oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 1 )

2019 ( 208 )

2018 ( 288 )

2017 ( 313 )

Custom range...

Search Results: 1 - 10 of 138750 matches for " K. Siemensmeyer "
All listed articles are free for downloading (OA Articles)
Page 1 /138750
Display every page Item
Magnetic structure and phase diagram of TmB4
S. Gabani,S. Matas,P. Priputen,K. Flachbart,K. Siemensmeyer,E. Wulf,A. Evdokimova,N. Shitsevalova
Physics , 2007,
Abstract: Magnetic structure of single crystalline TmB4 has been studied by magnetization, magnetoresistivity and specific heat measurements. A complex phase diagram with different antiferromagnetic (AF) phases was observed below TN1 = 11.7 K. Besides the plateau at half-saturated magnetization (1/2 MS), also plateaus at 1/9, 1/8 and 1/7 of MS were observed as function of applied magnetic field B//c. From additional neutron scattering experiments on TmB4, we suppose that those plateaus arise from a stripe structure which appears to be coherent domain boundaries between AF ordered blocks of 7 or 9 lattice constants. The received results suggest that the frustration among the Tm3+ magnetic ions, which maps to a geometrically frustrated Shastry-Sutherland lattice lead to strong competition between AF and ferromagnetic (FM) order. Thus, stripe structures in intermediate field appear to be the best way to minimize the magnetostatic energy against other magnetic interactions between the Tm ions combined with very strong Ising anisotropy.
Neutron scattering on HoB$_{12}$ - short-range correlations above T$_{N}$
K. Siemensmeyer,K. Flachbart,S. Gabani,S. Matas,Y. Paderno,N. Shitsevalova
Physics , 2006,
Abstract: Neutron scattering experiments on frustrated fcc - antiferromagnet HoB$_{12}$ have been performed above T$_{N}$ = 7.4 K. Diffuse scattering patterns indicate that above Neel temperature correlations between neighboring magnetic moments of Ho - ions appear, similar to the appearance of coupled spin-pairs (dimers) in low dimensional magnets. Moreover, the diffuse patterns show a symmetry reduction from fcc to simple cubic. Analogous behavior in 3D systems is not known, although it was predicted by theory. The role of various interactions leading to this behavior is being analyzed and discussed.
Investigation of the magnetic structure and crystal field states of pyrochlore antiferromagnet Nd2Zr2O7
J. Xu,V. K. Anand,A. K. Bera,M. Frontzek,D. L. Abernathy,N. Casati,K. Siemensmeyer,B. Lake
Physics , 2015,
Abstract: We present synchrotron x-ray diffraction, neutron powder diffraction and time-of-flight inelastic neutron scattering measurements on the rare earth pyrochlore oxide Nd2Zr2O7 to study the ordered state magnetic structure and cystal field states. The structural characterization by high-resolution synchrotron x-ray diffraction confirms that the pyrochlore structure has no detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals long range all-in/all-out antiferromagnetic order below T_N ~ 0.4 K with propagation vector k = (0 0 0) and an ordered moment of 1.26(2) \mu_B/Nd at 0.1 K. The ordered moment is much smaller than the estimated moment of 2.65 \mu_B/Nd for the local <111> Ising ground state of Nd3+ (J=9/2) suggesting that the ordering is partially suppressed by quantum fluctuations. The strong Ising anisotropy is further confirmed by the inelastic neutron scattering data which reveals a well-isolated dipolar-octupolar type Kramers doublet ground state. The crystal field level scheme and ground state wavefunction have been determined.
Fractional magnetization plateaus and magnetic order in the Shastry Sutherland magnet TmB4
K. Siemensmeyer,E. Wulf,H. -J. Mikeska,K. Flachbart,S. Gabani,S. Matas,P. Priputen,A. Efdokimova,N. Shitsevalova
Physics , 2007, DOI: 10.1103/PhysRevLett.101.177201
Abstract: We investigate the phase diagram of TmB4, an Ising magnet on a frustrated Shastry-Sutherland lattice by neutron diffraction and magnetization experiments. At low temperature we find Neel order at low field, ferrimagnetic order at high field and an intermediate phase with magnetization plateaus at fractional values M/Msat = 1/7, 1/8, 1/9 ... and spatial stripe structures. Using an effective S = 1/2 model and its equivalent two-dimensional (2D) fermion gas we suggest that the magnetic properties of TmB4 are related to the fractional quantum Hall effect of a 2D electron gas.
Samarium hexaboride: A trivial surface conductor
P. Hlawenka,K. Siemensmeyer,E. Weschke,A. Varykhalov,J. Sánchez-Barriga,N. Y. Shitsevalova,A. V. Dukhnenko,V. B. Filipov,S. Gabáni,K. Flachbart,O. Rader,E. D. L. Rienks
Physics , 2015,
Abstract: Recent theoretical and experimental studies suggest that SmB$_6$ is the first topological Kondo insulator: A material in which the interaction between localized and itinerant electrons renders the bulk insulating at low temperature, while topological surface states leave the surface metallic. While this would elegantly explain the material's puzzling conductivity, we find the experimentally observed candidates for both predicted topological surface states to be of trivial character instead: The surface state at $\bar{\Gamma}$ is very heavy and shallow with a mere $\sim 2$ meV binding energy. It exhibits large Rashba splitting which excludes a topological nature. We further demonstrate that the other metallic surface state, located at $\bar{X}$, is not an independent in-gap state as supposed previously, but part of a massive band with much higher binding energy (1.7 eV). We show that it remains metallic down to 1 K due to reduced hybridization with the energy-shifted surface 4$f$ level.
Dissimilarities between the electronic structure of chemically doped and chemically pressurized iron pnictides from an angle-resolved photoemission spectroscopy study
S. Thirupathaiah,E. D. L. Rienks,H. S. Jeevan,R. Ovsyannikov,E. Slooten,J. Kaas,E. van Heumen,S. de Jong,H. A. Duerr,K. Siemensmeyer,R. Follath,P. Gegenwart,M. S. Golden,J. Fink
Physics , 2010, DOI: 10.1103/PhysRevB.84.014531
Abstract: We have studied the electronic structure of EuFe2As2-xPx using high resolution angle-resolved photoemission spectroscopy. Upon substituting As with the isovalent P, which leads to a chemical pressure and to superconductivity, we observe a non-rigid-band like change of the electronic structure along the center of the Brillouin zone (BZ): an orbital and kz dependent increase or decrease in the size of the hole pockets near the Gamma - Z line. On the other hand, the diameter of the Fermi surface cylinders at the BZ corner forming electron pockets, hardly changes. This is in stark contrast to p and n-type doped iron pnictides where, on the basis of ARPES experiments, a more rigid-band like behavior has been proposed. These findings indicate that there are different ways in which the nesting conditions can be reduced causing the destabilization of the antiferromagnetic order and the appearance of the superconducting dome.
Surface and bulk components of electrical conductivity in the (presumably special topological) Kondo insulator SmB6 at lowest temperatures
Slavomir Gabani,Gabriel Pristas,Iveta Takacova,Nikolay Sluchanko,Konrad Siemensmeyer,Natalia Shitsevalova,Volodymyr Filipov,Karol Flachbart
Physics , 2014, DOI: 10.1016/j.solidstatesciences.2015.03.005
Abstract: Samarium hexaboride (SmB6) has recently been considered to be a topological Kondo insulator (TKI), the first strongly correlated electron system to exhibit topological surface conduction states. In this contribution, results of electrical resistivity measurements between 80 K and 0.08 K of various SmB6 single crystalline samples are presented, analyzed and discussed. The received results imply that the residual conductivity of SmB6 below about 4 K is of non-activated (metallic-like) nature. It is shown that this metallic-like behavior can be attributed both to surface (2D) conduction states, as may be expected in case of a topological insulator, as well as to the highly correlated many-body (3D) bulk ground state which is formed within the gap of this compound. From this it follows that in SmB6, where surface conductivity states are clearly present, there is in parallel also a bulk contribution to residual electrical conductivity originating from the strongly correlated electron system with valence fluctuations. This raises the question whether SmB6 does not form a new / special type of topological insulator in which in the energy gap besides the surface conduction states, there is also a conducting narrow in-gap band originating from the bulk strongly correlated electron system.
The Constrained Mean-Semivariance Portfolio Optimization Problem with the Support of a Novel Multiobjective Evolutionary Algorithm  [PDF]
K. Liagkouras, K. Metaxiotis
Journal of Software Engineering and Applications (JSEA) , 2013, DOI: 10.4236/jsea.2013.67B005
Abstract:

