Reentrant spin glass ordering in an Fe-based bulk metallic glass
Luo, Qiang; Shen, Jun
2015-02-07
We report the results of the complex susceptibility, temperature, and field dependence of DC magnetization and the nonequilibrium dynamics of a bulk metallic glass Fe{sub 40}Co{sub 8}Cr{sub 15}Mo{sub 14}C{sub 15}B{sub 6}Er{sub 2}. Solid indication of the coexistence of reentrant spin glass (SG) and ferromagnetic orderings is determined from both DC magnetization and AC susceptibility under different DC fields. Dynamics scaling of AC susceptibility indicates critical slowing down to a reentrant SG state with a static transition temperature T{sub s} = ∼17.8 K and a dynamic exponent zv = ∼7.3. The SG nature is further corroborated from chaos and memory effects, magnetic hysteresis, and aging behavior. We discuss the results in terms of the competition among random magnetic anisotropy and exchange interactions and compare them with simulation predictions.
Reentrant spin-glass state in a geometrical frustrated multiferroic system: Role of disorder
Chattopadhyay, S.; Giri, S.; Majumdar, S.; Ganesan, V.; Venkateshwarlu, D.
2014-05-07
We investigated the effect of magnetic (Mn) and nonmagnetic (Ga) doping at the Cr site of the layered geometrically frustrated antiferromagnetic compound LiCrO{sub 2}. 10% Ga doping at the Cr site does not invoke any metastability typical of a glassy magnetic state. However, similar amount of Mn doping drives the system to a spin glass (SG) state which is particularly evident from the magnetic memory and heat capacity studies. The onset of glassy state in 10% Mn doped sample is of reentrant type developing out of higher temperature antiferromagnetic state. The SG state in the Mn-doped sample shows a true reentry with the complete disappearance of the antiferromagnetic phase below the SG transition. The lack of SG state on Ga doping indicates the importance of random ferromagnetic/antiferromagnetic bonds for the glassy ground state in LiCrO{sub 2}.
Scaling and memory effects in the reentrant spin glass phase of nanostructured MnxTaS2
NASA Astrophysics Data System (ADS)
Shand, Paul; Danker, John; Xiao, Xun; Kidd, Tim; Strauss, Laura
2015-03-01
We have investigated the nature of the reentrant spin glass phase of nanostructured Mn-intercalated TaS2. The sample consisted of bundles of nanoscale fibers with an average atomic concentration of intercalated Mn of 22%. The sample exhibits a ferromagnetic transition at 74 K and a transition to a cluster glass state at 40 K. The ac susceptibility measured in small dc bias fields near the cluster glass transition exhibited scaling behavior, indicating a magnetic-field dependent crossover to glassy dynamics. At temperatures below the cluster-glass transition, the nature of the dynamics was probed by ac susceptibility and zero-field cooled (ZFC) magnetization measurements. Aging and memory effects were observed, consistent with the non-equilibrium dynamics exhibited by glassy magnetic systems. In particular, we probed the ZFC magnetization memory effect as a function of cooling rate, aging time and magnetic field. The behavior is explained in terms of domain growth within the framework of droplet theory. Supported by National Science Foundation Grant No. DMR 1206530.
NASA Astrophysics Data System (ADS)
Stephanovich, V. A.; Laguta, V. V.
We propose experimental verification and theoretical explanation of magnetic anomalies in the complex Fe-contained double perovskite multiferroics like PbFe$_{1/2}$Nb$_{1/2}$O$_3$. The theoretical part is based on our model of coexistence of long-range magnetic order and spin glass in the above substances. In our model, the exchange interaction is anisotropic, coupling antiferromagnetically $z$ spin components of Fe$^{3+}$ ions. At the same time, the $xy$ components are coupled by much weaker exchange interaction of ferromagnetic sign. In the system with spatial disorder (half of corresponding lattice cites are occupied by spinless Nb$^{5+}$ ions) such frustrating interaction results in the fact that antiferromagnetic order is formed by $z$ projection of the spins, while their $xy$ components contribute to spin glass behaviour. Our theoretical findings are supported by the experimental evidence of coexistence of antiferromagnetic and spin glass phases in chemically disordered Fe-contained double perovskite multiferroics.
Stephanovich, V A; Laguta, V V
2016-03-14
We propose experimental verification and theoretical explanation of magnetic anomalies in the complex Fe-containing perovskite multiferroics like PbFe1/2Nb1/2O3 and PbFe1/2Ta1/2O3. The theoretical part is based on our model of coexistence of the long-range magnetic order and spin glass in the above compounds. In our model, the exchange interaction is anisotropic, coupling antiferromagnetically z spin components of Fe(3+) ions. At the same time, the xy components are coupled by much weaker exchange interaction of ferromagnetic sign. In the system with spatial disorder (half of the corresponding lattice sites are occupied by spinless Nb(5+) ions) such frustrating interaction results in the fact that the antiferromagnetic order is formed by the z projection of the spins, while their xy components contribute to spin glass behaviour. Our theoretical findings are supported by the experimental evidence of such a coexistence of antiferromagnetic and spin glass phases in chemically disordered Fe-containing complex perovskite multiferroics. PMID:26890550
NASA Astrophysics Data System (ADS)
Nayak, S.; Joshi, D. C.; Krautz, M.; Waske, A.; Eckert, J.; Thota, S.
2016-01-01
We report the co-existence of longitudinal ferrimagnetic behavior with Néel temperature TN ˜ 46.1 K and reentrant transverse spin-glass state at 44.05 K in Tin (Sn) doped cobalt-orthotitanate (Co2TiO4). The ferrimagnetic ordering is resulting from different magnetic moments of Co2+ on the A-sites (3.87 μB) and B-sites (5.069 μB). The magnetic compensation temperature (TCOMP) shifts from 31.74 K to 27.1 K when 40 at. % of "Sn4+" substitutes "Ti4+" at B-sites where the bulk-magnetization of two-sublattices balance each other. For T > TN, the dc-magnetic susceptibility (χdc = M/Hdc) fits well with the Néel's expression for the two-sublattice model with antiferromagnetic molecular field constants NBB ˜ 15.44, NAB ˜ 32.01, and NAA ˜ 20.88. The frequency dependence of ac-magnetic susceptibility χac data follows the Vogel-Fulcher law, and the power-law of critical slowing-down with "zν" = 6.01 suggests the existence of spin-clusters (where "z" and "ν" being dynamic critical-exponent and correlation length of critical-exponent, respectively). This system exhibits unusual hysteresis loops with large bipolar exchange-bias effect (HEB ˜ 13.6 kOe at 7 K) after zero-field cooling process from an un-magnetized state, and a dramatic collapse of remanence (MR) and coercive field (HC) across TCOMP. The possible origins of such anomalous characteristics were discussed.
NASA Astrophysics Data System (ADS)
Kim, T. H.; Cadeville, M. C.; Dinia, A.; Rakoto, H.
1996-01-01
The magnetic properties and the magnetic phase diagram of the pseudobinary Co1-xMnxPt3 system resulting from alloying two ferromagnetic CoPt3 and MnPt3 compounds have been investigated. Structural and microstructural characterizations added to thorough preparation conditions yield well-ordered samples having the L12 structure, large ordered domains, and a long-range order parameter close to its maximum value. Magnetic properties including ac and dc susceptibilities, zero-field-cooled and field-cooled magnetizations as a function of temperature and field (0-35 T) have been investigated. The resulting magnetic phase diagram displays, below a ferromagnetic region spreading over the whole (0<=x<=1) concentration range, a reentrant spin-glass phase for 0
Spin freezing process in a reentrant ferromagnet studied by neutron depolarization analysis
Sato, T.; Shinohara, T.; Ogawa, T.; Takeda, M.
2004-10-01
The spin freezing process and the magnetic nature of reentrant spin-glass (RSG) and the ferromagnetic (FM) phases of a typical reentrant ferromagnet Ni{sub 78}Mn{sub 22} were investigated based on neutron depolarization analysis, and the results were compared with the previous Moessbauer measurements [Phys. Rev. B 64, 184432 (2001)]. The wavelength-dependent polarization, under a field cooled (FC) condition, showed the damped oscillatory behavior in both the RSG and FM phases, except in the temperature region just above the RSG temperature T{sub RSG}{approx}60 K. At a temperature of around 80 K, however, it showed a double oscillatory behavior. The field integral I, which is proportional to the mean local magnetic induction, was deduced as a function of the temperature. Two branches of temperature-dependent field integrals were found: a low-temperature I{sub low}-branch, which has a small value of I, stopped at a temperature below the Curie temperature T{sub C}{approx}160 K, and a high temperature I{sub high}-branch, which has a large value of I, appeared just below 80 K. This means that there are two kinds of magnetic environments, and they have different values of magnetization. This is consistent with the observation of the double peak spectrum of the hyperfine field in the previous Moessbauer measurements. The present neutron data and the Moessbauer data can be interpreted along a scenario of reentrant behavior, which consists of the low-temperature spin canting state and the ''melting of frustrated spins'' mechanism introduced by Saslow and Parker [Phys. Rev. Lett. 56, 1074 (1986)], except for the absence of the observation of singularity in the temperature-dependent magnetization. Based on such considerations, we constructed a comprehensive picture of the spin freezing process and the magnetic nature of the RSG and FM phases in the reentrant ferromagnet.
Ribeiro, P. R. T.; Machado, F. L. A.; Dahlberg, E. Dan
2015-05-07
Low temperature magnetization (M) and ac susceptibility (χ{sub ac}) data were used to investigate the reentrant spin-glass state in lengths of melt-spun ribbons of Fe{sub 100−x}Zr{sub x} (x = 9, 10) amorphous alloys. The temperature range investigated was from 2 to 300 K, while the applied magnetic field H was varied in the range of ±85 kOe. The magnetic properties were found to be strongly influenced by the sample composition despite the fact that the amount of Fe varies by 1 at. %. For instance, the Curie temperature (T{sub C}) is reduced from 232.5 K to 213.0 K with decreasing Fe concentration, while M for the lower Fe concentration, measured at the highest applied magnetic field (H = 85 kOe) was nearly double the value for that of the higher; the coercivity in the ferromagnetic regime is reduced by a factor close to five when x is increased from 9 at. % to 10 at. %. The ac susceptibility measured for frequencies f in the range of 10–10{sup 4 }Hz showed a sharp drop in the magnitude of the in-phase contribution (χ{sub ac}{sup ′}) and a peak at the out-of-phase component (χ{sub ac}{sup ″}), which shifts to higher temperatures with increasing values of f. The Voguel-Fulcher law applied to the χ{sub ac}{sup ″} data yielded an activation energy E{sub a}/k{sub B} = 21.3 K (40.1 K), the glassy temperature T{sub G} = 15.5 K (38.2 K), and a relaxation time τ{sub 0}=9.1×10{sup −7} s (8.3×10{sup −7} s), for the sample with x = 10 (x = 9). A plot of χ{sub ac}{sup ″}vsχ{sub ac}{sup ′} for a broad range of T and f yielded a broad maximum near the glassy temperature T{sub G} for both sample concentrations.
Dynamic scaling in spin glasses
NASA Astrophysics Data System (ADS)
Pappas, C.; Mezei, F.; Ehlers, G.; Manuel, P.; Campbell, I. A.
2003-08-01
We present neutron spin echo (NSE) results and a revisited analysis of historical data on spin glasses, which reveal a pure power-law time decay of the spin autocorrelation function s(Q,t)=S(Q,t)/S(Q) at the glass temperature Tg. The power law exponent is in excellent agreement with that calculated from dynamic and static critical exponents deduced from macroscopic susceptibility measurements made on a quite different time scale. This scaling relation involving exponents of different physical quantities determined by completely independent experimental methods is stringently verified experimentally in a spin glass. As spin glasses are a subgroup of the vast family of glassy systems also comprising structural glasses and other noncrystalline systems the observed strict critical scaling behavior is important. Above the phase transition the strikingly nonexponential relaxation, best fitted by the Ogielski (power-law times stretched exponential) function, appears as an intrinsic, homogeneous feature of spin glasses.
Evidence for reentrant strain glass behavior in a ferroelastic-martensitic system Ti-Pd-V
NASA Astrophysics Data System (ADS)
Zhang, Xiaoming; Xu, Guizhou; Liu, Enke; Wang, Wenhong; Wu, Guangheng; Institute of Physics Team
2015-03-01
The concept of strain glass (SG) has recently received much attention because of its unique properties such as shape memory effect, superelasticity, and stress-tuned intelligent damping behavior. Recent in-situ TEM experiments have proved that, only local-symmetry change in the crystal structure has been observed during the SG transition, but the macroscopic symmetry or average structure is still keeping unchanged. In this presentation, we report the discovery of reentrant-strain-glass (RSG) behavior in a ferroelastic-martensitic system Ti50Pd50-xVx (x is from 6 to 12). Unlike the SG, with decreasing of temperature, the RSG system first undergoes a macroscopic martensitic transition and then the martensite variants further transforms to a frustrated glassy state below a critical temperature. The X-ray diffraction and high resolution TEM results further indicate the RSG no longer remains the average structure of the high-temperature parent phase, but rather low-temperature martensitic phase. This new discovery may open a new research field and may lead to new insights into a range of possible applications of this unique class of materials.
Universality in bipartite mean field spin glasses
NASA Astrophysics Data System (ADS)
Genovese, Giuseppe
2012-12-01
In this work, we give a proof of universality with respect to the choice of the statistical distribution of the quenched noise, for mean field bipartite spin glasses. We use mainly techniques of spin glasses theory, as Guerra's interpolation and the cavity approach.
Spin glasses in the nonextensive regime
NASA Astrophysics Data System (ADS)
Wittmann, Matthew; Young, A. P.
2012-04-01
Spin systems with long-range interactions are “nonextensive” if the strength of the interactions falls off sufficiently slowly with distance. It has been conjectured for ferromagnets and, more recently, for spin glasses that, everywhere in the nonextensive regime, the free energy is exactly equal to that for the infinite range model in which the characteristic strength of the interaction is independent of distance. In this paper we present the results of Monte Carlo simulations of the one-dimensional long-range spin glasses in the nonextensive regime. Using finite-size scaling, our results for the transition temperatures are consistent with this prediction. We also propose and provide numerical evidence for an analogous result for diluted long-range spin glasses in which the coordination number is finite, namely, that the transition temperature throughout the nonextensive regime is equal to that of the infinite-range model known as the Viana-Bray model.
Krayzman, Victor; Levin, Igor Woicik, Joseph C.; Bridges, Frank
2015-11-09
The local structure of the pseudo-cubic solid solution 0.6BaTiO{sub 3}-0.4BiScO{sub 3}, which exhibits reentrant dipole-glass behavior, has been determined using the Reverse Monte Carlo method to simultaneously fit (1) neutron and X-ray total scattering data (including the corresponding real-space pair-distribution functions), (2) Bi and Sc extended X-ray absorption fine structure, and (3) patterns of diffuse scattering in electron diffraction. These structural refinements revealed the multi-site probability density distributions for both Bi (14-sites) and Ti (8 sites), whereas Ba and Sc featured normal unimodal distributions. Bi atoms are displaced along both the 〈111〉 and 〈100〉 directions, while Ti atoms are shifted along 〈111〉. Correlated dynamic hopping of Bi and Ti over their corresponding split sites combined with chemical disorder is proposed as the origin of the strong frequency dispersion observed in dielectric measurements. The existence of split sites also explains the reentrant dipole-glass behavior reported for this system.
Spin glasses and error-correcting codes
NASA Technical Reports Server (NTRS)
Belongie, M. L.
1994-01-01
In this article, we study a model for error-correcting codes that comes from spin glass theory and leads to both new codes and a new decoding technique. Using the theory of spin glasses, it has been proven that a simple construction yields a family of binary codes whose performance asymptotically approaches the Shannon bound for the Gaussian channel. The limit is approached as the number of information bits per codeword approaches infinity while the rate of the code approaches zero. Thus, the codes rapidly become impractical. We present simulation results that show the performance of a few manageable examples of these codes. In the correspondence that exists between spin glasses and error-correcting codes, the concept of a thermal average leads to a method of decoding that differs from the standard method of finding the most likely information sequence for a given received codeword. Whereas the standard method corresponds to calculating the thermal average at temperature zero, calculating the thermal average at a certain optimum temperature results instead in the sequence of most likely information bits. Since linear block codes and convolutional codes can be viewed as examples of spin glasses, this new decoding method can be used to decode these codes in a way that minimizes the bit error rate instead of the codeword error rate. We present simulation results that show a small improvement in bit error rate by using the thermal average technique.
Dynamics of ferromagnetic spin glass: randomly canted ferromagnet versus skewed spin glass
NASA Astrophysics Data System (ADS)
Janutka, Andrzej
2003-12-01
A ferromagnetic spin glass (FSG) is one of the three isotropic and homogeneous phases of the long-range partially ordered magnets with spin and atomic disorder which are selected by symmetry (Andreev 1978 Sov. Phys.—JETP 47 411) (the others are genuine and antiferromagnetic spin glasses). The linear dynamical response to a magnetic field of two sub-phases of a FSG with drastically different dynamics, a randomly canted ferromagnet, in which the component spins create an acute angle with the summary magnetic moment, and a less-ordered skewed spin glass is analysed in the spin-wave approximation in the framework of phenomenological theory. The spin-wave damping coefficients and frequency shifts due to a magnon-magnon interaction are evaluated as functions of temperature and wavevector as well as the spectral-weight functions of the linear response to a magnetic field and the neutron scattering cross section which provides the possibility for experimental verification of the results. Substantial differences in the spin-wave characteristics of the FSG compared to those of the Heisenberg spin glass and the Heisenberg ferromagnet are found to be due to non-linear anisotropy effects in a FSG.
Spin correlations near the ferromagnetic-spin glass crossover in Eu/sub x/Sr/sub 1-x/S
Maletta, H.; Aeppli, G.; Shapiro, S.M.
1982-09-01
Bulk susceptibility and high-resolution neutron-diffraction measurements have been performed on single crystals of Eu/sub x/Sr/sub 1-x/S for x = 0.52 and 0.54 near the ferromagnet (FM) - spin glass (SG) crossover. A reentrant phase is established, which is induced by random-field effects. As the temperature is reduced the FM correlation length xi passes through a resolution-limited maximum where a frustrated FM phase is observed. In the SG at lower temperature xi decreases again and a coexisting FM component can be excluded. 6 figures.
Almost sure convergence in quantum spin glasses
Buzinski, David Meckes, Elizabeth
2015-12-15
Recently, Keating, Linden, and Wells [Markov Processes Relat. Fields 21(3), 537-555 (2015)] showed that the density of states measure of a nearest-neighbor quantum spin glass model is approximately Gaussian when the number of particles is large. The density of states measure is the ensemble average of the empirical spectral measure of a random matrix; in this paper, we use concentration of measure and entropy techniques together with the result of Keating, Linden, and Wells to show that in fact the empirical spectral measure of such a random matrix is almost surely approximately Gaussian itself with no ensemble averaging. We also extend this result to a spherical quantum spin glass model and to the more general coupling geometries investigated by Erdős and Schröder [Math. Phys., Anal. Geom. 17(3-4), 441–464 (2014)].
Almost sure convergence in quantum spin glasses
NASA Astrophysics Data System (ADS)
Buzinski, David; Meckes, Elizabeth
2015-12-01
Recently, Keating, Linden, and Wells [Markov Processes Relat. Fields 21(3), 537-555 (2015)] showed that the density of states measure of a nearest-neighbor quantum spin glass model is approximately Gaussian when the number of particles is large. The density of states measure is the ensemble average of the empirical spectral measure of a random matrix; in this paper, we use concentration of measure and entropy techniques together with the result of Keating, Linden, and Wells to show that in fact the empirical spectral measure of such a random matrix is almost surely approximately Gaussian itself with no ensemble averaging. We also extend this result to a spherical quantum spin glass model and to the more general coupling geometries investigated by Erdős and Schröder [Math. Phys., Anal. Geom. 17(3-4), 441-464 (2014)].
Nature of ordering in Potts spin glasses
NASA Astrophysics Data System (ADS)
Banavar, Jayanth R.; Cieplak, Marek
1989-09-01
The zero-temperature scaling approach is applied to the three-state Potts spin glass. Our results suggest that the +/-J model has a lower critical dimensionality greater than 3, whereas for the Gaussian model this dimensionality is slightly less than 3. The T=0 scaling exponents are estimated in D=2 and 3. The results are based mostly on exact transfer-matrix calculations and on a Monte Carlo quenching procedure.
Spin Effects in Bose-Glass Phases
NASA Astrophysics Data System (ADS)
Paganelli, S.; ŁaÇki, M.; Ahufinger, V.; Zakrzewski, J.; Sanpera, A.
2011-12-01
We study the mechanism of formation of Bose glass (BG) phases in the spin-1 Bose Hubbard model when diagonal disorder is introduced. To this aim, we analyze first the phase diagram in the zero-hopping limit, there disorder induces superposition between Mott insulator (MI) phases with different filling numbers. Then BG appears as a compressible but still insulating phase. The phase diagram for finite hopping is also calculated with the Gutzwiller approximation. The bosons' spin degree of freedom introduces another scattering channel in the two-body interaction modifying the stability of MI regions with respect to the action of disorder. This leads to some peculiar phenomena such as the creation of BG of singlets, for very strong spin correlation, or the disappearance of BG phase in some particular cases where fluctuations are not able to mix different MI regions.
Spin glass dynamics at the mesoscale
NASA Astrophysics Data System (ADS)
Guchhait, Samaresh; Kenning, Gregory G.; Orbach, Raymond L.; Rodriguez, Gilberto F.
2015-01-01
The mesoscale allows a new probe of spin glass dynamics. Because the spin glass lower critical dimension dl>2 , the growth of the correlation length ξ (t ,T ) can change the nature of the spin glass state at a crossover time tco when ξ (tco,T )=ℓ , a minimum characteristic sample length (e.g., film thickness for thin films and crystallite size for bulk samples). For thin films, and times t
Lookman, Turab; Vasseur, Romain
2009-01-01
We demonstrate that a strain pseudo-spin model for martensitic alloys predicts a glass phase in the presence of disorder, consistent with recent experiments on binary and temary alloys that have established the existence of such a phase above a critical composition. We find that the glass phase, as characterized by the Edwards-Andersen order parameter, exists even in the absence of elastic long-range interactions which compete with the disorder to shift the glass transition to higher values of disorder. Our model predicts a second order phase transition between the martensite and strain glass phases as a function of the disorder. Together with the cusp in the susceptibility and the history dependence in the glass phase in zero-field-cooling and field-cooling curves, these predictions may be tested experimentally by varying the alloy composition. Our approach using mean-field analysis and Monte Carlo simulations may be generalized to the study of glassy behavior in more complex structural transformations in two and three dimensions.
Quantum Optimization of Fully Connected Spin Glasses
NASA Astrophysics Data System (ADS)
Venturelli, Davide; Mandrà, Salvatore; Knysh, Sergey; O'Gorman, Bryan; Biswas, Rupak; Smelyanskiy, Vadim
2015-07-01
Many NP-hard problems can be seen as the task of finding a ground state of a disordered highly connected Ising spin glass. If solutions are sought by means of quantum annealing, it is often necessary to represent those graphs in the annealer's hardware by means of the graph-minor embedding technique, generating a final Hamiltonian consisting of coupled chains of ferromagnetically bound spins, whose binding energy is a free parameter. In order to investigate the effect of embedding on problems of interest, the fully connected Sherrington-Kirkpatrick model with random ±1 couplings is programmed on the D-Wave TwoTM annealer using up to 270 qubits interacting on a Chimera-type graph. We present the best embedding prescriptions for encoding the Sherrington-Kirkpatrick problem in the Chimera graph. The results indicate that the optimal choice of embedding parameters could be associated with the emergence of the spin-glass phase of the embedded problem, whose presence was previously uncertain. This optimal parameter setting allows the performance of the quantum annealer to compete with (and potentially outperform, in the absence of analog control errors) optimized simulated annealing algorithms.
NASA Astrophysics Data System (ADS)
Trepakov, V. A.; Savinov, M. E.; Prosandeev, S. A.; Kapphan, S. E.; Jastrabik, L.; Boatner, L. A.
2005-01-01
Impurity induced structural transformations are studied for KTa1-xNbxO3 with x = 0.0018 (KTN-1.8) by low-frequency linear and non-linear dielectric spectroscopy techniques. Nb admixture leads to the appearance of a sharp (T) maximum accompanying the ferroelectric phase transition at TC 27 K, and a glass-like state formation at lower temperatures. The linear permittivity evidences properties inherent to systems being near the quantum-mechanical displacive limit and shows the long range polar order with macroscopic polarization formation at 27 K. This conclusion was proven by nonlinear polarization response stuidy under dc electric field action, which evidenced also the proximity of the three-critical point. Above 27 K, the nonlinearity increases at cooling in accordance with the Devonshire theory for the paraelectric phase of conventional ferroelectrics. Below 27 K, the random distribution of Nb5+ ions and related system's inhomogeneities provoke a new low temperature phase state formation, which can be treated as reentrant polar-glass.
Finite-connectivity spin-glass phase diagrams and low-density parity check codes
NASA Astrophysics Data System (ADS)
Migliorini, Gabriele; Saad, David
2006-02-01
We obtain phase diagrams of regular and irregular finite-connectivity spin glasses. Contact is first established between properties of the phase diagram and the performance of low-density parity check (LDPC) codes within the replica symmetric (RS) ansatz. We then study the location of the dynamical and critical transition points of these systems within the one step replica symmetry breaking theory (RSB), extending similar calculations that have been performed in the past for the Bethe spin-glass problem. We observe that the location of the dynamical transition line does change within the RSB theory, in comparison with the results obtained in the RS case. For LDPC decoding of messages transmitted over the binary erasure channel we find, at zero temperature and rate R=1/4 , an RS critical transition point at pc≃0.67 while the critical RSB transition point is located at pc≃0.7450±0.0050 , to be compared with the corresponding Shannon bound 1-R . For the binary symmetric channel we show that the low temperature reentrant behavior of the dynamical transition line, observed within the RS ansatz, changes its location when the RSB ansatz is employed; the dynamical transition point occurs at higher values of the channel noise. Possible practical implications to improve the performance of the state-of-the-art error correcting codes are discussed.
Heineman Prize Talk: Spin Glasses Between Mathematics and Physics
NASA Astrophysics Data System (ADS)
Parisi, Giorgio
2005-03-01
The amount of work that has been done theoretical on spin glasses is quite large and I will concentrate on some of the main results. I will start from the physical explanation of the very slow response of many disordered systems (e.g. glasses and spin glasses). I will introduce a soluble model for spin glasses, the Sherrington-Kirkpatrick model, that generalizes the local Edwards- Anderson model in infinite dimensions. The model, where each spin is connected to all other spins, should be solved by using the appropriate mean field approximation. I will show how it can be heuristically solved using algebraic or probabilistic methods. I will briefly describe the recent rigorous mathematical proof that shows that this solution is correct. Finally I will describe the results and the problems that are present in extending the mean field theory to finite dimensions.
Spin glasses: redux: an updated experimental/materials survey
NASA Astrophysics Data System (ADS)
Mydosh, J. A.
2015-05-01
This article reviews the 40+ year old spin-glass field and one of its earliest model interpretations as a spin density wave. Our description is from an experimental phenomenological point of view with emphasis on new spin glass materials and their relation to topical problems and strongly correlated materials in condensed matter physics. We first simply define a spin glass (SG), give its basic ingredients and explain how the spin glasses enter into the statistical mechanics of classical phase transitions. We then consider the four basic experimental properties to solidly characterize canonical spin glass behavior and introduce the early theories and models. Here the spin density wave (SDW) concept is used to explain the difference between a short-range SDW, i.e. a SG and, in contrast, a long-range SDW, i.e. a conventional magnetic phase transition. We continue with the present state of SG, its massive computer simulations and recent proposals of chiral glasses and quantum SG. We then collect and mention the various SG ‘spin-off’s'. A major section uncovers the fashionable unconventional materials that display SG-like freezing and glassy ground states, such as (high temperature) superconductors, heavy fermions, intermetallics and Heuslers, pyrochlor and spinels, oxides and chalogenides and exotics, e.g. quasicrystals. Some conclusions and future directions complete the review.
