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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. Superconductivity in magnetic multipole states

    NASA Astrophysics Data System (ADS)

    Sumita, Shuntaro; Yanase, Youichi

    2016-06-01

    Stimulated by recent studies of superconductivity and magnetism with local and global broken inversion symmetry, we investigate the superconductivity in magnetic multipole states in locally noncentrosymmetric metals. We consider a one-dimensional zigzag chain with sublattice-dependent antisymmetric spin-orbit coupling and suppose three magnetic multipole orders: monopole order, dipole order, and quadrupole order. It is demonstrated that the Bardeen-Cooper-Schrieffer state, the pair-density wave (PDW) state, and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state are stabilized by these multipole orders, respectively. We show that the PDW state is a topological superconducting state specified by the nontrivial Z2 number and winding number. The origin of the FFLO state without macroscopic magnetic moment is attributed to the asymmetric band structure induced by the magnetic quadrupole order and spin-orbit coupling.

  3. 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.

  4. 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.

  5. 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.

  6. Magnetization ground state and reversal modes of magnetic nanotori

    NASA Astrophysics Data System (ADS)

    Vojkovic, Smiljan; Nunez, Alvaro S.; Altbir, Dora; Carvalho-Santos, Vagson L.

    2016-07-01

    In this work, and by means of micromagnetic simulations, we study the magnetic properties of toroidal nanomagnets. The magnetization ground state for different values of the aspect ratio between the toroidal and polar radii of the nanotorus has been obtained. Besides, we have shown that the vortex and the in-plane single domain states can appear as ground states for different ranges of the aspect ratio, while a single domain state with an out-of-plane magnetization is not observed. The hysteresis curves are also obtained, evidencing the existence of two reversal modes depending on the geometry: a vortex mode and a coherent rotation. A comparison between toroidal and cylindrical nanoparticles has been performed evidencing that nanotori can accommodate a vortex as the ground state for smaller volume than cylindrical nanorings.

  7. Magnetic properties of ground-state mesons

    NASA Astrophysics Data System (ADS)

    Šimonis, V.

    2016-04-01

    Starting with the bag model a method for the study of the magnetic properties (magnetic moments, magnetic dipole transition widths) of ground-state mesons is developed. We calculate the M1 transition moments and use them subsequently to estimate the corresponding decay widths. These are compared with experimental data, where available, and with the results obtained in other approaches. Finally, we give the predictions for the static magnetic moments of all ground-state vector mesons including those containing heavy quarks. We have a good agreement with experimental data for the M1 decay rates of light as well as heavy mesons. Therefore, we expect our predictions for the static magnetic properties ( i.e., usual magnetic moments) to be of sufficiently high quality, too.

  8. Relaxed States in Magnetized Pair Plasmas

    NASA Astrophysics Data System (ADS)

    Shukla, P. K.; Mahajan, S. M.

    2004-01-01

    We discuss possibility of possible relaxed states in magnetized pair plasmas. It is shown that stationary relaxed states are described by the double curl Beltrami/Mahajan-Yoshida equation. We can thus have steady state tructures on the scale sizes of the order of the electron (ion) skin depth in an electron-positron (electron-positron-ion) plasma.

  9. Multi-vortex states in magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Gan, W. L.; Chandra Sekhar, M.; Wong, D. W.; Purnama, I.; Chiam, S. Y.; Wong, L. M.; Lew, W. S.

    2014-10-01

    We demonstrate a fabrication technique to create cylindrical NiFe magnetic nanoparticles (MNPs) with controlled dimensions and composition. MNPs thicker than 200 nm can form a double vortex configuration, which consists of a pair of vortices with opposite chirality. When MNPs thicker than 300 nm are relaxed after saturation, it forms a frustrated triple vortex state which produces a higher net magnetization as verified by light transmissivity measurements. Therefore, a greater magnetic torque can be actuated on a MNP in the triple vortex state.

  10. Study of dysprosium in different magnetic states

    NASA Astrophysics Data System (ADS)

    Lakhani, Archana; Baidya, Arunmay; Jena, Rudra Parasad

    2016-05-01

    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 (TN ~ 180K) via second order phase transition and another at Curie temperature (TC ~ 90K) via first order magnetic phase transition (FOMT). These two transitions merge at the magnetic field above 1.5T. 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 8T reveals distinct features in the para, antiferromagnetic spiral and ferromagnetic regions.

  11. Majorana bound states in magnetic skyrmions

    NASA Astrophysics Data System (ADS)

    Yang, Guang; Stano, Peter; Klinovaja, Jelena; Loss, Daniel

    2016-06-01

    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 trijunction to realize non-Abelian statistics of such Majorana bound states.

  12. Magnetic surface states in high polarization materials

    NASA Astrophysics Data System (ADS)

    Wu, Ning; Dowben, Peter A.

    2011-10-01

    Surfaces are often different materials, and typically have a different electronic structure from the bulk and since the dawn of surface science, surface-localized electronic states, surface states, have been extensively studied and investigated with growing accuracy. Of particular importance to spintronics are magnetic surface states. Interfaces will play a very important role in many spintronics devices, yet the interface properties are often ignored, poorly understood or badly characterized. For many nominally half metal materials, materials that in some ground state calculations exhibit 100% spin polarization, the magnetic surface states may significantly reduce the effective spin polarization. We review the magnetic surface states of several well known and often highly touted high spin polarized materials such as NiMnSb, Fe3O4, CoS2 and CrO2. Finally, we summarize surface state measurements of magnetoelectric antiferromagnets Cr2O3, which has electrically controllable net surface spins, a major complication to the study of CrO2 by photoemission.

  13. 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

  14. 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

    2016-01-01

    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

  15. Magnetic ground state of FeSe

    NASA Astrophysics Data System (ADS)

    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

    2016-07-01

    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.

  16. 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.

  17. 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.

  18. Equation of state for magnetized Coulomb plasmas

    NASA Astrophysics Data System (ADS)

    Potekhin, A. Y.; Chabrier, G.

    2013-02-01

    We have developed an analytical equation of state (EOS) for magnetized fully-ionized plasmas that cover a wide range of temperatures and densities, from low-density classical plasmas to relativistic, quantum plasma conditions. This EOS directly applies to calculations of structure and evolution of strongly magnetized white dwarfs and neutron stars. We review available analytical and numerical results for thermodynamic functions of the nonmagnetized and magnetized Coulomb gases, liquids, and solids. We propose a new analytical expression for the free energy of solid Coulomb mixtures. Based on recent numerical results, we have constructed analytical approximations for the thermodynamic functions of harmonic Coulomb crystals in quantizing magnetic fields. The analytical description ensures a consistent evaluation of all astrophysically important thermodynamic functions based on the first, second, and mixed derivatives of the free energy. Our numerical code for calculation of thermodynamic functions based on these approximations has been made publicly available. Using this code, we calculate and discuss the effects of electron screening and magnetic quantization on the position of the melting point in a range of densities and magnetic fields relevant to white dwarfs and outer envelopes of neutron stars. We consider also the thermal and mechanical structure of a magnetar envelope and argue that it can have a frozen surface which covers the liquid ocean above the solid crust. The Fortran code that realizes the analytical approximations described in this paper is available at http://www.ioffe.ru/astro/EIP/ and at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/550/A43

  19. 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.

  20. 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.

  1. Evolutions of nonsteady state magnetic reconnection

    SciTech Connect

    Wan, Weigang; Lapenta, Giovanni

    2008-01-01

    The full evolutions of collisionless non-steady-state magnetic reconnection are studied with full kinetic particle-in-cell simulations. There are different stages of reconnection: the onset or early growing stage when the out-of-plane electric field (Ey) structure is a monopole at the X-point, the bipolar stage when the Ey structure is bipolar and the outer electron diffusion region (EDR) is being elongated over time, and the possible final steady-state stage when E{sub y} is uniform in the reconnection plane. We find the change of reconnection rate is not empowered or dependent on the length of the EDR. During the early growing stage, the EDR is elongated while the reconnection rate is growing. During the later stage, the reconnection rate may significantly decrease but the length of the inner EDR is largely stable. The results indicate that reconnection is not controlled by the downstream physics, but rather by the availability of plasma inflows from upstream. The physical mechanism of the EDR elongation is studied. The Hall current induced by the quadrupole magnetic field (B{sub y}) is discovered to play an important role in this process. The condition of forming an extended electron super-Alfvenic outflow jet structure in nature is discussed. The jet structure could be elongated during the bipolar stage, and remains stable during steady state. The sufficiency of the electron inflow is crucial for the elongation. Open boundary conditions are applied in the outflow direction.

  2. 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.

  3. Quantum critical state in a magnetic quasicrystal.

    PubMed

    Deguchi, Kazuhiko; Matsukawa, Shuya; Sato, Noriaki K; Hattori, Taisuke; Ishida, Kenji; Takakura, Hiroyuki; Ishimasa, Tsutomu

    2012-12-01

    Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984, there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states--whether they are extended as in periodic crystals or localized as in amorphous materials--are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal--the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T→0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals. PMID:23042414

  4. 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.

  5. Magnetic vortex state stability, reversal and dynamics in restricted geometries.

    PubMed

    Guslienko, K Yu

    2008-06-01

    Magnetic vortices are typically the ground states in geometrically confined ferromagnets with small magnetocrystalline anisotropy. In this article I review static and dynamic properties of the magnetic vortex state in small particles with nanoscale thickness and sub-micron and micron lateral sizes (magnetic dots). Magnetic dots made of soft magnetic material shaped as flat circular and elliptic cylinders are considered. Such mesoscopic dots undergo magnetization reversal through successive nucleation, displacement and annihilation of magnetic vortices. The reversal process depends on the stability of different possible zero-field magnetization configurations with respect to the dot geometrical parameters and application of an external magnetic field. The interdot magnetostatic interaction plays an important role in magnetization reversal for dot arrays with a small dot-to-dot distance, leading to decreases in the vortex nucleation and annihilation fields. Magnetic vortices reveal rich, non-trivial dynamical properties due to existance of the vortex core bearing topological charges. The vortex ground state magnetization distribution leads to a considerable modification of the nature of spin excitations in comparison to those in the uniformly magnetized state. A magnetic vortex confined in a magnetically soft ferromagnet with micron-sized lateral dimensions possesses a characteristic dynamic excitation known as a translational mode that corresponds to spiral-like precession of the vortex core around its equilibrium position. The translation motions of coupled vortices are considered. There are, above the vortex translation mode eigenfrequencies, several dynamic magnetization eigenmodes localized outside the vortex core whose frequencies are determined principally by dynamic demagnetizing fields appearing due to restricted dot geometry. The vortex excitation modes are classified as translation modes and radially or azimuthally symmetric spin waves over the vortex

  6. 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.

  7. Manipulation of magnetic state in nanostructures by perpendicular anisotropy and magnetic field

    SciTech Connect

    Chen, J. P.; Xie, Y. L.; Chu, P.; Wang, Y. L.; Wang, Z. Q.; Gao, X. S.; Liu, J.-M.

    2014-06-28

    We investigate the transitions of spin configurations in ultrathin nanostructures by tuning the perpendicular anisotropy (K{sub z}) and out-of-plane magnetic field (H), using the Monte Carlo simulation. It is revealed that enhancing the anisotropy K{sub z} can drive the evolution of in-plane vortex state into intriguing saturated magnetization states under various H, such as the bubble domain state and quadruple-block-domain state etc. The spin configurations of these states exhibit remarkable H-dependence. In addition, the strong effects of geometry and size on the spin configurations of nanostructures are observed. In particular, a series of edged states occur in the circular disk-shaped lattices, and rich intricate saturated magnetization patterns appear in big lattices. It is suggested that the magnetic states can be manipulated by varying the perpendicular anisotropy, magnetic field, and geometry/size of the nanostructures. Furthermore, the stability (retention capacity) of the saturated magnetization states upon varying magnetic field is predicted, suggesting the potential applications of these saturated magnetization states in magnetic field-controlled data storages.

  8. 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.

  9. Vortex states and magnetization curve of square mesoscopic superconductors.

    SciTech Connect

    Melnikov, A. S.; Nefedov, I. M.; Ryzhov, D. A.; Shereshevskii, I. A.; Vinokur, V. M.; Vysheslavtsev, P. P.; Materials Science Division; Russian Academy of Sciences

    2002-03-22

    The structure of the vortex states in a square mesoscopic superconductor is analyzed in detail using the numerical simulation within the time-dependent Ginzburg-Landau (TDGL) theory. Various vortex states (vortices, vortex molecules, multiquanta vortices) are observed and the magnetization curve is obtained. Different changes in vortex structures are identified with the peculiarities on the magnetization curve. Stability of a state consisting of vortices and antivortices is discussed.

  10. Magnetic edge states and magnetotransport in graphene antidot barriers

    NASA Astrophysics Data System (ADS)

    Thomsen, M. R.; Power, S. R.; Jauho, A.-P.; Pedersen, T. G.

    2016-07-01

    Magnetic fields are often used for characterizing transport in nanoscale materials. Recent magnetotransport experiments have demonstrated that ballistic transport is possible in graphene antidot lattices (GALs). These experiments have inspired the present theoretical study of GALs in a perpendicular magnetic field. We calculate magnetotransport through graphene antidot barriers (GABs), which are finite rows of antidots arranged periodically in a pristine graphene sheet, using a tight-binding model and the Landauer-Büttiker formula. We show that GABs behave as ideal Dirac mass barriers for antidots smaller than the magnetic length and demonstrate the presence of magnetic edge states, which are localized states on the periphery of the antidots due to successive reflections on the antidot edge in the presence of a magnetic field. We show that these states are robust against variations in lattice configuration and antidot edge chirality. Moreover, we calculate the transmittance of disordered GABs and find that magnetic edge states survive a moderate degree of disorder. Due to the long phase-coherence length in graphene and the robustness of these states, we expect magnetic edge states to be observable in experiments as well.

  11. Heterogeneous magnetic state in nanocrystalline cupric oxide CuO

    NASA Astrophysics Data System (ADS)

    Yermakov, A. Ye.; Uimin, M. A.; Korolyov, A. V.; Mikhalev, K. N.; Pirogov, A. N.; Teplykh, A. E.; Shchegoleva, N. N.; Gaviko, V. S.; Byzov, I. V.; Maikov, V. V.

    2015-02-01

    This paper presents the results of investigations of the structural state and magnetic properties of nanocrystalline cupric oxide samples with average particle sizes of approximately 40 and 13 nm, which were synthesized by the electric explosion and gas phase methods, respectively. The samples have been studied using X-ray diffraction, neutron diffraction, magnetic measurements, high-resolution transmission electron microscopy, and copper nuclear magnetic resonance. It has been shown that, in the initial state, regardless of the synthesis method, CuO nanoparticles are characterized by a heterogeneous magnetic state, i.e., by the existence of long-range antiferromagnetic order, spontaneous magnetization, especially at low temperatures, and paramagnetic centers in the material. The ferromagnetic contribution is probably caused by the formation of magnetic polaron states due to the phase separation induced in the system by excess charge carriers as a result of the existence of point defects (vacancies in the anion sublattice) in the nanocrystalline state. In this state, there is an inhomogeneously broadened nuclear magnetic resonance spectrum, which is a superposition of the spectrum of the initial antiferromagnetic matrix and the spectrum of ferromagnetically ordered regions. At high concentrations of ferromagnetically ordered regions, the antiferromagnetic matrix exhibits a nuclear magnetic resonance spectrum of CuO nanoparticles, predominantly from regions with the ferromagnetic phase. The appearance of magnetization can also be partly due to the frustration of spins in CuO, and this state is presumably localized near the most imperfect surface of the nanoparticles. The magnetic susceptibility of nanoparticles in the initial state in strong magnetic fields is significantly higher than that for the annealed samples, which, most likely, is associated with the influence of the high concentration of magnetic polarons. No correlation between the ferromagnetic

  12. 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.

