Study on elimination of screening-current-induced field in pancake-type non-insulated HTS coil

NASA Astrophysics Data System (ADS)

Kim, K. L.; Song, J. B.; Yang, D. G.; Kim, Y. G.; Kim, T. H.; Kim, S. K.; Park, M. W.; Lee, H. G.

2016-03-01

This paper presents the details of a recent study on the removal of the screening-current-induced field (SCIF) in a pancake-type non-insulated high-temperature superconductor coil (NI coil). To determine the SCIF in the NI coil, the magnetic flux density (B z ) was calculated using the equivalent circuit model of the coil and compared to the B z obtained empirically. The experimental results indicate that the SCIF elimination in the NI coil was enhanced upon increasing the amplitude and frequency of the AC current being supplied to the background coil. Moreover, the SCIF in the NI coil was successfully removed by applying the appropriate external AC magnetic field intensity. This is because the magnetization direction of the SCIF changed completely from radial to spiral, a phenomenon termed the ‘vortex shaking effect.’ Overall, this study confirmed that the SCIF in a pancake-type NI coil can be effectively removed by exposing the coil to an external AC magnetic field.

Nonlinear spin susceptibility in topological insulators

NASA Astrophysics Data System (ADS)

Shiranzaei, Mahroo; Fransson, Jonas; Cheraghchi, Hosein; Parhizgar, Fariborz

2018-05-01

We revise the theory of the indirect exchange interaction between magnetic impurities beyond the linear response theory to establish the effect of impurity resonances in the surface states of a three-dimensional topological insulator. The interaction is composed of isotropic Heisenberg, anisotropic Ising, and Dzyaloshinskii-Moriya types of couplings. We find that all three contributions are finite at the Dirac point, which is in stark contrast to the linear response theory which predicts a vanishing Dzyaloshinskii-Moriya-type contribution. We show that the spin-independent component of the impurity scattering can generate large values of the Dzyaloshinskii-Moriya-type coupling in comparison with the Heisenberg and Ising types of couplings, while these latter contributions drastically reduce in magnitude and undergo sign changes. As a result, both collinear and noncollinear configurations are allowed magnetic configurations of the impurities.

Unconventional dynamics of electrons in topological insulators in a magnetic field: Berry phase effects

NASA Astrophysics Data System (ADS)

Demikhovskii, V. Ya.; Turkevich, R. V.

2015-04-01

The semiclassical dynamics of charge carriers moving over the surface of a Bi2Te3-type 3D topological insulator in a static magnetic field is studied. The effects related to the changes in the symmetry of constant energy surfaces (contours), as well as to the nonzero Berry curvature, are taken into account. It is shown that effects related both to the anomalous velocity proportional to the Berry curvature and to the distortions of the trajectories stemming from the additional contribution to the energy proportional the orbital magnetic moment of a wave packet appear in contrast to the conventional dynamics of electrons moving in a uniform static magnetic field along trajectories determined by the conditions E( k) = const and p z = const. This should lead to changes in the cyclotron resonance conditions for surface electrons. Although the magnetic field breaks the time-reversal symmetry and the topological order, the studies of the cyclotron resonance allow finding out whether a given insulator is a trivial one or not in zero magnetic field.

Effect of oxygen vacancies on magnetic and transport properties of Sr2IrO4

NASA Astrophysics Data System (ADS)

Dwivedi, Vinod Kumar; Mukhopadhyay, Soumik

2018-05-01

Iridates have recently attracted growing interest because of their potential for realizing various interesting phases like interaction driven Mott-type insulator and magnetically driven Slater-type. In this paper, we present the magnetic and electrical transport properties of polycrystalline Sr2IrO4 synthesized by solid state reaction route. We find a ferromagnetic transition at 240 K. The Curie-Weiss law behavior hold good above the magnetic transition temperature TMag = 240 K with a small effective paramagnetic magnetic moment μeff = 0.25 µB/f.u. and a Curie-Weiss temperature, θCW = +100 K. Zero field cooled (ZFC) magnetization shows a gradual dcrease below 150 K, while same for field cooled (FC) below 50 K. Interestingly, below temperatures, ⁓ 10 K, a sharp increase in ZFC and FC magnetization can be seen. A temperature dependent resistivity reveals insulating behavior followed by power law mechanism. The sintering of sample in air leads to the very low value of resistivity is likely related to Sr or oxygen vacancies.

Thermal conductivity and Kapitza resistance of epoxy resin fiberglass tape at superfluid helium temperature

NASA Astrophysics Data System (ADS)

Baudouy, B.; Polinski, J.

2009-03-01

The system of materials composed of fiberglass epoxy resin impregnated tape constitutes in many cases the electrical insulation for "dry"-type superconducting accelerator magnet such as Nb 3Sn magnets. Nb 3Sn magnet technology is still under development in a few programs to reach higher magnetic fields than what NbTi magnets can produce. The European program, Next European Dipole (NED), is one of such programs and it aims to develop and construct a 15 T class Nb 3Sn magnet mainly for upgrading the Large Hardron Collider. Superfluid helium is considered as one possible coolant and since the magnet has been designed with a "dry" insulation, the thermal conductivity and the Kapitza resistance of the electrical insulation are the key properties that must be know for the thermal design of such a magnet. Accordingly, property measurements of the epoxy resin fiberglass tape insulation system developed for the NED project was carried out in superfluid helium. Four sheets with thicknesses varying from 40 to 300 μm have been tested in a steady-state condition. The determined thermal conductivity, k, is [(25.8 ± 2.8) · T - (12.2 ± 4.9)] × 10 -3 W m -1 K -1 and the Kapitza resistance is given by R K = (1462 ± 345) · T(-1.86 ± 0.41) × 10 -6 Km 2 W -1 in the temperature range of 1.55-2.05 K.

Heat transfer through the flat surface of Rutherford superconducting cable samples with novel pattern of electrical insulation immersed in He II

NASA Astrophysics Data System (ADS)

Strychalski, M.; Chorowski, M.; Polinski, J.

2014-05-01

Future accelerator magnets will be exposed to heat loads that exceed even by an order of magnitude presently observed heat fluxes transferred to superconducting magnet coils. To avoid the resistive transition of the superconducting cables, the efficiency of heat transfer between the magnet structure and the helium must be significantly increased. This can be achieved through the use of novel concepts of the cable’s electrical insulation wrapping, characterized by an enhanced permeability to helium while retaining sufficient electrical resistivity. This paper presents measurement results of the heat transfer through Rutherford NbTi cable samples immersed in a He II bath and subjected to the pressure loads simulating the counteracting of the Lorentz forces observed in powered magnets. The Rutherford cable samples that were tested used different electrical insulation wrapping schemes, including the scheme that is presently used and the proposed scheme for future LHC magnets. A new porous polyimide cable insulation with enhanced helium permeability was proposed in order to improve the evacuation of heat form the NbTi coil to He II bath. These tests were performed in a dedicated Claudet-type cryostat in pressurized He II at 1.9 K and 1 bar.

Floquet Engineering of Optical Solenoids and Quantized Charge Pumping along Tailored Paths in Two-Dimensional Chern Insulators

NASA Astrophysics Data System (ADS)

Wang, Botao; Ünal, F. Nur; Eckardt, André

2018-06-01

The insertion of a local magnetic flux, as the one created by a thin solenoid, plays an important role in gedanken experiments of quantum Hall physics. By combining Floquet engineering of artificial magnetic fields with the ability of single-site addressing in quantum gas microscopes, we propose a scheme for the realization of such local solenoid-type magnetic fields in optical lattices. We show that it can be employed to manipulate and probe elementary excitations of a topological Chern insulator. This includes quantized adiabatic charge pumping along tailored paths inside the bulk, as well as the controlled population of edge modes.

Development of crawler type device using new measuring system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maruyama, T.; Sasaki, T.; Yagi, T.

1995-08-01

This paper reports the development and field application of a new device which examine shell to shell weld joints of RPV. In a BWR type nuclear power plant, there is narrow space around the Reactor Pressure Vessel (RPV) because RPV is enclosed by the Reactor Shield Wall (RSW) and thermal insulations. The developed device is characterized by a new position measuring system and magnet wheels for driving. The new position measuring system uses laser beam and ultrasonic wave. The magnet wheels make the device travel freely in the narrow space between RPV and insulation. This device is tested on mock-upsmore » and applied examination of RPVs to verify field applicability.« less

Pressure-induced metal-insulator transitions in chalcogenide NiS2-xSex

NASA Astrophysics Data System (ADS)

Hussain, Tayyaba; Oh, Myeong-jun; Nauman, Muhammad; Jo, Younjung; Han, Garam; Kim, Changyoung; Kang, Woun

2018-05-01

We report the temperature-dependent resistivity ρ(T) of chalcogenide NiS2-xSex (x = 0.1) using hydrostatic pressure as a control parameter in the temperature range of 4-300 K. The insulating behavior of ρ(T) survives at low temperatures in the pressure regime below 7.5 kbar, whereas a clear insulator-to-metallic transition is observed above 7.5 kbar. Two types of magnetic transitions, from the paramagnetic (PM) to the antiferromagnetic (AFM) state and from the AFM state to the weak ferromagnetic (WF) state, were evaluated and confirmed by magnetization measurement. According to the temperature-pressure phase diagram, the WF phase survives up to 7.5 kbar, and the transition temperature of the WF transition decreases as the pressure increases, whereas the metal-insulator transition temperature increases up to 9.4 kbar. We analyzed the metallic behavior and proposed Fermi-liquid behavior of NiS1.9Se0.1.

Materials Development and Spin Transport Study of Magnetic Insulator Based Heterostructures

NASA Astrophysics Data System (ADS)

Tang, Chi

The subfield of magnetic insulator (MI) based spintronics is playing a substantial role in modern solid state physics research. Spin current in the MI is propagated in spin wave with a much longer decay length than spin-polarized carriers in conducting ferromagnet. In the MI-based hetereostructures, the adjacent non-magnetic materials can be magnetized in proximity of MI. Therefore, it is a promising system to study exotic transport phenomena such as quantum Anomalous Hall effect in topological insulator and graphene. Rare-earth Iron garnet (ReIG), a class of magnetic insulators with large electronic bandgap and high Curie temperature, stands out among various magnetic insulator materials and have attracted a great deal of attention in recent magnetic insulator based spintronics research. The first chapter of this dissertation gives a brief introduction to the spintronics research by introducing some essential concepts in the spintronics field and the most recent spin transport phenomena. The second chapter of this dissertation summarizes my work in the materials development of ReIG ferrimagnetic insulators, including exquisite control of high quality ultra-flat yttrium iron garnet (YIG) thin films with extremely low magnetic damping and engineering of strain induced robust perpendicular magnetic anisotropy in thulium iron garnet (TIG) and Bi-doped YIG films. The last chapter of this dissertation shows a systematic study in various ReIG based heterostructures, mainly divided into groups: ReIG (YIG & TIG)/heavy metal bilayers (Pd & Pt) and ReIG (YIG & TIG)/Dirac systems (graphene & topological insulator). The magneto-transport study disentangles the contribution from a spin current origin and proximity induced magnetism. Furthermore, the demonstration in the proximity coupling induced high-temperature ferromagnetic phase in low-dimensional Dirac systems, i.e. graphene and topological insulator surface states, provides new possibilities in the future spintronics applications. The modulation on the spin dynamics of magnetic insulator layer by topological insulator surface states is investigated at last, further confirming the superb properties of such magnetic insulator based spintronics systems.

Cloaking magnetic field and generating electric field with topological insulator and superconductor bi-layer sphere

NASA Astrophysics Data System (ADS)

Xu, Jin

2017-12-01

When an electric field is applied on a topological insulator, not only the electric field is generated, but also the magnetic field is generated, vice versa. I designed topological insulator and superconductor bi-layer magnetic cloak, derived the electric field and magnetic field inside and outside the topological insulator and superconductor sphere. Simulation and calculation results show that the applied magnetic field is screened by the topological insulator and superconductor bi-layer, and the electric field is generated in the cloaked region.

Positive magnetoresistance effect in rare earth cobaltites

NASA Astrophysics Data System (ADS)

Troyanchuk, I. O.; Bushinskii, M. V.; Karpinsky, D. V.; Dobryanskii, V. M.; Sikolenko, V. V.; Balagurov, A. M.

2009-06-01

The structure, magnetic, and magnetotransport properties of the Pr0.5Sr0.5Co1 - x Fe x O3 system have been studied. The ferromagnet-spin glass ( x = 0.5)- G-type antiferromagnet ( x = 0.7) transitions and the metal—insulator transitions ( x = 0.25) have been revealed. It has been established that the magnetoresistance of the metallic ferromagnetic cobaltites changes sign from positive to negative as the external magnetic field increases. The positive component increases and the negative component decreases with decreasing temperature. The negative magnetoresistance increases sharply in the insulating spinglass phase. Possible causes of the low-magnetic-field positive magnetoresistance in the rare earth metallic cobaltites are discussed.

Slater Insulator in Iridate Perovskites with Strong Spin-Orbit Coupling.

PubMed

Cui, Q; Cheng, J-G; Fan, W; Taylor, A E; Calder, S; McGuire, M A; Yan, J-Q; Meyers, D; Li, X; Cai, Y Q; Jiao, Y Y; Choi, Y; Haskel, D; Gotou, H; Uwatoko, Y; Chakhalian, J; Christianson, A D; Yunoki, S; Goodenough, J B; Zhou, J-S

2016-10-21

The perovskite SrIrO_{3} is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn^{4+} for Ir^{4+} in the SrIr_{1-x}Sn_{x}O_{3} perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic (AF) phase at T_{N}≥225  K. The continuous change of the cell volume as detected by x-ray diffraction and the λ-shape transition of the specific heat on cooling through T_{N} demonstrate that the metal-insulator transition is of second order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type-G AF spin ordering below T_{N}. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. A reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T_{N} in the same way as proposed by Slater.

Imaging of β-cell mass and insulitis in insulin-dependent (Type 1) diabetes mellitus.

PubMed

Di Gialleonardo, Valentina; de Vries, Erik F J; Di Girolamo, Marco; Quintero, Ana M; Dierckx, Rudi A J O; Signore, Alberto

2012-12-01

Insulin-dependent (type 1) diabetes mellitus is a metabolic disease with a complex multifactorial etiology and a poorly understood pathogenesis. Genetic and environmental factors cause an autoimmune reaction against pancreatic β-cells, called insulitis, confirmed in pancreatic samples obtained at autopsy. The possibility to noninvasively quantify β-cell mass in vivo would provide important biological insights and facilitate aspects of diagnosis and therapy, including follow-up of islet cell transplantation. Moreover, the availability of a noninvasive tool to quantify the extent and severity of pancreatic insulitis could be useful for understanding the natural history of human insulin-dependent (type 1) diabetes mellitus, to early diagnose children at risk to develop overt diabetes, and to select patients to be treated with immunotherapies aimed at blocking the insulitis and monitoring the efficacy of these therapies. In this review, we outline the imaging techniques currently available for in vivo, noninvasive detection of β-cell mass and insulitis. These imaging techniques include magnetic resonance imaging, ultrasound, computed tomography, bioluminescence and fluorescence imaging, and the nuclear medicine techniques positron emission tomography and single-photon emission computed tomography. Several approaches and radiopharmaceuticals for imaging β-cells and lymphocytic insulitis are reviewed in detail.

Magnetic, Electrical and Dielectric Properties of LaMnO3+η Perovskite Manganite.

NASA Astrophysics Data System (ADS)

v, Punith Kumar; Dayal, Vijaylakshmi

The high pure polycrystalline LaMnO3+η perovskite manganite has been synthesized using conventional solid state reaction method. The studied sample crystallizes into orthorhombic O', phase indexed with Pbnm space group. The magnetization measurement exhibits that the studied sample shows paramagnetic (PM) to ferromagnetic (FM) phase transition at TC = 191.6K followed with a frustration due to antiferromagnetic (AFM) kind of spin ordering at low temperature, Tf = 85.8K. The electrical resistivity measurements carried out at 0 tesla and 8 tesla magnetic field exhibits insulating kind of behavior throughout the measured temperature range. The resistivity at 0 tesla exhibits low temperature FM insulator to high temperature PM insulator type phase transition at TC = 191.6K similarly as observed from magnetization measurement. The application of the magnetic field (8 tesla) shifts TC to higher temperature side and the charge transport follows Shklovskii Efros variable range hopping (SE VRH) mechanism. The temperature and frequency dependent dielectric permittivity studied for the sample exhibits relaxation process explained based on Debye +Maxwell-Wagner relaxation mechanism. Department of Atomic Energy-Board of Research in Nuclear Sciences, Government of INDIA.

Plated lamination structures for integrated magnetic devices

DOEpatents

Webb, Bucknell C.

2014-06-17

Semiconductor integrated magnetic devices such as inductors, transformers, etc., having laminated magnetic-insulator stack structures are provided, wherein the laminated magnetic-insulator stack structures are formed using electroplating techniques. For example, an integrated laminated magnetic device includes a multilayer stack structure having alternating magnetic and insulating layers formed on a substrate, wherein each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by an insulating layer, and a local shorting structure to electrically connect each magnetic layer in the multilayer stack structure to an underlying magnetic layer in the multilayer stack structure to facilitate electroplating of the magnetic layers using an underlying conductive layer (magnetic or seed layer) in the stack as an electrical cathode/anode for each electroplated magnetic layer in the stack structure.

Slater insulator in iridate perovskites with strong spin-orbit coupling

DOE PAGES

Cui, Q.; Cheng, J. -G.; Fan, W.; ...

2016-10-20

The perovskite SrIrO 3 is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn 4+ for Ir 4+ in the SrIr 1–xSn xO 3 perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic (AF) phase at T N ≥ 225 K. The continuous change of the cell volume as detected by x-ray diffractionmore » and the λ-shape transition of the specific heat on cooling through T N demonstrate that the metal-insulator transition is of second order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type- G AF spin ordering below T N. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. Furthermore, a reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T N in the same way as proposed by Slater.« less

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

DOE PAGES

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

2017-06-13

Here, we show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronicmore » devices based on the coupling between magnetic materials and topological surface states. We demonstrate that the magnetization coming from individual Co atoms deposited on the surface can disrupt the spin coherence of the carriers in the archetypal topological insulator Bi 2Te 3, while in Bi 2Se 2Te the spin texture remains unperturbed. This is concluded from the observation of elastic backscattering events in quasiparticle interference patterns obtained by scanning tunneling spectroscopy. The mechanism responsible for the protection is investigated by energy resolved spectroscopy and ab initio calculations, and it is ascribed to the distorted adsorption geometry of localized magnetic moments due to Se–Te disorder, which suppresses the Co hybridization with the surface states.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

Here, we show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronicmore » devices based on the coupling between magnetic materials and topological surface states. We demonstrate that the magnetization coming from individual Co atoms deposited on the surface can disrupt the spin coherence of the carriers in the archetypal topological insulator Bi 2Te 3, while in Bi 2Se 2Te the spin texture remains unperturbed. This is concluded from the observation of elastic backscattering events in quasiparticle interference patterns obtained by scanning tunneling spectroscopy. The mechanism responsible for the protection is investigated by energy resolved spectroscopy and ab initio calculations, and it is ascribed to the distorted adsorption geometry of localized magnetic moments due to Se–Te disorder, which suppresses the Co hybridization with the surface states.« less

Strong interband Faraday rotation in 3D topological insulator Bi2Se3.

PubMed

Ohnoutek, L; Hakl, M; Veis, M; Piot, B A; Faugeras, C; Martinez, G; Yakushev, M V; Martin, R W; Drašar, Č; Materna, A; Strzelecka, G; Hruban, A; Potemski, M; Orlita, M

2016-01-11

The Faraday effect is a representative magneto-optical phenomenon, resulting from the transfer of angular momentum between interacting light and matter in which time-reversal symmetry has been broken by an externally applied magnetic field. Here we report on the Faraday rotation induced in the prominent 3D topological insulator Bi2Se3 due to bulk interband excitations. The origin of this non-resonant effect, extraordinarily strong among other non-magnetic materials, is traced back to the specific Dirac-type Hamiltonian for Bi2Se3, which implies that electrons and holes in this material closely resemble relativistic particles with a non-zero rest mass.

Development of the heat treatment system for the 40 T hybrid magnet superconducting outsert.

PubMed

Chen, W G; Chen, Z M; Chen, Z Y; Huang, P C; He, P; Zhu, J W

2011-10-01

The heat treatment of Nb(3)Sn coil with the glass fabric insulation is one of the key and critical processes for the outsert solenoids of the 40 T hybrid magnet, which could be wound with cable-in-conduit conductors using the insulation-wind-and-react technique. The manufacturing of the large vertical type vacuum/Ar atmosphere-protection heat treatment system has been completed and recently installed in the High Magnetic Filed Laboratory, Chinese Academy of Sciences. The heat treatment system composed mainly the furnace, the purging gas supply system, the control system, the gas impurities monitoring system, and so on. At present, the regulation and testing of the heat treatment system has been successfully finished, and all of technical parameters meet or exceed specifications.

Development of the heat treatment system for the 40 T hybrid magnet superconducting outsert

NASA Astrophysics Data System (ADS)

Chen, W. G.; Chen, Z. M.; Chen, Z. Y.; Huang, P. C.; He, P.; Zhu, J. W.

2011-10-01

The heat treatment of Nb3Sn coil with the glass fabric insulation is one of the key and critical processes for the outsert solenoids of the 40 T hybrid magnet, which could be wound with cable-in-conduit conductors using the insulation-wind-and-react technique. The manufacturing of the large vertical type vacuum/Ar atmosphere-protection heat treatment system has been completed and recently installed in the High Magnetic Filed Laboratory, Chinese Academy of Sciences. The heat treatment system composed mainly the furnace, the purging gas supply system, the control system, the gas impurities monitoring system, and so on. At present, the regulation and testing of the heat treatment system has been successfully finished, and all of technical parameters meet or exceed specifications.

Magnetic Orders of LaTiO3 and YTiO3 Under Epitaxial Strain: a First-Principles study

NASA Astrophysics Data System (ADS)

Weng, Yakui; Huang, Xin; Tang, Yankun; Dong, Shuai

2014-03-01

Perovskite RTiO3 family is a typical Mott-insulator with localized 3d electrons. In this work, the epitaxial strain effects on the ground magnetic orders of LaTiO3 and YTiO3 films have been studied using the first-principles density-functional theory. For the YTiO3 films, A-type antiferromagnetic order emerges against the original ferromagnetic order under the in-plane compressive strain by LaAlO3 (001) substrate, although the A-type antiferromagnetic order does not exist in any RTiO3 bulks. Then, for the LaTiO3 films under the compressive strain, e.g. LaTiO3 films grown on LaAlO3, LaGaO3, and SrTiO3 substrates, undergo a phase transition from the original G-type antiferromagnetism to A-type antiferromagnetism. While under the tensile strain, e.g. grown on the BaTiO3 and LaScO3 substrate, LaTiO3 films show a tendency to transit to the C-type antiferromagnetism. Furthermore, our calculations find that the magnetic transitions under epitaxial strain do not change the insulating fact of LaTiO3 and YTiO3.

Thermal spin current generation and spin transport in Pt/magnetic-insulator/Py heterostructures

NASA Astrophysics Data System (ADS)

Chen, Ching-Tzu; Safranski, Christopher; Krivorotov, Ilya; Sun, Jonathan

Magnetic insulators can transmit spin current via magnon propagation while blocking charge current. Furthermore, under Joule heating, magnon flow as a result of the spin Seeback effect can generate additional spin current. Incorporating magnetic insulators in a spin-orbit torque magnetoresistive memory device can potentially yield high switching efficiencies. Here we report the DC magneto-transport studies of these two effects in Pt/magnetic-insulator/Py heterostructures, using ferrimagnetic CoFexOy (CFO) and antiferromagnet NiO as the model magnetic insulators. We observe the presence and absence of the inverse spin-Hall signals from the thermal spin current in Pt/CFO/Py and Pt/NiO/Py structures. These results are consistent with our spin-torque FMR linewidths in comparison. We will also report investigations into the magnetic field-angle dependence of these observations.

Superconducting applications in propulsion systems. Magnetic insulation for plasma propulsion devices

NASA Technical Reports Server (NTRS)

Gonzalez, Dora E.; Karr, Gerald R.

1990-01-01

The purpose of this paper is to review the status of knowledge of the basic concepts needed to establish design parameters for effective magnetic insulation. The objective is to estimate the effectiveness of the magnetic field in insulating the plasma, to calculate the magnitude of the magnetic field necessary to reduce the heat transfer to the walls sufficiently enough to demonstrate the potential of magnetically driven plasma rockets.

Physical properties of Ce-TZP at cryogenic temperature

NASA Astrophysics Data System (ADS)

Han, Y. M.; Chen, Z.; Zhou, M.; Huang, R. J.; Huang, C. J.; Li, L. F.

2014-01-01

Electrical insulators, which are used to insulate cryogenic supply lines and conductor windings, are critical units in superconducting TOKAMAK magnets. Electrical insulators used in superconducting magnets fall into axial and radial insulators. These insulators can be made from glass ribbon epoxy densification and have been used in the Experiment Advanced Superconducting Tokamak (EAST). The properties of Ce-TZP can satisfy the requirement of electrical insulators. In this paper, thermal conductivity, mechanical properties and coefficient of thermal expansion of Ce-TZP have been investigated at cryogenic temperatures. Results indicate that the Ce-TZP shows better properties than epoxy and it demonstrates that the Ce-TZP can be used as insulation material in superconducting magnets.

Andreev Reflection in an s-Type Superconductor Proximized 3D Topological Insulator.

PubMed

Tikhonov, E S; Shovkun, D V; Snelder, M; Stehno, M P; Huang, Y; Golden, M S; Golubov, A A; Brinkman, A; Khrapai, V S

2016-09-30

We investigate transport and shot noise in lateral normal-metal-3D topological-insulator-superconductor contacts, where the 3D topological insulator (TI) is based on Bi. In the normal state, the devices are in the elastic diffusive transport regime, as demonstrated by a nearly universal value of the shot noise Fano factor F_{N}≈1/3 in magnetic field and in a reference normal-metal contact. In the absence of magnetic field, we identify the Andreev reflection (AR) regime, which gives rise to the effective charge doubling in shot noise measurements. Surprisingly, the Fano factor F_{AR}≈0.22±0.02 is considerably reduced in the AR regime compared to F_{N}, in contrast to previous AR experiments in normal metals and semiconductors. We suggest that this effect is related to a finite thermal conduction of the proximized, superconducting TI owing to a residual density of states at low energies.

Josephson supercurrent through a topological insulator surface state.

PubMed

Veldhorst, M; Snelder, M; Hoek, M; Gang, T; Guduru, V K; Wang, X L; Zeitler, U; van der Wiel, W G; Golubov, A A; Hilgenkamp, H; Brinkman, A

2012-02-19

The long-sought yet elusive Majorana fermion is predicted to arise from a combination of a superconductor and a topological insulator. An essential step in the hunt for this emergent particle is the unequivocal observation of supercurrent in a topological phase. Here, direct evidence for Josephson supercurrents in superconductor (Nb)-topological insulator (Bi(2)Te(3))-superconductor electron-beam fabricated junctions is provided by the observation of clear Shapiro steps under microwave irradiation, and a Fraunhofer-type dependence of the critical current on magnetic field. Shubnikov-de Haas oscillations in magnetic fields up to 30 T reveal a topologically non-trivial two-dimensional surface state. This surface state is attributed to mediate the ballistic Josephson current despite the fact that the normal state transport is dominated by diffusive bulk conductivity. The lateral Nb-Bi(2)Te(3)-Nb junctions hence provide prospects for the realization of devices supporting Majorana fermions.

Mobile metallic domain walls in an all-in-all-out magnetic insulator

DOE PAGES

Ma, Eric Yue; Cui, Yong -Tao; Ueda, Kentaro; ...

2015-10-30

Magnetic domain walls are boundaries between regions with different configurations of the same magnetic order. In a magnetic insulator, where the magnetic order is tied to its bulk insulating property, it has been postulated that electrical properties are drastically different along the domain walls, where the order is inevitably disturbed. Here we report the discovery of highly conductive magnetic domain walls in a magnetic insulator, Nd 2Ir 2O 7, that has an unusual all-in-all-out magnetic order, via transport and spatially resolved microwave impedance microscopy. The domain walls have a virtually temperature-independent sheet resistance of ~1 kilohm per square, show smoothmore » morphology with no preferred orientation, are free from pinning by disorders, and have strong thermal and magnetic field responses that agree with expectations for all-in-all-out magnetic order.« less

Mobile metallic domain walls in an all-in-all-out magnetic insulator.

PubMed

Ma, Eric Yue; Cui, Yong-Tao; Ueda, Kentaro; Tang, Shujie; Chen, Kai; Tamura, Nobumichi; Wu, Phillip M; Fujioka, Jun; Tokura, Yoshinori; Shen, Zhi-Xun

2015-10-30

Magnetic domain walls are boundaries between regions with different configurations of the same magnetic order. In a magnetic insulator, where the magnetic order is tied to its bulk insulating property, it has been postulated that electrical properties are drastically different along the domain walls, where the order is inevitably disturbed. Here we report the discovery of highly conductive magnetic domain walls in a magnetic insulator, Nd2Ir2O7, that has an unusual all-in-all-out magnetic order, via transport and spatially resolved microwave impedance microscopy. The domain walls have a virtually temperature-independent sheet resistance of ~1 kilohm per square, show smooth morphology with no preferred orientation, are free from pinning by disorders, and have strong thermal and magnetic field responses that agree with expectations for all-in-all-out magnetic order. Copyright © 2015, American Association for the Advancement of Science.

Lieb-Schultz-Mattis-type filling constraints in the 1651 magnetic space groups

NASA Astrophysics Data System (ADS)

Watanabe, Haruki

2018-04-01

We present a systematic study of the filling constraints to realize a "trivial" insulator symmetric under magnetic space group M . The filling ν must be an integer multiple of mM to avoid spontaneous symmetry breaking or fractionalization in gapped phases. We improve the value of mM in the literature and prove the tightness of the constraint for the majority of magnetic space groups. The result may shed light on the material search of exotic magnets with fractionalization.

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir1−xRux)O3

PubMed Central

Gunasekera, J.; Harriger, L.; Dahal, A.; Heitmann, T.; Vignale, G.; Singh, D. K.

2015-01-01

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1−xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund’s orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems. PMID:26647965

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir(1-x)Rux)O3.

PubMed

Gunasekera, J; Harriger, L; Dahal, A; Heitmann, T; Vignale, G; Singh, D K

2015-12-09

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1-xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund's orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems.

Coupling of Crystal Structure and Magnetism in the Layered, Ferromagnetic Insulator CrI 3

DOE PAGES

McGuire, Michael A.; Dixit, Hemant; Cooper, Valentino R.; ...

2014-12-23

Here, we examine the crystallographic and magnetic properties of single crystals of CrI 3, an easily cleavable, layered and insulating ferromagnet with a Curie temperature of 61 K. Our X-ray diffraction studies reveal a first-order crystallographic phase transition occurring near 210–220 K upon warming, with significant thermal hysteresis. The low-temperature structure is rhombohedral (Rmore » $$\\bar{3}$$, BiI 3-type) and the high-temperature structure is monoclinic (C2/m, AlCl 3-type). Evidence for coupling between the crystallographic and magnetic degrees of freedom in CrI 3 was found; we observed an anomaly in the interlayer spacing at the Curie temperature and an anomaly in the magnetic susceptibility at the structural transition. First-principles calculations reveal the importance of proper treatment of the long-ranged interlayer forces, and van der Waals density functional theory does an excellent job of predicting the crystal structures and their relative stability. Our calculations suggest that the ferromagnetic order found in the bulk material may persist into monolayer form, suggesting that CrI 3 and other chromium trihalides may be promising materials for spintronic and magnetoelectronic research.« less

Properties of radiation stable insulation composites for fusion magnet

NASA Astrophysics Data System (ADS)

Wu, Zhixiong; Huang, Rongjin; Huang, Chuanjun; Li, Laifeng

2017-09-01

High field superconducting magnets made of Nb3Al will be a suitable candidate for future fusion device which can provide magnetic field over 15T without critical current degradation caused by strain. The higher magnetic field and the larger current will produce a huge electromagnetic force. Therefore, it is necessary to develop high strength cryogenic structural materials and electrical insulation materials with excellent performance. On the other hand, superconducting magnets in fusion devices will experience significant nuclear radiation exposure during service. While typical structural materials like stainless steel and titanium have proven their ability to withstand these conditions, electrical insulation materials used in these coils have not fared as well. In fact, recent investigations have shown that electrical insulation breakdown is a limiting factor in the performance of high field magnets. The insulation materials used in the high field fusion magnets should be characterized by excellent mechanical properties, high radiation resistivity and good thermal conductivity. To meet these objectives, we designed various insulation materials based on epoxy resins and cyanate ester resins and investigated their processing characteristic and mechanical properties before and after irradiation at low temperature. In this paper, the recent progress of the radiation stable insulation composites for high field fusion magnet is presented. The materials have been irradiated by 60Co γ-ray irradiation in air at ambient temperature with a dose rate of 300 Gy/min. The total doses of 1 MGy, 5 MGy and 10 MGy were selected to the test specimens.

The Fabrication Technique and Property Analysis of Racetrack-Type High Temperature Superconducting Magnet for High Power Motor

NASA Astrophysics Data System (ADS)

Xie, S. F.; Wang, Y.; Wang, D. Y.; Zhang, X. J.; Zhao, B.; Zhang, Y. Y.; Li, L.; Li, Y. N.; Chen, P. M.

2013-03-01

The superconducting motor is now the focus of the research on the application of high temperature superconducting (HTS) materials. In this manuscript, we mainly introduce the recent progress on the fabrication technique and property research of the superconducting motor magnet in Luoyang Ship Material Research Institute (LSMRI) in China, including the materials, the winding and impregnation technique, and property measurement of magnet. Several techniques and devices were developed to manufacture the magnet, including the technique of insulation and thermal conduction, the device for winding the racetrack-type magnet, etc. At last, the superconducting magnet used for the MW class motor were successfully developed, which is the largest superconducting motor magnet in china at present. The critical current of the superconducting magnet exceeds the design value (90 A at 30 K).

Design of space-type electronic power transformers

NASA Technical Reports Server (NTRS)

Ahearn, J. F.; Lagadinos, J. C.

1977-01-01

Both open and encapsulated varieties of high reliability, low weight, and high efficiency moderate and high voltage transformers were investigated to determine the advantages and limitations of their construction in the ranges of power and voltage required for operation in the hard vacuum environment of space. Topics covered include: (1) selection of the core material; (2) preliminary calculation of core dimensions; (3) selection of insulating materials including magnet wire insulation, coil forms, and layer and interwinding insulation; (4) coil design; (5) calculation of copper losses, core losses and efficiency; (6) calculation of temperature rise; and (7) optimization of design with changes in core selection or coil design as required to meet specifications.

Nature of the superconductor-insulator transition in disordered superconductors.

PubMed

Dubi, Yonatan; Meir, Yigal; Avishai, Yshai

2007-10-18

The interplay of superconductivity and disorder has intrigued scientists for several decades. Disorder is expected to enhance the electrical resistance of a system, whereas superconductivity is associated with a zero-resistance state. Although superconductivity has been predicted to persist even in the presence of disorder, experiments performed on thin films have demonstrated a transition from a superconducting to an insulating state with increasing disorder or magnetic field. The nature of this transition is still under debate, and the subject has become even more relevant with the realization that high-transition-temperature (high-T(c)) superconductors are intrinsically disordered. Here we present numerical simulations of the superconductor-insulator transition in two-dimensional disordered superconductors, starting from a microscopic description that includes thermal phase fluctuations. We demonstrate explicitly that disorder leads to the formation of islands where the superconducting order is high. For weak disorder, or high electron density, increasing the magnetic field results in the eventual vanishing of the amplitude of the superconducting order parameter, thereby forming an insulating state. On the other hand, at lower electron densities or higher disorder, increasing the magnetic field suppresses the correlations between the phases of the superconducting order parameter in different islands, giving rise to a different type of superconductor-insulator transition. One of the important predictions of this work is that in the regime of high disorder, there are still superconducting islands in the sample, even on the insulating side of the transition. This result, which is consistent with experiments, explains the recently observed huge magneto-resistance peak in disordered thin films and may be relevant to the observation of 'the pseudogap phenomenon' in underdoped high-T(c) superconductors.

Micro-fabricated integrated coil and magnetic circuit and method of manufacturing thereof

DOEpatents

Mihailovich, Robert E.; Papavasiliou, Alex P.; Mehrotra, Vivek; Stupar, Philip A.; Borwick, III, Robert L.; Ganguli, Rahul; DeNatale, Jeffrey F.

2017-03-28

A micro-fabricated electromagnetic device is provided for on-circuit integration. The electromagnetic device includes a core. The core has a plurality of electrically insulating layers positioned alternatingly between a plurality of magnetic layers to collectively form a continuous laminate having alternating magnetic and electrically insulating layers. The electromagnetic device includes a coil embedded in openings of the semiconductor substrate. An insulating material is positioned in the cavity and between the coil and an inner surface of the core. A method of manufacturing the electromagnetic device includes providing a semiconductor substrate having openings formed therein. Windings of a coil are electroplated and embedded in the openings. The insulating material is coated on or around an exposed surface of the coil. Alternating magnetic layers and electrically insulating layers may be micro-fabricated and electroplated as a single and substantially continuous segment on or around the insulating material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, Q.; Cheng, J. -G.; Fan, W.

The perovskite (Pv) SrIrO 3 is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn 4+ for Ir 4+ in the SrIr 1-xSn xO 3 perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic phase at TN ≥ 225 K. The continuous change of the cell volume as detected by X-ray diffraction andmore » the l-shape transition of the specific heat on cooling through TN demonstrate that the metal-insulator transition is of second-order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type-G AF spin ordering below TN. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. A reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below TN in the same way as proposed by Slater.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, Q.; Cheng, J. -G.; Fan, W.

The perovskite SrIrO 3 is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn 4+ for Ir 4+ in the SrIr 1–xSn xO 3 perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic (AF) phase at T N ≥ 225 K. The continuous change of the cell volume as detected by x-ray diffractionmore » and the λ-shape transition of the specific heat on cooling through T N demonstrate that the metal-insulator transition is of second order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type- G AF spin ordering below T N. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. Furthermore, a reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T N in the same way as proposed by Slater.« less

Study of the Insulating Magnetic Field in an Accelerating Ion Diode

NASA Astrophysics Data System (ADS)

Kozlovsky, K. I.; Martynenko, A. S.; Vovchenko, E. D.; Lisovsky, M. I.; Isaev, A. A.

2017-12-01

The results of examination of the insulating magnetic field in an accelerating ion diode are presented. This field is produced in order to suppress the electron current and thus enhance the neutron yield of the D( d, n)3He nuclear reaction. The following two designs are discussed: a gas-filled diode with inertial electrostatic confinement of ions and a vacuum diode with a laser-plasma ion source and pulsed magnetic insulation. Although the insulating field of permanent magnets is highly nonuniform, it made it possible to extend the range of accelerating voltages to U = 200 kV and raise the neutron yield to Q = 107 in the first design. The nonuniform field structure is less prominent in the device with pulsed magnetic insulation, which demonstrated efficient deuteron acceleration with currents up to 1 kA at U = 400 kV. The predicted neutron yield is as high as 109 neutrons/pulse.

Chern Insulator Phase in a Lattice of an Organic Dirac Semimetal with Intracellular Potential and Magnetic Modulations

NASA Astrophysics Data System (ADS)

Osada, Toshihito

2017-12-01

We demonstrate that a Chern insulator can be realized on an actual two-dimensional lattice of an organic Dirac semimetal, α-(BEDT-TTF)2I3, by introducing potential and magnetic modulations in a unit cell. It is a topologically-nontrivial insulator that exhibits the quantum Hall effect even at zero magnetic field. We assume a pattern of site potential and staggered plaquette magnetic flux on the lattice to imitate the observed stripe charge ordering pattern. When magnetic modulation is sufficiently large, the system becomes a Chern insulator, where the Berry curvatures around two gapped Dirac cones have the same sign on each band, and one chiral edge state connects the conduction and valence bands at each crystal edge. The present model is an organic version of Haldane's model, which discusses the Chern insulator on a honeycomb lattice with second nearest neighbor couplings.

Interface induced ferromagnetism in topological insulator above room temperature

NASA Astrophysics Data System (ADS)

Tang, Chi; Chang, Cui-Zu; Liu, Yawen; Chen, Tingyong; Moodera, Jagadeesh; Shi, Jing

The quantum anomalous Hall effect (QAHE) observed in magnetic topological insulators (TI), an outcome of time reversal symmetry broken surface states, exhibits many exotic properties. However, a major obstacle towards high temperature QAHE is the low Curie temperature in the disordered magnetically doped TI systems. Here we report a study on heterostructures of TI and magnetic insulator in which the magnetic insulator, namely thulium iron garnet or TIG, has perpendicular magnetic anisotropy. At the TIG/TI interface, TIG magnetizes the surface states of the TI film by exchange coupling, as revealed by the anomalous Hall effect (AHE). We demonstrate that squared AHE hysteresis loops persist well above room temperature. The interface proximity induced high-temperature ferromagnetism in topological insulators opens up new possibilities for the realization of QAHE at high temperatures. This work was supported as part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # SC0012670.

Quantum anomalous Hall effect in magnetic topological insulators

DOE PAGES

Wang, Jing; Lian, Biao; Zhang, Shou -Cheng

2015-08-25

The search for topologically non-trivial states of matter has become an important goal for condensed matter physics. Here, we give a theoretical introduction to the quantum anomalous Hall (QAH) effect based on magnetic topological insulators in two-dimensions (2D) and three-dimensions (3D). In 2D topological insulators, magnetic order breaks the symmetry between the counter-propagating helical edge states, and as a result, the quantum spin Hall effect can evolve into the QAH effect. In 3D, magnetic order opens up a gap for the topological surface states, and chiral edge state has been predicted to exist on the magnetic domain walls. We presentmore » the phase diagram in thin films of a magnetic topological insulator and review the basic mechanism of ferromagnetic order in magnetically doped topological insulators. We also review the recent experimental observation of the QAH effect. Furthermore, we discuss more recent theoretical work on the coexistence of the helical and chiral edge states, multi-channel chiral edge states, the theory of the plateau transition, and the thickness dependence in the QAH effect.« less

Current-induced switching of magnetic molecules on topological insulator surfaces

NASA Astrophysics Data System (ADS)

Locane, Elina; Brouwer, Piet W.

2017-03-01

Electrical currents at the surface or edge of a topological insulator are intrinsically spin polarized. We show that such surface or edge currents can be used to switch the orientation of a molecular magnet weakly coupled to the surface or edge of a topological insulator. For the edge of a two-dimensional topological insulator as well as for the surface of a three-dimensional topological insulator the application of a well-chosen surface or edge current can lead to a complete polarization of the molecule if the molecule's magnetic anisotropy axis is appropriately aligned with the current direction. For a generic orientation of the molecule a nonzero but incomplete polarization is obtained. We calculate the probability distribution of the magnetic states and the switching rates as a function of the applied current.

Analysis and comparison of magnetic sheet insulation tests

NASA Astrophysics Data System (ADS)

Marion-Péra, M. C.; Kedous-Lebouc, A.; Cornut, B.; Brissonneau, P.

1994-05-01

Magnetic circuits of electrical machines are divided into coated sheets in order to limit eddy currents. The surface insulation resistance of magnetic sheets is difficult to evaluate because it depends on parameters like pressure and covers a wide range of values. Two methods of measuring insulation resistance are analyzed: the standardized 'Franklin device' and a tester developed by British Steel Electrical. Their main drawback is poor local repeatability. The Franklin method allows better quality control of industrial process because it measures only one insulating layer at a time. It also gives more accurate images of the distribution of possible defects. Nevertheless, both methods lead to similar classifications of insulation efficiency.

Space and Missile Systems Center Standard: Parts, Materials, and Processes Control Program for Launch Vehicles -SMC-S-011 (2012)

DTIC Science & Technology

2012-07-03

Specification for MIL-PRF-39008 Resistor Fixed, Composition ( Insulated ), Established Reliability, General Specification for MIL-S-45743 Soldering, Manual...2.1.5 Prohibited Relays 1. Plug-in types 2. Solder-sealed relays 2.1.6 Prohibited Resistors 1. All hollow glass or hollow ceramic core devices 2...lowest maximum temperature. This may be the core material, the insulation of the magnet, etc. 2/ Current rating for each winding shall be less than

J1-J2 square lattice antiferromagnetism in the orbitally quenched insulator MoOPO4

NASA Astrophysics Data System (ADS)

Yang, L.; Jeong, M.; Babkevich, P.; Katukuri, V. M.; Náfrádi, B.; Shaik, N. E.; Magrez, A.; Berger, H.; Schefer, J.; Ressouche, E.; Kriener, M.; Živković, I.; Yazyev, O. V.; Forró, L.; Rønnow, H. M.

2017-07-01

We report magnetic and thermodynamic properties of a 4 d1 (Mo5 +) magnetic insulator MoOPO4 single crystal, which realizes a J1-J2 Heisenberg spin-1 /2 model on a stacked square lattice. The specific-heat measurements show a magnetic transition at 16 K which is also confirmed by magnetic susceptibility, ESR, and neutron diffraction measurements. Magnetic entropy deduced from the specific heat corresponds to a two-level degree of freedom per Mo5 + ion, and the effective moment from the susceptibility corresponds to the spin-only value. Using ab initio quantum chemistry calculations, we demonstrate that the Mo5 + ion hosts a purely spin-1 /2 magnetic moment, indicating negligible effects of spin-orbit interaction. The quenched orbital moments originate from the large displacement of Mo ions inside the MoO6 octahedra along the apical direction. The ground state is shown by neutron diffraction to support a collinear Néel-type magnetic order, and a spin-flop transition is observed around an applied magnetic field of 3.5 T. The magnetic phase diagram is reproduced by a mean-field calculation assuming a small easy-axis anisotropy in the exchange interactions. Our results suggest 4 d molybdates as an alternative playground to search for model quantum magnets.

Magnon spectrum of the helimagnetic insulator Cu 2OSeO 3

DOE PAGES

Portnichenko, P. Y.; Romhányi, J.; Onykiienko, Y. A.; ...

2016-02-25

We report that complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu 2OSeO 3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu 2OSeO 3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a modelmore » of entangled Cu 4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu 2OSeO 3 that are essential for understanding its abundant low-temperature magnetically ordered phases.« less

Magnon spectrum of the helimagnetic insulator Cu2OSeO3

PubMed Central

Portnichenko, P. Y.; Romhányi, J.; Onykiienko, Y. A.; Henschel, A.; Schmidt, M.; Cameron, A. S.; Surmach, M. A.; Lim, J. A.; Park, J. T.; Schneidewind, A.; Abernathy, D. L.; Rosner, H.; van den Brink, Jeroen; Inosov, D. S.

2016-01-01

Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases. PMID:26911567

Magnon spectrum of the helimagnetic insulator Cu2OSeO3.

PubMed

Portnichenko, P Y; Romhányi, J; Onykiienko, Y A; Henschel, A; Schmidt, M; Cameron, A S; Surmach, M A; Lim, J A; Park, J T; Schneidewind, A; Abernathy, D L; Rosner, H; van den Brink, Jeroen; Inosov, D S

2016-02-25

Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases.

The metal-insulator transition in Fe(1.01-x)Cu(x)Se.

PubMed

Williams, A J; McQueen, T M; Ksenofontov, V; Felser, C; Cava, R J

2009-07-29

Iron selenide, Fe(1.01)Se, the layered parent compound of the recently discovered superconducting arsenide family, has previously been shown to be non-magnetic and superconducting with a critical temperature of 8 K. Here we show that copper can be substituted at the iron site in Fe(1.01)Se up to a solubility limit of 20-30%, after which a first-order transition to the three-dimensional CuFeSe(2) structure type is observed. As little as 1.5% copper is sufficient to suppress the superconductivity, and 4% drives the system through a metal-insulator transition. A local magnetic moment is introduced, which maximizes near 12% doping, where a spin-glass transition near 15 K is observed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matvejeff, M., E-mail: mikko.matvejeff@picosun.com; Department of Chemistry, Aalto University, Kemistintie 1, 02150 Espoo; Ahvenniemi, E.

We study magnetic coupling between hole-doped manganite layers separated by either a perovskite or a rock-salt barrier of variable thickness. Both the type and the quality of the interface have a strong impact on the minimum critical barrier thickness where the manganite layers become magnetically decoupled. A rock-salt barrier layer only 1 unit cell (0.5 nm) thick remains insulating and is able to magnetically de-couple the electrode layers. The technique can therefore be used for developing high-performance planar oxide electronic devices such as magnetic tunnel junctions and quantum well structures that depend on magnetically and electronically sharp heterointerfaces.

Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures

NASA Astrophysics Data System (ADS)

Kally, James; Lv, Yang; Zhang, Delin; Lee, Joon Sue; Samarth, Nitin; Wang, Jian-Ping; Department of Electrical; Computer Engineering, University of Minnesota, Minneapolis Collaboration; Department of Physics, Pennsylvania State University Collaboration

The surface states of topological insulators offer a potentially very efficient way to generate spins and spin-orbit torques to magnetic moments in proximity. The switching by spin-orbit torque itself only requires two terminals so that a charge current can be applied. However, a third terminal with additional magnetic tunneling junction structure is needed to sense the magnetization state if such devices are used for memory and logic applications. The recent discovery of unidirectional spin Hall magnetoresistance in heavy metal/ferromagnetic and topological insulator/magnetically doped topological insulator systems offers an alternative way to sense magnetization while still keeping the number of terminals to minimal two. The unidirectional spin Hall magnetoresistance in topological insulator/strong ferromagnetic layer heterostructure system has yet not been reported. In this work, we report our experimental observations of such magnetoresistance. It is found to be present and comparable to the best result of the previous reported Ta/Co systems in terms of magnetoresistance per current density per total resistance.

Magnetic second-order topological insulators and semimetals

NASA Astrophysics Data System (ADS)

Ezawa, Motohiko

2018-04-01

We propose magnetic second-order topological insulators (SOTIs). First, we study a three-dimensional model. It is pointed out that the previously proposed topological hinge insulator has actually surface states along the [001] direction in addition to hinge states. We gap out these surface states by introducing magnetization, obtaining a SOTI only with hinge states. The bulk topological number is the Z2 index protected by the combined symmetry of the fourfold rotation and the inversion symmetry. We next study two-dimensional magnetic SOTIs, where the corner states are robust also in the presence of the magnetization. Finally, we construct a magnetic second-order topological semimetal by layering the two-dimensional magnetic SOTIs, where hinge-arc states are robust also in the presence of the magnetization.

Coupling of an applied field magnetically insulated ion diode to a high power magnetically insulated transmission line system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maenchen, J.E.

1983-01-01

The coupling of energy from a high power pulsed accelerator through a long triplate magnetically insulated transmission line (MITL) in vacuum to an annular applied magnetic field insulated extraction ion diode is examined. The narrow power transport window and the wave front erosion of the MITL set stringent impedance history conditions on the diode load. A new ion diode design developed to satisfy these criteria with marginal electron insulation is presented. The LION accelerator is used to provide a positive polarity 1.5 MV, 350 kA, 40 ns FWHM pulse with a 30 kA/ns current rate from a triplate MITL source.more » A transition converts the triplate into a cylindrical cross section which flares into the ion diode load. Extensive current and voltage measurements performed along this structure and on the extracted ion beam provide conclusive evidence that the self insulation condition of the MITL is maintained in the transition by current loss alone. The ion diode utilizes a radial magnetic field between a grounded cathode annular emission tip and a disk anode. A 50 cm/sup 2/ dielectric/metal anode area serves as the ion plasma source subject to direct electron bombardment from the opposing cathode tip under marginal magnetic insulation conditions. The ions extracted cross the radial magnetic field and exit the diode volume as an annular cross section beam of peak current about 100 kA. The diode current gradually converts from the initial electron flow to nearly 100% ion current af« less

Hg-Based Epitaxial Materials for Topological Insulators

DTIC Science & Technology

2014-07-01

Research Laboratory for investigation of properties. 15. SUBJECT TERMS EOARD, topological insulator , diluted magnetic ...topological superconductors and spintronics to quantum computation (e.g. see C.L.Kane and J.E.Moore "Topological Insulators " Physics World (2011) 24...tetradymite semiconductors Bi2Te3, Bi2Se3, and Sb2Te3 which form magnetically ordered insulators when doped with transition metal elements Cr or Fe (Rui Yu et

Magnetically insulated transmission line oscillator

DOEpatents

Bacon, Larry D.; Ballard, William P.; Clark, M. Collins; Marder, Barry M.

1988-01-01

A magnetically insulated transmission line oscillator employs self-generated magnetic fields to generate microwave energy. An anode of the oscillator includes slow-wave structures which are formed of a plurality of thin conductive vanes defining cavities therebetween, and a gap is formed between the anode and a cathode of the oscillator. In response to a pulsed voltage applied to the anode and cathode, self-generated magnetic fields arfe produced in a cross-field orientation with respect to the orientation of the electric field between the anode and the cathode. The cross-field magnetic fields insulate the flow of electrons in the gap and confine the flow of electrons within the gap.

Magnetically insulated transmission line oscillator

DOEpatents

Bacon, L.D.; Ballard, W.P.; Clark, M.C.; Marder, B.M.

1987-05-19

A magnetically insulated transmission line oscillator employs self-generated magnetic fields to generate microwave energy. An anode of the oscillator includes slow-wave structures which are formed of a plurality of thin conductive vanes defining cavities therebetween, and a gap is formed between the anode and a cathode of the oscillator. In response to a pulsed voltage applied to the anode and cathode, self-generated magnetic fields are produced in a cross-field orientation with respect to the orientation of the electric field between the anode and the cathode. The cross-field magnetic fields insulate the flow of electrons in the gap and confine the flow of electrons within the gap. 11 figs.

Tunnel Magneto Resistance of Fe/Insulator/Fe

NASA Astrophysics Data System (ADS)

Aryee, Dennis; Seifu, Dereje

Tri-layer thin films of Fe/Insulator/Fe were synthesized using magnetron DC/ RF sputtering with MgO insulator and Bi2Te3 topological insulators as middle buffer layer. The multi-layered samples thus produced were studied using in-house built magneto-optic Kerr effect (MOKE) instrument, vibrating sample magnetometer (VSM), torque magnetometer (TMM), AFM, MFM, and magneto-resistance (MR). This system, that is Fe/Insulator/Fe on MgO(100) substrate, is a well-known tunnel magneto resistance (TMR) structure often used in magnetic tunnel junction (MTJ) devices. TMR effect is a method by which MTJs are used in developing magneto-resistive random access memory (MRAM), magnetic sensors, and novel logic devices. The main purpose behind this research is to measure the magnetic anisotropy of Fe/Insulator /Fe structure and correlate it to magneto-resistance. In this presentation, we will present results from MOKE, VSM, TMM, AFM, MFM, and MR studies of Fe/Insulator/Fe on MgO(100). We would like to acknowledge support by NSF-MRI-DMR-1337339.

Entropy generation in a parallel-plate active magnetic regenerator with insulator layers

NASA Astrophysics Data System (ADS)

Mugica Guerrero, Ibai; Poncet, Sébastien; Bouchard, Jonathan

2017-02-01

This paper proposes a feasible solution to diminish conduction losses in active magnetic regenerators. Higher performances of these machines are linked to a lower thermal conductivity of the Magneto-Caloric Material (MCM) in the streamwise direction. The concept presented here involves the insertion of insulator layers along the length of a parallel-plate magnetic regenerator in order to reduce the heat conduction within the MCM. This idea is investigated by means of a 1D numerical model. This model solves not only the energy equations for the fluid and solid domains but also the magnetic circuit that conforms the experimental setup of reference. In conclusion, the addition of insulator layers within the MCM increases the temperature span, cooling load, and coefficient of performance by a combination of lower heat conduction losses and an increment of the global Magneto-Caloric Effect. The generated entropy by solid conduction, fluid convection, and conduction and viscous losses are calculated to help understand the implications of introducing insulator layers in magnetic regenerators. Finally, the optimal number of insulator layers is studied.

Thickness-dependent phase transition in graphite under high magnetic field

NASA Astrophysics Data System (ADS)

Taen, Toshihiro; Uchida, Kazuhito; Osada, Toshihito

2018-03-01

Various electronic phases emerge when applying high magnetic fields in graphite. However, the origin of a semimetal-insulator transition at B ≃30 T is still not clear, while an exotic density-wave state is theoretically proposed. In order to identify the electronic state of the insulator phase, we investigate the phase transition in thin-film graphite samples that were fabricated on silicon substrate by a mechanical exfoliation method. The critical magnetic fields of the semimetal-insulator transition in thin-film graphite shift to higher magnetic fields, accompanied by a reduction in temperature dependence. These results can be qualitatively reproduced by a density-wave model by introducing a quantum size effect. Our findings establish the electronic state of the insulator phase as a density-wave state standing along the out-of-plane direction, and help determine the electronic states in other high-magnetic-field phases.