Thermodynamic glass transition in a spin glass without time-reversal symmetry
Baños, Raquel Alvarez; Cruz, Andres; Fernandez, Luis Antonio; Gil-Narvion, Jose Miguel; Gordillo-Guerrero, Antonio; Guidetti, Marco; Iñiguez, David; Maiorano, Andrea; Marinari, Enzo; Martin-Mayor, Victor; Monforte-Garcia, Jorge; Muñoz Sudupe, Antonio; Navarro, Denis; Parisi, Giorgio; Perez-Gaviro, Sergio; Ruiz-Lorenzo, Juan Jesus; Schifano, Sebastiano Fabio; Seoane, Beatriz; Tarancon, Alfonso; Tellez, Pedro; Tripiccione, Raffaele; Yllanes, David
2012-01-01
Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method. PMID:22493229
Novel disordering mechanisms in dipolar spin glasses and ferromagnets
NASA Astrophysics Data System (ADS)
Schechter, Moshe; Andersen, Juan Carlos; Katzgraber, Helmut
2012-02-01
At and below the critical dimension the disordering of an ordered phase by a random field occurs via a collective effect of large domains at infinitesimal random field [Imry & Ma, Phys. Rev. Lett. 35, 1399 (1975)]. At larger space dimensions the disordering requires a large random field, of the order of the interaction energy. In a random field, the lower critical dimension is 2 for Ising ferromagnets, whereas it is infinity for spin glasses. We have generalized the Imry-Ma argument for ferromagnets with competing interactions and an underlying spin-glass phase, and for dilute dipolar spin glasses. For dilute dipolar spin glasses we have found [EPL 88, 66002 (2009)] that the broad distribution of random fields dictates more efficient disordering of the glass phase, and domain sizes which depend explicitly on the concentration, i.e., do not obey simple scaling. Here we show that as a result of a competing spin-glass phase, the disordering of the ferromagnet occurs at a finite random field, which is yet much smaller than the interactions. Our results are verified numerically, explain the recently-observed peculiar linear dependence of Tc on the random field strength [Nature 448, 567 (2007)], and predict a zero-temperature random-field driven transition between a ferromagnetic and a quasi spin glass phase.
Non-perturbative effects in spin glasses.
Castellana, Michele; Parisi, Giorgio
2015-01-01
We present a numerical study of an Ising spin glass with hierarchical interactions--the hierarchical Edwards-Anderson model with an external magnetic field (HEA). We study the model with Monte Carlo (MC) simulations in the mean-field (MF) and non-mean-field (NMF) regions corresponding to d ≥ 4 and d < 4 for the d-dimensional ferromagnetic Ising model respectively. We compare the MC results with those of a renormalization-group (RG) study where the critical fixed point is treated as a perturbation of the MF one, along the same lines as in the -expansion for the Ising model. The MC and the RG method agree in the MF region, predicting the existence of a transition and compatible values of the critical exponents. Conversely, the two approaches markedly disagree in the NMF case, where the MC data indicates a transition, while the RG analysis predicts that no perturbative critical fixed point exists. Also, the MC estimate of the critical exponent ν in the NMF region is about twice as large as its classical value, even if the analog of the system dimension is within only ~2% from its upper-critical-dimension value. Taken together, these results indicate that the transition in the NMF region is governed by strong non-perturbative effects. PMID:25733337
Bond chaos in spin glasses revealed through thermal boundary conditions
NASA Astrophysics Data System (ADS)
Wang, Wenlong; Machta, Jonathan; Katzgraber, Helmut G.
2016-06-01
Spin glasses have competing interactions that lead to a rough energy landscape which is highly susceptible to small perturbations. These chaotic effects strongly affect numerical simulations and, as such, gaining a deeper understanding of chaos in spin glasses is of much importance. The use of thermal boundary conditions is an effective approach to study chaotic phenomena. Here we generalize population annealing Monte Carlo, combined with thermal boundary conditions, to study bond chaos due to small perturbations in the spin-spin couplings of the three-dimensional Edwards-Anderson Ising spin glass. We show that bond and temperature-induced chaos share the same scaling exponents and that bond chaos is stronger than temperature chaos.
Efficient Cluster Algorithm for Spin Glasses in Any Space Dimension.
Zhu, Zheng; Ochoa, Andrew J; Katzgraber, Helmut G
2015-08-14
Spin systems with frustration and disorder are notoriously difficult to study, both analytically and numerically. While the simulation of ferromagnetic statistical mechanical models benefits greatly from cluster algorithms, these accelerated dynamics methods remain elusive for generic spin-glass-like systems. Here, we present a cluster algorithm for Ising spin glasses that works in any space dimension and speeds up thermalization by at least one order of magnitude at temperatures where thermalization is typically difficult. Our isoenergetic cluster moves are based on the Houdayer cluster algorithm for two-dimensional spin glasses and lead to a speedup over conventional state-of-the-art methods that increases with the system size. We illustrate the benefits of the isoenergetic cluster moves in two and three space dimensions, as well as the nonplanar chimera topology found in the D-Wave Inc. quantum annealing machine. PMID:26317743
Efficient Cluster Algorithm for Spin Glasses in Any Space Dimension
NASA Astrophysics Data System (ADS)
Zhu, Zheng; Ochoa, Andrew J.; Katzgraber, Helmut G.
2015-08-01
Spin systems with frustration and disorder are notoriously difficult to study, both analytically and numerically. While the simulation of ferromagnetic statistical mechanical models benefits greatly from cluster algorithms, these accelerated dynamics methods remain elusive for generic spin-glass-like systems. Here, we present a cluster algorithm for Ising spin glasses that works in any space dimension and speeds up thermalization by at least one order of magnitude at temperatures where thermalization is typically difficult. Our isoenergetic cluster moves are based on the Houdayer cluster algorithm for two-dimensional spin glasses and lead to a speedup over conventional state-of-the-art methods that increases with the system size. We illustrate the benefits of the isoenergetic cluster moves in two and three space dimensions, as well as the nonplanar chimera topology found in the D-Wave Inc. quantum annealing machine.
Finite block pseudo-spin approach of proton glass
NASA Astrophysics Data System (ADS)
Lee, Kwang-Sei; Koo, Je Huan; Lee, Cheol Eui
2016-08-01
We herein propose an alternative phenomenology to explain the phase of proton glass by reference to finite block spin theory in magnetism, in which the phase may be considered as being a short-range ferroelectric ordering of block pseudo-spins comprised of random pseudo-spins that have a majority of individual pseudo-spins in a given sense. By making use of the Curie law of block pseudo-spins, we obtained the dielectric susceptibility for the lower and higher temperature approximations of the Brillouin function. The experimental results for the susceptibility in hydrogen-bonded mixed crystals of ferroelectric RbH2P(As)O4 and antiferroelectric NH4H2P(As)O4 were thus fitted fairly well at low temperatures in the proton glass phase whereas some deviation from our formulation was seen at high temperatures in the paraelectric phase.
Strong Suppression of the Spin Hall Effect in the Spin Glass State
NASA Astrophysics Data System (ADS)
Niimi, Y.; Kimata, M.; Omori, Y.; Gu, B.; Ziman, T.; Maekawa, S.; Fert, A.; Otani, Y.
2015-11-01
We have measured spin Hall effects in spin glass metals, CuMnBi alloys, with the spin absorption method in the lateral spin valve structure. Far above the spin glass temperature Tg where the magnetic moments of Mn impurities are randomly frozen, the spin Hall angle of a CuMnBi ternary alloy is as large as that of a CuBi binary alloy. Surprisingly, however, it starts to decrease at about 4 Tg and becomes as little as 7 times smaller at 0.5 Tg. A similar tendency was also observed in anomalous Hall effects in the ternary alloys. We propose an explanation in terms of a simple model considering the relative dynamics between the localized moment and the conduction electron spin.
Deviations from Curie-Weiss behavior in spin-glasses
NASA Astrophysics Data System (ADS)
Rao, K. V.; Fähnle, M.; Figueroa, E.; Beckman, O.; Hedman, L.
1983-03-01
The magnetic susceptibility in the spin-glass concentration regime of amorphous alloys (FexNi1-x)75P16B6Al3 with x=0.04, 0.06, and 0.08 has been measured using a superconducting quantum interference detector magnetometer with an external field of 5 Oe for temperatures 5<=T<=60.5 K, and a Faraday balance with an external field of 5 kOe for 4.3<=T<=300 K. We observe a high-temperature (T>20Tf) Curie-Weiss law with positive values for the paramagnetic Curie temperature, indicating predominantly ferromagnetic exchange couplings. At temperatures approaching the spin-glass freezing temperature, however, there are strong deviations from Curie-Weiss behavior. A simple theory is developed which allows a determination of the angular spin correlations in the spin-glass ground state from these deviations. The number of such correlated spins (1.5 to 4.4) determined from our data compares well with computer-simulation studies by Walker and Walstedt as well as data obtained by other authors for Au-Fe, Cu-Mn, and Co- and Mn-aluminosilicate spin-glasses.
Improved fair sampling of ground states in Ising spin glasses
NASA Astrophysics Data System (ADS)
Katzgraber, Helmut G.; Zhu, Zheng; Ochoa, Andrew J.
2015-03-01
Verifying that an optimization approach can sample all solutions that minimize a Hamiltonian is a stringent test for any newly-developed algorithm. While most solvers easily compute the minimum of a cost function for small to moderate input sizes, equiprobable sampling of all ground-state configurations (within Poissonian fluctuations) is much harder to obtain. Most notably, methods such as transverse-field quantum annealing fail in passing this test for certain highly-degenerate problems. Here we present an attempt to sample ground states for Ising spin glasses based on a combination of low-temperature parallel tempering Monte Carlo combined with the cluster algorithm by Houdayer. Because the latter is rejection free and obeys details balance, the ground-state manifold is efficiently sampled. We illustrate the approach for Ising spin glasses on the D-Wave Two quantum annealer topology, known as the Chimera graph, as well as two-dimensional Ising spin glasses.
Aging dynamics of quantum spin glasses of rotors
NASA Astrophysics Data System (ADS)
Kennett, Malcolm P.; Chamon, Claudio; Ye, Jinwu
2001-12-01
We study the long time dynamics of quantum spin glasses of rotors using the nonequilibrium Schwinger-Keldysh formalism. These models are known to have a quantum phase transition from a paramagnetic to a spin-glass phase, which we approach by looking at the divergence of the spin-relaxation rate at the transition point. In the aging regime, we determine the dynamical equations governing the time evolution of the spin response and correlation functions, and show that all terms in the equations that arise solely from quantum effects are irrelevant at long times under time reparametrization group (RPG) transformations. At long times, quantum effects enter only through the renormalization of the parameters in the dynamical equations for the classical counterpart of the rotor model. Consequently, quantum effects only modify the out-of-equilibrium fluctuation-dissipation relation (OEFDR), i.e. the ratio X between the temperature and the effective temperature, but not the form of the classical OEFDR.
Zero-Temperature Fluctuations in Short-Range Spin Glasses
NASA Astrophysics Data System (ADS)
Arguin, L.-P.; Newman, C. M.; Stein, D. L.; Wehr, J.
2016-06-01
We consider the energy difference restricted to a finite volume for certain pairs of incongruent ground states (if they exist) in the d-dimensional Edwards-Anderson Ising spin glass at zero temperature. We prove that the variance of this quantity with respect to the couplings grows proportionally to the volume in any d ≥ 2. An essential aspect of our result is the use of the excitation metastate. As an illustration of potential applications, we use this result to restrict the possible structure of spin glass ground states in two dimensions.
Non-compact local excitations in spin-glasses
NASA Astrophysics Data System (ADS)
Lamarcq, J.; Bouchaud, J.-P.; Martin, O. C.; Mézard, M.
2002-05-01
We study numerically the local low-energy excitations in the 3d Edwards-Anderson model for spin-glasses. Given the ground state, we determine the lowest-lying connected cluster of flipped spins with a fixed volume containing one given spin. These excitations are not compact, having a fractal dimension close to two, suggesting an analogy with lattice animals. Also, their energy does not grow with their size; the associated exponent is slightly negative whereas the one for compact clusters is positive. These findings call for a modification of the basic hypotheses underlying the droplet model.
Non-self-averaging in Ising spin glasses and hyperuniversality
NASA Astrophysics Data System (ADS)
Lundow, P. H.; Campbell, I. A.
2016-01-01
Ising spin glasses with bimodal and Gaussian near-neighbor interaction distributions are studied through numerical simulations. The non-self-averaging (normalized intersample variance) parameter U22(T ,L ) for the spin glass susceptibility [and for higher moments Un n(T ,L ) ] is reported for dimensions 2 ,3 ,4 ,5 , and 7. In each dimension d the non-self-averaging parameters in the paramagnetic regime vary with the sample size L and the correlation length ξ (T ,L ) as Un n(β ,L ) =[Kdξ (T ,L ) /L ] d and so follow a renormalization group law due to Aharony and Harris [Phys. Rev. Lett. 77, 3700 (1996), 10.1103/PhysRevLett.77.3700]. Empirically, it is found that the Kd values are independent of d to within the statistics. The maximum values [Unn(T,L ) ] max are almost independent of L in each dimension, and remarkably the estimated thermodynamic limit critical [Unn(T,L ) ] max peak values are also practically dimension-independent to within the statistics and so are "hyperuniversal." These results show that the form of the spin-spin correlation function distribution at criticality in the large L limit is independent of dimension within the ISG family. Inspection of published non-self-averaging data for three-dimensional Heisenberg and X Y spin glasses the light of the Ising spin glass non-self-averaging results show behavior which appears to be compatible with that expected on a chiral-driven ordering interpretation but incompatible with a spin-driven ordering scenario.
Compressible Sherrington-Kirkpatrick spin-glass model
NASA Astrophysics Data System (ADS)
Liarte, Danilo B.; Salinas, Silvio R.; Yokoi, Carlos S. O.
2009-05-01
We introduce a Sherrington-Kirkpatrick spin-glass model with the addition of elastic degrees of freedom. The problem is formulated in terms of an effective four-spin Hamiltonian in the pressure ensemble, which can be treated by the replica method. In the replica-symmetric approximation, we analyze the pressure-temperature phase diagram, and obtain expressions for the critical boundaries between the disordered and the ordered (spin-glass and ferromagnetic) phases. The second-order para-ferromagnetic border ends at a tricritical point, beyond which the transition becomes discontinuous. We use these results to make contact with the temperature-concentration phase diagrams of mixtures of hydrogen-bonded crystals.
Effect of glass structure on spin Hamiltonian parameters: Cu doped tellurite glasses
Ramamoorthy, Raj Kumar; Bhatnagar, Anil K.
2015-06-24
Cu-doped glasses with compositions [(70TeO{sub 2}−(30−x)ZnO−xPbO){sub 0.98}− (CuO){sub 0.02}] (x = 5, 10, 15, 20) were prepared using the melt quenching technique and characterized by EPR. Cu{sup 2+} ions are found to be in distorted oxygen octahedral cage and their corresponding spin Hamiltonian (splitting) parameters are deduced for all glasses as a function of increasing PbO. Finally, effect of the matrix on spin Hamiltonian parameters of Cu{sup 2+} ions are correlated with the help of EPR and earlier Raman analysis.
Avalanches and hysteresis in frustrated superconductors and XY spin glasses.
Sharma, Auditya; Andreanov, Alexei; Müller, Markus
2014-10-01
We study avalanches along the hysteresis loop of long-range interacting spin glasses with continuous XY symmetry, which serves as a toy model of granular superconductors with long-range and frustrated Josephson couplings. We identify sudden jumps in the T=0 configurations of the XY phases as an external field is increased. They are initiated by the softest mode of the inverse susceptibility matrix becoming unstable, which induces an avalanche of phase updates (or spin alignments). We analyze the statistics of these events and study the correlation between the nonlinear avalanches and the soft mode that initiates them. We find that the avalanches follow the directions of a small fraction of the softest modes of the inverse susceptibility matrix, similarly as was found in avalanches in jammed systems. In contrast to the similar Ising spin glass (Sherrington-Kirkpatrick) studied previously, we find that avalanches are not distributed with a scale-free power law but rather have a typical size which scales with the system size. We also observe that the Hessians of the spin-glass minima are not part of standard random matrix ensembles as the lowest eigenvector has a fractal support. PMID:25375434
Chaotic nature of the spin-glass phase
NASA Technical Reports Server (NTRS)
Bray, A. J.; Moore, M. A.
1987-01-01
The microscopic structure of the ordered phase of spin glasses is investigated theoretically in the framework of the T = 0 fixed-point model (McMillan, 1984; Fisher and Huse, 1986; and Bray and Moore, 1986). The sensitivity of the ground state to changes in the interaction strengths at T = 0 is explored, and it is found that for sufficiently large length scales the ground state is unstable against arbitrarily weak perturbations to the bonds. Explicit results are derived for d = 1, and the implications for d = 2 and d = 3 are considered in detail. It is concluded that there is no hidden order pattern for spin glasses at all T less than T(C), the ordered-phase spin correlations being chaotic functions of spin separation at fixed temperature or of temperature (for a given pair of spins) at scale lengths L greater than (T delta T) exp -1/zeta, where zeta = d(s)/2 - y, d(s) is the interfacial fractal dimension, and -y is the thermal eigenvalue at T = 0.
Local excitations of a spin glass in a magnetic field
NASA Astrophysics Data System (ADS)
Lamarcq, J.; Bouchaud, J.-P.; Martin, O. C.
2003-07-01
We study the minimum energy clusters (MEC) above the ground state for the 3-d Edwards-Anderson Ising spin glass in a magnetic field. For fields B below 0.4, we find that the field has almost no effect on the excitations that we can probe, of volume V⩽64. As found previously for B=0, their energies decrease with V, and their magnetization remains very small (even slightly negative). For larger fields, both the MEC energy and magnetization grow with V, as expected in a paramagnetic phase. However, all results appear to scale as BV (instead of B(V) as expected from droplet arguments), suggesting that the spin glass phase is destroyed by any small field. Finally, the geometry of the MEC is completely insensitive to the field, giving further credence that they are lattice animals, in the presence or the absence of a field.
Universality in p-spin glasses with correlated disorder
NASA Astrophysics Data System (ADS)
Bonzom, Valentin; Gurau, Razvan; Smerlak, Matteo
2013-02-01
We introduce a new method, based on the recently developed random tensor theory, for studying the p-spin glass model with non-Gaussian, correlated disorder. Using a suitable generalization of Gurau’s theorem on the universality of the large N limit of the p-unitary ensemble of random tensors, we exhibit an infinite family of such non-Gaussian distributions which leads to the same low temperature phase as the Gaussian distribution. While this result is easy to show (and well known) for uncorrelated disorder, its robustness with respect to strong quenched correlations is surprising. We show in detail how the critical temperature is renormalized by these correlations. We close with speculation on possible applications of random tensor theory to finite-range spin glass models.
Structural approaches to spin glasses and optimization problems
NASA Astrophysics Data System (ADS)
de Sanctis, Luca
We introduce the concept of Random Multi-Overlap Structure (RaMOSt) as a generalization of the one introduced by M. Aizenman et al. for non-diluted spin glasses. We use this concept to find generalized bounds for the free energy of the Viana-Bray model of diluted spin glasses and to formulate and prove the Extended Variational Principle that implicitly provides the free energy of the model. Then we exhibit a theorem for the limiting RaMOSt, analogous to the one found by F. Guerra for the Sherrington-Kirkpatrick model, that describes some stability properties of the model. We also show how our technique can be used to prove the existence of the thermodynamic limit of the free energy. We then propose an ultrametric breaking of replica symmetry for diluted spin glasses in the framework of Random Multi-Overlap Structures (RaMOSt). Such a proposal is closer to the Parisi theory for non-diluted spin glasses than the theory based on the iterative approach. Our approach allows to formulate an ansatz in which the Broken Replica Symmetry trial function depends on a set of numbers, over which one has to take the infimum (as opposed to a nested chain of probabilty distributions). Our scheme suggests that the order parameter is determined by the probability distribution of the multi-overlap in a similar sense as in the non-diluted case, and it is not necessarily a functional. Such results are then extended to the K-SAT and p-XOR-SAT optimization problems, and to the spherical mean field spin glass. The ultrametric structure exhibits a factorization property similar to the one of the optimal structures for the Viana-Bray model. The present work paves the way to a revisited Parisi theory for diluted spin systems. Moreover, it emphasizes some structural analogies among different models, which also seem to be plausible for models that still escape good mathematical control. This structural analysis seems quite promising both mathematically and physically.
Optimal protein-folding codes from spin-glass theory.
Goldstein, R A; Luthey-Schulten, Z A; Wolynes, P G
1992-01-01
Protein-folding codes embodied in sequence-dependent energy functions can be optimized using spin-glass theory. Optimal folding codes for associative-memory Hamiltonians based on aligned sequences are deduced. A screening method based on these codes correctly recognizes protein structures in the "twilight zone" of sequence identity in the overwhelming majority of cases. Simulated annealing for the optimally encoded Hamiltonian generally leads to qualitatively correct structures. Images PMID:1594594
The glass crossover from mean-field Spin-Glasses to supercooled liquids
NASA Astrophysics Data System (ADS)
Rizzo, Tommaso
2016-03-01
Stochastic-Beta-Relaxation provides a characterisation of the glass crossover in discontinuous Spin-Glasses and supercoooled liquid. Notably it can be derived through a rigorous computation from a dynamical Landau theory. In this paper, I will discuss the precise meaning of this connection in a language that does not require familiarity with statistical field theory. I will discuss finite-size corrections in mean-field Spin-Glass models and loop corrections in finite-dimensional models that are both described by the dynamical Landau theory considered. Then I will argue that the same Landau theory can be associated to supercooled liquid described by Mode-Coupling Theory invoking a physical principle of time-scale invariance.
NASA Astrophysics Data System (ADS)
Harrison, Richard J.
2009-02-01
Magnetic ordering in the ilmenite-hematite solid solution (Fe2-xTixO3) has been investigated using Monte Carlo simulations, with particular emphasis on the low-temperature spin glass region of the phase diagram. Complex magnetic behavior is observed due to the presence of two competing magnetic order parameters: a "hematite-like" ordering with a two-layer repeat (Q2) and an "ilmenite-like" ordering with a four-layer repeat (Q4). The susceptibility and degree of magnetic order were calculated from the Fourier transform of the layer-averaged spin distribution, allowing long-range and short-range contributions from Q2 and Q4 to be analyzed separately. For x < 0.8, the ferrimagnetic (FM) phase remains stable down to 0 K. For x ≥ 0.8 a heterogeneous FM phase (HFM) followed by a modulated FM phase (MFM) develops. There is an increasing contribution from Q4 with increasing x, and a pronounced cusp in both Q2 and Q4 susceptibilities develops at 30 K. The superposition of Q2 and Q4 leads to frustrated layers containing dynamically disordered spins. Freezing of this spin disorder below 30 K is responsible for the cusp in susceptibility, which can be classified as a reentrant spin glass (RSG) transition. A gradual loss of long-range FM order occurs as the percolation threshold is approached, resulting in a conventional spin glass (CSG) with no long-range order below 30 K for x ≥ 0.92. For x > 0.95, a transition to an antiferromagnetic (AF) phase occurs at 40-55 K, followed by an RSG transition at 20-30 K. Changes to the phase diagram caused by chemical clustering are determined using a preannealing algorithm. Clustering expands the AF field to x > 0.9 and the HFM field to x ≥ 0.55. The topology of the simulated phase diagram compares favorably with experiments but suggests that the nature of some phase boundaries should be reexamined from both experimental and computational perspectives.
Collective nature of the reentrant integer quantum Hall states in the second Landau level.
Deng, N; Kumar, A; Manfra, M J; Pfeiffer, L N; West, K W; Csáthy, G A
2012-02-24
We report an unexpected sharp peak in the temperature dependence of the magnetoresistance of the reentrant integer quantum Hall states in the second Landau level. This peak defines the onset temperature of these states. We find that in different spin branches the onset temperatures of the reentrant states scale with the Coulomb energy. This scaling provides direct evidence that Coulomb interactions play an important role in the formation of these reentrant states evincing their collective nature. PMID:22463555
Collective Nature of the Reentrant Integer Quantum Hall States in the Second Landau Level
NASA Astrophysics Data System (ADS)
Deng, N.; Kumar, A.; Manfra, M. J.; Pfeiffer, L. N.; West, K. W.; Csáthy, G. A.
2012-02-01
We report an unexpected sharp peak in the temperature dependence of the magnetoresistance of the reentrant integer quantum Hall states in the second Landau level. This peak defines the onset temperature of these states. We find that in different spin branches the onset temperatures of the reentrant states scale with the Coulomb energy. This scaling provides direct evidence that Coulomb interactions play an important role in the formation of these reentrant states evincing their collective nature.
Spin-polarized nitroxide radicals in organic glasses.
Tarasov, V. F.; Shkrob, I. A.; Trifunac, A. D.; Chemistry
2002-01-01
Nonequilibrium spin polarization formed in a stable nitroxide radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempo) due to the occurrence of Chemically Induced Dynamic Electron Polarization (CIDEP) in photoexcited molecular complexes of this radical with 1,4-benzoquinone, 1,4-naphthaquinone, 9,10-anthraquinone, and their derivatives is observed. These complexes occur spontaneously in low-temperature organic glasses (20-70 K) upon freezing the concentrated liquid solutions. The emissive net polarization in the nitroxide radical is observed 0.1-10 {mu}s after the photoexcitation of the p-quinone moiety. No degradation of the polarized magnetic resonance signal from Tempo after >104 excitation cycles was observed. This spin polarization is shown to be mainly due to a polarization transfer from the lowest triplet state of the p-quinone. This transfer is driven by the electron spin exchange interaction between the nitroxide radical and the triplet p-quinone; it occurs simultaneously with a spin-selective electronic relaxation of the photoexcited complex. The resulting mechanism combines the features of the electron spin polarization transfer (ESPT) and radical-triplet pair mechanisms (RTPM) in liquid. A theoretical model of such a mechanism is suggested.
Spin-glass-like behaviour in IrSr{sub 2}RECu{sub 2}O{sub 8} (RE=Sm and Eu)
Santos-Garcia, A.J. dos Duijn, J. van; Alario-Franco, M.A.
2008-12-15
We report the results of magnetic and specific heat measurements on the 1212-type compounds IrSr{sub 2}RECu{sub 2}O{sub 8} with RE=Sm and Eu, prepared by high-pressure and high-temperature synthesis. The magnetic susceptibility of these compounds shows a large difference in the temperature dependence of the magnetization measured under zero-field-cooled and field-cooled conditions below 87 and 71 K, respectively, and upon further cooling below {approx}10 K substantial maxima are observed too. Further AC susceptibility measurements support a glassy behaviour in lower magnetic transitions whereas the specific heat measurements do not show the typical long-range ordering commonly displayed in ferro, ferri or antiferromagnetic transitions. Hysteresis loops suggest the presence of magnetic clusters in the otherwise paramagnetic zone, indicating that these compounds probably display a reentrant spin-glass transition. Results are presented and discussed. - Graphical abstract: IrSr{sub 2}RECu{sub 2}O{sub 8} with RE=Sm and Eu were prepared by high-pressure and high-temperature synthesis. Both samples adopt a M-1212-type perovskite structure and a microdomain texturing of the long c-axis is observed by TEM. A very interesting magnetic behaviour is observed in these materials. A 'cluster by cluster freezing' model is proposed, instead of the classical individual spin freezing one to explain the spin-glass-like behaviour that seems to coexist with weak ferromagnetism in both compounds.
Some Spin Glass Ideas Applied to the Clique Problem
NASA Astrophysics Data System (ADS)
Iovanella, Antonio; Scoppola, Benedetto; Scoppola, Elisabetta
2007-03-01
In this paper we introduce a new algorithm to study some NP-complete problems. This algorithm is a Markov Chain Monte Carlo (MCMC) inspired by the cavity method developed in the study of spin glass. We will focus on the maximum clique problem and we will compare this new algorithm with several standard algorithms on some DIMACS benchmark graphs and on random graphs. The performances of the new algorithm are quite surprising. Our effort in this paper is to be clear as well to those readers who are not in the field.
Spin Glass a Bridge Between Quantum Computation and Statistical Mechanics
NASA Astrophysics Data System (ADS)
Ohzeki, Masayuki
2013-09-01
In this chapter, we show two fascinating topics lying between quantum information processing and statistical mechanics. First, we introduce an elaborated technique, the surface code, to prepare the particular quantum state with robustness against decoherence. Interestingly, the theoretical limitation of the surface code, accuracy threshold, to restore the quantum state has a close connection with the problem on the phase transition in a special model known as spin glasses, which is one of the most active researches in statistical mechanics. The phase transition in spin glasses is an intractable problem, since we must strive many-body system with complicated interactions with change of their signs depending on the distance between spins. Fortunately, recent progress in spin-glass theory enables us to predict the precise location of the critical point, at which the phase transition occurs. It means that statistical mechanics is available for revealing one of the most interesting parts in quantum information processing. We show how to import the special tool in statistical mechanics into the problem on the accuracy threshold in quantum computation. Second, we show another interesting technique to employ quantum nature, quantum annealing. The purpose of quantum annealing is to search for the most favored solution of a multivariable function, namely optimization problem. The most typical instance is the traveling salesman problem to find the minimum tour while visiting all the cities. In quantum annealing, we introduce quantum fluctuation to drive a particular system with the artificial Hamiltonian, in which the ground state represents the optimal solution of the specific problem we desire to solve. Induction of the quantum fluctuation gives rise to the quantum tunneling effect, which allows nontrivial hopping from state to state. We then sketch a strategy to control the quantum fluctuation efficiently reaching the ground state. Such a generic framework is called
Microwires fabricated by glass-coated melt spinning
Zhao, Y. Y.; Li, H.; Hao, H. Y.; Li, M.; Zhang, Y.; Liaw, P. K.