  13. Ground state alignment as a tracer of interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Yan, H.

    2012-12-01

    We demonstrate a new way of studying interplanetary magnetic field -- spectropolarimetry based on ground state alignment. Ground state alignment is a new promising way of sub-gausian magnetic fields in radiation-dominated environment. The polarization of spectral lines that are pumped by the anisotropic radiation from the sun is influenced by the magnetic alignment, which happens for sub-gausian magnetic field. As a result, the linear polarization becomes an excellent tracer of the embedded magnetic field. The method is illustrated by our synthetic obser- vation of the Jupiter's Io and comet Halley. A uniform density distribution of Na was considered and polar- ization at each point was then constructed. Both spa- tial and temporal variations of turbulent magnetic field can be traced with this technique as well. Instead of sending thousands of space probes, ground state alignment allows magnetic mapping with any ground telescope facilities equipped with spectrometer and polarimeter. For remote regions like the the boundary of interstellar medium, ground state alignment provides a unique diagnostics of magnetic field, which is crucial for understanding the physical processes such as the IBEX ribbons.

  14. Effect of strain-polarization fields on optical transitions in AlGaN/GaN multi-quantum well structures

    NASA Astrophysics Data System (ADS)

    Kladko, V.; Kuchuk, A.; Naumov, A.; Safriuk, N.; Kolomys, O.; Kryvyi, S.; Stanchu, H.; Belyaev, A.; Strelchuk, V.; Yavich, B.; Mazur, Yu. I.; Ware, M. E.; Salamo, G. J.

    2016-02-01

    The influence of strain and barrier/well thickness ratio on recombination processes in multi-quantum well (MQW) Al0.1Ga0.9N/GaN structures was investigated using X-ray diffraction and Raman and photoluminescence spectroscopies. The deformation state of the wells and barriers was determined. In addition, the value of the polarization fields, the density of polarization charges, and the positions of energy levels for optical transitions within the quantum wells were calculated. It was established that compressive strain in the buffer layer as well as in the layers of the MQWs with respect to the buffer layer lead to the piezoelectric fields having equal sign in the well and the barrier. As a result, the recombination of donor-acceptor pairs dominates over transitions between electron and hole states in the quantum well.

  15. 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.

  16. 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.

  17. 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. PMID:26406851

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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 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).

  2. 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.

  3. 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).

  4. Electric-field manipulation of spin states in confined non-magnetic/magnetic heterostructures.

    PubMed

    Borza, S; Peeters, F M; Vasilopoulos, P; Papp, G

    2007-04-30

    The energy spectrum and states of an electron in a non-magnetic/magnetic heterostructure placed between two materials (e.g. oxides) acting as barriers is studied in the presence of a magnetic field perpendicular or parallel to the well. A potential step is formed at the interface between the non-magnetic and magnetic material in the presence of a magnetic field since spin-up electrons see a barrier whereas the spin-down ones see a well. A rich band structure is obtained which can be tuned by a perpendicular electric field. Numerical results are presented for a ZnSe/Zn(1-x)Mn(x)Se heterostructure and their pertinence to spin-polarized transport is pointed out. PMID:21690966

  5. 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.

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

    DOE PAGESBeta

    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 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

  7. Magnetization ground states and phase diagrams for a nanosized Co hollow sphere: An onion-type magnetization state

    NASA Astrophysics Data System (ADS)

    Kong, Desheng; Wang, Siming; Chen, Chinping

    2008-07-01

    The magnetization ground states (MGSs) for a nanosized Co hollow sphere, with the outer radius, R <50 nm, have been studied numerically by micromagnetic simulation using object oriented micromagnetic framework (OOMMF). In addition to the originally known single domain and vortex-curling states, a three dimensional "onion" state with a corresponding analytical expression is proposed and confirmed as one of the ground states. Two phase diagrams, one for a single crystalline and the other for a polycrystalline nanosphere, are obtained for the three MGSs. The result reveals that the magnetic anisotropy has a significant effect on the phase line in the diagrams. The finite temperature effect and the blocking properties of the nanosphere for the magnetization reversal are discussed.

  8. Long-lived states to sustain hyperpolarized magnetization

    PubMed Central

    Vasos, P. R.; Comment, A.; Sarkar, R.; Ahuja, P.; Jannin, S.; Ansermet, J.-P.; Konter, J. A.; Hautle, P.; van den Brandt, B.; Bodenhausen, G.

    2009-01-01

    Major breakthroughs have recently been reported that can help overcome two inherent drawbacks of NMR: the lack of sensitivity and the limited memory of longitudinal magnetization. Dynamic nuclear polarization (DNP) couples nuclear spins to the large reservoir of electrons, thus making it possible to detect dilute endogenous substances in magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). We have designed a method to preserve enhanced (“hyperpolarized”) magnetization by conversion into long-lived states (LLS). It is shown that these enhanced long-lived states can be generated for proton spins, which afford sensitive detection. Even in complex molecules such as peptides, long-lived proton states can be sustained effectively over time intervals on the order of tens of seconds, thus allowing hyperpolarized substrates to reach target areas and affording access to slow metabolic pathways. The natural abundance carbon-13 polarization has been enhanced ex situ by almost four orders of magnitude in the dipeptide Ala-Gly. The sample was transferred by the dissolution process to a high-resolution magnet where the carbon-13 polarization was converted into a long-lived state associated with a pair of protons. In Ala-Gly, the lifetime TLLS associated with the two nonequivalent Hα glycine protons, sustained by suitable radio-frequency irradiation, was found to be seven times longer than their spin-lattice relaxation time constant (TLLS/T1 = 7). At desired intervals, small fractions of the populations of long-lived states were converted into observable magnetization. This opens the way to observing slow chemical reactions and slow transport phenomena such as diffusion by enhanced magnetic resonance. PMID:19841270

  9. Competing magnetic states, disorder, and the magnetic character of Fe3Ga4

    NASA Astrophysics Data System (ADS)

    Mendez, J. H.; Ekuma, C. E.; Wu, Y.; Fulfer, B. W.; Prestigiacomo, J. C.; Shelton, W. A.; Jarrell, M.; Moreno, J.; Young, D. P.; Adams, P. W.; Karki, A.; Jin, R.; Chan, Julia Y.; DiTusa, J. F.

    2015-04-01

    The physical properties of metamagnetic Fe3Ga4 single crystals are investigated to explore the sensitivity of the magnetic states to temperature, magnetic field, and sample history. The data reveal a moderate anisotropy in the magnetization and the metamagnetic critical field along with features in the specific heat at the magnetic transitions T1=68 K and T2=360 K. Both T1 and T2 are found to be sensitive to the annealing conditions of the crystals suggesting that disorder affects the competition between the ferromagnetic (FM) and antiferromagnetic (AFM) states. Resistivity measurements reveal metallic transport with a sharp anomaly associated with the transition at T2. The Hall effect is dominated by the anomalous contribution, which rivals that of magnetic semiconductors in magnitude (-5 μ Ω cm at 2 T and 350 K) and undergoes a change of sign upon cooling into the low-temperature FM state. The temperature and field dependence of the Hall effect indicate that the magnetism is likely to be highly itinerant in character and that a significant change in the electronic structure accompanies the magnetic transitions. We observe a contribution from the topological Hall effect in the AFM phase suggesting a noncoplanar contribution to the magnetism. Electronic structure calculations predict an AFM ground state with a wave vector parallel to the crystallographic c -axis preferred over the experimentally measured FM state by ≈50 meV per unit cell. However, supercell calculations with a small density of Fe antisite defects introduced tend to stabilize the FM over the AFM state indicating that antisite defects may be the cause of the sensitivity to sample synthesis conditions.

  10. 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.

  11. 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.

  12. 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.

  13. Long-lived nuclear spin states far from magnetic equivalence.

    PubMed

    Stevanato, Gabriele; Roy, Soumya Singha; Hill-Cousins, Joe; Kuprov, Ilya; Brown, Lynda J; Brown, Richard C D; Pileio, Giuseppe; Levitt, Malcolm H

    2015-02-28

    Clusters of coupled nuclear spins may form long-lived nuclear spin states, which interact weakly with the environment, compared to ordinary nuclear magnetization. All experimental demonstrations of long-lived states have so far involved spin systems which are close to the condition of magnetic equivalence, in which the network of spin-spin couplings is conserved under all pair exchanges of symmetry-related nuclei. We show that the four-spin system of trans-[2,3-(13)C2]-but-2-enedioate exhibits a long-lived nuclear spin state, even though this spin system is very far from magnetic equivalence. The 4-spin long-lived state is accessed by slightly asymmetric chemical substitutions of the centrosymmetric molecular core. The long-lived state is a consequence of the locally centrosymmetric molecular geometry for the trans isomer, and is absent for the cis isomer. A general group theoretical description of long-lived states is presented. It is shown that the symmetries of coherent and incoherent interactions are both important for the existence of long-lived states. PMID:25633837

  14. 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.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  17. 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

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

    PubMed

    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

  19. 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)

  20. Equation of state of a dense and magnetized fermion system

    SciTech Connect

    Ferrer, Efrain J.; Incera, Vivian de la; Keith, Jason P.; Portillo, Israel; Springsteen, Paul L.

    2010-12-15

    The equation of state of a system of fermions in a uniform magnetic field is obtained in terms of the thermodynamic quantities of the theory by using functional methods. It is shown that the breaking of the O(3) rotational symmetry by the magnetic field results in a pressure anisotropy, which leads to the distinction between longitudinal- and transverse-to-the-field pressures. A criterion to find the threshold field at which the asymmetric regime becomes significant is discussed. This threshold magnetic field is shown to be the same as the one required for the pure field contribution to the energy and pressures to be of the same order as the matter contribution. A graphical representation of the field-dependent anisotropic equation of state of the fermion system is given. Estimates of the upper limit for the inner magnetic field in self-bound stars, as well as in gravitationally bound stars with inhomogeneous distributions of mass and magnetic fields, are also found.

  1. Cobaltites: Emergence of magnetism and metallicity from a non-magnetic, insulating state

    NASA Astrophysics Data System (ADS)

    Phelan, Daniel Patrick

    In cobalt oxides, the energy splitting between different spin-states of Co3+ ions can be quite small, which means that more than one spin-state can simultaneously co-exist in the same compound and that transitions between different spin-state can occur. This makes understanding the magnetic coupling between cobalt sites rather complex. Such is the case for pure and hole-doped LaCoO3. In its ground state, LaCoO3 is a non-magnetic insulator. The lack of a magnetic moment, is due to the fact that the ground spin-state of Co3+ ions is a low-spin, S=0, state. However, since a spin-state that has a net spin is on the order of 100 K higher in energy than the ground spin-state, a magnetic moment appears as the temperature is increased, and the system behaves as a paramagnet above 100 K. The higher-energy spin-state is either an intermediate-spin (S=1) state of a high-spin (S=2) state - an issue that has been debated for quite some time. When holes are chemically doped into the system, as in La1- xSrxCoO3 (LSCO), the non-magnetic, insulating ground state evolves into a ferromagnetic, metallic state. This evolution is complicated because it occurs due to the convoluted effects of Co4+ ions being doped into the system and the fact that the ground spin-state of Co3+ ions changes as a function of the hole concentration. In this dissertation, the magnetic transitions in pure and hole-doped LaCoO3 are investigated by neutron scattering techniques. In the pure compound, it is shown that thermally excited spins have both fluctuating ferromagnetic and antiferro-magnetic spin-correlations, which is suggested to result from a dynamic orbital ordering of the occupied e. g orbitals of the intermediate-spin state. It is also shown that the thermally excited spin-state is split in energy by 0.6 meV. In the hole-doped compound, LSCO, it is shown that the evolution into a metallic ferromagnet occurs by the percolation of isotropic ferromagnetic droplets. It is also shown that incommensurate

  2. 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.

  3. Magnetic quantum well states in ultrathin film and wedge structures

    SciTech Connect

    Li, D.; Bader, S.D.

    1996-04-01

    Magnetic quantum-well (QW) states are probed with angle- and spin-resolved photoemission to address critical issues pertaining to the origin of the giant magnetoresistance (GMR) optimization and oscillatory coupling of magnetic multilayers. Two epitaxial systems are highlighted: Cu/Co(wedge)/Cu(100) and Cr/Fe(100)-whisker. The confinement of Cu sp-QW states by a Co barrier requires a characteristic Co thickness of 2.2 {+-} 0.6 {angstrom}, which is consistent with the interfacial Co thickness reported to optimize the GMR of permalloy-Cu structures. The controversial k-space origin of the 18-{angstrom} long period oscillation in Fe/Cr multilayers is identified by the vector that spans the d-derived lens feature of the Cr Fermi surface, based on the emergence of QW states with 17 {+-} 2 {angstrom} periodicity in this region.

  4. 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.

  5. Ground States of a Disordered Frustrated Quantum Dimer Magnet

    NASA Astrophysics Data System (ADS)

    Hristov, Alexander; Shapiro, Maxwell; Fisher, Ian; Lee, Minseong; Rodenbach, Linsey; Bernheisel, Ashley; Choi, Eun Sang; Park, Ju-Hyun; Civale, Leonardo; Munsie, Tim; Luke, Graeme

    2015-03-01

    We present results of thermodynamic measurements of the site-diluted spin-dimer magnet Ba3 (Mn1-xVx)2 O8, including magnetization, torque magnetometry, and AC susceptibility. The parent compound Ba3Mn2O8 is a frustrated S = 1 quantum dimer-magnet with a singlet ground state, and triplet and quintuplet excitations. A magnetic field can be used to tune the energy spectrum of this system, yielding successive triplet and quintuplet condensates at low temperatures. Site substitution with S = 0 V breaks Mn-dimers, introducing site disorder into the high-field ordered states. This substitution also introduces unpaired S = 1 Mn ions, and it has been an open question whether such spins order at low temperatures. Here, we present evidence of the spin-freezing of unpaired Mn ions below 240mK for all compositions measured, from x=0.05 to 0.85. We also present the evolution of the high field ordered state with increasing disorder. NSF DMR-Award 1205165.

  6. 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.

  7. Wireless Majorana Bound States: From Magnetic Tunability to Braiding

    NASA Astrophysics Data System (ADS)

    Fatin, Geoffrey L.; Matos-Abiague, Alex; Scharf, Benedikt; Žutić, Igor

    2016-08-01

    We propose a versatile platform to investigate the existence of Majorana bound states (MBSs) and their non-Abelian statistics through braiding. This implementation combines a two-dimensional electron gas formed in a semiconductor quantum well grown on the surface of an s -wave superconductor with a nearby array of magnetic tunnel junctions (MTJs). The underlying magnetic textures produced by MTJs provide highly controllable topological phase transitions to confine and transport MBSs in two dimensions, overcoming the requirement for a network of wires. Obtained scaling relations confirm that various semiconductor quantum well materials are suitable for this proposal.