Superconductivity and ferromagnetism in topological insulators

NASA Astrophysics Data System (ADS)

Zhang, Duming

Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi2Se3 thin films and chemical vapor deposition for the growth of Bi2Se3 nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to exist when topological insulators are interfaced with superconductors. The observation of Majorana fermions would not only be fundamentally important, but would also lead to applications in fault-tolerant topological quantum computation. By interfacing topological insulator nanoribbons with superconducting electrodes, we observe distinct signatures of proximity-induced superconductivity, which is found to be present in devices with channel lengths that are much longer than the normal transport characteristic lengths. This might suggest preferential coupling of the proximity effect to a ballistic surface channel of the topological insulator. In addition, when the electrodes are in the superconducting state, we observe periodic magnetoresistance oscillations which suggest the formation of vortices in the proximity-induced region of the nanoribbons. Our results demonstrate that proximity-induced superconductivity and vortices can be realized in our nanoribbon geometry, which accomplishes a first important step towards the search for Majorana fermions in condensed matter. In Chapter 5, I will discuss experiments on a magnetically-doped topological insulator (Mn-doped Bi2Se3) to induce a surface state gap. The metallic Dirac cone surface states of a topological insulator are expected to be protected against small perturbations by time-reversal symmetry. However, these surface states can be dramatically modified and a finite energy gap can be opened at the Dirac point by breaking the time-reversal symmetry via magnetic doping. The interplay between magnetism and topological surface states is predicted to yield novel phenomena of fundamental interest such as a topological magneto-electric effect, a quantized anomalous Hall effect, and the induction of magnetic monopoles. Our systematic measurements reveal a close correlation between the onset of ferromagnetism and quantum corrections to diffusive transport, which crosses over from the symplectic (weak anti-localization) to the unitary (weak localization) class. A comprehensive interpretation of data obtained from electrical transport, angle-resolved photoemission spectroscopy, superconducting quantum interference device magnetometry, and scanning tunneling microscopy indicates that the ferromagnetism responsible for modifications in the surface states occurs in nanoscale regions on the surface where magnetic atoms segregate during sample growth. This suggests that some aspects of the observed magnetoconductance may indeed originate from surface transport despite the non-ideal nature of the samples. These observations are consistent with the prediction of a time-reversal symmetry breaking gap, which is further supported by angle-resolved photoemission spectroscopy measurements.

Fuel magnetization without external field coils (AutoMag)

NASA Astrophysics Data System (ADS)

Slutz, Stephen; Jennings, Christopher; Awe, Thomas; Shipley, Gabe; Lamppa, Derek; McBride, Ryan

2016-10-01

Magnetized Liner Inertial Fusion (MagLIF) has produced fusion-relevant plasma conditions on the Z accelerator where the fuel was magnetized using external field coils. We present a novel concept that does not need external field coils. This concept (AutoMag) magnetizes the fuel during the early part of the drive current by using a composite liner with helical conduction paths separated by insulating material. The drive is designed so the current rises slowly enough to avoid electrical breakdown of the insulators until a sufficiently strong magnetic field is established. Then the current rises more quickly, which causes the insulators to break down allowing the drive current to follow an axial path and implode the liner. Low inductance magnetically insulated power feeds can be used with AutoMag to increase the drive current without interfering with diagnostic access. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Spin-transfer torque in spin filter tunnel junctions

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Downhole data transmission system

DOEpatents

Hall, David R.; Hall, Jr., H. Tracy; Pixton, David S; Dahlgren, Scott; Fox, Joe

2006-06-20

A system for transmitting data through a string of downhole components. In one aspect, the system includes first and second magnetically conductive, electrically insulating elements at both ends of the component. Each element includes a first U-shaped trough with a bottom, first and second sides and an opening between the two sides. Electrically conducting coils are located in each trough. An electrical conductor connects the coils in each component. In operation, a varying current applied to a first coil in one component generates a varying magnetic field in the first magnetically conductive, electrically insulating element, which varying magnetic field is conducted to and thereby produces a varying magnetic field in the second magnetically conductive, electrically insulating element of a connected component, which magnetic field thereby generates a varying electrical current in the second coil in the connected component.

Downhole Data Transmission System

DOEpatents

Hall, David R.; Hall, Jr., H. Tracy; Pixton, David; Dahlgren, Scott; Fox, Joe

2003-12-30

A system for transmitting data through a string of downhole components. In one aspect, the system includes first and second magnetically conductive, electrically insulating elements at both ends of the component. Each element includes a first U-shaped trough with a bottom, first and second sides and an opening between the two sides. Electrically conducting coils are located in each trough. An electrical conductor connects the coils in each component. In operation, a varying current applied to a first coil in one component generates a varying magnetic field in the first magnetically conductive, electrically insulating element, which varying magnetic field is conducted to and thereby produces a varying magnetic field in the second magnetically conductive, electrically insulating element of a connected component, which magnetic field thereby generates a varying electrical current in the second coil in the connected component.

Electric and Magnetic Manipulation of Biological Systems

NASA Astrophysics Data System (ADS)

Lee, H.; Hunt, T. P.; Liu, Y.; Ham, D.; Westervelt, R. M.

2005-06-01

New types of biological cell manipulation systems, a micropost matrix, a microelectromagnet matrix, and a microcoil array, were developed. The micropost matrix consists of post-shaped electrodes embedded in an insulating layer. With a separate ac voltage applied to each electrode, the micropost matrix generates dielectrophoretic force to trap and move individual biological cells. The microelectromagnet matrix consists of two arrays of straight wires aligned perpendicular to each other, that are covered with insulating layers. By independently controlling the current in each wire, the microelectromagnet matrix creates versatile magnetic fields to manipulate individual biological cells attached to magnetic beads. The microcoil array is a set of coils implemented in a foundry using a standard silicon fabrication technology. Current sources to the coils, and control circuits are integrated on a single chip, making the device self-contained. Versatile manipulation of biological cells was demonstrated using these devices by generating optimized electric or magnetic field patterns. A single yeast cell was trapped and positioned with microscopic resolution, and multiple yeast cells were trapped and independently moved along the separate paths for cell-sorting.

Proximity-driven enhanced magnetic order at ferromagnetic-insulator-magnetic-topological-insulator interface

DOE PAGES

Li, Mingda; Zhu, Yimei; Chang, Cui -Zu; ...

2015-08-17

Magnetic exchange driven proximity effect at a magnetic-insulator–topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. In this study, we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS/Sb 2–xV xTe 3 hybrid heterostructure, where V doping is used to drive the TI (Sb 2Te 3) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magneticmore » ordering.« less

Transport Experiments on Topological Insulators

DTIC Science & Technology

2016-08-16

neutral currents as well. In insulating magnets, the heat current below 2 K is largely carried by spin waves or magnons (phonons die out rapidly below 2 K...Ong’s group recently showed that  leads to prominent effects on neutral currents as well. In insulating magnets, the heat current below 2 K is...UU UU UU 16-08-2016 15-Sep-2011 14-Oct-2014 Final Report: Transport Experiments on Topological Insulators The views, opinions and/or findings contained

Spin-current emission governed by nonlinear spin dynamics.

PubMed

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-10-16

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators.

Spin-current emission governed by nonlinear spin dynamics

PubMed Central

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-01-01

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators. PMID:26472712

Topological triplon modes and bound states in a Shastry-Sutherland magnet

NASA Astrophysics Data System (ADS)

McClarty, P. A.; Krüger, F.; Guidi, T.; Parker, S. F.; Refson, K.; Parker, A. W.; Prabhakaran, D.; Coldea, R.

2017-08-01

The twin discoveries of the quantum Hall effect, in the 1980s, and of topological band insulators, in the 2000s, were landmarks in physics that enriched our view of the electronic properties of solids. In a nutshell, these discoveries have taught us that quantum mechanical wavefunctions in crystalline solids may carry nontrivial topological invariants which have ramifications for the observable physics. One of the side effects of the recent topological insulator revolution has been that such physics is much more widespread than was appreciated ten years ago. For example, while topological insulators were originally studied in the context of electron wavefunctions, recent work has initiated a hunt for topological insulators in bosonic systems: in photonic crystals, in the vibrational modes of crystals, and in the excitations of ordered magnets. Using inelastic neutron scattering along with theoretical calculations, we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu2(BO3)2 is a bosonic topological insulator with topologically protected chiral edge modes of triplon excitations.

Magnetoconductance signatures of chiral domain-wall bound states in magnetic topological insulators

NASA Astrophysics Data System (ADS)

Tiwari, Kunal L.; Coish, W. A.; Pereg-Barnea, T.

2017-12-01

Recent magnetoconductance measurements performed on magnetic topological insulator candidates have revealed butterfly-shaped hysteresis. This hysteresis has been attributed to the formation of gapless chiral domain-wall bound states during a magnetic-field sweep. We treat this phenomenon theoretically, providing a link between microscopic magnetization dynamics and butterfly hysteresis in magnetoconductance. Further, we illustrate how a spatially resolved conductance measurement can probe the most striking feature of the domain-wall bound states: their chirality. This work establishes a regime where a definitive link between butterfly hysteresis in longitudinal magneto-conductance and domain-wall bound states can be made. This analysis provides an important tool for the identification of magnetic topological insulators.

Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl.

PubMed

Naka, Takashi; Nikitin, Artem M; Pan, Yu; de Visser, Anne; Nakane, Takayuki; Ishikawa, Fumihiro; Yamada, Yuh; Imai, Motoharu; Matsushita, Akiyuki

2016-07-20

We report the magnetism and transport properties of the Heusler compound Fe2+x V1-x Al at  -0.10  ⩽  x  ⩽  0.20 under pressure and a magnetic field. A metal-insulator quantum phase transition occurred at x  ≈  -0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity σ 0 around the critical point, which scaled approximately according to the power law (P  -  P c ) (γ) . At x  ⩽  -0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x  ≈  0.05, itinerant ferromagnetism was established. At the quantum critical points at x  =  -0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state.

Strong magnetization and Chern insulators in compressed graphene/CrI 3 van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Jiayong; Zhao, Bao; Zhou, Tong; Xue, Yang; Ma, Chunlan; Yang, Zhongqin

2018-02-01

Graphene-based heterostructures are a promising material system for designing the topologically nontrivial Chern insulating devices. Recently, a two-dimensional monolayer ferromagnetic insulator CrI3 was successfully synthesized in experiments [B. Huang et al., Nature (London) 546, 270 (2017), 10.1038/nature22391]. Here, these two interesting materials are proposed to build a heterostructure (Gr /CrI3). Our first-principles calculations show that the system forms a van der Waals (vdW) heterostructure, which is relatively facilely fabricated in experiments. A Chern insulating state is acquired in the Gr /CrI3 heterostructure if the vdW gap is compressed to a distance between about 3.3 and 2.4 Å, corresponding to a required external pressure between about 1.4 and 18.3 GPa. Amazingly, very strong magnetization (about 150 meV) is found in graphene, induced by the substrate CrI3, despite the vdW interactions between them. A low-energy effective model is employed to understand the mechanism. The work functions, contact types, and band alignments of the Gr /CrI3 heterostructure system are also studied. Our work demonstrates that the Gr /CrI3 heterostructure is a promising system to observe the quantum anomalous Hall effect at high temperatures (up to 45 K) in experiments.

Optical Boron Nitride Insulator Erosion Characterization of a 200 W Xenon Hall Thruster

DTIC Science & Technology

2005-05-01

Hall thruster boron nitride insulator is evaluated as a diagnostic for real-time evaluation of thruster insulator erosion. Three Hall thruster plasma control variables are examined: ion energy (discharge potential), ion flux (propellant flow), and plasma conductivity (magnetic field strength). The boron emission, and hence the insulator erosion rate, varies linearly with ion energy and ion flux. A minimum erosion rate appears at intermediate magnetic field strengths. This may indicate that local plasma conductivity significantly affects the divergence

Quantum metallicity on the high-field side of the superconductor-insulator transition.

PubMed

Baturina, T I; Strunk, C; Baklanov, M R; Satta, A

2007-03-23

We investigate ultrathin superconducting TiN films, which are very close to the localization threshold. Perpendicular magnetic field drives the films from the superconducting to an insulating state, with very high resistance. Further increase of the magnetic field leads to an exponential decay of the resistance towards a finite value. In the limit of low temperatures, the saturation value can be very accurately extrapolated to the universal quantum resistance h/e2. Our analysis suggests that at high magnetic fields a new ground state, distinct from the normal metallic state occurring above the superconducting transition temperature, is formed. A comparison with other studies on different materials indicates that the quantum metallic phase following the magnetic-field-induced insulating phase is a generic property of systems close to the disorder-driven superconductor-insulator transition.

Magnetic structures of REPdBi half-Heusler bismuthides (RE = Gd, Tb, Dy, Ho, Er)

NASA Astrophysics Data System (ADS)

Pavlosiuk, Orest; Fabreges, Xavier; Gukasov, Arsen; Meven, Martin; Kaczorowski, Dariusz; Wiśniewski, Piotr

2018-05-01

We present results of neutron diffraction on single crystals of several equiatomic ternary compounds of rare-earth elements with palladium and bismuth, crystallizing with cubic MgAgAs-type structure (half-Heusler phases). Band structure calculations showed that many members of that family possess electronic band inversion, which may lead to occurrence of topological insulator or topological semimetal. But even for the compounds without intrinsic band inversion another way of topologically non-trivial state realization, through a specific antiferromagnetic order, has been theoretically proposed. Our results show that the antiferromagnetic structures of all studied bismuthides are characterized by the propagation vector, allowing for antiferromagnetic topological insulator state. Therefore, the antiferromagnetic representatives of half-Heusler family are excellent candidates for extended investigations of coexistence of superconductivity, magnetic order and non-trivial topology of electronic states.

Antiferromagnetic Ordering in Organic Conductor λ-(BEDT-TTF)2GaCl4 Probed by 13C NMR

NASA Astrophysics Data System (ADS)

Saito, Yohei; Fukuoka, Shuhei; Kobayashi, Takuya; Kawamoto, Atsushi; Mori, Hatsumi

2018-01-01

The ground state of λ-(BEDT-TTF)2GaCl4, which has the same structure as the organic superconductor λ-(BETS)2GaCl4, was investigated by magnetic susceptibility and 13C NMR measurements. The temperature dependence of the magnetic susceptibility revealed an antiferromagnetic (AF) correlation with J/kB ≃ 98 K. NMR spectrum splitting and the divergence of 1/T1 were observed at approximately 13 K, which is associated with the AF transition. We found that the AF structure is commensurate according to discrete NMR peak splitting, suggesting that the ground state of λ-(BEDT-TTF)2GaCl4 is an AF dimer-Mott insulating state. Our results suggest that the superconducting phase of λ-type salts would be located near the AF insulating phase.

Deficiency of the bulk spin Hall effect model for spin-orbit torques in magnetic-insulator/heavy-metal heterostructures

NASA Astrophysics Data System (ADS)

Li, Junxue; Yu, Guoqiang; Tang, Chi; Liu, Yizhou; Shi, Zhong; Liu, Yawen; Navabi, Aryan; Aldosary, Mohammed; Shao, Qiming; Wang, Kang L.; Lake, Roger; Shi, Jing

2017-06-01

Electrical currents in a magnetic-insulator/heavy-metal heterostructure can induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on the heavy-metal side and spin-orbit torques (SOTs) on the magnetic-insulator side. Within the framework of a pure spin current model based on the bulk spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall effect (SH-AHE) to SMR should be equal to the ratio of the fieldlike torque (FLT) to the dampinglike torque (DLT). We perform a quantitative study of SMR, SH-AHE, and SOTs in a series of thulium iron garnet/platinum or T m3F e5O12/Pt heterostructures with different T m3F e5O12 thicknesses, where T m3F e5O12 is a ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the ratio between the measured effective fields of FLT and DLT is at least two times larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model grossly underestimates the spin-torque efficiency of FLT. Our results reveal deficiencies of the bulk SHE model and also address the importance of interfacial effects such as the Rashba and magnetic proximity effects in magnetic-insulator/heavy-metal heterostructures.

Cryogenic electrical properties of irradiated cyanate ester/epoxy insulation for fusion magnets

NASA Astrophysics Data System (ADS)

Li, X.; Wu, Z. X.; Li, J.; Xu, D.; Liu, H. M.; Huang, R. J.; Li, L. F.

2017-12-01

The insulation materials used in high field fusion magnets require excellent mechanical properties, high electrical breakdown strength, good thermal conductivity and high radiation tolerance. Previous investigations showed that cyanate ester/epoxy (CE/EP) insulation material, a candidate insulation for fusion magnets, can maintain good mechanical performance at cryogenic temperature after 10 MGy irradiation and has a much longer pot life than traditional epoxy insulation material. In order to quantify the electrical properties of the CE/EP insulation material at low temperature, a cryogenic electrical property testing system cooled by a G-M cryocooler was developed for this study. An insulation material with 40% cyanate ester and 60% epoxy was subjected to 60Co γ-ray irradiation in air at ambient temperature with a dose rate of 300 Gy/min, and total doses of 1 MGy, 5 MGy and 10 MGy. The electrical breakdown strength of this CE/EP insulation material was measured before and after irradiation. The results show that cryogenic temperature has a positive effect on the electrical breakdown strength of this composite, while the influence of 60Co γ-ray irradiation is not obvious at 6.1 K.

Magnetic study of M-type Ru–Ti doped strontium hexaferrite nanocrystalline particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alsmadi, A. M.; Bsoul, I.; Mahmood, S. H.

2015-11-01

We carried out a systematic study on the effect of the substitution of Ti2+ and Ru4+ ions for Fe3+ ions on the structural and magnetic properties of the strontium ferrite SrFe12-2xRuxTixO19 nanoparticles with (0 <= x <= 0: 3), using x-ray diffraction, Quantum Design PPMS-9 magnetometry, and electrical resistivity. A clear irreversibility between the zero-field-cooled and field-cooled curves was observed below room temperature and the zero-field-cooled magnetization curves displayed a broad peak at a temperature TM. These results were discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The resistivity data showedmore » some kind of a transition from insulator to perfect insulator around TM. The high-temperature magnetization measurements exhibited sharp peaks just below T-c indicating a superparamagnetic behavior. With Ru-Ti substitution, the saturation magnetization at 5 K showed small variations were it slightly increased with increasing x up to 0.2, and then decrease for x = 0.3, while the coercivity decreased monotonically, recording a reduction of about 78% at x = 0.3. These results were discussed in light of the cationic distributions based on the results of the structural refinements.« less

Photoinduced Topological Phase Transitions in Topological Magnon Insulators.

PubMed

Owerre, S A

2018-03-13

Topological magnon insulators are the bosonic analogs of electronic topological insulators. They are manifested in magnetic materials with topologically nontrivial magnon bands as realized experimentally in a quasi-two-dimensional (quasi-2D) kagomé ferromagnet Cu(1-3, bdc), and they also possess protected magnon edge modes. These topological magnetic materials can transport heat as well as spin currents, hence they can be useful for spintronic applications. Moreover, as magnons are charge-neutral spin-1 bosonic quasiparticles with a magnetic dipole moment, topological magnon materials can also interact with electromagnetic fields through the Aharonov-Casher effect. In this report, we study photoinduced topological phase transitions in intrinsic topological magnon insulators in the kagomé ferromagnets. Using magnonic Floquet-Bloch theory, we show that by varying the light intensity, periodically driven intrinsic topological magnetic materials can be manipulated into different topological phases with different sign of the Berry curvatures and the thermal Hall conductivity. We further show that, under certain conditions, periodically driven gapped topological magnon insulators can also be tuned to synthetic gapless topological magnon semimetals with Dirac-Weyl magnon cones. We envision that this work will pave the way for interesting new potential practical applications in topological magnetic materials.

Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2

NASA Astrophysics Data System (ADS)

Oogarah, Reeya K.; Suard, Emmanuelle; McCabe, Emma E.

2018-01-01

The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour and we report here a neutron diffraction investigation into the magnetic ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the anti-Sr2MnO2Mn2Sb2-type structure (described by space group I4/mmm) and orders antiferromagnetically below TN = 105 K. We consider both its long-range magnetic structure and its magnetic microstructure, and the onset of magnetic order. It adopts the multi-k vector "2k" magnetic structure (k = (1/2 0 1/2) and k = (0 1/2 1/2) and has similarities with related iron oxychalcogenides, illustrating the robust nature of the "2k" magnetic structure.

Visualizing ferromagnetic domains in magnetic topological insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wenbo; Gu, G. D.; Yang, Fang

2015-05-13

We report a systematic study of ferromagnetic domains in both single-crystal and thin-film specimens of magnetic topological insulators Cr doped (Bi 0.1Sb 0.9) 2Te 3 using magnetic force microscopy (MFM). The temperature and field dependences of MFM and in situ resistance data are consistent with previous bulk transport and magnetic characterization. Bubble-like ferromagnetic domains were observed in both single crystals and thin films. Significantly, smaller domain size (~500 nm) with narrower domain wall (~150 – 300 nm) was observed in thin films of magnetic topological insulators, likely due to vertical confinement effect. As a result, these results suggest that thinmore » films are more promising for visualization of chiral edge states.« less

Two dimensional topological insulator in quantizing magnetic fields

NASA Astrophysics Data System (ADS)

Olshanetsky, E. B.; Kvon, Z. D.; Gusev, G. M.; Mikhailov, N. N.; Dvoretsky, S. A.

2018-05-01

The effect of quantizing magnetic field on the electron transport is investigated in a two dimensional topological insulator (2D TI) based on a 8 nm (013) HgTe quantum well (QW). The local resistance behavior is indicative of a metal-insulator transition at B ≈ 6 T. On the whole the experimental data agrees with the theory according to which the helical edge states transport in a 2D TI persists from zero up to a critical magnetic field Bc after which a gap opens up in the 2D TI spectrum.

Magnetic gating of a 2D topological insulator

NASA Astrophysics Data System (ADS)

Dang, Xiaoqian; Burton, J. D.; Tsymbal, Evgeny Y.

2016-09-01

Deterministic control of transport properties through manipulation of spin states is one of the paradigms of spintronics. Topological insulators offer a new playground for exploring interesting spin-dependent phenomena. Here, we consider a ferromagnetic ‘gate’ representing a magnetic adatom coupled to the topologically protected edge state of a two-dimensional (2D) topological insulator to modulate the electron transmission of the edge state. Due to the locked spin and wave vector of the transport electrons the transmission across the magnetic gate depends on the mutual orientation of the adatom magnetic moment and the current. If the Fermi energy matches an exchange-split bound state of the adatom, the electron transmission can be blocked due to the full back scattering of the incident wave. This antiresonance behavior is controlled by the adatom magnetic moment orientation so that the transmission of the edge state can be changed from 1 to 0. Expanding this consideration to a ferromagnetic gate representing a 1D chain of atoms shows a possibility to control the spin-dependent current of a strip of a 2D topological insulator by magnetization orientation of the ferromagnetic gate.

Dielectric Meta-Holograms Enabled with Dual Magnetic Resonances in Visible Light.

PubMed

Li, Zile; Kim, Inki; Zhang, Lei; Mehmood, Muhammad Q; Anwar, Muhammad S; Saleem, Murtaza; Lee, Dasol; Nam, Ki Tae; Zhang, Shuang; Luk'yanchuk, Boris; Wang, Yu; Zheng, Guoxing; Rho, Junsuk; Qiu, Cheng-Wei

2017-09-26

Efficient transmission-type meta-holograms have been demonstrated using high-index dielectric nanostructures based on Huygens' principle. It is crucial that the geometry size of building blocks be judiciously optimized individually for spectral overlap of electric and magnetic dipoles. In contrast, reflection-type meta-holograms using the metal/insulator/metal scheme and geometric phase can be readily achieved with high efficiency and small thickness. Here, we demonstrate a general platform for design of dual magnetic resonance based meta-holograms based on the geometric phase using silicon nanostructures that are quarter wavelength thick for visible light. Significantly, the projected holographic image can be unambiguously observed without a receiving screen even under the illumination of natural light. Within the well-developed semiconductor industry, our ultrathin magnetic resonance-based meta-holograms may have promising applications in anticounterfeiting and information security.

Processing of n+/p-/p+ strip detectors with atomic layer deposition (ALD) grown Al2O3 field insulator on magnetic Czochralski silicon (MCz-si) substrates

NASA Astrophysics Data System (ADS)

Härkönen, J.; Tuovinen, E.; Luukka, P.; Gädda, A.; Mäenpää, T.; Tuominen, E.; Arsenovich, T.; Junkes, A.; Wu, X.; Li, Z.

2016-08-01

Detectors manufactured on p-type silicon material are known to have significant advantages in very harsh radiation environment over n-type detectors, traditionally used in High Energy Physics experiments for particle tracking. In p-type (n+ segmentation on p substrate) position-sensitive strip detectors, however, the fixed oxide charge in the silicon dioxide is positive and, thus, causes electron accumulation at the Si/SiO2 interface. As a result, unless appropriate interstrip isolation is applied, the n-type strips are short-circuited. Widely adopted methods to terminate surface electron accumulation are segmented p-stop or p-spray field implantations. A different approach to overcome the near-surface electron accumulation at the interface of silicon dioxide and p-type silicon is to deposit a thin film field insulator with negative oxide charge. We have processed silicon strip detectors on p-type Magnetic Czochralski silicon (MCz-Si) substrates with aluminum oxide (Al2O3) thin film insulator, grown with Atomic Layer Deposition (ALD) method. The electrical characterization by current-voltage and capacitance-voltage measurement shows reliable performance of the aluminum oxide. The final proof of concept was obtained at the test beam with 200 GeV/c muons. For the non-irradiated detector the charge collection efficiency (CCE) was nearly 100% with a signal-to-noise ratio (S/N) of about 40, whereas for the 2×1015 neq/cm2 proton irradiated detector the CCE was 35%, when the sensor was biased at 500 V. These results are comparable with the results from p-type detectors with the p-spray and p-stop interstrip isolation techniques. In addition, interestingly, when the aluminum oxide was irradiated with Co-60 gamma-rays, an accumulation of negative fixed oxide charge in the oxide was observed.

Data transmission element for downhole drilling components

DOEpatents

Hall, David R.; Hall, Jr., H. Tracy; Pixton, David S.; Dahlgren, Scott; Fox, Joe; Sneddon, Cameron; Briscoe, Michael

2006-01-31

A robust data transmission element for transmitting information between downhole components, such as sections of drill pipe, in the presence of hostile environmental conditions, such as heat, dirt, rocks, mud, fluids, lubricants, and the like. The data transmission element components include a generally U-shaped annular housing, a generally U-shaped magnetically conductive, electrically insulating element such as ferrite, and an insulated conductor. Features on the magnetically conducting, electrically insulating element and the annular housing create a pocket when assembled. The data transmission element is filled with a polymer to retain the components within the annular housing by filling the pocket with the polymer. The polymer can bond with the annular housing and the insulated conductor but preferably not the magnetically conductive, electrically insulating element. A data transmission element is mounted within a recess proximate a mating surface of a downhole drilling component, such as a section of drill pipe.

Resistivity of the insulating phase approaching the 2D metal-insulator transition: the effect of spin polarization

NASA Astrophysics Data System (ADS)

Li, Shiqi; Sarachik, Myriam

We compare the resistivity of the dilute, strongly-interacting 2D electron system in the insulating phase of a silicon MOSFET for unpolarized electrons in the absence of magnetic field and in the presence of an in-plane magnetic field sufficient to fully polarize the electrons. In both cases the resistivity obeys Efros-Shklovskii variable range hopping ρ (T) =ρ0exp [(TES / T) 1 / 2 ] , with TES and 1 /ρ0 mapping onto each other provided one applies a shift reported earlier of the critical density nc with magnetic field: the transport properties of the insulator are the same for unpolarized and fully polarized electron spins. Interestingly, the parameters TES and 1 /ρ0 =σ0 are consistent with critical behavior approaching a metal-insulator transition. This work was supported by the National Science Foundation Grant DMR-1309008 and the Binational Science Foundation Grant 2012210.

Thermoelectric properties of an ultra-thin topological insulator.

PubMed

Islam, S K Firoz; Ghosh, T K

2014-04-23

Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In the absence of a magnetic field, the thermopower increases and thermal conductivity decreases with an increase in the hybridization energy. In the presence of a magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and whose phase factor is governed by the product of the Landé g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results for the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, at a frequency that depends on the Landé g-factor.

Topological Triplon Modes and Bound States in a Shastry-Sutherland Magnet

NASA Astrophysics Data System (ADS)

McClarty, Paul; Kruger, Frank; Guidi, Tatiana; Parker, Stewart; Refson, Keith; Parker, Tony; Prabhakaran, Dharmalingam; Coldea, Radu

The twin discoveries of the quantum Hall effect, in the 1980's, and of topoogical band insulators, in the 2000's, were landmarks in physics that enriched our view of the electronic properties of solids. In a nutshell, these discoveries have taught us that quantum mechanical wavefunctions in crystalline solids may carry nontrivial topological invariants which have ramifications for the observable physics. One of the side effects of the recent topological insulator revolution has been that such physics is much more widespread than was appreciated ten years ago. For example, while topological insulators were originally studied in the context of electron wavefunctions, recent work has led to proposals of topological insulators in bosonic systems: in photonic crystals, in the vibrational modes of crystals, and in the excitations of ordered magnets. Using inelastic neutron scattering along with theoretical calculations we demonstrate that, in a weak magnetic field, the dimerized quantum magnet SrCu2(BO3)2 is a bosonic topological insulator with nonzero Chern number in the triplon bands and topologically protected chiral edge excitations.

Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure.

PubMed

Prajapat, C L; Singh, Surendra; Paul, Amitesh; Bhattacharya, D; Singh, M R; Mattauch, S; Ravikumar, G; Basu, S

2016-05-21

Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

Direct measurement of proximity-induced magnetism at the interface between a topological insulator and a ferromagnet

DOE PAGES

Lee, Changmin; Katmis, Ferhat; Jarillo-Herrero, Pablo; ...

2016-06-27

When a topological insulator (TI) is in contact with a ferromagnet, both time-reversal and inversion symmetries are broken at the interface. An energy gap is formed at the TI surface, and its electrons gain a net magnetic moment through short-range exchange interactions. Magnetic TIs can host various exotic quantum phenomena, such as massive Dirac fermions, Majorana fermions, the quantum anomalous Hall effect and chiral edge currents along the domain boundaries. However, selective measurement of induced magnetism at the buried interface has remained a challenge. Using magnetic second-harmonic generation, we directly probe both the in-plane and out-of-plane magnetizations induced at themore » interface between the ferromagnetic insulator (FMI) EuS and the three-dimensional TI Bi 2Se 3. Furthermore, our findings not only allow characterizing magnetism at the TI–FMI interface but also lay the groundwork for imaging magnetic domains and domain boundaries at the magnetic TI surfaces.« less

Individual Magnetic Molecules on Ultrathin Insulating Surfaces

NASA Astrophysics Data System (ADS)

El Hallak, Fadi; Warner, Ben; Hirjibehedin, Cyrus

2012-02-01

Single molecule magnets have attracted ample interest because of their exciting magnetic and quantum properties. Recent studies have demonstrated that some of these molecules can be evaporated on surfaces without losing their magnetic properties [M. Mannini et al., Nature 468, 417, (2010)]. This remarkable progress enhances the chances of real world applications for these molecules. We present STM imaging and spectroscopy data on iron phthalocyanine molecules deposited on Cu(100) and on a Cu2N ultrathin insulating surface. These molecules have been shown to display a large magnetic anisotropy on another thin insulating surface, oxidized Cu(110) [N. Tsukahara et al., Phys. Rev. Lett. 102, 167203 (2009)]. By using a combination of elastic and inelastic electron tunnelling spectroscopy, we investigate the binding of the molecules to the surface and the impact that the surface has on their electronic and magnetic properties.

Magnetic Insulation in Coaxial Transmission Lines with an External Magnetic Field

DTIC Science & Technology

1980-03-13

A. Mostrom, Michael E. Jones, and Lester E. Thode SUBMITTED TO: Physical Review Letters March 13, 1980 SöKOK_Kä^MJ!L;; ÄgEie?©d tea gas &c...Number Assigned by Contract Monitor: SLL 81- 262 Comments on Document: Archive, RRI, DEW . From Physical Review Letters Descriptors, Keywords: Magnetic...Source of Document: DEW MAGNETIC INSULATION IN COAXIAL TRANSMISSION LINES WITH AN EXTERNAL MAGNETIC FIELD Michael A. Mostrom, Michael E. Jones, and

Dirac spin-orbit torques and charge pumping at the surface of topological insulators

NASA Astrophysics Data System (ADS)

Ndiaye, Papa B.; Akosa, C. A.; Fischer, M. H.; Vaezi, A.; Kim, E.-A.; Manchon, A.

2017-07-01

We address the nature of spin-orbit torques at the magnetic surfaces of topological insulators using the linear-response theory. We find that the so-called Dirac torques in such systems possess a different symmetry compared to their Rashba counterpart, as well as a high anisotropy as a function of the magnetization direction. In particular, the damping torque vanishes when the magnetization lies in the plane of the topological-insulator surface. We also show that the Onsager reciprocal of the spin-orbit torque, the charge pumping, induces an enhanced anisotropic damping. Via a macrospin model, we numerically demonstrate that these features have important consequences in terms of magnetization switching.

Enhancement of pairing interaction and magnetic fluctuations toward a band insulator in an electron-doped Li(x)ZrNCl Superconductor.

PubMed

Kasahara, Yuichi; Kishiume, Tsukasa; Takano, Takumi; Kobayashi, Katsuki; Matsuoka, Eiichi; Onodera, Hideya; Kuroki, Kazuhiko; Taguchi, Yasujiro; Iwasa, Yoshihiro

2009-08-14

The doping dependence of specific heat and magnetic susceptibility has been investigated for Li(x)ZrNCl superconductors derived from a band insulator. As the carrier concentration is decreased, the anisotropy of superconducting gap changes from highly anisotropic to almost isotropic. It was also found that, upon reducing carrier density, the superconducting coupling strength and the magnetic susceptibility are concomitantly enhanced in parallel with T(c), while the density of states at the Fermi level is kept almost constant. Theoretical calculations taking into account the on-site Coulomb interaction reproduced the experimental results, suggesting a possible pairing mediated by magnetic fluctuations, even in the doped band insulators.

Effect of Sr doping on the magnetic exchange interactions in manganites of type L a 1 - x S r x M n y A 1 - y O 3 ( A = Ga , Ti ; 0.1 ≤ y ≤ 1 )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furrer, Albert; Podlesnyak, Andrey A.; Pomjakushina, Ekaterina

Strontium doping transforms manganites of type La 1 - x Sr x Mn O 3 from an insulating antiferromagnet ( x = 0 ) to a metallic ferromagnet ( x > 0.16 ) due to the induced charge carriers (holes). We employed neutron scattering experiments in order to investigate the effect of Sr doping on a tailor-made compound of composition La 0.7 S r 0.3 M n 0.1 Ti 0.3 G a 0.6 O 3 . By the simultaneous doping with S r 2 + and Ti 4 + ions, the compound remains in the insulating state so thatmore » the magnetic interactions for large Sr doping can be studied in the absence of charge carriers. At T C = 215 K , there is a first-order reconstructive phase transition from the trigonal R - 3 c structure to the orthorhombic Pnma structure via an intermediate virtual configuration described by the common monoclinic subgroup P2 1 / c . The magnetic excitations associated with Mn 3 + dimers give evidence for two different nearest-neighbor ferromagnetic exchange interactions, in contrast to the undoped compound LaM n y A 1 - y O 3 where both ferromagnetic and antiferromagnetic interactions are present. Furthemore, the doping-induced changes of the exchange coupling originates from different Mn-O-Mn bond angles determined by neutron diffraction. The large fourth-nearest-neighbor interaction found for metallic manganites is absent in the insulating state. Here, we argue that the Ruderman-Kittel-Kasuya-Yosida interaction reasonably accounts for all the exchange couplings derived from the spin-wave dispersion in metallic manganites.« less

Effect of Sr doping on the magnetic exchange interactions in manganites of type L a 1 - x S r x M n y A 1 - y O 3 ( A = Ga , Ti ; 0.1 ≤ y ≤ 1 )

DOE PAGES

Furrer, Albert; Podlesnyak, Andrey A.; Pomjakushina, Ekaterina; ...

2017-03-14

Strontium doping transforms manganites of type La 1 - x Sr x Mn O 3 from an insulating antiferromagnet ( x = 0 ) to a metallic ferromagnet ( x > 0.16 ) due to the induced charge carriers (holes). We employed neutron scattering experiments in order to investigate the effect of Sr doping on a tailor-made compound of composition La 0.7 S r 0.3 M n 0.1 Ti 0.3 G a 0.6 O 3 . By the simultaneous doping with S r 2 + and Ti 4 + ions, the compound remains in the insulating state so thatmore » the magnetic interactions for large Sr doping can be studied in the absence of charge carriers. At T C = 215 K , there is a first-order reconstructive phase transition from the trigonal R - 3 c structure to the orthorhombic Pnma structure via an intermediate virtual configuration described by the common monoclinic subgroup P2 1 / c . The magnetic excitations associated with Mn 3 + dimers give evidence for two different nearest-neighbor ferromagnetic exchange interactions, in contrast to the undoped compound LaM n y A 1 - y O 3 where both ferromagnetic and antiferromagnetic interactions are present. Furthemore, the doping-induced changes of the exchange coupling originates from different Mn-O-Mn bond angles determined by neutron diffraction. The large fourth-nearest-neighbor interaction found for metallic manganites is absent in the insulating state. Here, we argue that the Ruderman-Kittel-Kasuya-Yosida interaction reasonably accounts for all the exchange couplings derived from the spin-wave dispersion in metallic manganites.« less

Evaluation of the Fretting Resistance of the High Voltage Insulation on the ITER Magnet Feeder Busbars

NASA Astrophysics Data System (ADS)

Clayton, N.; Crouchen, M.; Evans, D.; Gung, C.-Y.; Su, M.; Devred, A.; Piccin, R.

2017-12-01

The high voltage (HV) insulation on the ITER magnet feeder superconducting busbars and current leads will be prepared from S-glass fabric, pre-impregnated with an epoxy resin, which is interleaved with polyimide film and wrapped onto the components and cured during feeder manufacture. The insulation architecture consists of nine half-lapped layers of glass/Kapton, which is then enveloped in a ground-screen, and two further half-lapped layers of glass pre-preg for mechanical protection. The integrity of the HV insulation is critical in order to inhibit electrical arcs within the feeders. The insulation over the entire length of the HV components (bus bar, current leads and joints) must provide a level of voltage isolation of 30 kV. In operation, the insulation on ITER busbars will be subjected to high mechanical loads, arising from Lorentz forces, and in addition will be subjected to fretting erosion against stainless steel clamps, as the pulsed nature of some magnets results in longitudinal movement of the busbar. This work was aimed at assessing the wear on, and the changes in, the electrical properties of the insulation when subjected to typical ITER operating conditions. High voltage tests demonstrated that the electrical isolation of the insulation was intact after the fretting test.

Quantum phase transitions and local magnetism in Mott insulators: A local probe investigation using muons, neutrons, and photons

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.

Mott insulators are materials in which strong correlations among the electrons induce an unconventional insulating state. Rich interplay between the structural, magnetic, and electronic degrees of freedom resulting from the electron correlation can lead to unusual complexity of Mott materials on the atomic scale, such as microscopically heterogeneous phases or local structural correlations that deviate significantly from the average structure. Such behavior must be studied by suitable experimental techniques, i.e. "local probes", that are sensitive to this local behavior rather than just the bulk, average properties. In this thesis, I will present results from our studies of multiple families of Mott insulators using two such local probes: muon spin relaxation (muSR), a probe of local magnetism; and pair distribution function (PDF) analysis of x-ray and neutron total scattering, a probe of local atomic structure. In addition, I will present the development of magnetic pair distribution function analysis, a novel method for studying local magnetic correlations that is highly complementary to the muSR and atomic PDF techniques. We used muSR to study the phase transition from Mott insulator to metal in two archetypal Mott insulating systems: RENiO3 (RE = rare earth element) and V2O3. In both of these systems, the Mott insulating state can be suppressed by tuning a nonthermal parameter, resulting in a "quantum" phase transition at zero temperature from the Mott insulating state to a metallic state. In RENiO3, this occurs through variation of the rare-earth element in the chemical composition; in V 2O3, through the application of hydrostatic pressure. Our results show that the metallic and Mott insulating states unexpectedly coexist in phase-separated regions across a large portion of parameter space near the Mott quantum phase transition and that the magnitude of the ordered antiferromagnetic moment remains constant across the phase diagram until it is abruptly destroyed at the quantum phase transition. Taken together, these findings point unambiguously to a first-order quantum phase transition in these systems. We also conducted x-ray and neutron PDF experiments, which suggest that the distinct atomic structures associated with the insulating and metallic phases similarly coexist near the quantum phase transition. These results have significant implications for our understanding of the Mott metal-insulator quantum phase transition in real materials. The second part of this thesis centers on the derivation and development of the magnetic pair distribution function (mPDF) technique and its application to the antiferromagnetic Mott insulator MnO. The atomic PDF method involves Fourier transforming the x-ray or neutron total scattering intensity from reciprocal space into real space to directly reveal the local atomic correlations in a material, which may deviate significantly from the average crystallographic structure of that material. Likewise, the mPDF method involves Fourier transforming the magnetic neutron total scattering intensity to probe the local correlations of magnetic moments in the material, which may exist on short length scales even when the material has no long-range magnetic order. After deriving the fundamental mPDF equations and providing a proof-of-principle by recovering the known magnetic structure of antiferromagnetic MnO, we used this technique to investigate the short-range magnetic correlations that persist well into the paramagnetic phase of MnO. By combining the mPDF measurements with ab initio calculations of the spin-spin correlation function in paramagnetic MnO, we were able to quantitatively account for the observed mPDF. We also used the mPDF data to evaluate competing ab initio theories, thereby resolving some longstanding questions about the magnetic exchange interactions in MnO.

Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

DOE PAGES

Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; ...

2015-11-24

In this study, the anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gatecontrol of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHEmore » in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.« less

Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure

PubMed Central

Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

2015-01-01

The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured. PMID:26596472

Spin-orbit driven magnetic insulating state with J eff=1/2 character in a 4d oxide

DOE PAGES

Calder, S.; Li, Ling; Okamoto, Satoshi; ...

2015-11-30

The unusual magnetic and electronic ground states of 5d iridates has been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogousmore » J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy and find a magnetic insulating ground state with J eff =1/2 character.The unusual magnetic and electronic ground states of 5d iridates have been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here, we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogous J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy, and find a magnetic insulating ground state with J eff=12 character.« less

Nontrivial interplay of strong disorder and interactions in quantum spin-Hall insulators doped with dilute magnetic impurities

NASA Astrophysics Data System (ADS)

Zheng, Jun-Hui; Cazalilla, Miguel A.

2018-06-01

We investigate nonperturbatively the effect of a magnetic dopant impurity on the edge transport of a quantum spin Hall (QSH) insulator. We show that for a strongly coupled magnetic dopant located near the edge of a system, a pair of transmission antiresonances appear. When the chemical potential is on resonance, interaction effects broaden the antiresonance width with decreasing temperature, thus suppressing transport for both repulsive and moderately attractive interactions. Consequences for the recently observed QSH insulating phase of the 1 -T' of WTe2 are briefly discussed.

Two-order parameters theory of the metal-insulator phase transition kinetics in the magnetic field

NASA Astrophysics Data System (ADS)

Dubovskii, L. B.

2018-05-01

The metal-insulator phase transition is considered within the framework of the Ginzburg-Landau approach for the phase transition described with two coupled order parameters. One of the order parameters is the mass density which variation is responsible for the origin of nonzero overlapping of the two different electron bands and the appearance of free electron carriers. This transition is assumed to be a first-order phase one. The free electron carriers are described with the vector-function representing the second-order parameter responsible for the continuous phase transition. This order parameter determines mostly the physical properties of the metal-insulator transition and leads to a singularity of the surface tension at the metal-insulator interface. The magnetic field is involved into the consideration of the system. The magnetic field leads to new singularities of the surface tension at the metal-insulator interface and results in a drastic variation of the phase transition kinetics. A strong singularity in the surface tension results from the Landau diamagnetism and determines anomalous features of the metal-insulator transition kinetics.

Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB6

NASA Astrophysics Data System (ADS)

Hartstein, M.; Toews, W. H.; Hsu, Y.-T.; Zeng, B.; Chen, X.; Hatnean, M. Ciomaga; Zhang, Q. R.; Nakamura, S.; Padgett, A. S.; Rodway-Gant, G.; Berk, J.; Kingston, M. K.; Zhang, G. H.; Chan, M. K.; Yamashita, S.; Sakakibara, T.; Takano, Y.; Park, J.-H.; Balicas, L.; Harrison, N.; Shitsevalova, N.; Balakrishnan, G.; Lonzarich, G. G.; Hill, R. W.; Sutherland, M.; Sebastian, Suchitra E.

2018-02-01

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator-metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. Here we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB6 positioned close to the insulator-metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including a sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Thus, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.

Local spin density functional investigations of a manganite with perovskite-type derived structures

NASA Astrophysics Data System (ADS)

Matar, S. F.; Studer, F.; Siberchicot, B.; Subramanian, M. A.; Demazeau, G.; Etourneau, J.

1998-11-01

The electronic and magnetic structures of the perovskite CaMnO3 are self-consistently calculated assuming two crystal structures at the same formula unit volume within the local spin density functional theory and the augmented spherical wave (ASW) method. From the comparisons of energy differences between the different magnetic states the ground state configuration is an insulator with G-type ordering. This result together with the magnitudes of the magnetic moments are in agreement with experiment. The influence of mixing between Mn and O is found spin dependent from the analysis of the crystal orbital overlap population (COOP) which enable to describe the chemical bond. The calculations underline a feature of a half metallic ferromagnet which could be connected with the colossal magnetoresistance (CMR) property of related compounds.

Magnetic-proximity-induced magnetoresistance on topological insulators

NASA Astrophysics Data System (ADS)

Chiba, Takahiro; Takahashi, Saburo; Bauer, Gerrit E. W.

2017-03-01

We theoretically study the magnetoresistance (MR) of two-dimensional massless Dirac electrons as found on the surface of three-dimensional topological insulators (TIs) that are capped by a ferromagnetic insulator (FI). We calculate charge and spin transport by Kubo and Boltzmann theories, taking into account the ladder-vertex correction and the in-scattering due to normal and magnetic disorder. The induced exchange splitting is found to generate an electric conductivity that depends on the magnetization orientation, but its form is very different from both the anisotropic and the spin Hall MR. The in-plane MR vanishes identically for nonmagnetic disorder, while out-of-plane magnetizations cause a large MR ratio. On the other hand, we do find an in-plane MR and planar Hall effect in the presence of magnetic disorder aligned with the FI magnetization. Our results may help us understand recent transport measurements on TI |FI systems.

Ab initio study of MF2 (M=Mn, Fe, Co, Ni) rutile-type compounds using the periodic unrestricted Hartree-Fock approach

NASA Astrophysics Data System (ADS)

de P. R. Moreira, Ibério; Dovesi, Roberto; Roetti, Carla; Saunders, Victor R.; Orlando, Roberto

2000-09-01

The ab initio periodic unrestricted Hartree-Fock method has been applied in the investigation of the ground-state structural, electronic, and magnetic properties of the rutile-type compounds MF2 (M=Mn, Fe, Co, and Ni). All electron Gaussian basis sets have been used. The systems turn out to be large band-gap antiferromagnetic insulators; the optimized geometrical parameters are in good agreement with experiment. The calculated most stable electronic state shows an antiferromagnetic order in agreement with that resulting from neutron scattering experiments. The magnetic coupling constants between nearest-neighbor magnetic ions along the [001], [111], and [100] (or [010]) directions have been calculated using several supercells. The resulting ab initio magnetic coupling constants are reasonably satisfactory when compared with available experimental data. The importance of the Jahn-Teller effect in FeF2 and CoF2 is also discussed.

The strength of electron electron correlation in Cs3C60

NASA Astrophysics Data System (ADS)

Baldassarre, L.; Perucchi, A.; Mitrano, M.; Nicoletti, D.; Marini, C.; Pontiroli, D.; Mazzani, M.; Aramini, M.; Riccó, M.; Giovannetti, G.; Capone, M.; Lupi, S.

2015-10-01

Cs3C60 is an antiferromagnetic insulator that under pressure (P) becomes metallic and superconducting below Tc = 38 K. The superconducting dome present in the T - P phase diagram close to a magnetic state reminds what found in superconducting cuprates and pnictides, strongly suggesting that superconductivity is not of the conventional Bardeen-Cooper-Schrieffer (BCS) type We investigate the insulator to metal transition induced by pressure in Cs3C60 by means of infrared spectroscopy supplemented by Dynamical Mean-Field Theory calculations. The insulating compound is driven towards a metallic-like behaviour, while strong correlations survive in the investigated pressure range. The metallization process is accompanied by an enhancement of the Jahn-Teller effect. This shows that electronic correlations are crucial in determining the insulating behaviour at ambient pressure and the bad metallic nature for increasing pressure. On the other hand, the relevance of the Jahn-Teller coupling in the metallic state confirms that phonon coupling survives in the presence of strong correlations.

Organic-inorganic proximity effect in the magneto-conductance of vertical organic field effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khachatryan, B.; Devir-Wolfman, A. H.; Ehrenfreund, E., E-mail: eitane@technion.ac.il

Vertical organic field effect transistors having a patterned source electrode and an a-SiO{sub 2} insulation layer show high performance as a switching element with high transfer characteristics. By measuring the low field magneto-conductance under ambient conditions at room temperature, we show here that the proximity of the inorganic a-SiO{sub 2} insulation to the organic conducting channel affects considerably the magnetic response. We propose that in n-type devices, electrons in the organic conducting channel and spin bearing charged defects in the inorganic a-SiO{sub 2} insulation layer (e.g., O{sub 2} = Si{sup +·}) form oppositely charged spin pairs whose singlet-triplet spin configurations are mixedmore » through the relatively strong hyperfine field of {sup 29}Si. By increasing the contact area between the insulation layer and the conducting channel, the ∼2% magneto-conductance response may be considerably enhanced.« less

Auto-magnetizing liners for magnetized inertial fusion

DOE PAGES

Slutz, S. A.; Jennings, C. A.; Awe, T. J.; ...

2017-01-20

Here, the MagLIF (Magnetized Liner Inertial Fusion) concept has demonstrated fusion-relevant plasma conditions on the Z accelerator using external field coils to magnetize the fuel before compression. We present a novel concept (AutoMag), which uses a composite liner with helical conduction paths separated by insulating material to provide fuel magnetization from the early part of the drive current, which by design rises slowly enough to avoid electrical breakdown of the insulators. Once the magnetization field is established, the drive current rises more quickly, which causes the insulators to break down allowing the drive current to follow an axial path andmore » implode the liner in the conventional z-pinch manner. There are two important advantages to AutoMag over external field coils for the operation of MagLIF. Low inductance magnetically insulated power feeds can be used to increase the drive current, and AutoMag does not interfere with diagnostic access. Also, AutoMag enables a pathway to energy applications for MagLIF, since expensive field coils will not be damaged each shot. Finally, it should be possible to generate Field Reversed Configurations (FRC) by using both external field coils and AutoMag in opposite polarities. This would provide a means to studying FRC liner implosions on the 100 ns time scale.« less

Magnetic field dependent dynamics and field-driven metal-to-insulator transition of the half-filled Hubbard model: A DMFT+DMRG study

DOE PAGES

Zhu, Wei; Sheng, D. N.; Zhu, Jian -Xin

2017-08-14

Here, we study the magnetic field-driven metal-to-insulator transition in half-filled Hubbard model on the Bethe lattice, using the dynamical mean-field theory by solving the quantum impurity problem with density-matrix renormalization group algorithm. The method enables us to obtain a high-resolution spectral densities in the presence of a magnetic field. It is found that the Kondo resonance at the Fermi level splits at relatively high magnetic field: the spin-up and -down components move away from the Fermi level and finally form a spin-polarized band insulator. By calculating the magnetization and spin susceptibility, we clarify that an applied magnetic field drives amore » transition from a paramagnetic metallic phase to a band insulating phase. In the weak interaction regime, the nature of the transition is continuous and captured by the Stoner's description, while in the strong interaction regime the transition is very likely to be metamagnetic, evidenced by the hysteresis curve. Furthermore, we determine the phase boundary by tracking the kink in the magnetic susceptibility, and the steplike change of the entanglement entropy and the entanglement gap closing. Interestingly, the phase boundaries determined from these two different ways are largely consistent with each other.« less

Magnetic field dependent dynamics and field-driven metal-to-insulator transition of the half-filled Hubbard model: A DMFT+DMRG study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Wei; Sheng, D. N.; Zhu, Jian -Xin

Here, we study the magnetic field-driven metal-to-insulator transition in half-filled Hubbard model on the Bethe lattice, using the dynamical mean-field theory by solving the quantum impurity problem with density-matrix renormalization group algorithm. The method enables us to obtain a high-resolution spectral densities in the presence of a magnetic field. It is found that the Kondo resonance at the Fermi level splits at relatively high magnetic field: the spin-up and -down components move away from the Fermi level and finally form a spin-polarized band insulator. By calculating the magnetization and spin susceptibility, we clarify that an applied magnetic field drives amore » transition from a paramagnetic metallic phase to a band insulating phase. In the weak interaction regime, the nature of the transition is continuous and captured by the Stoner's description, while in the strong interaction regime the transition is very likely to be metamagnetic, evidenced by the hysteresis curve. Furthermore, we determine the phase boundary by tracking the kink in the magnetic susceptibility, and the steplike change of the entanglement entropy and the entanglement gap closing. Interestingly, the phase boundaries determined from these two different ways are largely consistent with each other.« less

Improvement of microwave feeding on a large bore ECRIS with permanent magnets by using coaxial semi-dipole antenna

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurisu, Yosuke; Sakamoto, Naoki; Kiriyama, Ryutaro

2012-11-06

We are constructing a tandem type electron cyclotron resonance (ECR) ion source (ECRIS). The first stage of this ECRIS has a large-bore with cylindrically comb-shaped permanent magnets. 2.45GHz and 11-13GHz microwaves can be supplied individually and simultaneously to the plasma chamber. For 2.45GHz, a coaxial semi-dipole antenna is used to feed the microwaves. In previous experiments, there were two problems encountered when running the 2.45GHz microwaves. High incident power was necessary to keep ECR discharge at low operating pressure because of high reflected microwave power. The surface of a support insulator between the inner and the outer electrodes of coaxialmore » semi-dipole antenna was easily metalized by sputtering of the metal wall inside the chamber. The purpose of this study was to solve these problems. Performing several simulation experiments supports the hypothesis that the position of the support insulator is significant for microwave power efficiency. The end result was the ability to sustain ECR discharges at extremely low incident microwave power, several tens of watts, by optimized matching of the position and shape of the insulator.« less

Topological magnetic phase in LaMnO3 (111) bilayer

NASA Astrophysics Data System (ADS)

Weng, Yakui; Huang, Xin; Yao, Yugui; Dong, Shuai

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as Hubbard type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO3 (111) bilayer sandwiched in LaScO3 barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO3 (111) bilayer just stays at the Dirac point, rendering a semi-metal (graphene-like) which is also a half-metal (different from graphene nor previous studied LaNiO3 (111) bilayer). The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice (~ 1 . 7 meV) than the undistorted one (~11 meV).

Systems and methods for the magnetic insulation of accelerator electrodes in electrostatic accelerators

DOEpatents

Grisham, Larry R

2013-12-17

The present invention provides systems and methods for the magnetic insulation of accelerator electrodes in electrostatic accelerators. Advantageously, the systems and methods of the present invention improve the practically obtainable performance of these electrostatic accelerators by addressing, among other things, voltage holding problems and conditioning issues. The problems and issues are addressed by flowing electric currents along these accelerator electrodes to produce magnetic fields that envelope the accelerator electrodes and their support structures, so as to prevent very low energy electrons from leaving the surfaces of the accelerator electrodes and subsequently picking up energy from the surrounding electric field. In various applications, this magnetic insulation must only produce modest gains in voltage holding capability to represent a significant achievement.

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r3(Ru1-xM nx) 2O7

NASA Astrophysics Data System (ADS)

Zhang, Qiang; Ye, Feng; Tian, Wei; Cao, Huibo; Chi, Songxue; Hu, Biao; Diao, Zhenyu; Tennant, David A.; Jin, Rongying; Zhang, Jiandi; Plummer, Ward

2017-06-01

Bilayered S r3R u2O7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in S r3(Ru1-xM nx) 2O7 . Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in S r3(Ru1-xM nx) 2O7 (x =0.06 and 0.12). With the increase of Mn doping (x ) from 0.06 to 0.12 or the decrease of temperatures for x =0.12 , an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C4 v crystal lattice to a C2 v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.

Spin injection and spin transport in paramagnetic insulators

DOE PAGES

Okamoto, Satoshi

2016-02-22

We investigate the spin injection and the spin transport in paramagnetic insulators described by simple Heisenberg interactions using auxiliary particle methods. Some of these methods allow access to both paramagnetic states above magnetic transition temperatures and magnetic states at low temperatures. It is predicted that the spin injection at an interface with a normal metal is rather insensitive to temperatures above the magnetic transition temperature. On the other hand below the transition temperature, it decreases monotonically and disappears at zero temperature. We also analyze the bulk spin conductance. We show that the conductance becomes zero at zero temperature as predictedmore » by linear spin wave theory but increases with temperature and is maximized around the magnetic transition temperature. These findings suggest that the compromise between the two effects determines the optimal temperature for spintronics applications utilizing magnetic insulators.« less

Theoretical study on the perpendicular anisotropic magnetoresistance using Rashba-type ferromagnetic model

NASA Astrophysics Data System (ADS)

Yahagi, Y.; Miura, D.; Sakuma, A.