2013-07-15
The glass-coated melt spinning method offers a route for the manufacture of metal filaments with a few micrometers in diameter in a single operation directly from the melt. Cobalt-based amorphous wires, Cu-15.0 atomic percent (at. %) Sn shape-memory wires, and Ni{sub 2}MnGa (atomic percent) ferromagnetic wires were successfully produced by this method. The cobalt-based amorphous wire is flexible, and Cu-15.0 at. % Sn shape-memory wires have the tensile elongation of 14%. However, because of chemical reaction with glass and oxidation, it is hard to make Cu–Al–Ni shape-memory wires and Ni–Nb–Sn amorphous wires. Conditions for preparing these materials were summarized, and the differences of the solidification processes among glass-coated amorphous cobalt-based wires, Cu-15.0 at. % Sn shape-memory wires, and Ni{sub 2}MnGa wires were analyzed and discussed.
Mean-field theory of spin-glasses with finite coordination number
NASA Technical Reports Server (NTRS)
Kanter, I.; Sompolinsky, H.
1987-01-01
The mean-field theory of dilute spin-glasses is studied in the limit where the average coordination number is finite. The zero-temperature phase diagram is calculated and the relationship between the spin-glass phase and the percolation transition is discussed. The present formalism is applicable also to graph optimization problems.
Local excitations in mean-field spin glasses
NASA Astrophysics Data System (ADS)
Krzakala, F.; Parisi, G.
2004-06-01
We address the question of geometrical as well as energetic properties of local excitations in mean-field Ising spin glasses. We study analytically the Random Energy Model and numerically a dilute mean-field model, first on tree-like graphs, equivalent to a replica-symmetric computation, and then directly on finite-connectivity random lattices. In the first model, characterized by a discontinuous replica symmetry breaking, we found that the energy of finite-volume excitation is infinite, whereas in the dilute mean-field model, described by a continuous replica symmetry breaking, it slowly decreases with sizes and saturates at a finite value, in contrast with what would be naively expected. The geometrical properties of these excitations are similar to those of lattice animals or branched polymers. We discuss the meaning of these results in terms of replica symmetry breaking and also possible relevance in finite-dimensional systems.
Superexchange and spin-glass formation in semimagnetic semiconductors
NASA Astrophysics Data System (ADS)
Rusin, Tomasz M.
1996-05-01
The Mn-Mn superexchange interaction in semimagnetic semiconductors A1-xMnxB (where A=Zn, Cd and B=S, Se, Te) is studied within the three-level model of the band structure. We focus on the dependence of the interaction on the interion distance Jdd(r)=J0f(r). In the present work, the function f(r) is obtained analytically. This, only weakly material-dependent function is found to decrease with Mn-Mn distance much slower than its Gaussian approximation derived previously. The exact form of the decay of the superexchange can be approximated by a power law J0r-8.5. This is close to an experimental result, J0r-6.8, determined on the basis of the spin-glass transition temperature on the composition.
Spin glass model for dynamics of cell reprogramming
NASA Astrophysics Data System (ADS)
Pusuluri, Sai Teja; Lang, Alex H.; Mehta, Pankaj; Castillo, Horacio E.
2015-03-01
Recent experiments show that differentiated cells can be reprogrammed to become pluripotent stem cells. The possible cell fates can be modeled as attractors in a dynamical system, the ``epigenetic landscape.'' Both cellular differentiation and reprogramming can be described in the landscape picture as motion from one attractor to another attractor. We perform Monte Carlo simulations in a simple model of the landscape. This model is based on spin glass theory and it can be used to construct a simulated epigenetic landscape starting from the experimental genomic data. We re-analyse data from several cell reprogramming experiments and compare with our simulation results. We find that the model can reproduce some of the main features of the dynamics of cell reprogramming.
The decoupling of the glass transitions in the two-component p-spin spherical model
NASA Astrophysics Data System (ADS)
Ikeda, Harukuni; Ikeda, Atsushi
2016-07-01
Binary mixtures of large and small particles with a disparate size ratio exhibit a rich phenomenology at their glass transition points. In order to gain insights on such systems, we introduce and study a two-component version of the p-spin spherical spin glass model. We employ the replica method to calculate the free energy and the phase diagram. We show that when the strengths of the interactions of each component are not widely separated, the model has only one glass phase characterized by the conventional one-step replica symmetry breaking. However when the strengths of the interactions are well separated, the model has three glass phases depending on the temperature and component ratio. One is the ‘single’ glass phase in which only the spins of one component are frozen while the spins of the other component remain mobile. This phase is characterized by the one-step replica symmetry breaking. The second is the ‘double’ glass phase obtained by cooling the single glass phase further, in which the spins of the remaining mobile component are also frozen. This phase is characterized by the two-step replica symmetry breaking. The third is also the ‘double’ glass phase, which, however, is formed by the simultaneous freezing of the spins of both components at the same temperatures and is characterized by the one-step replica symmetry breaking. We discuss the implications of these results for the glass transitions of binary mixtures.
Magnetostriction of rare-earth random magnetic anisotropy spin glasses
del Moral, A.; Arnaudas, J.I.
1989-05-01
A model of magnetostriction for single-ion random magnetic anisotropy (RMA) spin glasses (SG) is developed, the calculation being based on the replica technique. An overall uniform strain is assumed and coupled to the local easy axis (or easy plane) by an adequate projection. The obtained bulk magnetostriction becomes proportional to the average quadrupolar moment, which depends upon the assumed ferromagnetic uniform exchange, J/sub 0/, and the RMA crystal field (CEF), D/sub 0/, strengths. Magnetostriction measurements parallel (lambda/sub X/) and perpendicular (lambda/sub perpendicular/) to the applied magnetic field (up to 7 T) have been performed between 4.2 and 150 K (much larger than the SG temperature, T/sub SG/) for the amorphous spin glasses R/sub 40/Y/sub 23/Cu/sub 37/ (R = Tb, Dy, Ho, and Er). Anisotropic magnetostriction is a forced effect, with no sign of saturation, and is quite large well above T/sub SG/. The developed model fits quantitatively and remarkably well the temperature variation of the anisotropic magnetostriction, lambda/sub t/ = lambda/sub X/-lambda/sub perpendicular/, in the case of Tb, Dy, and Ho alloys. The values obtained from the fit for D/sub 0/, respectively, are +3.0, +1.25, and +0.6 K. For Er, D/sub 0/ becomes -0.37 K. The signs of D/sub 0/ are in agreement with having local axial anisotropy for the Tb, Dy, and Ho compounds, and planar for the Er one, in good agreement with the signs of the ..cap alpha../sub J/ Stevens quadrupolar parameter.
Mamiya, Hiroaki; Nimori, Shigeki
2012-04-01
Universality of spin configuration restoration is studied in Heisenberg spin glasses: a dilute magnetic semiconductor Cd{sub 55}Mn{sub 45}Te as well as a dilute magnetic alloy Cu{sub 97}Mn{sub 3}. Reversions of the relaxations of magnetization were observed in both systems undergoing positive/negative temperature cycling under a constant magnetic field. Because the magnetization mirrors evolution of the spin configuration, these reversions indicate that the spin configurations are spontaneously restored to the initially stabilized states when the temperature is returned to the original. Whereas such spin restoration does not occur if the spin glasses are simply frozen, it is possible in the alternative ghost domain scenario of the droplet picture. This finding thus provides fresh insight into the nature of glassy systems.
Reentrant Wetting of Network Fluids
NASA Astrophysics Data System (ADS)
Bernardino, N. R.; Telo da Gama, M. M.
2012-09-01
We use a simple mesoscopic Landau-Safran theory of network fluids to show that a reentrant phase diagram, in the “empty liquid” regime, leads to nonmonotonic surface tension and reentrant wetting, as previously reported for binary mixtures. One of the wetting transitions is of the usual kind, but the low temperature transition may allow the display of the full range of fluctuation regimes predicted by renormalization group theory.
Numerical simulation of spin-glass transition phenomena (invited)
NASA Astrophysics Data System (ADS)
Walstedt, R. E.; Walker, L. R.
1982-11-01
Results are presented from a continuing investigation of spin-glass transition effects by numerical simulation. The model is one of classical unit vectors randomly distributed on an fcc lattice, with RKKY exchange coupling and nearest-neighbor dipolar coupling in an approximate representation of dilute Mn in Cu. Results for system energy and for dipolar energy as a function of temperature show no resolvable features at the freezing temperature TG* in accord with the high-precision specific heat data of Fogle, Boyer, Phillips, and Van Curen. Additional details of shattered susceptibility behavior in the vicinity of the ground-state transition are presented. Further data on freezing temperatures as a function of dipolar coupling strength D show a trend toward macroscopic behavior (i.e., TG* independent of D) with a sample of 4928 spins. Finally, a moderately sharp onset of freezing transverse to an applied magnetic field is found, as predicted by the mean-field calculations of Toulouse and Gabay. As expected, this transition is unrelated to transverse susceptibilities.
Inverse spin glass and related maximum entropy problems.
Castellana, Michele; Bialek, William
2014-09-12
If we have a system of binary variables and we measure the pairwise correlations among these variables, then the least structured or maximum entropy model for their joint distribution is an Ising model with pairwise interactions among the spins. Here we consider inhomogeneous systems in which we constrain, for example, not the full matrix of correlations, but only the distribution from which these correlations are drawn. In this sense, what we have constructed is an inverse spin glass: rather than choosing coupling constants at random from a distribution and calculating correlations, we choose the correlations from a distribution and infer the coupling constants. We argue that such models generate a block structure in the space of couplings, which provides an explicit solution of the inverse problem. This allows us to generate a phase diagram in the space of (measurable) moments of the distribution of correlations. We expect that these ideas will be most useful in building models for systems that are nonequilibrium statistical mechanics problems, such as networks of real neurons. PMID:25260004
Classical mutual information in mean-field spin glass models
NASA Astrophysics Data System (ADS)
Alba, Vincenzo; Inglis, Stephen; Pollet, Lode
2016-03-01
We investigate the classical Rényi entropy Sn and the associated mutual information In in the Sherrington-Kirkpatrick (S-K) model, which is the paradigm model of mean-field spin glasses. Using classical Monte Carlo simulations and analytical tools we investigate the S-K model in the n -sheet booklet. This is achieved by gluing together n independent copies of the model, and it is the main ingredient for constructing the Rényi entanglement-related quantities. We find a glassy phase at low temperatures, whereas at high temperatures the model exhibits paramagnetic behavior, consistent with the regular S-K model. The temperature of the paramagnetic-glassy transition depends nontrivially on the geometry of the booklet. At high temperatures we provide the exact solution of the model by exploiting the replica symmetry. This is the permutation symmetry among the fictitious replicas that are used to perform disorder averages (via the replica trick). In the glassy phase the replica symmetry has to be broken. Using a generalization of the Parisi solution, we provide analytical results for Sn and In and for standard thermodynamic quantities. Both Sn and In exhibit a volume law in the whole phase diagram. We characterize the behavior of the corresponding densities, Sn/N and In/N , in the thermodynamic limit. Interestingly, at the critical point the mutual information does not exhibit any crossing for different system sizes, in contrast with local spin models.
Efficient cluster Monte Carlo algorithm for Ising spin glasses in more than two space dimensions
NASA Astrophysics Data System (ADS)
Ochoa, Andrew J.; Zhu, Zheng; Katzgraber, Helmut G.
2015-03-01
A cluster algorithm that speeds up slow dynamics in simulations of nonplanar Ising spin glasses away from criticality is urgently needed. In theory, the cluster algorithm proposed by Houdayer poses no advantage over local moves in systems with a percolation threshold below 50%, such as cubic lattices. However, we show that the frustration present in Ising spin glasses prevents the growth of system-spanning clusters at temperatures roughly below the characteristic energy scale J of the problem. Adding Houdayer cluster moves to simulations of Ising spin glasses for T ~ J produces a speedup that grows with the system size over conventional local moves. We show results for the nonplanar quasi-two-dimensional Chimera graph of the D-Wave Two quantum annealer, as well as conventional three-dimensional Ising spin glasses, where in both cases the addition of cluster moves speeds up thermalization visibly in the physically-interesting low temperature regime.
NASA Astrophysics Data System (ADS)
Dubiel, S. M.
2016-06-01
Non-linear ac magnetic susceptibility terms viz. quadratic χ2 and cubic χ3 were measured versus temperature and frequency for a series of the σ-phase Fe100-xMox (47≤x≤53) compounds. Clear evidence was found that the ground magnetic state of the samples is mixed i.e. constituted by a mixture of two phases: a spin glass (SG) and ferromagnetic (FM) clusters, hence the magnetism of the investigated samples can be regarded as re-entrant. Based on the present data, previously reported magnetic phase diagram has been upgraded [Przewoznik and Dubiel (2015) [12
Mean field spin glasses treated with PDE techniques
NASA Astrophysics Data System (ADS)
Barra, Adriano; Del Ferraro, Gino; Tantari, Daniele
2013-07-01
Following an original idea of Guerra, in these notes we analyze the Sherrington-Kirkpatrick model from different perspectives, all sharing the underlying approach which consists in linking the resolution of the statistical mechanics of the model (e.g. solving for the free energy) to well-known partial differential equation (PDE) problems (in suitable spaces). The plan is then to solve the related PDE using techniques involved in their native field and lastly bringing back the solution in the proper statistical mechanics framework. Within this strand, after a streamlined test-case on the Curie-Weiss model to highlight the methods more than the physics behind, we solve the SK both at the replica symmetric and at the 1-RSB level, obtaining the correct expression for the free energy via an analogy to a Fourier equation and for the self-consistencies with an analogy to a Burger equation, whose shock wave develops exactly at critical noise level (triggering the phase transition). Our approach, beyond acting as a new alternative method (with respect to the standard routes) for tackling the complexity of spin glasses, links symmetries in PDE theory with constraints in statistical mechanics and, as a novel result from the theoretical physics perspective, we obtain a new class of polynomial identities (namely of Aizenman-Contucci type, but merged within the Guerra's broken replica measures), whose interest lies in understanding, via the recent Panchenko breakthroughs, how to force the overlap organization to the ultrametric tree predicted by Parisi.
Practical engineering of hard spin-glass instances
NASA Astrophysics Data System (ADS)
Marshall, Jeffrey; Martin-Mayor, Victor; Hen, Itay
2016-07-01
Recent technological developments in the field of experimental quantum annealing have made prototypical annealing optimizers with hundreds of qubits commercially available. The experimental demonstration of a quantum speedup for optimization problems has since then become a coveted, albeit elusive goal. Recent studies have shown that the so far inconclusive results, regarding a quantum enhancement, may have been partly due to the benchmark problems used being unsuitable. In particular, these problems had inherently too simple a structure, allowing for both traditional resources and quantum annealers to solve them with no special efforts. The need therefore has arisen for the generation of harder benchmarks which would hopefully possess the discriminative power to separate classical scaling of performance with size from quantum. We introduce here a practical technique for the engineering of extremely hard spin-glass Ising-type problem instances that does not require "cherry picking" from large ensembles of randomly generated instances. We accomplish this by treating the generation of hard optimization problems itself as an optimization problem, for which we offer a heuristic algorithm that solves it. We demonstrate the genuine thermal hardness of our generated instances by examining them thermodynamically and analyzing their energy landscapes, as well as by testing the performance of various state-of-the-art algorithms on them. We argue that a proper characterization of the generated instances offers a practical, efficient way to properly benchmark experimental quantum annealers, as well as any other optimization algorithm.
NASA Astrophysics Data System (ADS)
Sanpera, A.; Kantian, A.; Sanchez-Palencia, L.; Zakrzewski, J.; Lewenstein, M.
2004-07-01
We investigate strongly interacting atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. We derive an effective Hamiltonian for the system and discuss its low temperature physics. We demonstrate the possibility of controlling the interactions at local level in inhomogeneous but regular lattices. Such a control leads to the achievement of Fermi glass, quantum Fermi spin-glass, and quantum percolation regimes involving bare and/or composite fermions in random lattices.
NASA Astrophysics Data System (ADS)
Sen, S.; Stebbins, J. F.
1994-07-01
A comparative study of the 29Si spin-lattice relaxation behavior (induced by trace amounts of paramagnetic dopants in the glass) in phase-separated Li2Si4O9 and monophasic Li2Si2O5 and Na2Si2O5 glasses has been made in order to understand the nature of clustering and the resulting intermediate-range ordering. Optically clear tetrasilicate and disilicate glasses were prepared with 500 to 2000 ppm of Gd2O3, a paramagnetic dopant. The constituent structural units (Q3 and Q4 species) in all tetrasilicate glasses show strong differential relaxation following a power-law behavior. This is due to preferential partitioning of Gd3+ into the lower silica (Q3-rich) regions of these glasses, indicating the presence of Q species clusters too small to produce optical opalescence (a few nm to perhaps tens of nm). Preliminary results on 6Li spin-lattice relaxation in these glasses support this hypothesis. Differential relaxation becomes more pronounced on annealing due to growth of such clusters. No such differential relaxation was observed in the monophase disilicate glasses. For spin-lattice relaxation induced by direct dipolar coupling to paramagnetic ions, the recovery of magnetization is proportional to time as M(t)~tα where α is a function of the dimensionality D of mass distribution of the constituent Q species around the Gd3+ paramagnetic centers in the glass. For tetrasilicate glasses D~=2.62+/-0.22 and the system behaves as a mass fractal up to a length scale of 2 to 3 nm. D is thus equal to, within error, the theoretical value of 2.6 for an infinite percolation cluster of one type of Q species in another. For disilicate glasses, D~=3.06+/-0.18 which indicates a three-dimensional (and thus nonfractal) mass distribution of the constituent Q species over the same length scale.
Time Dependence of the freezing temperature for thin film spin glasses
NASA Astrophysics Data System (ADS)
Orbach, Raymond
There have been many measurements of the dependence of the ``freezing temperature'', Tf, on the thickness o of thin film spin glasses. Tf decreases with decreasing o, but never vanishes. This contribution suggests that the dependence of Tf on o is a time dependent relationship. Because the lower critical dimension of a spin glass, dl ~ 2 . 5 , when the spin glass correlation length ξ (t , T) grows to o, the spin glass dimensionality crosses over from d = 3 to d = 2 . What remains are spin glass correlations for length scales <= o . The time dependence of the magnetization dynamics are then activated, with activation energy equal to a largest barrier Δmax (o) , and an associated activation time τ. For measurements at time scales such that ξ (t , T) < o , the effective dimension d = 3 , and the characteristic cusp and knee of a spin glass is observed. For experimental time scales greater than τ, with ξ (t , T) ~ o , the zero-field cooled magnetization has grown to the field-cooled value of the magnetization, leading to the identification of Tf. Quantitative agreement with experiment is exhibited. Supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award DE-SC0013599.
NASA Astrophysics Data System (ADS)
Neto, Minos A.; de Sousa, J. Ricardo; Padilha, Igor T.; Rodriguez Salmon, Octavio D.; Roberto Viana, J.; Dinóla Neto, F.
2016-06-01
We study the three-dimensional antiferromagnetic Ising model in both uniform longitudinal (H) and transverse (Ω) magnetic fields by using the effective-field theory (EFT) with finite cluster N = 1 spin (EFT-1). We analyzed the behavior of the magnetic susceptibility to investigate the reentrant phenomena that we have seen in the same phase diagram previously obtained in other papers. Our results shows the presence of two divergences in the susceptibility that indicates the existence of a reentrant behavior.
Observation of Temperature Chaos in Mesoscopic Spin Glasses
NASA Astrophysics Data System (ADS)
Guchhait, Samaresh
Temperature Chaos (TC) results from a change in temperature for spin glasses (SG), polymers, and other glassy materials. When the temperature is changed, TC means that the new state has no memory of the preparation of the initial state. TC was predicted long ago [PRL 48, 767 (1982)]. However, ``An experimental measurement of TC is still missing'' [EPL 103, 67003 (2013)]. One reason for this is the question of length scale. In the thermodynamic limit, even an infinitesimal temperature change, ΔT , will create a chaotic condition. However, by working at the mesoscale, one can establish a length scale sufficiently small to exhibit reversible behavior before crossing over to chaotic behavior as the temperature change increases. Observation of TC is possible because, on reasonable laboratory time scales, the SG correlation length can grow to the size of the thickness of the film, L. The lower critical dimension for a SG is ~ 2 . 5 , so that the thin film SG crosses over to a glass temperature Tg = 0 . However, there remains quasi-equilibrium SG states with length scales < L . After crossover, a small ΔT will generate a TC coherence length which, if greater than L, will leave the system in a reversible state. However, when ΔT is sufficiently large, such that the TC coherence length is less than L, and chaos will ensue. I will discuss our recent results of temperature cycling on 15.5 nm SG films of amorphous Ge:Mn. By use of end of aging and temperature cycling, both the reversible region and the chaotic region are observed. Remarkably, the transition from a reversible to chaotic behavior is abrupt, and not smooth as a function of ΔT . This is in contrast to previous work using polycrystalline materials where the distribution of length scales smoothed out the transition to chaos. Using the calculated TC critical exponent, the range of ΔT for reversible behavior is calculated and is in very good agreement with the measured range. This work was supported by the U
Bimodal and Gaussian Ising spin glasses in dimension two.
Lundow, P H; Campbell, I A
2016-02-01
An analysis is given of numerical simulation data to size L=128 on the archetype square lattice Ising spin glasses (ISGs) with bimodal (±J) and Gaussian interaction distributions. It is well established that the ordering temperature of both models is zero. The Gaussian model has a nondegenerate ground state and thus a critical exponent η≡0, and a continuous distribution of energy levels. For the bimodal model, above a size-dependent crossover temperature T(*)(L) there is a regime of effectively continuous energy levels; below T(*)(L) there is a distinct regime dominated by the highly degenerate ground state plus an energy gap to the excited states. T(*)(L) tends to zero at very large L, leaving only the effectively continuous regime in the thermodynamic limit. The simulation data on both models are analyzed with the conventional scaling variable t=T and with a scaling variable τ(b)=T(2)/(1+T(2)) suitable for zero-temperature transition ISGs, together with appropriate scaling expressions. The data for the temperature dependence of the reduced susceptibility χ(τ(b),L) and second moment correlation length ξ(τ(b),L) in the thermodynamic limit regime are extrapolated to the τ(b)=0 critical limit. The Gaussian critical exponent estimates from the simulations, η=0 and ν=3.55(5), are in full agreement with the well-established values in the literature. The bimodal critical exponents, estimated from the thermodynamic limit regime analyses using the same extrapolation protocols as for the Gaussian model, are η=0.20(2) and ν=4.8(3), distinctly different from the Gaussian critical exponents. PMID:26986300
Bimodal and Gaussian Ising spin glasses in dimension two
NASA Astrophysics Data System (ADS)
Lundow, P. H.; Campbell, I. A.
2016-02-01
An analysis is given of numerical simulation data to size L =128 on the archetype square lattice Ising spin glasses (ISGs) with bimodal (±J ) and Gaussian interaction distributions. It is well established that the ordering temperature of both models is zero. The Gaussian model has a nondegenerate ground state and thus a critical exponent η ≡0 , and a continuous distribution of energy levels. For the bimodal model, above a size-dependent crossover temperature T*(L ) there is a regime of effectively continuous energy levels; below T*(L ) there is a distinct regime dominated by the highly degenerate ground state plus an energy gap to the excited states. T*(L ) tends to zero at very large L , leaving only the effectively continuous regime in the thermodynamic limit. The simulation data on both models are analyzed with the conventional scaling variable t =T and with a scaling variable τb=T2/(1 +T2) suitable for zero-temperature transition ISGs, together with appropriate scaling expressions. The data for the temperature dependence of the reduced susceptibility χ (τb,L ) and second moment correlation length ξ (τb,L ) in the thermodynamic limit regime are extrapolated to the τb=0 critical limit. The Gaussian critical exponent estimates from the simulations, η =0 and ν =3.55 (5 ) , are in full agreement with the well-established values in the literature. The bimodal critical exponents, estimated from the thermodynamic limit regime analyses using the same extrapolation protocols as for the Gaussian model, are η =0.20 (2 ) and ν =4.8 (3 ) , distinctly different from the Gaussian critical exponents.
Evidence of spin glass dynamics in dilute LiHoxY1-xF4.
Quilliam, J A; Meng, S; Mugford, C G A; Kycia, J B
2008-10-31
ac susceptibility measurements are presented on the dilute, dipolar coupled, Ising magnet LiHoxY1-xF4 for a concentration x=0.045. The frequency and temperature dependences of the susceptibility show characteristic glassy relaxation. The absorption spectrum is found to broaden with decreasing temperature suggesting that the material is behaving as a spin glass and not as an exotic spin liquid as was previously observed. A dynamical scaling analysis suggests a spin glass transition temperature of 43+/-2 mK with an exponent znu=7.8+/-0.2. PMID:18999860
Evidence of Spin Glass Dynamics in Dilute LiHoxY1-xF4
NASA Astrophysics Data System (ADS)
Quilliam, J. A.; Meng, S.; Mugford, C. G. A.; Kycia, J. B.
2008-10-01
ac susceptibility measurements are presented on the dilute, dipolar coupled, Ising magnet LiHoxY1-xF4 for a concentration x=0.045. The frequency and temperature dependences of the susceptibility show characteristic glassy relaxation. The absorption spectrum is found to broaden with decreasing temperature suggesting that the material is behaving as a spin glass and not as an exotic spin liquid as was previously observed. A dynamical scaling analysis suggests a spin glass transition temperature of 43±2mK with an exponent zν=7.8±0.2.
Efficient rotamer elimination applied to protein side-chains and related spin glasses.
Goldstein, R F
1994-01-01
Folded proteins and spin glasses share various properties, such as seemingly random interactions between residues (spins), and one might presume that some generic behaviors of spin glasses would also be exhibited in a general way by proteins. But a comparison here shows that the side-chain conformation systems of apo-myoglobin and lysozyme are qualitatively different from specific closely related spin glass systems. This difference is manifest in the number of rotamers that can be identified as definitely not contributing to the global energy minimum. This identification is effected by using a significantly enhanced version of the Dead End Elimination theorem (Desmet, J., M. De Maeyer, B. Hazes, and I. Lasters. 1992. The dead-end elimination theorem and its use in protein side-chain positioning. Nature. 356:539-542), which is much more effective and efficient in eliminating rotamers. In several cases (for proteins, although not for spin glasses) this improved Dead End Elimination theorem succeeded in identifying the absolute global minimum of rotamer conformations, with no statistical uncertainty. The difference between protein and spin glass is due to correlations between the interactions of one residue pair with another pair, and probably will play an important role in the thermodynamic behavior of the protein system. PMID:8061189
Kariya, Fumihiro; Ebisu, Shuji; Nagata, Shoichi
2009-03-15
Successive changes from ferromagnetic, re-entrant mixed, to spin-glass regime have been manifestly found with increasing Ti-composition x in the quaternary spinel-type Cu(Cr{sub 1-x}Ti{sub x}){sub 2}S{sub 4} system. The Curie temperature T{sub c} decreases steeply with increasing x and this transition becomes ill-defined around x=0.47. Two distinct transitions appear below T{sub c} over the range x=0.40-0.47. Coexistence of the ferromagnetism and spin-glass order would be observed below the Gabay and Toulouse transition (T{sub GT}), owing to freezing of the transverse-spin components without changing of the ferromagnetic order parameter. Finally, at a yet lower temperature de Almeida-Thouless transition (T{sub AT}), the longitudinal-spin component freezes randomly at which an irreversibility arises between zero-field-cooled (ZFC) and field-cooled (FC) magnetizations. Over the range of 0.47{<=}x{<=}0.85, a cusp of the ZFC magnetization is seen at T{sub g} like conventional spin-glass. Specimens with x{>=}0.90 remain paramagnetic down to 2.0 K. A magnetic phase diagram between T versus x has been obtained experimentally. The values of the multicritical point in 100 Oe is detected to be x=0.47 and T=7.40K. The low-field magnetization and the phase diagram are satisfactorily explained by the theory of Gabay and Toulouse on the basis of Heisenberg isotropic vector spin model rather than the Ising spin model. - An enlargement of the magnetic phase diagram for Cu(Cr{sub 1-x}Ti{sub x}){sub 2}S{sub 4} at a constant field of 100 Oe over the range of 0.40{<=}x{<=}0.70. The curves give a guide to the eye: para, paramagnetic; ferro, ferromagnetic; SGI, spin-glass I (GT-phase), and SGII: spin-glass II (AT-phase). Three characteristic temperatures of T{sub c},T{sub GT}, and T{sub AT} merge into 7.40 K at x=0.47 in H=100 Oe. This is a multicritical point.