  8. Wireless Majorana Bound States: From Magnetic Tunability to Braiding.

    PubMed

    Fatin, Geoffrey L; Matos-Abiague, Alex; Scharf, Benedikt; Žutić, Igor

    2016-08-12

    We propose a versatile platform to investigate the existence of Majorana bound states (MBSs) and their non-Abelian statistics through braiding. This implementation combines a two-dimensional electron gas formed in a semiconductor quantum well grown on the surface of an s-wave superconductor with a nearby array of magnetic tunnel junctions (MTJs). The underlying magnetic textures produced by MTJs provide highly controllable topological phase transitions to confine and transport MBSs in two dimensions, overcoming the requirement for a network of wires. Obtained scaling relations confirm that various semiconductor quantum well materials are suitable for this proposal. PMID:27563991

  9. 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.

  10. Thin Disk Accretion in the Magnetically-Arrested State

    NASA Astrophysics Data System (ADS)

    Avara, Mark J.; McKinney, Jonathan; Reynolds, Christopher S.

    2016-01-01

    Shakura-Sunyaev thin disk theory is fundamental to black hole astrophysics. Though applications of the theory are wide-spread and powerful tools for explaining observations, such as Soltan's argument using quasar power, broadened iron line measurements, continuum fitting, and recently reverberation mapping, a significant large-scale magnetic field causes substantial deviations from standard thin disk behavior. We have used fully 3D general relativistic MHD simulations with cooling to explore the thin (H/R~0.1) magnetically arrested disk (MAD) state and quantify these deviations. This work demonstrates that accumulation of large-scale magnetic flux into the MAD state is possible, and then extends prior numerical studies of thicker disks, allowing us to measure how jet power scales with the disk state, providing a natural explanation of phenomena like jet quenching in the high-soft state of X-ray binaries. We have also simulated thin MAD disks with a misaligned black hole spin axis in order to understand further deviations from thin disk theory that may significantly affect observations.

  11. Electronic States of Nickel Effected By Magnetic Doping

    NASA Astrophysics Data System (ADS)

    Podolak, Ken; Smith, Jamie

    2012-02-01

    Spin currents have a great potential to replace charge currents. This would revolutionize how we read/write information. The generation and switching of spin currents however must be well understood. Transport measurements suggest that magnetic impurities can alter the mean free path of carriers and thereby create spin currents. Angle-resolved photoemission is used to determine the change in the electronic states of Ni induced by doping with iron, chromium, and manganese near the Fermi Energy. The samples were single crystals of nickel(110) with variable amounts of dopant diffused into it. Alloy single crystals were used over epitaxial thin films due to the sharper features at the Fermi Energy that they produced. The mean free path, magnetic splitting, and carrier density are affected by a few percent of each of the dopants. Iron suppresses the mean free path of minority spins only, while chromium and manganese suppresses both spins and decreases the magnetic splitting. The strong variation of these affects from one impurity to the other supports the concept of tailoring spin transport by magnetic doping. [1] K. N. Altmann et al., Phys. Rev. Lett. 87, 137201 (2001) [2] K.R. Podolak, Ph.D. Thesis, Penn. State (2008)

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

    SciTech Connect

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

  13. 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

  14. MOVPE growth of Ga(AsBi)/GaAs multi quantum well structures

    NASA Astrophysics Data System (ADS)

    Ludewig, P.; Knaub, N.; Stolz, W.; Volz, K.

    2013-05-01

    This paper summarizes results of the epitaxial growth of Ga(AsBi) by metal organic vapor phase epitaxy (MOVPE) using all-liquid group V precursors. Ga(AsBi)/GaAs multi quantum well (MQW) samples are grown on GaAs (001) substrates at temperatures as low as 375 °C and 400 °C using triethylgallium (TEGa), tertiarybutylarsine (TBAs) and trimethylbismuth (TMBi) as precursors. High resolution x-ray diffraction (HR-XRD), transmission electron microscopy (TEM) as well as atomic force microscopy (AFM) measurements show that MQW structures with good crystalline quality are realized. Under specific growth conditions, the Bi droplet formation can be avoided completely. The incorporated Bi-content is limited depending on the growth temperature used. Surplus Bi segregates at the surface and incorporates into the subsequent GaAs barrier when the Bi supply is stopped. The MQW samples show room temperature photoluminescence (PL) already after growth. A redshift and a decreasing PL signal intensity with increasing Bi fraction is observed.

  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. Multicanonical sampling of vortex states in magnetic nanoelements

    NASA Astrophysics Data System (ADS)

    Reitzner, D.; Horváth, D.

    2007-06-01

    An auto-adaptive multicanonical Monte Carlo (MMC) simulation method is suggested and tested on a single-vortex model of magnetic nanoelement. Simulation process consisting of nonequilibrium and equilibrium stages that circumvents ergodicity sampling problems which stem from a potential barrier standing between the vortex and counter-vortex states is proposed. The method is formulated by the means of an effective Hamiltonian with additional term proportional to the overlap of given configuration and bistable ground-state vortex configuration. The self-organized neural network is used to construct the synopsis of the vortex reversal process.

  17. Tail states in clean superconductors with magnetic impurities.

    SciTech Connect

    Vekhter, I.; Shytov, A. V.; Gruzberg, I. A.; Balatsky, A. V.

    2002-01-01

    We analyse the behavior of the density of states in a singlet s-wave superconductor with weak magnetic impurities in the clean limit. By using the method of optimal fluctuation and treating the order parameter self-consistently we show that the density of states is finite everywhere in the superconducting gap, and that it varies as in N(E) {proportional_to} -|E-{Delta}{sub 0}|{sup (7-d)/4} the mean field gap edge {Delta}{sub 0} in a d-dimensional superconductor. In contrast to most studied cases the optimal fluctuation is strongly anisotropic.

  18. 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.

  19. 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.

  20. Universal dynamic magnetism in Yb pyrochlores with disparate ground states

    NASA Astrophysics Data System (ADS)

    Hallas, A. M.; Gaudet, J.; Butch, N. P.; Tachibana, M.; Freitas, R. S.; Luke, G. M.; Wiebe, C. R.; Gaulin, B. D.

    2016-03-01

    The ytterbium pyrochlore magnets, Yb2B2O7 (B =Sn ,Ti ,Ge ) are well described by Seff=1 /2 quantum spins decorating a network of corner-sharing tetrahedra and interacting via anisotropic exchange. Structurally, only the nonmagnetic B -site cation, and hence primarily the lattice parameter, changes across the series. Nonetheless, a range of magnetic behaviors is observed: the low-temperature magnetism in Yb2Ti2O7 and Yb2Sn2O7 has a ferromagnetic character, while Yb2Ge2O7 displays an antiferromagnetically ordered Néel state at low temperatures. While the static properties of the ytterbium pyrochlores are distinct, inelastic neutron scattering measurements reveal a common character to their exotic spin dynamics. All three ytterbium pyrochlores show a gapless continuum of spin excitations, resembling overdamped ferromagnetic spin waves at low Q . Furthermore, the specific heat of the series also follows a common form, with a broad, high-temperature anomaly followed by a sharp low-temperature anomaly at TC or TN. The novel spin dynamics we report correlate strongly with the broad specific heat anomaly only, remaining unchanged across the sharp anomaly. This result suggests that the primary order parameter in the ytterbium pyrochlores associated with the sharp anomaly is "hidden" and not simple magnetic dipole order.

  1. Hyperbolic method for magnetic reconnection process in steady state magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Baty, Hubert; Nishikawa, Hiroaki

    2016-06-01

    A recent numerical approach for solving the advection-diffusion and Navier-Stokes equations is extended for the first time to a magnetohydrodynamic (MHD) model, aiming in particular consistent improvements over classical methods for investigating the magnetic reconnection process. In this study, we mainly focus on a two-dimensional incompressible set of resistive MHD equations written in flux-vorticity scalar variables. The originality of the method is based on hyperbolic reformulation of the dissipative terms, leading to the construction of an equivalent hyperbolic first-order (spatial derivatives) system. This enables the use of approximate Riemann solvers for handling dissipative and advective flux in the same way. A simple second-order finite-volume discretization on rectangular grids using an upwind flux is employed. The advantages of this method are illustrated by a comparison to two particular analytical steady state solutions of the inviscid magnetic reconnection mechanism, namely the magnetic annihilation and the reconnective diffusion problems. In particular, the numerical solution is obtained with the same order of accuracy for the solution and gradient for a wide range of magnetic Reynolds numbers, without any deterioration characteristic of more conventional schemes. The amelioration of the hyperbolic method and its extension to time-dependent MHD problems related to solar flares mechanisms is also discussed.

  2. 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.

  3. 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.

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

    SciTech Connect

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

    1989-02-01

    The authors present a two-dimensional, force-balanced magnetic field model in which flux tubes have constant pV{gamma} throughout an extended region of the nightside plasma sheet, between approximately 36 R{sub E} geocentric distance and the region of the inner edge of the plasma sheet. They have thus demonstrated the theoretical existence of a steady state magnetic field configuration that is force-balanced and also consistent with slow, lossless, adiabatic, earthward convection within the limit of the ideal MHD (isotropic pressure, perfect conductivity). The numerical solution was constructed for a two-dimensional magnetosphere with a rectangular magnetopause and nonflaring tail. The primary characteristics of the steady state convection solution are (1) a pressure maximum just tailward of the inner edge of the plasma sheet and (2) a deep, broad minimum in equatorial magnetic field strength B{sub ze}, also just tailward of the inner edge. The results are consistent with Erickson's (1985) convection time sequences, which exhibited analogous pressure peaks and B{sub ze} minima. Observations do not indicate the existence of a B{sub ze} minimum, on the average. They suggest that the configurations with such deep minima in B{sub ze} may be tearing-mode unstable, thus leading to substorm onset in the inner plasma sheet.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  6. 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.

  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. High magnetic field science and its application in the United States: A magnetic resonance perspective

    NASA Astrophysics Data System (ADS)

    Frydman, Lucio

    2014-05-01

    The National Research Council published the assessments of a blue-ribbon panel on the future of high magnetic field science in the United States. Many of this report recommendations pertain the current status and the future of high-field NMR, MRI and in vivo MRS. Among the committee’s most significant recommendations count the installation of several 1.2 GHz spectrometers, and jump-starting efforts to develop 1.6 GHz NMR and ⩾600 MHz MRI scanners.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    SmB6 is a Kondo insulator with a band structure that is topologically distinct from the vacuum. This is theoretically predicted to produce metallic topological surface states that are robust to perturbations that do not break time reversal symmetry, such as non-magnetic defects. However, 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. 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.

  12. 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.

  13. 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. PMID:26893217

  14. Optical pumping in solid state nuclear magnetic resonance

    SciTech Connect

    Tycko, R.; Reimer, J.A.

    1996-08-01

    An important current trend in solid state nuclear magnetic resonance (NMR) is the growing exploitation of optical pumping of nuclear spin polarizations as a means of enhancing and localizing NMR signals. Recent work has been concentrated in two areas, namely optically pumped NMR in semiconductors and optical pumping of noble gases. Progress in these two areas, including technical developments and new applications in physical chemistry, condensed matter physics, and biomedical sciences, is reviewed. Likely directions for future developments are suggested. 58 refs., 13 figs.

  15. 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.

  16. Magnetic characterization of the primary state of bacterial photosynthesis

    PubMed Central

    Norris, J. R.; Bowman, M. K.; Budil, D. E.; Tang, J.; Wraight, C. A.; Closs, G. L.

    1982-01-01

    The results of reaction yield-detected magnetic resonance (RYDMR) experiments carried out on modified bacterial photosynthetic reaction centers (RCs) are interpreted in terms of a model that assigns the initial charge-separated radical ion-pair state, PF, as the carrier of the spectrum. The radical pair theory, which has been invoked to explain magnetic field effects in RCs, was significantly expanded to take into consideration the electron dipole-dipole interaction. It is shown that this is the largest interaction between the components of the radical ion pair. Quantum statistical calculations are described simulating the RYDMR spectra and low-field effects in quinone-depleted RCs. The experimental data on which the simulations are based are (i) the magnitude of the field effect at 3,000 G, (ii) the field at which 0.5 of the maximal field effect is observed, (iii) the PF population as a function of time at zero magnetic field, (iv) the RYDMR linewidth for low microwave field strength, (v) the RYDMR intensity and width as a function of microwave field, and (vi) the maximum RYDMR intensity at HI ≃ 2ǀJǀ. With this information it was found possible to characterize PF in terms of four parameters, two containing structural information and two with kinetic implications. These are the dipole-dipole interaction, D = -47 ± 10 × 10-4 cm-1; the exchange interaction, J = -7.5 ± 1.9 × 10-4 cm-1; and the inverse rate constants of the decay of the radical pair states with singlet and triplet spin functions, respectively, kS-1 = 15 ± 4 nsec and kT-1 = 1.8 ± 0.2 nsec. The structural and dynamic implications of these parameters are discussed. PMID:16593226

  17. 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.

  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. Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

    PubMed Central

    2010-01-01

    Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV. PMID:21170404

  20. 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.

  1. Novel magnetic and electronic states in manganite-iridate heterostructures

    NASA Astrophysics Data System (ADS)

    Nichols, John; Lee, Shinbuhm; Petrie, Jon; Meyer, Tricia; Gao, Xiang; Guo, Erjia; Freeland, John; Yi, Di; Liu, Jian; Haskel, Daniel; Ward, Thomas Zac; Eres, Gyula; Lauter, Valeria; Fitzsimmons, Michael R.; Lee, Ho Nyung

    Strong correlation between spin, charge, lattice, and orbital order parameters has proven to give rise to exotic physical phenomena, while epitaxial design of materials with strong interfacial coupling is an efficient technique to tune such parameters. Although there have been numerous studies of interfaces between 3 d-3 d and 4 d-3 d compounds, only few studies reported work on 3 d and 5 d materials and there has been no report on strong interfacial coupling in such systems. We have synthesized high quality [(AMnO3)m /(SrIrO3)n ]z (A = Sr, La) heterostructures by pulsed laser epitaxy on SrTiO3 (001) substrates and have observed interesting novel magnetic and electronic ground states, which are highly sensitive to the degree of dimensional confinement in the heterostructures. Based on studies with x-ray diffraction, SQUID, dc-transport, x-ray circular dichroism, and polarized neutron reflectometry measurements, we will report intriguing magnetic and transport properties that provide the first evidence of strong interfacial coupling between 5 d and 3 d materials. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

  2. 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. PMID:26603579

  3. Reliable absolute palaeointensities independent of magnetic domain state

    NASA Astrophysics Data System (ADS)

    Dekkers, Mark J.; Böhnel, Harald N.