2018-05-01

We investigated the anisotropic magnetoresistance (AMR) effects in ferromagnetic-metal multi-layers stacked on non-magnetic insulators in the context of microscopic theory. We represented this situation with tight-binding models that included the exchange and Rashba fields, where the Rashba field was assumed to originate from spin-orbit interactions as junction effects with the insulator. To describe the AMR ratios, the DC conductivity was calculated based on the Kubo formula. As a result, we showed that the Rashba field induced both perpendicular and in-plane AMR effects and that the perpendicular AMR effect rapidly decayed with increasing film thickness.

Chern structure in the Bose-insulating phase of Sr2RuO4 nanofilms

NASA Astrophysics Data System (ADS)

Nobukane, Hiroyoshi; Matsuyama, Toyoki; Tanda, Satoshi

2017-01-01

The quantum anomaly that breaks the symmetry, for example the parity and the chirality, in the quantization leads to a physical quantity with a topological Chern invariant. We report the observation of a Chern structure in the Bose-insulating phase of Sr2RuO4 nanofilms by employing electric transport. We observed the superconductor-to-insulator transition by reducing the thickness of Sr2RuO4 single crystals. The appearance of a gap structure in the insulating phase implies local superconductivity. Fractional quantized conductance was observed without an external magnetic field. We found an anomalous induced voltage with temperature and thickness dependence, and the induced voltage exhibited switching behavior when we applied a magnetic field. We suggest that there was fractional magnetic-field-induced electric polarization in the interlayer. These anomalous results are related to topological invariance. The fractional axion angle Θ = π/6 was determined by observing the topological magneto-electric effect in the Bose-insulating phase of Sr2RuO4 nanofilms.

Magnon diffusion theory for the spin Seebeck effect in ferromagnetic and antiferromagnetic insulators

NASA Astrophysics Data System (ADS)

Rezende, Sergio M.; Azevedo, Antonio; Rodríguez-Suárez, Roberto L.

2018-05-01

In magnetic insulators, spin currents are carried by the elementary excitations of the magnetization: spin waves or magnons. In simple ferromagnetic insulators there is only one magnon mode, while in two-sublattice antiferromagnetic insulators (AFIs) there are two modes, which carry spin currents in opposite directions. Here we present a theory for the diffusive magnonic spin current generated in a magnetic insulator layer by a thermal gradient in the spin Seebeck effect. We show that the formulations describing magnonic perturbation using a position-dependent chemical potential and those using a magnon accumulation are completely equivalent. Then we develop a drift–diffusion formulation for magnonic spin transport treating the magnon accumulation governed by the Boltzmann transport and diffusion equations and considering the full boundary conditions at the surfaces and interfaces of an AFI/normal metal bilayer. The theory is applied to the ferrimagnetic yttrium iron garnet and to the AFIs MnF2 and NiO, providing good quantitative agreement with experimental data.

Design of load-to-failure tests of high-voltage insulation breaks for ITER's cryogenic network

NASA Astrophysics Data System (ADS)

Langeslag, S. A. E.; Rodriguez Castro, E.; Aviles Santillana, I.; Sgobba, S.; Foussat, A.

2015-12-01

The development of new generation superconducting magnets for fusion research, such as the ITER experiment, is largely based on coils wound with so-called cable-in-conduit conductors. The concept of the cable-in-conduit conductor is based on a direct cooling principle, by supercritical helium, flowing through the central region of the conductor, in close contact with the superconducting strands. Consequently, a direct connection exists between the electrically grounded helium coolant supply line and the highly energised magnet windings. Various insulated regions, constructed out of high-voltage insulation breaks, are put in place to isolate sectors with different electrical potential. In addition to high voltages and significant internal helium pressure, the insulation breaks will experience various mechanical forces resulting from differential thermal contraction phenomena and electro-magnetic loads. Special test equipment was designed, prepared and employed to assess the mechanical reliability of the insulation breaks. A binary test setup is proposed, where mechanical failure is assumed when leak rate of gaseous helium exceeds 10-9·Pa·m3/s. The test consists of a load-to-failure insulation break charging, in tension, while immersed in liquid nitrogen at the temperature of 77 K. Leak tightness during the test is monitored by measuring the leak rate of the gaseous helium, directly surrounding the insulation break, with respect to the existing vacuum inside the insulation break. The experimental setup is proven effective, and various insulation breaks performed beyond expectations.

Strain driven sequential magnetic transitions in strained GdTiO3 on compressive substrates: a first-principles study.

PubMed

Yang, Li-Juan; Weng, Ya-Kui; Zhang, Hui-Min; Dong, Shuai

2014-11-26

The compressive strain effect on the magnetic ground state and electronic structure of strained GdTiO3 has been studied using the first-principles method. Unlike the cases of congeneric YTiO3 and LaTiO3, both of which become the A-type antiferromagnetism on the (0 0 1) LaAlO3 substrate despite their contrastive magnetism, the ground state of strained GdTiO3 on the LaAlO3 substrate changes from the original ferromagnetism to a G-type antiferromagnetim, instead of the A-type one although Gd(3+) is between Y(3+) and La(3+). It is only when the in-plane compressive strain is large enough, e.g. on the (0 0 1) YAlO3 substrate, that the ground state finally becomes the A-type. The band structure calculation shows that the compressive strained GdTiO3 remains insulating, although the band gap changes a little in the strained GdTiO3.

Irradiation effect of the insulating materials for fusion superconducting magnets at cryogenic temperature

NASA Astrophysics Data System (ADS)

Kobayashi, Koji; Akiyama, Yoko; Nishijima, Shigehiro

2017-09-01

In ITER, superconducting magnets should be used in such severe environment as high fluence of fast neutron, cryogenic temperature and large electromagnetic forces. Insulating material is one of the most sensitive component to radiation. So radiation resistance on mechanical properties at cryogenic temperature are required for insulating material. The purpose of this study is to evaluate irradiation effect of insulating material at cryogenic temperature by gamma-ray irradiation. Firstly, glass fiber reinforced plastic (GFRP) and hybrid composite were prepared. After irradiation at room temperature (RT) or liquid nitrogen temperature (LNT, 77 K), interlaminar shear strength (ILSS) and glass-transition temperature (Tg) measurement were conducted. It was shown that insulating materials irradiated at room temperature were much degraded than those at cryogenic temperature.

Localized superconductivity in the quantum-critical region of the disorder-driven superconductor-insulator transition in TiN thin films.

PubMed

Baturina, T I; Mironov, A Yu; Vinokur, V M; Baklanov, M R; Strunk, C

2007-12-21

We investigate low-temperature transport properties of thin TiN superconducting films in the vicinity of the disorder-driven superconductor-insulator transition. In a zero magnetic field, we find an extremely sharp separation between superconducting and insulating phases, evidencing a direct superconductor-insulator transition without an intermediate metallic phase. At moderate temperatures, in the insulating films we reveal thermally activated conductivity with the magnetic field-dependent activation energy. At very low temperatures, we observe a zero-conductivity state, which is destroyed at some depinning threshold voltage V{T}. These findings indicate the formation of a distinct collective state of the localized Cooper pairs in the critical region at both sides of the transition.

Negative ion generator

DOEpatents

Stinnett, R.W.

1984-05-08

A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions. 8 figs.

Negative ion generator

DOEpatents

Stinnett, Regan W.

1984-01-01

A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions.

Magnetic field tuning of an excitonic insulator between the weak and strong coupling regimes in quantum limit graphite [Tunable excitonic insulator in quantum limit graphite

DOE PAGES

Zhu, Zengwei; McDonald, R. D.; Shekhter, A.; ...

2017-05-04

Here, the excitonic insulator phase has long been predicted to form in proximity to a band gap opening in the underlying band structure. The character of the pairing is conjectured to crossover from weak (BCS-like) to strong coupling (BEC-like) as the underlying band structure is tuned from the metallic to the insulating side of the gap opening. Here we report the high-magnetic field phase diagram of graphite to exhibit just such a crossover. By way of comprehensive angle-resolved magnetoresistance measurements, we demonstrate that the underlying band gap opening occurs inside the magnetic field-induced phase, paving the way for a systematicmore » study of the BCS-BEC-like crossover by means of conventional condensed matter probes.« less

Magnetic field tuning of an excitonic insulator between the weak and strong coupling regimes in quantum limit graphite [Tunable excitonic insulator in quantum limit graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Zengwei; McDonald, R. D.; Shekhter, A.

Here, the excitonic insulator phase has long been predicted to form in proximity to a band gap opening in the underlying band structure. The character of the pairing is conjectured to crossover from weak (BCS-like) to strong coupling (BEC-like) as the underlying band structure is tuned from the metallic to the insulating side of the gap opening. Here we report the high-magnetic field phase diagram of graphite to exhibit just such a crossover. By way of comprehensive angle-resolved magnetoresistance measurements, we demonstrate that the underlying band gap opening occurs inside the magnetic field-induced phase, paving the way for a systematicmore » study of the BCS-BEC-like crossover by means of conventional condensed matter probes.« less

Strain effect on magnetic property of antiferromagnetic insulator SmFeO3

NASA Astrophysics Data System (ADS)

Kuroda, M.; Tanahashi, N.; Hajiri, T.; Ueda, K.; Asano, H.

2018-05-01

Thin films and heterostructures of antiferromagnetic insulator SmFeO3 were fabricated on LaAlO3 (001) substrates by magnetron sputtering, and their structural, magnetic properties were investigated. It was found that epitaxially strained thin films showed a pronounced magnetic anisotropy with the enhanced magnetization up to 65 emu/cc, which is approximately ten times larger than the bulk value. The observed enhancement of magnetization was considered to be due to the lattice distortion and the non-collinear antiferromagnetic spin ordering of SmFeO3.

Dimensionality-strain phase diagram of strontium iridates

NASA Astrophysics Data System (ADS)

Kim, Bongjae; Liu, Peitao; Franchini, Cesare

2017-03-01

The competition between spin-orbit coupling, bandwidth (W ), and electron-electron interaction (U ) makes iridates highly susceptible to small external perturbations, which can trigger the onset of novel types of electronic and magnetic states. Here we employ first principles calculations based on density functional theory and on the constrained random phase approximation to study how dimensionality and strain affect the strength of U and W in (SrIrO3)m/(SrTiO3) superlattices. The result is a phase diagram explaining two different types of controllable magnetic and electronic transitions, spin-flop and insulator-to-metal, connected with the disruption of the Jeff=1 /2 state which cannot be understood within a simplified local picture.

High-Frequency Response and Voltage Noise in Magnetic Nanocomposites

NASA Astrophysics Data System (ADS)

Buznikov, N. A.; Iakubov, I. T.; Rakhmanov, A. L.; Kugel, K. I.; Sboychakov, A. O.

We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials consisting of single-domain magnetic nanoparticles embedded into an insulating matrix. Possible mechanisms of 1/f voltage noise in phase-separated manganites is analyzed. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in insulating antiferromagnetic or paramagnetic matrix. The electron transport is related to tunnelling of charge carriers between droplets. One of the sources of the 1/f noise in such a system stems from fluctuations of the number of droplets with extra electron. In the case of strong magnetic anisotropy, the 1/f noise can arise also due to the fluctuations of the magnetic moments of ferrons. The high frequency magnetic permeability of nanocomposite film with magnetic particles in insulating non-magnetic matrix is studied in detail. The case of strong magnetic dipole interaction and strong magnetic anisotropy of ferromagnetic granules is considered. The composite is modelled by a cubic regular array of ferromagnetic particles. The high-frequency permeability tensor components are found as a functions of frequency, temperature, ferromagnetic phase content, and magnetic anisotropy. The results demonstrate that magnetic dipole interaction leads to a shift of the resonance frequencies towards higher values, and nanocomposite film could have rather high value of magnetic permeability in the microwave range.

High-Frequency Response and Voltage Noise in Magnetic Nanocomposites

NASA Astrophysics Data System (ADS)

Buznikov, N. A.; Iakubov, I. T.; Rakhmanov, A. L.; Kugel, K. I.; Sboychakov, A. O.

2010-12-01

We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials consisting of single-domain magnetic nanoparticles embedded into an insulating matrix. Possible mechanisms of 1/f voltage noise in phase-separated manganites is analyzed. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in insulating antiferromagnetic or paramagnetic matrix. The electron transport is related to tunnelling of charge carriers between droplets. One of the sources of the 1/f noise in such a system stems from fluctuations of the number of droplets with extra electron. In the case of strong magnetic anisotropy, the 1/f noise can arise also due to the fluctuations of the magnetic moments of ferrons. The high frequency magnetic permeability of nanocomposite film with magnetic particles in insulating non-magnetic matrix is studied in detail. The case of strong magnetic dipole interaction and strong magnetic anisotropy of ferromagnetic granules is considered. The composite is modelled by a cubic regular array of ferromagnetic particles. The high-frequency permeability tensor components are found as a functions of frequency, temperature, ferromagnetic phase content, and magnetic anisotropy. The results demonstrate that magnetic dipole interaction leads to a shift of the resonance frequencies towards higher values, and nanocomposite film could have rather high value of magnetic permeability in the microwave range.

Voltage Control of Rare-Earth Magnetic Moments at the Magnetic-Insulator-Metal Interface

NASA Astrophysics Data System (ADS)

Leon, Alejandro O.; Cahaya, Adam B.; Bauer, Gerrit E. W.

2018-01-01

The large spin-orbit interaction in the lanthanides implies a strong coupling between their internal charge and spin degrees of freedom. We formulate the coupling between the voltage and the local magnetic moments of rare-earth atoms with a partially filled 4 f shell at the interface between an insulator and a metal. The rare-earth-mediated torques allow the power-efficient control of spintronic devices by electric-field-induced ferromagnetic resonance and magnetization switching.

Evolution of competing magnetic order in the J eff=1/2 insulating state of Sr 2Ir 1-xRu xO 4

DOE PAGES

Calder, Stuart A.; Kim, Jong-Woo; Cao, Guixin; ...

2015-10-27

We investigate the magnetic properties of the series Sr 2Ir 1-xRu xO 4 with neutron, resonant x-ray and magnetization measurements. The results indicate an evolution and coexistence of magnetic structures via a spin flop transition from ab-plane to c-axis collinear order as the 5d Ir4 + ions are replaced with an increasing concentration of 4d Ru4 + ions. The magnetic structures within the ordered regime of the phase diagram (x<0.3) are reported. Despite the changes in magnetic structure no alteration of the J eff=1/2 ground state is observed. This behavior of Sr 2Ir 1-xRu xO 4 is consistent with electronicmore » phase separation and diverges from a standard scenario of hole doping. The role of lattice alterations with doping on the magnetic and insulating behavior is considered. Our results presented here provide insight into the magnetic insulating states in strong spin-orbit coupled materials and the role perturbations play in altering the behavior.« less

Electronic localization in an extreme 1-D conductor: the organic salt (TTDM-TTF) [Au(mnt)

NASA Astrophysics Data System (ADS)

Lopes, E. B.; Alves, H.; Ribera, E.; Mas-Torrent, M.; Auban-Senzier, P.; Canadell, E.; Henriques, R. T.; Almeida, M.; Molins, E.; Veciana, J.; Rovira, C.; Jérome, D.

2002-09-01

This article reports the investigation of a new low-dimensional organic salt, (TTDM-TTF)2 [ Au(mnt)2] , by single crystal X-ray diffraction, static magnetic susceptibility, EPR, thermopower, electrical resistivity measurements under pressure up to 25 kbar and band structure calculations. The crystal structure consists in a dimerized head to tail stacking of TTDM-TTF molecules separated by layers of orthogonal Au(mnt)2 anions. The absence of overlap between neighboring chains coming from this particular crystal structure leads to an extreme one-dimensionality (1-D) for which the carriers of the half-filled conduction band become strongly localized in a Mott-Hubbard insulating state. This material is the first 1-D conductor in which the Mott-Hubbard insulating character cannot be suppressed under pressure.

Structural and electronic properties of Li-ion battery cathode material MoF{sub 3} from first-principles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, A.Y.; Wu, S.Q.; Yang, Y.

2015-07-15

The transition metal fluorides have been extensively investigated recently as the electrode materials with high working voltage and large capacity. The structural, electronic and magnetic properties of MoF{sub 3} are studied by the first-principles calculations within both the generalized gradient approximation (GGA) and GGA+U frameworks. Our results show that the antiferromagnetic configuration of MoF{sub 3} is more stable than the ferromagnetic one, which is consistent with experimental results. The analysis of the electronic density of states shows that MoF{sub 3} is a Mott–Hubbard insulator with a d–d type band gap, which is similar to the case of FeF{sub 3}. Moreover,more » small spin polarizations were found on the sites of fluorine ions, which accords with a fluorine-mediated superexchange mechanism for the Mo–Mo magnetic interaction. - Graphical abstract: Deformation charge density and spin-density for MoF{sub 3} in the AF configuration. - Highlights: • The ground state of MoF{sub 3} is shown to be antiferromagnetic, in consistent with experiments. • The electronic states show that MoF{sub 3} is a Mott–Hubbard insulator with a d–d type band gap. • A fluorine-mediated super-exchange mechanism for the Mo–Mo magnetic interaction is shown.« less

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4.

PubMed

Dean, M P M; Cao, Y; Liu, X; Wall, S; Zhu, D; Mankowsky, R; Thampy, V; Chen, X M; Vale, J G; Casa, D; Kim, Jungho; Said, A H; Juhas, P; Alonso-Mori, R; Glownia, J M; Robert, A; Robinson, J; Sikorski, M; Song, S; Kozina, M; Lemke, H; Patthey, L; Owada, S; Katayama, T; Yabashi, M; Tanaka, Yoshikazu; Togashi, T; Liu, J; Rayan Serrao, C; Kim, B J; Huber, L; Chang, C-L; McMorrow, D F; Först, M; Hill, J P

2016-06-01

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

Spin-transfer torque induced spin waves in antiferromagnetic insulators

DOE PAGES

Daniels, Matthew W.; Guo, Wei; Stocks, George Malcolm; ...

2015-01-01

We explore the possibility of exciting spin waves in insulating antiferromagnetic films by injecting spin current at the surface. We analyze both magnetically compensated and uncompensated interfaces. We find that the spin current induced spin-transfer torque can excite spin waves in insulating antiferromagnetic materials and that the chirality of the excited spin wave is determined by the polarization of the injected spin current. Furthermore, the presence of magnetic surface anisotropy can greatly increase the accessibility of these excitations.

Scanning-SQUID investigation of spin-orbit torque acting on yttrium iron garnet devices

NASA Astrophysics Data System (ADS)

Rosenberg, Aaron J.; Jermain, Colin L.; Aradhya, Sriharsha V.; Brangham, Jack T.; Nowack, Katja C.; Kirtley, John R.; Yang, Fengyuan; Ralph, Daniel C.; Moler, Kathryn A.

Successful manipulation of electrically insulating magnets, such as yttrium iron garnet, by by current-driven spin-orbit torques could provide a highly efficient platform for spintronic memory. Compared to devices fabricated using magnetic metals, magnetic insulators have the advantage of the ultra-low magnetic damping and the elimination of shunting currents in the magnet that reduce the torque efficiency. Here, we apply current in the spin Hall metal β-Ta to manipulate the magnetic orientation of micron-sized, electrically-insulating yttrium iron garnet devices. We do not observe spin-torque switching even for applied currents well above the critical current expected in a macrospin switching model. This suggests either inefficient transfer of spin torque at our Ta/YIG interface or a breakdown of the macrospin approximation. This work is supported by FAME, one of six centers of STARnet sponsored by MARCO and DARPA. The SQUID microscope and sensors were developed with support from the NSF-sponsored Center NSF-NSEC 0830228, and from NSF IMR-MIP 0957616.

Pressure measurements with a precision of 0.001 ppm in magnetic fields at low temperatures

NASA Astrophysics Data System (ADS)

Miura, Y.; Matsushima, N.; Ando, T.; Kuno, S.; Inoue, S.; Ito, K.; Mamiya, T.

1993-11-01

Pressure measurements made by an ac bridge technique with a precision of 0.001 ppm in magnetic fields at low temperatures using a Straty-Adams type gauge are described. In order to improve the sensitivity and the long-term stability of the bridge system, coaxial cables without dielectric insulator were developed, with a small cable capacitance temperature coefficient of the impedance. This pressure measurement system has a sensitivity of dP/P˜5×10-10 and a long-term stability of dP/P˜2.4×10-9 over 18 h. This is especially useful for measurements such as electric and magnetic susceptibility measurements in magnetic fields at low temperatures requiring a high precision.

Using fiberglass volumes for VPI of superconductive magnetic systems’ insulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreev, I. S.; Bezrukov, A. A.; Pischugin, A. B.

2014-01-29

The paper describes the method of manufacturing fiberglass molds for vacuum pressure impregnation (VPI) of high-voltage insulation of superconductive magnetic systems (SMS) with epoxidian hot-setting compounds. The basic advantages of using such vacuum volumes are improved quality of insulation impregnation in complex-shaped areas, and considerable cost-saving of preparing VPI of large-sized components due to dispensing with the stage of fabricating a metal impregnating volume. Such fiberglass vacuum molds were used for VPI of high-voltage insulation samples of an ITER reactor’s PF1 poloidal coil. Electric insulation of these samples has successfully undergone a wide range of high-voltage and mechanical tests atmore » room and cryogenic temperatures. Some results of the tests are also given in this paper.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mironov, Alexey Yu.; Silevitch, Daniel M.; Proslier, Thomas

Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this duality-the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT-has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance,more » and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.« less

Rheological behavior and cryogenic properties of cyanate ester/epoxy insulation material for fusion superconducting magnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Z. X.; Huang, C. J.; Li, L. F.

2014-01-27

In a Tokamak fusion reactor device like ITER, insulation materials for superconducting magnets are usually fabricated by a vacuum pressure impregnation (VPI) process. Thus these insulation materials must exhibit low viscosity, long working life as well as good radiation resistance. Previous studies have indicated that cyanate ester (CE) blended with epoxy has an excellent resistance against neutron irradiation which is expected to be a candidate insulation material for a fusion magnet. In this work, the rheological behavior of a CE/epoxy (CE/EP) blend containing 40% CE was investigated with non-isothermal and isothermal viscosity experiments. Furthermore, the cryogenic mechanical and electrical propertiesmore » of the composite were evaluated in terms of interlaminar shear strength and electrical breakdown strength. The results showed that CE/epoxy blend had a very low viscosity and an exceptionally long processing life of about 4 days at 60 °C.« less

Pure electronic metal-insulator transition at the interface of complex oxides

DOE PAGES

Meyers, D.; Liu, Jian; Freeland, J. W.; ...

2016-06-21

We observed complex materials in electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. We demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. Furthermore, these findings illustrate the utility of heterointerfaces as amore » powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.« less

Spin-Orbit Torque-Assisted Switching in Magnetic Insulator Thin Films with Perpendicular Magnetic Anisotropy

NASA Astrophysics Data System (ADS)

Wu, Mingzhong

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque that can induce magnetization switching in a neighboring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. This presentation reports the SOT-assisted switching in heavy metal/magnetic insulator systems.1 The experiments made use of Pt/BaFe12O19 bi-layered structures. Thanks to its strong spin-orbit coupling, Pt has been widely used to produce pure spin currents in previous studies. BaFe12O19 is an M-type barium hexagonal ferrite and is often referred as BaM. It is one of the few magnetic insulators with strong magneto-crystalline anisotropy and shows an effective uniaxial anisotropy field of about 17 kOe. It's found that the switching response in the BaM film strongly depends on the charge current applied to the Pt film. When a constant magnetic field is applied in the film plane, the charge current in the Pt film can switch the normal component of the magnetization (M⊥) in the BaM film between the up and down states. The current also dictates the up and down states of the remnant magnetization when the in-plane field is reduced to zero. When M⊥ is measured by sweeping an in-plane field, the response manifests itself as a hysteresis loop, which evolves in a completely opposite manner if the sign of the charge current is flipped. When the coercivity is measured by sweeping an out-of-plane field, its value can be reduced or increased by as much as about 500 Oe if an appropriate charge current is applied. 1. P. Li, T. Liu, H. Chang, A. Kalitsov, W. Zhang, G. Csaba, W. Li, D. Richardson, A. Demann, G. Rimal, H. Dey, J. S. Jiang, W. Porod, S. Field, J. Tang, M. C. Marconi, A. Hoffmann, O. Mryasov, and M. Wu, Nature Commun. 7:12688 doi: 10.1038/ncomms12688 (2016).

Theory of metal-insulator transition in the family of perovskite iridium oxides

NASA Astrophysics Data System (ADS)

Carter, Jean-Michel; Shankar V., Vijay; Kee, Hae-Young

2013-07-01

Perovskite iridium oxides Srn+1IrnO3n+1 exhibit fascinating phenomena due to the combined effects of spin-orbit coupling (SOC) and electronic interactions. It was suggested that electronic correlation amplified via the strong SOC leads to a spin-orbit Mott insulator for n=1 and 2, while three-dimensional (3D) SrIrO3 remains metallic because of the large bandwidth from the 3D structure. However, this bandwidth-controlled metal-insulator transition (MIT) is only valid when SOC is large enough to split Jeff=1/2 and 3/2 bands, while the mixing of 1/2 and 3/2 bands is conspicuous among the occupied bands. Here, we investigate the MIT as a function of n using weak-coupling theory. In this approach, the magnetic instability is determined by the states near the Fermi level rather than the entire band structure. Starting from t2g tight-binding models for n=1, 2, and ∞, the states near the Fermi level are found to be predominantly Jeff=1/2 allowing an effective single-band model. Supplementing this effective Jeff=1/2 model with Hubbard-type interactions, transitions from a metal to magnetically ordered states are obtained. Strong-coupling spin models are derived to compare the magnetic ordering patterns obtained in the weak- and strong-coupling limits. We find that they are identical, indicating that these iridates are likely in an intermediate-coupling regime.

Exfoliated BN shell-based high-frequency magnetic core-shell materials.

PubMed

Zhang, Wei; Patel, Ketan; Ren, Shenqiang

2017-09-14

The miniaturization of electric machines demands high frequency magnetic materials with large magnetic-flux density and low energy loss to achieve a decreased dimension of high rotational speed motors. Herein, we report a solution-processed high frequency magnetic composite (containing a nanometal FeCo core and a boron nitride (BN) shell) that simultaneously exhibits high electrical resistivity and magnetic permeability. The frequency dependent complex initial permeability and the mechanical robustness of nanocomposites are intensely dependent on the content of BN insulating phase. The results shown here suggest that insulating magnetic nanocomposites have potential for application in next-generation high-frequency electric machines with large electrical resistivity and permeability.

Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr 2IrO 4

DOE PAGES

Wang, J. C.; Aswartham, S.; Ye, Feng; ...

2015-12-08

Sr 2IrO 4 is a spin-orbit coupled insulator with an antiferromagnetic (AFM) transition at T N = 240 K. We report results of a comprehensive study of single-crystal Sr 2Ir 1-xTb xO 4 (0≤x≤0.03). This study found that mere 3% (x=0.03) tetravalent Tb 4+(4f 7) substituting for Ir 4+ (rather than Sr 2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensuratemore » magnetic state having magnetic peaks at (0.95, 0, 0) and (0, 0.95, 0) in the neutron diffraction, suggesting a spiral or spin density wave order. It is apparent that Tb doping effectively changes the relative strength of the SOI and the tetragonal CEF and enhances the Hund’s rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM accompanies no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and renders a persistent insulating state. Furthermore, this work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.« less

Chern structure in the Bose-insulating phase of Sr2RuO4 nanofilms

PubMed Central

Nobukane, Hiroyoshi; Matsuyama, Toyoki; Tanda, Satoshi

2017-01-01

The quantum anomaly that breaks the symmetry, for example the parity and the chirality, in the quantization leads to a physical quantity with a topological Chern invariant. We report the observation of a Chern structure in the Bose-insulating phase of Sr2RuO4 nanofilms by employing electric transport. We observed the superconductor-to-insulator transition by reducing the thickness of Sr2RuO4 single crystals. The appearance of a gap structure in the insulating phase implies local superconductivity. Fractional quantized conductance was observed without an external magnetic field. We found an anomalous induced voltage with temperature and thickness dependence, and the induced voltage exhibited switching behavior when we applied a magnetic field. We suggest that there was fractional magnetic-field-induced electric polarization in the interlayer. These anomalous results are related to topological invariance. The fractional axion angle Θ = π/6 was determined by observing the topological magneto-electric effect in the Bose-insulating phase of Sr2RuO4 nanofilms. PMID:28112269

Time-resolved magnetic spectrometer measurements of the SABRE positive polarity magnetically insulated transmission line voltage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menge, P.R.; Cuneo, M.E.; Hanson, D.L.

A magnetic spectrometer has been fielded on the coaxial magnetically insulated transmission line (MITL) of the SABRE ten-cavity inductive voltage adder operated in positive polarity (6 MV, 300 kA, 50 ns). Located 1 m upstream from an extraction ion diode, this diagnostic is capable of measuring the SABRE voltage pulse with a 2 ns resolution. Ions (protons and carbon) from either a flashover or plasma gun source are accelerated from the inner anode across the gap to the outer cathode and into a drift tube terminated by the magnetic spectrometer. The magnetically deflected ions are recorded on up to sixteenmore » PIN diodes (diameter = 1 mm, thickness = 35 {mu}). The voltage waveform is produced from the time-of-flight information. Results confirm previous observations of a vacuum wave precursor separated from the magnetically insulated wave. Verification of upstream precursor erosion techniques are possible with this instrument. Measurements of peak voltage show good agreement with other time-integrated voltage diagnostics. Comparisons with theoretical voltage predictions derived from a flow impedance model of MITL behavior will be presented.« less

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r 3 ( R u 1 - x M n x ) 2 O 7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Qiang; Ye, Feng; Tian, Wei

Bilayered Sr 3Ru 2O 7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr 3(Ru 1-xMn x) 2O 7. Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in Sr 3(Ru 1-xMn x) 2O 7 (x=0.06 and 0.12). With the increase of Mn doping (x) from 0.06 to 0.12 or the decrease of temperatures for x=0.12,more » an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C 4v crystal lattice to a C 2v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.« less

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r 3 ( R u 1 - x M n x ) 2 O 7

DOE PAGES

Zhang, Qiang; Ye, Feng; Tian, Wei; ...

2017-06-12

Bilayered Sr 3Ru 2O 7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr 3(Ru 1-xMn x) 2O 7. Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in Sr 3(Ru 1-xMn x) 2O 7 (x=0.06 and 0.12). With the increase of Mn doping (x) from 0.06 to 0.12 or the decrease of temperatures for x=0.12,more » an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C 4v crystal lattice to a C 2v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.« less

Observation of non-Fermi liquid behavior in hole-doped Eu2Ir2O7

NASA Astrophysics Data System (ADS)

Banerjee, A.; Sannigrahi, J.; Giri, S.; Majumdar, S.

2017-12-01

The Weyl semimetallic compound Eu2Ir2O7 and its hole-doped derivatives (which are achieved by substituting trivalent Eu by divalent Sr) are investigated through transport, magnetic, and calorimetric studies. The metal-insulator transition (MIT) temperature is found to get substantially reduced with hole doping, and for 10% Sr doping the composition is metallic down to temperature as low as 5 K. These doped compositions are found to violate the Mott-Ioffe-Regel condition for minimum electrical conductivity and show a distinct signature of non-Fermi liquid behavior at low temperature. The MIT in the doped compounds does not correlate with the magnetic transition point, and Anderson-Mott-type disorder-induced localization may be attributed to the ground-state insulating phase. The observed non-Fermi liquid behavior can be understood on the basis of disorder-induced distribution of the spin-orbit-coupling parameter, which is markedly different in the case of Ir4 + and Ir5 + ions.

Superconducting and magnetic properties of Bi 2Sr 2Ca 1- xY xCu 2O y (0≦ x≦1)

NASA Astrophysics Data System (ADS)

Yoshizaki, R.; Saito, Y.; Abe, Y.; Ikeda, H.

1988-07-01

The effect of substitution of Y atoms for Ca atoms has been studied in the Bi 2Sr 2Ca 1- xY xCu 2O y compound system. For x<0.5, superconductivity is observed and its fractional volume is reduced with increasing x, though the transition temperature of about 85 K is maintained. For x≧0.5 samples, the electrical resistivity behavior can be well described by the three-dimensional variable range hopping conduction, indicating that the system is essentially insulating. In this range of x, magnetic susceptibility shows spin-glass-type cusp at 13 K in the heating process after zero-field cooling and an enhanced cusp at 11 K in the field-cooling process. In the temperature range above about 150 K the Curie-Weiss dependence holds well with a positive paramagnetic Curie temperature, which increases to 40 K with increasing x in the insulating region.

Wiring assembly and method of forming a channel in a wiring assembly for receiving conductor and providing separate regions of conductor contact with the channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stelzer, Gerald; Meinke, Rainer; Senti, Mark

A conductor assembly and method for constructing an assembly of the type which, when conducting current, generates a magnetic field or which, in the presence of a changing magnetic field, induces a voltage. In one embodiment the method provides a first insulative layer tubular in shape and including a surface along which a conductor segment may be positioned. A channel formed in the surface of the insulative layer defines a first conductor path and includes a surface of first contour in cross section along a first plane transverse to the conductor path. A segment of conductor having a surface ofmore » second contour in cross section is positioned at least partly in the channel and extends along the conductor path. Along the first plane, contact between the conductor surface of second contour and the channel surface of first contour includes at least two separate regions of contact.« less

Tunneling magnetoresistance from a symmetry filtering effect

PubMed Central

Butler, William H

2008-01-01

This paper provides a brief overview of the young, but rapidly growing field of spintronics. Its primary objective is to explain how as electrons tunnel through simple insulators such as MgO, wavefunctions of certain symmetries are preferentially transmitted. This symmetry filtering property can be converted into a spin-filtering property if the insulator is joined epitaxially to a ferromagnetic electrode with the same two-dimensional symmetry parallel to the interface. A second requirement of the ferromagnetic electrodes is that a wavefunction with the preferred symmetry exists in one of the two spin channels but not in the other. These requirements are satisfied for electrons traveling perpendicular to the interface for Fe–MgO–Fe tunnel barriers. This leads to a large change in the resistance when the magnetic moment of one of the electrodes is rotated relative to those of the other electrode. This large tunneling magnetoresistance effect is being used as the read sensor in hard drives and may form the basis for a new type of magnetic memory. PMID:27877932

Topological magnetic phase in LaMnO3 (111) bilayer

NASA Astrophysics Data System (ADS)

Weng, Yakui; Huang, Xin; Yao, Yugui; Dong, Shuai

2015-11-01

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as the Hubbard-type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO3 (111) bilayer sandwiched in LaScO3 barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO3 (111) bilayer just stays at the Dirac point, rendering a semimetal (graphenelike) which is also a half metal [different from graphene or the previously studied LaNiO3 (111) bilayer]. The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice (˜1.7 meV) than the undistorted one (˜11 meV). Therefore, to suppress the lattice distortion can be helpful to enhance the robustness of the topological phase in perovskite (111) bilayers.

Superconductor to weak-insulator transitions in disordered tantalum nitride films

NASA Astrophysics Data System (ADS)

Breznay, Nicholas P.; Tendulkar, Mihir; Zhang, Li; Lee, Sang-Chul; Kapitulnik, Aharon

2017-10-01

We study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents z ν ≈1.3 , with a corresponding critical field Hc≪Hc 2 , the upper critical field. The Hall effect exhibits a crossing point near Hc, but with a nonuniversal critical value ρxy c comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.

Quantum transport of two-species Dirac fermions in dual-gated three-dimensional topological insulators

DOE PAGES

Xu, Yang; Miotkowski, Ireneusz; Chen, Yong P.

2016-05-04

Topological insulators are a novel class of quantum matter with a gapped insulating bulk, yet gapless spin-helical Dirac fermion conducting surface states. Here, we report local and non-local electrical and magneto transport measurements in dual-gated BiSbTeSe 2 thin film topological insulator devices, with conduction dominated by the spatially separated top and bottom surfaces, each hosting a single species of Dirac fermions with independent gate control over the carrier type and density. We observe many intriguing quantum transport phenomena in such a fully tunable two-species topological Dirac gas, including a zero-magnetic-field minimum conductivity close to twice the conductance quantum at themore » double Dirac point, a series of ambipolar two-component half-integer Dirac quantum Hall states and an electron-hole total filling factor zero state (with a zero-Hall plateau), exhibiting dissipationless (chiral) and dissipative (non-chiral) edge conduction, respectively. As a result, such a system paves the way to explore rich physics, ranging from topological magnetoelectric effects to exciton condensation.« less

Dynamic Jahn-Teller effect in the parent insulating state of the molecular superconductor Cs₃C₆₀.

PubMed

Klupp, Gyöngyi; Matus, Péter; Kamarás, Katalin; Ganin, Alexey Y; McLennan, Alec; Rosseinsky, Matthew J; Takabayashi, Yasuhiro; McDonald, Martin T; Prassides, Kosmas

2012-06-19

The 'expanded fulleride' Cs(3)C(60) is an antiferromagnetic insulator in its normal state and becomes a molecular superconductor with T(c) as high as 38 K under pressure. There is mounting evidence that superconductivity is not of the conventional BCS type and electron-electron interactions are essential for its explanation. Here we present evidence for the dynamic Jahn-Teller effect as the source of the dramatic change in electronic structure occurring during the transition from the metallic to the localized state. We apply infrared spectroscopy, which can detect subtle changes in the shape of the C(60)3- ion due to the Jahn-Teller distortion. The temperature dependence of the spectra in the insulating phase can be explained by the gradual transformation from two temperature-dependent solid-state conformers to a single one, typical and unique for Jahn-Teller systems. These results unequivocally establish the relevance of the dynamic Jahn-Teller effect to overcoming Hund's rule and forming a low-spin state, leading to a magnetic Mott-Jahn-Teller insulator.

A Method to have Multi-Layer Thermal Insulation Provide Damage Detection

NASA Technical Reports Server (NTRS)

Woodward, Stanley E.; Taylor, Bryant D.; Jones, Thomas W.; Shams, Qamar A.; Lyons, Frankel; Henderson, Donald

2007-01-01

Design and testing of a multi-layer thermal insulation system that also provides debris and micrometeorite damage detection is presented. One layer of the insulation is designed as an array of passive open-circuit electrically conductive spiral trace sensors. The sensors are a new class of sensors that are electrically open-circuits that have no electrical connections thereby eliminating one cause of failure to circuits. The sensors are powered using external oscillating magnetic fields. Once electrically active, they produce their own harmonic magnetic fields. The responding field frequency changes if any sensor is damaged. When the sensors are used together in close proximity, the inductive coupling between sensors provides a means of telemetry. The spiral trace design using reflective electrically conductive material provides sufficient area coverage for the sensor array to serves as a layer of thermal insulation. The other insulation layers are designed to allow the sensor s magnetic field to permeate the insulation layers while having total reflective surface area to reduce thermal energy transfer. Results of characterizing individual sensors and the sensor array s response to punctures are presented. Results of hypervelocity impact testing using projectiles of 1-3.6 millimeter diameter having speeds ranging from 6.7-7.1 kilometers per second are also presented.

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary.

PubMed

Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y; Prassides, Kosmas; Rosseinsky, Matthew J; Arčon, Denis

2014-03-03

The alkali fullerides, A(3)C(60) (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs(3)C(60) polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/k(B)T(c) = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/k(B)T(c) decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached.

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary

PubMed Central

Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y.; Prassides, Kosmas; Rosseinsky, Matthew J.; Arčon, Denis

2014-01-01

The alkali fullerides, A3C60 (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs3C60 polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/kBTc = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/kBTc decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached. PMID:24584087

Dielectric evidence for possible type-II multiferroicity in α-RuCl3

NASA Astrophysics Data System (ADS)

Zheng, JiaCheng; Cui, Yi; Li, TianRun; Ran, KeJing; Wen, JinSheng; Yu, WeiQiang

2018-05-01

$\\alpha$-RuCl$_3$ is a Mott insulator with a honeycomb lattice with strong spin-orbit coupling. We report dielectric measurements on $\\alpha$-RuCl$_3$ single crystals under field. At zero field, the dielectric constant, $\\epsilon$, drops rapidly when cooled through the magnetic transition temperature T$_N$. With increasing field, the onset of the drop in $\\epsilon$ tracks the T$_N$. Such behavior is absent with field above a critical value H$_c$ ~ 7.5 T, indicating the onset of a quantum phase transition. Our data suggest that the dielectric constant can be used as a probe of magnetic ordering in $\\alpha$-RuCl$_3$, and $\\alpha$-RuCl$_3$ is a possible type-II multiferroics.

Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr 2IrO 4

DOE PAGES

Dean, M. P. M.; Cao, Y.; Liu, X.; ...

2016-05-09

Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity 1, 2, 3, 4. Recently, photo-excitation has been used to induce similarly exotic states transiently 5, 6, 7. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr 2IrO 4. We find that the non-equilibrium state, 2more » ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. In conclusion, the marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.« less

The upper limit of thermoelectric power factors in the metal-band-insulator crossover of the perovskite-type oxygen deficient system SrTiO(₃- δ/₂).

PubMed

Onoda, Masashige; Tsukahara, Shuichi

2011-02-02

The electronic properties and the thermoelectric power factors in the metal-band-insulator crossover of the perovskite-type oxygen deficient system SrTiO(3 - δ/2) with 0.0046 ≤ δ < 0.06 are explored through measurements of x-ray diffraction, electrical resistivity, thermoelectric power, Hall coefficient and magnetic susceptibility. The metallic transport is confirmed to be basically explained through scattering by electron correlations, acoustic phonons and polar optical phonons, where each scattering coefficient is almost linear in the inverse of the effective carrier concentration estimated from the Hall coefficient. The upper limit of the thermoelectric power factor is 2 × 10( - 3) W m( - 1) K( - 2) with the carrier concentration of 2 × 10(20) cm( - 3) at around the Fermi energy comparable to the Debye temperature.

The upper limit of thermoelectric power factors in the metal-band-insulator crossover of the perovskite-type oxygen deficient system SrTiO3 - δ/2

NASA Astrophysics Data System (ADS)

Onoda, Masashige; Tsukahara, Shuichi

2011-02-01

The electronic properties and the thermoelectric power factors in the metal-band-insulator crossover of the perovskite-type oxygen deficient system SrTiO3 - δ/2 with 0.0046 <= δ < 0.06 are explored through measurements of x-ray diffraction, electrical resistivity, thermoelectric power, Hall coefficient and magnetic susceptibility. The metallic transport is confirmed to be basically explained through scattering by electron correlations, acoustic phonons and polar optical phonons, where each scattering coefficient is almost linear in the inverse of the effective carrier concentration estimated from the Hall coefficient. The upper limit of the thermoelectric power factor is 2 × 10 - 3 W m - 1 K - 2 with the carrier concentration of 2 × 1020 cm - 3 at around the Fermi energy comparable to the Debye temperature.

Dimensionality-strain phase diagram of strontium iridates superlattices

NASA Astrophysics Data System (ADS)

Kim, Bongjae; Liu, Peitao; Franchini, Cesare

Using ab initio approach, we study the electronic and magnetic behavior of strontium iridates as a function of dimensionality and epitaxial strain by employing a (SrIrO3)m/(SrTiO3) superlattice structure. We quantitatively evaluate the dimensional and strain-dependent change of the interaction parameters U and J using the constraint random phase approximation and construct a comprehensive phase diagram describing the evolution of the electronic and magnetic ground state upon strain and dimensionality. We find that compressive strain and increasing the dimensionality perturb the insulating relativistic Mott Jeff = 1 / 2 state, a characteristic of the m = 1 system, and induce two distinct types of insulator-to-metal transition (IMT) that can be explained from the entanglement of U and the bandwidth of the Ir-t2 g manifold. The IMTs are associated with distinctive changes of the spin ordering manifested by spin-flop transitions, correlated with the modulation of the interlayer exchange interaction, and with a complete quenching of any spin-ordered state in the m -> ∞ limit. The fundamental origin of these electronic and magnetic transitions will be discussed and compared with the corresponding situation in the Ruddlesden-Popper series.

Short review of high-pressure crystal growth and magnetic and electrical properties of solid-state osmium oxides

NASA Astrophysics Data System (ADS)

Yamaura, Kazunari

2016-04-01

High-pressure crystal growth and synthesis of selected solid-state osmium oxides, many of which are perovskite-related types, are briefly reviewed, and their magnetic and electrical properties are introduced. Crystals of the osmium oxides, including NaOsO3, LiOsO3, and Na2OsO4, were successfully grown under high-pressure and high-temperature conditions at 6 GPa in the presence of an appropriate amount of flux in a belt-type apparatus. The unexpected discovery of a magnetic metal-insulator transition in NaOsO3, a ferroelectric-like transition in LiOsO3, and high-temperature ferrimagnetism driven by a local structural distortion in Ca2FeOsO6 may represent unique features of the osmium oxides. The high-pressure and high-temperature synthesis and crystal growth has played a central role in the development of solid-state osmium oxides and the elucidation of their magnetic and electronic properties toward possible use in multifunctional devices.

Measurement of Resistance and Strength of Conductor Splices in the Mice Coupling Magnets

NASA Astrophysics Data System (ADS)

Xu, F. Y.; Pan, H.; Wu, H.; Lui, X. K.; Li, E.; Green, M. A.; Dietderich, D.; Higley, H. C.; Tam, D. G.; Trillaud, F.; Wang, Li

2010-04-01

The superconducting magnets for the Muon Ionization Cooling Experiment [1] (MICE) use a copper based Nb-Ti conductor with un-insulated dimensions of 0.95 by 1.60 mm. There may be as many as twelve splices in one MICE superconducting coupling coil. These splices are to be wound in the coil. The conductor splices produce Joule heating, which may cause the magnet to quench. A technique of making conductor splices was developed by ICST. Two types of 1-meter long of soldered lap-joints have been tested. Side-by-side splices and up-down one splices were studied theoretically and experimentally using two types of soft solder made of eutectic tin-lead solder and tin-silver solder. The resistances of the splices made by ICST were tested at LBNL at liquid helium temperatures over a range of magnetic fields up to 5 T. The breaking strength of 250 mm long splices was also measured at room temperature and liquid nitrogen temperature.

Scaling of terahertz conductivity at the metal-insulator transition in doped manganites

NASA Astrophysics Data System (ADS)

Pimenov, A.; Biberacher, M.; Ivannikov, D.; Loidl, A.; Mukhin, A. A.; Goncharov, Yu. G.; Balbashov, A. M.

2006-06-01

Magnetic field and temperature dependence of the terahertz conductivity and permittivity of the colossal magnetoresistance manganite Pr0.65Ca0.28Sr0.07MnO3 (PCSMO) is investigated approaching the metal-to-insulator transition (MIT) from the insulating side. In the charge-ordered state of PCSMO both conductivity and dielectric permittivity increase as a function of magnetic field and temperature. Universal scaling relationships Δɛ∝Δσ are observed in a broad range of temperatures and magnetic fields. Similar scaling is also seen in La1-xSrxMnO3 for different doping levels. The observed proportionality points towards the importance of pure ac-conductivity and phononic energy scale at MIT in manganites.

Zero-bias photocurrent in ferromagnetic topological insulator.

PubMed

Ogawa, N; Yoshimi, R; Yasuda, K; Tsukazaki, A; Kawasaki, M; Tokura, Y

2016-07-20

Magnetic interactions in topological insulators cause essential modifications in the originally mass-less surface states. They offer a mass gap at the Dirac point and/or largely deform the energy dispersion, providing a new path towards exotic physics and applications to realize dissipation-less electronics. The nonequilibrium electron dynamics at these modified Dirac states unveil additional functions, such as highly efficient photon to spin-current conversion. Here we demonstrate the generation of large zero-bias photocurrent in magnetic topological insulator thin films on mid-infrared photoexcitation, pointing to the controllable band asymmetry in the momentum space. The photocurrent spectra with a maximal response to the intra-Dirac-band excitations can be a sensitive measure for the correlation between Dirac electrons and magnetic moments.

Observation of the Zero Hall Plateau in a Quantum Anomalous Hall Insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Yang; Feng, Xiao; Ou, Yunbo

We report experimental investigations on the quantum phase transition between the two opposite Hall plateaus of a quantum anomalous Hall insulator. We observe a well-defined plateau with zero Hall conductivity over a range of magnetic field around coercivity when the magnetization reverses. The features of the zero Hall plateau are shown to be closely related to that of the quantum anomalous Hall effect, but its temperature evolution exhibits a significant difference from the network model for a conventional quantum Hall plateau transition. We propose that the chiral edge states residing at the magnetic domain boundaries, which are unique to amore » quantum anomalous Hall insulator, are responsible for the novel features of the zero Hall plateau.« less

Cr-doped TiSe 2 - A layered dichalcogenide spin glass

DOE PAGES

Luo, Huixia; Tao, Jing; Krizan, Jason W.; ...

2015-09-17

We report the magnetic characterization of the Cr-doped layered dichalcogenide TiSe 2. The temperature dependent magnetic susceptibilities are typical of those seen in geometrically frustrated insulating antiferromagnets. The Cr moment is close to the spin-only value, and the Curie–Weiss temperatures (θ cw) are between –90 and –230 K. Freezing of the spin system, which is glassy, characterized by peaks in the ac and dc susceptibility and specific heat, does not occur until below T/θ cw = 0.05. The CDW transition seen in the resistivity for pure TiSe 2 is still present for 3% Cr substitution but is absent by 10%more » substitution, above which the materials are metallic and p-type. Structural refinements, magnetic characterization, and chemical considerations indicate that the materials are of the type Ti 1–xCr xSe 2-x/2 for 0 ≤ x ≤ 0.6.« less

Magnetic Excitations across the Metal-Insulator Transition in the Pyrochlore Iridate Eu2Ir2O7

NASA Astrophysics Data System (ADS)

Chun, Sae Hwan; Yuan, Bo; Casa, Diego; Kim, Jungho; Kim, Chang-Yong; Tian, Zhaoming; Qiu, Yang; Nakatsuji, Satoru; Kim, Young-June

2018-04-01

We report a resonant inelastic x-ray scattering study of the magnetic excitation spectrum in a highly insulating Eu2 Ir2 O7 single crystal that exhibits a metal-insulator transition at TMI=111 (7 ) K . A propagating magnon mode with a 20 meV bandwidth and a 28 meV magnon gap is found in the excitation spectrum at 7 K, which is expected in the all-in-all-out magnetically ordered state. This magnetic excitation exhibits substantial softening as the temperature is raised towards TMI and turns into a highly damped excitation in the paramagnetic phase. Remarkably, the softening occurs throughout the whole Brillouin zone including the zone boundary. This observation is inconsistent with the magnon renormalization expected in a local moment system and indicates that the strength of the electron correlation in Eu2 Ir2 O7 is only moderate, so that electron itinerancy should be taken into account in describing its magnetism.

Analysis of Lightning-induced Impulse Magnetic Fields in the Building with an Insulated Down Conductor

NASA Astrophysics Data System (ADS)

Du, Patrick Y.; Zhou, Qi-Bin

This paper presents an analysis of lightning-induced magnetic fields in a building. The building of concern is protected by the lightning protection system with an insulated down conductor. In this paper a system model for metallic structure of the building is constructed first using the circuit approach. The circuit model of the insulated down conductor is discussed extensively, and explicit expressions of the circuit parameters are presented. The system model was verified experimentally in the laboratory. The modeling approach is applied to analyze the impulse magnetic fields in a full-scale building during a direct lightning strike. It is found that the impulse magnetic field is significantly high near the down conductor. The field is attenuated if the down conductor is moved to a column in the building. The field can be reduced further if the down conductor is housed in an earthed metal pipe. Recommendations for protecting critical equipment against lightning-induced magnetic fields are also provided in the paper.

Magnetically insulated diode for generating pulsed neutron and gamma ray emissions

DOEpatents

Kuswa, G.W.; Leeper, R.J.

1984-08-16

A magnetically insulated diode employs a permanent magnet to generate a magnetic insulating field between a spaced anode and cathode in a vacuum. An ion source is provided in the vicinity of the anode and used to liberate ions for acceleration toward the cathode. The ions are virtually unaffected by the magnetic field and are accelerated into a target for generating a nuclear reaction. The ions and target material may be selected to generate either neutrons or gamma ray emissions from the reaction of the accelerated ions and the target. In another aspect of the invention, a field coil is employed as part of one of the electrodes. A plasma prefill is provided between the electrodes prior to the application of a pulsating potential to one of the electrodes. The field coil multiplies the applied voltage for high diode voltage applications. The diode may be used to generate a /sup 7/Li(p,..gamma..)/sup 8/Be reaction to produce 16.5 MeV gamma emission.

Magnetically insulated diode for generating pulsed neutron and gamma ray emissions

DOEpatents

Kuswa, Glenn W.; Leeper, Ramon J.

1987-01-01

A magnetically insulated diode employs a permanent magnet to generate a magnetic insulating field between a spaced anode and cathode in a vacuum. An ion source is provided in the vicinity of the anode and used to liberate ions for acceleration toward the cathode. The ions are virtually unaffected by the magnetic field and are accelerated into a target for generating an nuclear reaction. The ions and target material may be selected to generate either neutrons or gamma ray emissions from the reaction of the accelerated ions and the target. In another aspect of the invention, a field coil is employed as part of one of the electrodes. A plasma prefill is provided between the electrodes prior to the application of a pulsating potential to one of the electrodes. The field coil multiplies the applied voltage for high diode voltage applications. The diode may be used to generate a .sup.7 Li(p,.gamma.).sup.8 Be reaction to produce 16.5 MeV gamma emission.

Temperature and composition phase diagram in the iron-based ladder compounds Ba 1 - x Cs x Fe 2 Se 3

DOE PAGES

Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; ...

2015-05-28

We investigated the iron-based ladder compounds (Ba,Cs)Fe₂Se₃. Their parent compounds BaFe₂Se₃ and CsFe₂Se₃ have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe₂Se₃ is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe₂Se₃ is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe₂Se₃, but interladder spin configuration is different. Intermediatemore » compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures.« less

Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3

NASA Astrophysics Data System (ADS)

Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; Du, Fei; Hirata, Yasuyuki; Avdeev, Maxim; Uwatoko, Yoshiya; Sekine, Yurina; Fukazawa, Hiroshi; Ma, Jie; Chi, Songxue; Ueda, Yutaka; Yoshizawa, Hideki; Sato, Taku J.

2015-05-01

We investigated the iron-based ladder compounds (Ba,Cs ) Fe2Se3 . Their parent compounds BaFe2Se3 and CsFe2Se3 have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe2Se3 is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe2Se3 is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe2Se3 , but interladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless a finite T -linear contribution in specific heat was obtained at low temperatures.

Quantum oscillations in insulators with neutral Fermi surfaces

NASA Astrophysics Data System (ADS)

Sodemann, Inti; Chowdhury, Debanjan; Senthil, T.

2018-02-01

We develop a theory of quantum oscillations in insulators with an emergent Fermi sea of neutral fermions minimally coupled to an emergent U(1 ) gauge field. As pointed out by Motrunich [Phys. Rev. B 73, 155115 (2006), 10.1103/PhysRevB.73.155115], in the presence of a physical magnetic field the emergent magnetic field develops a nonzero value leading to Landau quantization for the neutral fermions. We focus on the magnetic field and temperature dependence of the analog of the de Haas-van Alphen effect in two and three dimensions. At temperatures above the effective cyclotron energy, the magnetization oscillations behave similarly to those of an ordinary metal, albeit in a field of a strength that differs from the physical magnetic field. At low temperatures, the oscillations evolve into a series of phase transitions. We provide analytical expressions for the amplitude and period of the oscillations in both of these regimes and simple extrapolations that capture well their crossover. We also describe oscillations in the electrical resistivity of these systems that are expected to be superimposed with the activated temperature behavior characteristic of their insulating nature and discuss suitable experimental conditions for the observation of these effects in mixed-valence insulators and triangular lattice organic materials.

Ba2NiOsO6: a Dirac-Mott insulator with ferromagnetism near 100 K

NASA Astrophysics Data System (ADS)

Feng, Hl; Calder, S.; Ghimire, M.; Yuan, Yh; Shirako, Y.; Tsujimoto, Y.; Matsushita, Y.; Hu, Z.; Kuo, Cy; Tjeng, Lh; Pi, Tw; Soo, Yl; He, Jf; Tanaka, M.; Katsuya, Y.; Richte, M.; Yamaura, Kazunari

The ferromagnetic semiconductor Ba2NiOsO6(Tmag 100 K) was synthesized at 6 GPa and 1500 ° C. It crystallizes into a double perovskite structure [Fm-3 m; a = 8.0428(1)], where the Ni2+ and Os6+ ions are perfectly ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21-kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag<180 K), the spin-gapless semiconductor Mn2CoAl (Tmag 720 K), and the ferromagnetic insulators EuO (Tmag 70 K) and Bi3Cr3O11(Tmag 220 K). It is also qualitatively different from known ferrimagnetic insulator/semiconductors, which are characterized by an antiparallel spin arrangement. Our report of cubic Ba2NiOsO6 heralds a new class of FM insulator oxides, which may be useful in developing a practical magnetic semiconductor that can be employed in spintronic and quantum magnetic devices.

Ceramic electrical insulation for electrical coils, transformers, and magnets

DOEpatents

Rice, John A.; Hazelton, Craig S.; Fabian, Paul E.