Disorder, cluster spin glass, and hourglass spectra in striped magnetic insulators.
Andrade, Eric C; Vojta, Matthias
2012-10-01
Hourglass-shaped magnetic excitation spectra have been detected in a variety of doped transition-metal oxides with stripelike charge order. Compared to the predictions of spin-wave theory for perfect stripes, these spectra display a different intensity distribution and anomalous broadening. Here we show, based on a comprehensive modeling for La5/3Sr1/3CoO4, how quenched disorder in the charge sector causes frustration, and consequently cluster-glass behavior at low temperatures, in the spin sector. This spin-glass physics, which is insensitive to the detailed nature of the charge disorder, but sensitive to the relative strength of the magnetic interstripe coupling, ultimately determines the distribution of magnetic spectral weight: The excitation spectrum, calculated using spin waves in finite disordered systems, is found to match in detail the observed hour-glass spectrum. PMID:23083273
Proposal of a checking parameter in the simulated annealing method applied to the spin glass model
NASA Astrophysics Data System (ADS)
Yamaguchi, Chiaki
2016-02-01
We propose a checking parameter utilizing the breaking of the Jarzynski equality in the simulated annealing method using the Monte Carlo method. This parameter is based on the Jarzynski equality. By using this parameter, to detect that the system is in global minima of the free energy under gradual temperature reduction is possible. Thus, by using this parameter, one is able to investigate the efficiency of annealing schedules. We apply this parameter to the ± J Ising spin glass model. The application to the Gaussian Ising spin glass model is also mentioned. We discuss that the breaking of the Jarzynski equality is induced by the system being trapped in local minima of the free energy. By performing Monte Carlo simulations of the ± J Ising spin glass model and a glassy spin model proposed by Newman and Moore, we show the efficiency of the use of this parameter.
Classical spin glass system in external field with taking into account relaxation effects
Gevorkyan, A. S. Abajyan, H. G.
2013-08-15
We study statistical properties of disordered spin systems under the influence of an external field with taking into account relaxation effects. For description of system the spatial 1D Heisenberg spin-glass Hamiltonian is used. In addition, we suppose that interactions occur between nearest-neighboring spins and they are random. Exact solutions which define angular configuration of the spin in nodes were obtained from the equations of stationary points of Hamiltonian and the corresponding conditions for the energy local minimum. On the basis of these recurrent solutions an effective parallel algorithm is developed for simulation of stabile spin-chains of an arbitrary length. It is shown that by way of an independent order of N{sup 2} numerical simulations (where N is number of spin in each chain) it is possible to generate ensemble of spin-chains, which is completely ergodic which is equivalent to full self-averaging of spin-chains' vector polarization. Distributions of different parameters (energy, average polarization by coordinates, and spin-spin interaction constant) of unperturbed system are calculated. In particular, analytically is proved and numerically is shown, that for the Heisenberg nearest-neighboring Hamiltonian model, the distribution of spin-spin interaction constants as opposed to widely used Gauss-Edwards-Anderson distribution satisfies Levy alpha-stable distribution law. This distribution is nonanalytic function and does not have variance. In the work we have in detail studied critical properties of an ensemble depending on value of external field parameters (from amplitude and frequency) and have shown that even at weak external fields the spin-glass systemis strongly frustrated. It is shown that frustrations have fractal behavior, they are selfsimilar and do not disappear at scale decreasing of area. By the numerical computation is shown that the average polarization of spin-glass on a different coordinates can have values which can lead to
NASA Astrophysics Data System (ADS)
Singh, Nidhi; Borgohain, Barsha; Srivastava, A. K.; Dhar, Ajay; Singh, H. K.
2016-03-01
Nanocrystalline ribbons of inverse Heusler alloy Mn2Ni1.6Sn0.4 have been synthesised by melt spinning of the arc-melted bulk precursor. The single-phase ribbons crystallize into a cubic structure and exhibit very fine crystallite size of <2 nm. Temperature-dependent magnetization ( M- T) measurements reveal ferromagnetic-austenite (FM-A)-antiferromagnetic-martensite (AFM-M) phase transition that begins at M S ≈ 249 K and finishes at M f ≈ 224 K. During warming, the reverse AFM-M to FM-A transitions begins at A s ≈ 240 K and finishes at A f ≈ 261 K. A re-entrant FM transition is observed in the M-phase at T_{{CM}} ≈ 145 K. These transitions are also confirmed by temperature-dependent resistivity ( ρ- T) measurements. The hysteretic behaviour of M- T and ρ- T in the temperature regime spanned by the A-M transition is a manifestation of the first-order phase transition. M- T and ρ- T data also provide unambiguous evidence in favour of spin glass at T < T_{{CM}}. The scaling of the glass freezing temperature ( T f) with frequency, extracted from the frequency-dependent AC susceptibility measurements, confirms the existence of canonical spin glass at T < T_{{CM}} ≈ 145 K. The occurrence of canonical spin glass has been explained in terms of the nanostructuring modified interactions between the coexisting FM and AFM correlations in the martensitic phase.
NASA Astrophysics Data System (ADS)
Das, Arnab; Chakrabarti, Bikas K.
2008-12-01
Here we discuss the annealing behavior of an infinite-range ±J Ising spin glass in the presence of a transverse field using a zero-temperature quantum Monte Carlo method. Within the simulation scheme, we demonstrate that quantum annealing not only helps finding the ground state of a classical spin glass, but can also help simulating the ground state of a quantum spin glass, in particular, when the transverse field is low, much more efficiently.
Das, Arnab; Chakrabarti, Bikas K
2008-12-01
Here we discuss the annealing behavior of an infinite-range +/-J Ising spin glass in the presence of a transverse field using a zero-temperature quantum Monte Carlo method. Within the simulation scheme, we demonstrate that quantum annealing not only helps finding the ground state of a classical spin glass, but can also help simulating the ground state of a quantum spin glass, in particular, when the transverse field is low, much more efficiently. PMID:19256816
A fast vectorized program for the CDC cyber 205 to simulate the ising spin glass in three dimensions
NASA Astrophysics Data System (ADS)
Bhanot, Gyan; Salvador, Román; Duke, Dennis; Moriarty, K. J. M.
1988-06-01
We describe a computer program that performs the Metropolis algorithm for the three-dimensional ( J = ±1) Ising spin glass problem at a peak speed of 80 million spin updates per second on a 2-pipe CDC CYBER 205.
Magnetoelectric relaxor and reentrant behaviours in multiferroic Pb(Fe2/3W1/3)O3 crystal
Chen, Ling; Bokov, Alexei A.; Zhu, Weimin; Wu, Hua; Zhuang, Jian; Zhang, Nan; Tailor, Hamel N.; Ren, Wei; Ye, Zuo-Guang
2016-01-01
Significant quenched disorder in crystal structure can break ferroic (magnetic or electric) long-range order, resulting in the development of ferroic glassy states at low temperatures such as magnetic spin glasses, electric dipolar glasses, relaxor ferroelectrics, etc. These states have been widely studied due to novel physical phenomena they reveal. Much less known are the effects of quenched disorder in multiferroics, i.e. the materials where magnetic and electric correlations coexist. Here we report an unusual behaviour in complex perovskite Pb(Fe2/3W1/3)O3 (PFW) crystals: the coexistence of electric relaxor, magnetic relaxor and antiferromagnetic (AFM) states. The most striking finding is the transformation of the AFM phase into a new reentrant-type magnetic glassy phase below Tg ≅ 10 K. We show that the behaviour at this transformation contrasts the typical behaviour of canonical spin glasses and is similar to the behaviour of relaxor ferroelectrics. Magnetoelectric effect is also observed in the AFM phase in the temperature range of the transition into electric relaxor phase at Tf ≅ 200. The mechanism of magnetic relaxor behaviour is supposed to arise from the frustrated interactions among the spins located at the AFM domain walls. Our results should inspire further studies of multirelaxor behaviour in other multiferroic systems. PMID:26936414
Magnetoelectric relaxor and reentrant behaviours in multiferroic Pb(Fe2/3W1/3)O3 crystal
NASA Astrophysics Data System (ADS)
Chen, Ling; Bokov, Alexei A.; Zhu, Weimin; Wu, Hua; Zhuang, Jian; Zhang, Nan; Tailor, Hamel N.; Ren, Wei; Ye, Zuo-Guang
2016-03-01
Significant quenched disorder in crystal structure can break ferroic (magnetic or electric) long-range order, resulting in the development of ferroic glassy states at low temperatures such as magnetic spin glasses, electric dipolar glasses, relaxor ferroelectrics, etc. These states have been widely studied due to novel physical phenomena they reveal. Much less known are the effects of quenched disorder in multiferroics, i.e. the materials where magnetic and electric correlations coexist. Here we report an unusual behaviour in complex perovskite Pb(Fe2/3W1/3)O3 (PFW) crystals: the coexistence of electric relaxor, magnetic relaxor and antiferromagnetic (AFM) states. The most striking finding is the transformation of the AFM phase into a new reentrant-type magnetic glassy phase below Tg ≅ 10 K. We show that the behaviour at this transformation contrasts the typical behaviour of canonical spin glasses and is similar to the behaviour of relaxor ferroelectrics. Magnetoelectric effect is also observed in the AFM phase in the temperature range of the transition into electric relaxor phase at Tf ≅ 200. The mechanism of magnetic relaxor behaviour is supposed to arise from the frustrated interactions among the spins located at the AFM domain walls. Our results should inspire further studies of multirelaxor behaviour in other multiferroic systems.
Magnetoelectric relaxor and reentrant behaviours in multiferroic Pb(Fe2/3W1/3)O3 crystal.
Chen, Ling; Bokov, Alexei A; Zhu, Weimin; Wu, Hua; Zhuang, Jian; Zhang, Nan; Tailor, Hamel N; Ren, Wei; Ye, Zuo-Guang
2016-01-01
Significant quenched disorder in crystal structure can break ferroic (magnetic or electric) long-range order, resulting in the development of ferroic glassy states at low temperatures such as magnetic spin glasses, electric dipolar glasses, relaxor ferroelectrics, etc. These states have been widely studied due to novel physical phenomena they reveal. Much less known are the effects of quenched disorder in multiferroics, i.e. the materials where magnetic and electric correlations coexist. Here we report an unusual behaviour in complex perovskite Pb(Fe2/3W1/3)O3 (PFW) crystals: the coexistence of electric relaxor, magnetic relaxor and antiferromagnetic (AFM) states. The most striking finding is the transformation of the AFM phase into a new reentrant-type magnetic glassy phase below Tg ≅ 10 K. We show that the behaviour at this transformation contrasts the typical behaviour of canonical spin glasses and is similar to the behaviour of relaxor ferroelectrics. Magnetoelectric effect is also observed in the AFM phase in the temperature range of the transition into electric relaxor phase at Tf ≅ 200. The mechanism of magnetic relaxor behaviour is supposed to arise from the frustrated interactions among the spins located at the AFM domain walls. Our results should inspire further studies of multirelaxor behaviour in other multiferroic systems. PMID:26936414
CALL FOR PAPERS: Special issue on Spin Glasses
NASA Astrophysics Data System (ADS)
Coolen, Ton; Nishimori, Hidetoshi; Sourlas, Nicolas; Wong, Michael
2007-10-01
This is a call for contributions to a special issue of Journal of Physics A: Mathematical and Theoretical dedicated to the subject of the conference `Viewing The World Through Spin Glasses', in honour of David Sherrington on the occasion of his 65th birthday, 31 August-1 September 2007 (http://www.nottingham.ac.uk/\\verb.~.ppzjpg/DS2007/). Invited speakers and participants at that meeting and other researchers working in the field are invited to submit a research paper to this issue. The Editorial Board has invited Ton Coolen, Hidetoshi Nishimori, Nicolas Sourlas and Michael Wong to serve as Guest Editors for the special issue. Their criteria for acceptance of contributions are as follows: •The subject of the paper should relate to the subject of the conference (see the website of the conference http://www.nottingham.ac.uk/\\verb.~.ppzjpg/DS2007/). •Contributions will be refereed and processed according to the usual procedure of the journal. •Conference papers may be based on already published work but should either contain significant additional new results and/or insights or give a survey of the present state of the art, a critical assessment of the present understanding of a topic, and a discussion of open problems. •Papers submitted by non-participants should be original and contain substantial new results. The guidelines for the preparation of contributions are the following: •The DEADLINE for submission of contributions is 1 December 2007. This deadline will allow the special issue to appear in July 2008. •There is a nominal page limit of 16 printed pages per contribution. For papers exceeding this limit, the Guest Editors reserve the right to request a reduction in length. •Further advice on publishing your work in Journal of Physics A: Mathematical and Theoretical may be found at www.iop.org/Journals/jphysa. •Contributions to the special issue should, if possible, be submitted electronically by web upload at www.iop.org/Journals/jphysa or by
Radiation Dose from Reentrant Electrons
NASA Technical Reports Server (NTRS)
Badhwar, G.D.; Cleghorn, T. E.; Watts, J.
2003-01-01
In estimating the crew exposures during an EVA, the contribution of reentrant electrons has always been neglected. Although the flux of these electrons is small compared to the flux of trapped electrons, their energy spectrum extends to several GeV compared to about 7 MeV for trapped electrons. This is also true of splash electrons. Using the measured reentrant electron energy spectra, it is shown that the dose contribution of these electrons to the blood forming organs (BFO) is more than 10 times greater than that from the trapped electrons. The calculations also show that the dose-depth response is a very slowly changing function of depth, and thus adding reasonable amounts of additional shielding would not significantly lower the dose to BFO.
Exact algorithm for sampling the two-dimensional Ising spin glass.
Thomas, Creighton K; Middleton, A Alan
2009-10-01
A sampling algorithm is presented that generates spin-glass configurations of the two-dimensional Edwards-Anderson Ising spin glass at finite temperature with probabilities proportional to their Boltzmann weights. Such an algorithm overcomes the slow dynamics of direct simulation and can be used to study long-range correlation functions and coarse-grained dynamics. The algorithm uses a correspondence between spin configurations on a regular lattice and dimer (edge) coverings of a related graph: Wilson's algorithm [D. B. Wilson, Proceedings of the Eighth Symposium on Discrete Algorithms (SIAM, Philadelphia, 1997), p 258] for sampling dimer coverings on a planar lattice is adapted to generate samplings for the dimer problem corresponding to both planar and toroidal spin-glass samples. This algorithm is recursive: it computes probabilities for spins along a "separator" that divides the sample in half. Given the spins on the separator, sample configurations for the two separated halves are generated by further division and assignment. The algorithm is simplified by using Pfaffian elimination rather than Gaussian elimination for sampling dimer configurations. For n spins and given floating point precision, the algorithm has an asymptotic run-time of O(n(3/2)); it is found that the required precision scales as inverse temperature and grows only slowly with system size. Sample applications and benchmarking results are presented for samples of size up to n=128(2), with fixed and periodic boundary conditions. PMID:19905483
Ren, Jin-Li; Wang, Bo; Xiao, Yun-Feng; Gong, Qihuang; Li, Yan
2015-09-14
We theoretically and experimentally demonstrate that it is possible to directly observe the resolvable spin separation in the spin Hall effect of light at an air-glass interface by choosing optimal parameters. When a P-polarized light with a beam waist of 10 μm is incident around Brewster's angle, the two spin components of the reflected beam can be completely separated by eliminating the influence of the in-plane wavevector spread. This not only obviously reveals the strong impacts of the polarization state, the incident angle, the beam waist, and the in-plane wavevector spread, but also intuitively visualizes the observation of the spin Hall effect of light.
NASA Astrophysics Data System (ADS)
Zhang, X. K.; Tang, S. L.; Xu, L. Q.; Yuan, J. J.; Yu, H. J.; Zhu, X. R.; Xie, Y. M.
2014-07-01
Spin glass behavior and exchange bias effect have been observed in antiferromagnetic SrMn3O6-x nanoribbons synthesized via a self-sacrificing template process. The magnetic field dependence of thermoremanent magnetization and isothermal remanent magnetization shows that the sample is good correspondence to spin glass and diluted antiferromagnetic system for the applied field H < 2 T and H > 2 T, respectively. By detailed analysis of training effect using Binek's model, we argue that the observed exchange bias effect in SrMn3O6-x nanoribbons arises entirely from an interface exchange coupling between the antiferromagnetic core and spin glass shell. The present study is useful for understanding the nature of shell layer and the origin of exchange bias effect in other antiferromagnetic nanosystems as well.
Zhang, X. K. Yuan, J. J.; Yu, H. J.; Zhu, X. R.; Xie, Y. M.; Tang, S. L.; Xu, L. Q.
2014-07-14
Spin glass behavior and exchange bias effect have been observed in antiferromagnetic SrMn{sub 3}O{sub 6−x} nanoribbons synthesized via a self-sacrificing template process. The magnetic field dependence of thermoremanent magnetization and isothermal remanent magnetization shows that the sample is good correspondence to spin glass and diluted antiferromagnetic system for the applied field H < 2 T and H > 2 T, respectively. By detailed analysis of training effect using Binek's model, we argue that the observed exchange bias effect in SrMn{sub 3}O{sub 6−x} nanoribbons arises entirely from an interface exchange coupling between the antiferromagnetic core and spin glass shell. The present study is useful for understanding the nature of shell layer and the origin of exchange bias effect in other antiferromagnetic nanosystems as well.
Quantum annealing for the number-partitioning problem using a tunable spin glass of ions
Graß, Tobias; Raventós, David; Juliá-Díaz, Bruno; Gogolin, Christian; Lewenstein, Maciej
2016-01-01
Exploiting quantum properties to outperform classical ways of information processing is an outstanding goal of modern physics. A promising route is quantum simulation, which aims at implementing relevant and computationally hard problems in controllable quantum systems. Here we demonstrate that in a trapped ion setup, with present day technology, it is possible to realize a spin model of the Mattis-type that exhibits spin glass phases. Our method produces the glassy behaviour without the need for any disorder potential, just by controlling the detuning of the spin-phonon coupling. Applying a transverse field, the system can be used to benchmark quantum annealing strategies which aim at reaching the ground state of the spin glass starting from the paramagnetic phase. In the vicinity of a phonon resonance, the problem maps onto number partitioning, and instances which are difficult to address classically can be implemented. PMID:27230802
Quantum annealing for the number-partitioning problem using a tunable spin glass of ions
NASA Astrophysics Data System (ADS)
Graß, Tobias; Raventós, David; Juliá-Díaz, Bruno; Gogolin, Christian; Lewenstein, Maciej
2016-05-01
Exploiting quantum properties to outperform classical ways of information processing is an outstanding goal of modern physics. A promising route is quantum simulation, which aims at implementing relevant and computationally hard problems in controllable quantum systems. Here we demonstrate that in a trapped ion setup, with present day technology, it is possible to realize a spin model of the Mattis-type that exhibits spin glass phases. Our method produces the glassy behaviour without the need for any disorder potential, just by controlling the detuning of the spin-phonon coupling. Applying a transverse field, the system can be used to benchmark quantum annealing strategies which aim at reaching the ground state of the spin glass starting from the paramagnetic phase. In the vicinity of a phonon resonance, the problem maps onto number partitioning, and instances which are difficult to address classically can be implemented.
Quantum annealing for the number-partitioning problem using a tunable spin glass of ions.
Graß, Tobias; Raventós, David; Juliá-Díaz, Bruno; Gogolin, Christian; Lewenstein, Maciej
2016-01-01
Exploiting quantum properties to outperform classical ways of information processing is an outstanding goal of modern physics. A promising route is quantum simulation, which aims at implementing relevant and computationally hard problems in controllable quantum systems. Here we demonstrate that in a trapped ion setup, with present day technology, it is possible to realize a spin model of the Mattis-type that exhibits spin glass phases. Our method produces the glassy behaviour without the need for any disorder potential, just by controlling the detuning of the spin-phonon coupling. Applying a transverse field, the system can be used to benchmark quantum annealing strategies which aim at reaching the ground state of the spin glass starting from the paramagnetic phase. In the vicinity of a phonon resonance, the problem maps onto number partitioning, and instances which are difficult to address classically can be implemented. PMID:27230802
Study of a microcanonical algorithm on the ± J spin glass model in d =3
NASA Astrophysics Data System (ADS)
Ruiz-Lorenzo, J. J.; Ullod, C. L.
2000-03-01
We consider a microcanonical local algorithm to be applied on the ± J spin glass model. We have compared the results coming from a microcanonical Monte Carlo simulation with those from a canonical one: Thermalization times, spin glass susceptibilities and Binder parameters. For a fixed lattice size we found different results between the two thermodynamic ensembles, which tend to vanish at bigger volumes. Moreover, microcanonical thermalization times are longer than the canonical ones. Finally we have checked that one of the Guerra relations is satisfied with good precision for the two largest lattices.
Unconventional critical activated scaling of two-dimensional quantum spin glasses
NASA Astrophysics Data System (ADS)
Matoz-Fernandez, D. A.; Romá, F.
2016-07-01
We study the critical behavior of two-dimensional short-range quantum spin glasses by numerical simulations. Using a parallel tempering algorithm, we calculate the Binder cumulant for the Ising spin glass in a transverse magnetic field with two different short-range bond distributions, the bimodal and the Gaussian ones. Through an exhaustive finite-size analysis, we show that the cumulant probably follows an unconventional activated scaling, which we interpret as new evidence supporting the hypothesis that the quantum critical behavior is governed by an infinite randomness fixed point.
Symmetry, complexity and multicritical point of the two-dimensional spin glass
NASA Astrophysics Data System (ADS)
Maillard, Jean-Marie; Nemoto, Koji; Nishimori, Hidetoshi
2003-09-01
We analyse models of spin glasses on the two-dimensional square lattice by exploiting symmetry arguments. The replicated partition functions of the Ising and related spin glasses are shown to have many remarkable symmetry properties as functions of the edge Boltzmann factors. It is shown that the applications of homogeneous and Hadamard inverses to the edge Boltzmann matrix indicate reduced complexities when the elements of the matrix satisfy certain conditions, suggesting that the system has special simplicities under such conditions. Using these duality and symmetry arguments we present a conjecture on the exact location of the multicritical point in the phase diagram.
Monolithically integrated active waveguides and lasers using rare-earth doped spin-on glass
Ashby, C.I.H.; Sullivan, C.T.; Vawter, G.A.
1996-09-01
This LDRD program No. 3505.230 explored a new approach to monolithic integration of active waveguides and rare-earth solid state lasers directly onto III-V substrates. It involved selectively incorporating rare-earth ions into spin-on glasses (SOGs) that could be solvent cast and then patterned with conventional microelectronic processing. The patterned, rare-earth spin-on glasses (RESOGs) were to be photopumped by laser diodes prefabricated on the wafer and would serve as directly integrated active waveguides and/or rare-earth solid state lasers.
Chaos and stiffness exponents for short-range Gaussian Ising spin glasses
NASA Astrophysics Data System (ADS)
Almeida, Sebastião T. O.; Curado, Evaldo M. F.; Nobre, Fernando D.
2013-06-01
Two important exponents in spin-glass theory, namely, the chaos (ζ) and stiffness (y) exponents, are studied for Ising spin glasses with nearest-neighbor Gaussian interactions on different approaches to Bravais lattices. We consider hierarchical lattices of the Migdal-Kadanoff type (both diamond and tress families), with varying fractal dimensions, as well as two lattices of the Wheatstone-bridge family, more specifically, those with fractal dimensions D ≈ 2.32 and D ≈ 3.58. Whenever it is possible to compare, our estimates agree with those obtained from extensive numerical simulations on Bravais lattices, suggesting the present results represent good approximations for these exponents.
Observation of spin glass transition in spinel LiCoMnO4
NASA Astrophysics Data System (ADS)
Chen, Hong; Yang, Xu; Zhang, Pei-Song; Liang, Lei; Hong, Yuan-Ze; Wei, Ying-Jin; Chen, Gang; Du, Fei; Wang, Chun-Zhong
2015-12-01
Spinel LiCoMnO4 is prepared by solid-state reaction and its magnetic properties are comprehensively studied by direct current (DC) and alternating current (AC) susceptibilities, isothermal remanent magnetizations, and magnetic hysteresis. Fitting to the Curie-Weiss law by using high-temperature zero-field-cooled susceptibility confirms a low-spin state of Co3+ with S = 0. Both the fitting parameters first increase and then tend to be saturated at high magnetic fields through using isothermal remanent magnetizations, which suggests a spin glass transition at low temperature. AC susceptibility study also supports this conclusion since the frequency dependence of peak position and intensity follows the tendency of a spin glass transition. The origin of the spin-glass transition in LiCoMnO4 might be attributed to a spatial segregation between non-magnetic Co3+ regions and spin glass ordered regions of Mn4+ ions. Project supported by the National Key Basic Research Program of China (Grant No. 2015CB251103), the Development Program of Science and Technology of Jilin Province, China (Grant No. 20140101093JC), and the Program of Science and Technology of Jilin City, China (Grant No. 201434006).
NASA Astrophysics Data System (ADS)
Shinaoka, Hiroshi; Tomita, Yusuke; Motome, Yukitoshi
2014-10-01
Motivated by puzzling aspects of spin-glass behavior reported in frustrated magnetic materials, we theoretically investigate effects of magnetoelastic coupling in geometrically frustrated classical spin models. In particular, we consider bond-disordered Heisenberg antiferromagnets on a pyrochlore lattice coupled to local lattice distortions. By integrating out the lattice degree of freedom, we derive an effective spin-only model, the bilinear-biquadratic model with bond disorder. The effective model is analyzed by classical Monte Carlo simulations using an extended loop algorithm. First, we discuss the phase diagrams in detail by showing the comprehensive Monte Carlo data for thermodynamic and magnetic properties. We show that the spin-glass transition temperature Tf is largely enhanced by the spin-lattice coupling b in the weakly disordered regime. By considering the limit of strong spin-lattice coupling, this enhancement is ascribed to the suppression of thermal fluctuations in semidiscrete degenerate manifold formed in the presence of the spin-lattice coupling. We also find that, by increasing the strength of disorder Δ, the system shows a concomitant transition of the nematic order and spin glass at a temperature determined by b, being almost independent of Δ. This is due to the fact that the spin-glass transition is triggered by the spin collinearity developed by the nematic order. Although further-neighbor exchange interactions originating in the cooperative lattice distortions result in spin-lattice order in the weakly disordered regime, the concomitant transition remains robust with Tf almost independent of Δ. We find that the magnetic susceptibility shows hysteresis between the field-cooled and zero-field-cooled data below Tf, and that the nonlinear susceptibility shows a negative divergence at the transition. These features are common to conventional spin-glass systems. Meanwhile, we find that the specific heat exhibits a broad peak at Tf, and that the
Intuitive understanding of T → 0 behavior of 2d spin glasses via renormalization group analysis
NASA Astrophysics Data System (ADS)
Hartmann, A. K.
2012-07-01
Commentary on 'The nature of the different zero-temperature phases in discrete two-dimensional spin glasses: entropy, universality, chaos and cascades in the renormalization group flow', by Thomas Jörg and Florent Krzakala, 2012 J. Stat. Mech. L01001.
Monolithically integrated solid state laser and waveguide using spin-on glass
Ashby, Carol I. H.; Hohimer, John P.; Neal, Daniel R.; Vawter, G. Allen
1995-01-01
A monolithically integrated photonic circuit combining a semiconductor source of excitation light with an optically active waveguide formed on the substrate. The optically active waveguide is preferably formed of a spin-on glass to which are added optically active materials which can enable lasing action, optical amplification, optical loss, or frequency conversion in the waveguide, depending upon the added material.
NASA Astrophysics Data System (ADS)
Manssen, Markus; Hartmann, Alexander K.
2015-05-01
We study the nonequilibrium aging behavior of the ±J Edwards-Anderson model in three dimensions for samples of size up to N =1283 and for up to 108 Monte Carlo sweeps. In particular we are interested in the change of the aging when crossing from the spin-glass phase to the ferromagnetic phase. The necessary long simulation times are reached by employing a CUDA-based GPU implementation, which allows for single-spin flip times as small as 8 ps. We measure typical spin-glass correlation functions in space and time to determine the growing length scale and extract the constituting exponents. We observe a clear signature of the disorder-driven equilibrium transition in the nonequilibrium behavior.