    2006-08-01

    Knowledge of palaeointensity variation is required for determining the full vector variation of the geomagnetic field as a function of geological time. This provides essential constraints for numerical geodynamo models. To date, most palaeointensity determination methods are laborious, characterised by rather low success rates, and demand substantial processing time. The rocks under investigation must obey stringent criteria to yield faithful palaeointensities: the magnetic particles must be single domain, the natural remanent magnetisation must be a thermoremanent magnetisation, and during the successive heating steps in the laboratory no chemical alteration should occur. Here, we describe a new method that allows all magnetic domain states to be processed, i.e. it does not require single domain particles. The method makes use of the linearity of partial thermoremanent magnetisation (pTRM) with the applied laboratory field. Multiple specimens are used so that every sample is exposed only once to a laboratory field, warranting that all samples experienced the same magnetic history. Through the limited number of thermal steps alteration effects are reduced as well. The laboratory pTRM and natural remanent magnetisation (NRM) of the specimens are oriented parallel to minimise the effects of high-temperature tails that affect multidomain minerals. The pTRM acquisition temperature is selected below the temperature at which chemical alteration sets in and above the temperature trajectory where secondary viscous NRM components occur. The procedure requires a lower number of steps than any other palaeointensity method, reducing significantly the total time needed per rock unit. We propose to name the new protocol 'multispecimen parallel differential pTRM method'. It provides the correct answer to ˜ 5% for artificial samples and natural rocks containing multidomain magnetic particles that were given a laboratory TRM of known intensity. Application to the Paricutin

  4. Ultrafast quantum spin-state switching in the Co-octaethylporphyrin molecular magnet with a terahertz pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Farberovich, Oleg V.; Mazalova, Victoria L.

    2016-05-01

    Molecular spin crossover switches are the objects of intense theoretical and experimental studies in recent years. This interest is due to the fact that these systems allow one to control their spin state by applying an external photo-, thermo-, piezo-, or magnetic stimuli. The greatest amount of research is currently devoted to the study of the effect of the photoexcitation on the bi-stable states of spin crossover single molecular magnets (SMMs). The main limitation of photo-induced bi-stable states is their short lifetime. In this paper we present the results of a study of the spin dynamics of the Co-octaethylporphyrin (CoOEP) molecule in the Low Spin (LS) state and the High Spin (HS) state induced by applying the magnetic pulse of 36.8 T. We show that the spin switching in case of the HS state of the CoOEP molecule is characterized by a long lifetime and is dependent on the magnitude and duration of the applied field. Thus, after applying an external stimuli the system in the LS state after the spin switching reverts to its ground state, whereas the system in the HS state remains in the excited state for a long time. We found that the temperature dependency of magnetic susceptibility shows an abrupt thermal spin transition between two spin states at 40 K. Here the proposed theoretical approach opens the way to create modern devices for spintronics with the controllable spin switching process.

  5. 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

    2015-01-01

    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

  6. 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.

  7. Meta-Stable Magnetic Domain States That Prevent Reliable Absolute Palaeointensity Experiments Revealed By Magnetic Force Microscopy

    NASA Astrophysics Data System (ADS)

    de Groot, L. V.; Fabian, K.; Bakelaar, I. A.; Dekkers, M. J.

    2014-12-01

    Obtaining reliable estimates of the absolute palaeointensity of the Earth's magnetic field is notoriously difficult. Many methods to obtain paleointensities from suitable records such as lavas and archeological artifacts involve heating the samples. These heating steps are believed to induce 'magnetic alteration' - a process that is still poorly understood but prevents obtaining correct paleointensity estimates. To observe this magnetic alteration directly we imaged the magnetic domain state of titanomagnetite particles - a common carrier of the magnetic remanence in samples used for paleointensity studies. We selected samples from the 1971-flow of Mt. Etna from a site that systematically yields underestimates of the known intensity of the paleofield - in spite of rigorous testing by various groups. Magnetic Force Microscope images were taken before and after a heating step typically used in absolute palaeointensity experiments. Before heating, the samples feature distinct, blocky domains that sometimes seem to resemble a classical magnetite domain structure. After imparting a partial thermo-remanent magnetization at a temperature often critical to paleointensity experiments (250 °C) the domain state of the same titanomagnetite grains changes into curvier, wavy domains. Furthermore, these structures appeared to be unstable over time: after one-year storage in a magnetic field-free environment the domain states evolved into a viscous remanent magnetization state. Our observations may qualitatively explain reported underestimates from technically successful paleointensity experiments for this site and other sites reported previously. Furthermore the occurrence of intriguing observations such as 'the drawer storage effect' by Shaar et al (EPSL, 2011), and viscous magnetizations observed by Muxworthy and Williams (JGR, 2006) may be (partially) explained by our observations. The major implications of our study for all palaeointensity methods involving heating may be

  8. Seeing the magnetic monopole through the mirror of topological surface states

    SciTech Connect

    Qi, Xiao-Liang; Li, Rundong; Zang, Jiadong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept. /Fudan U.

    2010-03-25

    Existence of the magnetic monopole is compatible with the fundamental laws of nature, however, this illusive particle has yet to be detected experimentally. In this work, we show that an electric charge near the topological surface state induces an image magnetic monopole charge due to the topological magneto-electric effect. The magnetic field generated by the image magnetic monopole can be experimentally measured, and the inverse square law of the field dependence can be determined quantitatively. We propose that this effect can be used to experimentally realize a gas of quantum particles carrying fractional statistics, consisting of the bound states of the electric charge and the image magnetic monopole charge.

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

    PubMed

    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

  10. 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

  11. Four-state magnetic configuration in a tri-layer asymmetric ring

    NASA Astrophysics Data System (ADS)

    Popescu, Horia; Fortuna, Franck; Delaunay, Renaud; Spezzani, Carlo; Lopez-Flores, Victor; Jaouen, Nicolas; Sacchi, Maurizio

    2015-11-01

    Ring-shaped multilayered sub-micron dots have the potential for the development of non-volatile multi-bit devices. We show that a Co/Cu/FeNi asymmetric ring can take four distinct remanent magnetic states, each one stabilized by applying a magnetic field pulse along one of four in-plane orthogonal directions. We use element selective x-ray holography for imaging the Co magnetic configuration following a magnetic pulse. Micro-magnetic simulations support our experimental findings; they also provide an estimate of the system magnetization dynamics, setting out the conditions for further time-resolved experiments.

  12. 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.

  13. Magnetic dipoles at topological defects in the Meissner state of a nanostructured superconductor

    NASA Astrophysics Data System (ADS)

    Ge, Jun-Yi; Gladilin, Vladimir N.; Xue, Cun; Tempere, Jacques; Devreese, Jozef T.; Van de Vondel, Joris; Zhou, Youhe; Moshchalkov, Victor V.

    2016-06-01

    In a magnetic field, superconductivity is manifested by total magnetic field expulsion (Meissner effect) or by the penetration of integer multiples of the flux quantum Φ0. Here we present experimental results revealing magnetic dipoles formed by Meissner current flowing around artificially introduced topological defects (lattice of antidots). By using scanning Hall probe microscopy, we have detected ordered magnetic dipole lattice generated at spatially periodic antidots in a Pb superconducting film. While the conventional homogeneous Meissner state breaks down, the total magnetic flux of the magnetic dipoles remains quantized and is equal to zero. The observed magnetic dipoles strongly depend on the intensity and direction of the locally flowing Meissner current, making the magnetic dipoles an effective way to monitor the local supercurrent. We have also investigated the first step of the vortex depinning process, where, due to the generation of magnetic dipoles, the pinned Abrikosov vortices are deformed and shifted from their original pinning sites.

  14. 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

    2016-03-01

    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. PMID:26879291

  15. 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.

  16. 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.

  17. Phase instability of magnetic ground state in antiperovskite Mn3ZnN: Giant magnetovolume effects related to magnetic structure

    NASA Astrophysics Data System (ADS)

    Hamada, T.; Takenaka, K.

    2012-04-01

    We verified the intimate relation between magnetism and volume in Mn3ZnN. The sample sintered at 900 °C is characterized by the Γ5g triangular antiferromagnetic (AF) state with larger volume below 170 K. However, for the sample sintered at 700 °C, the re-entrant phase transition appears at 80 K and the ground state is a different AF state with smaller volume. These results indicate that the ground state of Mn3ZnN is sensitive to the disorder in the N site and that the magnetic structure drastically alters magnetovolume effects. More detailed consideration is necessary beyond the conventional scheme, which incorporates only the amplitude of the magnetic moment.

  18. Control of Magnetic States of Cobalt Nanorings by an External Azimuthal Field

    NASA Astrophysics Data System (ADS)

    Pradhan, Nihar; Yang, Tianyu; Licht, Abbey; Li, Yihan; Tuominen, Mark; Aidala, Katherine

    2011-03-01

    Ferromagnetic nanorings attract interest due to their potential application in high density data storage and Magnetoresistive Random Access Memory (MRAM) devices. These nanorings show multidomain stable states that need to be well controlled by external in-plane or circular magnetic fields. This talk presents a new method to generate circular magnetic fields to control the magnetic states in different geometries of Cobalt nanoring structures, of varying diameter, width and thickness. A solid platinum AFM tip was used to pass current through a single nanoring, generating a circular magnetic field. In applying this field we were able to change the state of the individual ring without affecting the states of other neighboring rings. The evolution of the magnetic states of individual symmetric and asymmetric Cobalt nanorings with applied azimuthal field will be presented. The work was supported by the National Science Foundation under DMR Grant 906832 and Research Corporation Grant 7889.

  19. Temperature dependent investigation of carrier transport, injection, and densities in 808 nm AlGaAs multi-quantum-well active layers for VCSELs

    NASA Astrophysics Data System (ADS)

    Engelhardt, Andreas P.; Kolb, Johanna S.; Römer, Friedhard; Weichmann, Ulrich; Moench, Holger; Witzigmann, Bernd

    2014-05-01

    The electro-optical efficiency of semiconductor vertical-cavity surface-emitting lasers (VCSELs) strongly depends on the efficient carrier injection into the quantum wells (QWs) in the laser active region. However, carrier injection degrades with increasing temperature which limits the VCSEL performance particularly in high power applications where self heating imposes high temperatures in operation. By simulation we investigate the transport of charge carriers in 808 nm AlGaAs multi-quantum-well active layers with special attention to the temperature dependence of carrier injection into the QWs. Experimental reference data was extracted from oxide-confined, top-emitting VCSELs. The transport simulations follow a drift-diffusion-model complemented by a customized, energy-resolved, semi-classical carrier capture theory. QW gain was calculated in the screened Hartree-Fock approximation with band structures from 8x8 k.p-theory. Using the gain data and by setting losses and the optical confinement factor according to experimental reference results, the appropriate threshold condition and threshold carrier densities in the QWs for a VCSEL are established in simulation for all transport considerations. With the combination of gain and transport model, we can explain experimental reference data for the injection efficiency and threshold current density. Our simulations show that the decreasing injection efficiency with temperature is not solely due to increased thermionic escape of carriers from the QWs. Carrier injection is also hampered by state filling in the QWs initiated from higher threshold carrier densities with temperature. Consequently, VCSEL properties not directly related to the active layer design like optical out-coupling or internal losses link the temperature dependent carrier injection to VCSEL mirror design.

  20. 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

  1. Magnetic field effects and the role of spin states in singlet fission

    NASA Astrophysics Data System (ADS)

    Burdett, Jonathan J.; Piland, Geoffrey B.; Bardeen, Christopher J.

    2013-10-01

    Singlet fission is a photophysical process that has promise for increasing the efficiency of solar cells. The dynamics depend on triplet spin states and can be influenced by external magnetic fields. In 4-electron systems, fission takes an initial singlet state into a superposition of triplet pair states. Direct evidence for this superposition state is provided by quantum beats in the delayed fluorescence of tetracene crystals. The beat frequencies depend on crystal orientation with respect to the magnetic field, consistent with predictions based on solving the full spin Hamiltonian. Magnetic field effects on the kinetics are analyzed in terms of a hybrid quantum-kinetic model. The magnetic field has no effect on the initial fluorescence decay rate but affects the decay after the triplet pair states begin to equilibrate with the singlets. The long-time behavior of the fluorescence decay reflects association and separation of triplet pairs and relaxation into different spin states.

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

    PubMed

    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

  3. 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.

  4. Ground State of Magnetic Dipoles on a Two-Dimensional Lattice: Structural Phases in Complex Plasmas

    SciTech Connect

    Feldmann, J. D.; Kalman, G. J.; Hartmann, P.; Rosenberg, M.

    2008-02-29

    We study analytically and by molecular dynamics simulations the ground state configuration of a system of magnetic dipoles fixed on a two-dimensional lattice. We find different phases, in close agreement with previous results. Building on this result and on the minimum energy requirement we determine the equilibrium lattice configuration, the magnetic order (ferromagnetic versus antiferromagnetic), and the magnetic polarization direction of a system of charged mesoscopic particles with magnetic dipole moments, in the domain where the strong electrostatic coupling leads to a crystalline ground state. Orders of magnitudes of the parameters of the system relevant to possible future dusty plasma experiments are discussed.

  5. 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.

  6. 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.

  7. 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

  8. Emergence of magnetic topological states in topological insulators doped with magnetic impurities

    NASA Astrophysics Data System (ADS)

    Tran, Minh-Tien; Nguyen, Hong-Son; Le, Duc-Anh

    2016-04-01

    Emergence of the topological invariant and the magnetic moment in topological insulators doped with magnetic impurities is studied based on a mutual cooperation between the spin-orbit coupling of electrons and the spin exchange of these electrons with magnetic impurity moments. The mutual cooperation is realized based on the Kane-Mele model in the presence of magnetic impurities. The topological invariants and the spontaneous magnetization are self-consistently determined within the dynamical mean-field theory. We find different magnetic topological phase transitions, depending on the electron filling. At half filling an antiferromagnetic topological insulator, which exhibits the quantum spin Hall effect, exists in the phase region between the paramagnetic topological insulator and the trivially topological antiferromagnetic insulator. At quarter and three-quarter fillings, a ferromagnetic topological insulator, which exhibits the quantum anomalous Hall effect, occurs in the strong spin-exchange regime.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

  12. 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.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  15. 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.

  16. A fully implicit method for 3D quasi-steady state magnetic advection-diffusion.

    SciTech Connect

    Siefert, Christopher; Robinson, Allen Conrad

    2009-09-01

    We describe the implementation of a prototype fully implicit method for solving three-dimensional quasi-steady state magnetic advection-diffusion problems. This method allows us to solve the magnetic advection diffusion equations in an Eulerian frame with a fixed, user-prescribed velocity field. We have verified the correctness of method and implementation on two standard verification problems, the Solberg-White magnetic shear problem and the Perry-Jones-White rotating cylinder problem.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

  18. 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

  19. 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.