2002-01-01

A high temperature electrical insulation is described, which is suitable for electrical windings for any number of applications. The inventive insulation comprises a cured preceramic polymer resin, which is preferably a polysiloxane resin. A method for insulating electrical windings, which are intended for use in high temperature environments, such as superconductors and the like, advantageously comprises the steps of, first, applying a preceramic polymer layer to a conductor core, to function as an insulation layer, and second, curing the preceramic polymer layer. The conductor core preferably comprises a metallic wire, which may be wound into a coil. In the preferred method, the applying step comprises a step of wrapping the conductor core with a sleeve or tape of glass or ceramic fabric which has been impregnated by a preceramic polymer resin. The inventive insulation system allows conducting coils and magnets to be fabricated using existing processing equipment, and maximizes the mechanical and thermal performance at both elevated and cryogenic temperatures. It also permits co-processing of the wire and the insulation to increase production efficiencies and reduce overall costs, while still remarkably enhancing performance.

Spin transport in normal metal/insulator/topological insulator coupled to ferromagnetic insulator structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kondo, Kenji, E-mail: kkondo@es.hokudai.ac.jp

In this study, we investigate the spin transport in normal metal (NM)/insulator (I)/topological insulator (TI) coupled to ferromagnetic insulator (FI) structures. In particular, we focus on the barrier thickness dependence of the spin transport inside the bulk gap of the TI with FI. The TI with FI is described by two-dimensional (2D) Dirac Hamiltonian. The energy profile of the insulator is assumed to be a square with barrier height V and thickness d along the transport-direction. This structure behaves as a tunnel device for 2D Dirac electrons. The calculation is performed for the spin conductance with changing the barrier thicknessmore » and the components of magnetization of FI layer. It is found that the spin conductance decreases with increasing the barrier thickness. Also, the spin conductance is strongly dependent on the polar angle θ, which is defined as the angle between the axis normal to the FI and the magnetization of FI layer. These results indicate that the structures are promising candidates for novel tunneling magnetoresistance devices.« less

Simultaneous Magnetic and Charge Doping of Topological Insulators with Carbon

NASA Astrophysics Data System (ADS)

Shen, Lei; Zeng, Minggang; Lu, Yunhao; Yang, Ming; Feng, Yuan Ping

2013-12-01

A two-step doping process, magnetic followed by charge or vice versa, is required to produce massive topological surface states (TSS) in topological insulators for many physics and device applications. Here, we demonstrate simultaneous magnetic and hole doping achieved with a single dopant, carbon, in Bi2Se3 by first-principles calculations. Carbon substitution for Se (CSe) results in an opening of a sizable surface Dirac gap (up to 82 meV), while the Fermi level remains inside the bulk gap and close to the Dirac point at moderate doping concentrations. The strong localization of 2p states of CSe favors spontaneous spin polarization via a p-p interaction and formation of ordered magnetic moments mediated by surface states. Meanwhile, holes are introduced into the system by CSe. This dual function of carbon doping suggests a simple way to realize insulating massive TSS.

New self-magnetically insulated connection of multilevel accelerators to a common load

DOE PAGES

VanDevender, J. Pace; Langston, William L.; Pasik, Michael F.; ...

2015-03-04

A new way to connect pulsed-power modules to a common load is presented. Unlike previous connectors, the clam shell magnetically insulated transmission line (CSMITL) has magnetic nulls only at large radius where the cathode electric field is kept below the threshold for emission, has only a simply connected magnetic topology to avoid plasma motion along magnetic field lines into highly stressed gaps, and has electron injectors that ensure efficient electron flow even in the limiting case of self-limited MITLs. Multilevel magnetically insulated transmission lines with a posthole convolute are the standard solution but associated losses limit the performance of state-of-the-artmore » accelerators. Mitigating these losses is critical for the next generation of pulsed-power accelerators. A CSMITL has been successfully implemented on the Saturn accelerator. A reference design for the Z accelerator is derived and presented. The design conservatively meets the design requirements and shows excellent transport efficiency in three simulations of increasing complexity: circuit simulations, electromagnetic fields only with Emphasis, fields plus electron and ion emission with Quicksilver.« less

Strain driven sequential magnetic transitions in strained GdTiO3 on compressive substrates: a first-principles study

NASA Astrophysics Data System (ADS)

Yang, Li-Juan; Weng, Ya-Kui; Zhang, Hui-Min; Dong, Shuai

2014-11-01

The compressive strain effect on the magnetic ground state and electronic structure of strained GdTiO3 has been studied using the first-principles method. Unlike the cases of congeneric YTiO3 and LaTiO3, both of which become the A-type antiferromagnetism on the (0 0 1) LaAlO3 substrate despite their contrastive magnetism, the ground state of strained GdTiO3 on the LaAlO3 substrate changes from the original ferromagnetism to a G-type antiferromagnetim, instead of the A-type one although Gd3+ is between Y3+ and La3+. It is only when the in-plane compressive strain is large enough, e.g. on the (0 0 1) YAlO3 substrate, that the ground state finally becomes the A-type. The band structure calculation shows that the compressive strained GdTiO3 remains insulating, although the band gap changes a little in the strained GdTiO3.

Megagauss-level magnetic field production in cm-scale auto-magnetizing helical liners pulsed to 500 kA in 125 ns

DOE PAGES

Shipley, Gabriel A.; Awe, Thomas James; Hutsel, Brian Thomas; ...

2018-05-03

We present Auto-magnetizing (AutoMag) liners [Slutz et al., Phys. Plasmas 24, 012704 (2017)] are designed to generate up to 100 T of axial magnetic field in the fuel for Magnetized Liner Inertial Fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010)] without the need for external field coils. AutoMag liners (cylindrical tubes) are composed of discrete metallic helical conduction paths separated by electrically insulating material. Initially, helical current in the AutoMag liner produces internal axial magnetic field during a long (100 to 300 ns) current prepulse with an average current rise rate dI/dt=5 kA/ns. After the cold fuel is magnetized,more » a rapidly rising current (200 kA/ns) generates a calculated electric field of 64 MV/m between the helices. Such field is sufficient to force dielectric breakdown of the insulating material after which liner current is reoriented from helical to predominantly axial which ceases the AutoMag axial magnetic field production mechanism and the z-pinch liner implodes. Proof of concept experiments have been executed on the Mykonos linear transformer driver to measure the axial field produced by a variety of AutoMag liners and to evaluate what physical processes drive dielectric breakdown. Lastly, a range of field strengths have been generated in various cm-scale liners in agreement with magnetic transient simulations including a measured field above 90 T at I = 350 kA. By varying the helical pitch angle, insulator material, and insulator geometry, favorable liner designs have been identified for which breakdown occurs under predictable and reproducible field conditions.« less

Megagauss-level magnetic field production in cm-scale auto-magnetizing helical liners pulsed to 500 kA in 125 ns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shipley, Gabriel A.; Awe, Thomas James; Hutsel, Brian Thomas

We present Auto-magnetizing (AutoMag) liners [Slutz et al., Phys. Plasmas 24, 012704 (2017)] are designed to generate up to 100 T of axial magnetic field in the fuel for Magnetized Liner Inertial Fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010)] without the need for external field coils. AutoMag liners (cylindrical tubes) are composed of discrete metallic helical conduction paths separated by electrically insulating material. Initially, helical current in the AutoMag liner produces internal axial magnetic field during a long (100 to 300 ns) current prepulse with an average current rise rate dI/dt=5 kA/ns. After the cold fuel is magnetized,more » a rapidly rising current (200 kA/ns) generates a calculated electric field of 64 MV/m between the helices. Such field is sufficient to force dielectric breakdown of the insulating material after which liner current is reoriented from helical to predominantly axial which ceases the AutoMag axial magnetic field production mechanism and the z-pinch liner implodes. Proof of concept experiments have been executed on the Mykonos linear transformer driver to measure the axial field produced by a variety of AutoMag liners and to evaluate what physical processes drive dielectric breakdown. Lastly, a range of field strengths have been generated in various cm-scale liners in agreement with magnetic transient simulations including a measured field above 90 T at I = 350 kA. By varying the helical pitch angle, insulator material, and insulator geometry, favorable liner designs have been identified for which breakdown occurs under predictable and reproducible field conditions.« less

Megagauss-level magnetic field production in cm-scale auto-magnetizing helical liners pulsed to 500 kA in 125 ns

NASA Astrophysics Data System (ADS)

Shipley, G. A.; Awe, T. J.; Hutsel, B. T.; Slutz, S. A.; Lamppa, D. C.; Greenly, J. B.; Hutchinson, T. M.

2018-05-01

Auto-magnetizing (AutoMag) liners [Slutz et al., Phys. Plasmas 24, 012704 (2017)] are designed to generate up to 100 T of axial magnetic field in the fuel for Magnetized Liner Inertial Fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010)] without the need for external field coils. AutoMag liners (cylindrical tubes) are composed of discrete metallic helical conduction paths separated by electrically insulating material. Initially, helical current in the AutoMag liner produces internal axial magnetic field during a long (100 to 300 ns) current prepulse with an average current rise rate d I / d t = 5 k A / n s . After the cold fuel is magnetized, a rapidly rising current ( 200 k A / n s ) generates a calculated electric field of 64 M V / m between the helices. Such field is sufficient to force dielectric breakdown of the insulating material after which liner current is reoriented from helical to predominantly axial which ceases the AutoMag axial magnetic field production mechanism and the z-pinch liner implodes. Proof of concept experiments have been executed on the Mykonos linear transformer driver to measure the axial field produced by a variety of AutoMag liners and to evaluate what physical processes drive dielectric breakdown. A range of field strengths have been generated in various cm-scale liners in agreement with magnetic transient simulations including a measured field above 90 T at I = 350 kA. By varying the helical pitch angle, insulator material, and insulator geometry, favorable liner designs have been identified for which breakdown occurs under predictable and reproducible field conditions.

Time-Reversal Symmetry Breaking and Consequent Physical Responses Induced by All-In-All-Out Type Magnetic Order on the Pyrochlore Lattice

NASA Astrophysics Data System (ADS)

Arima, Taka-Hisa

2014-03-01

Pyrochlore-type 5d transition-metal oxide compounds Cd2Os2O7 and R2Ir2O7 (R =rare earth) undergo a metal-insulator transition accompanied by a magnetic transition. Recently, the magnetic structures of Cd2Os2O7 and Eu2Ir2O7 were investigated by means of resonant x-ray magnetic scattering. The x-ray data indicated the all-in/all-out type magnetic order. The all-in/all-out order breaks the time-reversal symmetry, while the spontaneous magnetization is essentially absent. The magnetic order can be viewed as ferroic magnetic octupolar order. The magnetic order is expected to provide several unique physical properties like quadratic magnetization. linear magneto-capacitance, linear magneto-resistance, linear magneto-mechanical coupling and so on. The symmetry breaking results in two non-equivalent domains, ``all-in/all-out'' and ``all-out/all-in.'' Interestingly, some theoretical works predict that a peculiar metallic state would appear on the domain wall. The observation and control of the domain distribution are essential for studying verious exotic physical responses. We have developed an x-ray technique for domain imaging and started studying the effects of external stimuli on the domain distribution. This work was performed in collaboration with S. Tardif, S. Takeshita, H. Ohsumi, D. Uematsu, H. Sagayama, J. J. Ishikawa, S. Nakatsuji, J. Yamaura, and Z. Hiroi.

Quantized topological magnetoelectric effect of the zero-plateau quantum anomalous Hall state

DOE PAGES

Wang, Jing; Lian, Biao; Qi, Xiao-Liang; ...

2015-08-10

The topological magnetoelectric effect in a three-dimensional topological insulator is a novel phenomenon, where an electric field induces a magnetic field in the same direction, with a universal coefficient of proportionality quantized in units of $e²/2h$. Here in this paper, we propose that the topological magnetoelectric effect can be realized in the zero-plateau quantum anomalous Hall state of magnetic topological insulators or a ferromagnet-topological insulator heterostructure. The finite-size effect is also studied numerically, where the magnetoelectric coefficient is shown to converge to a quantized value when the thickness of the topological insulator film increases. We further propose a device setupmore » to eliminate nontopological contributions from the side surface.« less

Neutron Scattering Studies on Correlated Transition-Metal Oxides

NASA Astrophysics Data System (ADS)

Zhu, Mengze

We have explored the collective phenomena of correlated electrons in two different transition-metal oxides, Ruddlesden-Popper type ruthenates (Sr,Ca) n+1RunO3n+1 and inverse-trirutile chromates Cr2MO6 (M = Te, Mo and W), using neutron scattering in combination with various material characterization methods. (Sr,Ca)n+1RunO 3n+1 are 4d transition-metal oxides exhibiting competing magnetic and electronic tendencies. The delicate balance among the competing states can be readily tuned by perturbations, such as chemical doping and magnetic field, which gives rise to emergent phenomena. We have investigated the effects of 3d transition-metal doping on the magnetic and electronic properties of layered ruthenates. For instance, the single-layer (n = 1) Sr2RuO4 is an unconventional superconductor possessing an incommensurate spin density wave instability with a wave vector qic= (0.3 0.3 L) driven by Fermi surface nesting. Upon Fe substitution, we have unveiled an unexpected commensurate spin density wave order with a propagation vector qc= (0.25 0.25 0) in Sr2Ru1-xFexO 4 (x = 0.03 and 0.05), despite the magnetic fluctuations persisting at qic. The latter feature is corroborated by the first principles calculations, which show that Fe doping barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping. We have also studied the effects of a magnetic field. For example, the bilayer (n = 2) Ca3(Ru1-xTi x)2O7 (x = 0.03) is a G-type antiferromagnetic Mott insulator. We have revealed that a modest magnetic field can lead to colossal magnetoresistance arising from an anomalous collapse of the Mott insulating state. Such an insulator-to-metal transition is accompanied by magnetic and structural transitions. These findings call for deeper theoretical studies to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities, as a magnetic field usually stabilizes the insulating ground state in Mott-Hubbard systems. Cr2MO6 (M = Te, W and Mo) are spin dimer systems with the magnetic ions Cr3+ structurally dimerized favoring a singlet ground state. However, all three compounds investigated exhibit long-range antiferromagnetic orders at low temperature owing to the inter-dimer interactions. We have shown that the inter-dimer exchange coupling can be tuned from antiferromagnetic in Cr2TeO6 to ferromagnetic in Cr2WO6 and Cr2MoO6, by altering the degree of d-p orbital hybridization between W(Mo) and O atoms. The tunability of the inter-dimer interactions without introducing additional complexities such as structural distortions and carrier doping offers a rare opportunity to drive the system toward the quantum critical point (QCP) separating the dimer-based quantum disordered state and the classical long-range antiferromagnetic order. Moreover, we have unraveled Higgs amplitude modes in the magnetic excitation spectra of Cr2TeO6 and Cr2WO6, which are generally believed to survive only in systems close to the QCP where the ordered moment is suppressed significantly from its fully saturated value by quantum fluctuations. However, these two compounds are away from the QCP with the ordered moment reduced only by 24%. This study suggests that Higgs amplitude modes are not the privilege of ordered systems in the vicinity of the QCP, but may be common excitation modes in ordered spin dimer systems.

Coupled dielectric permittivity and magnetic susceptibility in the insulating antiferromagnet Ba2FeSbSe5

NASA Astrophysics Data System (ADS)

Maier, S.; Moussa, C.; Berthebaud, D.; Gascoin, F.; Maignan, A.

2018-05-01

We report on coupled changes in the dielectric permittivity and the magnetic susceptibility in the insulating antiferromagnet Ba2FeSbSe5. The real part of the dielectric permittivity (ɛ') and the thermal conductivity (κ) shows pronounced anomalies at the Néel temperature (TN). Our findings show that there is a weak coupling between electric dipoles and magnetic spins, which is mediated by spin-lattice coupling possibly through exchange striction effects.

Origin of nonlinear transport across the magnetically induced superconductor-metal-insulator transition in two dimensions.

PubMed

Seo, Y; Qin, Y; Vicente, C L; Choi, K S; Yoon, Jongsoo

2006-08-04

We have studied the effect of perpendicular magnetic fields and temperatures on nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field-induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the phase-identifying nonlinear transport in the superconducting and metallic phases arises from an intrinsic origin, not from an electron heating effect. The nonlinear transport is found to accompany an extraordinarily long voltage response time.

Large Spin-Wave Bullet in a Ferrimagnetic Insulator Driven by the Spin Hall Effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jungfleisch, M. B.; Zhang, W.; Sklenar, J.

2016-02-01

Due to its transverse nature, spin Hall effects (SHE) provide the possibility to excite and detect spin currents and magnetization dynamics even in magnetic insulators. Magnetic insulators are outstanding materials for the investigation of nonlinear phenomena and for novel low power spintronics applications because of their extremely low Gilbert damping. Here, we report on the direct imaging of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the ferrimagnetic insulator Y 3Fe 5O 12 based on the excitation and detection by SHEs. The driven spin dynamics in Y 3Fe 5O 12 is directly imaged by spatially-resolved microfocused Brillouin light scattering (BLS) spectroscopy.more » Previously, ST-FMR experiments assumed a uniform precession across the sample, which is not valid in our measurements. A strong spin-wave localization in the center of the sample is observed indicating the formation of a nonlinear, self-localized spin-wave `bullet'.« less

Superconductor to weak-insulator transitions in disordered tantalum nitride films

DOE PAGES

Breznay, Nicholas P.; Tendulkar, Mihir; Zhang, Li; ...

2017-10-31

Here, we study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents zν ≈ 1.3, with a corresponding critical field H c << H c2, the upper critical field. The Hall effect exhibits a crossing point near H c, but with a nonuniversal critical valuemore » ρ c xy comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.« less

Mott insulator-to-metal transition in yttrium-doped CaIrO₃.

PubMed

Gunasekera, J; Chen, Y; Kremenak, J W; Miceli, P F; Singh, D K

2015-02-11

We report on the study of insulator-to-metal transition in post-perovskite compound CaIrO3. It is discovered that a gradual chemical substitution of calcium by yttrium leads to the onset of strong metallic behavior in this compound. This observation is in stark contrast to BaIrO3, which preserves its Mott insulating behavior despite excess of the charge carriers due to yttrium doping. Magnetic measurements reveal that both compounds tend to exhibit magnetic character irrespective of the chemical substitution of Ca or Ba. We analyze these unusual observations in light of recent researches that suggest that CaIrO3 does not necessarily possess j = 1/2 ground state due to structural distortion. The insulator-to-metal transition in CaIrO3 will spur new researches to explore more exotic ground state, including superconductivity, in post-perovskite Mott insulators.

Improving Powder Magnetic Core Properties via Application of Thin, Insulating Silica-Nanosheet Layers on Iron Powder Particles

PubMed Central

Ishizaki, Toshitaka; Nakano, Hideyuki; Tajima, Shin; Takahashi, Naoko

2016-01-01

A thin, insulating layer with high electrical resistivity is vital to achieving high performance of powder magnetic cores. Using layer-by-layer deposition of silica nanosheets or colloidal silica over insulating layers composed of strontium phosphate and boron oxide, we succeeded in fabricating insulating layers with high electrical resistivity on iron powder particles, which were subsequently used to prepare toroidal cores. The compact density of these cores decreased after coating with colloidal silica due to the substantial increase in the volume, causing the magnetic flux density to deteriorate. Coating with silica nanosheets, on the other hand, resulted in a higher electrical resistivity and a good balance between high magnetic flux density and low iron loss due to the thinner silica layers. Transmission electron microscopy images showed that the thickness of the colloidal silica coating was about 700 nm, while that of the silica nanosheet coating was 30 nm. There was one drawback to using silica nanosheets, namely a deterioration in the core mechanical strength. Nevertheless, the silica nanosheet coating resulted in nanoscale-thick silica layers that are favorable for enhancing the electrical resistivity. PMID:28336835

Acquisition of He3 Cryostat Insert for Experiments on Topological Insulators

DTIC Science & Technology

2016-02-03

facilitated transport experiments on topological insulators and Dirac and Weyl semimetals. These experiments resulted in several notable achievements and...Approved for Public Release; Distribution Unlimited Final Report: Acquisition of He3 Cryostat Insert for Experiments on Topological Insulators . The views...Experiments on Topological Insulators . Report Title The award enabled the PI to acquire a complete cryogenic system with a 9-Tesla superconducting magnet. The

Hall effect at a tunable metal-insulator transition

NASA Astrophysics Data System (ADS)

Teizer, W.; Hellman, F.; Dynes, R. C.

2003-03-01

Using a rotating magnetic field, the Hall effect in three-dimensional amorphous GdxSi1-x has been measured in the critical regime of the metal-insulator transition for a constant total magnetic field. The Hall coefficient R0 is negative, indicating electronlike conductivity, with a magnitude that increases with decreasing conductivity. R0 diverges at the metal-insulator transition, and displays critical behavior with exponent -1 [R0˜(H-HC)-1]. This dependence is interpreted as a linear decrease in the density of mobile carriers n˜R-10˜H-HC, indicative of the dominant influence of interaction effects.

Multi-Dimensional Sensors and Sensing Systems

NASA Technical Reports Server (NTRS)

Stetter, Joseph R. (Inventor); Shirke, Amol G. (Inventor)

2014-01-01

A universal microelectromechanical (MEMS) nano-sensor platform having a substrate and conductive layer deposited in a pattern on the surface to make several devices at the same time, a patterned insulation layer, wherein the insulation layer is configured to expose one or more portions of the conductive layer, and one or more functionalization layers deposited on the exposed portions of the conductive layer to make multiple sensing capability on a single MEMS fabricated device. The functionalization layers are adapted to provide one or more transducer sensor classes selected from the group consisting of: radiant, electrochemical, electronic, mechanical, magnetic, and thermal sensors for chemical and physical variables and producing more than one type of sensor for one or more significant parameters that need to be monitored.

Role of degeneracy, hybridization, and nesting in the properties of multiorbital systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nicholson, Andrew D; Liu, Jia-Ming; Ge, Weihao

2011-01-01

To understand the role that degeneracy, hybridization, and nesting play in the magnetic and pairing properties of multiorbital Hubbard models we here study numerically two types of two-orbital models, both with holelike and electron-like Fermi surfaces (FS s) that are related by nesting vectors ( ,0) and (0, ). In one case the bands that determine the FS s arise from strongly hybridized degenerate dxz and dyz orbitals, while in the other the two bands are determined by nondegenerate and nonhybridized s-like orbitals. Using a variety of techniques, in the weak-coupling regime it is shown that only the model withmore » hybridized bands develops metallic magnetic order, while the other model exhibits an ordered excitonic orbital-transverse spin state that is insulating and does not have a local magnetization. However, both models display similar insulating magnetic stripe ordering in the strong-coupling limit. These results indicate that nesting is a necessary but not sufficient condition for the development of ordered states with finite local magnetization in multiorbital Hubbard systems; the additional ingredient appears to be that the nested portions of the bands need to have the same orbital flavor. This condition can be achieved via strong hybridization of the orbitals in weak coupling or via the FS reconstruction induced by the Coulomb interactions in the strong-coupling regime. This effect also affects the pairing symmetry as demonstrated by the study of the dominant pairing channels for the two models.« less

Intense ion beam generator

DOEpatents

Humphries, Jr., Stanley; Sudan, Ravindra N.

1977-08-30

Methods and apparatus for producing intense megavolt ion beams are disclosed. In one embodiment, a reflex triode-type pulsed ion accelerator is described which produces ion pulses of more than 5 kiloamperes current with a peak energy of 3 MeV. In other embodiments, the device is constructed so as to focus the beam of ions for high concentration and ease of extraction, and magnetic insulation is provided to increase the efficiency of operation.

Microscopic effects of Dy doping in the topological insulator Bi2Te3

NASA Astrophysics Data System (ADS)

Duffy, L. B.; Steinke, N.-J.; Krieger, J. A.; Figueroa, A. I.; Kummer, K.; Lancaster, T.; Giblin, S. R.; Pratt, F. L.; Blundell, S. J.; Prokscha, T.; Suter, A.; Langridge, S.; Strocov, V. N.; Salman, Z.; van der Laan, G.; Hesjedal, T.

2018-05-01

Magnetic doping with transition metal ions is the most widely used approach to break time-reversal symmetry in a topological insulator (TI)—a prerequisite for unlocking the TI's exotic potential. Recently, we reported the doping of Bi2Te3 thin films with rare-earth ions, which, owing to their large magnetic moments, promise commensurately large magnetic gap openings in the topological surface states. However, only when doping with Dy has a sizable gap been observed in angle-resolved photoemission spectroscopy, which persists up to room temperature. Although disorder alone could be ruled out as a cause of the topological phase transition, a fundamental understanding of the magnetic and electronic properties of Dy-doped Bi2Te3 remained elusive. Here, we present an x-ray magnetic circular dichroism, polarized neutron reflectometry, muon-spin rotation, and resonant photoemission study of the microscopic magnetic and electronic properties. We find that the films are not simply paramagnetic but that instead the observed behavior can be well explained by the assumption of slowly fluctuating, inhomogeneous, magnetic patches with increasing volume fraction as the temperature decreases. At liquid helium temperatures, a large effective magnetization can be easily introduced by the application of moderate magnetic fields, implying that this material is very suitable for proximity coupling to an underlying ferromagnetic insulator or in a heterostructure with transition-metal-doped layers. However, the introduction of some charge carriers by the Dy dopants cannot be excluded at least in these highly doped samples. Nevertheless, we find that the magnetic order is not mediated via the conduction channel in these samples and therefore magnetic order and carrier concentration are expected to be independently controllable. This is not generally the case for transition-metal-doped topological insulators, and Dy doping should thus allow for improved TI quantum devices.

Feasible voltage-tap based quench detection in a Ag/Bi-2212 coil enabled by fast 3D normal zone propagation

DOE PAGES

Shen, Tengming; Ye, Liyang; Li, Pei

2016-07-01

For this study, small insert solenoids have been built using a commercial Ag/Bi-2212 multifilamentary round wire, insulated with a new thin TiO 2– polymer coating insulation (thickness in ~20 μm versus ~100 μm for a commonly used mullite braided sleeve insulation), and characterized in background magnetic field up to 14 T at 4.2 K to explore the high-field performance and quench detection of Bi-2212 magnets. The coil has no visible leakage and no electrical shorts after reaction, and it carries 280 A/mm -2 in a background field 14 T and generates an additional 1.7 T. A notable result is that,more » despite normal zones propagate slowly along the conductor, the hot spot temperature upon detection increases only from 40 K to 60 K when the resistive quench detection voltage threshold increases from 0.1 V to 1 V for all operating current density investigated, showing that quench detection using voltage taps is feasible for this coil. This is in a strong contrast to a coil we previously built to the same specifications but from wires insulated with the mullite braided sleeve insulation, for which the hot spot temperature upon detection increases from ~80 K to ~140 K while increasing from the detection voltage threshold from 0.1 V to 1 V, and thus for which quench detection using voltage taps presents significant risks, consistent with the common belief that the effectiveness of quench detection using voltage taps for superconducting magnets built using high temperature superconductors is seriously compromised by their slow normal zone propagation. This striking difference is ascribed to the fast transverse quench propagation enabled by thin insulation and improved thermal coupling between conductor turns. Finally, this work demonstrates that quench detection for high-temperature superconducting magnets highly depends on the design and construction of the coils such as insulation materials used and this dependence should be factored into the overall magnet design.« less

Feasible voltage-tap based quench detection in a Ag/Bi-2212 coil enabled by fast 3D normal zone propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Tengming; Ye, Liyang; Li, Pei

For this study, small insert solenoids have been built using a commercial Ag/Bi-2212 multifilamentary round wire, insulated with a new thin TiO 2– polymer coating insulation (thickness in ~20 μm versus ~100 μm for a commonly used mullite braided sleeve insulation), and characterized in background magnetic field up to 14 T at 4.2 K to explore the high-field performance and quench detection of Bi-2212 magnets. The coil has no visible leakage and no electrical shorts after reaction, and it carries 280 A/mm -2 in a background field 14 T and generates an additional 1.7 T. A notable result is that,more » despite normal zones propagate slowly along the conductor, the hot spot temperature upon detection increases only from 40 K to 60 K when the resistive quench detection voltage threshold increases from 0.1 V to 1 V for all operating current density investigated, showing that quench detection using voltage taps is feasible for this coil. This is in a strong contrast to a coil we previously built to the same specifications but from wires insulated with the mullite braided sleeve insulation, for which the hot spot temperature upon detection increases from ~80 K to ~140 K while increasing from the detection voltage threshold from 0.1 V to 1 V, and thus for which quench detection using voltage taps presents significant risks, consistent with the common belief that the effectiveness of quench detection using voltage taps for superconducting magnets built using high temperature superconductors is seriously compromised by their slow normal zone propagation. This striking difference is ascribed to the fast transverse quench propagation enabled by thin insulation and improved thermal coupling between conductor turns. Finally, this work demonstrates that quench detection for high-temperature superconducting magnets highly depends on the design and construction of the coils such as insulation materials used and this dependence should be factored into the overall magnet design.« less

Feasibility study on partial insulation winding technique for the development of self-protective MgB2 magnet

NASA Astrophysics Data System (ADS)

Kim, Y. G.; Kim, J. C.; Kim, J. M.; Yoo, B. H.; Hwang, D. Y.; Lee, H. G.

2018-06-01

This study investigates the feasibility of using the partial insulation winding technique for the development of a self-protective MgB2 MRI magnet with a fast charge-discharge rate. Charge-discharge and quench tests for a prototype PI MgB2 magnet confirmed that the magnet was successfully operated at full-field performance and exhibited self-protecting behavior in the event of a quench. Nonetheless, the required time to charge the 0.5-T/300-mm PI MgB2 magnet was almost five days, implying that the charge-discharge delay of the PI MgB2 magnet still needs to be ameliorated further to develop a real-scale MgB2 MRI magnet with a fast charge-discharge rate.

Modulation of pure spin currents with a ferromagnetic insulator

NASA Astrophysics Data System (ADS)

Villamor, Estitxu; Isasa, Miren; Vélez, Saül; Bedoya-Pinto, Amilcar; Vavassori, Paolo; Hueso, Luis E.; Bergeret, F. Sebastián; Casanova, Fèlix

2015-01-01

We propose and demonstrate spin manipulation by magnetically controlled modulation of pure spin currents in cobalt/copper lateral spin valves, fabricated on top of the magnetic insulator Y3F e5O12 (YIG). The direction of the YIG magnetization can be controlled by a small magnetic field. We observe a clear modulation of the nonlocal resistance as a function of the orientation of the YIG magnetization with respect to the polarization of the spin current. Such a modulation can only be explained by assuming a finite spin-mixing conductance at the Cu/YIG interface, as it follows from the solution of the spin-diffusion equation. These results open a path towards the development of spin logics.

Engineering topological phases in the Luttinger semimetal α -Sn

NASA Astrophysics Data System (ADS)

Zhang, Dongqin; Wang, Huaiqiang; Ruan, Jiawei; Yao, Ge; Zhang, Haijun

2018-05-01

α -Sn is well known as a typical Luttinger semimetal with a quadratic band touching at the Γ point. Based on the effective k .p analysis as well as first-principles calculations, we demonstrate that multiple topological phases with a rich diagram, including topological insulator, Dirac semimetal, and Weyl semimetal phases, can be induced and engineered in α -Sn by external strains, magnetic fields, and circularly polarized light (CPL). Intriguingly, not only the conventional type-I Weyl nodes but also type-II Weyl nodes and double-Weyl nodes can be generated directly from the quadratic semimetal by applying a magnetic field or CPL. Our results apply equally well to other Luttinger semimetals with similar crystal and electronic structures, and thus open an avenue for realizing and engineering multiple topological phases on a versatile platform.

Comparative studies on the room-temperature ferrielectric and ferrimagnetic Ni3TeO6-type A2FeMoO6 compounds (A = Sc, Lu)

PubMed Central

Song, Guang; Zhang, Weiyi

2016-01-01

First-principles calculations have been carried out to study the structural, electric, and magnetic properties of Ni3TeO6-type A2FeMoO6 compounds (A = Sc, Lu). Their electric and magnetic properties behave like room-temperature ferrielectric and ferrimagnetic insulators where polarization comes from the un-cancelled antiparallel dipoles of (A(1), Fe3+) and (A(2), Mo3+) ion groups, and magnetization from un-cancelled antiparallel moments of Fe3+ and Mo3+ ions. The net polarization increases with A’s ionic radius and is 7.1 and 8.7 μCcm−2 for Sc2FeMoO6 and Lu2FeMoO6, respectively. The net magnetic moment is 2 μB per formula unit. The magnetic transition temperature is estimated well above room-temperature due to the strong antiferromagnetic superexchange coupling among Fe3+ and Mo3+ spins. The estimated paraelectric to ferrielectric transition temperature is also well above room-temperature. Moreover, strong magnetoelectric coupling is also anticipated because the magnetic ions are involved both in polarization and magnetization. The fully relaxed Ni3TeO6-type A2FeMoO6 structures are free from soft-phonon modes and correspond to stable structures. As a result, Ni3TeO6-type A2FeMoO6 compounds are possible candidates for room-temperature multiferroics with large magnetization and polarization. PMID:26831406

Large linear magnetoresistance in topological crystalline insulator Pb{sub 0.6}Sn{sub 0.4}Te

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roychowdhury, Subhajit; Ghara, Somnath; Guin, Satya N.

2016-01-15

Classical magnetoresistance generally follows the quadratic dependence of the magnetic field at lower field and finally saturates when field is larger. Here, we report the large positive non-saturating linear magnetoresistance in topological crystalline insulator, Pb{sub 0.6}Sn{sub 0.4}Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. Magnetoresistance value as high as ∼200% was achieved at 3 K at magnetic field of 9 T. Linear magnetoresistance observed in Pb{sub 0.6}Sn{sub 0.4}Te is mainly governed by the spatial fluctuation carrier mobility due to distortions in the current paths in inhomogeneous conductor. - Graphical abstract: Largemore » non-saturating linear magnetoresistance has been evidenced in topological crystalline insulator, Pb{sub 0.6}Sn{sub 0.4}Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. - Highlights: • Large non-saturating linear magnetoresistance was achieved in the topological crystalline insulator, Pb{sub 0.6}Sn{sub 0.4}Te. • Highest magnetoresistance value as high as ~200% was achieved at 3 K at magnetic field of 9 T. • Linear magnetoresistance in Pb{sub 0.6}Sn{sub 0.4}Te is mainly governed by the spatial fluctuation of the carrier mobility.« less

Intrinsic Josephson effects in the magnetic superconductor RuSr2GdCu2O8.

PubMed

Nachtrab, T; Koelle, D; Kleiner, R; Bernhard, C; Lin, C T

2004-03-19

We have measured interlayer current transport in small-sized RuSr2GdCu2O8 single crystals. We find a clear intrinsic Josephson effect showing that the material acts as a natural superconductor-insulator-ferromagnet-insulator-superconductor superlattice. Thus far, we detected no unconventional behavior due to the magnetism of the RuO2 layers.

Low temperature resistivity plateau and non-saturating magnetoresistance in Type-II Weyl semimetal WP2

NASA Astrophysics Data System (ADS)

Nagpal, V.; Kumar, P.; Sudesh, Patnaik, S.

2018-04-01

We have studied the resistivity and magnetoresistance (MR) properties of the recently predicted type-II Weyl semimetal WP2. Polycrystalline WP2 is synthesized using solid state reaction and crystallizes in an orthorhombic structure with the Cmc21 spacegroup. The temperature dependent resistivity is enhanced with the application of magnetic field and a resistivity plateau is observed at low temperatures. We find a small dip in resistivity around 30K at 5T field suggesting that there might be a metal-insulator-like transition at higher magnetic fields. A non-saturating magnetoresistance is observed at low temperatures with maximum MR ˜ 94% at 2K and 6T. The value of MR decreases with the increase in temperature. We see a deviation from Kohler's power law which implies that the system comprises of two types of charge carriers.

Design of Chern insulating phases in honeycomb lattices

NASA Astrophysics Data System (ADS)

Pickett, Warren E.; Lee, Kwan-Woo; Pentcheva, Rossitza

2018-06-01

The search for robust examples of the magnetic version of topological insulators, referred to as quantum anomalous Hall insulators or simply Chern insulators, so far lacks success. Our groups have explored two distinct possibilities based on multiorbital 3d oxide honeycomb lattices. Each has a Chern insulating phase near the ground state, but materials parameters were not appropriate to produce a viable Chern insulator. Further exploration of one of these classes, by substituting open shell 3d with 4d and 5d counterparts, has led to realistic prediction of Chern insulating ground states. Here we recount the design process, discussing the many energy scales that are active in participating (or resisting) the desired Chern insulator phase.

Spin-polarized two-dimensional electron gas at GdTi O3/SrTi O3 interfaces: Insight from first-principles calculations

NASA Astrophysics Data System (ADS)

Betancourt, J.; Paudel, T. R.; Tsymbal, E. Y.; Velev, J. P.

2017-07-01

Two-dimensional electron gases (2DEGs) at oxide interfaces have been a topic of intensive research due to their high carrier mobility and strong confinement. Additionally, strong correlations in the oxide materials can give rise to new and interesting physics, such as magnetism and metal-insulator transitions at the interface. Using first-principles calculations based on density functional theory, we demonstrate the presence of a highly spin-polarized 2DEG at the interface between the Mott insulator GdTi O3 and a band insulator SrTi O3 . The strong correlations in the dopant cause ferromagnetic alignment of the interface Ti atoms and result in a fully spin-polarized 2DEG. The 2DEG consists of two types of carriers distinguished by their orbital character. The majority of the interface charge is strongly localized on the Ti dx y orbitals at the interface and a smaller fraction resides on the delocalized Ti dx z ,y z states.

Effect of impurity resonant states on optical and thermoelectric properties on the surface of a topological insulator.

PubMed

Zhong, Min; Li, Shuai; Duan, Hou-Jian; Hu, Liang-Bin; Yang, Mou; Wang, Rui-Qiang

2017-06-21

We investigate the thermoelectric effect on a topological insulator surface with particular interest in impurity-induced resonant states. To clarify the role of the resonant states, we calculate the dc and ac conductivities and the thermoelectric coefficients along the longitudinal direction within the full Born approximation. It is found that at low temperatures, the impurity resonant state with strong energy de-pendence can lead to a zero-energy peak in the dc conductivity, whose height is sensitively dependent on the strength of scattering potential, and even can reverse the sign of the thermopower, implying the switching from n- to p-type carriers. Also, we exhibit the thermoelectric signatures for the filling process of a magnetic band gap by the resonant state. We further study the impurity effect on the dynamic optical conductivity, and find that the resonant state also generates an optical conductivity peak at the absorption edge for the interband transition. These results provide new perspectives for understanding the doping effect on topological insulator materials.

Linear magneto-resistance in Bi{sub 2}SeTe{sub 2} topological insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amaladass, E. P., E-mail: edward@igcar.gov.in; Sharma, Shilpam; Devidas, T. R.

2016-05-23

Magnetic field and temperature dependent electronic transport measurements have been carried out on Bi{sub 2}SeTe{sub 2} topological insulator single crystals. The measurements reveal an insulating behavior and the carriers were found to be electrons (n-type) from Hall measurement. Magneto-resistance (MR) measurements in the field range (B) of 15 T to -15 T carried out at 4.2 K showed a cusp like weak anti-localization behavior for lower fields (-5 T 5 T. Upon increasing temperature, MR transforms to linear dependence of B at 40, 50 and 100 K. On further increasing temperatures (> 200 K), a parabolic MR is observed. Temperaturemore » dependent Hall data also showed a transition from a nonlinear to linear behavior upon increasing temperatures. Disorder induced changes in the electronic transport characteristics of bulk and surface electrons are believed to cause such changes in the magneto-transport behavior of this system.« less

Transport and magnetic properties of Fe doped CaMnO3

NASA Astrophysics Data System (ADS)

Neetika; Das, A.; Dhiman, I.; Nigam, A. K.; Yadav, A. K.; Bhattacharyya, D.; Meena, S. S.

2012-12-01

The structural, transport, and magnetic properties of CaMn1-xFexO3-δ (0.0 ≤ x ≤ 0.3) have been studied by using resistivity, magnetization, and neutron powder diffraction techniques. The compounds are found to be isostructural and crystallize in GdFeO3-type orthorhombic structure (space group Pnma). With Fe doping, no structural change is observed. Mössbauer and paramagnetic susceptibility measurements show that Fe substitutes in 4+ valence state, and XANES measurements indicate the presence of mixed valence state of Mn. The compounds exhibit insulating behavior in the studied temperature range. The temperature dependence of resistivity is found to be described by small polaron model for x = 0 and variable range hopping model for x = 0.1. For higher x values, it follows a parallel combination resistance model. A small reduction in TN from 120 K to 100 K with increase in x is found. The magnetic structure changes from Gz-type collinear antiferromagnetic (AFM) structure for x = 0.0 to canted AFM structure GZFY-type for Fe doped compounds. The AFM component of the moment progressively decreases with x while FM component exhibits a maximum at x = 0.2.

Resonant magneto-optic Kerr effect in the magnetic topological insulator Cr:(Sb x,Bi 1–x) 2Te 3

DOE PAGES

Patankar, Shreyas; Hinton, J. P.; Griesmar, Joel; ...

2015-12-31

Here, we report measurements of the polar Kerr effect, proportional to the out-of-plane component of the magnetization, in thin films of the magnetically doped topological insulator (Cr 0.12Bi 0.26Sb 0.62) 2Te 3. Measurements of the complex Kerr angle ΘK were performed as a function of photon energy in the range 0.8eV < ℏω < 3.0eV. We observed a peak in the real part of Θ K(ω) and zero crossing in the imaginary part that we attribute to a resonant interaction with a spin-orbit avoided crossing located ≈ 1.6 eV above the Fermi energy. The resonant enhancement allows measurement of themore » temperature and magnetic field dependence of Θ K in the ultrathin film limit, d ≥ 2 quintuple layers (QL). We find a sharp transition to zero remanent magnetization at 6 K for d < 8 QL, consistent with theories of the dependence of impurity spin interactions on film thickness and their location relative to topological insulator surfaces.« less

Pressure-induced magnetic collapse and metallization of TlF e1.6S e2

NASA Astrophysics Data System (ADS)

Naumov, P. G.; Filsinger, K.; Shylin, S. I.; Barkalov, O. I.; Ksenofontov, V.; Qi, Y.; Palasyuk, T.; Schnelle, W.; Medvedev, S. A.; Greenblatt, M.; Felser, C.

2017-08-01

The crystal structure, magnetic ordering, and electrical resistivity of TlF e1.6S e2 were studied at high pressures. Below ˜7 GPa , TlF e1.6S e2 is an antiferromagnetically ordered semiconductor with a ThC r2S i2 -type structure. The insulator-to-metal transformation observed at a pressure of ˜7 GPa is accompanied by a loss of magnetic ordering and an isostructural phase transition. In the pressure range ˜7.5 -11 GPa a remarkable downturn in resistivity, which resembles a superconducting transition, is observed below 15 K. We discuss this feature as the possible onset of superconductivity originating from a phase separation in a small fraction of the sample in the vicinity of the magnetic transition.

Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states

DOE PAGES

Jiang, Zilong; Chang, Cui -Zu; Masir, Massoud Ramezani; ...

2016-05-04

Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (Bi xSb 1–x) 2Te 3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (Bi xSbmore » 1–x) 2Te 3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. Lastly, the enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.« less

Visualization of a stable intermediate phase in photoinduced metal-to-insulator transition in manganites

NASA Astrophysics Data System (ADS)

Lin, Hanxuan; Liu, Hao; Bai, Yu; Miao, Tian; Yu, Yang; Zhu, Yinyan; Chen, Hongyan; Kou, Yunfang; Niu, Jiebin; Wang, Wenbin; Yin, Lifeng; Shen, Jian

First order metal-insulator transition, accounting for various intriguing phenomena, is one of the most important phase transitions in condensed matter systems. Aside from the initial and final states, i.e. the metallic and insulating phases, no stable intermediate phase has been experimentally identified in such first order phase transition, though some transient phases do exist at the ultrafast time scale. Here, using our unique low-temperature, high-field magnetic force microscopy with photoexcitation, we directly observed a stable intermediate phase emerging and mediating the photoinduced first order metal-insulator transition in manganites. This phase is characteristic of low net magnetization and high resistivity. Our observations unveil the microscopic details of the photoinduced metal-insulator transition in manganites, which may be insightful to study first order metal-insulator transition in other condensed matter systems. This work was supported by National Key Research Program of China (2016YFA0300702), National Basic Research Program of China (973 Program) under the Grant No. 2013CB932901 and 2014CB921104; National Natural Science Foundation of China (11274071, 11504053).

Magnetically Defined Qubits on 3D Topological Insulators

NASA Astrophysics Data System (ADS)

Ferreira, Gerson J.; Loss, Daniel

2014-03-01

We explore potentials that break time-reversal symmetry to confine the surface states of 3D topological insulators into quantum wires and quantum dots. A magnetic domain wall on a ferromagnet insulator cap layer provides interfacial states predicted to show the quantum anomalous Hall effect. Here, we show that confinement can also occur at magnetic domain heterostructures, with states extended in the inner domain, as well as interfacial QAHE states at the surrounding domain walls. The proposed geometry allows the isolation of the wire and dot from spurious circumventing surface states. For the quantum dots, we find that highly spin-polarized quantized QAHE states at the dot edge constitute a promising candidate for quantum computing qubits. See [Ferreira and Loss, Phys. Rev. Lett. 111, 106802 (2013)]. We explore potentials that break time-reversal symmetry to confine the surface states of 3D topological insulators into quantum wires and quantum dots. A magnetic domain wall on a ferromagnet insulator cap layer provides interfacial states predicted to show the quantum anomalous Hall effect. Here, we show that confinement can also occur at magnetic domain heterostructures, with states extended in the inner domain, as well as interfacial QAHE states at the surrounding domain walls. The proposed geometry allows the isolation of the wire and dot from spurious circumventing surface states. For the quantum dots, we find that highly spin-polarized quantized QAHE states at the dot edge constitute a promising candidate for quantum computing qubits. See [Ferreira and Loss, Phys. Rev. Lett. 111, 106802 (2013)]. We acknowledge support from the Swiss NSF, NCCR Nanoscience, NCCR QSIT, and the Brazillian Research Support Center Initiative (NAP Q-NANO) from Pró-Reitoria de Pesquisa (PRP/USP).

No-insulation multi-width winding technique for high temperature superconducting magnet.

PubMed

Hahn, Seungyong; Kim, Youngjae; Keun Park, Dong; Kim, Kwangmin; Voccio, John P; Bascuñán, Juan; Iwasa, Yukikazu

2013-10-21

We present a No-Insulation ( NI ) Multi-Width ( MW ) winding technique for an HTS (high temperature superconductor) magnet consisting of double-pancake (DP) coils. The NI enables an HTS magnet self-protecting and the MW minimizes the detrimental anisotropy in current-carrying capacity of HTS tape by assigning tapes of multiple widths to DP coils within a stack, widest tape to the top and bottom sections and the narrowest in the midplane section. This paper presents fabrication and test results of an NI-MW HTS magnet and demonstrates the unique features of the NI-MW technique: self-protecting and enhanced field performance, unattainable with the conventional technique.

Thermoelectric current in topological insulator nanowires with impurities.

PubMed

Erlingsson, Sigurdur I; Bardarson, Jens H; Manolescu, Andrei

2018-01-01

In this paper we consider charge current generated by maintaining a temperature difference over a nanowire at zero voltage bias. For topological insulator nanowires in a perpendicular magnetic field the current can change sign as the temperature of one end is increased. Here we study how this thermoelectric current sign reversal depends on the magnetic field and how impurities affect the size of the thermoelectric current. We consider both scalar and magnetic impurities and show that their influence on the current are quite similar, although the magnetic impurities seem to be more effective in reducing the effect. For moderate impurity concentration the sign reversal persists.

Possible field-tuned superconductor-insulator transition in high-Tc superconductors: implications for pairing at high magnetic fields.

PubMed

Steiner, M A; Boebinger, G; Kapitulnik, A

2005-03-18

The behavior of some high temperature superconductors (HTSC), such as La(2-x)Sr(x)CuO(4) and Bi(2)Sr(2-x)La(x)CuO(6 + delta), at very high magnetic fields, is similar to that of thin films of amorphous InOx near the magnetic-field-tuned superconductor-insulator transition. Analyzing the InOx data at high fields in terms of persisting local pairing amplitude, we argue by analogy that the local pairing amplitude also persists well into the dissipative state of the HTSCs, the regime commonly denoted as the "normal state" in very high magnetic field experiments.

Phase diagram of pressure-induced superconductor β-(BDA-TTP)2MX4 (M=Fe, Ga and X=Cl, Br) with localized magnetic moments

NASA Astrophysics Data System (ADS)

Choi, E. S.; Graf, D.; Tokumoto, T.; Brooks, J. S.; Yamada, Jun-Ichi

2007-03-01

We have investigated transport and magnetization properties of β-(BDA-TTP)2MX4 (M=Fe, Ga and X=Cl, Br) as a function of pressure, temperature and magnetic field. The title material undergoes metal-insulator transitions above 100 K at ambient pressure. The insulating phase is suppressed with pressure and superconductivity eventually appears above Pc= 4.5 kbar (X=Cl) and 13 kbar (X=Br). The general temperature-pressure (TP) phase diagram is similar each other, while higher pressure is required for X=Br compounds to suppress the insulating state and induce the superconductivity. Pressure dependent DC magnetization studies on β-(BDA-TTP)2FeCl4 compound revealed that the AFM ordering persist well above Pc. In spite of similarity of phase diagram between M=Fe and M=Ga compounds, magnetoresistance results show distinct behaviors, which indicates the magnetic interaction with the conduction electrons are still effective. The comparison between X=Cl and X=Br compounds suggests the anion-size effect rather than the existence of localized magnetic moments plays more important role in determining the ground state.

Metal-insulator transition in Ba3Fe1 -xRu2 +xO9 : Interplay between site disorder, chemical percolation, and electronic structure

NASA Astrophysics Data System (ADS)

Middey, S.; Aich, Payel; Meneghini, C.; Mukherjee, K.; Sampathkumaran, E. V.; Siruguri, V.; Mahadevan, P.; Ray, Sugata

2016-11-01

Perovskites containing barium metal at the A site often take up unusual hexagonal structures having more than one type of possible sites for the B cation to occupy. This opens up various different B -B - or B -O-B -type connectivities and consequent physical properties which are naturally missing in cubic perovskites. BaRuO3 is one such system where doping of Ru (4 d4 ) by other transition metals (Mn +) creates similar conditions, giving rise to various M -Ru interactions. Interestingly, the 6 H hexagonal structure of doped barium ruthenate triple perovskite (Ba3M Ru2O9 ) seems to possess some internal checks because within the structure M ion always occupies the 2 a site and Ru goes to the 4 f site, allowing only M -O-Ru 180∘ and Ru-O-Ru 90∘ interactions to occur. The only exception is observed in the case of the Fe dopant, which allows us to study almost the full Ba3Fe1 -xRu2 +xO9 series of compounds with wide ranges of x because here Fe ions have the ability to freely go to the 4 f sites and Ru readily takes up the 2 a positions. Therefore, here one has the opportunity to probe the evolution of electronic and magnetic properties as a function of doping by going from BaRuO3 (paramagnetic metal) to BaFeO3 (ferromagnetic insulator). Our detailed experimental and theoretical results show that the series does exhibit a percolative metal-insulator transition with an accompanying but not coincidental magnetic transition as a function of x .

Experimental research on time-resolved evolution of cathode plasma expansion velocity in a long pulsed magnetically insulated coaxial diode

NASA Astrophysics Data System (ADS)

Zhu, Danni; Zhang, Jun; Zhong, Huihuang; Ge, Xingjun; Gao, Jingming

2018-02-01

Unlike planar diodes, separate research of the axial and radial plasma expansion velocities is difficult for magnetically insulated coaxial diodes. Time-resolved electrical diagnostic which is based on the voltage-ampere characteristics has been employed to study the temporal evolution of the axial and radial cathode plasma expansion velocities in a long pulsed magnetically insulated coaxial diode. Different from a planar diode with a "U" shaped profile of temporal velocity evolution, the temporal evolution trend of the axial expansion velocity is proved to be a "V" shaped profile. Apart from the suppression on the radial expansion velocity, the strong magnetic field is also conducive to slowing down the axial expansion velocity. Compared with the ordinary graphite cathode, the carbon velvet and graphite composite cathode showed superior characteristics as judged by the low plasma expansion velocity and long-term electrical stability as a promising result for applications where long-pulsed and reliable operation at high power is required.

Theoretical and experimental investigation of magnetic field related helium leak in helium vessel of a large superconducting magnet

NASA Astrophysics Data System (ADS)

Bhattachryya, Pranab; Gupta, Anjan Dutta; Dhar, S.; Sarma, P. R.; Mukherjee, Paramita

2017-06-01

The helium vessel of the superconducting cyclotron (SCC) at the Variable Energy Cyclotron centre (VECC), Kolkata shows a gradual loss of insulation vacuum from 10-7 mbar to 10-4 mbar with increasing coil current in the magnet. The insulation vacuum restores back to its initial value with the withdrawal of current. The origin of such behavior has been thought to be related to the electromagnetic stress in the magnet. The electromagnetic stress distribution in the median plane of the helium vessel was studied to figure out the possible location of the helium leak. The stress field from the possible location was transferred to a simplified 2D model with different leak geometries to study the changes in conductance with coil current. The leak rate calculated from the changes in the leak geometry was compared with the leak rate calculated from the experimental insulation vacuum degradation behavior to estimate the initial leak shape and size.

Spin Hall driven domain wall motion in magnetic bilayers coupled by a magnetic oxide interlayer

NASA Astrophysics Data System (ADS)

Liu, Yang; Furuta, Masaki; Zhu, Jian-Gang Jimmy

2018-05-01

mCell, previously proposed by our group, is a four-terminal magnetoresistive device with isolated write- and read-paths for all-spin logic and memory applications. A mCell requires an electric-insulating magnetic layer to couple the spin Hall driven write-path to the magnetic free layer of the read-path. Both paths are magnetic layers with perpendicular anisotropy and their perpendicularly oriented magnetization needs to be maintained with this insertion layer. We have developed a magnetic oxide (FeOx) insertion layer to serve for these purposes. We show that the FeOx insertion layer provides sufficient magnetic coupling between adjacent perpendicular magnetic layers. Resistance measurement shows that this magnetic oxide layer can act as an electric-insulating layer. In addition, spin Hall driven domain wall motion in magnetic bi-layers coupled by the FeOx insertion layer is significantly enhanced compared to that in magnetic single layer; it also requires low voltage threshold that poses possibility for power-efficient device applications.

Electric Motors for Non-Cryogenic Hybrid Electric and Turboelectric Propulsion

NASA Technical Reports Server (NTRS)

Duffy, Kirsten P.

2015-01-01

NASA Glenn Research Center is investigating hybrid electric and turboelectric propulsion concepts for future aircraft to reduce fuel burn, emissions, and noise. Systems studies show that the weight and efficiency of the electric system components need to be improved for this concept to be feasible. However, advances in motor component materials such as soft magnetic materials, hard magnetic materials, conductors, thermal insulation, and structural materials are expected in the coming years, and should improve motor performance. This study investigates several motor types for a one megawatt application, and projects the motor performance benefits of new component materials that might be available in the coming decades.

Electric Motor Considerations for Non-Cryogenic Hybrid Electric and Turboelectric Propulsion

NASA Technical Reports Server (NTRS)

Duffy, Kirsten P.

2015-01-01

NASA Glenn Research Center is investigating hybrid electric and turboelectric propulsion concepts for future aircraft to reduce fuel burn, emissions, and noise. Systems studies show that the weight and efficiency of the electric system components need to be improved for this concept to be feasible. However, advances in motor component materials such as soft magnetic materials, hard magnetic materials, conductors, thermal insulation, and structural materials are expected in the coming years, and should improve motor performance. This study investigates several motor types for a one megawatt application, and projects the motor performance benefits of new component materials that might be available in the coming decades.

Magnetic Proximity Effect in a Transferred Topological Insulator Thin Film on a Magnetic Insulator

NASA Astrophysics Data System (ADS)

Che, Xiaoyu; Murata, Koichi; Pan, Lei; He, Qinglin; Yin, Gen; Fan, Yabin; Bi, Lei; Wang, Kang Lung

Exotic physical phenomena such as the quantum anomalous Hall effect (QAHE) arise by breaking the time-reversal symmetry (TRS) in topological insulators. However, substantial efforts have been made in improving the temperature for realizing the QAHE via magnetically doping, while the proximity coupling is another approach to develop the magnetic order without the introduction of additional carriers or the presence of local Fermi level fluctuation. Here we demonstrate the experimental signature of magnetic proximity effect in a molecular beam epitaxy-grown TI thin film of Bi2Se3 transferred to a magnetic substrate of yttrium iron garnet using a wet transfer technique. Comparing to the TI/GaAs control sample, the magnetic order is manifested by the anomalous Hall effect in magneto-transport characterization. Furthermore, due to TRS breaking by the proximity effect we observed a constituent weak localization component accompanied with the weak antilocalization behavior. The present work takes a step further toward realizing QAHE at higher temperature and opens up a new path in TI device designs for applications. We acknowledge the support from the ARO program under contract 15-1-10561, the SHINES Center under Award # S000686, NSF DMR-1350122, and the FAME Center, one of six centers of STARnet, sponsored by MARCO and DARPA.

Development of indigenous insulation material for superconducting magnets and study of its characteristics under influence of intense neutron irradiation

NASA Astrophysics Data System (ADS)

Sharma, Rajiv; Tanna, V. L.; Rao, C. V. S.; Abhangi, Mitul; Vala, Sudhirsinh; Sundaravel; Varatharajan, S.; Sivakumar, S.; Sasi, K.; Pradhan, S.