Diffusivity Maximum in a Reentrant Nematic Phase
Stieger, Tillmann; Mazza, Marco G.; Schoen, Martin
2012-01-01
We report molecular dynamics simulations of confined liquid crystals using the Gay–Berne–Kihara model. Upon isobaric cooling, the standard sequence of isotropic–nematic–smectic A phase transitions is found. Upon further cooling a reentrant nematic phase occurs. We investigate the temperature dependence of the self-diffusion coefficient of the fluid in the nematic, smectic and reentrant nematic phases. We find a maximum in diffusivity upon isobaric cooling. Diffusion increases dramatically in the reentrant phase due to the high orientational molecular order. As the temperature is lowered, the diffusion coefficient follows an Arrhenius behavior. The activation energy of the reentrant phase is found in reasonable agreement with the reported experimental data. We discuss how repulsive interactions may be the underlying mechanism that could explain the occurrence of reentrant nematic behavior for polar and non-polar molecules. PMID:22837730
Diffusivity maximum in a reentrant nematic phase.
Stieger, Tillmann; Mazza, Marco G; Schoen, Martin
2012-01-01
We report molecular dynamics simulations of confined liquid crystals using the Gay-Berne-Kihara model. Upon isobaric cooling, the standard sequence of isotropic-nematic-smectic A phase transitions is found. Upon further cooling a reentrant nematic phase occurs. We investigate the temperature dependence of the self-diffusion coefficient of the fluid in the nematic, smectic and reentrant nematic phases. We find a maximum in diffusivity upon isobaric cooling. Diffusion increases dramatically in the reentrant phase due to the high orientational molecular order. As the temperature is lowered, the diffusion coefficient follows an Arrhenius behavior. The activation energy of the reentrant phase is found in reasonable agreement with the reported experimental data. We discuss how repulsive interactions may be the underlying mechanism that could explain the occurrence of reentrant nematic behavior for polar and non-polar molecules. PMID:22837730
Effect of modularity on the Glauber dynamics of the dilute spin glass model
NASA Astrophysics Data System (ADS)
Park, Jeong-Man
2014-11-01
We study the Glauber dynamics of the dilute, infinite-ranged spin glass model, the so-called dilute Sherrington-Kirkpatrick (dSK) model. The dSK model has sparse couplings and can be classified by the modularity ( M) of the coupling matrix. We investigate the effect of the modularity on the relaxation dynamics starting from a random initial state. By using the Glauber dynamics and the replica method, we derive the relaxation dynamics equations for the magnetization ( m) and the energy per spin ( r), in addition to the equation for the spin glass order parameter ( q αβ ). In the replica symmetric (RS) analysis, we find that there are two solutions for the RS spin glass order parameter ( q): q = 0which is stable for r < 1/2 and q = (-1+4 r 2)/(32 r 4) which is stable for r > 1/2 in the non-modular system and q = 0 which is stable for r < 1/ and q = (-1+8 r 2)/(128 r 4) which is stable for r > 1/ in the completely modular system. By substituting the proper q values into the equations for r, we find that the relaxation dynamics of r depends on the modularity, M. These results suggest that, in the context of evolutionary theory, the modularity may emerge spontaneously in the point-mutation-only framework (Glauber dynamics) under a changing environment.
Spin-glass freezing in a Ni-vermiculite intercalation compound
NASA Astrophysics Data System (ADS)
Marcos, C.; Argüelles, A.; Khainakov, S. A.; Rodríguez Fernández, J.; Blanco, J. A.
2012-08-01
We report on the magnetic properties of a Ni2+-vermiculite intercalation compound from Santa Olalla, Huelva (Spain). This modified vermiculite was studied by means of DC and AC magnetic measurements. The existence of two maxima in magnetic susceptibility below 10 K was interpreted in terms of the Cole-Cole formalism as being due to spin-glass freezing in this material. The temperature, frequency and external magnetic field dependences of these anomalies located at temperatures around 2-3 K and 8-10 K in the imaginary part of the magnetic susceptibility, χ″, seem to suggest the existence of spin-relaxation phenomena between the magnetic moments of the Ni2+ ions. A dynamic study of the relaxation processes associated with these phenomena considering the Cole-Cole formalism allows us to interpret the anomaly found at 2-3 K according to a law of activated dynamics, obtaining values for the critical exponent, ψν < 1, characteristic of a d = 2 spin-glass-like system, while the maximum observed in χ″ at 8-10 K can be described by means of a law of standard dynamics with a value of the exponent z of around 5, representative of a d = 3 spin-glass-like system.
Exact ground states of large two-dimensional planar Ising spin glasses
NASA Astrophysics Data System (ADS)
Pardella, G.; Liers, F.
2008-11-01
Studying spin-glass physics through analyzing their ground-state properties has a long history. Although there exist polynomial-time algorithms for the two-dimensional planar case, where the problem of finding ground states is transformed to a minimum-weight perfect matching problem, the reachable system sizes have been limited both by the needed CPU time and by memory requirements. In this work, we present an algorithm for the calculation of exact ground states for two-dimensional Ising spin glasses with free boundary conditions in at least one direction. The algorithmic foundations of the method date back to the work of Kasteleyn from the 1960s for computing the complete partition function of the Ising model. Using Kasteleyn cities, we calculate exact ground states for huge two-dimensional planar Ising spin-glass lattices (up to 30002 spins) within reasonable time. According to our knowledge, these are the largest sizes currently available. Kasteleyn cities were recently also used by Thomas and Middleton in the context of extended ground states on the torus. Moreover, they show that the method can also be used for computing ground states of planar graphs. Furthermore, we point out that the correctness of heuristically computed ground states can easily be verified. Finally, we evaluate the solution quality of heuristic variants of the L. Bieche approach.
Cluster spin glass behavior in geometrically frustrated Zn3V3O8.
Chakrabarty, T; Mahajan, A V; Kundu, S
2014-10-01
We report the bulk magnetic properties of a yet unexplored vanadium-based multi-valenced spinel system, Zn3V3O8. A Curie-Weiss fit of our dc magnetic susceptibility χ(T) data in the temperature region of 140-300 K yields a Curie constant C = 0.75 cm(3)K mole(-1) V(-1), θCW = -370 K. We have observed a splitting between the zero field cooled (ZFC) and field cooled (FC) susceptibility curves below a temperature Tirr of about 6.3 K. The value of the 'frustration parameter' (|θcw|/T(N) ~ 100) suggests that the system is strongly frustrated. From the ac susceptibility measurements we find a logarithmic variation of freezing temperature (Tf) with frequency ν attesting to the formation of a spin glass below Tf. However, the value of the characteristic frequency obtained from the Vogel-Fulcher fit suggests that the ground state is closer to a cluster glass rather than a conventional spin glass. We explored further consequences of the spin glass behavior and observed aging phenomena and memory effect (both in ZFC and FC). We found that a positive temperature cycle erases the memory, as predicted by the hierarchical model. From the heat capacity CP data, a hump-like anomaly was observed in CP/T at about 3.75 K. Below this temperature the magnetic heat capacity shows a nearly linear dependence with T which is consistent with the formation of a spin glass state below Tf in Zn(3)V(3)O(8). PMID:25210922
Surface spin-glass in cobalt ferrite nanoparticles dispersed in silica matrix
NASA Astrophysics Data System (ADS)
Zeb, F.; Sarwer, W.; Nadeem, K.; Kamran, M.; Mumtaz, M.; Krenn, H.; Letofsky-Papst, I.
2016-06-01
Surface effects in cobalt ferrite (CoFe2O4) nanoparticles dispersed in a silica (SiO2) matrix were studied by using AC and DC magnetization. Nanoparticles with different concentration of SiO2 were synthesized by using sol-gel method. Average crystallite size lies in the range 25-34 nm for different SiO2 concentration. TEM image showed that particles are spherical and elongated in shape. Nanoparticles with higher concentration of SiO2 exhibit two peaks in the out-of-phase ac-susceptibility. First peak lies in the high temperature regime and corresponds to average blocking temperature of the nanoparticles. Second peak lies in the low temperature regime and is attributed to surface spin-glass freezing in these nanoparticles. Low temperature peak showed SiO2 concentration dependence and was vanished for large uncoated nanoparticles. The frequency dependence of the AC-susceptibility of low temperature peak was fitted with dynamic scaling law which ensures the presence of spin-glass behavior. With increasing applied DC field, the low temperature peak showed less shift as compared to blocking peak, broaden, and decreased in magnitude which also signifies its identity as spin-glass peak for smaller nanoparticles. M-H loops showed the presence of more surface disorder in nanoparticles dispersed in 60% SiO2 matrix. All these measurements revealed that surface effects become strengthen with increasing SiO2 matrix concentration and surface spins freeze in to spin-glass state at low temperatures.
Typical versus averaged overlap distribution in spin glasses: Evidence for droplet scaling theory
NASA Astrophysics Data System (ADS)
Monthus, Cécile; Garel, Thomas
2013-10-01
We consider the statistical properties over disordered samples (J) of the overlap distribution PJ(q) which plays the role of an order parameter in spin glasses. We show that near zero temperature (i) the typical overlap distribution is exponentially small in the central region of -1spins (in order to consider also fully connected models in which the notion of length does not exist); (ii) the rescaled variable v=-[lnPJ(q)]/Nθ remains an O(1) random positive variable describing sample-to-sample fluctuations; (iii) the averaged distribution PJ(q)¯ is nontypical and dominated by rare anomalous samples. Similar statements hold for the cumulative overlap distribution IJ(q0)≡∫0q0dqPJ(q). These results are derived explicitly for the spherical mean-field model with θ=1/3, ϕ(q)=1-q2, and the random variable v corresponds to the rescaled difference between the two largest eigenvalues of Gaussian orthogonal ensemble random matrices. Then we compare numerically the typical and averaged overlap distributions for the long-ranged one-dimensional Ising spin glass with random couplings decaying as J(r)∝r-σ for various values of the exponent σ, corresponding to various droplet exponents θ(σ), and for the mean-field Sherrington-Kirkpatrick model (corresponding formally to the σ=0 limit of the previous model). Our conclusion is that future studies on spin glasses should measure the typical values of the overlap distribution Ptyp(q) or of the cumulative overlap distribution Ityp(q0)=elnIJ(q0)¯ to obtain clearer conclusions on the nature of the spin-glass phase.
Spin-polarized lithium diffusion in a glass hot-vapor cell
NASA Astrophysics Data System (ADS)
Ishikawa, Kiyoshi
2016-08-01
We report diffusion coefficients of optically pumped lithium atoms in helium buffer gas. The free-induction decay and the spin-echo signals of ground-state atoms were optically detected in an external magnetic field with the addition of field gradient. Lithium hot vapor was produced in a borosilicate-glass cell at a temperature between 290 and 360°C. The simple setup using the glass cells enabled lithium atomic spectroscopy in a similar way to other alkali-metal atoms and study of the collisional properties of lithium atoms in a hot-vapor phase.
Magnetic surfactants as molecular based-magnets with spin glass-like properties.
Brown, Paul; Smith, Gregory N; Hernández, Eduardo Padrón; James, Craig; Eastoe, Julian; Nunes, Wallace C; Settens, Charles M; Hatton, T Alan; Baker, Peter J
2016-05-01
This paper reports the use of muon spin relaxation spectroscopy to study how the aggregation behavior of magnetic surfactants containing lanthanide counterions may be exploited to create spin glass-like materials. Surfactants provide a unique approach to building in randomness, frustration and competing interactions into magnetic materials without requiring a lattice of ordered magnetic species or intervening ligands and elements. We demonstrate that this magnetic behavior may also be manipulated via formation of micelles rather than simple dilution, as well as via design of surfactant molecular architecture. This somewhat unexpected result indicates the potential of using novel magnetic surfactants for the generation and tuning of molecular magnets. PMID:27028571
Magnetic surfactants as molecular based-magnets with spin glass-like properties
NASA Astrophysics Data System (ADS)
Brown, Paul; Smith, Gregory N.; Padrón Hernández, Eduardo; James, Craig; Eastoe, Julian; Nunes, Wallace C.; Settens, Charles M.; Hatton, T. Alan; Baker, Peter J.
2016-05-01
This paper reports the use of muon spin relaxation spectroscopy to study how the aggregation behavior of magnetic surfactants containing lanthanide counterions may be exploited to create spin glass-like materials. Surfactants provide a unique approach to building in randomness, frustration and competing interactions into magnetic materials without requiring a lattice of ordered magnetic species or intervening ligands and elements. We demonstrate that this magnetic behavior may also be manipulated via formation of micelles rather than simple dilution, as well as via design of surfactant molecular architecture. This somewhat unexpected result indicates the potential of using novel magnetic surfactants for the generation and tuning of molecular magnets.
Metal-ion spin-on glasses: Novel materials for active waveguides
Ashby, C.I.H.; Sullivan, C.T.; Vawter, G.A.; Hohimer, J.P.; Hadley, G.R.; Neal, D.R.
1993-12-31
Monolithic integration of a rare-earth-ion-based active waveguide on the same wafer as its diode pump laser would permit compact packaging of the technology demonstrated in fiber lasers and amplifiers. This new monolithic technology would offer the potential for developing compact infrared and visible (up-conversion) lasers, amplifiers, and other photonic integrated circuit components. One approach that we are investigating for such monolithic integration uses a high concentration of one or more rare-earth ions incorporated into polysiloxane spin-on glasses that are solvent-cast onto III-V semiconductor wafers. This ``fiber on a chip`` technology substitute a relatively high-ion-concentration, short-length metal-ion spin-on glass (MISOG) waveguide for the low-ion-concentration, long-length fiber. Progress to data on developing MISOG waveguide materials and technology is discussed.
Temperature chaos in a Ge:Mn thin-film spin glass
NASA Astrophysics Data System (ADS)
Guchhait, Samaresh; Orbach, Raymond L.
2015-12-01
Temperature changes in thin-film Ge:Mn spin-glass dynamics are presented that exhibit temperature chaos (TC) when the spin-glass correlation length ξ (t ,T ) grows to its thickness L . For small L ≈15.5 nm, the transition to chaos takes place over a temperature range Δ T sufficiently large to exhibit both reversible and chaotic behavior. The value of Δ T can be related to the critical exponent for TC, ζ . Experimentally, ζ is found to be ≈1.06 , in the range of recent simulations. The presence of a specific length scale L allows the transition to chaos to be examined over measurable laboratory temperature changes. The transition is found to be abrupt. Bulk materials, with a distribution of crystallite sizes, will smear out the transition, resulting in a very slow crossover. The abruptness of the transition and its nature are compared with recent theoretical calculations.
A spin glass approach to the directed feedback vertex set problem
NASA Astrophysics Data System (ADS)
Zhou, Hai-Jun
2016-07-01
A directed graph (digraph) is formed by vertices and arcs (directed edges) from one vertex to another. A feedback vertex set (FVS) is a set of vertices that contains at least one vertex of every directed cycle in this digraph. The directed feedback vertex set problem aims at constructing a FVS of minimum cardinality. This is a fundamental cycle-constrained hard combinatorial optimization problem with wide practical applications. In this paper we construct a spin glass model for the directed FVS problem by converting the global cycle constraints into local arc constraints, and study this model through the replica-symmetric (RS) mean field theory of statistical physics. We then implement a belief propagation-guided decimation (BPD) algorithm for single digraph instances. The BPD algorithm slightly outperforms the simulated annealing algorithm on large random graph instances. The RS mean field results and algorithmic results can be further improved by working on a more restrictive (and more difficult) spin glass model.
Laser photoablation of spin-on-glass and poly(ethyl cyanoacrylate) photoresist
NASA Astrophysics Data System (ADS)
Hogan, M.; Magan, J. D.; Blau, W.; Lunney, J. G.; Woods, J.
The laser photoablation characteristics, at 193 and 248 nm, of a spin-on-glass (Allied Accuglass 204) in the pre-cured state, and a novel poly(ethyl cyanoacrylate) photoresist material have been studied using a low power He-Ne laser to monitor interferometrically the ablation. The etching behaviour of the photoresist material is compared with the photoablation model of Sutcliffe and Srinavasan. The dry microlithographic potential of both materials was investigated.
Monolithically integrated solid state laser and waveguide using spin-on glass
Ashby, C.I.H.; Hohimer, J.P.; Neal, D.R.; Vawter, G.A.
1995-10-31
A monolithically integrated photonic circuit is disclosed combining a semiconductor source of excitation light with an optically active waveguide formed on the substrate. The optically active waveguide is preferably formed of a spin-on glass to which are added optically active materials which can enable lasing action, optical amplification, optical loss, or frequency conversion in the waveguide, depending upon the added material. 4 figs.
Spin glass in semiconducting KFe1.05Ag0.88Te2 single crystals
Ryu, H.; Lei, H.; Klobes, B.; Warren, J. B.; Hermann, R. P.; Petrovic, C.
2015-05-26
We report discovery of KFe1.05Ag0.88Te2 single crystals with semiconducting spin glass ground state. Composition and structure analysis suggest nearly stoichiometric I4/mmm space group but allow for the existence of vacancies, absent in long range semiconducting antiferromagnet KFe1.05Ag0.88Te2. The subtle change in stoichometry in Fe/Ag sublattice changes magnetic ground state but not conductivity, giving further insight into the semiconducting gap mechanism.
About a solvable mean field model of a Gaussian spin glass
NASA Astrophysics Data System (ADS)
Barra, Adriano; Genovese, Giuseppe; Guerra, Francesco; Tantari, Daniele
2014-04-01
In a series of papers, we have studied a modified Hopfield model of a neural network, with learned words characterized by a Gaussian distribution. The model can be represented as a bipartite spin glass, with one party described by dichotomic Ising spins, and the other party by continuous spin variables, with an a priori Gaussian distribution. By application of standard interpolation methods, we have found it useful to compare the neural network model (bipartite) from one side, with two spin glass models, each monopartite, from the other side. Of these, the first is the usual Sherrington-Kirkpatrick model, the second is a spin glass model, with continuous spins and inbuilt highly nonlinear smooth cut-off interactions. This model is an invaluable laboratory for testing all techniques which have been useful in the study of spin glasses. The purpose of this paper is to give a synthetic description of the most peculiar aspects, by stressing the necessary novelties in the treatment. In particular, it will be shown that the control of the infinite volume limit, according to the well-known Guerra-Toninelli strategy, requires in addition one to consider the involvement of the cut-off interaction in the interpolation procedure. Moreover, the control of the ergodic region, the annealed case, cannot be directly achieved through the standard application of the Borel-Cantelli lemma, but requires previous modification of the interaction. This remark could find useful application in other cases. The replica symmetric expression for the free energy can be easily reached through a suitable version of the doubly stochastic interpolation technique. However, this model shares the unique property that the fully broken replica symmetry ansatz can be explicitly calculated. A very simple sum rule connects the general expression of the fully broken free energy trial function with the replica symmetric one. The definite sign of the error term shows that the replica solution is optimal. Then
NASA Astrophysics Data System (ADS)
Ferré, J.; Rajchenbach, J.; Maletta, H.
1981-03-01
We report here on a detailed study of the relaxation of the magnetization in an external field and of the remanent magnetization for the insulating spin glass: Eu0.4Sr0.6S. The Faraday rotation has allowed us to extend previous experiments near and just above the spin glass temperature Tfo = 1.55 K on a large time scale (10-6
Monte Carlo and mean field slow cooling simulations for spin glasses: relation to NP-completeness
NASA Astrophysics Data System (ADS)
Grest, Gary S.; Soukoulis, C. M.; Levin, K.; Randelman, R. E.
We discuss the dependence of the ground state energy as the Monte Carlo (MC) cooling rate in a variety of spin glass and other optimization problems. Our work is motivated by recent interest in the concept of simulated annealing and the need to find efficient numerical optimization schemes. We find that the ground state energy for six spin-glass models and the optimal tour length for the N-city traveling salesman problem are a sensitive function of the cooling rate. For the one dimensional nearest neighbor Gaussian and two two dimensional spin-glass models, the nearest neighbor ± J and Gaussian models, we find E(r) = E0 + C1 rx, while for the three dimensional t J model, a two layer t J model, the infinite range model and the N-city traveling salesman problem, the dependence on r is slower, E(r) = Eo - C2 (Inr)-1.Here C1 and C2 are constants.We believe that this difference is related to the fact that finding the ground state energy for the latter four problems is an intractable problem, i.e., it is Np-complete. We assert that a logarithmic cooling rate dependence for finding the ground state is a necessary consequence of Np-completeness. Non Np-complete problems may depend on the cooling rate either as a power-law or logarithmically. However, we have found no example for the latter.
Observation of spin-glass behavior in nickel adsorbed few layer graphene
Mitra, Sreemanta; Mondal, Oindrila; Banerjee, Sourish; Chakravorty, Dipankar
2013-01-14
Nickel-adsorbed graphene was prepared by first synthesizing graphite oxide (GO) by modified Hummers' method and then reducing a solution containing both GO and Ni{sup 2+}. Energy dispersive X-ray spectroscopy analysis showed 31 at. % nickel was present. Magnetization measurements under both dc and ac magnetic fields were carried out in the temperature range 2 K to 300 K. The zero field cooled and field cooled magnetization data showed a pronounced irreversibility at a temperature around 20 K. The analysis of the ac susceptibility data was carried out by both Vogel-Fulcher as well as power law. From dynamic scaling analysis, the microscopic flipping time {tau}{sub 0}{approx}10{sup -13}s and critical exponent z{nu}=5.9{+-}0.1 were found, indicating the presence of conventional spin glass in the system. The spin glass transition temperature was estimated as 19.5 K. Decay of thermoremanent magnetization was explained by stretched exponential function with a value of the exponent as 0.6. From the results, it is concluded that nickel adsorbed graphene behaves like a spin-glass.
Finite-size corrections for ground states of Edwards-Anderson spin glasses
NASA Astrophysics Data System (ADS)
Boettcher, Stefan; Falkner, Stefan
2012-05-01
Extensive computations of ground-state energies of the Edwards-Anderson spin glass on bond-diluted, hypercubic lattices are conducted in dimensions d=3, ..., 7. Results are presented for bond densities exactly at the percolation threshold, p=pc, and deep within the glassy regime, p>pc, where finding ground states is one of the hardest combinatorial optimization problems. Finite-size corrections of the form 1/Nω are shown to be consistent throughout with the prediction ω=1-y/d, where y refers to the "stiffness" exponent that controls the formation of domain wall excitations at low temperatures. At p=pc, an extrapolation for d→∞ appears to match our mean-field results for these corrections. In the glassy phase, however, ω does not approach its anticipated mean-field value of 2/3, obtained from simulations of the Sherrington-Kirkpatrick spin glass on an N-clique graph. Instead, the value of ω reached at the upper critical dimension matches another type of mean-field spin glass models, namely those on sparse random networks of regular degree called Bethe lattices.
Exchange bias and coercivity for ferromagnets coupled to the domain state and spin glass state
NASA Astrophysics Data System (ADS)
Zhan, Xiaozhi; Mao, Zhongquan; Chen, Xi
2016-05-01
The exchange bias (EB) effect for systems with a ferromagnetic (FM) layer coupled to bond-diluted pinning layers has been investigated by Monte Carlo simulations. Two bond dilution concentrations are chosen to obtain two kinds of pinning layers: the antiferromagnetic domain state (DS) and the spin glass (SG) state. It is found that when coupled to the more disordered SG state, the ferromagnet shows enhanced EB with higher coercivity due to larger amounts of both frozen and reversible spins at the pinning interface. Spin configurations of the FM/DS interface layer reveal that reversible spins are mostly found in domain boundaries and small domains, while most spins in large domains maintain antiferromagnetic coupling and contribute to the EB effect. The coercivity is linear to the amount of interface reversible spins, but with different slopes in the temperature ranges above or below the blocking temperature t B. This bimodal temperature-dependent coercivity indicates a sudden change in macroscopic interface coupling at the temperature t B.
Structure of Finite-RSB Asymptotic Gibbs Measures in the Diluted Spin Glass Models
NASA Astrophysics Data System (ADS)
Panchenko, Dmitry
2016-01-01
We suggest a possible approach to proving the Mézard-Parisi formula for the free energy in the diluted spin glass models, such as diluted K-spin or random K-sat model at any positive temperature. In the main contribution of the paper, we show that a certain small modification of the Hamiltonian in any of these models forces all finite-RSB asymptotic Gibbs measures in the sense of the overlaps to satisfy the Mézard-Parisi ansatz for the distribution of spins. Unfortunately, what is still missing is a description of the general full-RSB asymptotic Gibbs measures. If one could show that the general case can be approximated by finite-RSB case in the right sense then one could a posteriori remove the small modification of the Hamiltonian to recover the Mézard-Parisi formula for the original model.
Spin glass state and enhanced spiral phase in doped delafossite oxide CuCr O2
NASA Astrophysics Data System (ADS)
Yan, Z. R.; Qin, M. H.; Dong, S.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.
2016-07-01
In this paper, we study the doping effects on the magnetic states of CuCr O2 based on the classical frustrated spin model [13aa Lin et al., Phys. Rev. B 89, 220405(R) (2014), 10.1103/PhysRevB.89.220405]. Several experimental observations can be well reproduced by the Monte Carlo simulations of the modified spin models. Our paper suggests that the disorder induced by V/Al doping cooperating with the frustration in the system may contribute to the emergence of the spin glass state. Furthermore, the hole doping by M g2 + substituting C r3 + enhances the quantum fluctuations and bond disorder which modulate the biquadratic exchanges and in turn results in the promotion of the spiral phase, consistent with the experimental report.
Spin Correlations and Excitations in the Quasi-2D Triangular Bilayer Spin Glass LuCoGaO4
NASA Astrophysics Data System (ADS)
Fritsch, K.; Granroth, G. E.; Savici, A. T.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.
2012-02-01
LuCoGaO4 is a layered magnetic-bilayer material wherein Co2+ magnetic moments and nonmagnetic Ga3+ ions are randomly distributed on planar triangular bilayers. This makes it an ideal case to study the interplay between geometric frustration, site disorder and low dimensionality and its influence on the magnetic ground of the system. This novel material has been grown for the first time in single crystal form at McMaster University. We have performed magnetization measurements, revealing a previously identified spin glass transition near Tf˜19K, and a Curie Weiss temperature of Tcw˜-96K, consistent with antiferromagnetic interactions[1]. We discuss time-of-flight neutron scattering measurements using SEQUOIA at SNS which elucidate the evolution of the static and dynamic spin correlations in LuCoGaO4 over a range of temperatures from T<< Tf to T>Tcw. We observe quasielastic scattering at (1/3,1/3,L) positions in reciprocal space and rods of scattering along the c*-direction, consistent with short range antiferromagnetic correlations within decoupled bilayers, and which comfirm the 2-dimensional character of this system. Inelastic scattering measurements show a gapped ˜ 12 meV spin excitation which softens and broadens in energy, filling in the gap on a temperature scale of ˜ Tcw/2. [1] Cava et al., J. Solid State Chem. 140, 337 (1998).
Reentrant Processing in Intuitive Perception
Luu, Phan; Geyer, Alexandra; Fidopiastis, Cali; Campbell, Gwendolyn; Wheeler, Tracey; Cohn, Joseph; Tucker, Don M.
2010-01-01
The process of perception requires not only the brain's receipt of sensory data but also the meaningful organization of that data in relation to the perceptual experience held in memory. Although it typically results in a conscious percept, the process of perception is not fully conscious. Research on the neural substrates of human visual perception has suggested that regions of limbic cortex, including the medial orbital frontal cortex (mOFC), may contribute to intuitive judgments about perceptual events, such as guessing whether an object might be present in a briefly presented fragmented drawing. Examining dense array measures of cortical electrical activity during a modified Waterloo Gestalt Closure Task, results show, as expected, that activity in medial orbital frontal electrical responses (about 250 ms) was associated with intuitive judgments. Activity in the right temporal-parietal-occipital (TPO) region was found to predict mOFC (∼150 ms) activity and, in turn, was subsequently influenced by the mOFC at a later time (∼300 ms). The initial perception of gist or meaning of a visual stimulus in limbic networks may thus yield reentrant input to the visual areas to influence continued development of the percept. Before perception is completed, the initial representation of gist may support intuitive judgments about the ongoing perceptual process. PMID:20209101
Nanocomposites of silver nanoparticles embedded in glass nanofibres obtained by laser spinning
NASA Astrophysics Data System (ADS)
Cabal, Belén; Quintero, Félix; Díaz, Luís Antonio; Rojo, Fernando; Dieste, Oliver; Pou, Juan; Torrecillas, Ramón; Moya, José Serafín
2013-04-01
Nanocomposites made of non-woven glass fibres with diameters ranging from tens of nanometers up to several micrometers, containing silver nanoparticles, were successfully fabricated by the laser spinning technique. Pellets of a soda-lime silicate glass containing silver nanoparticles with varying concentrations (5 and 10 wt%) were used as a precursor. The process followed to obtain the silver nanofibres did not agglomerate significantly the metallic nanoparticles, and the average particle size is still lower than 50 nm. This is the first time that glass nanofibres containing silver nanoparticles have been obtained following a process different from electrospinning of a sol-gel, thus avoiding the limitations of this method and opening a new route to composite nanomaterials. Antibacterial efficiency of the nanosilver glass fibres, tested against one of the most common Gram negative bacteria, was greater than 99.99% compared to the glass fibres free of silver. The silver nanoparticles are well-dispersed not only on the surface but are also embedded into the uniform nanofibres, which leads to a long lasting durable antimicrobial effect. All these novel characteristics will potentially open up a whole new range of applications.