  20. Electrical and optical study of an indium gallium arsenide/gallium arsenide multi-quantum well structure for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    An, Sangwoo

    2000-08-01

    InGaAs is a III-V material system that has recently attracted a lot of interest for possible optoelectronic applications. When grown over a GaAs substrate, it provides an example of a strained-layer system, due to the lattice mismatch of the layers. As long as the strained layers are grown shorter than a critical thickness, the material is pseudomorphic and presents no catastrophic degrading. Thus, it can be used for different devices, such as lasers, detectors, switches, and spatial light modulators. In this work a low-dimensional structure, composed of different stacks of InGaAs quantum wells embedded in a matrix of GaAs barriers, is investigated. This work addresses a number of important issues involving material properties and basic physical effects. In addition it discloses the concept of an improved, multicolor, spatial light modulator. Material information about InGaAs is abundant but not exhaustive as for the GaAs system. We have performed an in-depth spectroscopic study of a complex structure, composed of serially grown stacks of stepped quantum wells, where it is possible, in principle, to observe large Stark shifts. In this sample we have studied the formation of electrical high and low-field domains along the multi-quantum well region with a number of spectroscopic techniques. Electrical and optical measurements have been performed and have given an extensive characterization of the sample. Experimental results closely match theoretical calculations performed under the effective mass approximation. Excitonic peaks at room temperatures have been clearly resolved, a first for InGaAs stepped quantum well samples. Formation and expansion of electric field domains along the shallow multi-quantum well region have been recorded. For the first time an observation of the interplay of high field domains involving shallow quantum well levels and resonances in the continuum, have been observed. New techniques to probe such high field domains have been developed

  1. 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.

  2. 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.

  3. 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

    2016-01-01

    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

  4. Interlayer coupling through a dimensionality-induced magnetic state

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  5. 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

  6. Dependence of the Bose-Glass state on the magnetic field angle

    NASA Astrophysics Data System (ADS)

    Smith, A. W.; Anders, S.; Parthasarathy, R.; Fabijanic, J. M.; Jaeger, H. M.; Rosenbaum, T. F.; Kwok, W.; Crabtree, G.

    1998-03-01

    We investigate the effect of a transverse magnetic field, H_⊥, on the Bose-Glass state in heavy ion irradiated YBa_2Cu_3O_7-δ single crystals. Using InAs Hall probe arrays we measure the local component of the magnetic field parallel to the columnar defects with single vortex resolution. We study the critical current density and the relaxation rate of local magnetic field gradients as a function of H_⊥. A sufficiently large transverse magnetic field is expected to pull vortices off the columnar defects and melt the Bose-Glass(D. R. Nelson and V. M. Vinokur, Phys. Rev. B 48), 13 060 (1993)..

  7. Local Magnetic Suppression of Topological Surface States in Bi2Te3 Nanowires.

    PubMed

    Gooth, Johannes; Zierold, Robert; Sergelius, Philip; Hamdou, Bacel; Garcia, Javier; Damm, Christine; Rellinghaus, Bernd; Pettersson, Håkan Jan; Pertsova, Anna; Canali, Carlo; Borg, Mattias; Nielsch, Kornelius

    2016-07-26

    Locally induced, magnetic order on the surface of a topological insulator nanowire could enable room-temperature topological quantum devices. Here we report on the realization of selective magnetic control over topological surface states on a single facet of a rectangular Bi2Te3 nanowire via a magnetic insulating Fe3O4 substrate. Low-temperature magnetotransport studies provide evidence for local time-reversal symmetry breaking and for enhanced gapping of the interfacial 1D energy spectrum by perpendicular magnetic-field components, leaving the remaining nanowire facets unaffected. Our results open up great opportunities for development of dissipation-less electronics and spintronics. PMID:27351276

  8. New spiral state and skyrmion lattice in 3D model of chiral magnets

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    We present the phase diagram of magnetic states for films of isotropic chiral magnets (ChMs) calculated as function of applied magnetic field and thickness of the film. We have found a novel magnetic state driven by the natural confinement of the crystal, localized at the surface and stacked on top of the conical bulk phase. This magnetic surface state has a three-dimensional (3D) chiral spin-texture described by the superposition of helical and cycloidal spin spirals. This surface state exists for a large range of applied magnetic fields and for any film thickness beyond a critical one. We also identified the whole thickness and field range for which the skyrmion lattice becomes the ground state of the system. Below a certain critical thickness the surface state and bulk conical phase are suppressed in favor of the skyrmion lattice. Unraveling of those phases and the construction of the phase diagram became possible using advanced computational techniques for direct energy minimization applied to a basic 3D model for ChMs. Presented results provide a comprehensive theoretical description for those effects already observed in experiments on thin films of ChMs, predict new effects important for applications and open perspectives for experimental studies of such systems.

  9. 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.

  10. 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.

  11. 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.

  12. Ground states of spin-2 condensates in an external magnetic field

    SciTech Connect

    Zheng, G.-P.; Tong, Y.-G.; Wang, F.-L.

    2010-06-15

    The possible ground states of spin-2 Bose-Einstein condensates in an external magnetic field are obtained analytically and classified systematically according to the population of the condensed atoms at the hyperfine sublevels. It is shown that the atoms can populate simultaneously at four hyperfine sublevels in a weak magnetic field with only the linear Zeeman energy, in contrast to that in a stronger magnetic field with the quadratic Zeeman energy, where condensed atoms can at most populate at three hyperfine sublevels in the ground states. Any spin configuration we obtained will give a closed subspace in the order parameter space of the condensates.

  13. 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

  14. Ferromagnetic cluster glass state induced by non-magnetic ions in a paramagnetic host

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takafumi D.; Okazaki, Ryuji; Taniguchi, Hiroki; Terasaki, Ichiro

    A paramagnetic metal CaRuO3 has been known to show unique impurity effects, where a magnetic ordering is induced by a partial substitution of transition metal ions for Ru. Since this phenomenon occurs regardless of the magnetism of the substituted ions, it must reflect a magnetic instability of this ruthenate. Understanding such physical properties is one of intriguing issues in condensed matter physics. In this talk, we report an unconventional magnetic state induced by substituting non-magnetic Sc3+ ions. We find that the static magnetic susceptibilities of all Sc-substituted samples show ferromagnetic-like features below 40 K, while the Curie-Weiss temperature dramatically changes with increasing x. This inconsistency is a sign of non-uniform magnetic system. We propose a phenomenological model and show that the static magnetic properties can be described as a volume average of a paramagnetic component originated from Ru4+ ions and a ferromagnetic one driven by Sc substitution [T. D. Yamamoto et al., JPSJ 84, 014708 (2015).]. Furthermore our dynamic magnetic measurements reveal a ferromagnetic cluster glass state embedded in the paramagnetic and metallic host of CaRuO3.

  15. 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.

  16. Equilibrium State and Magnetic Permeability Tensor of the Epitaxial Ferrite Films

    NASA Astrophysics Data System (ADS)

    Bobkov, V. B.; Zavislyak, I. V.

    1997-12-01

    The analysis of the equilibrium state of an arbitrarily oriented epitaxial ferrite film with basic cubic symmetry has been carried out. The equilibrium orientation of the magnetization has been shown to coincide with the direction of the applied magnetic field for (n, n, m), (m, n, 0) and (112) films that are magnetized parallel to the surface along the axes 110, 100 and 111, respectively. Conditions of the stability of the equilibrium state have been found. For (100), (110) and (111) films a simple technique for determining the magnetic parameters of the films by the use of the spectra of magnetostatic waves has been proposed. For those films the magnetic permeability tensor has been obtained. Different algorithms have been proposed for processing the MSW spectra.

  17. Persistence of magnetic order in a highly excited Cu2+ state in CuO

    NASA Astrophysics Data System (ADS)

    Staub, U.; de Souza, R. A.; Beaud, P.; Möhr-Vorobeva, E.; Ingold, G.; Caviezel, A.; Scagnoli, V.; Delley, B.; Turner, J. J.; Krupin, O.; Lee, W.-S.; Chuang, Y.-D.; Patthey, L.; Moore, R. G.; Lu, D.; Yi, M.; Kirchmann, P. S.; Trigo, M.; Denes, P.; Doering, D.; Hussain, Z.; Shen, Z. X.; Prabhakaran, D.; Boothroyd, A. T.; Johnson, S. L.

    2014-06-01

    We use ultrafast resonant x-ray diffraction to study the magnetic order in CuO under conditions of high electronic excitation. By measuring changes in the spectral shape of the Cu2+ magnetic (1/2 0 -1/2) reflection we investigate how an intense optical pump pulse perturbs the electronic and magnetic states. We observe an energy shift in the magnetic resonance at short times after the pump pulse. This shift is compared with expectations from band structure calculations at different electronic temperatures. This spectral line shift indicates that although the electrons are heated to effective electron temperatures far above TN on a time scale faster than the experimental resolution, magnetic order persists in this highly excited state for several hundred femtoseconds.

  18. Electrical Control of the Magnetic State of Fe

    SciTech Connect

    Gerhard, Lukas; Yamada, Toyo Kazu; Balashov, T.; Takác, Albert; Wesselink, R.J.H.; Daene, Markus W; Fechner, M.; Ostanin, S.; Ernst, Arthur; Mertig, Ingrid; Wulfhekel, Wulf

    2011-01-01

    Magneto-electric coupling offers a new pathway to information storage in magnetic memory devices. This phenomenon has been observed in various materials ranging from insulators to semiconductors. In bulk metallic systems, magneto-electric coupling has been disregarded as the electric field cannot enter bulk metals. In this work, we show that a substantial magneto-electric coupling exists in metallic Fe nano-islands grown on Cu(111). Using the electric field in the tunnel junction of a scanning tunneling microscope, the magnetic order parameter and the crystal structure of Fe was changed on the nanometer scale. This allows high density nonvolatile information storage by means of magneto-electric coupling in a simple metallic system.

  19. Influence of pressure on the properties of GaN/AlN multi-quantum wells - Ab initio study

    NASA Astrophysics Data System (ADS)

    Strak, Pawel; Sakowski, Konrad; Kaminska, Agata; Krukowski, Stanislaw

    2016-06-01

    Pressure dependence of physical properties of GaN/AlN multi-quantum wells (MQWs) was investigated using ab intio calculations. The influence of pressure was divided into two main contributions: pressure affecting the properties of GaN and AlN bulk semiconductors and an influence on systems of polar quantum wells deposited on various substrates. An influence of hydrostatic, uniaxial, and tetragonal strain on the crystallographic structure, polarization (piezoelectricity), and the bandgap of the bulk systems is assessed using ab initio calculations. It was shown that when a partial relaxation of the structure is assumed, the tetragonal strain may explain an experimentally observed reduction of pressure coefficients for polar GaN/AlN MQWs. The MQWs were also simulated directly using density functional theory (DFT) calculations. A comparison of these two approaches confirmed that nonlinear effects induced by the tetragonal strain related to lattice mismatch between the substrates and the polar MQWs systems are responsible for a drastic decrease of the pressure coefficients of photoluminescence (PL) energy experimentally observed in polar GaN/AlGaN MQWs.

  20. 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. PMID:26625883

  1. 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

  2. Magnetic anisotropy in Shiba bound states across a quantum phase transition

    NASA Astrophysics Data System (ADS)

    Hatter, Nino; Heinrich, Benjamin W.; Ruby, Michael; Pascual, Jose I.; Franke, Katharina J.

    2015-11-01

    The exchange coupling between magnetic adsorbates and a superconducting substrate leads to Shiba states inside the superconducting energy gap and a Kondo resonance outside the gap. The exchange coupling strength determines whether the quantum many-body ground state is a Kondo singlet or a singlet of the paired superconducting quasiparticles. Here we use scanning tunnelling spectroscopy to identify the different quantum ground states of manganese phthalocyanine on Pb(111). We observe Shiba states, which are split into triplets by magnetocrystalline anisotropy. Their characteristic spectral weight yields an unambiguous proof of the nature of the quantum ground state. Our results provide experimental insights into the phase diagram of a magnetic impurity on a superconducting host and shine light on the effects induced by magnetic anisotropy on many-body interactions.

  3. Magnetic anisotropy in Shiba bound states across a quantum phase transition

    PubMed Central

    Hatter, Nino; Heinrich, Benjamin W.; Ruby, Michael; Pascual, Jose I.; Franke, Katharina J.

    2015-01-01

    The exchange coupling between magnetic adsorbates and a superconducting substrate leads to Shiba states inside the superconducting energy gap and a Kondo resonance outside the gap. The exchange coupling strength determines whether the quantum many-body ground state is a Kondo singlet or a singlet of the paired superconducting quasiparticles. Here we use scanning tunnelling spectroscopy to identify the different quantum ground states of manganese phthalocyanine on Pb(111). We observe Shiba states, which are split into triplets by magnetocrystalline anisotropy. Their characteristic spectral weight yields an unambiguous proof of the nature of the quantum ground state. Our results provide experimental insights into the phase diagram of a magnetic impurity on a superconducting host and shine light on the effects induced by magnetic anisotropy on many-body interactions. PMID:26603561

  4. Charge and magnetic states of rutile TiO2 doped with Cr ions.

    PubMed

    Kim, Rokyeon; Cho, Suyeon; Park, Won-Goo; Cho, Deok-Yong; Oh, Se-Jung; Saint-Martin, Romuald; Berthet, Patrick; Park, Je-Geun; Yu, Jaejun

    2014-04-01

    We observe that the electronic and magnetic properties of Cr-doped rutile TiO2 single crystals are highly dependent on growth conditions. The ferromagnetic component of magnetic susceptibility is observed to be enhanced for samples grown under oxygen-rich conditions. To understand the charge state of Cr dopants and their role in response to an external magnetic field, we carry out density functional theory calculations for Cr-doped rutile TiO2. Using the results of formation energy calculations in the presence of oxygen vacancies and Cr atom substitution at the Ti sites, we demonstrate that the Cr3+ state is a source of Curie-Weiss-type magnetic response, whereas the Cr4+ defect states contribute to the ferromagnetic component. We also provide the electronic structures of various defect configurations and attempt to explain the optical and electronic properties of the Cr-doped system. PMID:24651728

  5. Magnetic flux conversion and relaxation toward a minimum-energy state in S-1 spheromak plasmas

    SciTech Connect

    Janos, A.

    1985-09-01

    S-1 Spheromak currents and magnetic fluxes have been measured with Rogowski coils and flux loops external to the plasma. Toroidal plasma currents up to 350 kA and spheromak configuration lifetimes over 1.0 msec have been achieved at moderate power levels. The plasma formation in the S-1 Spheromak device is based on an inductive transfer of poloidal and toroidal magnetic flux from a toroidal ''flux core'' to the plasma. Formation is programmed to guide the configuration into a force-free, minimum-energy Taylor state. Properly detailed programming of the formation process is found not to be essential since plasmas adjust themselves during formation to a final equilibrium near the Taylor state. After formation, if the plasma evolves away from the stable state, then distinct relaxation oscillation events occur which restore the configuration to that stable state. The relaxation process involves reconnection of magnetic field lines, and conversion of poloidal to toroidal magnetic flux (and vice versa) has been observed and documented. The scaling of toroidal plasma current and toroidal magnetic flux in the plasma with externally applied currents is consistent with the establishment of a Taylor state after formation. In addition, the magnetic helicity is proportional to that injected from the flux core, independent of how that helicity is generated.