2017-02-01

Epoxy based glass fiber reinforced composites are the main insulation system for the superconducting magnets of fusion machines. 14MeV neutrons are generated during the DT fusion process, however the energy spectra and flux gets modified to a great extent when they reach the superconducting magnets. Mechanical properties of the GFRP insulation material is reported to degrade up to 30%. As a part of R & D activity, a joint collaboration with IGCAR, Kalpakkam has been established. The indigenous insulation material is subjected to fast neutron fluence of 1014 - 1019 n/m2 (E>0.1 MeV) in FBTR and KAMINI Reactor, India. TRIM software has been used to simulate similar kind of damage produced by neutrons by ion irradiation with 5 MeV Al ions and 3 MeV protons. Fluence of the ions was adjusted to get the same dpa. We present the test experiment of neutron irradiation of the composite material (E-glass, S-glass fiber boron free and DGEBA epoxy). The test results of tensile, inter laminar shear and electrical breakdown strength as per ASTM standards, assessment of micro-structure surface degradation before and after irradiation will be presented. MCNP simulations are carried out for neutron flux, dose and damages produced in the insulation material.

Asymmetric d-wave superconducting topological insulator in proximity with a magnetic order

NASA Astrophysics Data System (ADS)

Khezerlou, M.; Goudarzi, H.; Asgarifar, S.

2018-02-01

In the framework of the Dirac-Bogoliubov-de Gennes formalism, we investigate the transport properties in the surface of a 3-dimensional topological insulator-based hybrid structure, where the ferromagnetic and superconducting orders are simultaneously induced to the surface states via the proximity effect. The superconductor gap is taken to be spin-singlet d-wave symmetry. The asymmetric role of this gap respect to the electron-hole exchange, in one hand, affects the topological insulator superconducting binding excitations and, on the other hand, gives rise to forming distinct Majorana bound states at the ferromagnet/superconductor interface. We propose a topological insulator N/F/FS junction and proceed to clarify the role of d-wave asymmetry pairing in the resulting subgap and overgap tunneling conductance. The perpendicular component of magnetizations in F and FS regions can be at the parallel and antiparallel configurations leading to capture the experimentally important magnetoresistance (MR) of junction. It is found that the zero-bias conductance is strongly sensitive to the magnitude of magnetization in FS region mzfs and orbital rotated angle α of superconductor gap. The negative MR only occurs in zero orbital rotated angle. This result can pave the way to distinguish the unconventional superconducting state in the relating topological insulator hybrid structures.

Spin Currents and Ferromagnetic Resonance in Magnetic Thin Films

NASA Astrophysics Data System (ADS)

Ellsworth, David

Spin currents represent a new and exciting phenomenon. There is both a wealth of new physics to be discovered and understood, and many appealing devices which may result from this area of research. To fully realize the potential of this discipline it is necessary to develop new methods for realizing spin currents and explore new materials which may be suitable for spin current applications. Spin currents are an inherently dynamic phenomenon involving the transfer of angular momentum within and between different thin films. In order to understand and optimize such devices the dynamics of magnetization must be determined. This dissertation reports on novel approaches for spin current generation utilizing the magnetic insulators yttrium iron garnet (YIG) and M-type barium hexagonal ferrite (BaM). First, the light-induced spin Seebeck effect is reported for the first time in YIG. Additionally, the first measurement of the spin Seebeck effect without an external magnetic field is demonstrated. To accomplish this the self-biased BaM thin films are utilized. Second, a new method for the generation of spin currents is presented: the photo-spin-voltaic effect. In this new phenomenon, a spin current may be generated by photons in a non-magnetic metal that is in close proximity to a magnetic insulator. On exposure to light, there occurs a light induced, spin-dependent excitation of electrons in a few platinum layers near the metal/magnetic insulator interface. This excitation gives rise to a pure spin current which flows in the metal. This new effect is explored in detail and extensive measurements are carried out to confirm the photonic origin of the photo-spin-voltaic effect and exclude competing effects. In addition to the spin current measurements, magnetization dynamics were probed in thin films using ferromagnetic resonance (FMR). In order to determine the optimal material configuration for magnetic recording write heads, FMR measurements were used to perform damping studies on a set of FeCo samples with different numbers of lamination layers. The use of lamination layers has the potential to tune the damping in such films, while leaving the other magnetic properties unchanged. Finally, the sensitivity of the vector network analyzer FMR technique was improved. The use of field modulation and lock-in detection, along with the background subtraction of a Mach-Zehnder microwave interferometer working as a notch filter, is able to increase the sensitivity and lower the background noise of this measurement technique. This improved system opens the possibility of probing previously difficult samples with extremely low signals.

Mechanical engineering and design criteria for the Magnetically Insulated Transmission Experiment Accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Staller, G.E.; Hamilton, I.D.; Aker, M.F.

1978-02-01

A single-unit electron beam accelerator was designed, fabricated, and assembled in Sandia's Technical Area V to conduct magnetically insulated transmission experiments. Results of these experiments will be utilized in the future design of larger, more complex accelerators. This design makes optimum use of existing facilities and equipment. When designing new components, possible future applications were considered as well as compatibility with existing facilities and hardware.

Magnon-mediated current drag across a magnetic insulator

NASA Astrophysics Data System (ADS)

Shi, Jing

Electric current transmission can occur in a magnetic insulator via spin current inter-conversions at heavy metal/magnetic insulator interfaces. In magnetic insulators, spin current is carried by spin wave excitations or their quanta, magnons. This marvelous phenomenon was first theoretically predicted and dubbed as the magnon-mediated current drag in 2012 by Zhang et al.. Following a breakthrough in materials growth, i.e. yttrium iron garnet films or YIG ranging from 30 to 80 nm in thickness sandwiched between two heavy metal films, we successfully showed the nonlocal DC current transmission in such sandwich structures via spin current rather than charge current. To exclude the leakage effect, the experiments are conducted at temperatures below 250 K where the resistance between the metal layers exceeds 20 Gohms. In addition, by replacing the top Pt electrode with beta-Ta which is known to reverse the sign in the spin Hall angle, we found that the nonlocal signal reverses the polarity, which is a direct demonstration of the spin current nature. Furthermore, the temperature dependence of the nonlocal signal confirms the role of magnons in this effect. The work was supported as part of the SHINES, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award No. SC0012670.

The Property, Preparation and Application of Topological Insulators: A Review

PubMed Central

Tian, Wenchao; Shi, Jing; Wang, Yongkun

2017-01-01

Topological insulator (TI), a promising quantum and semiconductor material, has gapless surface state and narrow bulk band gap. Firstly, the properties, classifications and compounds of TI are introduced. Secondly, the preparation and doping of TI are assessed. Some results are listed. (1) Although various preparation methods are used to improve the crystal quality of the TI, it cannot reach the industrialization. Fermi level regulation still faces challenges; (2) The carrier type and lattice of TI are affected by non-magnetic impurities. The most promising property is the superconductivity at low temperature; (3) Magnetic impurities can destroy the time-reversal symmetry of the TI surface, which opens the band gap on the TI surface resulting in some novel physical effects such as quantum anomalous Hall effect (QAHE). Thirdly, this paper summarizes various applications of TI including photodetector, magnetic device, field-effect transistor (FET), laser, and so on. Furthermore, many of their parameters are compared based on TI and some common materials. It is found that TI-based devices exhibit excellent performance, but some parameters such as signal to noise ratio (S/N) are still lower than other materials. Finally, its advantages, challenges and future prospects are discussed. Overall, this paper provides an opportunity to improve crystal quality, doping regulation and application of TI. PMID:28773173

Divergent resistance at the Dirac point in graphene: Evidence for a transition in a high magnetic field

NASA Astrophysics Data System (ADS)

Checkelsky, Joseph G.; Li, Lu; Ong, N. P.

2009-03-01

We have investigated the behavior of the resistance of graphene at the n=0 Landau level in an intense magnetic field H . Employing a low-dissipation technique (with power P<3fW ), we find that at low temperature T , the resistance at the Dirac point R0(H) undergoes a 1000-fold increase from ˜10kΩ to 40MΩ within a narrow interval of field. The abruptness of the increase suggests that a transition to an insulating ordered state occurs at the critical field Hc . Results from five samples show that Hc depends systematically on the disorder, as measured by the offset gate voltage V0 . Samples with small V0 display a smaller critical field Hc . Empirically, the steep increase in R0 fits accurately a Kosterlitz-Thouless-type correlation length over three decades. The curves of R0 vs T at fixed H approach the thermal-activation form with a gap Δ˜15K as H→Hc- , consistent with a field-induced insulating state.

Ultralow Damping in Nanometer-Thick Epitaxial Spinel Ferrite Thin Films.

PubMed

Emori, Satoru; Yi, Di; Crossley, Sam; Wisser, Jacob J; Balakrishnan, Purnima P; Khodadadi, Behrouz; Shafer, Padraic; Klewe, Christoph; N'Diaye, Alpha T; Urwin, Brittany T; Mahalingam, Krishnamurthy; Howe, Brandon M; Hwang, Harold Y; Arenholz, Elke; Suzuki, Yuri

2018-06-08

Pure spin currents, unaccompanied by dissipative charge flow, are essential for realizing energy-efficient nanomagnetic information and communications devices. Thin-film magnetic insulators have been identified as promising materials for spin-current technology because they are thought to exhibit lower damping compared with their metallic counterparts. However, insulating behavior is not a sufficient requirement for low damping, as evidenced by the very limited options for low-damping insulators. Here, we demonstrate a new class of nanometer-thick ultralow-damping insulating thin films based on design criteria that minimize orbital angular momentum and structural disorder. Specifically, we show ultralow damping in <20 nm thick spinel-structure magnesium aluminum ferrite (MAFO), in which magnetization arises from Fe 3+ ions with zero orbital angular momentum. These epitaxial MAFO thin films exhibit a Gilbert damping parameter of ∼0.0015 and negligible inhomogeneous linewidth broadening, resulting in narrow half width at half-maximum linewidths of ∼0.6 mT around 10 GHz. Our findings offer an attractive thin-film platform for enabling integrated insulating spintronics.

Emergent Momentum-Space Skyrmion Texture on the Surface of Topological Insulators

NASA Astrophysics Data System (ADS)

Mohanta, Narayan; Kampf, Arno P.; Kopp, Thilo

The quantum anomalous Hall effect has been theoretically predicted and experimentally verified in magnetic topological insulators. In addition, the surface states of these materials exhibit a hedgehog-like ``spin'' texture in momentum space. Here, we apply the previously formulated low-energy model for Bi2Se3, a parent compound for magnetic topological insulators, to a slab geometry in which an exchange field acts only within one of the surface layers. In this sample set up, the hedgehog transforms into a skyrmion texture beyond a critical exchange field. This critical field marks a transition between two topologically distinct phases. The topological phase transition takes place without energy gap closing at the Fermi level and leaves the transverse Hall conductance unchanged and quantized to e2 / 2 h . The momentum-space skyrmion texture persists in a finite field range. It may find its realization in hybrid heterostructures with an interface between a three-dimensional topological insulator and a ferromagnetic insulator. The work was supported by the Deutsche Forschungsgemeinschaft through TRR 80.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breznay, Nicholas P.; Tendulkar, Mihir; Zhang, Li

Here, we study the two-dimensional superconductor-insulator transition (SIT) in thin films of tantalum nitride. At zero magnetic field, films can be disorder-tuned across the SIT by adjusting thickness and film stoichiometry; insulating films exhibit classical hopping transport. Superconducting films exhibit a magnetic-field-tuned SIT, whose insulating ground state at high field appears to be a quantum-corrected metal. Scaling behavior at the field-tuned SIT shows classical percolation critical exponents zν ≈ 1.3, with a corresponding critical field H c << H c2, the upper critical field. The Hall effect exhibits a crossing point near H c, but with a nonuniversal critical valuemore » ρ c xy comparable to the normal-state Hall resistivity. We propose that high-carrier-density metals will always exhibit this pattern of behavior at the boundary between superconducting and (trivially) insulating ground states.« less

Fermi surfaces in Kondo insulators

NASA Astrophysics Data System (ADS)

Liu, Hsu; Hartstein, Máté; Wallace, Gregory J.; Davies, Alexander J.; Ciomaga Hatnean, Monica; Johannes, Michelle D.; Shitsevalova, Natalya; Balakrishnan, Geetha; Sebastian, Suchitra E.

2018-04-01

We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB12 and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB12 exhibit similarities with the Kondo insulator SmB6, yet also crucial differences. Small heavy Fermi sections are observed in YbB12 with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB6 which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.

Measurement of a superconducting energy gap in a homogeneously amorphous insulator.

PubMed

Sherman, D; Kopnov, G; Shahar, D; Frydman, A

2012-04-27

We present tunneling spectroscopy measurements that directly reveal the existence of a superconducting gap in the insulating state of homogenously disordered amorphous indium oxide films. Two films on both sides of the disorder induced superconductor to insulator transition show the same energy gap scale. This energy gap persists up to relatively high magnetic fields and is observed across the magnetoresistance peak typical of disordered superconductors. The results provide useful information for understanding the nature of the insulating state in the disorder induced superconductor to insulator transition.

Donor Magneto-Spectroscopy and Magnetic Field - Metal-Insulator Transition in MERCURY(1-X) Cadmium(x)tellurium and Indium Antimonide

NASA Astrophysics Data System (ADS)

Choi, Jung Bum

Far infrared (FIR) magneto-transmission studies of n-type Hg_{1-x}Cd _{x}Te (x = 0.198, 0.204, 0.224, 0.237, 0.270) for temperatures down to 1.5K and magnetic fields up to 9T in Voigt and Faraday geometries have been performed. Magneto-optical transitions of donor bound electrons are observed; including the (000) --> (001) and (010) --> (01k_{z}) in the Voigt geometry, and the (000) --> (110) in the Faraday geometry. These identifications are confirmed by their resonance positions, selection rules, and temperature dependence. The experimental observations are consistent with calculations of resonance positions and lineshapes based on the hydrogenic donor model including central cell effects. This work confirms the donor bound electronic ground state for Hg_{1-x}Cd_{x} Te. The magneto-transport and FIR spectroscopy have been combined to probe the nature of the impurity band in the vicinity of the magnetic field induced metal-insulator transition. The results obtained in Hg_ {1-x}Cd_{x}Te and InSb show the persistance of the (000) --> (110) impurity transition through the metal-insulator critical field. This observation demonstrates the existence of the metallic impurity band which is split off from the conduction band. In the studies of the critical behavior of InSb, the conductivity measured for temperatures down to 0.45K shows a dominant linear dependence on temperature near the transition field. Furthermore, the zero-temperature extrapolated conductivity was found to drop continuously to zero at the transition field with a critical exponent of nu = 1.07 +/- 0.07.

No-insulation multi-width winding technique for high temperature superconducting magnet

PubMed Central

Hahn, Seungyong; Kim, Youngjae; Keun Park, Dong; Kim, Kwangmin; Voccio, John P.; Bascuñán, Juan; Iwasa, Yukikazu

2013-01-01

We present a No-Insulation (NI) Multi-Width (MW) winding technique for an HTS (high temperature superconductor) magnet consisting of double-pancake (DP) coils. The NI enables an HTS magnet self-protecting and the MW minimizes the detrimental anisotropy in current-carrying capacity of HTS tape by assigning tapes of multiple widths to DP coils within a stack, widest tape to the top and bottom sections and the narrowest in the midplane section. This paper presents fabrication and test results of an NI-MW HTS magnet and demonstrates the unique features of the NI-MW technique: self-protecting and enhanced field performance, unattainable with the conventional technique. PMID:24255549

Topological crystalline magnets: Symmetry-protected topological phases of fermions

DOE PAGES

Watanabe, Haruki; Fu, Liang

2017-02-27

Here, we introduce a novel class of interaction-enabled topological crystalline insulators in two- and three-dimensional electronic systems, which we call “topological crystalline magnet.” It is protected by the product of the time-reversal symmetry T and a mirror symmetry or a rotation symmetry R. A topological crystalline magnet exhibits two intriguing features: (i) it cannot be adiabatically connected to any Slater insulator and (ii) the edge state is robust against coupling electrons to the edge. These features are protected by the anomalous symmetry transformation property ( RT) 2 = -1 of the edge state. Finally, an anisotropic response to the externalmore » magnetic field can be an experimental signature.« less

Topological crystalline magnets: Symmetry-protected topological phases of fermions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Haruki; Fu, Liang

Here, we introduce a novel class of interaction-enabled topological crystalline insulators in two- and three-dimensional electronic systems, which we call “topological crystalline magnet.” It is protected by the product of the time-reversal symmetry T and a mirror symmetry or a rotation symmetry R. A topological crystalline magnet exhibits two intriguing features: (i) it cannot be adiabatically connected to any Slater insulator and (ii) the edge state is robust against coupling electrons to the edge. These features are protected by the anomalous symmetry transformation property ( RT) 2 = -1 of the edge state. Finally, an anisotropic response to the externalmore » magnetic field can be an experimental signature.« less

Chiral magnetic conductivity and surface states of Weyl semimetals in topological insulator ultra-thin film multilayer.

PubMed

Owerre, S A

2016-06-15

We investigate an ultra-thin film of topological insulator (TI) multilayer as a model for a three-dimensional (3D) Weyl semimetal. We introduce tunneling parameters t S, [Formula: see text], and t D, where the former two parameters couple layers of the same thin film at small and large momenta, and the latter parameter couples neighbouring thin film layers along the z-direction. The Chern number is computed in each topological phase of the system and we find that for [Formula: see text], the tunneling parameter [Formula: see text] changes from positive to negative as the system transits from Weyl semi-metallic phase to insulating phases. We further study the chiral magnetic effect (CME) of the system in the presence of a time dependent magnetic field. We compute the low-temperature dependence of the chiral magnetic conductivity and show that it captures three distinct phases of the system separated by plateaus. Furthermore, we propose and study a 3D lattice model of Porphyrin thin film, an organic material known to support topological Frenkel exciton edge states. We show that this model exhibits a 3D Weyl semi-metallic phase and also supports a 2D Weyl semi-metallic phase. We further show that this model recovers that of 3D Weyl semimetal in topological insulator thin film multilayer. Thus, paving the way for simulating a 3D Weyl semimetal in topological insulator thin film multilayer. We obtain the surface states (Fermi arcs) in the 3D model and the chiral edge states in the 2D model and analyze their topological properties.

Magnetic Field Driven Change of the Density of States of Amorphous Gd_xSi_1-x at the Metal Insulator Transition

NASA Astrophysics Data System (ADS)

Teizer, W.; Hellman, F.; Dynes, R. C.; Ucsd Physics Department Collaboration

2000-03-01

We have determined the density of states of amorphous Gd_xSi_1-x, N(E), through the Metal-Insulator transition by tunneling measurements. Gd_xSi_1-x shows a strong negative magnetoresistance at low temperature [1] and can be driven through the Metal-Insulator transition by applying a magnetic field [2]. In H=0, the conductance dI/dV across a Gd_xSi_1-x/oxide/Pb tunnel junction is dominated by a sharp superconducting Pb gap edge and Pb phonons indicating the presence of single step quantum tunneling. As a small magnetic field (H=1kOe) is applied, effects of the superconductivity of Pb disappear and at low voltages it is reasonable to approximate dI/dV N(E). We find that N(E) increases with magnetic field. On the metallic side of the Metal-Insulator transition, the density of states at zero bias, N(0), approximately scales with the extrapolated T=0 transport conductivity σ_0. A change of N(0) thus causes a change in σ_0. The Metal-Insulator transition occurs when N(0) goes to 0. [1] F. Hellman, M. Q. Tran, A. E. Gebala, E. M. Wilcox and R. C. Dynes. Phys. Rev. Lett. bf77, 4652 (1996). P. Xiong, B. I. Zink, S. I. Applebaum, F. Hellman and R. C. Dynes. Phys. Rev. B bf59, 3929 (1999). [2] W. Teizer, F. Hellman and R. C. Dynes. To be published.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyers, D.; Liu, Jian; Freeland, J. W.

We observed complex materials in electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. We demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. Furthermore, these findings illustrate the utility of heterointerfaces as amore » powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.« less

Specific heat and magnetic susceptibility of CeNiSn doped with Rh.

PubMed

Slebarski, A; Maple, M B; Fijałkowski, M; Goraus, J

2010-04-28

CeNiSn is known as a semimetallic system with a small pseudogap at the Fermi energy. We investigate the effect of Rh doping on the Kondo insulator CeNiSn by means of measurements of ac magnetic susceptibility and specific heat. We show that the formation of the Kondo insulator narrow gap in CeNi(1 - x)Rh(x)Sn is associated with disorder-induced f-electron localization. For doped CeNiSn with x ≤ 0.06, the electrical resistivity data follow an activation and variable range hopping behaviour at low T, consistent with weak disorder and localization, while C/T is large, which is not a common feature of Kondo insulators. For x > 0.06, the system is metallic and exhibits non-Fermi liquid behaviour with magnetic susceptibility χ ∼ T( - n) with n ∼ 0.4 and electrical resistivity ρ ∼ T.

Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

NASA Astrophysics Data System (ADS)

Cornelissen, L. J.; Peters, K. J. H.; Bauer, G. E. W.; Duine, R. A.; van Wees, B. J.

2016-07-01

We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position-dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation lengths. Proceeding from a linearized Boltzmann equation, we derive expressions for length scales and transport coefficients. For yttrium iron garnet (YIG) at room temperature we find that long-range transport is dominated by the magnon chemical potential. We compare the model's results with recent experiments on YIG with Pt contacts [L. J. Cornelissen et al., Nat. Phys. 11, 1022 (2015), 10.1038/nphys3465] and extract a magnon spin conductivity of σm=5 ×105 S/m. Our results for the spin Seebeck coefficient in YIG agree with published experiments. We conclude that the magnon chemical potential is an essential ingredient for energy and spin transport in magnetic insulators.

A novel no-insulation winding technique of high temperature-superconducting racetrack coil for rotating applications: A progress report in Korea university.

PubMed

Choi, Y H; Song, J B; Yang, D G; Kim, Y G; Hahn, S; Lee, H G

2016-10-01

This paper presents our recent progress on core technology development for a megawatt-class superconducting wind turbine generator supported by the international collaborative R&D program of the Korea Institute of Energy Technology Evaluation and Planning. To outperform the current high-temperature-superconducting (HTS) magnet technology in the wind turbine industry, a novel no-insulation winding technique was first proposed to develop the second-generation HTS racetrack coil for rotating applications. Here, we briefly report our recent studies on no-insulation (NI) winding technique for GdBCO coated conductor racetrack coils in the following areas: (1) Charging-discharging characteristics of no-insulation GdBCO racetrack coils with respect to external pressures applied to straight sections; (2) thermal and electrical stabilities of no-insulation GdBCO racetrack coils encapsulated with various impregnating materials; (3) quench behaviors of no-insulation racetrack coils wound with GdBCO conductor possessing various lamination layers; (4) electromagnetic characteristics of no-insulation GdBCO racetrack coils under time-varying field conditions. Test results confirmed that this novel NI winding technique was highly promising. It could provide development of a compact, mechanically dense, and self-protecting GdBCO magnet for use in real-world superconducting wind turbine generators.

A novel no-insulation winding technique of high temperature-superconducting racetrack coil for rotating applications: A progress report in Korea university

NASA Astrophysics Data System (ADS)

Choi, Y. H.; Song, J. B.; Yang, D. G.; Kim, Y. G.; Hahn, S.; Lee, H. G.

2016-10-01

This paper presents our recent progress on core technology development for a megawatt-class superconducting wind turbine generator supported by the international collaborative R&D program of the Korea Institute of Energy Technology Evaluation and Planning. To outperform the current high-temperature-superconducting (HTS) magnet technology in the wind turbine industry, a novel no-insulation winding technique was first proposed to develop the second-generation HTS racetrack coil for rotating applications. Here, we briefly report our recent studies on no-insulation (NI) winding technique for GdBCO coated conductor racetrack coils in the following areas: (1) Charging-discharging characteristics of no-insulation GdBCO racetrack coils with respect to external pressures applied to straight sections; (2) thermal and electrical stabilities of no-insulation GdBCO racetrack coils encapsulated with various impregnating materials; (3) quench behaviors of no-insulation racetrack coils wound with GdBCO conductor possessing various lamination layers; (4) electromagnetic characteristics of no-insulation GdBCO racetrack coils under time-varying field conditions. Test results confirmed that this novel NI winding technique was highly promising. It could provide development of a compact, mechanically dense, and self-protecting GdBCO magnet for use in real-world superconducting wind turbine generators.

Observation of chiral currents at the magnetic domain boundary of a topological insulator

DOE PAGES

Wang, Y. H.; Kirtley, J. R.; Katmis, F.; ...

2015-08-28

A magnetic domain boundary on the surface of a three-dimensional topological insulator is predicted to host a chiral edge state, but direct demonstration is challenging. Here, we used a scanning superconducting quantum interference device to show that current in a magnetized EuS/Bi 2Se 3 heterostructure flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micron-scale magnetic structures on the heterostructure, and detected a chiral edge current at the magnetic domain boundary. The chirality of the current was determined by magnetization of the surrounding domain and its magnitude by the local chemicalmore » potential rather than the applied current. As a result, such magnetic structures, provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics.« less

The DC and AC insulating properties of magnetic fluids based on transformer oil

NASA Astrophysics Data System (ADS)

Tomo, L.; Marton, K.; Herchl, F.; Kopanský, P.; Potoová, I.; Koneracká, M.; Timko, M.

2006-01-01

The AC-dielectric breakdown was investigated in magnetic fluids based on transformer oil TECHNOL US 4000 for two orientations of external magnetic field (B E and B E) and in B = 0. The found results were compared with those obtained formerly for the DC-dielectric breakdown. The observations of the time development of the AC-dielectric breakdown showed the presence of partial discharges long before the complete breakdown occurrence, while for DC-dielectric breakdown a complete breakdown of the gap next to the onset of a measurable ionization was characteristic. The comparison of the AC-dielectric breakdown strengths of pure transformer oil and transformer-oil-based magnetic fluid showed better dielectric properties of magnetic fluid in external magnetic field and comparable, but not worse, in B = 0. Regarding to the better heat transfer, provided by magnetic fluids, they could be used in power transformers as insulating fluids.

Annealing effects on magnetic properties of silicone-coated iron-based soft magnetic composites

NASA Astrophysics Data System (ADS)

Wu, Shen; Sun, Aizhi; Zhai, Fuqiang; Wang, Jin; Zhang, Qian; Xu, Wenhuan; Logan, Philip; Volinsky, Alex A.

2012-03-01

This paper focuses on novel iron-based soft magnetic composites synthesis utilizing high thermal stability silicone resin to coat iron powder. The effect of an annealing treatment on the magnetic properties of synthesized magnets was investigated. The coated silicone insulating layer was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Silicone uniformly coated the powder surface, resulting in a reduction of the imaginary part of the permeability, thereby increasing the electrical resistivity and the operating frequency of the synthesized magnets. The annealing treatment increased the initial permeability, the maximum permeability, and the magnetic induction, and decreased the coercivity. Annealing at 580 °C increased the maximum permeability by 72.5%. The result of annealing at 580 °C shows that the ferromagnetic resonance frequency increased from 2 kHz for conventional epoxy resin coated samples to 80 kHz for the silicone resin insulated composites.

Reliability of large superconducting magnets through design

NASA Astrophysics Data System (ADS)

Henning, C. D.

1981-01-01

Design and quality control of large superconducting magnets for reliability comparable to pressure vessels are discussed. The failure modes are analyzed including thermoelectric instabilities, electrical shorts, cryogenic/vacuum defects, and mechanical malfunctions. Design must take into consideration conductor stability, insulation based on the Paschen curves, and the possible burnout of cryogenic transition leads if the He flow is interrupted. The final stage of the metal drawing process should stress the superconductor material to a stress value higher than the magnet design stress, cabled conductors should be used to achieve mechanical redundancy, and ground-plane insulation must be multilayered for arc prevention.

Superconductivity in an organic insulator at very high magnetic fields.

PubMed

Balicas, L; Brooks, J S; Storr, K; Uji, S; Tokumoto, M; Tanaka, H; Kobayashi, H; Kobayashi, A; Barzykin, V; Gor'kov, L P

2001-08-06

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor lambda-(BETS)2FeCl4. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe3+ ions. We further argue that the Fe3+ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state.

Highly insulating ferromagnetic cobaltite heterostructures

DOE PAGES

Choi, Woo Seok; Kang, Kyeong Tae; Jeen, Hyoungjeen; ...

2017-04-02

Ferromagnetic insulators are rather rare but possess great technological potential in, for example, spintronics. Individual control of ferromagnetic properties and electronic transport provides a useful design concept of multifunctional oxide heterostructures. We studied the close correlation among the magnetism, atomic structure, and electronic structure of oxide heterostructures composed of the ferromagnetic perovskite LaCoO 3 and the antiferromagnetic brownmillerite SrCoO 2.5 epitaxial thin film layers. By reversing the stacking sequence of the two layers, we could individually modify the electric resistance and saturation magnetic moment. Lastly, the ferromagnetic insulating behavior in the heterostructures was understood in terms of the electronic reconstructionmore » at the oxide surface/interfaces and crystalline quality of the constituent layers.« less

Highly insulating ferromagnetic cobaltite heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Woo Seok; Kang, Kyeong Tae; Jeen, Hyoungjeen

Ferromagnetic insulators are rather rare but possess great technological potential in, for example, spintronics. Individual control of ferromagnetic properties and electronic transport provides a useful design concept of multifunctional oxide heterostructures. We studied the close correlation among the magnetism, atomic structure, and electronic structure of oxide heterostructures composed of the ferromagnetic perovskite LaCoO 3 and the antiferromagnetic brownmillerite SrCoO 2.5 epitaxial thin film layers. By reversing the stacking sequence of the two layers, we could individually modify the electric resistance and saturation magnetic moment. Lastly, the ferromagnetic insulating behavior in the heterostructures was understood in terms of the electronic reconstructionmore » at the oxide surface/interfaces and crystalline quality of the constituent layers.« less

Taking an electron-magnon duality shortcut from electron to magnon transport

NASA Astrophysics Data System (ADS)

Mook, Alexander; Göbel, Börge; Henk, Jürgen; Mertig, Ingrid

2018-04-01

The quasiparticles in insulating magnets are the charge-neutral magnons, whose magnetic moments couple to electromagnetic fields. For collinear easy-axis magnets, this coupling can be mapped elegantly onto the scenario of charged particles in electromagnetic fields. From this mapping we obtain equations of motion for magnon wave packets equal to those of electron wave packets in metals. Thus, well-established electronic transport phenomena can be carried over to magnons: this duality shortcut facilitates the discussion of magnon transport. We identify the magnon versions of normal and anomalous Hall, Nernst, Ettingshausen, and Righi-Leduc effects. They are discussed for selected types of easy-axis magnets: ferromagnets, antiferromagnets, and ferrimagnets. Besides a magnon Wiedemann-Franz law and the magnon counterpart of the negative magnetoresistance of electrons in Weyl semimetals, we predict that certain low-symmetry ferrimagnets exhibit a nonlinear version of the anomalous magnon Hall-effect family.

Magnetic properties of epitaxial β-Nb2N thin film on SiC substrate

NASA Astrophysics Data System (ADS)

Yang, Zihao; Myers, Roberto; Katzer, D. Scott; Nepal, Neeraj; Meyer, David J.

Previously superconductivity in Nb2N was studied in thin films synthesized by reactive magnetron sputtering or pulsed laser deposition. Recently, Nb2N was synthesized by molecular beam epitaxy (MBE). Here, we report on the magnetic properties of MBE grown Nb2N measured by SQUID magnetometry. The single hexagonal β phase Nb2N is grown on a semi-insulating Si-face 4H SiC (0001) substrate in nitrogen rich conditions at a substrate temperature of 850 °C. In-plane magnetization as a function of magnetic field measured at 5 K shows type-II superconductivity with critical fields Hc1 and Hc2 of 300 Oe and 10 kOe, respectively. In-plane field-cooled and zero-field-cooled a critical temperature (Tc) of 11.5 K, higher than in sputtered Nb2N films. This work was supported by Army Research Office and the Office of Naval Research.

Spin currents and magnon dynamics in insulating magnets

NASA Astrophysics Data System (ADS)

Nakata, Kouki; Simon, Pascal; Loss, Daniel

2017-03-01

Nambu-Goldstone theorem provides gapless modes to both relativistic and nonrelativistic systems. The Nambu-Goldstone bosons in insulating magnets are called magnons or spin-waves and play a key role in magnetization transport. We review here our past works on magnetization transport in insulating magnets and also add new insights, with a particular focus on magnon transport. We summarize in detail the magnon counterparts of electron transport, such as the Wiedemann-Franz law, the Onsager reciprocal relation between the Seebeck and Peltier coefficients, the Hall effects, the superconducting state, the Josephson effects, and the persistent quantized current in a ring to list a few. Focusing on the electromagnetism of moving magnons, i.e. magnetic dipoles, we theoretically propose a way to directly measure magnon currents. As a consequence of the Mermin-Wagner-Hohenberg theorem, spin transport is drastically altered in one-dimensional antiferromagnetic (AF) spin-1/2 chains; where the Néel order is destroyed by quantum fluctuations and a quasiparticle magnon-like picture breaks down. Instead, the low-energy collective excitations of the AF spin chain are described by a Tomonaga-Luttinger liquid (TLL) which provides the spin transport properties in such antiferromagnets some universal features at low enough temperature. Finally, we enumerate open issues and provide a platform to discuss the future directions of magnonics.

Advanced Plasma Propulsion

DTIC Science & Technology

2011-11-01

within these cusps where electrons collide with the ceramic insulator lining the channel. In the MIT design, the overall magnetic field strength...allow compression of the anode spring (Sp), which holds the anode insulator (AI) flush with the base core (1). The anode stem and anode (A) are...case Aluminum bulk material 3 Insulator Cone HP-BN St. Gobain/ Ferro- Ceramic Grinding Inc. M1-M3 Permanent

Evolution of ferromagnetism in two-dimensional electron gas of LaTiO3/SrTiO3

NASA Astrophysics Data System (ADS)

Wen, Fangdi; Cao, Yanwei; Liu, Xiaoran; Pal, B.; Middey, S.; Kareev, M.; Chakhalian, J.

2018-03-01

Understanding, creating, and manipulating spin polarization of two-dimensional electron gases at complex oxide interfaces present an experimental challenge. For example, despite almost a decade long research effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3 heterojunctions is still an open question. Here, by using a prototypical two-dimensional electron gas (2DEG) which emerges at the interface between band insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3, the experiment reveals the evidence for magnetic phase separation in a hole-doped Ti d1 t2g system, resulting in spin-polarized 2DEG. The details of electronic and magnetic properties of the 2DEG were investigated by temperature-dependent d.c. transport, angle-dependent X-ray photoemission spectroscopy, and temperature-dependent magnetoresistance. The observation of clear hysteresis in magnetotransport at low magnetic fields implies spin-polarization from magnetic islands in the hole rich LaTiO3 near the interface. These findings emphasize the role of magnetic instabilities in doped Mott insulators, thus providing another path for designing all-oxide structures relevant to spintronic applications.

Strain-induced high-temperature perovskite ferromagnetic insulator.

PubMed

Meng, Dechao; Guo, Hongli; Cui, Zhangzhang; Ma, Chao; Zhao, Jin; Lu, Jiangbo; Xu, Hui; Wang, Zhicheng; Hu, Xiang; Fu, Zhengping; Peng, Ranran; Guo, Jinghua; Zhai, Xiaofang; Brown, Gail J; Knize, Randy; Lu, Yalin

2018-03-20

Ferromagnetic insulators are required for many new magnetic devices, such as dissipationless quantum-spintronic devices, magnetic tunneling junctions, etc. Ferromagnetic insulators with a high Curie temperature and a high-symmetry structure are critical integration with common single-crystalline oxide films or substrates. So far, the commonly used ferromagnetic insulators mostly possess low-symmetry structures associated with a poor growth quality and widespread properties. The few known high-symmetry materials either have extremely low Curie temperatures (≤16 K), or require chemical doping of an otherwise antiferromagnetic matrix. Here we present compelling evidence that the LaCoO 3 single-crystalline thin film under tensile strain is a rare undoped perovskite ferromagnetic insulator with a remarkably high T C of up to 90 K. Both experiments and first-principles calculations demonstrate tensile-strain-induced ferromagnetism which does not exist in bulk LaCoO 3 The ferromagnetism is strongest within a nearly stoichiometric structure, disappearing when the Co 2+ defect concentration reaches about 10%. Significant impact of the research includes demonstration of a strain-induced high-temperature ferromagnetic insulator, successful elevation of the transition over the liquid-nitrogen temperature, and high potential for integration into large-area device fabrication processes. Copyright © 2018 the Author(s). Published by PNAS.

Strain-induced high-temperature perovskite ferromagnetic insulator

PubMed Central

Meng, Dechao; Guo, Hongli; Cui, Zhangzhang; Ma, Chao; Zhao, Jin; Lu, Jiangbo; Xu, Hui; Wang, Zhicheng; Hu, Xiang; Fu, Zhengping; Peng, Ranran; Guo, Jinghua; Zhai, Xiaofang; Brown, Gail J.; Knize, Randy; Lu, Yalin

2018-01-01

Ferromagnetic insulators are required for many new magnetic devices, such as dissipationless quantum-spintronic devices, magnetic tunneling junctions, etc. Ferromagnetic insulators with a high Curie temperature and a high-symmetry structure are critical integration with common single-crystalline oxide films or substrates. So far, the commonly used ferromagnetic insulators mostly possess low-symmetry structures associated with a poor growth quality and widespread properties. The few known high-symmetry materials either have extremely low Curie temperatures (≤16 K), or require chemical doping of an otherwise antiferromagnetic matrix. Here we present compelling evidence that the LaCoO3 single-crystalline thin film under tensile strain is a rare undoped perovskite ferromagnetic insulator with a remarkably high TC of up to 90 K. Both experiments and first-principles calculations demonstrate tensile-strain–induced ferromagnetism which does not exist in bulk LaCoO3. The ferromagnetism is strongest within a nearly stoichiometric structure, disappearing when the Co2+ defect concentration reaches about 10%. Significant impact of the research includes demonstration of a strain-induced high-temperature ferromagnetic insulator, successful elevation of the transition over the liquid-nitrogen temperature, and high potential for integration into large-area device fabrication processes. PMID:29507211

Magnetization reversal mechanism of magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Liu, Cun-Ye; Li, Jian; Wang, Yue; Chen, Jian-Yong; Xu, Qing-Yu; Ni, Gang; Sang, Hai; Du, You-Wei

2002-01-01

Using the ion-beam-sputtering technique, we have fabricated Fe/Al2O3/Fe magnetic tunnelling junctions (MTJs). We have observed double-peaked shapes of curves, which have a level summit and a symmetrical feature, showing the magnetoresistance of the junction as a function of applied field. We have measured the tunnel conductance of MTJs which have insulating layers of different thicknesses. We have studied the dependence of the magnetoresistance of MTJs on tunnel conductance. The microstructures of hard- and soft-magnetic layers and interfaces of ferromagnets and insulators were probed. Analysing the influence of MJT microstructures, including those having clusters or/and granules in magnetic and non-magnetic films, a magnetization reversal mechanism (MRM) is proposed, which suggests that the MRM of tunnelling junctions may be explained by using a group-by-group reversal model of magnetic moments of the mesoscopical particles. We discuss the influence of MTJ microstructures, including those with clusters or/and granules in the ferromagnetic and non-magnetic films, on the MRM.

Influence of gamma ray irradiation on thermal conductivity of bismaleimide-triazine-based insulation tape at cryogenic temperature

NASA Astrophysics Data System (ADS)

Yang, Y.; Yoshida, M.; Idesaki, A.; Ogitsu, T.

2018-01-01

Recent accelerator-based experiments for particle physics require the superconducting magnets that can be operated under high radiation environment. An electrical insulation tape, which is composed of polyimide film and a boron free glass fabric pre-impregnated with epoxy resin blended with bismaleimide-triazine resin, is developed to enhance the radiation tolerance for superconducting magnets. Since the thermal conductivity of insulation tape is one of key parameters that affects the coil temperature during the operation, the influence of gamma-ray irradiation on the thermal conductivity of the insulation tape is investigated with a maximum dose of 5 MGy. The thermal conductivity is measured at cryogenic temperature from 5 K to 20 K cooled by a Gifford-McMahon cryocooler. By comparing the thermal conductivity before and after the gamma ray irradiation, no significant degradation on the thermal conductivity has been observed.

Electron gas at the interface between two antiferromagnetic insulating manganites

NASA Astrophysics Data System (ADS)

Calderón, M. J.; Salafranca, J.; Brey, L.

2008-07-01

We study theoretically the magnetic and electric properties of the interface between two antiferromagnetic and insulating manganites: La0.5Ca0.5MnO3 , a strong correlated insulator, and CaMnO3 , a band insulator. We find that a ferromagnetic and metallic electron gas is formed at the interface between the two layers. We confirm the metallic character of the interface by calculating the in-plane conductance. The possibility of increasing the electron-gas density by selective doping is also discussed.

Bitter-type toroidal field magnet for zephyr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nathrath, N.; Keinath, W.; Kobusch, W.

1981-09-01

A feasibility study concerning stress computations, design and material technology of a Bitter-type magnet for the ZEPHYR project conducted in West Germany is reported. The big overall dimensions of the magnet (6.50 m diam 2.80 m high), access for diagnostics and neutral injection (16 ports), the possibility of remote handling of activated parts and high forces form the main requirements for design and material. A design with 16 identical modules (coils) was chosen, each coil consisting of 16 Bitter plates, plate housings and one diagnostic/neutral injection wedge. The structural parts are connected by bolts and form the bending stiff structuremore » of the magnet. The most critical area of the magnet is the inner wedge-shaped part of the coils (''throat area'') with extremely high tension, compression and shear stress values, to which temperature effects contribute heavily. Steel-copper compounds are found to be the best Bitter-plate materials. Copper-plating austenitic steel can be done galvanically or by explosive techniques. Cold-worked austenitic steels fulfil the requirements in the throat, in the flat-plate region milder steels can be used. Different plate concepts are being considered. Plasma-sprayed Al/sub 2/O/sub 3//TiO/sub 2/ and reinforced epoxy layers are provided as insulating materials in different magnet areas.« less

Observation of the Quantum Anomalous Hall Insulator to Anderson Insulator Quantum Phase Transition and its Scaling Behavior.

PubMed

Chang, Cui-Zu; Zhao, Weiwei; Li, Jian; Jain, J K; Liu, Chaoxing; Moodera, Jagadeesh S; Chan, Moses H W

2016-09-16

Fundamental insight into the nature of the quantum phase transition from a superconductor to an insulator in two dimensions, or from one plateau to the next or to an insulator in the quantum Hall effect, has been revealed through the study of its scaling behavior. Here, we report on the experimental observation of a quantum phase transition from a quantum-anomalous-Hall insulator to an Anderson insulator in a magnetic topological insulator by tuning the chemical potential. Our experiment demonstrates the existence of scaling behavior from which we extract the critical exponent for this quantum phase transition. We expect that our work will motivate much further investigation of many properties of quantum phase transition in this new context.

Transport studies of mesoscopic and magnetic topological insulators

NASA Astrophysics Data System (ADS)

Kandala, Abhinav

Topological Insulators (TI) are a novel class of materials that are ideally insulating in the bulk, but have gapless, metallic states at the surface. These surface states have very exciting properties such as suppressed backscattering and spin-momentum locking, which are of great interest for research efforts towards dissipation-less electronics and spintronics. The popular thermo-electrics from the Bi chalcogenide family -- Bi2Se3 and Bi 2Te3 -- have been experimentally demonstrated to be promising candidate TI materials, and form the chosen material system for this dissertation research. The first part of this dissertation research focuses on low temperature magneto-transport measurements of mesoscopic topological insulator devices (Chapter 3). The top-down patterning of epitaxial thin films of Bi2Se 3 and Bi2Te3 (that are plagued with bulk conduction) is motivated, in part, by an effort to enhance the surface-to-volume ratio in mesoscopic channels. At cryogenic temperatures, transport measurements of these devices reveal periodic conductance fluctuations in straight channel devices, despite the lack of any explicit patterning of the TI film into a ring or a loop. A careful analysis of the surface morphology and comparison with the transport data then demonstrate that scattering off the edges of triangular plateaus at the surface leads to the creation of Aharonov-Bohm electronic orbits responsible for the periodicity. Another major focus of this dissertation work is on combining topological insulators with magnetism. This has been shown to open a gap in the surface states leading to possibilities of magnetic "gating" and the realization of dissipation-less transport at zero-field, amongst several other exotic quantum phenomena. In this dissertation, I present two different schemes for probing these effects in electrical transport devices -- interfacing with insulating ferromagnets (Chapter 4) and bulk magnetic doping (Chapter 5). In Chapter 4, I shall present the integration of GdN with Bi2Se 3 thin films. Careful structural, magnetic and electrical characterization of the heterostructures is employed to confirm that the magnetic species is solely restricted to the surface, and that the ferromagnetic GdN layer to be insulating, ensuring current flow solely through the TI layer. We also devise a novel device geometry that enables direct comparison of the magneto-transport properties of TI films with and without proximate magnetism, all, in a single device. A comparative study of weak anti-localization suggested that the overlying GdN suppressed quantum interference in the top surface state. In our second generation heterostructure devices, GdN is interfaced with low-carrier density, gate-tunable thin films of (Bi,Sb)2Te3 grown on SrTiO 3 substrates. These devices enable us to map out the comparison of magneto-transport, as the chemical potential is tuned from the bulk conduction band into the bulk valence band. In a second approach to study the effects of magnetism on TI's, I shall present, in Chapter 5, our results from magnetic doping of (Bi,Sb) 2Te3 thin films with Cr -- a system that was recently demonstrated to be a Quantum Anomalous Hall (QAH) insulator. In a Cr-rich regime, a highly insulating, high Curie temperature ferromagnetic phase is achieved. However, a careful, iterative process of tuning the composition of this complex alloy enabled access to the QAHE regime, with the observation of near dissipation-less transport and perfect Hall quantization at zero external field. Furthermore, we demonstrate a field tilt driven crossover between a quantum anomalous Hall phase and a gapless, ferromagnetic TI phase. This crossover manifests itself in an electrically tunable, giant anisotropic magneto-resistance effect that we employ as a quantitative probe of edge transport in this system.

Helicon wave excitation to produce energetic electrons for manufacturing semiconductors

DOEpatents

Molvik, Arthur W.; Ellingboe, Albert R.

1998-01-01

A helicon plasma source is controlled by varying the axial magnetic field or rf power controlling the formation of the helicon wave. An energetic electron current is carried on the wave when the magnetic field is 90 G; but there is minimal energetic electron current when the magnetic field is 100 G in one particular plasma source. Similar performance can be expected from other helicon sources by properly adjusting the magnetic field and power to the particular geometry. This control for adjusting the production of energetic electrons can be used in the semiconductor and thin-film manufacture process. By applying energetic electrons to the insulator layer, such as silicon oxide, etching ions are attracted to the insulator layer and bombard the insulator layer at higher energy than areas that have not accumulated the energetic electrons. Thus, silicon and metal layers, which can neutralize the energetic electron currents will etch at a slower or non-existent rate. This procedure is especially advantageous in the multilayer semiconductor manufacturing because trenches can be formed that are in the range of 0.18-0.35 mm or less.

Helicon wave excitation to produce energetic electrons for manufacturing semiconductors

DOEpatents

Molvik, A.W.; Ellingboe, A.R.

1998-10-20

A helicon plasma source is controlled by varying the axial magnetic field or rf power controlling the formation of the helicon wave. An energetic electron current is carried on the wave when the magnetic field is 90 G; but there is minimal energetic electron current when the magnetic field is 100 G in one particular plasma source. Similar performance can be expected from other helicon sources by properly adjusting the magnetic field and power to the particular geometry. This control for adjusting the production of energetic electrons can be used in the semiconductor and thin-film manufacture process. By applying energetic electrons to the insulator layer, such as silicon oxide, etching ions are attracted to the insulator layer and bombard the insulator layer at higher energy than areas that have not accumulated the energetic electrons. Thus, silicon and metal layers, which can neutralize the energetic electron currents will etch at a slower or non-existent rate. This procedure is especially advantageous in the multilayer semiconductor manufacturing because trenches can be formed that are in the range of 0.18--0.35 mm or less. 16 figs.

Local optical control of ferromagnetism and chemical potential in a topological insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeats, Andrew L.; Mintun, Peter J.; Pan, Yu

Many proposed experiments involving topological insulators (TIs) require spatial control over time-reversal symmetry and chemical potential. We demonstrate reconfigurable micron-scale optical control of both magnetization (which breaks time-reversal symmetry) and chemical potential in ferromagnetic thin films of Cr-(Bi,Sb) 2Te 3 grown on SrTiO 3. By optically modulating the coercivity of the films, we write and erase arbitrary patterns in their remanent magnetization, which we then image with Kerr microscopy. Additionally, by optically manipulating a space charge layer in the underlying SrTiO 3 substrates, we control the local chemical potential of the films. This optical gating effect allows us to writemore » and erase p-n junctions in the films, which we study with photocurrent microscopy. Both effects are persistent and may be patterned and imaged independently on a few-micron scale. As a result, dynamic optical control over both magnetization and chemical potential of a TI may be useful in efforts to understand and control the edge states predicted at magnetic domain walls in quantum anomalous Hall insulators.« less

Electronic structure, magnetic properties, and mechanism of the insulator-metal transition in LaCoO3 taking into account strong electron correlations

NASA Astrophysics Data System (ADS)

Ovchinnikov, S. G.; Orlov, Yu. S.; Nekrasov, I. A.; Pchelkina, Z. V.

2011-01-01

The electronic structure of LaCoO3 at finite temperatures is calculated using the LDA+GTB method taking into account strong electron correlations and possible spin crossover upon an increase in temperature. Gap states revealed in the energy spectrum of LaCoO3 reduce the dielectric gap width upon heating; this allowed us to describe the insulator-metal transition observed in this compound at T = 500-600 K. The temperature dependence of the magnetic susceptibility with a peak at T ≈ 100 K is explained by the Curie contribution from thermally excited energy levels of the Co3+ ion. At high temperatures, the Pauli contribution from a band electron is added and the total magnetization of LaCoO3 is considered as the sum M tot = M loc + M band. The second term describes the band contribution appearing as a result of the insulator-metal transition and facilitating the emergence of a high-temperature anomaly in the magnetic susceptibility of LaCoO3.

Local optical control of ferromagnetism and chemical potential in a topological insulator

DOE PAGES

Yeats, Andrew L.; Mintun, Peter J.; Pan, Yu; ...

2017-09-12

Many proposed experiments involving topological insulators (TIs) require spatial control over time-reversal symmetry and chemical potential. We demonstrate reconfigurable micron-scale optical control of both magnetization (which breaks time-reversal symmetry) and chemical potential in ferromagnetic thin films of Cr-(Bi,Sb) 2Te 3 grown on SrTiO 3. By optically modulating the coercivity of the films, we write and erase arbitrary patterns in their remanent magnetization, which we then image with Kerr microscopy. Additionally, by optically manipulating a space charge layer in the underlying SrTiO 3 substrates, we control the local chemical potential of the films. This optical gating effect allows us to writemore » and erase p-n junctions in the films, which we study with photocurrent microscopy. Both effects are persistent and may be patterned and imaged independently on a few-micron scale. As a result, dynamic optical control over both magnetization and chemical potential of a TI may be useful in efforts to understand and control the edge states predicted at magnetic domain walls in quantum anomalous Hall insulators.« less

Dynamic trajectory analysis of superparamagnetic beads driven by on-chip micromagnets

PubMed Central

Abedini-Nassab, Roozbeh; Lim, Byeonghwa; Yang, Ye; Howdyshell, Marci; Sooryakumar, Ratnasingham; Yellen, Benjamin B.

2015-01-01

We investigate the non-linear dynamics of superparamagnetic beads moving around the periphery of patterned magnetic disks in the presence of an in-plane rotating magnetic field. Three different dynamical regimes are observed in experiments, including (1) phase-locked motion at low driving frequencies, (2) phase-slipping motion above the first critical frequency fc1, and (3) phase-insulated motion above the second critical frequency fc2. Experiments with Janus particles were used to confirm that the beads move by sliding rather than rolling. The rest of the experiments were conducted on spherical, isotropic magnetic beads, in which automated particle position tracking algorithms were used to analyze the bead dynamics. Experimental results in the phase-locked and phase-slipping regimes correlate well with numerical simulations. Additional assumptions are required to predict the onset of the phase-insulated regime, in which the beads are trapped in closed orbits; however, the origin of the phase-insulated state appears to result from local magnetization defects. These results indicate that these three dynamical states are universal properties of bead motion in non-uniform oscillators. PMID:26648596

Magnetic Compression Experiment at General Fusion with Simulation Results

NASA Astrophysics Data System (ADS)

Dunlea, Carl; Khalzov, Ivan; Hirose, Akira; Xiao, Chijin; Fusion Team, General

2017-10-01

The magnetic compression experiment at GF was a repetitive non-destructive test to study plasma physics applicable to Magnetic Target Fusion compression. A spheromak compact torus (CT) is formed with a co-axial gun into a containment region with an hour-glass shaped inner flux conserver, and an insulating outer wall. External coil currents keep the CT off the outer wall (levitation) and then rapidly compress it inwards. The optimal external coil configuration greatly improved both the levitated CT lifetime and the rate of shots with good compressional flux conservation. As confirmed by spectrometer data, the improved levitation field profile reduced plasma impurity levels by suppressing the interaction between plasma and the insulating outer wall during the formation process. We developed an energy and toroidal flux conserving finite element axisymmetric MHD code to study CT formation and compression. The Braginskii MHD equations with anisotropic heat conduction were implemented. To simulate plasma / insulating wall interaction, we couple the vacuum field solution in the insulating region to the full MHD solution in the remainder of the domain. We see good agreement between simulation and experiment results. Partly funded by NSERC and MITACS Accelerate.

Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB 6

DOE PAGES

Hartstein, M.; Toews, W. H.; Hsu, Y. -T.; ...

2017-10-23

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator–metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. In this paper, we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB 6 positioned close to the insulator–metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including amore » sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Finally, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB 6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.« less

Small Layer-wound ReBCO Solenoids

NASA Astrophysics Data System (ADS)

Polyakov, A. V.; Shcherbakov, V. I.; Shevchenko, S. A.; Surin, M. I.

The development of the next generation of high field superconducting magnet systems demands studies of new technological approach for its internal sections. Several small HTS solenoids (21 mm inner diameter, 32 layers) were fabricated by layer-winding technique from SuperPower type SCS-4050 ReBCO wire insulated by polyimide wrapping. Different designs of external and internal joints also were also tested. The highest field generated by HTS coil was 2.4 T in a 10 T background field (total field was 12.4 T) at 4.2 K and achieved current density in the coil was 498 A/mm2. The results will be used in development of HTS inner sections for 25 T superconducting magnet.

2D massless Dirac Fermi gas model of superconductivity in the surface state of a topological insulator at high magnetic fields

NASA Astrophysics Data System (ADS)

Zhuravlev, Vladimir; Duan, Wenye; Maniv, Tsofar

2017-10-01

The Nambu-Gorkov Green's function approach is applied to strongly type-II superconductivity in a 2D spin-momentum-locked (Weyl) Fermi gas model at high perpendicular magnetic fields. The resulting phase diagram can be mapped onto that derived for the standard, parabolic band-structure model, having the same Fermi surface parameters, E F and v, but with cyclotron effective mass m\\ast=EF/2v2 . Significant deviations from the predicted mapping are found only for very small E F , when the Landau-Level filling factors are smaller than unity, and E F shrinks below the cutoff energy.

Orientation-adjusted anomalous insulator-metal transition in NdNiO3/LaMnO3 bilayers

NASA Astrophysics Data System (ADS)

Pan, S. Y.; Shi, L.; Zhao, J. Y.; Zhou, S. M.; Xu, X. M.

2018-04-01

NdNiO3/LaMnO3 (NNO/LMO) bilayers were epitaxially grown on SrTiO3 (STO) substrates with different orientations by the polymer-assisted deposition technique. A well crystallization quality of the bilayers is confirmed by X-ray diffraction. Two consecutive transitions, an anomalous insulator-metal transition at ˜100 K followed by the typical metal-insulator transition at ˜171 K, are observed in the (001)-oriented NNO/LMO/STO bilayer. The anomalous insulator-metal transition temperature increases to 142 K for the (111)-oriented NNO/LMO/STO bilayer. Meanwhile, the magnetic properties of the NNO/LMO bilayers show an obvious difference with [100] and [111] orientations. Considering the different strain directions and the related oxygen octahedral distortion/rotation, it is suggested that the magnetic changes and the low-temperature anomalous insulator-metal transition in the NNO/LMO bilayers are attributed to the strong interlayer exchange coupling and charge transfer adjusted by the substrate orientation, which can be an effective technique to tune the properties of transition-metal oxide films.

Current-Nonlinear Hall Effect and Spin-Orbit Torque Magnetization Switching in a Magnetic Topological Insulator

NASA Astrophysics Data System (ADS)

Yasuda, K.; Tsukazaki, A.; Yoshimi, R.; Kondou, K.; Takahashi, K. S.; Otani, Y.; Kawasaki, M.; Tokura, Y.