The paper addresses the constrained mean-semivariance portfolio optimization problem with the support of a novel multi-objective evolutionary algorithm (n-MOEA). The use of semivariance as the risk quantification measure and the real world constraints imposed to the model make the problem difficult to be solved with exact methods. Thanks to the exploratory mechanism, n-MOEA concentrates the search effort where is needed more and provides a well formed efficient frontier with the solutions spread across the whole frontier. We also provide evidence for the robustness of the produced non-dominated solutions by carrying out, out-of-sample testing during both bull and bear market conditions on FTSE-100.

Design of a Cantilever - Type Rotating Bending Fatigue Testing Machine  [PDF]
K. K. Alaneme
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2011, DOI: 10.4236/jmmce.2011.1011078
Abstract: This research is centered on the design of a low–cost cantilever loading rotating bending fatigue testing machine using locally sourced materials. The design principle was based on the adaptation of the technical theory of bending of elastic beams. Design drawings were produced and components/materials selections were based on functionality, durability, cost and local availability. The major parts of the machine: the machine main frame, the rotating shaft, the bearing and the bearing housing, the specimen clamping system, pulleys, speed counter, electric motor, and dead weights; were fabricated and then assembled following the design specifications. The machine performance was evaluated using test specimens which were machined in conformity with standard procedures. It was observed that the machine has the potentials of generating reliable bending stress – number of cycles data; and the cost of design (171,000 Naira) was lower in comparison to that of rotating bending machines from abroad. Also the machine has the advantages of ease of operation and maintenance, and is safe for use.
Wireless Sensor Network Lifetime Enhancement Using Modified Clustering and Scheduling Algorithm  [PDF]
K. Ramesh, K. Somasundaram
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.78154
Abstract: Random distribution of sensor nodes in large scale network leads redundant nodes in the application field. Sensor nodes are with irreplaceable battery in nature, which drains the energy due to?repeated collection of data and decreases network lifetime. Scheduling algorithms are the one way?of addressing this issue. In proposed method, an optimized sleep scheduling used to enhance the?network lifetime. While using the scheduling algorithm, the target coverage and data collection?must be maintained throughout the network. In-network, aggregation method also used to remove the unwanted information in the collected data in level. Modified clustering algorithm?highlights three cluster heads in each cluster which are separated by minimum distance between them.?The simulation results show the 20% improvement in network lifetime, 25% improvement in?throughput and 30% improvement in end to end delay.
Page 1 /138750
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.