  6. Multi-bits memory cell using degenerated magnetic states in a synthetic antiferromagnetic reference layer

    NASA Astrophysics Data System (ADS)

    Fukushima, Akio; Yakushiji, Kay; Konoto, Makoto; Kubota, Hitoshi; Imamura, Hiroshi; Yuasa, Shinji

    2016-02-01

    We newly developed a magnetic memory cell having multi-bit function. The memory cell composed of a perpendicularly magnetized magnetic tunnel junction (MB-pMTJ) and a synthetic antiferromagnetic reference layer. The multi-bit function is realized by combining the freedom of states of the magnetic free layer and that in the antiferromagnetically coupled reference layer. The structure of the reference layer is (FeB/Ta/[Co/Pt]3)/Ru/([Co/Pt]6); the top and the bottom layers are coupled through Ru layer where the reference layer has two degrees of freedom of a head-to-head and a bottom-to-bottom magnetic configuration. A four-state memory cell is realized by combination of both degrees of freedom. The states in the reference layer however is hardly detected by the total resistance of MB-pMTJ, because the magnetoresistance effect in the reference layer is negligibly small. That implies that the resistance values for the different states in the reference layer are degenerated. On the other hand, the two different states in the reference layer bring different stray fields to the free layer, which generate two different minor loop with different switching fields. Therefore, the magnetic states in the reference layer can be differentiated by the two-step reading, before and after applying the appropriately pulsed magnetic field which can identify the initial state in the reference layer. This method is similar to distinguishing different magnetic states in an in-plane magnetized spin-valve element. We demonstrated that four different states in the MB-pMTJ can be distinguished by the two-step read-out. The important feature of the two-step reading is a practically large operation margins (large resistance change in reading) which is equal to that of a single MTJ. Even though the two-step reading is a destructive method by which 50% of the magnetic state is changed, this MB-pMTJ is promising for high density non-volatile memory cell with a minor cost of operation speed.

  7. 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.

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

    DOE PAGESBeta

    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.

  9. Solid-state magnetic resonance spectroscopy of fullerenes

    SciTech Connect

    Tycko, R.; Haddon, R.C.; Dabbagh, G.; Glarum, S.H.; Douglass, D.C.; Mujsce, A.M. )

    1991-01-24

    The authors report solid-state {sup 13}C NMR measurements on powder samples of C{sub 60} and of a mixture of C{sub 60} and C{sub 70}. The NMR results show that, at 296 K, C{sub 60} molecules rotate rapidly and isotropically in the solid state, while C{sub 70} molecules rotate somewhat more anisotropically. These results are consistent with the proposed spherical geometry of C{sub 60} and prolate spheroidal geometry of C{sub 70}. The rotational correlation time of C{sub 60} molecules in the solid state becomes greater than 50 {mu}s at about 100 K.

  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. Of the nature of a hot, ``strongly-'' magnetized plasma state -in thermal equilibrium- in astrophysics

    NASA Astrophysics Data System (ADS)

    Berdichevsky, Daniel

    2015-04-01

    The main outcome of this study of constitutive properties of the medium is the estimation of its magnetic permeability, two orders of magnitude smaller than that of the vacuum, i.e., a highly diamagnetic material. (This diamagnetic property is consistent with the superconductivity assumption in magnetohydrodynamics theory, baseline of any macroscopic-scale description of the interplanetary medium.) We propose that a 3-D amorphous Langmuir lattice state is a good representation of the properties of this class of self-organized magnetized matter in solar transients, coronal mass ejections, containing extremely dilute matter strongly dominated by a magnetic field. We further conjecture that the presented state of magnetized matter could be an adequate representation of the `local insterstellar medium region,' in which the solar-system as a whole moves, based on current observations by the spacecraft Voyager 1. The presented interpretation benefits from the observation of many strongly magnetized structures ejected by the Sun, in their march through the interplanetary space evolving consistently with a simple 3-D magnetohydrodynamic model representation. Understanding of the magnetized matter state is gained by means of a case study from 3s in-situ magnetic field and plasma observations in space, which will be outlined in the presentation. (These are SWE and MFI instruments data in spacecraft Wind.)

  12. Coronal Mass Ejections and Magnetic Clouds Modeled as MHD Bounded States

    NASA Astrophysics Data System (ADS)

    Fainberg, J.; Osherovich, V. A.

    2004-12-01

    Multiple loops can be seen in the solar corona before the onset of a coronal mass ejection (CME), during and after the event. We apply multi-toroidal configurations to model CMEs and their interplanetary counterparts - magnetic clouds. In the laboratory, plasma confinement is often achieved by conducting metal walls which introduce elastic forces to maintain equilibrium. Such walls, carrying electric surface currents, usually are taken as boundaries where the magnetic field is truncated to provide finite energy for the configuration. The idea of MHD bounded states as solutions with continuous magnetic field and finite magnetic energy was put forward in 1975 [1]. Such solutions describe a single toroid (ground state) and multiple toroids (excited states) [1],[2]. We analyze noncircular cross sections of such toroids and compare the components of the magnetic field vector with in situ observations in interplanetary magnetic clouds. We present Ulysses spacecraft observations in support of our multi-tube model for interplanetary magnetic clouds based on bounded state MHD configurations with axial and helical symmetry [3],[4]. The interaction of CMEs with the global coronal field will also be discussed. In our presentation, we stress the difference in boundary conditions for magnetic configurations in laboratory and space plasmas. [1] Osherovich, V.A., `On an equilibrium of an MHD config-uration with axial symmetry 1', Soln Dann, 5, p. 70, 1975. [2] Osherovich, V.A. and Lawrence, J.K., `Elaboration of the new magnetohydrostatic sunspot theory (Double return flux model)', Sol. Phys., 88, p. 117, 1983. [3] Krat, V.A. and Osherovich, V.A., `Note on the asymmetry of bipolar sunspot groups', Solar Phys., 59, pp. 43-47, 1978. [4] Osherovich, V.A., Fainberg, J. and Stone, R.G., `Multi-tube model for interplanetary magnetic clouds', Geophys. Res. L., 26(3), pp. 401-404, 1999.

  13. Half-Life and Magnetic Moment of the First Excited State in ^132I

    NASA Astrophysics Data System (ADS)

    Izumi, S.; Tanigaki, M.; Ouchi, H.; Sasaki, A.; Hoshino, S.; Miyashita, Y.; Sato, N.; Shimada, K.; Wakui, T.; Shinozuka, T.; Ohkubo, Y.

    2009-10-01

    The half-life and the magnetic moment of the first excited state in ^132I are reported. There have been a long time confusion on the half-life measurements of the first excited state in ^132I. Several groups performed the lifetime measurements, but the reported values range from 1 ns to 7 ns. The only reported value of the magnetic moment for this state was measured by Singh, but their result should be treated as unreliable because the time-integral perturbed angular correlation technique (TIPAC), which requires the life time data of this state, was used in their measurement. From this point of view, the half-life and the magnetic moment of this state were measured. ^132I was obtained as the radioactive beam of ^132Te and ^132Sb from the newly developed RF-IGISOL (Radio Frequency IGISOL system) at Tohoku University. The half-life for this state was determined to be 1.120 ± 0.015 ns by a conventional coincidence technique with a pair of BaF2 detectors. The TDPAC measurement for the ^132I implanted kinematically into nickel was performed with the help of a strong hyperfine field at iodine site in nickel, and the magnetic moment of this state was determined to be μ=+ (2.06 ± 0.18)μN. The configuration of this state based on the present results will be discussed.

  14. Chain of Majorana states from superconducting Dirac fermions at a magnetic domain wall.

    PubMed

    Neupert, Titus; Onoda, Shigeki; Furusaki, Akira

    2010-11-12

    We study theoretically a strongly type-II s-wave superconducting state of two-dimensional Dirac fermions in proximity to a ferromagnet having in-plane magnetization. It is shown that a magnetic domain wall can host a chain of equally spaced vortices in the superconducting order parameter, each of which binds a Majorana-fermion state. The overlap integral of neighboring Majorana states is sensitive to the position of the chemical potential of the Dirac fermions. Thermal transport and scanning tunneling microscopy experiments to probe the Majorana fermions are discussed. PMID:21231252

  15. 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.

  16. Solving quantum ground-state problems with nuclear magnetic resonance.

    PubMed

    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. 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.

  18. Magnetohydrodynamic modes in a periodic magnetic steady state medium

    NASA Astrophysics Data System (ADS)

    Marcu, A.; Ballai, I.; Pintér, B.

    2006-04-01

    The spatial structuring of solar and space plasmas is known to have a dispersive effect on waves. Many solar features possess a periodic structure with structures having alternating properties. Here the effect of periodic alternation of magnetic slabs on wave propagation is studied when the equilibrium has a steady motion (in line with observations). The dispersion relation for linear compressional waves is derived and analysed. The propagation of waves is studied, in particular modelling the cases of propagation in penumbral filamentary structures in the photosphere, the plume/interplume region and spaghetti structures in the solar wind. Depending on the width of structures (or the wavelength of oscillations) waves have different behaviour. It is shown that the strength of the equilibrium flow has a strong influence on the propagation speed and character of the wave.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Pramanik, Sourav; Ender, A. Ya.; Kuznetsov, V. I.; Chakrabarti, Nikhil

    2015-04-01

    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.

  1. 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.

  2. 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.

  3. Collective states of non-Abelian quasiparticles in a magnetic field

    NASA Astrophysics Data System (ADS)

    Levin, Michael; Halperin, Bertrand I.

    2009-05-01

    Motivated by the physics of the Moore-Read ν=1/2 state away from half filling, we investigate collective states of non-Abelian e/4 quasiparticles in a magnetic field. We consider two types of collective states: incompressible liquids and Wigner crystals. In the incompressible liquid case, we construct a natural series of states which can be thought of as a non-Abelian generalization of the Laughlin states. These states are associated with a series of hierarchical states derived from the Moore-Read state—the simplest of which occur at filling fraction 8/17 and 7/13. Interestingly, we find that the hierarchical states are Abelian even though their parent state is non-Abelian. In the Wigner crystal case, we construct two candidate states. We find that they, too, are Abelian—in agreement with previous analysis.

  4. Simultaneous stabilization of frequency and magnetic field with the tilted 0-0 state

    NASA Astrophysics Data System (ADS)

    Jau, Y.-Y.; Happer, W.

    2005-11-01

    "Tilted" versions of axially symmetric states of alkali-metal atoms can be readily generated by pumping with D1 light of appropriate modulation format. Of particular interest is the tilted 0-0 state, that can be generated by push-pull pumping with additional pulse modulation at the Zeeman frequency. The tilted 0-0 state can be used to simultaneously lock a magnetic field and a clock frequency.

  5. 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.

  6. 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

  7. 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.

  8. The magnetic ground state and relationship to Kitaev physics in α-RuCl3

    NASA Astrophysics Data System (ADS)

    Banerjee, Arnab

    The 2D Kitaev candidate alpha-RuCl3 consists of stacked honeycomb layers weakly coupled by Van der Waals interactions. Here we report the measurements of bulk properties and neutron diffraction in both powder and single crystal samples. Our results show that the full three dimensional magnetic ground state is highly pliable with at least two dominant phases corresponding to two different out-of-plane magnetic orders. They have different Neel temperatures dependent on the stacking of the 2D layers, such as a broad magnetic transition at TN = 14 K as observed in phase-pure powder samples, or a sharp magnetic transition at a lower TN = 7 K as observed in homogeneous single crystals with no evidence for stacking faults. The magnetic refinements of the neutron scattering data will be discussed, which in all cases shows the in-plane magnetic ground state is the zigzag phase common in Kitaev related materials including the honeycomb lattice Iridates. Inelastic neutron scattering in all cases shows that this material consistently exhibit strong two-dimensional magnetic fluctuations leading to a break-down of the classical spin-wave picture. Work performed at ORNL is supported by U.S. Dept. of Energy, Office of Basic Energy Sciences and Office of User Facilities Division.

  9. Mapping the structure and depth to magnetic basement in the United States using the magnetic tilt-depth method

    NASA Astrophysics Data System (ADS)

    Salem, A.; Williams, S.; Fairhead, J.; Ravat, D.; Blakely, R.

    2008-05-01

    We provide a rationale for rapidly assessing the depth and structure of sedimentary basins from magnetic anomaly data. Our methodology is based on "tilt-depth" calculated strictly from first-order derivatives of the total magnetic field. We assume a simple buried vertical contact model such that the 0 degree contour of the tilt derivative closely follows the edge of the vertical contact, while the distance between the 0 and +/-45 degree contours provides an estimate of the depth to the top of the buried contact. We have applied the tilt-depth method to two magnetic databases with very different scales. In the first application, we used the Magnetic Anomaly Map of North America covering the continental United States, gridded at a sample interval of 1 km. Calculated depths show a strong correlation with known areas of shallow basement and sedimentary basins. To quantitatively evaluate the results, we low-pass filtered the calculated depths, desampled the grid to a 1-degree sample interval, and compared with a grid of sediment thickness based on drilling data (Laske and Masters, 1997). In visual comparisons, these two datasets show a striking correlation between basement highs and lows, and, quantitatively, the overall correlation coefficient between the two grids is 0.87. We also applied the tilt-depth methodology to high-resolution aeromagnetic data from the Olympic Peninsula of Washington State. To first order, the Olympic Peninsula is a massive east-plunging anticline consisting of two distinct subduction-related terranes: An essentially nonmagnetic core of highly deformed Tertiary sedimentary rocks, and a periphery of highly magnetic, early Eocene volcanic rocks. The tilt-depth method successfully identified a number of important tectonic elements known from geologic mapping. The steeply dipping thrust contact between core and periphery rocks was clearly delineated, and other more subtle magnetic anomalies within the periphery volcanic rocks and even within the

  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. Massive Dirac surface states in topological insulator/magnetic insulator heterostructures

    NASA Astrophysics Data System (ADS)

    Luo, Weidong; Qi, Xiao-Liang

    2013-03-01

    We study the behavior of topological surface states in heterostructures formed by a topological insulator (TI) and a magnetic insulator (MI). Several MIs with compatible magnetic structure and relatively good lattice matching with TIs are identified, and the best candidate material is found to be MnSe, an anti-ferromagnetic insulator. We perform first-principles calculation in Bi2Se3/MnSe superlattices and obtain the surface state bandstructure. The magnetic exchange coupling with MnSe induces a gap of 54 meV at the surface states. In addition we tune the distance between Mn ions and TI surface to study the distance dependence of the exchange coupling. Finally, we study the band bending effect at the Bi2Se3/MnSe interface, and propose possible solutions to avoid band bending. We acknowledge funding support from the Defense Advanced Research Projects Agency (DARPA).

  12. 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. PMID:24567389

  13. Aging and memory effects in the spin jam states of densely populated frustrated magnets

    NASA Astrophysics Data System (ADS)

    Samarakoon, Anjana; Lee, Seung-Hun; Sato, Taku; Zhou, Haidong; Sinclair, Ryan; Yang, Junjie; Chen, Tianran; Chern, Gia-Wei; Klich, Israel

    Defects and randomness has been largely studied as the key mechanism of glassiness find in a dilute magnetic system. Even though the same argument has also been made to explain the spin glass like properties in dense frustrated magnets, the existence of a glassy state arise intrinsically from a defect free spin system, far from the conventional dilute limit with different mechanisms such as quantum fluctuations and topological features, has been theoretically proposed recently. We have studied field effects on zero-field cooled and field cooled susceptibility bifurcation and memory effects below freezing transition, of three different densely populated frustrated magnets which glassy states we call spin jam, and a conventional dilute spin glass. Our data show common behaviors among the spin jam states, which is distinct from that of the conventional spin glass. We have also performed Monte Carlo simulations to understand the nature of their energy landscapes.