Nanocomposites of silver nanoparticles embedded in glass nanofibres obtained by laser spinning.
Cabal, Belén; Quintero, Félix; Díaz, Luís Antonio; Rojo, Fernando; Dieste, Oliver; Pou, Juan; Torrecillas, Ramón; Moya, José Serafín
2013-05-01
Nanocomposites made of non-woven glass fibres with diameters ranging from tens of nanometers up to several micrometers, containing silver nanoparticles, were successfully fabricated by the laser spinning technique. Pellets of a soda-lime silicate glass containing silver nanoparticles with varying concentrations (5 and 10 wt%) were used as a precursor. The process followed to obtain the silver nanofibres did not agglomerate significantly the metallic nanoparticles, and the average particle size is still lower than 50 nm. This is the first time that glass nanofibres containing silver nanoparticles have been obtained following a process different from electrospinning of a sol-gel, thus avoiding the limitations of this method and opening a new route to composite nanomaterials. Antibacterial efficiency of the nanosilver glass fibres, tested against one of the most common gram negative bacteria, was greater than 99.99% compared to the glass fibres free of silver. The silver nanoparticles are well-dispersed not only on the surface but are also embedded into the uniform nanofibres, which leads to a long lasting durable antimicrobial effect. All these novel characteristics will potentially open up a whole new range of applications. PMID:23535995
Critical properties of short-range Ising spin glasses on a Wheatstone-bridge hierarchical lattice.
Almeida, Sebastião T O; Nobre, Fernando D
2015-08-01
An Ising spin-glass model with nearest-neighbor interactions, following a symmetric probability distribution, is investigated on a hierarchical lattice of the Wheatstone-bridge family characterized by a fractal dimension D≈3.58. The interaction distribution considered is a stretched exponential, which has been shown recently to be very close to the fixed-point coupling distribution, and such a model has been considered lately as a good approach for Ising spin glasses on a cubic lattice. An exact recursion procedure is implemented for calculating site magnetizations, mi=〈Si〉T, as well as correlations between pairs of nearest-neighbor spins, 〈SiSj〉T (〈〉T denote thermal averages), for a given set of interaction couplings on this lattice. From these local magnetizations and correlations, one can compute important physical quantities, such as the Edwards-Anderson order parameter, the internal energy, and the specific heat. Considering extrapolations to the thermodynamic limit for the order parameter, such as a finite-size scaling approach, it is possible to obtain directly the critical temperature and critical exponents. The transition between the spin-glass and paramagnetic phases is analyzed, and the associated critical exponents β and ν are estimated as β=0.82(5) and ν=2.50(4), which are in good agreement with the most recent results from extensive numerical simulations on a cubic lattice. Since these critical exponents were obtained from a fixed-point distribution, they are universal, i.e., valid for any coupling distribution considered. PMID:26382339
From spin induced ferroelectricity to dipolar glasses: Spinel chromites and mixed delafossites
Maignan, A.
2012-11-15
Magnetoelectric multiferroics showing coupling between polarization and magnetic order are attracting much attention. For instance, they could be used in memory devices. Metal-transition oxides are provided several examples of inorganic magnetoelectric multiferroics. In the present short review, spinel and delafossite chromites are described. For the former, an electric polarization is evidenced in the ferrimagnetic state for ACr{sub 2}O{sub 4} polycrystalline samples (A=Ni, Fe, Co). The presence of a Jahn-Teller cation such as Ni{sup 2+} at the A site is shown to yield larger polarization values. In the delafossites, substitution by V{sup 3+} at the Cr or Fe site in CuCrO{sub 2} (CuFeO{sub 2}) suppresses the complex antiferromagnetic structure at the benefit of a spin glass state. The presence of cation disorder, probed by transmission electron microscopy, favors relaxor-like ferroelectricity. The results on the ferroelectricity of ferrimagnets and insulating spin glasses demonstrate that, in this research field, transition-metal oxides are worth to be studied. - Graphical abstract: Electric polarization as a function of temperature is measured up to T{sub C} in three chromite ferrimagnetic spinels. Largest values are reached for spinels with Jahn-Teller cations at the A site (Ni or Fe). Highlights: Black-Right-Pointing-Pointer Electric polarization is evidenced in the ferrimagnetic state of the chromite spinels. Black-Right-Pointing-Pointer Jahn-Teller cations at the A site of these spinels lead to larger polarization values. Black-Right-Pointing-Pointer Vanadium substituted at the Cr (or Fe) site of delafossites changes the antiferromagnetic state to spin glass. Black-Right-Pointing-Pointer Electric polarization is not the result of magnetic ordering but magnetic disordering in Cr or Fe delafossites. Black-Right-Pointing-Pointer Relaxor-type ferroelectricity or spin induced ferroelectricity can be observed in the delafossites.
Critical properties of short-range Ising spin glasses on a Wheatstone-bridge hierarchical lattice
NASA Astrophysics Data System (ADS)
Almeida, Sebastião T. O.; Nobre, Fernando D.
2015-08-01
An Ising spin-glass model with nearest-neighbor interactions, following a symmetric probability distribution, is investigated on a hierarchical lattice of the Wheatstone-bridge family characterized by a fractal dimension D ≈3.58 . The interaction distribution considered is a stretched exponential, which has been shown recently to be very close to the fixed-point coupling distribution, and such a model has been considered lately as a good approach for Ising spin glasses on a cubic lattice. An exact recursion procedure is implemented for calculating site magnetizations, mi=
Spin glass instead of superconductivity in Ba(Fe1-xCrx/2Nix/2)2As2
NASA Astrophysics Data System (ADS)
Xu, Sheng-Gao; Sun, Yun-Lei; Jiang, Shuai; Xing, Hui; Jiao, Lin; Yuan, Hui-Qiu; Feng, Chun-Mu; Xu, Zhu-An; Cao, Guang-Han
2012-12-01
We have studied an “isoelectronic” Fe-site doping with Cr and Ni in Ba(Fe1-xCrx/2Nix/2)2As2 system. With increasing x, the antiferromagnetic SDW in the parent compound is suppressed quickly. Spin glass state emerges in the range of 0.1 <= x < 0.2. The spin glass state evolves into cluster glass with further doping, and finally becomes ferromagnetism at x = 1.0. No superconductivity was observed down to 0.5 K. The electronic phase diagram is established, and the underlying physics is discussed.
Hydration-induced spin-glass state in a frustrated Na-Mn-O triangular lattice
NASA Astrophysics Data System (ADS)
Bakaimi, Ioanna; Brescia, Rosaria; Brown, Craig M.; Tsirlin, Alexander A.; Green, Mark A.; Lappas, Alexandros
2016-05-01
Birnessite compounds are stable across a wide range of compositions that produces a remarkable diversity in their physical, electrochemical, and functional properties. These are hydrated analogs of the magnetically frustrated, mixed-valent manganese oxide structures, with general formula, N axMn O2 . Here we demonstrate that the direct hydration of layered rock-salt type α-NaMn O2 , with the geometrically frustrated triangular lattice topology, yields the birnessite type oxide, N a0.36Mn O2.0.2 H2O , transforming its magnetic properties. This compound has a much-expanded interlayer spacing compared to its parent α-NaMn O2 compound. We show that while the parent α-NaMn O2 possesses a Néel temperature of 45 K as a result of broken symmetry in the M n3 + sublattice, the hydrated derivative undergoes collective spin freezing at 29 K within the M n3 +/M n4 + sublattice. Scaling-law analysis of the frequency dispersion of the ac susceptibility, as well as the temperature-dependent, low-field dc magnetization confirm a cooperative spin-glass state of strongly interacting spins. This is supported by complementary spectroscopic analysis [high-angle annular dark-field scanning transmission electron miscroscopy (TEM), energy-dispersive x-ray spectroscopy, and electron energy-loss spectroscopy] as well as by a structural investigation (high-resolution TEM, x-ray, and neutron powder diffraction) that yield insights into the chemical and atomic structure modifications. We conclude that the spin-glass state in birnessite is driven by the spin frustration imposed by the underlying triangular lattice topology that is further enhanced by the in-plane bond-disorder generated by the mixed-valent character of manganese in the layers.
Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K; Mukherjee, Sundeep
2016-06-01
High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent 'Stoner type' magnetization for the amorphous alloys in contrast to 'Heisenberg type' in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study. PMID:27143686
NASA Astrophysics Data System (ADS)
Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep
2016-06-01
High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe–Co metallic glass system of composition [(Co1‑x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.
Spin-glass behaviors in carrier polarity controlled Fe3-xTixO4 semiconductor thin films
NASA Astrophysics Data System (ADS)
Yamahara, H.; Seki, M.; Adachi, M.; Takahashi, M.; Nasu, H.; Horiba, K.; Kumigashira, H.; Tabata, H.
2015-08-01
Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe3-xTixO4 thin films have been obtained on spinel MgAl2O4 substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films (x = 0.8) show p-type conduction, while Ti-poor films (x = 0.6-0.75) show n-type conduction. The systematic Fe(III) reduction to Fe(II) followed by Ti(IV) substitution in the octahedral sublattice is confirmed by the X-ray absorption spectra. All of the Fe3-xTixO4 films (x = 0.6-0.8) exhibit ferrimagnetism above room temperature. Next, the spin-glass behaviors of Ti-rich Fe2.2Ti0.8O4 film are studied, since this magnetically diluted system is expected to exhibit the spin-glass behaviors. The DC magnetization and AC susceptibility measurements for the Ti-rich Fe2.2Ti0.8O4 film reveal the presence of the spin glass phase. Thermal- and magnetic-field-history memory effects are observed and are attributed to the long time-decay nature of remanent magnetization. The detailed analysis of the time-dependent thermoremanent magnetization reveals the presence of the cluster spin glass state.
Probing quantum spin glass like system with a double quantum dot
NASA Astrophysics Data System (ADS)
Koh, C. Y.; Kwek, L. C.
2016-06-01
We study the ground state properties of a 4-qubit spin glass like (SGL) chain with probes at the end of the chain and compare our results with the non-spin glass like (NSGL) case. The SGL is modeled as a spin chain with nearest-neighbor couplings, taking on normal variates with mean J and variance Δ2. The entanglement between the probes is used to detect any discontinuity in the ground state energy spectrum. For the NSGL case, it was found that the concurrence of the probes exhibits sharp transitions whenever there are abrupt changes in the energy spectrum. In particular, for the 4-qubit case, there is a sudden change in the ground state energy at an external magnetic field B of around 0.66 (resulting in a drop in concurrence of the probes) and 1.7 (manifest as a spike). The latter spike persists for finite temperature case. For the SGL sample with sufficiently large Δ, however, the spike is absent. Thus, an absence in the spike could act as a possible signature of the presence of SGL effects. Moreover, the sudden drop in concurrence at B ≈ 0.66 does not disappear but gets smeared with increasing Δ. However, this drop can be accentuated with a smaller probe coupling. The finite temperature case is also briefly discussed.
Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles
Khurshid, Hafsa; Lampen-Kelley, Paula; Iglesias, Òscar; Alonso, Javier; Phan, Manh-Huong; Sun, Cheng-Jun; Saboungi, Marie-Louise; Srikanth, Hariharan
2015-01-01
Disorder among surface spins is a dominant factor in the magnetic response of magnetic nanoparticle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8 ± 0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K, and become frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins. Monte Carlo simulations of a hollow particle corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures. PMID:26503506
Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles
NASA Astrophysics Data System (ADS)
Khurshid, Hafsa; Lampen-Kelley, Paula; Iglesias, Òscar; Alonso, Javier; Phan, Manh-Huong; Sun, Cheng-Jun; Saboungi, Marie-Louise; Srikanth, Hariharan
2015-10-01
Disorder among surface spins is a dominant factor in the magnetic response of magnetic nanoparticle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8 ± 0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K, and become frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins. Monte Carlo simulations of a hollow particle corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures.
Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles.
Khurshid, Hafsa; Lampen-Kelley, Paula; Iglesias, Òscar; Alonso, Javier; Phan, Manh-Huong; Sun, Cheng-Jun; Saboungi, Marie-Louise; Srikanth, Hariharan
2015-01-01
Disorder among surface spins is a dominant factor in the magnetic response of magnetic nanoparticle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8 ± 0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K, and become frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins. Monte Carlo simulations of a hollow particle corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures. PMID:26503506
Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles
Khurshid, Hafsa; Lampen-Kelley, Paula; Iglesias, Òscar; Alonso, Javier; Phan, Manh-Huong; Sun, Cheng-Jun; Saboungi, Marie-Louise; Srikanth, Hariharan
2015-10-27
Disorder among surface spins largely dominates the magnetic response of ultrafine magnetic particle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8±0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K, and becomes frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point tomore » highly frustrated surface spins that rearrange much more slowly than interior spins with bulk coordination. Monte Carlo simulations of a hollow particle reproducing the experimental morphology corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Lastly, our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures.« less
Difference between nuclear spin relaxation and ionic conductivity relaxation in superionic glasses
NASA Astrophysics Data System (ADS)
Ngai, K. L.
1993-04-01
Tatsumisago, Angell, and Martin [J. Chem. Phys. 97, 6968 (1992)] have compared conductivity relaxation data and 7Li nuclear spin lattice relaxation (SLR) data measured on a lithium chloroborate glass and found pronounced differences in the most probable relaxation times. The electrical conductivity relaxation (ECR) time, τ*σ, at some temperature occurs on a time scale shorter by some two orders of magnitude than the 7Li spin lattice relaxation correlation time, τ*s, and has a significantly lower activation energy. SLR and ECR monitor the motions of ions through different dynamic variables and correlation functions. Using this fact and the coupling model, I am able to explain quantitatively all aspects of the difference between SLR and ECR, and to establish relations between their different relaxation characteristics. The large difference between the observed activation energies of SLR and ECR alone should have implications on the validity of any proposed theory of the dynamics of ionic transport.
Applying Tabu Search to the Two-Dimensional Ising Spin Glass
NASA Astrophysics Data System (ADS)
Laguna, Manuel; Laguna, Pablo
A variety of problems in statistical physics, such as Ising-like systems, can be modeled as integer programs. Physicists have relied mostly on Monte Carlo methods to find approximate solutions to these computationally difficult problems. In some cases, optimal solutions to relatively small problems have been found using standard optimization techniques, e.g., cutting plane and branch-and-bound algorithms. Motivated by the success of tabu search (TS) in finding optimal or near-optimal solutions to combinatorial optimization problems in a number of different settings, we study the application of this methodology to Ising-like systems. Particularly, we develop a TS method to find ground states of two-dimensional spin glasses. Our method performs a search at different levels of resolution in the spin lattice, and it is designed to obtain optimal or near-optimal solutions to problem instances with several different characteristics. Results are reported for computational experiments with up to 64×64 lattices.
NASA Astrophysics Data System (ADS)
Lisewski, Andreas Martin; Lichtarge, Olivier
2010-08-01
Recurrent international financial crises inflict significant damage to societies and stress the need for mechanisms or strategies to control risk and tamper market uncertainties. Unfortunately, the complex network of market interactions often confounds rational approaches to optimize financial risks. Here we show that investors can overcome this complexity and globally minimize risk in portfolio models for any given expected return, provided the margin requirement remains below a critical, empirically measurable value. In practice, for markets with centrally regulated margin requirements, a rational stabilization strategy would be keeping margins small enough. This result follows from ground states of the random field spin glass Ising model that can be calculated exactly through convex optimization when relative spin coupling is limited by the norm of the network’s Laplacian matrix. In that regime, this novel approach is robust to noise in empirical data and may be also broadly relevant to complex networks with frustrated interactions that are studied throughout scientific fields.
Lisewski, Andreas Martin; Lichtarge, Olivier
2010-01-01
Recurrent international financial crises inflict significant damage to societies and stress the need for mechanisms or strategies to control risk and tamper market uncertainties. Unfortunately, the complex network of market interactions often confounds rational approaches to optimize financial risks. Here we show that investors can overcome this complexity and globally minimize risk in portfolio models for any given expected return, provided the relative margin requirement remains below a critical, empirically measurable value. In practice, for markets with centrally regulated margin requirements, a rational stabilization strategy would be keeping margins small enough. This result follows from ground states of the random field spin glass Ising model that can be calculated exactly through convex optimization when relative spin coupling is limited by the norm of the network's Laplacian matrix. In that regime, this novel approach is robust to noise in empirical data and may be also broadly relevant to complex networks with frustrated interactions that are studied throughout scientific fields. PMID:20625477
Extended variational principle for the Sherrington-Kirkpatrick spin-glass model
NASA Astrophysics Data System (ADS)
Aizenman, Michael; Sims, Robert; Starr, Shannon L.
2003-12-01
The recent proof by Guerra that the Parisi ansatz provides a lower bound on the free energy of the Sherrington-Kirkpatrick (SK) spin-glass model could have been taken as offering some support to the validity of the purported solution. In this work we present a broader variational principle, in which the lower bound as well as the actual value are expressed through an optimization procedure for which ultrametric/hierarchal structures form only a subset of the variational class. The validity of Parisi’s ansatz for the SK model is still in question. The new variational principle may be of help in critical review of the issue.
A Self-Averaging ``Order Parameter'' for the Sherrington-Kirkpatrick Spin Glass Model
NASA Astrophysics Data System (ADS)
Wreszinski, Walter F.; Bolina, Oscar
2004-09-01
Following an idea of van Enter and Griffiths, we define a self-averaging parameter for the Sherrington-Kirkpatrick (SK) spin glass which is a self-averaging version of the order parameter introduced by Aizenman, Lebowitz and Ruelle. It is strictly positive at low temperature and zero at sufficiently high temperature. The proof is based on the recent construction of the thermodynamic limit of the free energy by Guerra and Toninelli. We also discuss how our definition compares with various existing definitions of order-parameter like quantities.
Evidence for nonuniversal scaling in dimension-four Ising spin glasses
NASA Astrophysics Data System (ADS)
Lundow, P. H.; Campbell, I. A.
2015-04-01
The critical behavior of the Binder cumulant for Ising spin glasses in dimension four is studied through simulation measurements. Data for the bimodal interaction model are compared with those for the Laplacian interaction model. Special attention is paid to scaling corrections. The limiting infinite size value at criticality for this dimensionless variable is a parameter characteristic of a universality class. This critical limit is estimated to be equal to 0.523(3) in the bimodal model and to 0.473(3) in the Laplacian model.
Universal critical behavior of the two-dimensional Ising spin glass
NASA Astrophysics Data System (ADS)
Fernandez, L. A.; Marinari, E.; Martin-Mayor, V.; Parisi, G.; Ruiz-Lorenzo, J. J.
2016-07-01
We use finite size scaling to study Ising spin glasses in two spatial dimensions. The issue of universality is addressed by comparing discrete and continuous probability distributions for the quenched random couplings. The sophisticated temperature dependency of the scaling fields is identified as the major obstacle that has impeded a complete analysis. Once temperature is relinquished in favor of the correlation length as the basic variable, we obtain a reliable estimation of the anomalous dimension and of the thermal critical exponent. Universality among binary and Gaussian couplings is confirmed to a high numerical accuracy.
Soft Modes, Localization, and Two-Level Systems in Spin Glasses.
Baity-Jesi, M; Martín-Mayor, V; Parisi, G; Perez-Gaviro, S
2015-12-31
In the three-dimensional Heisenberg spin glass in a random field, we study the properties of the inherent structures that are obtained by an instantaneous cooling from infinite temperature. For a not too large field the density of states g(ω) develops localized soft plastic modes and reaches zero as ω(4) (for large fields a gap appears). When we perturb the system adding a force along the softest mode, one reaches very similar minima of the energy, separated by small barriers, that appear to be good candidates for classical two-level systems. PMID:26765021
Statics and Dynamics of a Two-Dimensional Ising Spin-Glass Model
NASA Astrophysics Data System (ADS)
Young, A. P.
1983-03-01
The temperature and field dependence of spatial correlations and relaxation times are investigated in detail by Monte Carlo simulations for a two-dimensional Ising spin-glass model. There is no transition, but, in zero field, barrier heights and correlation range increase smoothly at low temperatures. This increase does not seem to be fast enough to explain experiments. In a field, barrier heights and the correlation length tend to a finite limit as T-->0. Points in the h-T plane with constant relaxation time satisfy T(h)-T(0)~h23 at moderately low temperatures.
Nonuniqueness of H23 and H2 field-temperature transition lines in spin-glasses
NASA Astrophysics Data System (ADS)
Wenger, L. E.; Mydosh, J. A.
1984-04-01
Including the magnetic field dependence on the superparamagnetic relaxation time τ, "transition" lines in the H-T plane are obtained for constant τ. These lines follow the relation TH-T0~Hν where ν~23 except for H-->0 which shows a crossover to ν=2. Thus a power law similar to that derived from mean-field models of spin-glasses is obtained, based strictly on a superparamagnetic relaxation-time approach. This questions the conclusion that experimental observations of H-T lines are solely the result of a mean-field phase transition.
Thermodynamic Identities and Symmetry Breaking in Short-Range Spin Glasses
NASA Astrophysics Data System (ADS)
Arguin, L.-P.; Newman, C. M.; Stein, D. L.
2015-10-01
We present a technique to generate relations connecting pure state weights, overlaps, and correlation functions in short-range spin glasses. These are obtained directly from the unperturbed Hamiltonian and hold for general coupling distributions. All are satisfied in phases with simple thermodynamic structure, such as the droplet-scaling and chaotic pairs pictures. If instead nontrivial mixed-state pictures hold, the relations suggest that replica symmetry is broken as described by a Derrida-Ruelle cascade, with pure state weights distributed as a Poisson-Dirichlet process.
Design of half-reentrant SRF cavities
NASA Astrophysics Data System (ADS)
Meidlinger, M.; Grimm, T. L.; Hartung, W.
2006-07-01
The shape of a TeSLA inner cell can be improved to lower the peak surface magnetic field at the expense of a higher peak surface electric field by making the cell reentrant. Such a single-cell cavity was designed and tested at Cornell, setting a world record accelerating gradient [V. Shemelin et al., An optimized shape cavity for TESLA: concept and fabrication, 11th Workshop on RF Superconductivity, Travemünde, Germany, September 8-12, 2003; R. Geng, H. Padamsee, Reentrant cavity and first test result, Pushing the Limits of RF Superconductivity Workshop, Argonne National Laboratory, September 22-24, 2004]. However, the disadvantage to a cavity is that liquids become trapped in the reentrant portion when it is vertically hung during high pressure rinsing. While this was overcome for Cornell’s single-cell cavity by flipping it several times between high pressure rinse cycles, this may not be feasible for a multi-cell cavity. One solution to this problem is to make the cavity reentrant on only one side, leaving the opposite wall angle at six degrees for fluid drainage. This idea was first presented in 2004 [T.L. Grimm et al., IEEE Transactions on Applied Superconductivity 15(6) (2005) 2393]. Preliminary designs of two new half-reentrant (HR) inner cells have since been completed, one at a high cell-to-cell coupling of 2.1% (high- kcc HR) and the other at 1.5% (low- kcc HR). The parameters of a HR cavity are comparable to a fully reentrant cavity, with the added benefit that a HR cavity can be easily cleaned with current technology.
NASA Astrophysics Data System (ADS)
Ma, Ji; Chen, Kezheng
2016-05-01
In this study, room-temperature spin-glass behaviors were observed in flake-like oriented attached hematite (α-Fe2O3) and iron phosphate hydroxide hydrate (Fe5(PO4)4(OH)3·2H2O) single crystals. Remarkably, their coercivity (HC) values were found to be almost invariable at various given temperatures from 5 to 300 K. The spin topographic map in these flakes was assumed as superparamagnetic (SPM) "islands" isolated by spin glass (SG)-like "bridges". A spin-glass model was then proposed to demonstrate the spin frustration within these "bridges", which were formed by the staggered atomic planes in the uneven surfaces belonging to different attached nanoparticles. Under the spatial limitation and coupling shield of these "bridges", the SPM "islands" were found to be collectively frozen to form a superspin glass (SSG) state below 80 K in weak applied magnetic fields; whereas, when strong magnetic fields were applied, the magnetic coupling of these "islands" would become superferromagnetic (SFM) through tunneling superexchange, so that, these SFM spins could antiferromagnetically couple with the SG-like "bridges" to yield pronounced exchange bias (EB) effect.
Reentrant transition in coupled noisy oscillators.
Kobayashi, Yasuaki; Kori, Hiroshi
2015-01-01
We report on a synchronization-breaking instability observed in a noisy oscillator unidirectionally coupled to a pacemaker. Using a phase oscillator model, we find that, as the coupling strength is increased, the noisy oscillator lags behind the pacemaker more frequently and the phase slip rate increases, which may not be observed in averaged phase models such as the Kuramoto model. Investigation of the corresponding Fokker-Planck equation enables us to obtain the reentrant transition line between the synchronized state and the phase slip state. We verify our theory using the Brusselator model, suggesting that this reentrant transition can be found in a wide range of limit cycle oscillators. PMID:25679676
Why the dipolar response in dielectrics and spin-glasses is unavoidably universal
NASA Astrophysics Data System (ADS)
Cuervo-Reyes, Eduardo
2016-07-01
Materials response to electric or magnetic fields is often dominated by the dynamics of dipoles in the system. This is for instance the case of polar dielectrics and many transition metal compounds. An essential and not yet well understood fact is that, despite their structural diversity, dielectric solids exhibit a striking universality of frequency and time responses, sharing many aspects with the behaviour of spin-glasses. In this article I propose a stochastic approach to dipole dynamics within which the “universal frequency response” derives naturally with Debye’s relaxation mechanism as a special case. This formulation reveals constraints to the form of the relaxation functions, which are essential for a consistent representation of the dynamical slowing-down at the spin-glass transition. Relaxation functions with algebraic-, and exponential-tails, as well as damped oscillations, are shown to have a unified representation in which the stable limit of the distribution of waiting-times between dipole flips determines the present type of dynamics.
Spin-glass phase transitions and minimum energy of the random feedback vertex set problem.
Qin, Shao-Meng; Zeng, Ying; Zhou, Hai-Jun
2016-08-01
A feedback vertex set (FVS) of an undirected graph contains vertices from every cycle of this graph. Constructing a FVS of sufficiently small cardinality is very difficult in the worst cases, but for random graphs this problem can be efficiently solved by converting it into an appropriate spin-glass model [H.-J. Zhou, Eur. Phys. J. B 86, 455 (2013)EPJBFY1434-602810.1140/epjb/e2013-40690-1]. In the present work we study the spin-glass phase transitions and the minimum energy density of the random FVS problem by the first-step replica-symmetry-breaking (1RSB) mean-field theory. For both regular random graphs and Erdös-Rényi graphs, we determine the inverse temperature β_{l} at which the replica-symmetric mean-field theory loses its local stability, the inverse temperature β_{d} of the dynamical (clustering) phase transition, and the inverse temperature β_{s} of the static (condensation) phase transition. These critical inverse temperatures all change with the mean vertex degree in a nonmonotonic way, and β_{d} is distinct from β_{s} for regular random graphs of vertex degrees K>60, while β_{d} are identical to β_{s} for Erdös-Rényi graphs at least up to mean vertex degree c=512. We then derive the zero-temperature limit of the 1RSB theory and use it to compute the minimum FVS cardinality. PMID:27627285
Why the dipolar response in dielectrics and spin-glasses is unavoidably universal.
