-bath algorithmic cooling. The experiment was carried out using nuclear magnetic resonance of a solid-state ensemble three-qubit system. We demonstrate the repeated repolarization of a particular qubit to an effective spin-bath temperature, and alternating logical operations within the three-qubit subspace to ultimately cool a second qubit below this temperature. Demonstration of the control necessary for these operations represents an important step forward in the manipulation of solid-state nuclear magnetic resonance qubits.

  20. Magnetic field processed solid-state dye-sensitized solar cells with nickel oxide modified agarose electrolyte

    NASA Astrophysics Data System (ADS)

    Yang, Ying; Yi, Pengfei; Zhou, Conghua; Cui, Jiarui; Zheng, Xiaolu; Xiao, Si; Guo, Xueyi; Wang, Wenyong

    2013-12-01

    In this work we investigate novel, agarose-based polymer electrolyte that is modified by magnetic NiO nanoparticles for solid-state dye-sensitized solar cells (DSSCs) applications. After proper treatment under an external magnetic field, the agarose electrolyte exhibits increased ionic conductivity and better penetration into the mesoporous TiO2 photoanode film, which improves the power conversion efficiency of the DSSCs. Electrochemical impedance spectroscopy measurement is also performed to analyze the magnetic field effect on cell performance. After applying proper magnetic filed intensity, the recombination resistance and redox transport resistance in the devices are improved. This method can be possibly applied to other solid-state electrolyte materials to improve their performance and can lead to more efficient DSSCs.