2017-09-01

The current-nonlinear Hall effect or second harmonic Hall voltage is widely used as one of the methods for estimating charge-spin conversion efficiency, which is attributed to the magnetization oscillation by spin-orbit torque (SOT). Here, we argue the second harmonic Hall voltage under a large in-plane magnetic field with an in-plane magnetization configuration in magnetic-nonmagnetic topological insulator (TI) heterostructures, Crx (Bi1 -ySby )2 -xTe3 /(Bi1 -ySby )2Te3 , where it is clearly shown that the large second harmonic voltage is governed not by SOT but mainly by asymmetric magnon scattering without macroscopic magnetization oscillation. Thus, this method does not allow an accurate estimation of charge-spin conversion efficiency in TI. Instead, the SOT contribution is exemplified by current pulse induced nonvolatile magnetization switching, which is realized with a current density of 2.5 ×1010 A m-2 , showing its potential as a spintronic material.

Fragile magnetic order in the honeycomb lattice Iridate Na2IrO3 revealed by magnetic impurity doping

NASA Astrophysics Data System (ADS)

Mehlawat, Kavita; Sharma, G.; Singh, Yogesh

2015-10-01

We report the structure, magnetic, and thermal property measurements on single-crystalline and polycrystalline samples of the Ru-substituted honeycomb lattice iridate Na2Ir1 -xRuxO3 (x =0 ,0.05 ,0.1 ,0.15 ,0.2 ,0.3 ,0.5 ) . The evolution of magnetism in Na2Ir1 -xRuxO3 has been studied using dc and ac magnetic susceptibilities and heat-capacity measurements. The parent compound Na2IrO3 is a spin-orbit-driven Mott insulator with magnetic order of reduced moments below TN=15 K . In the Ru-substituted samples the antiferromagnetic long-range state is replaced by a spin-glass-like state even for the smallest substitution suggesting that the magnetic order in Na2IrO3 is extremely fragile. We argue that these behaviors indicate the importance of nearest-neighbor magnetic exchange in the parent Na2IrO3 . Additionally, all samples show insulating electrical transport.

Current-Nonlinear Hall Effect and Spin-Orbit Torque Magnetization Switching in a Magnetic Topological Insulator.

PubMed

Yasuda, K; Tsukazaki, A; Yoshimi, R; Kondou, K; Takahashi, K S; Otani, Y; Kawasaki, M; Tokura, Y

2017-09-29

The current-nonlinear Hall effect or second harmonic Hall voltage is widely used as one of the methods for estimating charge-spin conversion efficiency, which is attributed to the magnetization oscillation by spin-orbit torque (SOT). Here, we argue the second harmonic Hall voltage under a large in-plane magnetic field with an in-plane magnetization configuration in magnetic-nonmagnetic topological insulator (TI) heterostructures, Cr_{x}(Bi_{1-y}Sb_{y})_{2-x}Te_{3}/(Bi_{1-y}Sb_{y})_{2}Te_{3}, where it is clearly shown that the large second harmonic voltage is governed not by SOT but mainly by asymmetric magnon scattering without macroscopic magnetization oscillation. Thus, this method does not allow an accurate estimation of charge-spin conversion efficiency in TI. Instead, the SOT contribution is exemplified by current pulse induced nonvolatile magnetization switching, which is realized with a current density of 2.5×10^{10}  A m^{-2}, showing its potential as a spintronic material.

Current-induced switching in a magnetic insulator

NASA Astrophysics Data System (ADS)

Avci, Can Onur; Quindeau, Andy; Pai, Chi-Feng; Mann, Maxwell; Caretta, Lucas; Tang, Astera S.; Onbasli, Mehmet C.; Ross, Caroline A.; Beach, Geoffrey S. D.

2017-03-01

The spin Hall effect in heavy metals converts charge current into pure spin current, which can be injected into an adjacent ferromagnet to exert a torque. This spin-orbit torque (SOT) has been widely used to manipulate the magnetization in metallic ferromagnets. In the case of magnetic insulators (MIs), although charge currents cannot flow, spin currents can propagate, but current-induced control of the magnetization in a MI has so far remained elusive. Here we demonstrate spin-current-induced switching of a perpendicularly magnetized thulium iron garnet film driven by charge current in a Pt overlayer. We estimate a relatively large spin-mixing conductance and damping-like SOT through spin Hall magnetoresistance and harmonic Hall measurements, respectively, indicating considerable spin transparency at the Pt/MI interface. We show that spin currents injected across this interface lead to deterministic magnetization reversal at low current densities, paving the road towards ultralow-dissipation spintronic devices based on MIs.

Surface Spin Glass Ordering and Exchange Bias in Nanometric Sm0.09Ca0.91MnO3 Manganites

NASA Astrophysics Data System (ADS)

Giri, S. K.; Nath, T. K.

2011-07-01

We have thoroughly investigated the entire magnetic state of under doped ferromagnetic insulating manganite Sm0.09Ca0.91MnO3 through temperature dependent linear and non-linear ac magnetic susceptibility and magnetization measurements. This ferromagnetic insulating manganite is found to have frequency dependent ferromagnetic to paramagnetic transition temperature at around 108 K. Exchange- bias effect are observed in field -cooled magnetic hysteresis loops for this nanoparticle. We have attributed our observation to the formation of ferromagnetic cluster which are formed as a consequence of intrinsic phase separation below certain temperature in this under doped manganites. We have carried out electronic- and magneto-transport measurements to support these observed results.

Inhomogeneous field induced magnetoelectric effect in Mott insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boulaevskii, Lev N; Batista, Cristian D

2008-01-01

We consider a Mott insulator like HoMnO{sub 3} whose magnetic lattice is geometrically frustrated and comprises a 3D array of triangular layers with magnetic moments ordered in a 120{sup o} structure. We show that the effect of a uniform magnetic field gradient, {gradient}H, is to redistribute the electronic charge of the magnetically ordered phase leading to a unfirom electric field gradient. The resulting voltage difference between the crystal edges is proportional to the square of the crystal thickness, or inter-edge distance, L. It can reach values of several volts for |{gradient}H| {approx} 0.01 T/cm and L {approx_equal} 1mm, as longmore » as the crystal is free of antiferromagnetic domain walls.« less

Unconventional Josephson effect in hybrid superconductor-topological insulator devices.

PubMed

Williams, J R; Bestwick, A J; Gallagher, P; Hong, Seung Sae; Cui, Y; Bleich, Andrew S; Analytis, J G; Fisher, I R; Goldhaber-Gordon, D

2012-08-03

We report on transport properties of Josephson junctions in hybrid superconducting-topological insulator devices, which show two striking departures from the common Josephson junction behavior: a characteristic energy that scales inversely with the width of the junction, and a low characteristic magnetic field for suppressing supercurrent. To explain these effects, we propose a phenomenological model which expands on the existing theory for topological insulator Josephson junctions.

Magnetic polarons in antiferromagnetic CaMnO3-x (x<0.01) probed by O17 NMR

NASA Astrophysics Data System (ADS)

Trokiner, A.; Verkhovskii, S.; Yakubovskii, A.; Gerashenko, A.; Monod, P.; Kumagai, K.; Mikhalev, K.; Buzlukov, A.; Litvinova, Z.; Gorbenko, O.; Kaul, A.; Kartavtzeva, M.

2009-06-01

We study with O17 NMR and bulk magnetization a lightly electron doped CaMnO3-x (x<0.01) polycrystalline sample in the G -type antiferromagnetic state. The O17 NMR spectra show two lines with very different intensities corresponding to oxygen sites with very different local magnetic environments. The more intense unshifted line is due to the antiferromagnetic (AF) matrix. The thermal dependence of the magnetic moment of the AF sublattice deduced from the O17 linewidth is typical of insulating three-dimensional Heisenberg antiferromagnets. The less intense, strongly shifted line directly evidences the existence of ferromagnetic (FM) domains embedded in the AF spin lattice. The extremely narrow line in zero magnetic field indicates a nearly perfect alignment of the manganese spins in the FM domains which also display an unusually weak temperature dependence of their magnetic moment. We show that these FM entities start to move above 40 K in a slow-diffusion regime. These static and dynamic properties bear a strong similarity with those of a small size self-trapped magnetic polaron.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Thi Minh Hien; Sandilands, Luke J.; Sohn, C. H.

5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd 2Os 2O 7. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii–Moriya and exchange interactions play a significant role in the spin-wavemore » dispersions. The Raman data also reveal complex spin–charge–lattice coupling and indicate that the metal–insulator transition in Cd 2Os 2O 7 is Lifshitz-type. In conclusion, our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.« less

Room-Temperature Spin-Orbit Torque Switching Induced by a Topological Insulator

NASA Astrophysics Data System (ADS)

Han, Jiahao; Richardella, A.; Siddiqui, Saima A.; Finley, Joseph; Samarth, N.; Liu, Luqiao

2017-08-01

The strongly spin-momentum coupled electronic states in topological insulators (TI) have been extensively pursued to realize efficient magnetic switching. However, previous studies show a large discrepancy of the charge-spin conversion efficiency. Moreover, current-induced magnetic switching with TI can only be observed at cryogenic temperatures. We report spin-orbit torque switching in a TI-ferrimagnet heterostructure with perpendicular magnetic anisotropy at room temperature. The obtained effective spin Hall angle of TI is substantially larger than the previously studied heavy metals. Our results demonstrate robust charge-spin conversion in TI and provide a direct avenue towards applicable TI-based spintronic devices.

Surface charge conductivity of a topological insulator in a magnetic field: The effect of hexagonal warping

NASA Astrophysics Data System (ADS)

Akzyanov, R. S.; Rakhmanov, A. L.

2018-02-01

We investigate the influence of hexagonal warping on the transport properties of topological insulators. We study the charge conductivity within Kubo formalism in the first Born approximation using low-energy expansion of the Hamiltonian near the Dirac point. The effects of disorder, magnetic field, and chemical-potential value are analyzed in detail. We find that the presence of hexagonal warping significantly affects the conductivity of the topological insulator. In particular, it gives rise to the growth of the longitudinal conductivity with the increase of the disorder and anisotropic anomalous in-plane magnetoresistance. Hexagonal warping also affects the quantum anomalous Hall effect and anomalous out-of-plane magnetoresistance. The obtained results are consistent with the experimental data.

Weak localization effect in topological insulator micro flakes grown on insulating ferrimagnet BaFe12O19

PubMed Central

Zheng, Guolin; Wang, Ning; Yang, Jiyong; Wang, Weike; Du, Haifeng; Ning, Wei; Yang, Zhaorong; Lu, Hai-Zhou; Zhang, Yuheng; Tian, Mingliang

2016-01-01

Many exotic physics anticipated in topological insulators require a gap to be opened for their topological surface states by breaking time reversal symmetry. The gap opening has been achieved by doping magnetic impurities, which however inevitably create extra carriers and disorder that undermine the electronic transport. In contrast, the proximity to a ferromagnetic/ferrimagnetic insulator may improve the device quality, thus promises a better way to open the gap while minimizing the side-effects. Here, we grow thin single-crystal Sb1.9Bi0.1Te3 micro flakes on insulating ferrimagnet BaFe12O19 by using the van der Waals epitaxy technique. The micro flakes show a negative magnetoresistance in weak perpendicular fields below 50 K, which can be quenched by increasing temperature. The signature implies the weak localization effect as its origin, which is absent in intrinsic topological insulators, unless a surface state gap is opened. The surface state gap is estimated to be 10 meV by using the theory of the gap-induced weak localization effect. These results indicate that the magnetic proximity effect may open the gap for the topological surface attached to BaM insulating ferrimagnet. This heterostructure may pave the way for the realization of new physical effects as well as the potential applications of spintronics devices. PMID:26891682

Utilization of low temperatures in electrical machines

NASA Astrophysics Data System (ADS)

Kwasniewska-Jankowicz, L.; Mirski, Z.

1983-09-01

The dimensions of conventional and superconducting direct and alternating current generators are compared and the advantages of using superconducting magnets are examined. The critical temperature, critical current, and critical magnetic field intensity of superconductors in an induction winding are discussed as well as the mechanical properties needed for bending connectors at small radii. Investigations of cryogenic cooling, cryostats, thermal insulation and rotary seals are reported as well as results of studies of the mechanical properties of austenitic Cr-Ni steels, welded joints and plastics for insulation.

Cryogenic Properties of Inorganic Insulation Materials for ITER Magnets: A Review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simon, N.J.

1994-12-01

Results of a literature search on the cryogenic properties of candidate inorganic insulators for the ITER TF magnets are reported. The materials investigated include: Al{sub 2}O{sub 3}, AlN, MgO, porcelain, SiO{sub 2}, MgAl{sub 2}O{sub 4}, ZrO{sub 2}, and mica. A graphical presentation is given of mechanical, elastic, electrical, and thermal properties between 4 and 300 K. A companion report reviews the low temperature irradiation resistance of these materials.

Electrical transport of spin-polarized carriers in disordered ultrathin films.

PubMed

Hernandez, L M; Bhattacharya, A; Parendo, Kevin A; Goldman, A M

2003-09-19

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of a collective state that forms when the carriers are spin polarized at low temperatures and in high magnetic fields.

Influence of magnetic disorders on quantum anomalous Hall effect in magnetic topological insulator films beyond the two-dimensional limit

NASA Astrophysics Data System (ADS)

Xing, Yanxia; Xu, Fuming; Cheung, King Tai; Sun, Qing-feng; Wang, Jian; Yao, Yugui

2018-04-01

Quantum anomalous Hall effect (QAHE) has been experimentally realized in magnetic topological insulator (MTI) thin films fabricated on magnetically doped {({{Bi}},{{Sb}})}2{{{Te}}}3. In an MTI thin film with the magnetic easy axis along the normal direction (z-direction), orientations of magnetic dopants are randomly distributed around the magnetic easy axis, acting as magnetic disorders. With the aid of the non-equilibrium Green's function and Landauer–Büttiker formalism, we numerically study the influence of magnetic disorders on QAHE in an MTI thin film modeled by a three-dimensional tight-binding Hamiltonian. It is found that, due to the existence of gapless side surface states, QAHE is protected even in the presence of magnetic disorders as long as the z-component of magnetic moment of all magnetic dopants are positive. More importantly, such magnetic disorders also suppress the dissipation of the chiral edge states and enhance the quality of QAHE in MTI films. In addition, the effect of magnetic disorders depends very much on the film thickness, and the optimal influence is achieved at certain thickness. These findings are new features for QAHE in three-dimensional systems, not present in two-dimensional systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henning, C.

This report contains papers on the following topics: conceptual design; radiation damage of ITER magnet systems; insulation system of the magnets; critical current density and strain sensitivity; toroidal field coil structural analysis; stress analysis for the ITER central solenoid; and volt-second capabilities and PF magnet configurations.

Processing and characterization of superconducting solenoids made of Bi-2212/Ag-alloy multifilament round wire for high field magnet applications

NASA Astrophysics Data System (ADS)

Chen, Peng

As the only high temperature superconductor with round wire (RW) geometry, Bi2Sr2CaCu2O8+x (Bi-2212) superconducting wire has the advantages of being multi-filamentary, macroscopically isotropic and twistable. With overpressure (OP) processing techniques recently developed by our group at the National High Magnetic Field Laboratory (NHMFL), the engineering current density (Je) of Bi-2212 RW can be dramatically increased. For example, Je of more than 600 A/mm 2 (4.2 K and 20 T) is achieved after 100 bar OP processing. With these intrinsically beneficial properties and recent processing progress, Bi-2212 RW has become very attractive for high field magnet applications, especially for nuclear magnetic resonance (NMR) magnets and accelerator magnets etc. This thesis summarizes my graduate study on Bi-2212 solenoids for high field and high homogeneity NMR magnet applications, which mainly includes performance study of Bi-2212 RW insulations, 1 bar and OP processing study of Bi-2212 solenoids, and development of superconducting joints between Bi-2212 RW conductors. Electrical insulation is one of the key components of Bi-2212 coils to provide sufficient electrical standoff within coil winding pack. A TiO 2/polymer insulation offered by nGimat LLC was systematically investigated by differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), dielectric property measurements, and transport critical current (Ic) property measurements. About 29% of the insulation by weight is polymer. When the Bi-2212 wire is fully heat treated, this decomposes with slow heating to 400 °C in flowing O2. After the full reaction, we found that the TiO2 did not degrade the critical current properties, adhered well to the conductor, and provided a breakdown voltage of more than 100 V. A Bi-2212 RW wound solenoid coil was built using this insulation being offered by nGimat LLC. The coil resistance was constant through coil winding, polymer burn-off and full coil reaction. The coil was successfully tested at the NHMFL generating 33.8 T combined magnetic field in a 31.2 T background field. Multiple quenches occurred safely, which also illustrates that the insulation provided sufficient dielectric standoff. For Bi-2212 RW with a typical as-drawn diameter of 1.0-1.5 mm, this 15 microm thick insulation allows a very high coil packing factor of ~0.74, whereas earlier alumino-silicate braid insulation only allows packing factors of 0.38-0.48. In addition to the commercial TiO2/polymer insulation, we have also investigated sol-gel based ceramic coatings through collaboration with Harran University and another TiO2 based insulation coating at the NHMFL. Since Bi-2212 superconducting coils employ the Wind-and-React (W&R) technology, there are some potential issues in processing Bi-2212 coils, in particular for coils with a large thermal mass and dense oxide insulation coating. For this study, several Bi-2212 test solenoids with an outer diameter (OD) of about 90 mm were built and heat treated in 1 bar flowing oxygen with deadweights applied so as to simulate large coil packs. After the heat treatment (HT), coils were epoxy impregnated and cut. Winding pack was checked using SEM in terms of conductor geometry and insulation. Some samples were extracted to measure transport critical current Ic and critical temperature Tc. The results are very promising: test coils presented low creep behavior after standard partial melt HT under mechanical load, and no Ic degradation was found due to the application of mechanical load, and no inadequate oxygenation issue was seen for thick coils with ceramic coating on the wire. However, coils were partially electrically shorted after 1 bar HT under mechanical load, and we believe that increasing insulation coating thickness is necessary. In addition, several small solenoids were manufactured to study OP processing of Bi-2212 coils. The preliminary results indicate that there are some gaps between turns due to densification of wires (~4% wire diameter reduction) during 50-100 bar OP processing, and the diameter shrinking of conductors will potentially lead to coil sagging. So far, we have developed some methods to solve the issue of coil sagging, such as using flexible coil flange to allow smooth sagging of winding pack during OP processing. We have also investigated electrical joints between Bi-2212 RW conductors, which include resistive joints and superconducting joints. For resistive Bi-2212 joints, we evaluated conventional diffusion bonding method and soldering method. In general, the joints (with 42 mm joint length) resistances are below 200 nO at 4.2 K and magnetic fields up to 13.5 T, and the effect of magnetoresistance is clearly present. In addition to resistive joints, we successfully developed a superconducting joint between Bi-2212 RW conductors for persistent current mode (PCM) operations. (Abstract shortened by UMI.).

First-order transition from a Kondo insulator to a ferromagnetic metal in single crystalline FeSi(1-x)Ge(x).

PubMed

Yeo, S; Nakatsuji, S; Bianchi, A D; Schlottmann, P; Fisk, Z; Balicas, L; Stampe, P A; Kennedy, R J

2003-07-25

The phase diagram of FeSi(1-x)Ge(x), obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, x(c) approximately 0.25. The gap of the insulating phase strongly decreases with x. The specific heat gamma coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si/Ge ligand site.

Flux pumping for non-insulated and metal-insulated HTS coils

NASA Astrophysics Data System (ADS)

Ma, Jun; Geng, Jianzhao; Coombs, T. A.

2018-01-01

High-temperature superconducting (HTS) coils wound from coated conductors without turn-to-turn insulation (non-insulated (NI) coils) have been proven with excellent electrical and thermal performances. However, the slow charging of NI coils has been a long-lasting problem. In this work, we explore using a transformer-rectifier HTS flux pump to charge an NI coil and a metal-insulated coil. The charging performance comparison is made between different coils. Comprehensive study is done to thoroughly understand the electrical-magnetic transience in charging these coils. We will show that the low-voltage high-current flux pump is especially suitable for charging NI coils with very low characteristic resistance.

Superconductivity-related insulating behavior.

PubMed

Sambandamurthy, G; Engel, L W; Johansson, A; Shahar, D

2004-03-12

We present the results of an experimental study of superconducting, disordered, thin films of amorphous indium oxide. These films can be driven from the superconducting phase to a reentrant insulating state by the application of a perpendicular magnetic field (B). We find that the high-B insulator exhibits activated transport with a characteristic temperature, TI. TI has a maximum value (TpI) that is close to the superconducting transition temperature (Tc) at B=0, suggesting a possible relation between the conduction mechanisms in the superconducting and insulating phases. Tp(I) and Tc display opposite dependences on the disorder strength.

Self-duality and a Hall-insulator phase near the superconductor-to-insulator transition in indium-oxide films.

PubMed

Breznay, Nicholas P; Steiner, Myles A; Kivelson, Steven Allan; Kapitulnik, Aharon

2016-01-12

We combine measurements of the longitudinal (ρxx) and Hall (ρxy) resistivities of disordered 2D amorphous indium-oxide films to study the magnetic-field tuned superconductor-to-insulator transition (H-SIT) in the T --> 0 limit. At the critical field, Hc, the full resistivity tensor is T independent with ρxx(Hc) = h/4e(2) and ρxy(Hc) = 0 within experimental uncertainty in all films (i.e., these appear to be "universal" values); this is strongly suggestive that there is a particle-vortex self-duality at H = Hc. The transition separates the (presumably) superconducting state at H < Hc from a "Hall-insulator" phase in which ρxx --> ∞ as T --> 0 whereas ρxy approaches a nonzero value smaller than its "classical value" H/nec; i.e., 0 < ρxy < H/nec. A still higher characteristic magnetic field, Hc* > Hc, at which the Hall resistance is T independent and roughly equal to its classical value, ρxy ≈ H/nec, marks an additional crossover to a high-field regime (probably to a Fermi insulator) in which ρxy > H/nec and possibly diverges as T --> 0. We also highlight a profound analogy between the H-SIT and quantum-Hall liquid-to-insulator transitions (QHIT).

Orbital Magnetization of Quantum Spin Hall Insulator Nanoparticles.

PubMed

Potasz, P; Fernández-Rossier, J

2015-09-09

Both spin and orbital degrees of freedom contribute to the magnetic moment of isolated atoms. However, when inserted in crystals, atomic orbital moments are quenched because of the lack of rotational symmetry that protects them when isolated. Thus, the dominant contribution to the magnetization of magnetic materials comes from electronic spin. Here we show that nanoislands of quantum spin Hall insulators can host robust orbital edge magnetism whenever their highest occupied Kramers doublet is singly occupied, upgrading the spin edge current into a charge current. The resulting orbital magnetization scales linearly with size, outweighing the spin contribution for islands of a few nm in size. This linear scaling is specific of the Dirac edge states and very different from Schrodinger electrons in quantum rings. By modeling Bi(111) flakes, whose edge states have been recently observed, we show that orbital magnetization is robust with respect to disorder, thermal agitation, shape of the island, and crystallographic direction of the edges, reflecting its topological protection.

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

PubMed

Udalov, O G; Beloborodov, I S

2017-05-04

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

Diagnosis of high-intensity pulsed heavy ion beam generated by a novel magnetically insulated diode with gas puff plasma gun.

PubMed

Ito, H; Miyake, H; Masugata, K

2008-10-01

Intense pulsed heavy ion beam is expected to be applied to materials processing including surface modification and ion implantation. For those applications, it is very important to generate high-purity ion beams with various ion species. For this purpose, we have developed a new type of a magnetically insulated ion diode with an active ion source of a gas puff plasma gun. When the ion diode was operated at a diode voltage of about 190 kV, a diode current of about 15 kA, and a pulse duration of about 100 ns, the ion beam with an ion current density of 54 A/cm(2) was obtained at 50 mm downstream from the anode. By evaluating the ion species and the energy spectrum of the ion beam via a Thomson parabola spectrometer, it was confirmed that the ion beam consists of nitrogen ions (N(+) and N(2+)) of energy of 100-400 keV and the proton impurities of energy of 90-200 keV. The purity of the beam was evaluated to be 94%. The high-purity pulsed nitrogen ion beam was successfully obtained by the developed ion diode system.

Effects of spin-orbit coupling on the structural, electronic and magnetic properties of 3 C -BaIrO3

NASA Astrophysics Data System (ADS)

Singh, Vijeta; Pulikkotil, J. J.

2017-08-01

3 C -BaIrO3 which crystallizes in the tetragonal structure has Ir in + 4 valence state. For such systems with near-perfect octahedrally coordinated Ir ions, spin-orbit coupling (SOC) in conjunction with moderate Coulomb correlations are expected to drive an insulating state by virtue of Jeff splitting of the Ir 5 d manifold. However, experiments find 3 C -BaIrO3 tobe a Pauli paramagnet with conducting ground state. We present a comprehensive investigation of its electronic structure by means of first principles density functional theory based calculations. The calculations show that SOC introduces a pseudo-gap like feature in the anti-bonding region, reminiscent of an incomplete splitting of the Jeff states due to the strong Ir t2g - O 2 p hybridization. Furthermore, it is anticipated from the electronic structure that p - type doping may introduce a metal-insulator transition in 3 C -BaIrO3, in contrast to iso-electronic SrIrO3. Besides, we also investigate the effects of Coulomb correlations and magnetic properties of 3 C -BaIrO3.

Evolution of the Magnetic Excitations in NaOsO3 through its Metal-Insulator Transition

NASA Astrophysics Data System (ADS)

Vale, J. G.; Calder, S.; Donnerer, C.; Pincini, D.; Shi, Y. G.; Tsujimoto, Y.; Yamaura, K.; Sala, M. Moretti; van den Brink, J.; Christianson, A. D.; McMorrow, D. F.

2018-06-01

The temperature dependence of the excitation spectrum in NaOsO3 through its metal-to-insulator transition (MIT) at 410 K has been investigated using resonant inelastic x-ray scattering at the Os L3 edge. High-resolution (Δ E ˜56 meV ) measurements show that the well-defined, low-energy magnons in the insulating state weaken and dampen upon approaching the metallic state. Concomitantly, a broad continuum of excitations develops which is well described by the magnetic fluctuations of a nearly antiferromagnetic Fermi liquid. By revealing the continuous evolution of the magnetic quasiparticle spectrum as it changes its character from itinerant to localized, our results provide unprecedented insight into the nature of the MIT in NaOsO3 [J. G. Vale, S. Calder, C. Donnerer, D. Pincini, Y. G. Shi, Y. Tsujimoto, K. Yamaura, M. M. Sala, J. van den Brink, A. D. Christianson, and D. F. McMorrow, Phys. Rev. B 97, 184429 (2018), 10.1103/PhysRevB.97.184429].

Zero-field edge plasmons in a magnetic topological insulator [Zero-field edge magnetoplasmons in a magnetic topological insulator

DOE PAGES

Mahoney, Alice C.; Colless, James I.; Peeters, Lucas; ...

2017-11-28

Incorporating ferromagnetic dopants into three-dimensional topological insulator thin films has recently led to the realisation of the quantum anomalous Hall effect. These materials are of great interest since they may support electrical currents that flow without resistance, even at zero magnetic field. To date, the quantum anomalous Hall effect has been investigated using low-frequency transport measurements. However, transport results can be difficult to interpret due to the presence of parallel conductive paths, or because additional non-chiral edge channels may exist. Here we move beyond transport measurements by probing the microwave response of a magnetised disk of Cr-(Bi,Sb) 2Te 3. Wemore » identify features associated with chiral edge plasmons, a signature that robust edge channels are intrinsic to this material system. Finally, our results provide a measure of the velocity of edge excitations without contacting the sample, and pave the way for an on-chip circuit element of practical importance: the zero-field microwave circulator.« less

Tuning the metal-insulator crossover and magnetism in SrRuO 3 by ionic gating

DOE PAGES

Yi, Hee Taek; Gao, Bin; Xie, Wei; ...

2014-10-13

Reversible control of charge transport and magnetic properties without degradation is a key for device applications of transition metal oxides. Chemical doping during the growth of transition metal oxides can result in large changes in physical properties, but in most of the cases irreversibility is an inevitable constraint. We report a reversible control of charge transport, metal-insulator crossover and magnetism in field-effect devices based on ionically gated archetypal oxide system - SrRuO 3. In these thin-film devices, the metal-insulator crossover temperature and the onset of magnetoresistance can be continuously and reversibly tuned in the range 90–250 K and 70–100 K,more » respectively, by application of a small gate voltage. We infer that a reversible diffusion of oxygen ions in the oxide lattice dominates the response of these materials to the gate electric field. These findings provide critical insights into both the understanding of ionically gated oxides and the development of novel applications.« less

Asymmetric Cherenkov acoustic reverse in topological insulators

NASA Astrophysics Data System (ADS)

Smirnov, Sergey

2014-09-01

A general phenomenon of the Cherenkov radiation known in optics or acoustics of conventional materials is a formation of a forward cone of, respectively, photons or phonons emitted by a particle accelerated above the speed of light or sound in those materials. Here we suggest three-dimensional topological insulators as a unique platform to fundamentally explore and practically exploit the acoustic aspect of the Cherenkov effect. We demonstrate that by applying an in-plane magnetic field to a surface of a three-dimensional topological insulator one may suppress the forward Cherenkov sound up to zero at a critical magnetic field. Above the critical field the Cherenkov sound acquires pure backward nature with the polar distribution differing from the forward one generated below the critical field. Potential applications of this asymmetric Cherenkov reverse are in the design of low energy electronic devices such as acoustic ratchets or, in general, in low power design of electronic circuits with a magnetic field control of the direction and magnitude of the Cherenkov dissipation.

Zero-field edge plasmons in a magnetic topological insulator [Zero-field edge magnetoplasmons in a magnetic topological insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahoney, Alice C.; Colless, James I.; Peeters, Lucas

Incorporating ferromagnetic dopants into three-dimensional topological insulator thin films has recently led to the realisation of the quantum anomalous Hall effect. These materials are of great interest since they may support electrical currents that flow without resistance, even at zero magnetic field. To date, the quantum anomalous Hall effect has been investigated using low-frequency transport measurements. However, transport results can be difficult to interpret due to the presence of parallel conductive paths, or because additional non-chiral edge channels may exist. Here we move beyond transport measurements by probing the microwave response of a magnetised disk of Cr-(Bi,Sb) 2Te 3. Wemore » identify features associated with chiral edge plasmons, a signature that robust edge channels are intrinsic to this material system. Finally, our results provide a measure of the velocity of edge excitations without contacting the sample, and pave the way for an on-chip circuit element of practical importance: the zero-field microwave circulator.« less

Tuning the metal-insulator crossover and magnetism in SrRuO₃ by ionic gating.

PubMed

Yi, Hee Taek; Gao, Bin; Xie, Wei; Cheong, Sang-Wook; Podzorov, Vitaly

2014-10-13

Reversible control of charge transport and magnetic properties without degradation is a key for device applications of transition metal oxides. Chemical doping during the growth of transition metal oxides can result in large changes in physical properties, but in most of the cases irreversibility is an inevitable constraint. Here we report a reversible control of charge transport, metal-insulator crossover and magnetism in field-effect devices based on ionically gated archetypal oxide system - SrRuO₃. In these thin-film devices, the metal-insulator crossover temperature and the onset of magnetoresistance can be continuously and reversibly tuned in the range 90-250 K and 70-100 K, respectively, by application of a small gate voltage. We infer that a reversible diffusion of oxygen ions in the oxide lattice dominates the response of these materials to the gate electric field. These findings provide critical insights into both the understanding of ionically gated oxides and the development of novel applications.

Above 400-K robust perpendicular ferromagnetic phase in a topological insulator

PubMed Central

Tang, Chi; Chang, Cui-Zu; Zhao, Gejian; Liu, Yawen; Jiang, Zilong; Liu, Chao-Xing; McCartney, Martha R.; Smith, David J.; Chen, Tingyong; Moodera, Jagadeesh S.; Shi, Jing

2017-01-01

The quantum anomalous Hall effect (QAHE) that emerges under broken time-reversal symmetry in topological insulators (TIs) exhibits many fascinating physical properties for potential applications in nanoelectronics and spintronics. However, in transition metal–doped TIs, the only experimentally demonstrated QAHE system to date, the QAHE is lost at practically relevant temperatures. This constraint is imposed by the relatively low Curie temperature (Tc) and inherent spin disorder associated with the random magnetic dopants. We demonstrate drastically enhanced Tc by exchange coupling TIs to Tm3Fe5O12, a high-Tc magnetic insulator with perpendicular magnetic anisotropy. Signatures showing that the TI surface states acquire robust ferromagnetism are revealed by distinct squared anomalous Hall hysteresis loops at 400 K. Point-contact Andreev reflection spectroscopy confirms that the TI surface is spin-polarized. The greatly enhanced Tc, absence of spin disorder, and perpendicular anisotropy are all essential to the occurrence of the QAHE at high temperatures. PMID:28691097

Spin-orbit tuned metal-insulator transitions in single-crystal Sr₂Ir 1–xRh xO₄ (0≤x≤1)

DOE PAGES

Qi, T. F.; Korneta, O. B.; Li, L.; ...

2012-09-06

Sr₂IrO₄ is a magnetic insulator driven by spin-orbit interaction (SOI) whereas the isoelectronic and isostructural Sr₂RhO₄ is a paramagnetic metal. The contrasting ground states have been shown to result from the critical role of the strong SOI in the iridate. Our investigation of structural, transport, magnetic, and thermal properties reveals that substituting 4d Rh⁴⁺ (4d⁵) ions for 5d Ir⁴⁺ (5d⁵) ions in Sr₂IrO₄ directly reduces the SOI and rebalances the competing energies so profoundly that it generates a rich phase diagram for Sr₂Ir 1–xRh xO₄ featuring two major effects: (1) Light Rh doping (0 ≤ x ≤ 0.16) prompts amore » simultaneous and precipitous drop in both the electrical resistivity and the magnetic ordering temperature TC, which is suppressed to zero at x = 0.16 from 240 K at x = 0. (2) However, with heavier Rh doping [0.24 < x < 0.85 (±0.05)] disorder scattering leads to localized states and a return to an insulating state with spin frustration and exotic magnetic behavior that only disappears near x = 1. The intricacy of Sr₂Ir 1–xRh xO₄ is further highlighted by comparison with Sr₂Ir 1–xRu xO₄ where Ru⁴⁺ (4d⁴) drives a direct crossover from the insulating to metallic states.« less

Metal-as-insulation variant of no-insulation HTS winding technique: pancake tests under high background magnetic field and high current at 4.2 K

NASA Astrophysics Data System (ADS)

Lécrevisse, T.; Badel, A.; Benkel, T.; Chaud, X.; Fazilleau, P.; Tixador, P.

2018-05-01

In the framework of a project aiming at fabricating a 10 T high temperature superconducting (HTS) insert to operate in a 20 T background field, we are investigating the behavior of pancakes consisting of a REBCO HTS tape co-wound with a stainless steel tape (metal-as-insulation (MI) coil). The MI winding is inducing a significant turn-to-turn electrical resistance which helps to reduce the charging time delay. Despite this resistance, the self-protection feature of no-insulation coils is still enabled, thanks to the voltage limit of the power supply. We have built a single pancake coil representative of the pancake that will be used in the insert and performed tests under very high background magnetic field. Our coil experienced over 100 heater induced quenches without a measureable increase of its internal resistance. We have gathered stability and quench behavior data for magnetic fields and engineering current densities (je ) in the range of 0–17 T and 0–635 A mm‑2 respectively. We also present our very first experiments on the insert/outsert interaction in the case of a resistive magnet fault. We show that if self-protection of the MI winding is really effective in the case of a MI coil quench, a major issue comes from the outsert fault which induces a huge current inside the MI coil.

Dominant Majorana bound energy and critical current enhancement in ferromagnetic-superconducting topological insulator

NASA Astrophysics Data System (ADS)

Khezerlou, Maryam; Goudarzi, Hadi; Asgarifar, Samin

2017-03-01

Among the potential applications of topological insulators, we theoretically study the coexistence of proximity-induced ferromagnetic and superconducting orders in the surface states of a 3-dimensional topological insulator. The superconducting electron-hole excitations can be significantly affected by the magnetic order induced by a ferromagnet. In one hand, the surface state of the topological insulator, protected by the time-reversal symmetry, creates a spin-triplet and, on the other hand, magnetic order causes to renormalize the effective superconducting gap. We find Majorana mode energy along the ferromagnet/superconductor interface to sensitively depend on the magnitude of magnetization m zfs from superconductor region, and its slope around perpendicular incidence is steep with very low dependency on m zfs . The superconducting effective gap is renormalized by a factor η( m zfs ), and Andreev bound state in ferromagnet-superconductor/ferromagnet/ferromagnet-superconductor (FS/F/FS) Josephson junction is more sensitive to the magnitude of magnetizations of FS and F regions. In particular, we show that the presence of m zfs has a noticeable impact on the gap opening in Andreev bound state, which occurs in finite angle of incidence. This directly results in zero-energy Andreev state being dominant. By introducing the proper form of corresponding Dirac spinors for FS electron-hole states, we find that via the inclusion of m zfs , the Josephson supercurrent is enhanced and exhibits almost abrupt crossover curve, featuring the dominant zero-energy Majorana bound states.

Experimental exploration of novel semimetal state in strong anisotropic Pyrochlore iridate Nd2lr2O7 under high magnetic field

NASA Astrophysics Data System (ADS)

Tian, Z. M.; Kohama, Y.; Tomita, T.; Ishikawa, J.; Mairo, H.; Kindo, K.; Nakatsuji, S.

2016-02-01

We report the anisotropic magnetotransport of Nd2Ir2O7 single crystal under high magnetic field (B) up to 50 T with B along various directions. Only for B // [001] direction, a novel semimetal state is realized under high magnetic field evidenced by a field-induced insulating-semimetalic phase transition with critical field BMI∼12 T related to the destruction of all-in-all-out (AIAO) state. In contrast, abnormal magnetotransport hysteresis behavior is observed for B // [111] direction below the metal-insulator transition temperature (TMI), and magnetotransport reveals the Ir spin structure keep in the AIAO state under high magnetic field with temperature just below TMI, in prospect to realize Weyl semimetal state.

RADLAC 2 performance summary

NASA Astrophysics Data System (ADS)

Shope, S. L.; Mazarakis, M. G.; Frost, C. A.; Crist, C. E.; Poukey, J. W.; Prestwich, K. R.; Turman, B. N.; Struve, K.; Welch, D.

1991-09-01

A 12.5-m long Self Magnetically Insulated Transmission LinE (SMILE) that sums the voltages of eight, 2-MV pulse forming lines was installed in the RADLAC-2 linear introduction accelerator. The magnetic insulation criteria were calculated using parapotential flow theory and found to agree with MAGIC simulations. High quality annular beams with a transverse velocity beta (perpendicular) equals v(perpendicular)/c is less than or equal to 0.1 and a radius r(sub b) less than 2 cm were measured for currents of 50 to 100 kA extracted from a magnetic immersed foilless diode. These parameters were achieved with 11 to 15-MV accelerating voltages and 6 to 16-kG diode magnetic fields. The experimental results exceeded our design expectations and are in good agreement with code simulations.

The low temperature specific heat and electrical transport, magnetic properties of Pr0.65Ca0.35MnO3

NASA Astrophysics Data System (ADS)

Han, Zhiyong

2017-02-01

The magnetic properties, electrical transport properties, and low temperature specific heat of polycrystalline perovskite manganese oxide Pr0.65Ca0.35MnO3 have been investigated experimentally. It is found that there exists cluster glass state in the sample at low temperature besides the antiferromagnetic insulating state. With the increase of magnetic field, antiferromagnetic insulating state converts to ferromagnetic metal state and the Debye temperature decreases gradually. In addition, the low temperature electron specific heat in zero magnetic field is obviously larger than that of ordinary rare-earth manganites oxide and this phenomenon is related to the itinerant electrons in ferromagnetic cluster state and the disorder in Pr0.65Ca0.35MnO3.

Suppression of shunting current in a magnetically insulated coaxial vacuum diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yalandin, M. I.; Sharypov, K. A.; Shpak, V. G.

2015-06-08

Real-time investigations of the dynamics of explosive electron emission from a high-voltage cathode holder made of nonmagnetic stainless steel in a magnetically insulated coaxial vacuum diode have been performed. It has been shown that aging the cathode with several tens of voltage pulses at a field of 1–2 MV/cm provides a stray emission delay ranging from hundreds of picoseconds to a nanosecond or more. In addition, the magnetic field must be configured so that the magnetic lines would not cross the vacuum gap between the diode case and the cathode holder in the region behind the emitting edge of themore » cathode. These efforts provide conditions for stable emission of the working beam from a graphite cathode with a sharp emitting edge.« less

The physics of inhomogeneous striped superconductors

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Eroles, J.; Balatsky, A. V.; Bishop, A. R.

2001-05-01

We present a minimal model of a doped Mott insulator that simultaneously supports antiferromagnetic stripes and d-wave superconductivity. At the unrestricted mean-field level, the various phases of the cuprates, including weak and strong pseudogap phases, and two different types of superconductivity in the underdoped and the overdoped regimes, find a natural interpretation. We argue that on the underdoped side, the superconductor is intrinsically inhomogeneous — striped nanoscale coexistence of superconductivity and magnetism — and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. On the overdoped side, the state is overall homogeneous and the superconductivity is of the classical BCS type.

Two-magnon scattering in the 5d all-in-all-out pyrochlore magnet Cd 2Os 2O 7

DOE PAGES

Nguyen, Thi Minh Hien; Sandilands, Luke J.; Sohn, C. H.; ...

2017-08-15

5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd 2Os 2O 7. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii–Moriya and exchange interactions play a significant role in the spin-wavemore » dispersions. The Raman data also reveal complex spin–charge–lattice coupling and indicate that the metal–insulator transition in Cd 2Os 2O 7 is Lifshitz-type. In conclusion, our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.« less

Domain wall in a quantum anomalous Hall insulator as a magnetoelectric piston

NASA Astrophysics Data System (ADS)

Upadhyaya, Pramey; Tserkovnyak, Yaroslav

2016-07-01

We theoretically study the magnetoelectric coupling in a quantum anomalous Hall insulator state induced by interfacing a dynamic magnetization texture to a topological insulator. In particular, we propose that the quantum anomalous Hall insulator with a magnetic configuration of a domain wall, when contacted by electrical reservoirs, acts as a magnetoelectric piston. A moving domain wall pumps charge current between electrical leads in a closed circuit, while applying an electrical bias induces reciprocal domain-wall motion. This pistonlike action is enabled by a finite reflection of charge carriers via chiral modes imprinted by the domain wall. Moreover, we find that, when compared with the recently discovered spin-orbit torque-induced domain-wall motion in heavy metals, the reflection coefficient plays the role of an effective spin-Hall angle governing the efficiency of the proposed electrical control of domain walls. Quantitatively, this effective spin-Hall angle is found to approach a universal value of 2, providing an efficient scheme to reconfigure the domain-wall chiral interconnects for possible memory and logic applications.

Mott-to-Goodenough insulator-insulator transition in LiVO2

NASA Astrophysics Data System (ADS)

Subedi, Alaska

2017-06-01

I critically examine Goodenough's explanation for the experimentally observed phase transition in LiVO2 using microscopic calculations based on density functional and dynamical mean field theories. The high-temperature rhombohedral phase exhibits both magnetic and dynamical instabilities. Allowing a magnetic solution for the rhombohedral structure does not open an insulating gap, and an explicit treatment of the on-site Coulomb U interaction is needed to stabilize an insulating rhombohedral phase. The non-spin-polarized phonon dispersions of the rhombohedral phase show two unstable phonon modes at the wave vector (1/3 ,-1/3 ,0 ) that corresponds to the experimentally observed trimer forming instability. A full relaxation of the supercell corresponding to this instability yields a nonmagnetic state containing V3 trimers. These results are consistent with Goodenough's suggestion that the high-temperature phase is in the localized-electron regime and the transition to the low-temperature phase in the itinerant-electron regime is driven by V-V covalency.

Metal-to-insulator switching in quantum anomalous Hall states

DOE PAGES

Kou, Xufeng; Pan, Lei; Wang, Jing; ...

2015-10-07

After decades of searching for the dissipationless transport in the absence of any external magnetic field, quantum anomalous Hall effect (QAHE) was recently achieved in magnetic topological insulator films. However, the universal phase diagram of QAHE and its relation with quantum Hall effect (QHE) remain to be investigated. Here, we report the experimental observation of the giant longitudinal resistance peak and zero Hall conductance plateau at the coercive field in the six quintuple-layer (Cr 0.12Bi 0.26Sb 0.62) 2Te 3 film, and demonstrate the metal-to-insulator switching between two opposite QAHE plateau states up to 0.3 K. Moreover, the universal QAHE phasemore » diagram is confirmed through the angle-dependent measurements. Our results address that the quantum phase transitions in both QAHE and QHE regimes are in the same universality class, yet the microscopic details are different. Additionally, the realization of the QAHE insulating state unveils new ways to explore quantum phase-related physics and applications.« less

Study of Thermomechanical Properties of The Epoxy-Impregnated Cable Composite for a 15 T Nb3Sn Dipole Demonstrator

NASA Astrophysics Data System (ADS)

Li, Pei; Krave, Steve; Zlobin, Alexander

2017-12-01

The knowledge of the thermomechanical properties of the composite of cable/insulation/epoxy impregnation are important for the design, fabrication and operation of superconducting accelerator magnets. As a part of the 15 T dipole magnet development at Fermi National Accelerator Laboratory (FNAL), we studied the thermomechanical properties of cable stack that represents the cable composites in the 15 T dipole. The measurements include thermal contraction and strain-stress characterization under compressive load along the principal directions. The cable stack samples show hysteresis behaviour in loading-unloading cycles, which is found to be most dramatic along the azimuthal direction. Also, the choice of insulation material/procedure is found to strongly impact the bonding between cables and epoxy/cable layers. The cable stacks measured in this study use E-glass tape wrapping insulation and show weaker bonding to cables than similar cable stacks using S-2 glass sleeves insulation previously studied.

Spintronics Based on Topological Insulators

NASA Astrophysics Data System (ADS)

Fan, Yabin; Wang, Kang L.

2016-10-01

Spintronics using topological insulators (TIs) as strong spin-orbit coupling (SOC) materials have emerged and shown rapid progress in the past few years. Different from traditional heavy metals, TIs exhibit very strong SOC and nontrivial topological surface states that originate in the bulk band topology order, which can provide very efficient means to manipulate adjacent magnetic materials when passing a charge current through them. In this paper, we review the recent progress in the TI-based magnetic spintronics research field. In particular, we focus on the spin-orbit torque (SOT)-induced magnetization switching in the magnetic TI structures, spin-torque ferromagnetic resonance (ST-FMR) measurements in the TI/ferromagnet structures, spin pumping and spin injection effects in the TI/magnet structures, as well as the electrical detection of the surface spin-polarized current in TIs. Finally, we discuss the challenges and opportunities in the TI-based spintronics field and its potential applications in ultralow power dissipation spintronic memory and logic devices.

Photodrive of magnetic bubbles via magnetoelastic waves

PubMed Central

Ogawa, Naoki; Koshibae, Wataru; Beekman, Aron Jonathan; Nagaosa, Naoto; Kubota, Masashi; Kawasaki, Masashi; Tokura, Yoshinori

2015-01-01

Precise control of magnetic domain walls continues to be a central topic in the field of spintronics to boost infotech, logic, and memory applications. One way is to drive the domain wall by current in metals. In insulators, the incoherent flow of phonons and magnons induced by the temperature gradient can carry the spins, i.e., spin Seebeck effect, but the spatial and time dependence is difficult to control. Here, we report that coherent phonons hybridized with spin waves, magnetoelastic waves, can drive magnetic bubble domains, or curved domain walls, in an iron garnet, which are excited by ultrafast laser pulses at a nonabsorbing photon energy. These magnetoelastic waves were imaged by time-resolved Faraday microscopy, and the resultant spin transfer force was evaluated to be larger for domain walls with steeper curvature. This will pave a path for the rapid spatiotemporal control of magnetic textures in insulating magnets. PMID:26150487

Photodrive of magnetic bubbles via magnetoelastic waves.

PubMed

Ogawa, Naoki; Koshibae, Wataru; Beekman, Aron Jonathan; Nagaosa, Naoto; Kubota, Masashi; Kawasaki, Masashi; Tokura, Yoshinori

2015-07-21

Precise control of magnetic domain walls continues to be a central topic in the field of spintronics to boost infotech, logic, and memory applications. One way is to drive the domain wall by current in metals. In insulators, the incoherent flow of phonons and magnons induced by the temperature gradient can carry the spins, i.e., spin Seebeck effect, but the spatial and time dependence is difficult to control. Here, we report that coherent phonons hybridized with spin waves, magnetoelastic waves, can drive magnetic bubble domains, or curved domain walls, in an iron garnet, which are excited by ultrafast laser pulses at a nonabsorbing photon energy. These magnetoelastic waves were imaged by time-resolved Faraday microscopy, and the resultant spin transfer force was evaluated to be larger for domain walls with steeper curvature. This will pave a path for the rapid spatiotemporal control of magnetic textures in insulating magnets.

Two-Dimensional Jeff=1 /2 Antiferromagnetic Insulator Unraveled from Interlayer Exchange Coupling in Artificial Perovskite Iridate Superlattices

NASA Astrophysics Data System (ADS)

Hao, Lin; Meyers, D.; Frederick, Clayton; Fabbris, Gilberto; Yang, Junyi; Traynor, Nathan; Horak, Lukas; Kriegner, Dominik; Choi, Yongseong; Kim, Jong-Woo; Haskel, Daniel; Ryan, Phil J.; Dean, M. P. M.; Liu, Jian

2017-07-01

We report an experimental investigation of the two-dimensional Jeff=1 /2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO3)1 , (SrTiO3)m ] (m =1 , 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the m =2 and m =3 samples than the m =1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO3 layer enhances the effective electron-electron correlation and strengthens the Mott phase. The significant reduction of the Néel temperature from 150 K for m =1 to 40 K for m =2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO3 layer number m , for maintaining canting-induced weak ferromagnetism. The nearly unaltered transition temperature between the m =2 and the m =3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.

Bulk Rotational Symmetry Breaking in Kondo Insulator SmB 6

DOE PAGES

Xiang, Z.; Lawson, B.; Asaba, T.; ...

2017-09-25

The Kondo insulator samarium hexaboride (SmB 6) has been intensely studied in recent years as a potential candidate of a strongly correlated topological insulator. One of the most exciting phenomena observed in SmB 6 is the clear quantum oscillations appearing in magnetic torque at a low temperature despite the insulating behavior in resistance. These quantum oscillations show multiple frequencies and varied effective masses. The origin of quantum oscillation is, however, still under debate with evidence of both two-dimensional Fermi surfaces and three-dimensional Fermi surfaces. Here, we carry out angle-resolved torque magnetometry measurements in a magnetic field up to 45 Tmore » and a temperature range down to 40 mK. With the magnetic field rotated in the (010) plane, the quantum oscillation frequency of the strongest oscillation branch shows a fourfold rotational symmetry. However, in the angular dependence of the amplitude of the same branch, this fourfold symmetry is broken and, instead, a twofold symmetry shows up, which is consistent with the prediction of a two-dimensional Lifshitz-Kosevich model. No deviation of Lifshitz-Kosevich behavior is observed down to 40 mK. Our results suggest the existence of multiple light-mass surface states in SmB 6, with their mobility significantly depending on the surface disorder level.« less

Non-Equilibrium Superconductivity and Magnetic Pair Breaking in Perovskite Half-Metallic Ferromagnet-Insulator-Superconductor (F-I-S) Heterostructures

NASA Technical Reports Server (NTRS)

Fu, C.-C.; Yeh, N.-C.; Samoilov, A. V.; Vakili, K.; Li, Y.; Vasquez, R. P.

1999-01-01

The effect of spin-polarized quasiparticle currents on the critical current density (J-c) of cuprate superconductors is studied in perovskite F-I-S heterostructures as a function of insulator thickness and of underlying magnetic materials. A pulsed current technique is employed to minimize extraneous Joule heating on the superconductor. At temperatures near T-c, F-I-S samples with insulator thicknesses\\1e2nm show precipitous decrease in J_c as current injection (I_m) is increased. In contrast, J_c in a controlled sample with a substituted non-magnetic material (N-I-S) exhibit no dependence on I_m. Similarly, a F-I-S sample with a 10 mn insulating barrier also show little J_c effect versus I_m. At low temperatures with I_m = 0, significant suppression of J-c is observed only in the thin barrier F-I-S samples, although T_c and the normal-state resistivity of all samples are comparable. These phenomena can be attributed to the Cooper pair breaking induced by externally-injected and internally-reflected spin-polarized quasiparticle currents. We estimate an order of magnitude range for the spin diffusion length of 100 nm to 100\\ mum.

Micromachined Active Magnetic Regenerator for Low-Temperature Magnetic Coolers

NASA Technical Reports Server (NTRS)

Chen, Weibo; Jaeger, Michael D.

2013-01-01

A design of an Active Magnetic Regenerative Refrigeration (AMRR) system has been developed for space applications. It uses an innovative 3He cryogenic circulator to provide continuous remote/distributed cooling at temperatures in the range of 2 K with a heat sink at about 15 K. A critical component technology for this cooling system is a highly efficient active magnetic regenerator, which is a regenerative heat exchanger with its matrix material made of magnetic refrigerant gadolinium gallium garnet (GGG). Creare Inc. is developing a microchannel GGG regenerator with an anisotropic structured bed for high system thermal efficiency. The regenerator core consists of a stack of thin, single-crystal GGG disks alternating with thin polymer insulating layers. The insulating layers help minimize the axial conduction heat leak, since GGG has a very high thermal conductivity in the regenerator s operating temperature range. The GGG disks contain micro channels with width near 100 micrometers, which enhance the heat transfer between the circulating flow and the refrigerant bed. The unique flow configuration of the GGG plates ensures a uniform flow distribution across the plates. The main fabrication challenges for the regenerator are the machining of high-aspect-ratio microchannels in fragile, single-crystal GGG disks and fabrication and assembly of the GGG insulation layers. Feasibility demonstrations to date include use of an ultrashort- pulse laser to machine microchannels without producing unacceptable microcracking or deposition of recast material, as shown in the figure, and attachment of a thin insulation layer to a GGG disk without obstructing the flow paths. At the time of this reporting, efforts were focused on improving the laser machining process to increase machining speed and further reduce microcracking.

Spin-orbit torque-driven magnetization switching in 2D-topological insulator heterostructure

NASA Astrophysics Data System (ADS)

Soleimani, Maryam; Jalili, Seifollah; Mahfouzi, Farzad; Kioussis, Nicholas

2017-02-01

Charge pumping and spin-orbit torque (SOT) are two reciprocal phenomena widely studied in ferromagnet (FM)/topological insulator (TI) heterostructures. However, the SOT and its corresponding switching phase diagram for a FM island in proximity to a two-dimensional topological insulator (2DTI) has not been explored yet. We have addressed these features, using the recently developed adiabatic expansion of time-dependent nonequilibrium Green's function (NEGF) in the presence of both precessing magnetization and bias voltage. We have calculated the angular and spatial dependence of different components of the SOT on the FM island. We determined the switching phase diagram of the FM for different orientations of the easy axis. The results can be used as a guideline for the future experiments on such systems.

Magnetic-field-modulated resonant tunneling in ferromagnetic-insulator-nonmagnetic junctions.

PubMed

Song, Yang; Dery, Hanan

2014-07-25

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

A modified Bitter-type electromagnet and control system for cold atom experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luan, Tian; Zhou, Tianwei; Chen, Xuzong, E-mail: xuzongchen@pku.edu.cn

2014-02-15

We present a modified Bitter-type electromagnet which features high magnetic field, fine electronic properties and efficient heat removal. The electromagnet is constructed from a stack of copper layers separated by mica layers that have the same shape. A distinctive design of cooling channels on the insulating layers and the parallel ducts between the layers ensures low resistance for cooling water to flow. A continuous current control system is also made to regulate the current through the electromagnet. In our experiment, versatile electromagnets are applied to generate magnetic field and gradient field. From our measurements, a peak magnetic field of 1000more » G and a peak gradient field of 80 G/cm are generated in the center of the apparatuses which are 7 cm and 5 cm away from the edge of each electromagnet with a current of 230 A and 120 A, respectively. With the effective feedback design in the current control system and cooling water flow of 3.8 l/min, the stability of the current through the electromagnets can reach 10{sup −5}.« less

Displacement-type ferroelectric transition with magnetic Mn ions in perovskite Sr1-xBaxMnO3

NASA Astrophysics Data System (ADS)

Sakai, Hideaki; Fujioka, Jun; Fukuda, Tatsuo; Okuyama, Daisuke; Hashizume, Daisuke; Kagawa, Fumitaka; Nakao, Hironori; Murakami, Youich; Arima, Takahisa; Baron, Alfred Q. R.; Taguchi, Yasujiro; Tokura, Yoshinori

2012-02-01

Almost all the proper ferroelectrics with a perovskite structure discovered so far have no d-electrons in the off-center transition metal site, as exemplified by BaTiO3 and Pb(Zr,Ti)O3. This empirical d^0 rule is incompatible with the emergence of magnetism and has significantly restricted the variety of multiferroic materials. In this work, we have discovered a displacement-type ferroelectric transition originating from off-center Mn^4+ ions in antiferromagnetic Mott insulators Sr1-xBaxMnO3. As Ba concentration increases, the perovskite lattice shows the typical soft mode dynamics, and the ferroelectricity shows up for x .45. In addition to the large polarization and high transition temperature comparable to BaTiO3, we demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ˜70% and increases the soft-phonon energy by ˜50%, indicating gigantic magnetoelectric effects [1]. This work was supported by the FIRST program on ``Quantum Science on Strong Correlation''. [4pt] [1] H. Sakai et al., Phys. Rev. Lett. 107, 137601 (2011).