Cuervo-Reyes, Eduardo
2016-01-01
Materials response to electric or magnetic fields is often dominated by the dynamics of dipoles in the system. This is for instance the case of polar dielectrics and many transition metal compounds. An essential and not yet well understood fact is that, despite their structural diversity, dielectric solids exhibit a striking universality of frequency and time responses, sharing many aspects with the behaviour of spin-glasses. In this article I propose a stochastic approach to dipole dynamics within which the "universal frequency response" derives naturally with Debye's relaxation mechanism as a special case. This formulation reveals constraints to the form of the relaxation functions, which are essential for a consistent representation of the dynamical slowing-down at the spin-glass transition. Relaxation functions with algebraic-, and exponential-tails, as well as damped oscillations, are shown to have a unified representation in which the stable limit of the distribution of waiting-times between dipole flips determines the present type of dynamics. PMID:27366866
Why the dipolar response in dielectrics and spin-glasses is unavoidably universal
Cuervo-Reyes, Eduardo
2016-01-01
Materials response to electric or magnetic fields is often dominated by the dynamics of dipoles in the system. This is for instance the case of polar dielectrics and many transition metal compounds. An essential and not yet well understood fact is that, despite their structural diversity, dielectric solids exhibit a striking universality of frequency and time responses, sharing many aspects with the behaviour of spin-glasses. In this article I propose a stochastic approach to dipole dynamics within which the “universal frequency response” derives naturally with Debye’s relaxation mechanism as a special case. This formulation reveals constraints to the form of the relaxation functions, which are essential for a consistent representation of the dynamical slowing-down at the spin-glass transition. Relaxation functions with algebraic-, and exponential-tails, as well as damped oscillations, are shown to have a unified representation in which the stable limit of the distribution of waiting-times between dipole flips determines the present type of dynamics. PMID:27366866
Spin-cluster glass state in U(Ga0.95Mn0.05)3
NASA Astrophysics Data System (ADS)
Dong-Hua, Xie; Wen, Zhang; Yi, Liu; Wei, Feng; Yun, Zhang; Shi-Yong, Tan; Xie-Gang, Zhu; Qiu-Yun, Chen; Qin, Liu; Bing-Kai, Yuan; Xin-Chun, Lai
2016-04-01
We report the study of a low temperature cluster glass state in 5% Mn-doped UGa3 heavy fermion compound. This compound transforms from a paramagnetic state to a spin-cluster glass state, which is confirmed by measuring the dc susceptibility and magnetization. The ac susceptibility exhibits a frequency-dependent peak around T f, which provides direct evidence of the cluster glass state. By analyzing the field-dependent magnetization and frequency-dependent ac susceptibility in detail, we deduce that this compound forms a spin-cluster glass state below T f. Project supported by the Natural Science Foundation of China Academy of Engineering Physic (Grant No. 2014A0301013) and the National Natural Science Foundation of China (Grant Nos. 11304291 and 11504342).
Scaling behavior of domain walls at the T = 0 ferromagnet to spin-glass transition
NASA Astrophysics Data System (ADS)
Melchert, O.; Hartmann, A. K.
2009-01-01
Using mappings to combinatorial optimization problems, one can often study physical systems better by means of sophisticated algorithms from computer science. Here, we study the geometric properties of domain-wall excitations in a two-dimensional random-bond Ising spin system, where each realization of the disorder consists of a random fraction ρ of ferromagnetic bonds and a fraction (1-ρ) of bonds drawn from a Gaussian distribution with zero mean and unit width. We formulate an auxiliary graph theoretical problem in which domain walls are given by undirected shortest paths with possibly negative distances [O. Melchert and A.K. Hartmann Phys. Rev. B 76, 174411 (2007)]. Due to the details of the mapping, standard shortest path algorithms (e.g. the Dijkstra algorithm) cannot be applied. To solve such shortest path problems it requires minimum weight perfect matching algorithms. We first locate the critical point ρc, where the ferromagnet (large ρ) to spin-glass transition occurs. For certain values of ρ close to the critical point we investigate the stiffness exponent θ and the fractal dimension df that describe the scaling of the average domain-wall energy and length, respectively. Performing a finite-size scaling analysis we find that both exponents remain constant in the spin-glass phase, i.e. θ~-0.28 and df~1.275. This is consistent with conformal field theory, where it seems to be possible [C. Amoruso et al. Phys. Rev. Lett. 97, 267202 (2006)] to relate the exponents via df-1 = 3/[4(3+θ)].
Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction
NASA Astrophysics Data System (ADS)
Surungan, Tasrief; Bansawang B., J.; Tahir, Dahlang
2016-03-01
Spin glass (SG) is a typical magnetic system with frozen random spin orientation at low temperatures. The system exhibits rich physical properties, such as infinite number of ground states, memory effect, and aging phenomena. There are two main ingredients considered to be pivotal for the existence of SG behavior, namely, frustration and randomness. For the canonical SG system, frustration is led by the presence of competing interaction between ferromagnetic (FM) and antiferromagnetic (AF) couplings. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)], reported the SG properties of the AF Ising spins on scale free network (SFN). It is a new type of SG, different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely caused by the topological factor and its randomness is related to the irregular connectvity. Recently, Surungan et. al. [Journal of Physics: Conference Series, 640, 012001 (2015)] reported SG bahavior of AF Heisenberg model on SFN. We further investigate this type of system by studying an AF Heisenberg model on rewired square lattices. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.
Multicritical point of Ising spin glasses on triangular and honeycomb lattices
NASA Astrophysics Data System (ADS)
de Queiroz, S. L. A.
2006-02-01
The behavior of two-dimensional Ising spin glasses at the multicritical point on triangular and honeycomb lattices is investigated with the help of finite-size scaling and conformal-invariance concepts. We use transfer-matrix methods on long strips to calculate domain-wall energies, uniform susceptibilities, and spin-spin correlation functions. Accurate estimates are provided for the location of the multicritical point on both lattices, which lend strong support to a conjecture recently advanced by Takeda, Sasamoto, and Nishimori. Correlation functions are shown to obey rather strict conformal-invariance requirements, once suitable adaptations are made to account for geometric aspects of the transfer-matrix description of triangular and honeycomb lattices. The universality class of critical behavior upon crossing the ferro-para-magnetic phase boundary is probed, with the following estimates for the associated critical indices: ν=1.49(2) , γ=2.71(4) , η1=0.183(3) , which are distinctly different from the percolation values.
Electron Spin Relaxation Rates for Semiquinones between 25 and 295 K in Glass-Forming Solvents
Kathirvelu, Velavan; Sato, Hideo; Eaton, Sandra S.; Eaton, Gareth R.
2009-01-01
Electron spin lattice relaxation rates for five semiquinones (2,5-di-t-butyl-1,4-benzosemiquinone, 2,5-di-t-amyl-1,4-benzosemiquinone, 2,5-di-phenyl-1,4-benzosemiquinone, 2,6-di-t-butyl-1,4-benzosemiquinone, tetrahydroxy-1,4-benzosemiquione) were studied by long-pulse saturation recovery EPR in 1:4 glycerol:ethanol, 1:1 glycerol:ethanol, and triethanolamine between 25 and 295 K. Although the dominant process changes with temperature, relaxation rates vary smoothly with temperature, even near the glass transition temperatures, and could be modeled as the sum of contributions that have the temperature dependence that is predicted for the direct, Raman, local mode and tumbling dependent processes. At 85 K, which is in a temperature range where the Raman process dominates, relaxation rates along the gxx (g~2.006) and gyy (g~2.005) axes are about 2.7 to 1.5 times faster than along the gzz axis (g = 2.0023). In highly viscous triethanolamine, contributions from tumbling-dependent processes are negligible. At temperatures above 100 K relaxation rates in triethanolamine are unchanged between X-band (9.5 GHz) and Q-band (34 GHz), so the process that dominates in this temperature interval was assigned as a local mode rather than a thermally-activated process. Because the largest proton hyperfine couplings are only 2.2 G, spin rotation makes a larger contribution than tumbling-dependent modulation of hyperfine anisotropy. Since g anisotropy is small, tumbling dependent modulation of g anisotropy make a smaller contribution than spin rotation at X-band. Although there was negligible impact of methyl rotation on T1, rotation of t-butyl or t-amyl methyl groups enhances spin echo dephasing between 85 and 150 K. PMID:19223213
A remark on the infinite-volume Gibbs measures of spin glasses
NASA Astrophysics Data System (ADS)
Arguin, Louis-Pierre
2008-12-01
In this note, we point out that infinite-volume Gibbs measures of spin glass models on the hypercube can be identified as random probability measures on the unit ball of a Hilbert space. This simple observation follows from a result of Dovbysh and Sudakov on weakly exchangeable random matrices. Limiting Gibbs measures can then be studied as single well-defined objects. This approach naturally extends the space of random overlap structures as defined by Aizenman et al. We discuss the Ruelle probability cascades and the stochastic stability within this framework. As an application, we use an idea of Parisi and Talagrand to prove that if a sequence of finite-volume Gibbs measures satisfies the Ghirlanda-Guerra identities, then the infinite-volume measure must be singular as a measure on a Hilbert space.
Zero-temperature quantum annealing bottlenecks in the spin-glass phase.
Knysh, Sergey
2016-01-01
A promising approach to solving hard binary optimization problems is quantum adiabatic annealing in a transverse magnetic field. An instantaneous ground state-initially a symmetric superposition of all possible assignments of N qubits-is closely tracked as it becomes more and more localized near the global minimum of the classical energy. Regions where the energy gap to excited states is small (for instance at the phase transition) are the algorithm's bottlenecks. Here I show how for large problems the complexity becomes dominated by O(log N) bottlenecks inside the spin-glass phase, where the gap scales as a stretched exponential. For smaller N, only the gap at the critical point is relevant, where it scales polynomially, as long as the phase transition is second order. This phenomenon is demonstrated rigorously for the two-pattern Gaussian Hopfield model. Qualitative comparison with the Sherrington-Kirkpatrick model leads to similar conclusions. PMID:27491338
Enhanced light extraction from UV LEDs using spin-on glass microlenses
NASA Astrophysics Data System (ADS)
Liu, Chi-Min; Su, Guo-Dung J.
2016-05-01
In this paper, we present a cost-effective method for fabricating spin-on glass (SOG) microlens arrays (MLAs) on ultra-violet light-emitting diodes. The SOG MLA is formed using thermal reflow molds and multiple replication processes, which can reduce the cost of the solution process. In this paper, we fabricate SOG MLA of different sizes, where the diameter of each microlens is approximately 50, 100, 150, and 200 μm. In each case, the light extraction efficiency is improved by 21.86%, 14.01%, 10.35%, and 7.31%, respectively. We also discuss the effects of different-shaped SOG microlenses, namely circular, square, and hexagonal. The light extraction efficiency is improved by 7.31%, 9.60%, and 13.80% for the circular, square, and hexagonal SOG MLAs, respectively. By applying an optimized lens pattern, an increase in light extraction efficiency of 21.86% is achieved.
Spin-glass transition in Ni carbide single crystal nanoparticles with Ni3C - type structure
NASA Astrophysics Data System (ADS)
Fujieda, S.; Kuboniwa, T.; Shinoda, K.; Suzuki, S.; Echigoya, J.
2016-05-01
Hexagonal shaped nanoparticles about 60 nm in size were successfully synthesized in tetraethylene glycol solution containing polyvinylpyrrolidone. By the analysis of the electron diffraction pattern, these were identified as a single crystal of Ni carbide with Ni3C - type structure. Their magnetization curve at 5 K was not completely saturated under a magnetic field of 5 T. The thermomagnetization curves after zero-field cooling and after field cooling exhibited the magnetic cooling effect at low temperatures. Furthermore, the 2nd order nonlinear term of AC magnetic susceptibility exhibited a negative divergence at about 17 K. It is concluded that Ni carbide single crystal nanoparticles with the Ni3C - type structure exhibit spin-glass transition at low temperatures.
Zero-temperature quantum annealing bottlenecks in the spin-glass phase
NASA Astrophysics Data System (ADS)
Knysh, Sergey
2016-08-01
A promising approach to solving hard binary optimization problems is quantum adiabatic annealing in a transverse magnetic field. An instantaneous ground state--initially a symmetric superposition of all possible assignments of N qubits--is closely tracked as it becomes more and more localized near the global minimum of the classical energy. Regions where the energy gap to excited states is small (for instance at the phase transition) are the algorithm's bottlenecks. Here I show how for large problems the complexity becomes dominated by O(log N) bottlenecks inside the spin-glass phase, where the gap scales as a stretched exponential. For smaller N, only the gap at the critical point is relevant, where it scales polynomially, as long as the phase transition is second order. This phenomenon is demonstrated rigorously for the two-pattern Gaussian Hopfield model. Qualitative comparison with the Sherrington-Kirkpatrick model leads to similar conclusions.
Zero-temperature quantum annealing bottlenecks in the spin-glass phase
Knysh, Sergey
2016-01-01
A promising approach to solving hard binary optimization problems is quantum adiabatic annealing in a transverse magnetic field. An instantaneous ground state—initially a symmetric superposition of all possible assignments of N qubits—is closely tracked as it becomes more and more localized near the global minimum of the classical energy. Regions where the energy gap to excited states is small (for instance at the phase transition) are the algorithm's bottlenecks. Here I show how for large problems the complexity becomes dominated by O(log N) bottlenecks inside the spin-glass phase, where the gap scales as a stretched exponential. For smaller N, only the gap at the critical point is relevant, where it scales polynomially, as long as the phase transition is second order. This phenomenon is demonstrated rigorously for the two-pattern Gaussian Hopfield model. Qualitative comparison with the Sherrington-Kirkpatrick model leads to similar conclusions. PMID:27491338
Amoruso, C.; Moore, M. A.; Hartmann, A. K.; Hastings, M. B.
2006-12-31
We present numerical evidence that the techniques of conformal field theory might be applicable to two-dimensional Ising spin glasses with Gaussian bond distributions. It is shown that certain domain wall distributions in one geometry can be related to that in a second geometry by a conformal transformation. We also present direct evidence that the domain walls are stochastic Loewner (SLE) processes with {kappa}{approx_equal}2.1. An argument is given that their fractal dimension d{sub f} is related to their interface energy exponent {theta} by d{sub f}-1=3/[4(3+{theta})], which is consistent with the commonly quoted values d{sub f}{approx_equal}1.27 and {theta}{approx_equal}-0.28.
Spin-on-glass coatings for the generation of super-polishedsubstrates for extreme ultraviolet optics
Salmassi, Farhad; Naulleau, Patrick P.; Gullikson, Eric M.
2005-01-01
Substrates intended for use as extreme ultraviolet (EUV) optics have extremely stringent requirements in terms of finish. These requirements can dramatically increase the cost and fabrication time, especially when non-conventional shapes, such as toroids, are required. Here we present a spin-on-glass resist process capable of generating super-polished parts from inexpensive substrates. The method has been used to render diamond-turned substrates compatible for use as EUV optics. Toroidal diamond-turned optics with starting rms roughness in the 3.3 to 3.7 nm range have been smoothed to the 0.4 to 0.6 nm range. EUV reflectometry characterization of these optics has demonstrated reflectivities of approximately 63%.
Fixed-point distributions of short-range Ising spin glasses on hierarchical lattices
NASA Astrophysics Data System (ADS)
Almeida, Sebastião T. O.; Nobre, Fernando D.
2015-03-01
Fixed-point distributions for the couplings of Ising spin glasses with nearest-neighbor interactions on hierarchical lattices are investigated numerically. Hierarchical lattices within the Migdal-Kadanoff family with fractal dimensions in the range 2.58 ≤D ≤7 , as well as a lattice of the Wheatstone-Bridge family with fractal dimension D ≈3.58 are considered. Three initial distributions for the couplings are analyzed, namely, the Gaussian, bimodal, and uniform ones. In all cases, after a few iterations of the renormalization-group procedure, the associated probability distributions approached universal fixed shapes. For hierarchical lattices of the Migdal-Kadanoff family, the fixed-point distributions were well fitted either by stretched exponentials, or by q -Gaussian distributions; both fittings recover the expected Gaussian limit as D →∞ . In the case of the Wheatstone-Bridge lattice, the best fit was found by means of a stretched-exponential distribution.
Spin glass-like behavior, giant magnetocaloric and giant magnetoresistance effect in PrPb manganites
NASA Astrophysics Data System (ADS)
Chau, N.; Hanh, D. T.; Tho, N. D.; Luong, N. H.
2006-08-01
The Pr 1-xPb xMnO 3 ( x=0.1-0.5) perovskites have been fabricated by solid-state reaction. The X-ray diffraction patterns show that the samples are of single phase with orthorhombic structure. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic curves measured at low field and low temperatures exhibit the spin glass-like state. The Curie temperature of samples increased with increase in Pb content. The maximum magnetic entropy change |Δ Sm| max reaches the giant values of 3.91 and 3.68 J/kg K for quite low magnetic field change of 1.35 T for the samples x=0.1 and 0.4, respectively. The resistance measurements show that there is insulator-metal phase transition on the R( T) curves for samples with x⩾0.3. The giant magnetoresistance effect is also observed for all samples studied.
Saturation of Ruderman-Kittel-Kasuya-Yosida interaction damping in high-resistivity spin glasses
NASA Astrophysics Data System (ADS)
Larsen, Ulf
1986-04-01
Saturation of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction damping at large resistivity or short mean free path in metallic alloys, as predicted in the Kaneyoshi model, is shown to account for the recently observed spin-glass freezing temperature, T0, in such systems as AuFe quench-condensed films and ternary XYcZx alloys, where X=Au,Ag,..., is a nonmagnetic metal host, Y=Fe,Mn,..., is the dilute magnetic species of concentration c, and Z=Cu,...,Ti,Sb,..., is a nonmagnetic impurity of concentration x. Some deeper aspects of the c dependence of the characteristic RKKY interaction energy scale are discussed, with emphasis on the necessary distinction between quenched and ergodic situations in the randomly dilute alloys. A consequent logarithmic correction to the c-scaling laws (at the marginal dimensionalities d=p=3, where d is the electronic dimension of RKKY interaction varying as R-d, and p is the space dimension of the magnetic structure), in the form of T0~c(-0.577-lnc)1/2, is shown to be due to broken dilatation invariance, by finite atomic size. The finite mean free path in real systems also breaks this invariance by providing a length scale. However, at the damping saturation limit a pseudo-c-scaling T0~c reappears, as was found in the amorphous spin-glass LaAuGd. This, and related predictions of the ``typical environment'' approach to the quenched-random-averaging problem agree remarkably well with the new data that have recently become available.
NASA Astrophysics Data System (ADS)
Lai, Pik-Yin
Methods of statistical mechanics are applied to two important NP-complete combinatorial optimization problems. The first is the chromatic number problem which seeks the minimal number of colors necessary to color a graph such that no two sites connected by an edge have the same color. The second is partitioning of a graph into q equal subgraphs so as to minimize inter-subgraph connections. Both models are mapped into a frustrated Potts model which is related to the q-state Potts spin glass. For the first problem, we obtain very good agreement with numerical simulations and theoretical bounds using the annealed approximation. The quenched model is also discussed. For the second problem we obtain analytic and numerical results by evaluating the ground state energy of the q = 3 and 4 Potts spin glass using Parisi's replica symmetry breaking. We also performed some numerical simulations to test the theoretical result and obtained very good agreement. In the second part of the thesis, we simulate the Ising spin-glass model on a random lattice with a finite (average) coordination number and also on the Bethe lattice with various different boundary conditions. In particular, we calculate the overlap function P(q) for two independent samples. For the random lattice, the results are consistent with a spin-glass transition above which P(q) converges to a Dirac delta -function for large N (number of sites) and below which P(q) has in addition a long tail similar to previous results obtained for the infinite ranged model. For the Bethe lattice, we obtain results in the interior by discarding the two outer shells of the Cayley tree when calculating the thermal averages. For fixed (uncorrelated) boundary conditions, P(q) seems to converge to a delta -function even below the spin-glass transition whereas for a "closed" lattice (correlated boundary conditions) P(q) has a long tail similar to its behavior in the random lattice case.
Real beards and real networks: a spin-glass model for interacting individuals
NASA Astrophysics Data System (ADS)
O'Neale, Dion
''I want to be different, just like all the other different people'' sang the band King Missile. Whether they are the Beatniks of the 1950s, the punks of the 1970s, or the hipsters of today, non-conformists often tend to look the same, seemingly at odds with their goal of non-conformity. The spin-glass model, originally developed to describe the interaction of magnetic spins, and since applied to situations as diverse as the electrical activity of networks of neurons, to trades on a financial market, has recently been used in social science to study populations of interacting individuals comprised of a mix of both conformists and anti-conformists - or hipsters. Including delay effects for the interactions between individuals has been shown to give a system with non-trivial dynamics with a phase transition from stable behaviour to periodic switching between two states (let's call them bushy bearded and clean shaven). Analytic solutions to such a model are possible, but only for particular assumptions about the interaction and delay matrices. In this work we will show what happens when the interactions in the model are based on real-world networks with ''small-world'' effects and clustering.
Seeking Quantum Speedup Through Spin Glasses: The Good, the Bad, and the Ugly*
NASA Astrophysics Data System (ADS)
Katzgraber, Helmut G.; Hamze, Firas; Zhu, Zheng; Ochoa, Andrew J.; Munoz-Bauza, H.
2015-07-01
There has been considerable progress in the design and construction of quantum annealing devices. However, a conclusive detection of quantum speedup over traditional silicon-based machines remains elusive, despite multiple careful studies. In this work we outline strategies to design hard tunable benchmark instances based on insights from the study of spin glasses—the archetypal random benchmark problem for novel algorithms and optimization devices. We propose to complement head-to-head scaling studies that compare quantum annealing machines to state-of-the-art classical codes with an approach that compares the performance of different algorithms and/or computing architectures on different classes of computationally hard tunable spin-glass instances. The advantage of such an approach lies in having to compare only the performance hit felt by a given algorithm and/or architecture when the instance complexity is increased. Furthermore, we propose a methodology that might not directly translate into the detection of quantum speedup but might elucidate whether quantum annealing has a "quantum advantage" over corresponding classical algorithms, such as simulated annealing. Our results on a 496-qubit D-Wave Two quantum annealing device are compared to recently used state-of-the-art thermal simulated annealing codes.
Characterization of nano-sized iron particle layers spin coated on glass substrate
NASA Astrophysics Data System (ADS)
Dehipawala, Sunil; Samarasekara, Pubudu; Dahanayake, Rasika; Tremberger, George; Cheung, Tak D.; Gafney, Harry D.
2015-08-01
Nanometer scale iron particles have a variety of technological applications. They are vastly utilized in optical and microwave devices. Thin films with varying compositions of iron (III) nitrate and ethylene glycol were deposited on glass substrate using a spin coating technique. The thicknesses of the films were controlled by the spin rate. Precursor films on the substrate were then annealed to different temperatures ranging from 200°C to 600°C for 1-3 hours in air. The microstructures of iron particles in films prepared under different conditions were investigated using X-ray Absorption spectroscopy and Mossbauer spectroscopy. The main absorption edge peak position and pre-edge energy position were identical in samples with different numbers of layers, but prepared under similar conditions. This indicates that there was no change in the charge state of the iron regardless of the number of layers. However the intensity of the pre-edge feature decreases as the number of layers increases, which shows a decrease of Fe-O compounds as the number of layers increases. Mossbauer spectrum of these iron particles contains only quadrupole doublets. The absence of six-linespectrum confirms the nano-size nature of the particles.
Magnetic anisotropy and spin-glass behavior in single crystalline U2PdSi3
NASA Astrophysics Data System (ADS)
Li, D. X.; Kimura, A.; Haga, Y.; Nimori, S.; Shikama, T.
2011-02-01
We present the magnetic and transport properties of single crystalline U2PdSi3 measured with the magnetic field (H) (or measuring current, I) applied along two typical crystallographic directions, i.e. H\\perp c -axis and H\\parallel c -axis (or I\\perp c -axis and I\\parallel c -axis). For both directions, a spin-glass state is confirmed to form at low temperature with the same spin freezing temperature Tf (= 11.5 K), initial frequency shift δTf (= 0.023) and activation energy Ea/kB (= 90.15 K) in zero dc field. Strong anisotropy in magnetic and transport behavior is found to be a significant feature of U2PdSi3. The unusual ferromagnetic-like anomaly in ac susceptibility and dc magnetization curves around Tm = 71 K is observed in the case of H\\parallel c -axis but not in the cases of H \\perp c -axis. The characteristic temperature Tir, below which evident irreversible magnetism originated from random spin freezing can be observed, shows much stronger field dependence for H \\perp c -axis than for H\\parallel c -axis. Moreover, an unusual finding is that the electrical resistivity measurements indicate the formation of magnetic Brillouin-zone boundary gaps and much larger magnetic scattering for I \\perp c -axis, while the coherent-Kondo-effect-like behavior is obvious for I\\parallel c -axis. We also emphasize that no resistivity minimum can be detected down to 2.5 K for either direction. The observed magnetic and transport behaviors are compared with those in polycrystalline U2PdSi3 and other 2:1:3 intermetallic compounds.
Microwave Reentrant Cavities for Quantum Devices
NASA Astrophysics Data System (ADS)
Carvalho, Natalia C.; Bourhill, Jeremy; Creedon, Daniel; Goryachev, Maxim; Galliou, Serge; Tobar, Michael
A microwave reentrant cavity is a device able to provide a very sensitive high-Q microwave mode. Its design can be highly advantageous for electromechanical devices and quantum measurements. In this sense, a tuneable device based on a narrow-gap superconducting reentrant cavity is under development. The resonant frequency is able to be fine-tuned over a range larger than 500 MHz at 10 mK with an electrical Q-factor of 105. Such a cavity could possibly accommodate a transmon qubit to control and manipulate its quantum state. We are also working on the investigation of bulk acoustic wave (BAW) resonators in microwave reentrant cavities. BAW resonators offer a promising way to process quantum information through the coupling between microwaves and acoustic phonons. Thus, we are developing a device able to excite phonons through non-linearities and the piezoelectricity of the plano-convex quartz crystal. We will detail our experiments that work towards cooling gram scale phonon resonances to the quantum ground state. Funded by ARC Grant No. CE110001013 (Australia) and National Counsel of Technological and Scientific Development (Brazil).
Zero-point entropy of the spinel spin glasses CuGa2O4 and CuAl2O4
NASA Astrophysics Data System (ADS)
Fenner, L. A.; Wills, A. S.; Bramwell, S. T.; Dahlberg, M.; Schiffer, P.
2009-01-01
The zero-point entropy of a spin glass is a difficult property to experimentally determine and interpret. Spin glass theory provides various predictions, including unphysical ones, for the value of the zero-point entropy, however experimental results have been lacking. We have investigated the magnetic properties and zero-point entropy of two spinel Cu2+ based spin glasses, CuGa2O4 and CuAl2O4. Dc- and ac-susceptibility and specific heat measurements show many characteristic spin glass features for both materials. The spin glass freezing temperature is determined to be Tf = 2.89 ± 0.05 K for CuGa2O4 and Tf = 2.30 ± 0.05 K for CuAl2O4. By integrating the specific heat data we have found that CuGa2O4 and CuAl2O4 have zero-point entropies of S0 = 4.96 JK-1mol-1 and S0 = 4.76 JK-1mol-1 respectively. These values are closest to the prediction for a Sherrington-Kirkpatrick XY spin glass, however they are notably higher than all of the theoretical predictions. This indicates that CuGa2O4 and CuAl2O4 have a greater degeneracy in their ground states than any of the spin glass models.
Spin-Glass Behavior in a Giant Unit Cell Compound Tb117Fe52Ge113.8(1)
Liu, Jing; Xie, Weiwei; Gschneidner, Karl A; Miller, Gordon J; Pecharsky, Vitalij K
2014-10-15
In this paper we demonstrate evidence of a cluster spin glass in Tb117Fe52Ge113.8(1) (a compound with a giant cubic unit cell) via ac and dc magnetic susceptibility, magnetization, magnetic relaxation and heat capacity measurements. The results clearly show that Tb117Fe52Ge113.8(1) undergoes a spin glass phase transition at the freezing temperature, ~38 K. The good fit of the frequency dependence of the freezing temperature to the critical slowing down model and Vogel-Fulcher law strongly suggest the formation of cluster glass in the Tb117Fe52Ge113.8(1) system. The heat capacity data exhibit no evidence for long-range magnetic order, and yield a large value of Sommerfeld coefficient. The spin glass behavior of Tb117Fe52Ge113.8(1) may be understood by assuming the presence of competing interactions among multiple non-equivalent Tb sites present in the highly complex unit cell.
Baltz, V.
2013-02-11
Controlling ferromagnetic/antiferromagnetic blocking temperatures in exchange biased based devices appears crucial for applications. The blocking temperature is ascribed to the ability of both antiferromagnetic grains and interfacial spin-glass-like phases to withstand ferromagnetic magnetization reversal. To better understand the respective contributions of grains versus spin-glass, blocking temperature distributions were measured after various thermal treatments for cobalt/iridium-manganese bilayers. The high-temperature contribution linked to antiferromagnetic grains shifts towards lower temperatures above a threshold thermal annealing. In contrast, the occurrence and evolution of training effects for the low-temperature contribution only agree with its inferred interfacial spin-glass-like origin.