  14. 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.

  15. Quantum pattern recognition with liquid-state nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Neigovzen, Rodion; Neves, Jorge L.; Sollacher, Rudolf; Glaser, Steffen J.

    2009-04-01

    A quantum pattern recognition scheme is presented, which combines the idea of a classic Hopfield neural network with adiabatic quantum computation. Both the input and the memorized patterns are represented by means of the problem Hamiltonian. In contrast to classic neural networks, the algorithm can return a quantum superposition of multiple recognized patterns. A proof of principle for the algorithm for two qubits is provided using a liquid-state NMR quantum computer.

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

    PubMed

    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

  18. 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.

  19. 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.

  20. 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.

  1. 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. PMID:27564572

  2. 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

    SciTech Connect

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

    2012-10-15

    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 Nb{sub 3}Sn 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 {sup 7}Li 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.

  3. Ground state and excitations of quantum dots with magnetic impurities

    NASA Astrophysics Data System (ADS)

    Kaul, Ribhu K.; Ullmo, Denis; Zaránd, Gergely; Chandrasekharan, Shailesh; Baranger, Harold U.

    2009-07-01

    We consider an “impurity” with a spin degree of freedom coupled to a finite reservoir of noninteracting electrons, a system which may be realized by either a true impurity in a metallic nanoparticle or a small quantum dot coupled to a large one. We show how the physics of such a spin impurity is revealed in the many-body spectrum of the entire finite-size system; in particular, the evolution of the spectrum with the strength of the impurity-reservoir coupling reflects the fundamental many-body correlations present. Explicit calculation in the strong- and the weak-coupling limits shows that the spectrum and its evolution are sensitive to the nature of the impurity and the parity of electrons in the reservoir. The effect of the finite-size spectrum on two experimental observables is considered. First, we propose an experimental setup in which the spectrum may be conveniently measured using tunneling spectroscopy. A rate equation calculation of the differential conductance suggests how the many-body spectral features may be observed. Second, the finite-temperature magnetic susceptibility is presented, both the impurity and the local susceptibilities. Extensive quantum Monte Carlo calculations show that the local susceptibility deviates from its bulk scaling form. Nevertheless, for special assumptions about the reservoir—the “clean Kondo box” model—we demonstrate that finite-size scaling is recovered. Explicit numerical evaluations of these scaling functions are given, both for even and odd parities and for the canonical and the grand-canonical ensembles.

  4. 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.

  5. Determination of the Magnetic Ground State of a Polycrystalline Compound Based on Susceptibility Measurements

    SciTech Connect

    Fishman, Randy Scott; Miller, Joel S.

    2011-01-01

    The diruthenium compound [Ru2(O2CMe)4]3[Cr(CN)6] contains two interpenetrating sublattices that behave like giant antiferromagnetically-coupled moments with strong anisotropy. The preferred orientations of the total moment of each sublattice are determined from susceptibility measurements on a polycrystalline sample. In agreement with previous mean-field calculations for the magnetic ground state, the fits to the experimental magnetization imply that the sublattice moments are restricted to cubic diagonals rather than the cubic axis or the edge diagonals. The parameterization of the sublattice susceptibility indicates that the sublattice spin states are more distorted when they are aligned antiparallel.

  6. 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

  7. 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.

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

    PubMed

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

    2015-01-01

    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. PMID:26469373

  9. Anomalous magnetic hyperfine structure of the 229Th ground-state doublet in muonic atoms

    NASA Astrophysics Data System (ADS)

    Tkalya, E. V.

    2016-07-01

    The magnetic hyperfine (MHF) splitting of the ground and low-energy 3 /2+(7.8 ±0.5 eV) levels in the 229Th nucleus in the muonic atom (μ1S1 /2 -229Th) * is calculated considering the distribution of the nuclear magnetization in the framework of the collective nuclear model with wave functions of the Nilsson model for the unpaired neutron. It is shown that (a) deviation of the MHF structure of the isomeric state exceeds 100% from its value for a pointlike nuclear magnetic dipole (the order of sublevels is reversed); (b) partial inversion of levels of the 229Th ground-state doublet and spontaneous decay of the ground state to the isomeric state occur; (c) the E 0 transition, which is sensitive to differences in the mean-square charge radii of the doublet states, is possible between mixed sublevels with F =2 ; and (d) MHF splitting of the 3 /2+ isomeric state may be in the optical range for certain values of the intrinsic gK factor and a reduced probability of a nuclear transition between the isomeric and the ground states.

  10. Magnetic ground state and electronic structure of CeRu(2)Al(10).

    PubMed

    Goraus, Jerzy; Ślebarski, Andrzej

    2012-03-01

    We present a combined theoretical and experimental study of the electronic structure for CeRu(2)Al(10) based on ab initio band structure calculations and x-ray photoemission spectroscopy (XPS) data. Our calculations were performed for the base unit cell and for the hypothetical unit cell which enables antiferromagnetic ordering. The stability of the magnetic phase was investigated within fixed spin moment calculations. When additional 4f correlations are not included in the LSDA C U approach, CeRu(2)Al(10) exhibits an unstable magnetic configuration with the difference in total energy per unit cell between the weakly magnetic state and the non-magnetic one of the order ~0.3 meV. We found that Coulomb correlations among 4f electrons, when they are included in the LSDA C U approach, stabilize the magnetic structure. In the weakly correlated system (small U) an antiferromagnetic (AFM) ground state with the lowest total energy is preferred. The situation is, however, the opposite when the 4f correlations are strong. In this case the ferromagnetic (FM) ground state is preferred. By comparing our calculations with the experimental data we conclude that the 4f correlations in CeRu(2)Al(10) are weak. We also carried out a structural relaxation of atomic positions within the Cmcm unit cell and we found that the Al atoms exhibit noticeable displacement from their positions known from x-ray diffraction (XRD) analysis. PMID:22329993

  11. Variable-State-Dimension Kalman-based Filter for orientation determination using inertial and magnetic sensors.

    PubMed

    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

  12. Magnetic Properties of Brazilian Peats From SA~o Paulo State

    NASA Astrophysics Data System (ADS)

    Berquó, T. S.; Thompson, R.; Partiti, C. S. M.

    The low temperature magnetic properties of peats from middle Paraíba do Sul Valley (São Paulo State) Brazil have been studied in 5 meter long cores with maximum radio- carbon ages of around 11,000 years BP. The magnetic susceptibility in general is low, but consistently presents an increase near the bottom of profile. Results from Möss- bauer spectroscopy indicate the presence of Fe3+ and Fe2+ at the bottom of cores, but only de presence of Fe3+ at the top of cores. The additional Fe2+ at the bottom of cores, may be related to the higher magnetic susceptibility. Measurements from a SQUID magnetometer MPMS XL show a strong (super)paramagnetic behavior in (i) hysteresis loops (fields up to 6 T, at both room temperature and 10K) and in (ii) low temperature magnetic curves. Slope changes on 1/ plots indicate that two mag- netic components are responsible for the low temperature magnetic properties. During heating using a Bartington (air atmosphere) susceptibility bridge, some peat samples generate new phases with higher magnetic susceptibility than initially. The new phases have reversible magnetic properties and Curie temperatures of around 580oC. These samples usually are from the bottom of the core.

  13. Investigation of complex magnetic state in LaBiMnO3

    NASA Astrophysics Data System (ADS)

    Dayal, Vijaylakshmi; Punith Kumar, V.

    2014-06-01

    We present here the results of a comprehensive study of the DC magnetization, linear and nonlinear AC susceptibility, DC resistivity and Magnetotransport behavior of the La0.8Bi0.2MnO3 polycrystalline manganite to understand its complex magnetic nature. The sample under study is synthesized by a conventional solid state route and is found to crystallize in rhombohedral structure having R3barc group. A significant irreversibility between zero-field-cooled and field-cooled magnetization data with a broad peak in ZFC is clearly observed. Temperature variation of first and third order AC susceptibilities is in good agreement with Wohlfarth's Model for Superparamagnetism (SPM). The analysis of history dependence of DC magnetization, linear and non-linear AC susceptibility provides evidence of SPM like behavior associated along with weak ferromagnetism in the sample at low temperature. The results are supported by the electrical resistivity and Magnetotransport measurements.

  14. 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

  15. Magnetic moment of the 3/2 + state in 165Ho

    NASA Astrophysics Data System (ADS)

    Tanigaki, M.; Ohkubo, Y.; Taniguchi, A.; Izumi, S.; Shinozuka, T.

    2010-06-01

    The Larmor precession for the 362 keV state in 165Ho( I π = 3/2 + , T 1/2 = 1.512 μs) in Dy2O3 with an external magnetic field of 0.3 T was determined to be - 32.3 ± 0.6 MHz by use of the perturbed angular correlation technique, intending to determine the magnetic moment and apply it to the measurement of the hyperfine field at Ho in Fe. The magnetic moment for this state was tentatively deduced under the assumption that the paramagnetic correction factor for a free Ho3 + ion is applicable to the present case. The independent A 22 measurement for the 633 - 362 keV γ cascade for the sign assignment of the Larmor frequency is inconsistent with that from known multipolarities and mixing ratios for this cascade, implying that the mixing ratios may be different from the reported values.

  16. Unusual Magnetic State in Lithium-Doped MoS2 Nanotubes

    NASA Astrophysics Data System (ADS)

    Mihailovic, D.; Jaglicic, Z.; Arcon, D.; Mrzel, A.; Zorko, A.; Remskar, M.; Kabanov, V. V.; Dominko, R.; Gaberscek, M.; Gómez-García, C. J.; Martínez-Agudo, J. M.; Coronado, E.

    2003-04-01

    We report on the very peculiar magnetic properties of an ensemble of very weakly coupled lithium-doped MoS2 nanotubes. The magnetic susceptibility χ of the system is nearly 3orders of magnitude greater than in typical Pauli metals, yet there is no evidence for any instability which would alleviate this highly frustrated state. Instead, the material exhibits peculiar paramagnetic stability down to very low temperatures, with no evidence of a quantum critical point as T→0 in spite of clear evidence for strongly correlated electron behavior. The exceptionally weak intertube interactions appear to lead to a realization of a near-ideal one-dimensional state in which fluctuations prevent the system from reordering magnetically or structurally.

  17. 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.

  18. Controlling the magnetic-field sensitivity of atomic-clock states by microwave dressing

    NASA Astrophysics Data System (ADS)

    Sárkány, L.; Weiss, P.; Hattermann, H.; Fortágh, J.

    2014-11-01

    We demonstrate control of the differential Zeeman shift between clock states of ultracold rubidium atoms by means of nonresonant microwave dressing. Using the dc field dependence of the microwave detuning, we suppress the first- and second-order differential Zeeman shift in magnetically trapped 87Rb atoms. By dressing the state pair 5 S1 /2 F =1 , mF=-1 and F =2 , mF=1 , a residual frequency spread of <0.1 Hz in a range of 100 mG around a chosen magnetic offset field can be achieved. This is one order of magnitude smaller than the shift of the bare states at the magic field of the Breit-Rabi parabola. We further identify double magic points, around which the clock frequency is insensitive to fluctuations both in the magnetic field and in the dressing Rabi frequency. The technique is compatible with chip-based cold-atom systems and allows the creation of clock and qubit states with reduced sensitivity to magnetic-field noise.

  19. Ion charge state distributions of pulsed vacuum arc plasmas in strong magnetic fields

    SciTech Connect

    Anders, A.; Yushkov, G.; Oks, E.; Nikolaev, A.; Brown, I.

    1998-02-01

    Vacuum arc plasmas with discharge currents of 300 A and duration 250 {mu}s have been produced in strong magnetic fields up to 4 T. Ion charge state distributions have been measured for C, Al, Ag, Ta, Pt, Ho, and Er with a time-of-flight charge-mass spectrometer. Our previous measurements have been confirmed which show that ion charge states can be considerably enhanced when increasing the magnetic field up to about 1 T. The new measurements address the question of whether or not the additional increase continues at even higher magnetic field strength. It has been found that the increase becomes insignificant for field strengths greater than 1 T. Ion charge state distributions are almost constant for magnetic field strengths between 2 and 4 T. The results are explained by comparing the free expansion length with the freezing length. The most significant changes of charge state distributions are observed when these lengths are similar. {copyright} {ital 1998 American Institute of Physics.}

  20. Frozen Spin Ice Ground States in the Pyrochlore Magnet Tb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Fritsch, Katharina

    2015-03-01

    The ground state nature of the candidate spin liquid pyrochlore magnet Tb2Ti2O7 has remained a puzzle for over 15 years. Despite theoretical expectations of magnetic order below ~ 1 K based on classical Ising-like Tb 3 + spins, early μSR and neutron scattering experiments showed no long range order down to 50 mK. This motivated two theoretical scenarios to account for the apparently disordered ground state: a quantum spin ice scenario in which the classical spin order is suppressed by virtual crystal field excitations that renormalize the antiferromagnetic exchange, or a scenario arising from a yet to be observed structural distortion creating a non-magnetic singlet ground state. I will discuss our time-of-flight neutron scattering measurements on Tb2Ti2O7 that reveal a glassy spin ice ground state, characterized by frozen antiferromagnetic short range order and the formation of a ~ 0.08 meV energy gap in its spin excitation spectrum at the (1/2,1/2,1/2) quasi-ordering wave vectors. A new H - T phase diagram for Tb2Ti2O7 in [110] magnetic field will be presented. I will further discuss recent experiments on slightly off-stoichiometric Tb2+xTi2-xO7-y samples, which also display the same gapped spin ice correlations at (1/2,1/2,1/2) wave vectors.

  1. 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

    2015-01-01

    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

  2. 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

  3. Spatially Resolved Observation of Static Magnetic Flux States in YBa_2Cu_3O7-δ Grain Boundary Josephson Junctions

    NASA Astrophysics Data System (ADS)

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

    1994-02-01

    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_2Cu_3O7-δ 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.

  4. Pressure dependence of the magnetic ground states in MnP

    NASA Astrophysics Data System (ADS)

    Dissanayake, Sachith; Matsuda, Masaaki; Cheng, J.-G.; Ye, F.; Chi, S.; Ma, J.; Zhou, H. D.; Yan, J.-Q.; Kasamatsu, S.; Sugino, O.; Kato, T.; Matsubayashi, K.; Okada, T.; Uwatoko, Y.