Odd-frequency superconducting pairing and subgap density of states at the edge of a two-dimensional topological insulator without magnetism

NASA Astrophysics Data System (ADS)

Cayao, Jorge; Black-Schaffer, Annica M.

2017-10-01

We investigate the emergence and consequences of odd-frequency spin-triplet s -wave pairing in superconducting hybrid junctions at the edge of a two-dimensional topological insulator without any magnetism. More specifically, we consider several different normal-superconductor hybrid systems at the topological insulator edge, where spin-singlet s -wave superconducting pairing is proximity induced from an external conventional superconductor. We perform fully analytical calculations and show that odd-frequency mixed spin-triplet s -wave pairing arises due to the unique spin-momentum locking in the topological insulator edge state and the naturally nonconstant pairing potential profile in hybrid systems. Importantly, we establish a one-to-one correspondence between the local density of states (LDOS) at low energies and the odd-frequency spin-triplet pairing in NS, NSN, and SNS junctions along the topological insulator edge; at interfaces the enhancement in the LDOS can directly be attributed to the contribution of odd-frequency pairing. Furthermore, in SNS junctions we show that the emergence of the zero-energy LDOS peak at the superconducting phase ϕ =π is associated purely with odd-frequency pairing in the middle of the junction.

Spin–orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

DOE PAGES

Li, Peng; Liu, Tao; Chang, Houchen; ...

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe 12O 19 bilayer where the BaFe 12O 19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control themore » up and down states of the remnant magnetization in the BaFe 12O 19 film when the film is magnetized by an in-plane magnetic field. Furthermore, it can reduce or increase the switching field of the BaFe 12O 19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.« less

Spin-orbit torque-assisted switching in magnetic insulator thin films with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Li, Peng; Liu, Tao; Chang, Houchen; Kalitsov, Alan; Zhang, Wei; Csaba, Gyorgy; Li, Wei; Richardson, Daniel; Demann, August; Rimal, Gaurab; Dey, Himadri; Jiang, J. S.; Porod, Wolfgang; Field, Stuart B.; Tang, Jinke; Marconi, Mario C.; Hoffmann, Axel; Mryasov, Oleg; Wu, Mingzhong

2016-09-01

As an in-plane charge current flows in a heavy metal film with spin-orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin-orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rice, John A.

A new, all ceramic magnet insulation system has been developed that can withstand the high radiation doses without significant damage. The insulation can be applied directly onto a Nb3Sn or copper cable as a ceramic based prepreg system using the same equipment and procedures used for the traditional epoxy systems. Excessive porosity was eliminated and compressions strength increased. Thermal expansion nearly matches the expansion of niobium tin conductor wire. A radiation test program has been defined and magnet fabrication issues have been identified. This report covers the results of the Phase I research program.

Capacitively-coupled inductive sensors for measurements of pulsed currents and pulsed magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekdahl, C.A.

In experiments involving pulsed high magnetic fields the appearance of the full induced voltage at the output terminals of large-area inductive sensors such as diamagnetic loops and Rogowski belts imposes severe requirements on the insulation near the output. Capacitive detection of the inductive-sensor output voltage provides an ideal geometry for high-voltage insulation, and also accomplishes the necessary voltage division. An inductive-shunt current monitor was designed to utilize the capacitive-detection principle. The contruction of this device and its performance are described in this paper.

The experimental study of the DC dielectric breakdown strength in magnetic fluids

NASA Astrophysics Data System (ADS)

Kopčanský, P.; Tomčo, L.; Marton, K.; Koneracká, M.; Potočová, I.; Timko, M.

2004-05-01

Magnetic fluids have been studied for use as a high-voltage insulation. High-voltage measurements on magnetic fluids based on transformer oil, as a function of volume concentrations of magnetite particles and applied magnetic field, showed the increase of the DC dielectric breakdown strength opposite transformer oil, if the saturation magnetization of magnetic fluid is up to 4 mT approximately.

Pressure-induced superconductivity in the iron-based ladder material BaFe2S3.

PubMed

Takahashi, Hiroki; Sugimoto, Akira; Nambu, Yusuke; Yamauchi, Touru; Hirata, Yasuyuki; Kawakami, Takateru; Avdeev, Maxim; Matsubayashi, Kazuyuki; Du, Fei; Kawashima, Chizuru; Soeda, Hideto; Nakano, Satoshi; Uwatoko, Yoshiya; Ueda, Yutaka; Sato, Taku J; Ohgushi, Kenya

2015-10-01

All the iron-based superconductors identified so far share a square lattice composed of Fe atoms as a common feature, despite having different crystal structures. In copper-based materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures. Yet iron-based superconductors without a square-lattice motif have not been found, despite being actively sought out. Here, we report the discovery of pressure-induced superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott insulator with striped-type magnetic ordering below ∼120 K. On the application of pressure this compound exhibits a metal-insulator transition at about 11 GPa, followed by the appearance of superconductivity below Tc = 14 K, right after the onset of the metallic phase. Our findings indicate that iron-based ladder compounds represent promising material platforms, in particular for studying the fundamentals of iron-based superconductivity.

High spin state driven magnetism and thermoelectricity in Mn doped topological insulator Bi2Se3

NASA Astrophysics Data System (ADS)

Maurya, V. K.; Dong, C. L.; Chen, C. L.; Asokan, K.; Patnaik, S.

2018-06-01

We report on the synthesis, and structural - magnetic characterizations of Mn doped Bi2Se3 towards achieving a magnetically doped topological insulator. High quality single crystals of MnxBi2-xSe3 (x = 0, 0.03, 0.05, 0.1) are grown and analysed by X-ray diffraction (XRD), Low Energy Electron Diffraction (LEED), Scanning electron microscopy (SEM), and X-ray absorption near-edge structure spectroscopy (XANES). Magnetic properties of these samples under ZFC-FC protocol and isothermal magnetization confirm ferromagnetic correlation above x = 0.03 value. XANES measurements confirm that the dopant Mn is in Mn2+ state. This is further reconfirmed to be in high spin state by fitting magnetic data with Brillouin function for J = 5/2. Both Hall and Seebeck measurements indicate a sign change of charge carriers above x = 0.03 value of Mn doping. We propose Mn doped Bi2Se3 to be a potential candidate for electromagnetic and thermoelectric device applications involving topological surface states.

Quantum control of topological defects in magnetic systems

NASA Astrophysics Data System (ADS)

Takei, So; Mohseni, Masoud

2018-02-01

Energy-efficient classical information processing and storage based on topological defects in magnetic systems have been studied over the past decade. In this work, we introduce a class of macroscopic quantum devices in which a quantum state is stored in a topological defect of a magnetic insulator. We propose noninvasive methods to coherently control and read out the quantum state using ac magnetic fields and magnetic force microscopy, respectively. This macroscopic quantum spintronic device realizes the magnetic analog of the three-level rf-SQUID qubit and is built fully out of electrical insulators with no mobile electrons, thus eliminating decoherence due to the coupling of the quantum variable to an electronic continuum and energy dissipation due to Joule heating. For a domain wall size of 10-100 nm and reasonable material parameters, we estimate qubit operating temperatures in the range of 0.1-1 K, a decoherence time of about 0.01-1 μ s , and the number of Rabi flops within the coherence time scale in the range of 102-104 .

Experimental results for 2D magnetic resonance electrical impedance tomography (MR-EIT) using magnetic flux density in one direction.

PubMed

Birgül, Ozlem; Eyüboğlu, B Murat; Ider, Y Ziya

2003-11-07

Magnetic resonance electrical impedance tomography (MR-EIT) is an emerging imaging technique that reconstructs conductivity images using magnetic flux density measurements acquired employing MRI together with conventional EIT measurements. In this study, experimental MR-EIT images from phantoms with conducting and insulator objects are presented. The technique is implemented using the 0.15 T Middle East Technical University MRI system. The dc current method used in magnetic resonance current density imaging is adopted. A reconstruction algorithm based on the sensitivity matrix relation between conductivity and only one component of magnetic flux distribution is used. Therefore, the requirement for object rotation is eliminated. Once the relative conductivity distribution is found, it is scaled using the peripheral voltage measurements to obtain the absolute conductivity distribution. Images of several insulator and conductor objects in saline filled phantoms are reconstructed. The L2 norm of relative error in conductivity values is found to be 13%, 17% and 14% for three different conductivity distributions.

Zigzag nanoribbons of two-dimensional silicene-like crystals: magnetic, topological and thermoelectric properties.

PubMed

Wierzbicki, Michał; Barnaś, Józef; Swirkowicz, Renata

2015-12-09

The effects of electron-electron and spin-orbit interactions on the ground-state magnetic configuration and on the corresponding thermoelectric and spin thermoelectric properties in zigzag nanoribbons of two-dimensional hexagonal crystals are analysed theoretically. The thermoelectric properties of quasi-stable magnetic states are also considered. Of particular interest is the influence of Coulomb and spin-orbit interactions on the topological edge states and on the transition between the topological insulator and conventional gap insulator states. It is shown that the interplay of both interactions also has a significant impact on the transport and thermoelectric characteristics of the nanoribbons. The spin-orbit interaction also determines the in-plane magnetic easy axis. The thermoelectric properties of nanoribbons with in-plane magnetic moments are compared to those of nanoribbons with edge magnetic moments oriented perpendicularly to their plane. Nanoribbons with ferromagnetic alignment of the edge moments are shown to reveal spin thermoelectricity in addition to the conventional one.

Structure and physical properties of YCoO3 at temperatures up to 1000K

NASA Astrophysics Data System (ADS)

Knížek, K.; Jirák, Z.; Hejtmánek, J.; Veverka, M.; Maryško, M.; Hauback, B. C.; Fjellvåg, H.

2006-06-01

The crystal structure of perovskite YCoO3 has been studied by neutron powder diffraction up to high temperatures. The orthorhombic Pbnm symmetry is confirmed in the whole temperature range. A significant isotropic enlargement of CoO6 octahedra is evidenced above 600K leading to unit cell expansion and increased octahedral tilting. Supported by complementary physical measurements, the origin of anomalous expansion is identified with a gradual transition of Co3+ ions from the diamagnetic low-spin (S=0) ground state to excited magnetic states with spin S=1 or 2. The magnetic transition is closely followed by a broad resistivity transition of the insulator-metal type, centered at 750K . The changes in magnetic susceptibility, electric resistivity, thermopower and thermal conductivity associated with transitions in YCoO3 are discussed in comparison with similar data on related perovskite LaCoO3 .

Robust ferromagnetism carried by antiferromagnetic domain walls

NASA Astrophysics Data System (ADS)

Hirose, Hishiro T.; Yamaura, Jun-Ichi; Hiroi, Zenji

2017-02-01

Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

Robust ferromagnetism carried by antiferromagnetic domain walls

PubMed Central

Hirose, Hishiro T.; Yamaura, Jun-ichi; Hiroi, Zenji

2017-01-01

Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics. PMID:28195565

Observation of spin-glass behavior in homogeneous (Ga,Mn)N layers grown by reactive molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Dhar, S.; Brandt, O.; Trampert, A.; Friedland, K. J.; Sun, Y. J.; Ploog, K. H.

2003-04-01

We present a detailed study of the magnetic properties of (Ga,Mn)N layers grown directly on 4H-SiC substrates by reactive molecular-beam epitaxy. X-ray diffraction and transmission electron microscopy demonstrates that homogeneous (Ga,Mn)N alloys of high crystal quality can be synthesized by this growth method up to a Mn-content of 10 12 %. Using a variety of magnetization experiments (temperature-dependent dc magnetization, isothermal remanent magnetization, frequency and field dependent ac susceptibility), we demonstrate that insulating (Ga,Mn)N alloys represent a Heisenberg spin-glass with a spin-freezing temperature around 4.5 K. We discuss the origins of this spin-glass characteristics in terms of the deep-acceptor nature of Mn in GaN and the resulting insulating character of this compound.

Phosphoric acid addition effect on the microstructure and magnetic properties of iron-based soft magnetic composites

NASA Astrophysics Data System (ADS)

Hsiang, Hsing-I.; Fan, Liang-Fang; Hung, Jia-Jing

2018-02-01

The phosphoric acid addition effect on phosphate insulation coating microstructure was investigated in this study. The relationships between the phosphate insulation coating microstructure and temperature resistance, corrosion resistance and magnetic properties of iron-based soft magnetic composites (SMCs) were studied by using SEM, TEM/EDS and FTIR. It was observed that an iron phosphate/carbonyl iron core/shell structure is formed with carbonyl iron powder after phosphatizing treatment. The iron phosphate phase was identified as amorphous and its thickness increased from 30 nm to 60 nm as the phosphoric acid concentration was increased from 1 wt% to 2 wt%. When the phosphoric acid concentration was further increased to 5 wt%, the excess iron phosphate precipitates between the soft magnetic composite particles. The temperature and corrosion resistance and resistivity of the iron-based SMCs can be effectively improved using carbonyl iron powders after phosphatizing. The initial permeability of the iron-based SMCs decreased with increasing phosphoric acid concentration due to thicker insulation layer formation. However, the imaginary permeability below the domain wall displacement resonance frequency decreased with increasing phosphoric acid concentration. The DC-bias superposition characteristic can also be improved by increasing the phosphoric acid concentration. Iron-based SMCs with superior temperature and corrosion resistance, initial permeability, magnetic loss and DC-bias superposition characteristics can be obtained by controlling the phosphoric acid concentration during phosphatizing to adjust the iron phosphate precipitate thickness on the iron powder surface.

An approach to improving the signal-to-optical-noise ratio of pulsed magnetic field photonic sensors

NASA Astrophysics Data System (ADS)

Wang, Jiang-ping; Li, Yu-quan

2008-12-01

During last years, interest in pulsed magnetic field sensors has widely increased. In fact, magnetic field measurement has a critical part in various scientific and technical areas. In order to research on pulsed magnetic field characteristic and corresponding measuring and defending means, a sensor with high immunity to electrical noise, high sensitivity, high accuracy and wide dynamic range is needed. The conventional magnetic field measurement system currently use active metallic probes which can disturb the measuring magnetic field and make sensor very sensitive to electromagnetic noise. Photonic magnetic field sensor exhibit great advantages with respect to the electronic ones: a very good galvanic insulation, high sensitivity and very wide bandwidth. Photonic sensing technology is fit for demand of a measure pulsed magnetic field. A type of pulsed magnetic field photonic sensor has been designed, analyzed, and tested. The cross polarization angle in photonic sensor effect on the signal-to-optical-noise ratio is theoretically analyzed in this paper. A novel approach for improving the signal-to-optical-noise ratio of pulsed magnetic field sensors was proposed. The experiments have proved that this approach is practical. The theoretical analysis and simulation results show that the signal-to-optical-noise ratio can potentially be considerably improved by setup suitable for the cross polarization angle.

Tailorable advanced blanket insulation using aluminoborosilicate and alumina batting

NASA Technical Reports Server (NTRS)

Calamito, Dominic P.

1989-01-01

Two types of Tailorable Advanced Blanket Insulation (TABI) flat panels for Advanced Space Transportation Systems were produced. Both types consisted of integrally woven, 3-D fluted core having parallel faces and connecting ribs of Nicalon yarns. The triangular cross section flutes of one type was filled with mandrels of processed Ultrafiber (aluminoborosilicate) stitchbonded Nextel 440 fibrous felt, and the second type wall filled with Saffil alumina fibrous felt insulation. Weaving problems were minimal. Insertion of the fragile insulation mandrels into the fabric flutes was improved by using a special insertion tool. An attempt was made to weave fluted core fabrics from Nextel 440 yarns but was unsuccessful because of the yarn's fragility. A small sample was eventually produced by an unorthodox weaving process and then filled with Saffil insulation. The procedures for setting up and weaving the fabrics and preparing and inserting insulation mandrels are discussed. Characterizations of the panels produced are also presented.

Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures

PubMed Central

Renshaw Wang, X.; Sun, L.; Huang, Z.; Lü, W. M.; Motapothula, M.; Annadi, A.; Liu, Z. Q.; Zeng, S. W.; Venkatesan, T.; Ariando

2015-01-01

We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context. PMID:26669575

Studies of an extractor geometry magnetically insulated ion diode with an exploding metal film anode plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rondeau, G.D.

1989-01-01

Magnetically insulated diodes (MIDs) are of interest as ion sources for inertial confinement fusion. The authors examined several issues that are of concern with MIDs, including ion turn-on delay and anode plasma production, and diode impedance history and particle current scaling with the applied magnetic field and gas spacing. The LION pulsed power generator (1.5 MV, 4 {Omega}, 40 ns pulse length) was used to power an extractor geometry magnetically insulated (radical magnetic field) ion beam diode. The diode was studied with three anode configurations. In the first, with epoxy-filled-groove (epoxy) anodes, scaling of the ion and electron currents withmore » the gap and the magnetic field was examined. He found that the observed ion current is consistent with a diode model that has been successful with barrel geometry MIDs. The electron leakage current scaled proportionally to 1/Bd{sup 2}, where d is the anode-cathode gap spacing and B is the magnetic field strength. Studies of ion beam propagation in vacuum showed that space charge non-neutrality near the magnetic field coils caused the beam to expand initially. Later in the ion pulse (20 to 30 ns), the beam expansion became much less severe. The second anode configuration utilized an electron collector protruding above an epoxy anode surface. With the collector, he observed less bremsstrahlung across the active anode region. The last anode configuration studied was the exploding metal film active anode plasma source (EMFAAPS). Current from the accelerator was directed by an electron collector or a plasma opening switch through a thin aluminum film, which exploded to form the anode plasma.« less

Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3Ru2O7

NASA Astrophysics Data System (ADS)

Hossain, M. A.; Bohnenbuck, B.; Chuang, Y.-D.; Geck, J.; Tokura, Y.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Sawatzky, G. A.; Damascelli, A.

2010-03-01

We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr3(Ru1-xMnx)2O7, performed at both Ru and Mn L-edges. Resonant magnetic superstructure reflections, which indicate an incipient instability of the parent compound, are detected below the transition. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x˜0.05 Mn substitution. In collaboration with A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley Lab), I. Zegkinoglou, M.W. Haverkort (MPI, Stuttgart), I.S. Elfimov, D.G. Hawthorn (UBC), R. Mathieu, S. Satow, H. Takagi (Tokyo), H.-H. Wu and C. Sch"ußler-Langeheine (Cologne).

Signatures of in-plane and out-of-plane magnetization generated by synchrotron radiation in magnetically doped and pristine topological insulators

NASA Astrophysics Data System (ADS)

Shikin, A. M.; Rybkina, A. A.; Estyunin, D. A.; Sostina, D. M.; Voroshnin, V. Yu.; Klimovskikh, I. I.; Rybkin, A. G.; Surnin, Yu. A.; Kokh, K. A.; Tereshchenko, O. E.; Petaccia, L.; Di Santo, G.; Skirdkov, P. N.; Zvezdin, K. A.; Zvezdin, A. K.; Kimura, A.; Chulkov, E. V.; Krasovskii, E. E.

2018-06-01

Possibility of in-plane and out-of-plane magnetization generated by synchrotron radiation (SR) in magnetically doped and pristine topological insulators (TIs) is demonstrated and studied by angle-resolved photoemission spectroscopy. We show experimentally and by ab initio calculations how nonequal depopulation of the Dirac cone (DC) states with opposite momenta in V-doped and pristine TIs generated by linearly polarized SR leads to the hole-generated uncompensated spin accumulation followed by the SR-induced magnetization via spin-torque effect. Moreover, the photoexcitation of the DC is asymmetric, and it varies with the photon energy. We find a relation between the photoexcitation asymmetry, the generated spin accumulation, and the induced in-plane and out-of-plane magnetic field. Experimentally the SR-generated in-plane and out-of-plane magnetization is confirmed by the k∥ shift of the DC position and by the gap opening at the Dirac point even above the Curie temperature. Theoretical predictions and estimations of the measurable physical quantities substantiate the experimental results.

Noncollinear magnetic ordering in the Shastry-Sutherland Kondo lattice model: Insulating regime and the role of Dzyaloshinskii-Moriya interaction

NASA Astrophysics Data System (ADS)

Shahzad, Munir; Sengupta, Pinaki

2017-12-01

We investigate the necessary conditions for the emergence of complex, noncoplanar magnetic configurations in a Kondo lattice model with classical local moments on the geometrically frustrated Shastry-Sutherland lattice and their evolution in an external magnetic field. We demonstrate that topologically nontrivial spin textures, including a new canted flux state, with nonzero scalar chirality arise dynamically from realistic short-range interactions. Our results establish that a finite Dzyaloshinskii-Moriya (DM) interaction is necessary for the emergence of these novel magnetic states when the system is at half filling, for which the ground state is insulating. We identify the minimal set of DM vectors that are necessary for the stabilization of chiral magnetic phases. The noncoplanarity of such structures can be tuned continually by applying an external magnetic field. This is the first part in a series of two papers; in the following paper the effects of frustration, thermal fluctuations, and magnetic field on the emergence of novel noncollinear states at metallic filling of itinerant electrons are discussed. Our results are crucial in understanding the magnetic and electronic properties of the rare-earth tetraboride family of frustrated magnets with separate spin and charge degrees of freedom.

Spin-polarized charge transport in HgTe/CdTe quantum well topological insulator under a ferromagnetic metal strip

NASA Astrophysics Data System (ADS)

Wu, Zhenhua; Luo, Kun; Yu, Jiahan; Wu, Xiaobo; Lin, Liangzhong

2018-02-01

Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.

Magnon rainbows filtered through phonon clouds

NASA Astrophysics Data System (ADS)

Boona, Stephen R.

2016-06-01

The study of heat flow in magnetic insulators is a topic of significant interest in spin caloritronics, especially for understanding the nuanced origins of the spin Seebeck effect (SSE). Recent work by Diniz and Costa (2016 New J. Phys. 18 052002) provides insight into this subject by presenting a microscopic model for the spectral dependence of magnon-phonon interactions in magnetic insulators, which has been a challenging puzzle for decades. Their new paper shows that phonon-mediated magnon-magnon interactions affect the lifetime of magnons differently depending on the magnon wavelength. As a result, low energy magnons transport spin more efficiently, and are more sensitive to applied magnetic fields. These results help explain some unexpected behavior in the SSE recently reported in several experiments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartstein, M.; Toews, W. H.; Hsu, Y. -T.

The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator–metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. In this paper, we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB 6 positioned close to the insulator–metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including amore » sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Finally, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB 6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.« less

Deuteron flux production in a small high-voltage high-current diode with pulsed magnetic insulation

NASA Astrophysics Data System (ADS)

Shikanov, A. E.; Vovchenko, E. D.; Isaev, A. A.; Kozlovskii, K. I.; Shatokhin, V. L.

2017-06-01

The results of new studies on the production of accelerated deuteron fluxes in a small ion diode with pulsed magnetic insulation of electrons have been presented. A plasma anode of the diode has been formed under the action of a 1.06 μm laser radiation with a pulse duration of 10 ns, a pulse energy of up to 1 J, and a power density on the target of 5 × 1015 W m-2. An accelerating voltage of up to 300 kV has been created using an Arkad'ev-Marx pulsed voltage generator with a stored energy of 50 J and a repetition rate of 1 Hz. A magnetic field of higher than 0.6 T for insulating electrons has been formed by a current pulse of the first cascade of the generator in a spiral line before a conical cascade. Stable deuteron acceleration to 300 keV with a current of up to 1.5 kA and a pulse duration of 0.3 μs has been achieved.

Requirements for self-magnetically insulated transmission lines

DOE PAGES

VanDevender, J. Pace; Pointon, Timothy D.; Seidel, David B.; ...

2015-03-01

Self-magnetically insulated transmission lines (MITLs) connect pulsed-power drivers with a load. Although the technology was originally developed in the 1970s and is widely used today in super power generators, failure of the technology is the principal limitation on the power that can be delivered to an experiment. We address issues that are often overlooked, rejected after inadequate simulations, or covered by overly conservative assumptions: (i) electron retrapping in coupling MITLs to loads, (ii) the applicability of collisionless versus collisional electron flow, (iii) power transport efficiency as a function of the geometry at the beginning of the MITL, (iv) gap closuremore » and when gap closure can be neglected, and (v) the role of negative ions in causing anode plasmas and enhancing current losses. We suggest a practical set of conservative design requirements for self-magnetically insulated electron flow based on the results discussed in this paper and on previously published results. The requirements are not necessarily severe constraints in all MITL applications; however, each of the 18 suggested requirements should be examined in the design of a MITL and in the investigation of excessive losses.« less

Current-induced strong diamagnetism in the Mott insulator Ca2RuO4

NASA Astrophysics Data System (ADS)

Sow, Chanchal; Yonezawa, Shingo; Kitamura, Sota; Oka, Takashi; Kuroki, Kazuhiko; Nakamura, Fumihiko; Maeno, Yoshiteru

2017-11-01

Mott insulators can host a surprisingly diverse set of quantum phenomena when their frozen electrons are perturbed by various stimuli. Superconductivity, metal-insulator transition, and colossal magnetoresistance induced by element substitution, pressure, and magnetic field are prominent examples. Here we report strong diamagnetism in the Mott insulator calcium ruthenate (Ca2RuO4) induced by dc electric current. The application of a current density of merely 1 ampere per centimeter squared induces diamagnetism stronger than that in other nonsuperconducting materials. This change is coincident with changes in the transport properties as the system becomes semimetallic. These findings suggest that dc current may be a means to control the properties of materials in the vicinity of a Mott insulating transition.

A Systematic Study of the Effect of Spin-Orbit Interaction on Properties of Tetravalent and Pentavalent Iridate Compounds

NASA Astrophysics Data System (ADS)

Terzic, Jasminka

Previous studies of iridates have shown that an interplay of strong SOI, Coulomb interaction U, Hund's rule coupling and crystalline electric fields result in unexpected insulating states with complex magnetic states. The novel Jeff =1/2 insulating state first observed in Sr2IrO4 is a direct consequence of such an intriguing interplay and is one of the central foci of this dissertation study. The work presented here consists of three projects: (1) Effects of Tb doping on Sr2IrO4 having tetravalent Ir4+ (5d5) ions; (2) Emergence of unexpected magnetic states in double-perovskite (Ba1-xSr x)2YIrO6 with pentavalent Ir5+ (5d4) ions in the presence of strong SOI, and ( 3) The coexistence of a charge and magnetic order in a magnetic dimer chain system, Ba5AlIr2O11, which has both tetravalent Ir4+ (5d5) and pentavalent Ir5+ (5d4) ions. A significant portion of this dissertation will focus on Tb doped Sr 2IrO4. A central finding of this work is that slight Tb doping (3%) readily suppresses the antiferromagnetic state but retains the insulating state, indicating an unusual correlation between the magnetic and insulating states as a result of the presence of the strong SOI. However, SOI is not the only significant phenomenon. The study on the double-perovskite (Ba1-xSrx)2YIrO6 revealed an exotic magnetic ground state, in sharp contrast to the anticipated singlet ground state in the strong SOI limit, raising an urgent question: is SOI as dominant as was initially anticipated in the iridates? Finally, this study turns to a system containing both Ir4+ and Ir5+ ions, Ba5AlIr2O11. This system features dimer chains of two inequivalent octahedra occupied by tetravalent Ir4+ (5d5) and pentavalent Ir 5+ (5d4) ions respectively. Ba5AlIr 2O11 undergoes charge and magnetic order transitions at 210 K and 4.5 K, respectively. SOI-driven physics is a rapidly evolving field with an ever growing list of theoretical proposals which have enjoyed very limited experimental confirmation thus far. This study has revealed a large range of interesting phenomena in the iridates that defy conventional theoretical arguments and that help to fill an experimental void in this field. Keywords: spin-orbit interaction (SOI), iridates, double exchange, Mott insulator, Coulomb interaction, Hund's rule coupling.

Two-Dimensional J eff = 1 / 2 Antiferromagnetic Insulator Unraveled from Interlayer Exchange Coupling in Artificial Perovskite Iridate Superlattices

DOE PAGES

Hao, Lin; Meyers, D.; Frederick, Clayton; ...

2017-07-14

We report an experimental investigation of the two-dimensional J eff=1/2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO 3) 1, (SrTiO 3) m] (m=1, 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the m = 2 and m = 3 samples than the m = 1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO 3 layer enhances the effective electron-electron correlation and strengthens the Mott phase. Themore » significant reduction of the Néel temperature from 150 K for m = 1 to 40 K for m = 2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO 3 layer number m, for maintaining canting-induced weak ferromagnetism. In conclusion, the nearly unaltered transition temperature between the m = 2 and the m = 3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.« less

Two-Dimensional J eff = 1 / 2 Antiferromagnetic Insulator Unraveled from Interlayer Exchange Coupling in Artificial Perovskite Iridate Superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Lin; Meyers, D.; Frederick, Clayton

We report an experimental investigation of the two-dimensional J eff=1/2 antiferromagnetic Mott insulator by varying the interlayer exchange coupling in [(SrIrO 3) 1, (SrTiO 3) m] (m=1, 2 and 3) superlattices. Although all samples exhibited an insulating ground state with long-range magnetic order, temperature-dependent resistivity measurements showed a stronger insulating behavior in the m = 2 and m = 3 samples than the m = 1 sample which displayed a clear kink at the magnetic transition. This difference indicates that the blocking effect of the excessive SrTiO 3 layer enhances the effective electron-electron correlation and strengthens the Mott phase. Themore » significant reduction of the Néel temperature from 150 K for m = 1 to 40 K for m = 2 demonstrates that the long-range order stability in the former is boosted by a substantial interlayer exchange coupling. Resonant x-ray magnetic scattering revealed that the interlayer exchange coupling has a switchable sign, depending on the SrTiO 3 layer number m, for maintaining canting-induced weak ferromagnetism. In conclusion, the nearly unaltered transition temperature between the m = 2 and the m = 3 demonstrated that we have realized a two-dimensional antiferromagnet at finite temperatures with diminishing interlayer exchange coupling.« less

Conductivity Variation Observed by Polarization and Depolarization Current Measurements of High-Voltage Equipment Insulation System

NASA Astrophysics Data System (ADS)

Jamail, Nor Akmal Mohd; Piah, Mohamed Afendi Mohamed; Muhamad, Nor Asiah

2012-09-01

Nondestructive and time domain dielectric measurement techniques such as polarization and depolarization current (PDC) measurements have recently been widely used as a potential tool for determining high-voltage insulation conditions by analyzing the insulation conductivity. The variation in the conductivity of an insulator was found to depend on several parameters: the difference between the polarization and depolarization currents, geometric capacitance, and the relative permittivity of the insulation material. In this paper the conductivities of different types of oil-paper insulation material are presented. The insulation conductivities of several types of electrical apparatus were simulated using MATLAB. Conductivity insulation was found to be high at high polarizations and at the lowest depolarization current. It was also found to increase with increasing relative permittivity as well as with decreasing geometric capacitance of the insulating material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larson, Amber M.; Wilfong, Brandon; Moetakef, Pouya

A metal–insulator transition tuned by application of an external magnetic field occurs in the quasi-one dimensional system Bi1.7V8O16, which contains a mix of S = 1 and S = 1/2 vanadium cations. Unlike all other known vanadates, the magnetic susceptibility of Bi1.7V8O16 diverges in its insulating state, although no long-range magnetic ordering is observed from neutron diffraction measurements, possibly due to the frustrated geometry of the triangular ladders. Magnetotransport measurements reveal that the transition temperature is suppressed upon application of an external magnetic field, from 62.5 K at zero field to 40 K at 8 T. This behavior is bothmore » hysteretic and anisotropic, suggesting t2g orbital ordering of the V3+ and V4+ cations drives a first-order structural transition. Single crystal X-ray diffraction reveals a charge density wave of Bi3+ cations with a propagation vector of 0.846c*, which runs parallel to the triangular chain direction. Neutron powder diffraction measurements show a first-order structural transition, characterized by the coexistence of two tetragonal phases near the metal–insulator transition. Finally, we discuss the likelihood that ferromagnetic V–V dimers coexist with a majority spin-singlet state below the transition in Bi1.7V8O16.« less

Static and Dynamic Performance of Newly Developed ITER Relevant Insulation Systems after Neutron Irradiation

NASA Astrophysics Data System (ADS)

Prokopec, R.; Humer, K.; Fillunger, H.; Maix, R. K.; Weber, H. W.

2006-03-01

Fiber reinforced plastics will be used as insulation systems for the superconducting magnet coils of ITER. The fast neutron and gamma radiation environment present at the magnet location will lead to serious material degradation, particularly of the insulation. For this reason, advanced radiation-hard resin systems are of special interest. In this study various R-glass fiber / Kapton reinforced DGEBA epoxy and cyanate ester composites fabricated by the vacuum pressure impregnation method were investigated. All systems were irradiated at ambient temperature (340 K) in the TRIGA reactor (Vienna) to a fast neutron fluence of 1×1022 m-2 (E>0.1 MeV). Short-beam shear and static tensile tests were carried out at 77 K prior to and after irradiation. In addition, tension-tension fatigue measurements were used in order to assess the mechanical performance of the insulation systems under the pulsed operation conditions of ITER. For the cyanate ester based system the influence of interleaving Kapton layers on the static and dynamic material behavior was investigated as well.

Polymorphous band structure model of gapping in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

NASA Astrophysics Data System (ADS)

Trimarchi, Giancarlo; Wang, Zhi; Zunger, Alex

2018-01-01

The existence of band gaps in both the antiferromagnetic (AFM) and paramagnetic (PM) phases of the classic NaCl-structure Mott insulators MnO, FeO, CoO, and NiO is traditionally viewed and taught as a manifestation of strong correlation whereby insulation results from electrons moving across the lattice forming states with doubly occupied d orbitals on certain atomic sites and empty d orbitals on other sites. Within such theories, the gap of the AFM and PM phases of these oxides emerges even in the absence of spatial symmetry breaking. The need for such a correlated picture is partially based on the known failure of the commonly used band models for the PM phase that assume for such a spin disordered state the macroscopically averaged NaCl structure, where all transition metal (TM) sites are symmetry-equivalent (a monomorphous description), producing a gapless PM state with zero magnetic moments, in sharp conflict with experiment. Here, we seek to understand the minimum theoretical description needed to capture the leading descriptors of ground state Mott insulation in the classic, 3 d monoxide Mott systems—gapping and moment formation in the AFM and PM phase. As noted by previous authors, the spin-ordered AFM phase in these materials already shows in band theory a significant band gap when one doubles the NaCl unit cell by permitting different potentials for transition-metal atoms with different spins. For the spin-disordered PM phase, we allow analogously larger NaCl-type supercells where each TM site can have different spin direction and local bonding environments (i.e., disordered), yet the total spin is zero. Such a polymorphous description has the flexibility to acquire symmetry-breaking energy-lowering patterns that can lift the degeneracy of the d orbitals and develop large on-site magnetic moments without violating the global, averaged NaCl symmetry. Electrons are exchanged between spin-up and spin-down bands to create closed-shell insulating configurations that lend themselves to a single determinental description. It turns out that such a polymorphous description of the structure within the single-determinant, mean-field, Bloch periodic band structure approach (based on DFT +U ) allows large on-site magnetic moments to develop spontaneously, leading to significant (1-3 eV) band gaps and large local moments in the AFM and PM phases of the classic NaCl-structure Mott insulators MnO, FeO, CoO, and NiO in agreement with experiment. We adapt to the spin disordered polymorphous configurations the "special quasirandom structure" (SQS) construct known from the theory of disordered substitutional alloys whereby supercell approximants which represent the best random configuration average (not individual snapshots) for finite (64, 216 atoms, or larger) supercells of a given lattice symmetry are constructed. We conclude that the basic features of these paradigmatic Mott insulators can be approximated by the physics included in energy-lowering symmetry broken DFT.

Direct measurement of magnon temperature: new insight into magnon-phonon coupling in magnetic insulators.

PubMed

Agrawal, M; Vasyuchka, V I; Serga, A A; Karenowska, A D; Melkov, G A; Hillebrands, B

2013-09-06

We present spatially resolved measurements of the magnon temperature in a magnetic insulator subject to a thermal gradient. Our data reveal an unexpectedly close correspondence between the spatial dependencies of the exchange magnon and phonon temperatures. These results indicate that if--as is currently thought--the transverse spin Seebeck effect is caused by a temperature difference between the magnon and phonon baths, it must be the case that the magnon temperature is spectrally nonuniform and that the effect is driven by the sparsely populated dipolar region of the magnon spectrum.

Intrinsic Tunneling in Phase Separated Manganites

NASA Astrophysics Data System (ADS)

Singh-Bhalla, G.; Selcuk, S.; Dhakal, T.; Biswas, A.; Hebard, A. F.

2009-02-01

We present evidence of direct electron tunneling across intrinsic insulating regions in submicrometer wide bridges of the phase-separated ferromagnet (La,Pr,Ca)MnO3. Upon cooling below the Curie temperature, a predominantly ferromagnetic supercooled state persists where tunneling across the intrinsic tunnel barriers (ITBs) results in metastable, temperature-independent, high-resistance plateaus over a large range of temperatures. Upon application of a magnetic field, our data reveal that the ITBs are extinguished resulting in sharp, colossal, low-field resistance drops. Our results compare well to theoretical predictions of magnetic domain walls coinciding with the intrinsic insulating phase.

Flow impedance in a uniform magnetically insulated transmission line

NASA Astrophysics Data System (ADS)

Mendel, C. W.; Seidel, D. B.

1999-12-01

In two recent publications [C. W. Mendel, Jr. and S. E. Rosenthal, Phys. of Plasmas 2, 1332 (1995), C. W. Mendel, Jr. and S. E. Rosenthal, Phys. of Plasmas 3, 4207 (1996)] relativistic electron flow in cylindrical magnetically insulated transmission lines was analyzed and modeled under the assumption of negligible electron pressure. The model allows power flow in these lines to be accurately calculated under most conditions. The model was developed for coaxial right circular cylindrical electrodes. It is shown here that the model applies equally well to arbitrary cylindrical systems, i.e., systems consisting of electrodes of arbitrary cross section.

Beta > 1 Plasmas

NASA Astrophysics Data System (ADS)

Jones, Robert

2017-10-01

I have suggested that fusion researchers should put more effort into the study of beta > 1 or wall confined plasmas. Magneto-Inertial Fusion and Magnetized Target Fusion projects at Los Alamos National Laboratory are recent examples of this sort of work. Unfortunately, theoretical studies of such systems may be employing overly optimistic models of the magnetic thermal insulation. One might well expect such systems to have stochastic field lines. If that is the case then we might want to employ turbulent thermal insulation as suggested in my papers: Current Science, pg 991, 1988 and Bull. Am. Phys. Soc., Nov. 4, 2009.

Revivals of electron currents and topological-band insulator transitions in 2D gapped Dirac materials

NASA Astrophysics Data System (ADS)

Romera, E.; Bolívar, J. C.; Roldán, J. B.; de los Santos, F.

2016-07-01

We have studied the time evolution of electron wave packets in silicene under perpendicular magnetic and electric fields to characterize topological-band insulator transitions. We have found that at the charge neutrality points, the periodicities exhibited by the wave packet dynamics (classical and revival times) reach maximum values, and that the electron currents reflect the transition from a topological insulator to a band insulator. This provides a signature of topological phase transition in silicene that can be extended to other 2D Dirac materials isostructural to graphene and with a buckled structure and a significant spin-orbit coupling.

Nonequilibrium restoration of duality symmetry in the vicinity of the superconductor-to-insulator transition

NASA Astrophysics Data System (ADS)

Tamir, I.; Doron, A.; Levinson, T.; Gorniaczyk, F.; Tewari, G. C.; Shahar, D.

2017-09-01

The magnetic field driven superconductor-to-insulator transition in thin films is theoretically understood in terms of the notion of vortex-charge duality symmetry. The manifestation of such symmetry is the exchange of roles of current and voltage between the superconductor and the insulator. While experimental evidence obtained from amorphous indium oxide films supported such duality symmetry, it is shown to be broken, counterintuitively, at low temperatures where the insulating phase exhibits discontinuous current-voltage characteristics. Here, we demonstrate that it is possible to effectively restore duality symmetry by driving the system beyond the discontinuity into its high current, far from equilibrium, state.

Self-duality and a Hall-insulator phase near the superconductor-to-insulator transition in indium-oxide films

PubMed Central

Breznay, Nicholas P.; Steiner, Myles A.; Kivelson, Steven Allan; Kapitulnik, Aharon

2016-01-01

We combine measurements of the longitudinal (ρxx) and Hall (ρxy) resistivities of disordered 2D amorphous indium-oxide films to study the magnetic-field tuned superconductor-to-insulator transition (H-SIT) in the T→0 limit. At the critical field, Hc, the full resistivity tensor is T independent with ρxx(Hc)=h/4e2 and ρxy(Hc)=0 within experimental uncertainty in all films (i.e., these appear to be “universal” values); this is strongly suggestive that there is a particle–vortex self-duality at H=Hc. The transition separates the (presumably) superconducting state at HHc, at which the Hall resistance is T independent and roughly equal to its classical value, ρxy≈H/nec, marks an additional crossover to a high-field regime (probably to a Fermi insulator) in which ρxy>H/nec and possibly diverges as T→0. We also highlight a profound analogy between the H-SIT and quantum-Hall liquid-to-insulator transitions (QHIT). PMID:26712029

Magnet-wire wrapping tool for integrated circuits

NASA Technical Reports Server (NTRS)

Takahashi, T. H.

1972-01-01

Wire-dispensing tool which resembles mechanical pencil is used to wrap magnet wire around integrated circuit terminals uniformly and securely without damaging insulative coating on wire. Tool is hand-held and easily manipulated to execute wire wrapping movements.

Understanding the Giant Enhancement of Exchange Interaction in Bi 2 Se 3 - EuS Heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jeongwoo; Kim, Kyoung-Whan; Wang, Hui

2017-07-01

A recent experiment indicated that a ferromagnetic EuS film in contact with a topological insulator Bi 2 Se 3 might show a largely enhanced Curie temperature and perpendicular magnetic anisotropy [F. Katmis et al., Nature (London) 533, 513 (2016).]. Through systematic density functional calculations, we demonstrate that in addition to the factor that Bi 2 Se 3 has a strong spin orbit coupling, the topological surface states are crucial to make these unusual behaviors robust as they hybridize with EuS states and extend rather far into the magnetic layers. The magnetic moments of Eu atoms are nevertheless not much enhanced,more » unlike what was reported in the experiment. Our results and model analyses provide useful insights for how these quantities are linked, and pave a way for the control of properties of magnetic films via contact with topological insulators.« less

Strain and thermally induced magnetic dynamics and spin current in magnetic insulators subject to transient optical grating

NASA Astrophysics Data System (ADS)

Wang, Xi-Guang; Chotorlishvili, Levan; Berakdar, Jamal

2017-07-01

We analyze the magnetic dynamics and particularlythe spin current in an open-circuit ferromagnetic insulator irradiated by two intense, phase-locked laser pulses. The interference of the laser beams generates a transient optical grating and a transient spatio-temporal temperature distribution. Both effects lead to elastic and heat waves at the surface and into the bulk of the sample. The strain induced spin current as well as the thermally induced magnonic spin current are evaluated numerically on the basis of micromagnetic simulations using solutions of the heat equation. We observe that the thermo-elastically induced magnonic spin current propagates on a distance larger than the characteristic size of thermal profile, an effect useful for applications in remote detection of spin caloritronics phenomena. Our findings point out that exploiting strain adds a new twist to heat-assisted magnetic switching and spin-current generation for spintronic applications.

Insulation systems for liquid methane fuel tanks for supersonic cruise aircraft

NASA Technical Reports Server (NTRS)

Brady, H. F.; Delduca, D.

1972-01-01

Two insulation systems for tanks containing liquid methane in supersonic cruise-type aircraft were designed and tested after an extensive materials investigation. One system is an external insulation and the other is an internal wet-type insulation system. Tank volume was maximized by making the tank shape approach a rectangular parallelopiped. One tank was designed to use the external insulation and the other tank to use the internal insulation. Performance of the external insulation system was evaluated on a full-scale tank under the temperature environment of -320 F to 700 F and ambient pressures of ground-level atmospheric to 1 psia. Problems with installing the internal insulation on the test tank prevented full-scale evaluation of performance; however, small-scale testing verified thermal conductivity, temperature capability, and installed density.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

NASA Astrophysics Data System (ADS)

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal-metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces.

PubMed

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M D

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

PubMed Central

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-01-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism. PMID:29333523

Gate- and Light-Tunable pn Heterojunction Microwire Arrays Fabricated via Evaporative Assembly.

PubMed

Park, Jae Hoon; Kim, Jong Su; Choi, Young Jin; Lee, Wi Hyoung; Lee, Dong Yun; Cho, Jeong Ho

2017-02-01

One-dimensional (1D) nano/microwires have attracted considerable attention as versatile building blocks for use in diverse electronic, optoelectronic, and magnetic device applications. The large-area assembly of nano/microwires at desired positions presents a significant challenge for developing high-density electronic devices. Here, we demonstrated the fabrication of cross-stacked pn heterojunction diode arrays by integrating well-aligned inorganic and organic microwires fabricated via evaporative assembly. We utilized solution-processed n-type inorganic indium-gallium-zinc-oxide (IGZO) microwires and p-type organic 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) microwires. The formation of organic TIPS-PEN semiconductor microwire and their electrical properties were optimized by controlling both the amounts of added insulating polymer and the widths of the microwires. The resulting cross-stacked IGZO/TIPS-PEN microwire pn heterojunction devices exhibited rectifying behavior with a forward-to-reverse bias current ratio exceeding 10 2 . The ultrathin nature of the underlying n-type IGZO microwires yielded gate tunability in the charge transport behaviors, ranging from insulating to rectifying. The rectifying behaviors of the heterojunction devices could be modulated by controlling the optical power of the irradiated light. The fabrication of semiconducting microwires through evaporative assembly provides a facile and reliable approach to patterning or positioning 1D microwires for the fabrication of future flexible large-area electronics.

Probing the spin-orbit Mott state in Sr3Ir2O7 by electron doping

NASA Astrophysics Data System (ADS)

Hogan, Thomas C.

Iridium-based members of the Ruddlesden-Popper family of oxide compounds are characterized by a unique combination of energetically comparable effects: crystal-field splitting, spin-orbit coupling, and electron-electron interactions are all present, and the combine to produce a Jeff = 1/2 ground state. In the bilayer member of this series, Sr3Ir2O7, this state manifests as electrically insulating, with unpaired Ir4+ spins aligned along the long axis of the unit cell to produce a G-type antiferromagnet with an ordered moment of 0.36 uB. In this work, this Mott state is destabilized by electron doping via La3+ substitution on the Sr-site to produce (Sr1-x Lax)3Ir2O7. The introduction of carriers initially causes nano-scale phase-separated regions to develop before driving a global insulator-to-metal transition at x=0.04. Coinciding with this transition is the disappearance of evidence of magnetic order in the system in either bulk magnetization or magnetic scattering experiments. The doping also enhances a structural order parameter observed in the parent compound at forbidden reciprocal lattice vectors. A more complete structural solution is proposed to account for this previously unresolved distortion, and also offers an explanation as to the anomalous net ferromagnetism seen prior in bulk measurements. Finally, spin dynamics are probed via a resonant x-ray technique to reveal evidence of spin-dimer-like behavior dominated by inter-plane interactions. This result supports a bond-operator treatment of the interaction Hamiltonian, and also explains the doping dependence of high temperature magnetic susceptibility.

Design and construction of the astronautics refrigerator magnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dresner, L.

1994-05-01

This document reports on the design, construction, and testing of a 7-Tesla, 4-in. bore superconducting magnet for use in the Astronautics Refrigerator Experiment. The magnet is a single-strand, layer-wound, potted solenoid wound with Formvar-insulated SSC strands. The magnet was constructed by American Magnetics, Inc. of Oak Ridge and has been installed in the Astronautics Refrigerator Experiment at the Astronautics Technology Center in Madison, Wisconsin.

Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by Fe impurities [Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by modest Fe substitution

DOE PAGES

Zhu, M.; Wang, Y.; Li, P. G.; ...

2017-05-19

We report the magnetic and electronic properties of the bilayer ruthenate Sr 3Ru 2O 7 upon Fe substitution for Ru. We find that Sr 3(Ru 1-xFe x) 2O 7 shows spin-glass-like phase below 4 K for x = 0.01 and commensurate E-type antiferromagnetically ordered insulating ground state characterized by the propagation vector q c = (0.25 0.25 0) for x ≥ 0.03, in contrast to the paramagnetic metallic state in the parent compound with strong spin fluctuations occurring at wave vectors q = (0.09 0 0) and (0.25 0 0). The observed antiferromagnetic ordering is quasitwo-dimensional with very short correlationmore » length along the c axis, a feature similar to the Mndoped Sr 3Ru 2O 7. Lastly, our results suggest that this ordered ground state is associated with the intrinsic magnetic instability in the pristine compound, which can be readily tipped by the local magnetic coupling between the 3d orbitals of the magnetic dopants and Ru 4d orbitals.« less

Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by Fe impurities [Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by modest Fe substitution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, M.; Wang, Y.; Li, P. G.

We report the magnetic and electronic properties of the bilayer ruthenate Sr 3Ru 2O 7 upon Fe substitution for Ru. We find that Sr 3(Ru 1-xFe x) 2O 7 shows spin-glass-like phase below 4 K for x = 0.01 and commensurate E-type antiferromagnetically ordered insulating ground state characterized by the propagation vector q c = (0.25 0.25 0) for x ≥ 0.03, in contrast to the paramagnetic metallic state in the parent compound with strong spin fluctuations occurring at wave vectors q = (0.09 0 0) and (0.25 0 0). The observed antiferromagnetic ordering is quasitwo-dimensional with very short correlationmore » length along the c axis, a feature similar to the Mndoped Sr 3Ru 2O 7. Lastly, our results suggest that this ordered ground state is associated with the intrinsic magnetic instability in the pristine compound, which can be readily tipped by the local magnetic coupling between the 3d orbitals of the magnetic dopants and Ru 4d orbitals.« less

Compact plasma accelerator

NASA Technical Reports Server (NTRS)

Foster, John E. (Inventor)

2004-01-01

A compact plasma accelerator having components including a cathode electron source, an anodic ionizing gas source, and a magnetic field that is cusped. The components are held by an electrically insulating body having a central axis, a top axial end, and a bottom axial end. The cusped magnetic field is formed by a cylindrical magnet having an axis of rotation that is the same as the axis of rotation of the insulating body, and magnetized with opposite poles at its two axial ends; and an annular magnet coaxially surrounding the cylindrical magnet, magnetized with opposite poles at its two axial ends such that a top axial end has a magnetic polarity that is opposite to the magnetic polarity of a top axial end of the cylindrical magnet. The ionizing gas source is a tubular plenum that has been curved into a substantially annular shape, positioned above the top axial end of the annular magnet such that the plenum is centered in a ring-shaped cusp of the magnetic field generated by the magnets. The plenum has one or more capillary-like orifices spaced around its top such that an ionizing gas supplied through the plenum is sprayed through the one or more orifices. The plenum is electrically conductive and is positively charged relative to the cathode electron source such that the plenum functions as the anode; and the cathode is positioned above and radially outward relative to the plenum.

Search for exotic short-range interactions using paramagnetic insulators

DOE PAGES

Chu, Pinghan; Weisman, E.; Liu, C. -Y.; ...

2015-05-26

We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, nonmagnetic mass in close proximity. An existing experiment has been used to set limits on the electric dipole moment of the electron by probing the magnetization induced in a cryogenic gadolinium gallium garnet sample on application of a strong electric field. With suitable additions, including a movable source mass, this experiment can be used to explore “monopole-dipole” forces on polarized electrons with unique ormore » unprecedented sensitivity. As a result, the solid-state, nonmagnetic construction, combined with the low-noise conditions and extremely sensitive magnetometry available at cryogenic temperatures could lead to a sensitivity over 10 orders of magnitude greater than exiting limits in the range below 1 mm.« less

Operation of a high impedance applied-B extraction ion diode on the SABRE positive polarity linear induction accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson, D.L.; Cuneo, M.E.; McKay, P.F.

We present results from initial experiments with a high impedance applied-B extraction diode on the SABRE ten stage linear induction accelerator (6.7 MV, 300 kA). We have demonstrated efficient coupling of power from the accelerator through an extended MITL (Magnetically Insulated Transmission Line) into a high intensity ion beam. Both MITL electron flow in the diode region and ion diode behavior, including ion source turn-on, virtual cathode formation and evolution, enhancement delay, and ion coupling efficiency, are strongly influenced by the geometry of the diode insulating magnetic field. For our present diode electrode geometry, electrons from the diode feed stronglymore » influence the evolution of the virtual cathode. Both experimental data and particle-in-cell numerical simulations show that uniform insulation of these feed electrons is required for uniform ion emission and efficient diode operation.« less

High-pressure electrical resistivity studies for Ba1-xCsxFe2Se3

NASA Astrophysics Data System (ADS)

Kawashima, C.; Soeda, H.; Takahashi, H.; Hawai, T.; Nambu, Y.; Sato, T. J.; Hirata, Y.; Ohgushi, K.

2017-10-01

High-pressure electrical resistance measurements were performed for iron-based ladder material Ba1-xCsxFe2Se3 (x = 0.25 and 0.65) using a diamond anvil cell (DAC). Recent high-pressure study revealed that iron-based ladder material BaFe2S3 exhibits an insulator-metal transition and superconductivity, and this discovery would provide important insight for understanding the mechanism of iron-based superconductors. Therefore, it is intriguing to investigate the high-pressure properties for the iron-based ladder material Ba1-xCsxFe2Se3 system. The parent compounds BaFe2Se3 and CsFe2Se3 show insulating and magnetic ordering features. For Ba1-xCsxFe2Se3 system, no magnetic ordering is observed for x = 0.25 and minimum charge gap was estimated for x = 0.65. The insulator-metal transitions are observed in both materials.

Magnetoresistance of an Anderson insulator of bosons.

PubMed

Gangopadhyay, Anirban; Galitski, Victor; Müller, Markus

2013-07-12

We study the magnetoresistance of two-dimensional bosonic Anderson insulators. We describe the change in spatial decay of localized excitations in response to a magnetic field, which is given by an interference sum over alternative tunneling trajectories. The excitations become more localized with increasing field (in sharp contrast to generic fermionic excitations which get weakly delocalized): the localization length ξ(B) is found to change as ξ(-1)(B)-ξ(-1)(0)~B(4/5). The quantum interference problem maps onto the classical statistical mechanics of directed polymers in random media (DPRM). We explain the observed scaling using a simplified droplet model which incorporates the nontrivial DPRM exponents. Our results have implications for a variety of experiments on magnetic-field-tuned superconductor-to-insulator transitions observed in disordered films, granular superconductors, and Josephson junction arrays, as well as for cold atoms in artificial gauge fields.

High-pressure electrical resistivity studies for Ba1-xCsxFe2Se3

NASA Astrophysics Data System (ADS)

Kawashima, C.; Soeda, H.; Takahashi, H.; Hawai, T.; Nambu, Y.; Sato, T. J.; Hirata, Y.; Ohgushi, K.

2017-10-01

High-pressure electrical resistance measurements were performed for iron-based ladder material Ba1-xCsxFe2Se3 (x = 0.25 and 0.65) using a diamond anvil cell (DAC). Recent high-pressure study revealed that iron-based ladder material BaFe2S3 exhibits an insulator- metal transition and superconductivity, and this discovery would provide important insight for understanding the mechanism of iron-based superconductors. Therefore, it is intriguing to investigate the high-pressure properties for the iron-based ladder material Ba1-xCsxFe2Se3 system. The parent compounds BaFe2Se3 and CsFe2Se3 show insulating and magnetic ordering features. For Ba1-xCsxFe2Se3 system, no magnetic ordering is observed for x = 0.25 and minimum charge gap was estimated for x = 0.65. The insulator-metal transitions are observed in both materials.

Low-temperature magnetic ordering in the perovskites Pr 1-xA xCoO 3 (A=Ca, Sr)

NASA Astrophysics Data System (ADS)

Deac, Iosif G.; Tetean, Romulus; Balasz, Istvan; Burzo, Emil

2010-05-01

The magnetic and electrical properties of polycrystalline Pr 1-xA xCoO 3 cobaltites with A=Ca, Sr and 0≤ x≤0.5 were studied in the temperature range 4 K≤ T≤1000 K and field up to 7 T. The X-ray analyses show the presence of only one phase having monoclinic or orthorhombic symmetry. The magnetic measurements indicate that the Ca-doped samples have at low temperatures, similar properties to the frustrated magnetic materials. PrCoO 3 is a paramagnetic insulator in the range from 4 to 1000 K. The Sr-doped cobaltites exhibit two phase transitions: a paramagnetic-ferromagnetic (or magnetic phase separated state) phase transition at about 240 K and a second one at about 100 K. The magnetic measurements suggest the presence of magnetic clusters and a change in the nature of magnetic coupling between Co ions at low temperatures. A semiconducting type behavior and high negative magnetoresistance was found for the Ca-doped samples, while the Sr-doped ones were metallic and with negligible magnetoresistance. The results are analyzed in the frame of a phase separation scenario in the presence of the spin-state transitions of Co ions.

Wide gap Chern Mott insulating phases achieved by design

NASA Astrophysics Data System (ADS)

Guo, Hongli; Gangopadhyay, Shruba; Köksal, Okan; Pentcheva, Rossitza; Pickett, Warren E.

2017-12-01

Quantum anomalous Hall insulators, which display robust boundary charge and spin currents categorized in terms of a bulk topological invariant known as the Chern number (Thouless et al Phys. Rev. Lett. 49, 405-408 (1982)), provide the quantum Hall anomalous effect without an applied magnetic field. Chern insulators are attracting interest both as a novel electronic phase and for their novel and potentially useful boundary charge and spin currents. Honeycomb lattice systems such as we discuss here, occupied by heavy transition-metal ions, have been proposed as Chern insulators, but finding a concrete example has been challenging due to an assortment of broken symmetry phases that thwart the topological character. Building on accumulated knowledge of the behavior of the 3d series, we tune spin-orbit and interaction strength together with strain to design two Chern insulator systems with bandgaps up to 130 meV and Chern numbers C = -1 and C = 2. We find, in this class, that a trade-off between larger spin-orbit coupling and strong interactions leads to a larger gap, whereas the stronger spin-orbit coupling correlates with the larger magnitude of the Hall conductivity. Symmetry lowering in the course of structural relaxation hampers obtaining quantum anomalous Hall character, as pointed out previously; there is only mild structural symmetry breaking of the bilayer in these robust Chern phases. Recent growth of insulating, magnetic phases in closely related materials with this orientation supports the likelihood that synthesis and exploitation will follow.

Spin reorientation and Ce-Mn coupling in antiferromagnetic oxypnictide CeMnAsO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Qiang; Tian, Wei; Peterson, Spencer G.

2015-02-18

Structure and magnetic properties of high-quality polycrystlline CeMnAsO, a parent compound of the “1111”-type oxypnictides, have been investigated using neutron powder diffraction and magnetization measurements. We find that CeMnAsO undergoes a C-type antiferromagnetic order with Mn 2+(S = 5/2) moments pointing along the c axis below a relatively high Néel temperature of T N = 347(1) K. Below T SR = 35 K, two simultaneous transitions occur where the Mn moments reorient from the c axis to the ab plane preserving the C-type magnetic order, and Ce moments undergo long-range AFM ordering with antiparallel moments pointing in the ab plane.more » Another transition to a noncollinear magnetic structure occurs below 7 K. The ordered moments of Mn and Ce at 2 K are 3.32(4) μ B and 0.81(4)μ B, respectively. We find that CeMnAsO primarily falls into the category of a local-moment antiferromagnetic insulator in which the nearest-neighbor interaction (J 1) is dominant with J 2 < J 1/2 in the context of J 1 – J 2 – J c model. The spin reorientation transition driven by the coupling between Ce and the transition metal seems to be common to Mn, Fe, and Cr ions, but not to Co and Ni ions in the isostructural oxypnictides. As a result, a schematic illustration of magnetic structures in Mn and Ce sublattices in CeMnAsO is presented.« less

Room-temperature multiferroic and magnetocapacitance effects in M-type hexaferrite BaFe10.2Sc1.8O19

NASA Astrophysics Data System (ADS)

Tang, Rujun; Zhou, Hao; You, Wenlong; Yang, Hao

2016-08-01

The room-temperature multiferroic and magnetocapacitance (MC) effects of polycrystalline M-type hexaferrite BaFe10.2Sc1.8O19 have been investigated. The results show that the magnetic moments of insulating BaFe10.2Sc1.8O19 can be manipulated by the electric field at room temperature, indicating the existence of magnetoelectric coupling. Moreover, large MC effects are also observed around the room temperature. A frequency dependence analysis shows that the Maxwell-Wagner type magnetoresistance effect is the dominant mechanism for MC effects at low frequencies. Both the magnetoelectric-type and non-magnetoelectric-type spin-phonon couplings contribute to the MC effects at high frequencies with the former being the dominant mechanism. The above results show that the hexaferrite BaFe10.2Sc1.8O19 is a room-temperature multiferroic material that can be potentially used in magnetoelectric devices.

Room temperature giant and linear magnetoresistance in topological insulator Bi2Te3 nanosheets.

PubMed

Wang, Xiaolin; Du, Yi; Dou, Shixue; Zhang, Chao

2012-06-29

Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi(2)Te(3) topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

Phase diagram of Ba 2 NaOsO 6, a Mott insulator with strong spin orbit interactions

NASA Astrophysics Data System (ADS)

Liu, W.; Cong, R.; Garcia, E.; Reyes, A. P.; Lee, H. O.; Fisher, I. R.; Mitrović, V. F.

2018-05-01

We report 23Na nuclear magnetic resonance (NMR) measurements of the Mott insulator with strong spin-orbit interaction Ba2NaOsO6 as a function of temperature in different magnetic fields ranging from 7 T to 29 T. The measurements, intended to concurrently probe spin and orbital/lattice degrees of freedom, are an extension of our work at lower fields reported in Lu et al. (2017) [1]. We have identified clear quantitative NMR signatures that display the appearance of a canted ferromagnetic phase, which is preceded by local point symmetry breaking. We have compiled the field temperature phase diagram extending up to 29 T. We find that the broken local point symmetry phase extends over a wider temperature range as magnetic field increases.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zuocheng; Wei, Wei; Yang, Fangyuan

In this paper, we report quantum oscillation studies on the Bi 2Te 3-xS x topological insulator single crystals in pulsed magnetic fields up to 91 T. For the x = 0.4 sample with the lowest bulk carrier density, the surface and bulk quantum oscillations can be disentangled by combined Shubnikov–de Haas and de Hass–van Alphen oscillations, as well as quantum oscillations in nanometer-thick peeled crystals. At high magnetic fields beyond the bulk quantum limit, our results suggest that the zeroth Landau level of topological surface states is shifted due to the Zeeman effect. The g factor of the topological surfacemore » states is estimated to be between 1.8 and 4.5. Lastly, these observations shed new light on the quantum transport phenomena of topological insulators in ultrahigh magnetic fields.« less

Charge transport and magnetization profile at the interface between the correlated metal CaRuO3 and the antiferromagnetic insulator CaMnO3

NASA Astrophysics Data System (ADS)

Freeland, J. W.; Chakhalian, J.; Boris, A. V.; Tonnerre, J.-M.; Kavich, J. J.; Yordanov, P.; Grenier, S.; Zschack, P.; Karapetrova, E.; Popovich, P.; Lee, H. N.; Keimer, B.

2010-03-01

A combination of spectroscopic probes was used to develop a detailed experimental description of the transport and magnetic properties of superlattices composed of the paramagnetic metal CaRuO3 and the antiferromagnetic insulator CaMnO3 . The charge-carrier density and Ru valence state in the superlattices are not significantly different from those of bulk CaRuO3 . The small charge transfer across the interface implied by these observations confirms predictions derived from density-functional calculations. However, a ferromagnetic polarization due to canted Mn spins penetrates 3-4 unit cells into CaMnO3 , far exceeding the corresponding predictions. The discrepancy may indicate the formation of magnetic polarons at the interface.

Chiral Majorana fermion modes in a quantum anomalous Hall insulator-superconductor structure.

PubMed

He, Qing Lin; Pan, Lei; Stern, Alexander L; Burks, Edward C; Che, Xiaoyu; Yin, Gen; Wang, Jing; Lian, Biao; Zhou, Quan; Choi, Eun Sang; Murata, Koichi; Kou, Xufeng; Chen, Zhijie; Nie, Tianxiao; Shao, Qiming; Fan, Yabin; Zhang, Shou-Cheng; Liu, Kai; Xia, Jing; Wang, Kang L

2017-07-21

Majorana fermion is a hypothetical particle that is its own antiparticle. We report transport measurements that suggest the existence of one-dimensional chiral Majorana fermion modes in the hybrid system of a quantum anomalous Hall insulator thin film coupled with a superconductor. As the external magnetic field is swept, half-integer quantized conductance plateaus are observed at the locations of magnetization reversals, giving a distinct signature of the Majorana fermion modes. This transport signature is reproducible over many magnetic field sweeps and appears at different temperatures. This finding may open up an avenue to control Majorana fermions for implementing robust topological quantum computing. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Composite Behavior of Insulated Concrete Sandwich Wall Panels Subjected to Wind Pressure and Suction.

PubMed

Choi, Insub; Kim, JunHee; Kim, Ho-Ryong

2015-03-19

A full-scale experimental test was conducted to analyze the composite behavior of insulated concrete sandwich wall panels (ICSWPs) subjected to wind pressure and suction. The experimental program was composed of three groups of ICSWP specimens, each with a different type of insulation and number of glass-fiber-reinforced polymer (GFRP) shear grids. The degree of composite action of each specimen was analyzed according to the load direction, type of the insulation, and number of GFRP shear grids by comparing the theoretical and experimental values. The failure modes of the ICSWPs were compared to investigate the effect of bonds according to the load direction and type of insulation. Bonds based on insulation absorptiveness were effective to result in the composite behavior of ICSWP under positive loading tests only, while bonds based on insulation surface roughness were effective under both positive and negative loading tests. Therefore, the composite behavior based on surface roughness can be applied to the calculation of the design strength of ICSWPs with continuous GFRP shear connectors.

Current-induced strong diamagnetism in the Mott insulator Ca2RuO4.

PubMed

Sow, Chanchal; Yonezawa, Shingo; Kitamura, Sota; Oka, Takashi; Kuroki, Kazuhiko; Nakamura, Fumihiko; Maeno, Yoshiteru

2017-11-24

Mott insulators can host a surprisingly diverse set of quantum phenomena when their frozen electrons are perturbed by various stimuli. Superconductivity, metal-insulator transition, and colossal magnetoresistance induced by element substitution, pressure, and magnetic field are prominent examples. Here we report strong diamagnetism in the Mott insulator calcium ruthenate (Ca 2 RuO 4 ) induced by dc electric current. The application of a current density of merely 1 ampere per centimeter squared induces diamagnetism stronger than that in other nonsuperconducting materials. This change is coincident with changes in the transport properties as the system becomes semimetallic. These findings suggest that dc current may be a means to control the properties of materials in the vicinity of a Mott insulating transition. Copyright © 2017, American Association for the Advancement of Science.

Evidence for a Finite-Temperature Insulator.

PubMed

Ovadia, M; Kalok, D; Tamir, I; Mitra, S; Sacépé, B; Shahar, D

2015-08-27

In superconductors the zero-resistance current-flow is protected from dissipation at finite temperatures (T) by virtue of the short-circuit condition maintained by the electrons that remain in the condensed state. The recently suggested finite-T insulator and the "superinsulating" phase are different because any residual mechanism of conduction will eventually become dominant as the finite-T insulator sets-in. If the residual conduction is small it may be possible to observe the transition to these intriguing states. We show that the conductivity of the high magnetic-field insulator terminating superconductivity in amorphous indium-oxide exhibits an abrupt drop, and seem to approach a zero conductance at T < 0.04 K. We discuss our results in the light of theories that lead to a finite-T insulator.

Investigations of surface structural, dynamical, and magnetic properties of systems exhibiting multiferroicity, and topological phases by helium scattering spectroscopies

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Batanouny, Maged

2015-08-03

We propose to investigate the surface structural, dynamics and magnetic properties of the novel class of topological insulator crystals, as well as crystals that exhibit multiferroicity, magnetoelectricity and thermoelectricity. Topological insulators (TIs) are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. These exotic metallic states are formed by topological conditions that also render the electrons travelling on such surfaces insensitive to scattering by impurities. The electronic quasi-particles populating the topological surface state are Dirac fermions; they have a linear dispersion and thus are massless just like photons. We propose to investigate the interaction of these massless Dirac fermions with the massive lattice in the newly discovered crystals, Bi2Se3, Bi2Te3 and Sb2Te3. We shall use inelastic helium beam scattering from surfaces to search for related signatures in surface phonon dispersions mappings that cover the entire surface Brillouin zone of these materials. Our recent investigations of the (001) surface of the multiferroic crystals (Li/Na)Cu2O2 revealed an anomalous surface structural behavior where surface Cumore » $$^{2+}$$ row rise above the surface plane as the crystal was cooled. Subsequent worming revealed the onset of a thermally activated incommensurate surface phase, driven by the elevated rows. We are currently investigating the structure of the magnetic phases in these quasi-one-dimensional magnetic rows. Multiferroics are excellent candidates for large magnetoelectric response. We propose to extend this investigation to the class of delafossites which are also multiferroics and have been investigated as good candidates for thermoelectric power devices. They are also typical triangular lattice antiferromagnets with geometric magnetic frustration that leads to helimagnetic structures.« less

Spin and charge ordering in organic conductors investigated by electron spin resonance

NASA Astrophysics Data System (ADS)

Tokumoto, Takahisa D.

This dissertation presents systematic studies on ordered states of organic conductors investigated mainly by Electron Spin Resonance (ESR). First, we describe an introduction to organic conductors. Organic conductors are based on conducting layers of highly planar donor molecules, separated by insulating layers of acceptors. The donor arrangements in the conducting layers determine the three simple parameters, transfer integral t between the donor molecules, onsite Coulomb interaction U and next neighboring Coulomb interaction V. Depending on the values of the above three parameters, a variety of ground states is realized and hence the organic conductors has become a main stream of condensed matter physics. Among many ground states, the main focus is on magnetic orders in this dissertation. Therefore we have employed ESR to probe local magnetic structures. And we cover a basic theory of ESR in paramagnetic/antiferromagnetically ordered states and the experimental realizations. Next, after an introduction to a system with an exchange interaction between d magnetic moments embedded at acceptor sites and pi spins at donor molecules is given, we discuss the effectiveness of systematic studies on isostructural magnetic and non-magnetic acceptor based organic conductors. Then, we go over one of the "exchange coupled" materials, beta-(BDA-TTP)2MCl 4 (M=Fe3+,Ga3+). We examine the origins of the Metal-Insulator transition and the long range antiferromangetic order in the magnetic acceptor based material, where we found the critical importance of the quantum fluctuations of pi spins. Finally, we delineate the magnetic order of alternating easy axes of a class of an organic conductor, tau-(P-(S,S)-DMEDT)2(AuBr2) 1+y, at low temperature/field by ESR. We briefly discuss the origin of this unprecedented magnetic structure in terms of the unstoichiometric ratio of donors to acceptors and the tetragonal symmetry of the unit cell. Then, we report the results of the ultra high field ESR to probe the magnetic structure changes around a hysteretic field induced metal insulator transition.

Structural and magnetic properties of SrMn1-xRuxO3 perovskites

NASA Astrophysics Data System (ADS)

Dabrowski, B.; Kolesnik, S.; Chmaissem, O.; Maxwell, T.

2007-03-01

Ferromagnetism of SrRuO3 is unique among 4d transition metal based perovskite oxides. On substitution of Mn its TC decreases from 163 K to 0 for x˜0.5-0.6 followed by a formation of an antiferromagnetic insulating state at a quantum critical point. The other end member of the SrMn1-xRuxO3 family, a cubic perovskite SrMnO3 is a G-type antiferromagnet with TN=233 K. We have synthesized the complete SrMn1-xRuxO3 solid solution. The polycrystalline samples were characterized by neutron difraction, magnetic, and transport experiments. The incorporation of Ru in the SrMnO3 matrix (0.1<=x<=0.4) results in a phase transition to a C-type antiferromagnetic state accompanied by a cubic-tetragonal transition. The intermediate substitution level induces a spin-glass behavior, due to competing ferro- and antiferromagnetic interactions. Mixed valence Mn^3+/Mn^4+ and Ru^4+/Ru^5+ pairs introduce additional frustration to the magnetic states. The glassy behavior can be observed for x up to 0.7 in the tetragonal structure. Supported by NSF (DMR-0302617) and the U.S. Department of Education

Energy Conservation in the Home.

DTIC Science & Technology

1985-01-01

inch of properly applied mineral wool insulation would provide. See Figure 2.1 (2:11...fiber. Mineral wool insulation is available in several different types, including blankets, blown insulation, poured insulation, and batts. Blankets...sidewalls can be insulated by a contractor who will blow in one ot several loose fill materials (National Mineral Wool Insulation Assn. Inc.). Figure 2.2

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 16 Commercial Practices 1 2014-01-01 2014-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 16 Commercial Practices 1 2013-01-01 2013-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

16 CFR 460.18 - Insulation ads.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Insulation ads. 460.18 Section 460.18... INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values.” (b) If...

High-temperature properties of ceramic fibers and insulations for thermal protection of atmospheric entry and hypersonic cruise vehicles

NASA Technical Reports Server (NTRS)

Kourtides, Demetrius A.; Pitts, William C.; Araujo, Myrian; Zimmerman, R. S.

1988-01-01

Multilayer insulations (MIs) which will operate in the 500 to 1000 C temperature range are being considered for possible applications on aerospace vehicles subject to convective and radiative heating during atmospheric entry. The insulations described consist of ceramic fibers, insulations, and metal foils quilted together with ceramic thread. As these types of insulations have highly anisotropic properties, the total heat transfer characteristics must be determined. Data are presented on the thermal diffusivity and thermal conductivity of four types of MIs and are compared to the baseline Advanced Flexible Reusable Surface Insulation currently used on the Space Shuttle Orbiter. In addition, the high temperature properties of the fibers used in these MIs are discussed. The fibers investigated included silica and three types of aluminoborosilicate (ABS). Static tension tests were performed at temperatures up to 1200 C and the ultimate strain, tensile strength, and tensile modulus of single fibers were determined.

High temperature properties of ceramic fibers and insulations for thermal protection of atmospheric entry and hypersonic cruise vehicles

NASA Technical Reports Server (NTRS)

Kourtides, Demetrius A.; Pitts, William C.; Araujo, Myrian; Zimmerman, R. S.

1988-01-01

Multilayer insulations (MIs) which will operate in the 500 to 1000 C temperature range are being considered for possible applications on aerospace vehicles subject to convective and radiative heating during atmospheric entry. The insulations described consist of ceramic fibers, insulations, and metal foils quilted together with ceramic thread. As these types of insulations have highly anisotropic properties, the total heat transfer characteristics must be determined. Data are presented on the thermal diffusivity and thermal conductivity of four types of MIs and are compared to the baseline Advanced Flexible Reusable Surface Insulation currently used on the Space Shuttle Orbiter. In addition, the high temperature properties of the fibers used in these MIs are discussed. The fibers investigated included silica and three types of aluminoborosilicate (ABS). Static tension tests were performed at temperatures up to 1200 C and the ultimate strain, tensile strength, and tensile modulus of single fibers were determined.

Spin-orbit torque induced switching in a magnetic insulator thin film with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Li, J. X.; Yu, G. Q.; Tang, C.; Wang, K. L.; Shi, J.

Spin-orbit torque (SOT) has been demonstrated to be efficient to manipulate the magnetization in heavy-metal/ferromagnetic metal (HM/FMM) heterostructures. In HM/magnetic insulator (MI) heterostructures, charge currents do not flow in MI, but pure spin currents generated by the spin Hall effect in HM can enter the MI layer to cause magnetization dynamics. Here we report SOT-induced magnetization switching in Tm3Fe5O12/Pt heterostructures, where Tm3Fe5O12 (TmIG) is a MI grown by pulsed laser deposition with perpendicular magnetic anisotropy. The anomalous Hall signal in Pt is used as a probe to detect the magnetization switching. Effective magnetic fields due to the damping-like and field-like torques are extracted using a harmonic Hall detection method. The experiments are carried out in heterostructures with different TmIG film thicknesses. Both the switching and harmonic measurements indicate a more efficient SOT generation in HM/MI than in HM/FMM heterostructures. Our comprehensive experimental study and detailed analysis will be presented. This work was supported as part of the SHINES, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award No. SC0012670.

LHC interaction region quadrupole cryostat design

NASA Astrophysics Data System (ADS)

Nicol, T. H.; Darve, Ch.; Huang, Y.; Page, T. M.

2002-05-01

The cryostat of a Large Hadron Collider (LHC) Interaction Region (IR) quadrupole magnet consists of all components of the inner triplet except the magnet assembly itself. It serves to support the magnet accurately and reliably within the vacuum vessel, to house all required cryogenic piping, and to insulate the cold mass from heat radiated and conducted from the environment. It must function reliably during storage, shipping and handling, normal magnet operation, quenches, and seismic excitations, and must be able to be manufactured at low cost. The major components of the cryostat are the vacuum vessel, thermal shield, multi-layer insulation system, cryogenic piping, and suspension system. The overall design of a cryostat for superconducting accelerator magnets requires consideration of fluid flow, proper selection of materials for their thermal and structural performance at both ambient and operating temperature, and knowledge of the environment to which the magnets will be subjected over the course of their expected operating lifetime. This paper describes the current LHC IR inner triplet quadrupole magnet cryostats being designed and manufactured at Fermilab as part of the US-LHC collaboration, and includes discussions on the structural and thermal considerations involved in the development of each of the major systems.

Metallic behavior induced by potassium doping of the trigonal antiferromagnetic insulator EuMn 2 As 2

DOE PAGES

Anand, V. K.; Johnston, D. C.

2016-07-22

Here, we report magnetic susceptibility χ, isothermal magnetization M, heat capacity C p, and electrical resistivity ρ measurements on undoped EuMn 2As 2 and K-doped Eu 0.96K 0.04Mn 2As 2 and Eu 0.93K 0.07Mn 2As 2 single crystals with the trigonal CaAl 2Si 2-type structure as a function of temperature T and magnetic field H. EuMn 2As 2 has an insulating ground state with an activation energy of 52 meV and exhibits antiferromagnetic (AFM) ordering of the Eu +2 spins S=7/2 at T N1=15 K from C p(T) and χ(T) data with a likely spin-reorientation transition at T N2=5.0 K.more » The Mn +2 3d 5 spins-5/2 exhibit AFM ordering at T N=142 K from all three types of measurements. The M(H) isotherm and χ(T) data indicate that the Eu AFM structure is both noncollinear and noncoplanar. The AFM structure of the Mn spins is also unclear. A 4% substitution of K for Eu in Eu 0.96K 0.04Mn 2As 2 is sufficient to induce a metallic ground state. We found evidence for a difference in the AFM structure of the Eu moments in the metallic crystals from that of undoped EuMn 2As 2 versus both T and H. For metallic Eu 0.96K 0.04Mn 2As 2 and Eu 0.93K 0.07Mn 2As 2, an anomalous S-shape T dependence of ρ related to the Mn magnetism is found. Upon cooling from 200 K, ρ exhibits a strong negative curvature, reaches maximum positive slope at the Mn T N≈150 K, and then continues to decrease but more slowly below T N. Finally, this suggests that dynamic short-range AFM order of the Mn spins above the Mn T N strongly suppresses the resistivity, contrary to the conventional decrease of ρ that is only observed upon cooling below T N of an antiferromagnet.« less

Raman scattering in the Mott insulators LaTiO3 and YTiO3: evidence for orbital excitations.

PubMed

Ulrich, C; Gössling, A; Grüninger, M; Guennou, M; Roth, H; Cwik, M; Lorenz, T; Khaliullin, G; Keimer, B

2006-10-13

Raman scattering is used to observe pronounced electronic excitations around 230 meV--well above the two-phonon range--in the Mott insulators LaTiO3 and YTiO3. Based on the temperature, polarization, and photon energy dependence, the modes are identified as orbital excitations. The observed profiles bear a striking resemblance to magnetic Raman modes in the insulating parent compounds of the superconducting cuprates, indicating an unanticipated universality of the electronic excitations in transition metal oxides.

Plasma/Wall interaction of an insulated material by laser-induced fluorescence diagnostic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Claire, N.; Doveil, F.

2015-07-01

We present Argon Ion Velocity Distribution Function (IVDF) in the vicinity of an insulated BNSiO{sub 2} ceramic and a glass plate in a non magnetized plasma by laser-induced fluorescence diagnostic. Results show the rather surprising self-consistent formation of a positive or inverse sheath in the two cases. The positive plasma potential repels ions from the insulated wall and is not explained by any sheath theory. Electron secondary emission of the ceramic can be a good candidate to explain these results. (authors)

Nanomodified composite magnetic materials and their molding technologies

NASA Astrophysics Data System (ADS)

Timoshkov, I.; Gao, Q.; Govor, G.; Sakova, A.; Timoshkov, V.; Vetcher, A.

2018-05-01

Advanced electro-magnetic machines and systems require new materials with improved properties. Heterogeneous 3D nanomodified soft magnetic materials could be efficiently applied. Multistage technology of iron particle surface nanomodification by sequential oxidation and Si-organic coatings will be reported. The thickness of layers is 0.5-5 nm. Compaction and annealing are the final steps of magnetic parts and components shaping. The soft magnetic composite material shows the features: resistivity is controlled by insulating coating thickness and equals up to ρ =10-4 Ωṡm for metallic state and ρ =104 Ωṡm for insulator state, maximum magnetic permeability is μm = 2500 and μm = 300 respectively, induction is up to Bm=2.1 T. These properties of composite soft magnetic material allow applying for transformers, throttles, stator-rotor of high-efficient and powerful electric machines in 10 kHz-1MGz frequency range. For microsystems and microcomponents application, good opportunity to improve their reliability is the use of nanocomposite materials. Electroplating technology of nanocomposite magnetic materials into the ultra-thick micromolds will be presented. Co-deposition of the soft magnetic alloys with inert hard nanoparticles allows obtaining materials with magnetic permeability up to μm=104, magnetic induction of Bs=(0.62-1.3) T. Such LIGA-like technology will be applied in MEMS to produce high reliable devices with advanced physical properties.

Experimental study of two-dimensional quantum Wigner solid in zero magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Jian; Pfeiffer, L. N.; West, K. W.

2014-03-31

At temperatures T → 0, strongly interacting two-dimensional (2D) electron systems manifest characteristic insulating behaviors that are key for understanding the nature of the ground state in light of the interplay between disorder and electron-electron interaction. In contrast to the hopping conductance demonstrated in the insulating side of the metal-to-insulator transition, the ultra-high quality 2D systems exhibit nonactivated T-dependence of the conductivity even for dilute carrier concentrations down to 7×10{sup 8} cm{sup −2}. The apparent metal-to-insulator transition (MIT) occurs for a large r{sub s} value around 40 for which a Wigner Crystalllization is expected. The magnetoresistance for a series ofmore » carrier densities in the vicinity of the transition exhibits a characteristic sign change in weak perpendicular magnetic field. Within the Wigner Crystallization regime (with r{sub s} > 40), we report an experimental observation of a characteristic nonlinear threshold behavior from a high-resolution dc dynamical response as an evidence for aWigner crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The system under an increasing current drive exhibits voltage oscillations with negative differential resistance. They confirm the coexistence of a moving crystal along with striped edge states as observed for electrons on helium surfaces. Moreover, the threshold is well below the typical classical levels due to a different pinning and depinning mechanism that is possibly related to quantum processes.« less

Magnon Spin Hall Magnetoresistance of a Gapped Quantum Paramagnet.

PubMed

Ulloa, Camilo; Duine, R A

2018-04-27

Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.

Magnon Spin Hall Magnetoresistance of a Gapped Quantum Paramagnet

NASA Astrophysics Data System (ADS)

Ulloa, Camilo; Duine, R. A.

2018-04-01

Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.

Distribution of leakage currents in the cylindrical and conical sections of the magnetically insulated transmission line of the Angara-5-1 facility in experiments with wire arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grabovski, E. V.; Gribov, A. N.; Samokhin, A. A.

2016-08-15

Current leakages in the magnetically insulated transmission lines (MITL) impose restrictions on the transmission of electromagnetic pulses to the load in high-power electrophysical facilities. The multimodule Angara-5-1 facility with an output electric power of up to 6 TW is considered. In this work, the experimental and calculated profiles of leakage currents in two sections of the line are compared when the eight-module facility is loaded by a wire array. The azimuthal distribution of the current in the cylindrical section of the MITL is also considered.

Magnetically driven metal-insulator transition in NaOsO3

NASA Astrophysics Data System (ADS)

Calder, Stuart

2013-03-01

The metal-insulator transition (MIT) is one of the most dramatic manifestations of electron correlations in materials, enjoying interest both for its fundamental nature and technological application. Various mechanisms producing MITs have been extensively considered over the years, including the Mott (electron localization via Coulomb repulsion), Anderson (localization via disorder) and Peierls (localization via distortion of a periodic one-dimensional lattice). One additional route to a MIT proposed by Slater in 1951, in which long-range magnetic order in a three dimensional system drives the MIT, has received relatively little attention, particularly from an experimental viewpoint. Using neutron and x-ray scattering we have shown that the MIT in NaOsO3 is coincident with the onset of long-range commensurate magnetic order at 410 K. Whilst candidate materials have been suggested, our experimental methodology allows the first definitive demonstration of the long predicted Slater MIT. We discuss our results in light of recent work on other 5d systems that contrastingly have been predicted to host a Mott spin-orbit insulating state. Work was supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy (DOE).

Transport in ultrathin gold films decorated with magnetic Gd atoms

NASA Astrophysics Data System (ADS)

Alemani, Micol; Helgren, Erik; Hugel, Addison; Hellman, Frances

2008-03-01

We have performed four-probe transport measurements of ultrathin Au films decorated with Gd ad-atoms. The samples were prepared by quench condensation, i.e., sequential evaporation on a cryogenically cooled substrate under UHV conditions while monitoring the film thickness and resistance. Electrically continuous Au films at thickness of about 2 mono-layers of material are grown on an amorphous Ge wetting layer. The quench condensation method provides a sensitive control on the sample growth process, allowing us to tune the morphological and electrical configuration of the system. The ultrathin gold films develop from an insulating to a metallic state as a function of film thickness. The temperature dependence of the Au conductivity for different thickness is studied. It evolves from hopping transport for the insulating films, to a ln T dependence for thicker films. For gold films in the insulating regime we found a decreasing resistance by adding Gd. This is in agreement with a decreasing tunneling barrier height between metallic atoms. The Gd magnetic moments are randomly oriented for isolated atoms. This magnetic disorder leads to scattering of the charge carriers and a reduced conductivity compared to nonmagnetic materials.

Reliability Improvement of Ground Fault Protection System Using an S-Type Horn Attachment Gap in AC Feeding System

NASA Astrophysics Data System (ADS)

Ajiki, Kohji; Morimoto, Hiroaki; Shimokawa, Fumiyuki; Sakai, Shinya; Sasaki, Kazuomi; Sato, Ryogo

Contact wires used in feeding system for electric railroad are insulated by insulators. However, insulation of an insulator sometimes breaks down by surface dirt of an insulator and contact with a bird. The insulator breakdown derives a ground fault in feeding system. Ground fault will cause a human electric shock and a destruction of low voltage electric equipment. In order to prevent the damage by ground fault, an S-type horn has been applicable as equipped on insulators of negative feeder and protective wire until present. However, a concrete pole breaks down at the time of the ground fault because a spark-over voltage of the S-type horn is higher than a breakdown voltage of a concrete pole. Farther, the S-type horn installed in the steel tube pole does not discharge a case, because the earth resistance of a steel tube pole is very small. We assumed that we could solve these troubles by changing the power frequency spark-over voltage of the S-type horn from 12kV to 3kV. Accordingly, we developed an attachment gap that should be used to change the power frequency spark-over voltage of the S-type horn from 12kV to 3kV. The attachment gap consists of a gas gap arrester and a zinc oxide element. By the dynamic current test and the artificial ground fault test, we confirmed that the attachment gap in the S-type horn could prevent a trouble at the time of the ground fault.

Preparation and properties of the multi-layer aerogel thermal insulation composites

NASA Astrophysics Data System (ADS)

Wang, Miao; Feng, Junzong; Jiang, Yonggang; Zhang, Zhongming; Feng, Jian

2018-03-01

Multi-layer insulation materials possess low radiation thermal conductivity, and excellent thermal insulation property in a vacuum environment. However, the spacers of the traditional multi-layer insulation materials are mostly loose fibers, which lead to more sensitive to the vacuum environmental of serviced. With the vacuum degree declining, gas phases thermal convection increase obviously, and the reflective screen will be severe oxidation, all of these make the thermal insulation property of traditional multi-layer insulation deteriorate, thus limits its application scope. In this paper, traditional multi-layer insulation material is combined with aerogel and obtain a new multi-layer aerogel thermal insulation composite, and the effects of the number, thickness and type of the reflective screens on the thermal insulation properties of the multi-layer composites are also studied. The result is that the thermal insulation property of the new type multi-layer aerogel composites is better than the pure aerogel composites and the traditional multi-layer insulation composites. When the 0.01 mm stainless steel foil as the reflective screen, and the aluminum silicate fiber and silica aerogel as the spacer layer, the layer density of composite with the best thermal insulation property is one layer per millimeter at 1000 °C.

Insulating nanomagnets driven by spin torque

DOE PAGES

Jungfleisch, Matthias B.; Ding, Junjia; Zhang, Wei; ...

2016-11-29

Magnetic insulators, such as yttrium iron garnet (Y 3Fe 5O 12), are ideal materials for ultra-low power spintronics applications due to their low energy dissipation and efficient spin current generation and transmission. Recently, it has been realized that spin dynamics can be driven very effectively in micrometer-sized Y 3Fe 5O 12/Pt heterostructures by spin-Hall effects. We demonstrate here the excitation and detection of spin dynamics in Y 3Fe 5O 12/Pt nanowires by spin-torque ferromagnetic resonance. The nanowires defined via electron-beam lithography are fabricated by conventional room temperature sputtering deposition on Gd 3Ga 5O 12 substrates and lift-off. We observe field-likemore » and anti-damping-like torques acting on the magnetization precession, which are due to simultaneous excitation by Oersted fields and spin-Hall torques. The Y 3Fe 5O 12/Pt nanowires are thoroughly examined over a wide frequency and power range. We observe a large change in the resonance field at high microwave powers, which is attributed to a decreasing effective magnetization due to microwave absorption. By comparing different nanowire widths, the importance of geometrical confinements for magnetization dynamics becomes evident. In conclusion, our results are the first stepping stones toward the realization of integrated magnonic logic devices based on insulators, where nanomagnets play an essential role.« less

B a2NiOs O6 : A Dirac-Mott insulator with ferromagnetism near 100 K

NASA Astrophysics Data System (ADS)

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad; Yuan, Ya-Hua; Shirako, Yuichi; Tsujimoto, Yoshihiro; Matsushita, Yoshitaka; Hu, Zhiwei; Kuo, Chang-Yang; Tjeng, Liu Hao; Pi, Tun-Wen; Soo, Yun-Liang; He, Jianfeng; Tanaka, Masahiko; Katsuya, Yoshio; Richter, Manuel; Yamaura, Kazunari

2016-12-01

The ferromagnetic semiconductor B a2NiOs O6 (Tmag˜100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [F m -3 m ; a =8.0428 (1 )Å ], where the N i2 + and O s6 + ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of O s6 + plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag<180 K ), the spin-gapless semiconductor M n2CoAl (Tmag˜720 K ), and the ferromagnetic insulators EuO (Tmag˜70 K ) and B i3C r3O11 (Tmag˜220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of B a2NiOs O6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.

B a 2 NiOs O 6 : A Dirac-Mott insulator with ferromagnetism near 100 K

DOE PAGES

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad; ...

2016-12-28

In this study, the ferromagnetic semiconductor Ba 2NiOsO 6 ( T mag ~ 100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m ; a = 8.0428 ( 1 ) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >more » 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te ( T mag < 180 K ), the spin-gapless semiconductor Mn 2 CoAl ( T mag ~ 720 K ), and the ferromagnetic insulators EuO ( T mag ~ 70 K ) and Bi 3Cr 3O 11 ( T mag ~ 220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.« less

B a 2 NiOs O 6 : A Dirac-Mott insulator with ferromagnetism near 100 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad

In this study, the ferromagnetic semiconductor Ba 2NiOsO 6 ( T mag ~ 100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m ; a = 8.0428 ( 1 ) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >more » 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te ( T mag < 180 K ), the spin-gapless semiconductor Mn 2 CoAl ( T mag ~ 720 K ), and the ferromagnetic insulators EuO ( T mag ~ 70 K ) and Bi 3Cr 3O 11 ( T mag ~ 220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.« less

Laser Heating of the Core-Shell Nanowires

NASA Astrophysics Data System (ADS)

Astefanoaei, Iordana; Dumitru, Ioan; Stancu, Alexandru

2016-12-01

The induced thermal stress in a heating process is an important parameter to be known and controlled in the magnetization process of core-shell nanowires. This paper analyses the stress produced by a laser heating source placed at one end of a core-shell type structure. The thermal field was computed with the non-Fourier heat transport equation using a finite element method (FEM) implemented in Comsol Multiphysics. The internal stresses are essentially due to thermal gradients and different expansion characteristics of core and shell materials. The stress values were computed using the thermo elastic formalism and are depending on the laser beam parameters (spot size, power etc.) and system characteristics (dimensions, thermal characteristics). Stresses in the GPa range were estimated and consequently we find that the magnetic state of the system can be influenced significantly. A shell material as the glass which is a good thermal insulator induces in the magnetic core, the smaller stresses and consequently the smaller magnetoelastic energy. These results lead to a better understanding of the switching process in the magnetic materials.

Phase diagram of electron systems near the superconductor-insulator transition.

PubMed

Pokrovsky, V L; Falco, G M; Nattermann, T

2010-12-31

The zero temperature phase diagram of Cooper pairs exposed to disorder and a magnetic field is determined theoretically from a variational approach. Four distinct phases are found: a Bose and a Fermi insulating, a metallic, and a superconducting phase, respectively. The results explain the giant negative magnetoresistance found experimentally in In-O, TiN, Be and high-T(c) materials.

Perovskite-structure TlMnO₃: a new manganite with new properties.

PubMed

Yi, Wei; Kumagai, Yu; Spaldin, Nicola A; Matsushita, Yoshitaka; Sato, Akira; Presniakov, Igor A; Sobolev, Alexey V; Glazkova, Yana S; Belik, Alexei A

2014-09-15

We synthesize a new member of the AMnO3 perovskite manganite family (where A is a trivalent cation)--thallium manganite, TlMnO3--under high-pressure (6 GPa) and high-temperature (1500 K) conditions and show that the structural and magnetic properties are distinct from those of all other AMnO3 manganites. The crystal structure of TlMnO3 is solved and refined using single-crystal X-ray diffraction data. We obtain a triclinically distorted structure with space group P1̅ (No. 2), Z = 4, and lattice parameters a = 5.4248(2) Å, b = 7.9403(2) Å, c = 5.28650(10) Å, α = 87.8200(10)°, β = 86.9440(10)°, and γ = 89.3130(10)° at 293 K. There are four crystallographic Mn sites in TlMnO3 forming two groups based on the degree of their Jahn-Teller distortions. Physical properties of insulating TlMnO3 are investigated with Mössbauer spectroscopy and resistivity, specific heat, and magnetization measurements. The orbital ordering, which persists to the decomposition temperature of 820 K, suggests A-type antiferromagnetic ordering with the ferromagnetic planes along the [-101] direction, consistent with the measured collinear antiferromagnetism below the Néel temperature of 92 K. Hybrid density functional calculations are consistent with the experimentally identified structure, insulating ground state, and suggested magnetism, and show that the low symmetry originates from the strongly Jahn-Teller distorted Mn(3+) ions combined with the strong covalency of the Tl(3+)-O bonds.

Structure and magnetic properties of FeSiAl-based soft magnetic composite with AlN and Al2O3 insulating layer prepared by selective nitridation and oxidation

NASA Astrophysics Data System (ADS)

Zhong, Xiaoxi; Liu, Ying; Li, Jun; Wang, Yiwei

2012-08-01

FeSiAl is widely used in switching power supply, filter inductors and pulse transformers. But when used under higher frequencies in some particular condition, it is required to reduce its high-frequency loss. Preparing a homogeneous insulating coating with good heat resistance and high resistivity, such as AlN and Al2O3, is supposed to be an effective way to reduce eddy current loss, which is less focused on. In this project, mixed AlN and Al2O3 insulating layers were prepared on the surface of FeSiAl powders after 30 min exposure at 1100 °C in high purity nitrogen atmosphere, by means of surface nitridation and oxidation. The results revealed that the insulating layers increase the electrical resistivity, and hence decrease the loss factor, improve the frequency stability and increase the quality factor, especially in the high-frequency range. The morphologies, microstructure and compositions of the oxidized and nitrided products on the surface were characterized by Scanning Electron Microscopy/Energy Disperse Spectroscopy, X-Ray Diffraction, Transmission Electron Microscopy, Selected Area Electron Diffraction and X-ray Photoelectron Spectroscopy.

Influence of the Coulomb interaction on the exchange coupling in granular magnets.

PubMed

Udalov, O G; Beloborodov, I S

2017-04-20

We develop a theory of the exchange interaction between ferromagnetic (FM) metallic grains embedded into insulating matrix by taking into account the Coulomb blockade effects. For bulk ferromagnets separated by the insulating layer the exchange interaction strongly depends on the height and thickness of the tunneling barrier created by the insulator. We show that for FM grains embedded into insulating matrix the exchange coupling additionally depends on the dielectric properties of this matrix due to the Coulomb blockade effects. In particular, the FM coupling decreases with decreasing the dielectric permittivity of insulating matrix. We find that the change in the exchange interaction due to the Coulomb blockade effects can be a few tens of percent. Also, we study dependence of the intergrain exchange interaction on the grain size and other parameters of the system.

Tunable-φ Josephson junction with a quantum anomalous Hall insulator

NASA Astrophysics Data System (ADS)

Sakurai, Keimei; Ikegaya, Satoshi; Asano, Yasuhiro

2017-12-01

We theoretically study the Josephson current in a superconductor/quantum anomalous Hall insulator/superconductor junction by using the lattice Green function technique. When an in-plane external Zeeman field is applied to the quantum anomalous Hall insulator, the Josephson current J flows without a phase difference across the junction θ . The phase shift φ appearing in the current-phase relationship J ∝sin(θ -φ ) is proportional to the amplitude of Zeeman fields and depends on the direction of Zeeman fields. A phenomenological analysis of the Andreev reflection processes explains the physical origin of φ . In a quantum anomalous Hall insulator, time-reversal symmetry and mirror-reflection symmetry are broken simultaneously. However, magnetic mirror-reflection symmetry is preserved. Such characteristic symmetry properties enable us to have a tunable φ junction with a quantum Hall insulator.

UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

2016-08-01

In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent conducting oxides.

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

DTIC Science & Technology

2013-12-01

the metal- insulator transition, a feature that has long been predicted theoretically. We showed that a similar picture is at play in magnetic doping of... magnetic atoms on the surface of a superconductor can be used as a versatile platform for creating a topological superconductor . These initial...topological superconductivity and Majorana fermions in a chain of magnetic atoms on the surface of a superconductor Students and postdocs supported

Magnon-induced superconductivity in field-cooled spin-1/2 antiferromagnets

NASA Astrophysics Data System (ADS)

Karchev, Naoum

2017-12-01

If, during the preparation, an external magnetic field is applied upon cooling we say it has been field cooled. A novel mechanism for insulator-metal transition and superconductivity in field-cooled spin-1 /2 antiferromagnets on bcc lattice is discussed. Applying a magnetic field along the sublattice B magnetization, we change the magnetic and transport properties of the material. There is a critical value Hcr1. When the magnetic field is below the critical one H Hcr1 the sublattice A electrons are delocalized and the material is metal. There is a second critical value Hcr2>Hcr1 . When H =Hcr2 , it is shown that the Zeeman splitting of the sublattice A electrons is zero and they do not contribute to the magnetization of the system. At this quantum partial order point (QPOP) the sublattice B transversal spin fluctuations (magnons) interact with sublattice A electrons inducing spin antiparallel p -wave superconductivity which coexists with magnetism. At zero temperature the magnetic moment of sublattice B electrons is maximal. Below the Néel temperature (TN) the gap is approximately constant with a small increase when the system approaches TN. It abruptly falls down to zero at temperatures above TN.

A 0.5 MV magnetically self-insulated pulsed transformer

NASA Astrophysics Data System (ADS)

Istenic, M.; Novac, B. M.; Luo, J.; Kumar, R.; Smith, I. R.

2006-11-01

This paper describes the successful development of a light and compact 0.5 MV spiral-strip transformer, with the secondary winding contained in vacuum and based on magnetic self-insulation. Ensuring trouble-free operation required the use of conductive elastomers in electric field grading techniques and the adoption in the secondary winding of glass/ceramic conductor spacers. It is demonstrated that the primary-current/secondary breakdown-voltage characteristic is a function of the vacuum pressure, with only 52 kA being necessary to produce 0.5 MV at 10-6 Torr. The difficult task of modelling the transformer required 3D electric and magnetic field computation, together with state-of-the-art calculation of the electron flow in the vacuum. Based on the results obtained to date, scaling up to multi-megavolt transformers can readily be envisaged.

Charge transport and magnetization profile at the interface between the correlated metal CaRuO3 and the antiferromagnetic insulator CaMnO3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freeland, J. W.; Chakhalian, J.; Boris, A. V.

2010-01-01

A combination of spectroscopic probes was used to develop a detailed experimental description of the transport and magnetic properties of superlattices composed of the paramagnetic metal CaRuO3 and the antiferromagnetic insulator CaMnO3. The charge carrier density and Ru valence state in the superlattices are not significantly different from those of bulk CaRuO3. The small charge transfer across the interface implied by these observations confirms predictions derived from density functional calculations. However, a ferromagnetic polarization due to canted Mn spins penetrates 3-4 unit cells into CaMnO3, far exceeding the corresponding predictions. The discrepancy may indicate the formation of magnetic polarons atmore » the interface.« less

Quantum simulation of strongly correlated condensed matter systems

NASA Astrophysics Data System (ADS)

Hofstetter, W.; Qin, T.

2018-04-01

We review recent experimental and theoretical progress in realizing and simulating many-body phases of ultracold atoms in optical lattices, which gives access to analog quantum simulations of fundamental model Hamiltonians for strongly correlated condensed matter systems, such as the Hubbard model. After a general introduction to quantum gases in optical lattices, their preparation and cooling, and measurement techniques for relevant observables, we focus on several examples, where quantum simulations of this type have been performed successfully during the past years: Mott-insulator states, itinerant quantum magnetism, disorder-induced localization and its interplay with interactions, and topological quantum states in synthetic gauge fields.

Nuclear spin warm up in bulk n -GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

2016-08-01

We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

Edge states and topological phase transitions in chains of dielectric nanoparticles

DOE PAGES

Kruk, Sergey; Slobozhanyuk, Alexey; Denkova, Denitza; ...

2017-01-12

Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. Here, it is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited.

Edge states and topological phase transitions in chains of dielectric nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruk, Sergey; Slobozhanyuk, Alexey; Denkova, Denitza

Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. Here, it is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited.

Comparative study of heterogeneous magnetic state above TC in La0.82Sr0.18CoO3 cobaltite and La0.83Sr0.17MnO3 manganite

NASA Astrophysics Data System (ADS)

Ryzhov, V. A.; Lazuta, A. V.; Molkanov, P. L.; Khavronin, V. P.; Kurbakov, A. I.; Runov, V. V.; Mukovskii, Ya. M.; Pestun, A. E.; Privezentsev, R. V.

2012-10-01

The magnetic, transport and structural properties are studied for La0.83Sr0.17MnO3 and La0.82Sr0.18CoO3 single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т*>TC in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator-metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn3+ and Co3+ ions.

Composite Behavior of Insulated Concrete Sandwich Wall Panels Subjected to Wind Pressure and Suction

PubMed Central

Choi, Insub; Kim, JunHee; Kim, Ho-Ryong

2015-01-01

A full-scale experimental test was conducted to analyze the composite behavior of insulated concrete sandwich wall panels (ICSWPs) subjected to wind pressure and suction. The experimental program was composed of three groups of ICSWP specimens, each with a different type of insulation and number of glass-fiber-reinforced polymer (GFRP) shear grids. The degree of composite action of each specimen was analyzed according to the load direction, type of the insulation, and number of GFRP shear grids by comparing the theoretical and experimental values. The failure modes of the ICSWPs were compared to investigate the effect of bonds according to the load direction and type of insulation. Bonds based on insulation absorptiveness were effective to result in the composite behavior of ICSWP under positive loading tests only, while bonds based on insulation surface roughness were effective under both positive and negative loading tests. Therefore, the composite behavior based on surface roughness can be applied to the calculation of the design strength of ICSWPs with continuous GFRP shear connectors. PMID:28788001

Magnetized Target Fusion: Prospects for Low-Cost Fusion Energy

NASA Technical Reports Server (NTRS)

Siemon, Richard E.; Turchi, Peter J.; Barnes, Daniel C.; Degnan, James; Parks, Paul; Ryutov, Dmitri D.; Thio, Y. C. Francis; Schafer, Charles (Technical Monitor)

2001-01-01

Magnetized Target Fusion (MTF) has attracted renewed interest in recent years because it has the potential to resolve one of the major problems with conventional fusion energy research - the high cost of facilities to do experiments and in general develop practical fusion energy. The requirement for costly facilities can be traced to fundamental constraints. The Lawson condition implies large system size in the case of conventional magnetic confinement, or large heating power in the case of conventional inertial confinement. The MTF approach is to use much higher fuel density than with conventional magnetic confinement (corresponding to megabar pressures), which results in a much-reduced system size to achieve Lawson conditions. Intrinsically the system must be pulsed because the pressures exceed the strength of any known material. To facilitate heating the fuel (or "target") to thermonuclear conditions with a high-power high-intensity source of energy, magnetic fields are used to insulate the high-pressure fuel from material surroundings (thus "magnetized target"). Because of magnetic insulation, the required heating power intensity is reduced by many orders of magnitude compared to conventional inertial fusion, even with relatively poor energy confinement in the magnetic field, such as that characterized by Bohm diffusion. In this paper we show semi-quantitatively why MTF-should allow fusion energy production without costly facilities within the same generally accepted physical constraints used for conventional magnetic and inertial fusion. We also briefly discuss potential applications of this technology ranging from nuclear rockets for space propulsion to a practical commercial energy system. Finally, we report on the exploratory research underway, and the interesting physics issues that arise in the MTF regime of parameters. Experiments at Los Alamos are focused on formation of a suitable plasma target for compression, utilizing the knowledge base for compact toroids called Field-Reversed Configurations. As reported earlier, it appears that the existing pulsed-power Shiva Star facility at the Air Force Research Laboratory in Albuquerque, NM can satisfy the heating requirements by means of imploding a thin metal cylinder (called a "liner") surrounding an FRC of the type presently being developed. The proposed next step is an integrated liner-on-plasma experiment in which an FRC would be heated to 10 keV by the imploding liner.

Microscopic Studies of Quantum Phase Transitions in Optical Lattices

NASA Astrophysics Data System (ADS)

Bakr, Waseem S.

2011-12-01

In this thesis, I report on experiments that microscopically probe quantum phase transitions of ultracold atoms in optical lattices. We have developed a "quantum gas microscope" that allowed, for the first time, optical imaging and manipulation of single atoms in a quantum-degenerate gas on individual sites of an optical lattice. This system acts as a quantum simulator of strongly correlated materials, which are currently the subject of intense research because of the technological potential of high--T c superconductors and spintronic materials. We have used our microscope to study the superfluid to Mott insulator transition in bosons and a magnetic quantum phase transition in a spin system. In our microscopic study of the superfluid-insulator transition, we have characterized the on-site number statistics in a space- and time-resolved manner. We observed Mott insulators with fidelities as high as 99%, corresponding to entropies of 0.06kB per particle. We also measured local quantum dynamics and directly imaged the shell structure of the Mott insulator. I report on the first quantum magnetism experiments in optical lattices. We have realized a quantum Ising chain in a magnetic field, and observed a quantum phase transition between a paramagnet and antiferromagnet. We achieved strong spin interactions by encoding spins in excitations of a Mott insulator in a tilted lattice. We detected the transition by measuring the total magnetization of the system across the transition using in-situ measurements as well as the Neel ordering in the antiferromagnetic state using noise-correlation techniques. We characterized the dynamics of domain formation in the system. The spin mapping introduced opens up a new path to realizing more exotic states in optical lattices including spin liquids and quantum valence bond solids. As our system sizes become larger, simulating their physics on classical computers will require exponentially larger resources because of entanglement build-up near a quantum phase transition. We have demonstrated a quantum simulator in which all degrees of freedom can be read out microscopically, allowing the simulation of quantum many-body systems with manageable resources. More generally, the ability to image and manipulate individual atoms in optical lattices opens an avenue towards scalable quantum computation.

Low-frequency and multiple-bands sound insulation using hollow boxes with membrane-type faces

NASA Astrophysics Data System (ADS)

Yu, Wei-wei; Fan, Li; Ma, Ren-hao; Zhang, Hui; Zhang, Shu-yi

2018-04-01

Hollow boxes with their faces made up of elastic membranes are used to block acoustic waves. It is demonstrated that placing a cuboid membrane-type box inside a pipe can effectively insulate acoustic waves even if the box is smaller than the cross-section of the pipe. The sound insulation is achieved within multiple frequency-bands below 500 Hz based on different mechanisms, which originate from the coaction of the cavity, membrane-type faces, and the intervals between the box and pipe walls. Furthermore, by adjusting the structural parameters and establishing an array of boxes, we can achieve better sound insulation at more frequency-bands.

Magnetism and electronic structure of (001)- and (111)-oriented LaTiO3 bilayers sandwiched in LaScO3 barriers

NASA Astrophysics Data System (ADS)

Weng, Yakui; Dong, Shuai

2015-05-01

In this study, the magnetism and electronic structure of LaTiO3 bilayers along both the (001) and (111) orientations are calculated using the density functional theory. The band insulator LaScO3 is chosen as the barrier layer and substrate to obtain the isolating LaTiO3 bilayer. For both the (001)- and (111)-oriented cases, LaTiO3 demonstrates the G-type antiferromagnetism as the ground state, similar to the bulk material. However, the electronic structure is significantly changed. The occupied bands of Ti are much narrower in the (111) case, giving a nearly flat band. As a result, the exchange coupling between nearest-neighbor Ti ions is reformed in these superlattices, which will affect the Néel temperature significantly.

Double layered tailorable advanced blanket insulation

NASA Technical Reports Server (NTRS)

Falstrup, D.

1983-01-01

An advanced flexible reusable surface insulation material for future space shuttle flights was investigated. A conventional fly shuttle loom with special modifications to weave an integral double layer triangular core fabric from quartz yarn was used. Two types of insulating material were inserted into the cells of the fabric, and a procedure to accomplish this was developed. The program is follow up of a program in which single layer rectangular cell core fabrics are woven and a single type of insulating material was inserted into the cells.

Phase diagram and neutron spin resonance of superconducting NaFe 1 - x Cu x As

DOE PAGES

Tan, Guotai; Song, Yu; Zhang, Rui; ...

2017-02-03

In this paper, we use transport and neutron scattering to study the electronic phase diagram and spin excitations of NaFe 1-xCu xAs single crystals. Similar to Co- and Ni-doped NaFeAs, a bulk superconducting phase appears near x≈2% with the suppression of stripe-type magnetic order in NaFeAs. Upon further increasing Cu concentration the system becomes insulating, culminating in an antiferromagnetically ordered insulating phase near x≈50%. Using transport measurements, we demonstrate that the resistivity in NaFe 1-xCu xAs exhibits non-Fermi-liquid behavior near x≈1.8%. Our inelastic neutron scattering experiments reveal a single neutron spin resonance mode exhibiting weak dispersion along c axis inmore » NaFe 0.98Cu 0.02As. The resonance is high in energy relative to the superconducting transition temperature T c but weak in intensity, likely resulting from impurity effects. These results are similar to other iron pnictides superconductors despite that the superconducting phase in NaFe 1-xCu xAs is continuously connected to an antiferromagnetically ordered insulating phase near x≈50% with significant electronic correlations. Finally, therefore, electron correlations is an important ingredient of superconductivity in NaFe 1-xCu xAs and other iron pnictides.« less

Magnon Valve Effect between Two Magnetic Insulators.

PubMed

Wu, H; Huang, L; Fang, C; Yang, B S; Wan, C H; Yu, G Q; Feng, J F; Wei, H X; Han, X F

2018-03-02

The key physics of the spin valve involves spin-polarized conduction electrons propagating between two magnetic layers such that the device conductance is controlled by the relative magnetization orientation of two magnetic layers. Here, we report the effect of a magnon valve which is made of two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer (Au). When a thermal gradient is applied perpendicular to the layers, the inverse spin Hall voltage output detected by a Pt bar placed on top of the magnon valve depends on the relative orientation of the magnetization of two YIG layers, indicating the magnon current induced by the spin Seebeck effect at one layer affects the magnon current in the other layer separated by Au. We interpret the magnon valve effect by the angular momentum conversion and propagation between magnons in two YIG layers and conduction electrons in the Au layer. The temperature dependence of the magnon valve ratio shows approximately a power law, supporting the above magnon-electron spin conversion mechanism. This work opens a new class of valve structures beyond the conventional spin valves.

Magnon Valve Effect between Two Magnetic Insulators

NASA Astrophysics Data System (ADS)

Wu, H.; Huang, L.; Fang, C.; Yang, B. S.; Wan, C. H.; Yu, G. Q.; Feng, J. F.; Wei, H. X.; Han, X. F.

2018-03-01

The key physics of the spin valve involves spin-polarized conduction electrons propagating between two magnetic layers such that the device conductance is controlled by the relative magnetization orientation of two magnetic layers. Here, we report the effect of a magnon valve which is made of two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer (Au). When a thermal gradient is applied perpendicular to the layers, the inverse spin Hall voltage output detected by a Pt bar placed on top of the magnon valve depends on the relative orientation of the magnetization of two YIG layers, indicating the magnon current induced by the spin Seebeck effect at one layer affects the magnon current in the other layer separated by Au. We interpret the magnon valve effect by the angular momentum conversion and propagation between magnons in two YIG layers and conduction electrons in the Au layer. The temperature dependence of the magnon valve ratio shows approximately a power law, supporting the above magnon-electron spin conversion mechanism. This work opens a new class of valve structures beyond the conventional spin valves.