    The newly discovered superconductor MnP shows a ferromagnetic order below T,SUB>C ~ 290 K followed by a helical order below Ts ~ 50 K in ambient pressure. An antiferromagnetic order is suggested in the vicinity of the pressure induced superconducting phase. We have performed single crystal neutron diffraction experiments to determine the magnetic structure 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 is gradually suppressed below a characteristic temperature. At 4 GPa no magnetic signal was observed down to 3.5 K. Our results suggested that the new magnetic phase in the vicinity of the superconducting phase is in a short-ranged magnetic state due to frustration or in an itinerant magnetic state, where the itinerant small Mn moments are weakly interacting. This research at ORNL's HFIR and SNS was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

  5. Stabilization of Ferromagnetic States by Electron Doping in ZnO-Based Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2001-03-01

    In order to investigate functionality of ZnO as a diluted magnetic semiconductor (DMS), we had studied the magnetism in ZnO doped with 3d transition metal atoms (TM) and showed that it was also a candidate for a new functional magnetic material [1]. In this paper, we develop our previous work and give detailed materials design with ZnO-based DMS based on ab initio calculations. The electronic structure of a TM-doped ZnO was calculated within the local density approximation by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation. Total energies of Zn_1-xTM^\\uparrow_xO and Zn_1-xTM^\\uparrow_x/2TM^downarrow_x/2O, where up and down arrows mean the directions of respective atomic magnetic moments, were compared and appearance of the ferromagnetism was discussed. Effects of carrier doping to these systems were also considered. It was found that their magnetic states were controllable by changing the carrier density. In particular, ferromagnetic states were stabilized by electron doping in the case of Fe, Co or Ni doped ZnO. From the point of practical applications, it is favorable feature to realize high Curie temperature ferromagnet, because n-type ZnO is easily available. [1] K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys. 39 (2000) L555.

  6. Rydberg states of helium in electric and magnetic fields of arbitrary relative orientation

    NASA Astrophysics Data System (ADS)

    Tkáč, Ondřej; Žeško, Matija; Agner, Josef A.; Schmutz, Hansjürg; Merkt, Frédéric

    2016-05-01

    A spectroscopic study of Rydberg states of helium (n = 30 and 45) in magnetic, electric and combined magnetic and electric fields with arbitrary relative orientations of the field vectors is presented. The emphasis is on two special cases where (i) the diamagnetic term is negligible and both paramagnetic Zeeman and Stark effects are linear (n = 30, B ≤ 120 mT and F = 0–78 V cm‑1), and (ii) the diamagnetic term is dominant and the Stark effect is linear (n = 45, B = 277 mT and F = 0–8 V cm‑1). Both cases correspond to regimes where the interactions induced by the electric and magnetic fields are much weaker than the Coulomb interaction, but much stronger than the spin–orbit interaction. The experimental spectra are compared to spectra calculated by determining the eigenvalues of the Hamiltonian matrix describing helium Rydberg states in the external fields. The spectra and the calculated energy-level diagrams in external fields reveal avoided crossings between levels of different m l values and pronounced m l -mixing effects at all angles between the electric- and magnetic-field vectors other than 0. These observations are discussed in the context of the development of a method to generate dense samples of cold atoms and molecules in a magnetic trap following Rydberg–Stark deceleration.

  7. Stable bound states of like charges on top of graphene in magnetic field

    NASA Astrophysics Data System (ADS)

    Slizovskiy, Sergey

    We show theoretically that in the external magnetic field like charges on top of graphene monolayer may be mutually attracted to form thermodinamically stable macro-molecules. For this to happen graphene needs to be in Quantum Hall plateau state with local chemical potential being between the Landau levels. Graphene electron(s) gets localized in the middle between charges and provides overscreening of Coulomb repulsion between the charges. The size of the resulting macro-molecules is of the order of the magnetic length (~ 10 nm for magnetic field 10 T). The possible stable macro-molecules that unit charges can form on graphene in magnetic field are classified. The binding survives significant temperatures, exceeding mobility barriers for many ionically bond impurities. The influence of possible lattice-scale effects of valley-mixing are discussed. Tuning the doping of graphene or the magnetic field, the binding of impurities can be turned on and off and the macro-molecule size may be tuned. This opens the perspective to nanoscopic manipulation of ions on graphene by using magnetic field and gating. Acknowledge EPSRC EP/l02669X/1 and EP/H049797/1 and RSF Grant 14-22-00281.

  8. Quasiparticle states and quantum interference induced by magnetic impurities on a two-dimensional topological superconductor

    NASA Astrophysics Data System (ADS)

    Fu, Zhen-Guo; Zhang, Ping; Wang, Zhigang; Li, Shu-Shen

    2012-04-01

    We theoretically study the effect of localized magnetic impurities on two-dimensional topological superconductor (TSC). We show that the local density of states (LDOS) can be tuned by the effective exchange field m, the chemical potential μ of TSC, and the distance Δr as well as the relative spin angle α between two impurities. The changes in Δr between two impurities alter the interference and result in significant modifications to the bonding and antibonding states. Furthermore, the bound-state spin LDOS induced by single and double magnetic impurity scattering, the quantum corrals and the quantum mirages are also discussed. Finally, we briefly compare the impurities in TSC with those in topological insulators.

  9. 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.

  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. Charge and magnetic states of Mn-, Fe-, and Co-doped monolayer MoS{sub 2}

    SciTech Connect

    Lin, Xianqing; Ni, Jun

    2014-07-28

    First-principles calculations have been performed to investigate the electronic and magnetic properties of monolayer MoS{sub 2} substitutionally doped with Mn, Fe, and Co in possible charge states (q). We find that the Mn, Fe, and Co dopants substituting for a Mo atom in monolayer MoS{sub 2} (Mn@Mo, Fe@Mo, and Co@Mo) are all magnetic in their neutral and charge states except in the highest positive charge states. Mn@Mo, Fe@Mo, and Co@Mo have the same highest negative charge states of q=−2 for chemical potential of electron just below the conduction band minimum, which corresponds to the electron doping. In the q=−2 state, Mn@Mo has a much larger magnetic moment than its neutral state with the antiferromagnetic coupling between the Mn dopant and its neighboring S atoms maintained, while Fe@Mo and Co@Mo have equal or smaller magnetic moments than their neutral states. The possible charge states of Mn@Mo, Fe@Mo, and Co@Mo and the variation of the magnetic moments for different dopants and charge states are due to the change of the occupation and energy of the anti-bonding defect levels in the band gap. The rich magnetic properties of the neutral and charge states suggest possible realization of the substitutionally Mn-, Fe-, and Co-doped monolayer MoS{sub 2} as dilute magnetic semiconductors.

  12. The Ground State of Monolayer Graphene in a Strong Magnetic Field

    NASA Astrophysics Data System (ADS)

    Wu, Lian-Ao; Guidry, Mike

    2016-03-01

    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.

  13. 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

  14. Atomic-Scale Imaging and Control of Interface Magnetic States in Vacancy Ordered Cobaltite Thin Films

    NASA Astrophysics Data System (ADS)

    Borisevich, Albina; Kim, Young-Min; Biegalski, Michael; He, Jun; Christen, Hans; Pantelides, Sokrates; Pennycook, Stephen

    2012-02-01

    Magnetic properties of complex oxide thin films are strongly affected by strain, chemical composition, and octahedral tilt of the substrate. Here, we study lanthanum/strontium cobaltite (La0.5Sr0.5CoO3-x, LSCO) thin films via quantitative aberration-corrected scanning transmission electron microscopy and Electron Energy Loss Spectroscopy (EELS) to explore the coupling between magnetic properties, ionic behavior, and oxygen octahedral tilts. LSCO films were grown by PLD in identical conditions on two different substrates, LSAT (cubic) and NGO (orthorhombic). These substrates have nearly identical lattice parameters, but different octahedral tilts. The film on NGO appears to be La0.5Sr0.5CoO2.5, while the film on LSAT is less oxygen deficient. Comparison of measured lattice parameters with the first-principles calculations allows us to determine oxygen content in the film. In La0.5Sr0.5CoO2.5/NGO films, EELS reveals different valence states of Co at the interface depending on termination, resulting in different magnetic states. Therefore changes in octahedral tilts can induce changes in oxygen stoichiometry and interface magnetic states of the vacancy ordered structures.

  15. A multi-state magnetic memory dependent on the permeability of Metglas

    SciTech Connect

    Petrie, J. R.; Wieland, K. A.; Timmerwilke, J. M.; Burke, R. A.; Newburgh, G. A.; Fischer, G. A.; Edelstein, A. S.; Barron, S. C.; Burnette, J. E.

    2015-04-06

    A three-state magnetic memory was developed based on differences in the magnetic permeability of a soft ferromagnetic media, Metglas 2826MB (Fe{sub 40}Ni{sub 38}Mo{sub 4}B{sub 18}). 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.

  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. 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.

  18. 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.

  19. 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. .

  20. 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.

  1. Thermo-magnetic history effects in the vortex state of YNi2B2C superconductor

    NASA Astrophysics Data System (ADS)

    Das, Pradip; Tomy, C. V.; Takeya, H.; Ramakrishnan, S.; Grover, A. K.

    2009-03-01

    The nature of five-quadrant magnetic isotherms for H parallel a is different from that for H parallel c in a single crystal of YNi2B2C, pointing towards an anisotropic behaviour of the flux line lattice (FLL). For H parallel a, a well defined peak effect (PE) and second magnetization peak (SMP) can be observed and the loop is open prior to the PE. However, for H parallel c, the loop is closed and one can observe only the PE. We have investigated the history dependence of magnetization hysteresis data for H parallel a by recording minor hysteresis loops. The observed history dependence in JC{H) across different anomalous regions are rationalized on the basis of superheating/supercooling of the vortex matter across the first-order-like phase transition and possible additional effects due to annealing of the disordered vortex bundles to the underlying equilibrium state.

  2. 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

  3. Enhanced diffusion and anomalous transport of magnetic colloids driven above a two-state flashing potential.

    PubMed

    Tierno, Pietro; Shaebani, M Reza

    2016-04-14

    We combine experiments and theory to investigate the diffusive and the 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 H0 of the driving field, the dynamics of the particle resemble an ordinary random walk with a frequency-dependent diffusion coefficient. However, subdiffusive and oscillatory dynamics at short time scales are observed when decreasing H0. 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 the slightly irregular shape of bubbles. PMID:26936328

  4. Novel magnetic states in insulating d4 oxides with strong spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Svoboda, Christopher; Trivedi, Nandini

    2015-03-01

    The comparable energy scales in 4 d and 5 d transition metal oxides, arising from Coulomb correlations, spin-orbit coupling and bandwidth, can lead to new phases and phenomena. With this motivation we examine an ion with d4 electron configuration in the t2 g sector separated from the other states by crystal field splitting. Upon including spin-orbit coupling, the completely filled j = 3 / 2 manifold is nonmagnetic but with a nonzero magnetic susceptibility. Upon introducing hopping between two d4 atoms, we find novel entangled ferromagnetism generated by the superexchange interaction in a significant part of the phase diagram. We further present results for the temperature dependent susceptibility calculated using exact diagonalization to illustrate this novel magnetic behavior and the role Hund's coupling plays in producing these phases. We make predictions for resonant X-ray scattering and magnetic measurements in pyrochlore osmates. We acknowledge the support of the CEM, and NSF MRSEC, under Grant DMR-1420451.

  5. 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

    2015-03-01

    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 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. PMID:25793847

  6. Precision Hyperfine Structure of 2;^3P State of ^3He with External Magnetic

    NASA Astrophysics Data System (ADS)

    Wu, Qixue; Drake, G. W. F.

    2007-06-01

    The theory of the Zeeman effect can be used to extrapolate precise measurements for the fine structure or the hyperfine structure to zero-field strength. In the present work, the hyperfine structure of 2;^3P state of ^3He with external magnetic fields is precisely calculated. The values of the fields for 32 crossings and five anticrossings of the magnetic sublevels are theoretically predicted for magnetic field strengths up to 1 Tesla. The results are compared with experimental work. We include the linear terms, diamagnetic terms, and the 2̂ relativistic correction terms in the Zeeman Hamiltonian. All related matrix elements are calculated with high accuracy by the use of double basis set Hylleraas type variational wave functions[1,2].[1] Z. -C. Yan and G.W.F. Drake, Phys. Rev. A 50, R1980 (1994).[2] Q. Wu and G.W.F. Drake, J. Phys. B 40, 393 (2007).

  7. Localization and magnetism of the resonant impurity states in Ti doped PbTe

    SciTech Connect

    Wiendlocha, Bartlomiej

    2014-09-29

    The problem of localization of the resonant impurity states is discussed for an illustrative example of Titanium doped Lead Telluride. Electronic structure of PbTe:Ti is studied using first principles methods, densities of states, and Bloch spectral functions are analyzed. We show that Ti creates resonant states in the conduction band of PbTe, however, spectral functions of the system strongly suggest localization of these states and show poor hybridization with PbTe electronic structure. The contrast between results presented here and previously reported spectral functions for PbTe:Tl correlate very well with the different effect of those impurities on thermopower (S) of PbTe, which is large increase is S for PbTe:Tl and almost no effect on S for PbTe:Ti. Moreover, magnetic properties of the system are studied and formation of magnetic moments on Ti atoms is found, both for ordered (ferromagnetic) and disordered (paramagnetic-like) phases, showing that PbTe:Ti can be a magnetic semiconductor.

  8. Compatible operation of the power system for steady state and pulse modes in a magnetic torus KT-5D

    NASA Astrophysics Data System (ADS)

    Yu, Yi; Wang, Zhi-jiang; Xu, Min; Zhu, Zhen-hua; Lu, Rong-hua; Wen, Yi-zhi; Yu, Chang-xuan; Wan, Shu-de; Liu, Wan-dong; Wang, Jun; Xu, Xiao-yuan; Hu, Ling-ying

    2006-12-01

    Compatible operation of steady state mode and pulse mode is realized in the KT-5D device. New power supplies with the operation control systems for the steady state toroidal magnetic field as well as for the vertical field are added, and the rf wave injection systems for sustaining steady state plasmas are upgraded. After the modification, the device now can work not only as a tokomak with pulsed plasma currents as it was but also as a simple magnetized torus with steady state plasma discharges. It allows more flexible and efficient experimental researches on the magnetically confined plasmas to be carried on in the same device.

  9. 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.

  10. Structural specifics of light-induced metastable states in copper(II)-nitroxide molecular magnets.

    PubMed

    Barskaya, I Yu; Veber, S L; Fokin, S V; Tretyakov, E V; Bagryanskaya, E G; Ovcharenko, V I; Fedin, M V

    2015-12-28

    Although light-induced magnetostructural switching in copper(II)-nitroxide molecular magnets Cu(hfac)2L(R) has been known for several years, structural characterization of metastable photoinduced states has not yet been accomplished due to significant technical demands. In this work we apply, for the first time, variable-temperature FTIR spectroscopy with photoexcitation to investigate the structural specifics of light-induced states in the Cu(hfac)2L(R) family represented by (i) Cu(hfac)2L(Me) comprising two-spin copper(II)-nitroxide clusters, and (ii) Cu(hfac)2L(Pr) comprising three-spin nitroxide-copper(II)-nitroxide clusters. The light-induced state of Cu(hfac)2L(Me) manifests the same set of vibrational bands as the corresponding thermally-induced state, implying their similar structures. For the second compound Cu(hfac)2L(Pr), the coordination environment of copper(II) is similar in light- and thermally-induced states, but distinct differences are found for packing of the peripheral n-propyl substituent of nitroxide. Thus, generally the structures of the corresponding thermally- and light-induced states in molecular magnets Cu(hfac)2L(R) might differ, and FTIR spectroscopy provides a useful approach for revealing and elucidating such differences. PMID:26571045