Sustained phase separation and spin glass in Co-doped KxFe2-ySe2 single crystals
Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.
2015-11-19
We describe Co substitution effects in KxFe2-y-zCozSe2 (0.06 ≤ z ≤ 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K2Fe4Se5 and superconducting/metallic KxFe2Se2 is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell, arrangement and connectivity of stripemore » conducting phase.« less
Short-range Ising spin glasses: the metastate interpretation of replica symmetry breaking.
Read, N
2014-09-01
Parisi's formal replica-symmetry-breaking (RSB) scheme for mean-field spin glasses has long been interpreted in terms of many pure states organized ultrametrically. However, the early version of this interpretation, as applied to the short-range Edwards-Anderson model, runs into problems because as shown by Newman and Stein (NS) it does not allow for chaotic size dependence, and predicts non-self-averaging that cannot occur. NS proposed the concept of the metastate (a probability distribution over infinite-size Gibbs states in a given sample that captures the effects of chaotic size dependence) and a nonstandard interpretation of the RSB results in which the metastate is nontrivial and is responsible for what was called non-self-averaging. In this picture, each state drawn from the metastate has the ultrametric properties of the old theory, but when the state is averaged using the metastate, the resulting mixed state has little structure. This picture was constructed so as to agree both with the earlier RSB results and with rigorous results. Here we use the effective field theory of RSB, in conjunction with the rigorous definitions of pure states and the metastate in infinite-size systems, to show that the nonstandard picture follows directly from the RSB mean-field theory. In addition, the metastate-averaged state possesses power-law correlations throughout the low-temperature phase; the corresponding exponent ζ takes the value 4 according to the field theory in high dimensions d, and describes the effective fractal dimension of clusters of spins. Further, the logarithm of the number of pure states in the decomposition of the metastate-averaged state that can be distinguished if only correlations in a window of size W can be observed is of order W(d-ζ). These results extend the nonstandard picture quantitatively; we show that arguments against this scenario are inconclusive. More generally, in terms of Parisi's function q(x), if q(0)≠∫(0)(1)dxq(x), then the
NASA Astrophysics Data System (ADS)
Morais, C. V.; Zimmer, F. M.; Lazo, M. J.; Magalhães, S. G.; Nobre, F. D.
2016-06-01
The behavior of the nonlinear susceptibility χ3 and its relation to the spin-glass transition temperature Tf in the presence of random fields are investigated. To accomplish this task, the Sherrington-Kirkpatrick model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure. In addition, the dependence of the Almeida-Thouless eigenvalue λAT (replicon) on the random fields is analyzed. Particularly, in the absence of random fields, the temperature Tf can be traced by a divergence in the spin-glass susceptibility χSG, which presents a term inversely proportional to the replicon λAT. As a result of a relation between χSG and χ3, the latter also presents a divergence at Tf, which comes as a direct consequence of λAT=0 at Tf. However, our results show that, in the presence of random fields, χ3 presents a rounded maximum at a temperature T* which does not coincide with the spin-glass transition temperature Tf (i.e., T*>Tf for a given applied random field). Thus, the maximum value of χ3 at T* reflects the effects of the random fields in the paramagnetic phase instead of the nontrivial ergodicity breaking associated with the spin-glass phase transition. It is also shown that χ3 still maintains a dependence on the replicon λAT, although in a more complicated way as compared with the case without random fields. These results are discussed in view of recent observations in the LiHoxY1 -xF4 compound.
Doping of ZnO nanowires using phosphorus diffusion from a spin-on doped glass source
Bocheux, A.; Robin, I. C.; Bonaimé, J.; Hyot, B.; Feuillet, G.; Kolobov, A. V.; Fons, P.; Mitrofanov, K. V.; Tominaga, J.; Tamenori, Y.
2014-05-21
In this article, we report on ZnO nanowires that were phosphorus doped using a spin on dopant glass deposition and diffusion method. Photoluminescence measurements suggest that this process yields p-doped ZnO. The spatial location of P atoms was studied using x-ray near-edge absorption structure spectroscopy and it is concluded that the doping is amphoteric with P atoms located on both Zn and O sites.
Doping of ZnO nanowires using phosphorus diffusion from a spin-on doped glass source
NASA Astrophysics Data System (ADS)
Bocheux, A.; Robin, I. C.; Bonaimé, J.; Hyot, B.; Kolobov, A. V.; Mitrofanov, K. V.; Fons, P.; Tominaga, J.; Tamenori, Y.; Feuillet, G.
2014-05-01
In this article, we report on ZnO nanowires that were phosphorus doped using a spin on dopant glass deposition and diffusion method. Photoluminescence measurements suggest that this process yields p-doped ZnO. The spatial location of P atoms was studied using x-ray near-edge absorption structure spectroscopy and it is concluded that the doping is amphoteric with P atoms located on both Zn and O sites.
Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics.
Turner, Robert M; Jack, Robert L; Garrahan, Juan P
2015-08-01
We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyze the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occurring at a coupling ɛ*(T), which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays "space-time" transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field sc(T)≳0 that appears to vanish at zero temperature in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions, we introduce the square pyramid model, which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states. PMID:26382352
Exact Solution of the Gauge Symmetric p-Spin Glass Model on a Complete Graph
NASA Astrophysics Data System (ADS)
Korada, Satish Babu; Macris, Nicolas
2009-07-01
We consider a gauge symmetric version of the p-spin glass model on a complete graph. The gauge symmetry guarantees the absence of replica symmetry breaking and allows to fully use the interpolation scheme of Guerra (Fields Inst. Commun. 30:161, 2001) to rigorously compute the free energy. In the case of pairwise interactions ( p=2), where we have a gauge symmetric version of the Sherrington-Kirkpatrick model, we get the free energy and magnetization for all values of external parameters. Our analysis also works for even p≥4 except in a range of parameters surrounding the phase transition line, and for odd p≥3 in a more restricted region. We also obtain concentration estimates for the magnetization and overlap parameter that play a crucial role in the proofs for odd p and justify the absence of replica symmetry breaking. Our initial motivation for considering this model came from problems related to communication over a noisy channel, and is briefly explained.
On one-step replica symmetry breaking in the Edwards–Anderson spin glass model
NASA Astrophysics Data System (ADS)
Del Ferraro, Gino; Wang, Chuang; Zhou, Hai-Jun; Aurell, Erik
2016-07-01
We consider a one-step replica symmetry breaking description of the Edwards–Anderson spin glass model in 2D. The ingredients of this description are a Kikuchi approximation to the free energy and a second-level statistical model built on the extremal points of the Kikuchi approximation, which are also fixed points of a generalized belief propagation (GBP) scheme. We show that a generalized free energy can be constructed where these extremal points are exponentially weighted by their Kikuchi free energy and a Parisi parameter y, and that the Kikuchi approximation of this generalized free energy leads to second-level, one-step replica symmetry breaking (1RSB), GBP equations. We then proceed analogously to the Bethe approximation case for tree-like graphs, where it has been shown that 1RSB belief propagation equations admit a survey propagation solution. We discuss when and how the one-step-replica symmetry breaking GBP equations that we obtain also allow a simpler class of solutions which can be interpreted as a class of generalized survey propagation equations for the single instance graph case.
Spin glass behavior in the weberite related structure Dy3-xYxTaO7
NASA Astrophysics Data System (ADS)
Gomez Garcia, Jose; Tavizon, Gustavo; Duran, Alejandro; Escudero, Roberto
2013-03-01
Crystalline structures with tetrahedral arrangement of magnetic cations are susceptible to present non-collinear magnetism. Dy3TaO7 with weberite-type crystal structure has this arrangement and could display non-conventional magnetic coupling. Previous magnetic studies on Dy3TaO7 have characterized this as an antiferromagnetic system with TN of about 3 K. In this work magnetic properties of polycrystalline samples of the Dy3-xYxTaO7, with weberite structure are presented. X-Ray diffraction of our samples are single phase in all range of compositions. Magnetic properties measured from 2 - 300 K shown a typical Curie-Weiss behavior with the Dy3+ effective magnetic moment about 10.35 μB. The compositions x =0.66, 0.33, and 0.0 display a maximum in the susceptibility vs. temperature at 2.3, 2.7, and 3 K respectively. This behavior has been previously assigned to an antiferromagnetic transition; however our AC magnetic measurements as a function of frequency indicate a spin glass behavior. Since magnetic cations have tetrahedral arrangement for x =0, a magnetic frustrated state is anticipated for this composition.
PREFACE: ELC International Meeting on Inference, Computation, and Spin Glasses (ICSG2013)
NASA Astrophysics Data System (ADS)
Kabashima, Yoshiyuki; Hukushima, Koji; Inoue, Jun-ichi; Tanaka, Toshiyuki; Watanabe, Osamu
2013-12-01
The close relationship between probability-based inference and statistical mechanics of disordered systems has been noted for some time. This relationship has provided researchers with a theoretical foundation in various fields of information processing for analytical performance evaluation and construction of efficient algorithms based on message-passing or Monte Carlo sampling schemes. The ELC International Meeting on 'Inference, Computation, and Spin Glasses (ICSG2013)', was held in Sapporo 28-30 July 2013. The meeting was organized as a satellite meeting of STATPHYS25 in order to offer a forum where concerned researchers can assemble and exchange information on the latest results and newly established methodologies, and discuss future directions of the interdisciplinary studies between statistical mechanics and information sciences. Financial support from Grant-in-Aid for Scientific Research on Innovative Areas, MEXT, Japan 'Exploring the Limits of Computation (ELC)' is gratefully acknowledged. We are pleased to publish 23 papers contributed by invited speakers of ICSG2013 in this volume of Journal of Physics: Conference Series. We hope that this volume will promote further development of this highly vigorous interdisciplinary field between statistical mechanics and information/computer science. Editors and ICSG2013 Organizing Committee: Koji Hukushima Jun-ichi Inoue (Local Chair of ICSG2013) Yoshiyuki Kabashima (Editor-in-Chief) Toshiyuki Tanaka Osamu Watanabe (General Chair of ICSG2013)
Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics
NASA Astrophysics Data System (ADS)
Turner, Robert M.; Jack, Robert L.; Garrahan, Juan P.
2015-08-01
We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyze the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occurring at a coupling ɛ*(T ) , which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays "space-time" transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field sc(T ) ≳0 that appears to vanish at zero temperature in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions, we introduce the square pyramid model, which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states.
Properties of the multicritical point of ±J Ising spin glasses on the square lattice
NASA Astrophysics Data System (ADS)
Lessa, Jean C.; de Queiroz, S. L. A.
2006-10-01
We use numerical transfer-matrix methods to investigate properties of the multicritical point of binary Ising spin glasses on a square lattice, whose location we assume to be given exactly by a conjecture advanced by Nishimori and Nemoto. We calculate the two largest Lyapunov exponents, as well as linear and nonlinear zero-field uniform susceptibilities, on strip of widths 4⩽L⩽16 sites, from which we estimate the conformal anomaly c , the decay-of-correlations exponent η , and the linear and nonlinear susceptibility exponents γ/ν and γnl/ν , with the help of finite-size scaling and conformal invariance concepts. Our results are c=0.46(1) ; 0.187≲η≲0.196 ; γ/ν=1.797(5) ; γnl/ν=5.59(2) . A direct evaluation of correlation functions on the strip geometry, and of the statistics of the zeroth moment of the associated probability distribution, gives η=0.194(1) , consistent with the calculation via Lyapunov exponents. Overall, these values tend to be inconsistent with the universality class of percolation, though by small amounts. The scaling relation γnl/ν=2γ/ν+d (with space dimensionality d=2 ) is obeyed to rather good accuracy, thus showing no evidence of multiscaling behavior of the susceptibilities.
Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers
Rui, W. B.; Hu, Y.; Du, A.; You, B.; Xiao, M. W.; Zhang, W.; Zhou, S. M.; Du, J.
2015-01-01
We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1 − x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1 − x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE ∼ T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties. PMID:26348277
Implosion of indirectly driven reentrant cone shell target
R.B. Stephens; S.P. Hatchett; R.E. Turner; K.A. Tanaka; R. Kodama
2003-10-31
In an x-ray driven reentrant cone fast ignition target the x-ray spectrum contains a high energy component that casuses preheating of the reentrant cone and mixing of the gold into the collapsing shell. Direct laser drive might avoid this problem.
Spin glass behavior in the Dy3-xYxTaO7 (0≤x≤1) system
NASA Astrophysics Data System (ADS)
Gomez-Garcia, J. Francisco; Escudero, Roberto; Tavizon, Gustavo
2014-09-01
Several x-compositions of the polycrystalline Dy3-xYxTaO7 system, crystallizing in the weberite-type structure, were synthesized and structurally characterized using Rietveld refinements based on X-ray diffraction data. In previous magnetic characterization of Dy3TaO7 (x=0), with the same crystal structure, an antiferromagnetic transition at T=2.3 K has been assigned to this compound. On the basis of DC and AC magnetic susceptibilities analyses, we show in this work that all compounds in the range of 0≤x≤1.0 exhibit a spin glass behavior. The nature of the spin glass behavior in Dy3-xYxTaO7, can be attributed to the highly frustrated antiferromagnetic interaction of the Dy3+ sublattice and to the Dy3+-Dy3+ distorted tetrahedra array in the weberite-type structure of this system. By fitting AC susceptibility data, using dynamical scaling theory equations, we conclude that a cluster spin glass is present in Dy3-xYxTaO7 in the low temperature range. Depending on the x-composition, Tg~2.2-3.2 K. In the range 15-300 K the system obeys a Curie-Weiss magnetic behavior.
Reentrant Phase Coherence in Superconducting Nanowire Composites.
Ansermet, Diane; Petrović, Alexander P; He, Shikun; Chernyshov, Dmitri; Hoesch, Moritz; Salloum, Diala; Gougeon, Patrick; Potel, Michel; Boeri, Lilia; Andersen, Ole Krogh; Panagopoulos, Christos
2016-01-26
The short coherence lengths characteristic of low-dimensional superconductors are associated with usefully high critical fields or temperatures. Unfortunately, such materials are often sensitive to disorder and suffer from phase fluctuations in the superconducting order parameter which diverge with temperature T, magnetic field H, or current I. We propose an approach to overcome synthesis and fluctuation problems: building superconductors from inhomogeneous composites of nanofilaments. Macroscopic crystals of quasi-one-dimensional Na2-δMo6Se6 featuring Na vacancy disorder (δ ≈ 0.2) are shown to behave as percolative networks of superconducting nanowires. Long-range order is established via transverse coupling between individual one-dimensional filaments, yet phase coherence remains unstable to fluctuations and localization in the zero (T,H,I) limit. However, a region of reentrant phase coherence develops upon raising (T,H,I). We attribute this phenomenon to an enhancement of the transverse coupling due to electron delocalization. Our observations of reentrant phase coherence coincide with a peak in the Josephson energy EJ at nonzero (T,H,I), which we estimate using a simple analytical model for a disordered anisotropic superconductor. Na2-δMo6Se6 is therefore a blueprint for a future generation of nanofilamentary superconductors with inbuilt resilience to phase fluctuations at elevated (T,H,I). PMID:26727335
NASA Astrophysics Data System (ADS)
Mamiya, H.; Tsujii, N.; Terada, N.; Nimori, S.; Kitazawa, H.; Hoshikawa, A.; Ishigaki, T.
2014-07-01
To clarify the universal features of spin glasses, we carefully studied slow dynamics in a geometrically frustrated magnet ZnFe2O4 with slight disorders, regarded as an "unconventional" Heisenberg spin glass, using time-resolved neutron diffractometry and magnetometry. The results indicate that "aging" can be attributed not to growth of the short-range order detected by a diffuse scattering but to aging of a hidden aperiodic correlation, as expected from theories for spin glasses. Concerning aging, peculiar behavior was found; the decay of thermoremanent magnetization is extremely accelerated if the sample is heated/cooled briefly midway through the isothermal slow relaxation. Conversely, magnetization surprisingly increases despite the absence of a magnetic field when the temperature returns after the brief heating/cooling. The behavior can be explained as a destabilization of the aged spin configuration due to the thermal perturbations and subsequent spontaneous restoration of the original spin configuration after the destabilization. Whereas such destabilization and restoration do not occur during freezing into numerous metastable states in a fixed energy landscape, these are possible in an energy landscape with a temperature-sensitive funnel-like structure. These features, consistent with the ghost domain scenario of the droplet picture, are the same as for conventional Heisenberg spin glasses such as dilute magnetic alloys and dilute magnetic semiconductors. In other words, they are universal features in Heisenberg spin glasses including unconventional ones.
Asymmetric electroresistance of cluster glass state in manganites
Lourembam, James; Lin, Weinan; Ding, Junfeng; Bera, Ashok; Wu, Tom
2014-03-31
We report the electrostatic modulation of transport in strained Pr{sub 0.65}(Ca{sub 0.75}Sr{sub 0.25}){sub 0.35}MnO{sub 3} thin films grown on SrTiO{sub 3} by gating with ionic liquid in electric double layer transistors (EDLT). In such manganite films with strong phase separation, a cluster glass magnetic state emerges at low temperatures with a spin freezing temperature of about 99 K, which is accompanied by the reentrant insulating state with high resistance below 30 K. In the EDLT, we observe bipolar and asymmetric modulation of the channel resistance, as well as an enhanced electroresistance up to 200% at positive gate bias. Our results provide insights on the carrier-density-dependent correlated electron physics of cluster glass systems.
Nature of the spin-glass phase in models with long-range interactions
NASA Astrophysics Data System (ADS)
Wittmann, Matthew C.
Despite decades of effort, our understanding of low-temperature phase of spin glass models with short-range interactions remains incomplete. Replica symmetry breaking (RSB) theory, based on the solution of the Sherrington-Kirkpatrick mean-field model, predicts many pure states; meanwhile, competing theories of short-range systems, such as the droplet picture, predict a single pair of pure states related by time-reversal symmetry, analogously to the ferromagnet. Since RSB certainly holds for the mean-field (infinite-range) model, it is interesting to study short-range models in high dimensions to observe whether RSB also holds here; however, computer simulations of short-range models in high dimensions are difficult because the number of spins to equilibrate grows so rapidly with the linear size of the system. A relatively recent idea which has been fruitful is to instead study one-dimensional models with long-range (power-law) interactions, which are argued to have the same critical behavior as corresponding short-range models in high dimensions, but for which simulations for a range of sizes (crucial for finite-size scaling analysis) are feasible. For these one-dimensional long-range (1DLR) models, we fill in a previously unexplored region of parameter space where the interactions become sufficiently long-range that they must be rescaled with the system size to maintain the thermodynamic limit. We find strong evidence that detailed behavior of the 1DLR models everywhere in this "nonextensive regime" is identical to that of the Sherrington-Kirkpatrick model, lending support to a recent conjecture. In an attempt to distinguish the RSB and droplet pictures, we study recently-proposed observables based on the statistics of individual disorder samples, rather than simply averaging over the disorder as is most frequently done in previous studies. We compare Monte Carlo results for 1DLR models which are proxies for short-range models in 3, 4, and 10 dimensions with
Molecular Dynamics in a Liquid Crystal with Reentrant Mesophases
NASA Astrophysics Data System (ADS)
Sebastião, P. J.; Ribeiro, A. C.; Nguyen, H. T.; Noack, F.
1995-11-01
It is well known that liquid crystalline compounds with a cyano terminal group can present peculiar polymorphisms in particular different types of smectic A mesophases and a reentrant behaviour for both nematic and smectic A mesophases. In this work we study by proton NMR relaxation the influence of these features on the molecular dynamics of the compound 4-cyanobenzoate-4'-octylbenzoyloxyphenyl (DB8CN Sym) in its nematic (N), partial bilayer smectic A (SAd), reentrant nematic (Nre) and reentrant smectic A (SA1) mesophases. Standard and fast field-cycling techniques were used for our spin-lattice relaxation's study over a broad frequency range of 6 decades (200 Hz up to 300 MHz). It was found that the molecular dynamics in the nematic mesophases is rather different from the molecular dynamics in the smectic A mesophases. However, the reentrant aspect present in both nematic and smectic A states is not associated to a major difference on the molecular dynamics of the nematic and reentrant nematic or smectic and reentrant smectic A mesophases. Order director fluctuations and rotations/reorientations are the most important relaxation mechanisms in the nematic mesophases in the lower and higher frequency limits, respectively, while self-diffusion has a very small contribution to the overall relaxation. As for the smectic A mesophases, self-diffusion and rotations/reorientations are the predominant relaxation mechanisms for frequencies above 20 kHz. The collective motions, which for these mesophases have to be associated with layer undulations with the frequency law T_1sim ν, are only important to the spin-lattice relaxation on the low part of the frequency spectrum (ν<10 kHz). The inclusion in the relaxation study of a contribution from the cross-relaxation between protons and nitrogen nuclei improves the quality of the 1/T_1 data fits in both kinds of mesophases. The combined study of the molecular dynamics in the N, SAd, Nre and SA1 mesophases of DB8CN Sym reveals
Spin-glass model predicts metastable brain states that diminish in anesthesia
Hudetz, Anthony G.; Humphries, Colin J.; Binder, Jeffrey R.
2014-01-01
Patterns of resting state connectivity change dynamically and may represent modes of cognitive information processing. The diversity of connectivity patterns (global brain states) reflects the information capacity of the brain and determines the state of consciousness. In this work, computer simulation was used to explore the repertoire of global brain states as a function of cortical activation level. We implemented a modified spin glass model to describe UP/DOWN state transitions of neuronal populations at a mesoscopic scale based on resting state BOLD fMRI data. Resting state fMRI was recorded in 20 participants and mapped to 10,000 cortical regions (sites) defined on a group-aligned cortical surface map. Each site represented the population activity of a ~20 mm2 area of the cortex. Cross-correlation matrices of the mapped BOLD time courses of the set of sites were calculated and averaged across subjects. In the model, each cortical site was allowed to interact with the 16 other sites that had the highest pair-wise correlation values. All sites stochastically transitioned between UP and DOWN states under the net influence of their 16 pairs. The probability of local state transitions was controlled by a single parameter T corresponding to the level of global cortical activation. To estimate the number of distinct global states, first we ran 10,000 simulations at T = 0. Simulations were started from random configurations that converged to one of several distinct patterns. Using hierarchical clustering, at 99% similarity, close to 300 distinct states were found. At intermediate T, metastable state configurations were formed suggesting critical behavior with a sharp increase in the number of metastable states at an optimal T. Both reduced activation (anesthesia, sleep) and increased activation (hyper-activation) moved the system away from equilibrium, presumably incompatible with conscious mentation. During equilibrium, the diversity of large-scale brain states was
Response to a field of the D = 3 Ising spin glass with Janus and JanusII dedicated computers
NASA Astrophysics Data System (ADS)
Seoane, Beatriz; Janus Collaboration Collaboration
Using the Janus dedicated computer, and its new generation JanusII, we study the linear response to a field of the Edwards-Anderson model for times that cover twelve orders of magnitude. The fluctuation-dissipation relations are investigated for several values of tw. We observe that the violations of the fluctuation-dissipation theorem can be directly related to the P (q) measured in equilibrium at finite sizes, although a simple statics-dynamics dictionary L <--> ξ (tw) is not enough to account for the behavior at large times. We show that the equivalence can be easily restored by taking into account the growth of ξ (t +tw) . Interestingly, experimental measurements of the spin glass correlation length rely precisely on the response of a spin glass to a field, although a direct relation between the measured object and the real ξ has never been established. In this work, we mimic the experimental protocol with Janus data, which lets us relate the experimental ξ with the length extracted from the spatial correlation function. These results allow us for the first time to make a quantitative comparison between experiments and simulations, finding a surprising good agreement with measurements in superspin glasses. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 654971, the ERC grant CRIPHERASY (no. 247328) and from the MINECO(Spain) (No. FIS2012-35719-C02).
Yamahara, H.; Seki, M.; Adachi, M.; Takahashi, M.; Nasu, H.; Tabata, H.; Horiba, K.; Kumigashira, H.
2015-08-14
Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe{sub 3−x}Ti{sub x}O{sub 4} thin films have been obtained on spinel MgAl{sub 2}O{sub 4} substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films (x = 0.8) show p-type conduction, while Ti-poor films (x = 0.6–0.75) show n-type conduction. The systematic Fe(III) reduction to Fe(II) followed by Ti(IV) substitution in the octahedral sublattice is confirmed by the X-ray absorption spectra. All of the Fe{sub 3−x}Ti{sub x}O{sub 4} films (x = 0.6–0.8) exhibit ferrimagnetism above room temperature. Next, the spin-glass behaviors of Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film are studied, since this magnetically diluted system is expected to exhibit the spin-glass behaviors. The DC magnetization and AC susceptibility measurements for the Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film reveal the presence of the spin glass phase. Thermal- and magnetic-field-history memory effects are observed and are attributed to the long time-decay nature of remanent magnetization. The detailed analysis of the time-dependent thermoremanent magnetization reveals the presence of the cluster spin glass state.
NASA Astrophysics Data System (ADS)
Yllanes, David
2013-03-01
Spin glasses are a longstanding model for the sluggish dynamics that appears at the glass transition. They enjoy a privileged status in this context, as they provide the simplest model system both for theoretical and experimental studies of glassy dynamics. However, in spite of forty years of intensive investigation, spin glasses still pose a formidable challenge to theoretical, computational and experimental physics. The main difficulty lies in their incredibly slow dynamics. A recent breakthrough has been made possible by our custom-built computer, Janus, designed and built in a collaboration formed by five universities in Spain and Italy. By employing a purpose-driven architecture, capable of fully exploiting the parallelization possibilities intrinsic to these simulations, Janus outperforms conventional computers by several orders of magnitude. After a brief introduction to spin glasses, the talk will focus on the new physics unearthed by Janus. In particular, we recall our numerical study of the nonequilibrium dynamics of the Edwards-Anderson Ising Spin Glass, for a time that spans eleven orders of magnitude, thus approaching the experimentally relevant scale (i.e. seconds). We have also studied the equilibrium properties of the spin-glass phase, with an emphasis on the quantitative matching between non-equilibrium and equilibrium correlation functions, through a time-length dictionary. Last but not least, we have clarified the existence of a glass transition in the presence of a magnetic field for a finite-range spin glass (the so-called de Almeida-Thouless line). We will finally mention some of the currently ongoing work of the collaboration, such as the characterization of the non-equilibrium dynamics in a magnetic field and the existence of a statics-dynamics dictionary in these conditions.
Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe_{2}O_{3} nanoparticles
Khurshid, Hafsa; Lampen-Kelley, Paula; Iglesias, Òscar; Alonso, Javier; Phan, Manh-Huong; Sun, Cheng-Jun; Saboungi, Marie-Louise; Srikanth, Hariharan
2015-10-27
Disorder among surface spins largely dominates the magnetic response of ultrafine magnetic particle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8±0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K, and becomes frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins with bulk coordination. Monte Carlo simulations of a hollow particle reproducing the experimental morphology corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures.
Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe_{2}O_{3} nanoparticles
Khurshid, Hafsa; Lampen-Kelley, Paula; Iglesias, Òscar; Alonso, Javier; Phan, Manh-Huong; Sun, Cheng-Jun; Saboungi, Marie-Louise; Srikanth, Hariharan
2015-10-27
Disorder among surface spins largely dominates the magnetic response of ultrafine magnetic particle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8±0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K, and becomes frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins with bulk coordination. Monte Carlo simulations of a hollow particle reproducing the experimental morphology corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Lastly, our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures.
Amjad, Jafar Mostafavi; Khalesifard, Hamid Reza; Slussarenko, Sergei; Karimi, Ebrahim; Santamato, Enrico; Marrucci, Lorenzo
2011-07-04
Samples of Ag{sup +}/Na{sup +} ion-exchanged glass that have been subject to intense laser irradiation may develop novel optical properties, as a consequence of the formation of patterns of silver nanoparticles and other structures. Here, we report the observation of a laser-induced permanent transverse birefringence, with the optical axis forming a radial pattern, as revealed by the spin-to-orbital angular momentum conversion occurring in a probe light beam. The birefringence pattern can be modeled well as resulting from thermally-induced stresses arising in the silver-doped glass during laser exposure, although the actual mechanism leading to the permanent anisotropy is probably more complex.
NASA Astrophysics Data System (ADS)
Franz, Silvio; Tria, Francesca
2006-01-01
The aim of this paper is to discuss the main ideas of the Talagrand proof of the Parisi Ansatz for the free-energy of Mean Field Spin Glasses with a physicist's approach. We consider the case of the spherical p-spin model, which has the following advantages: (1) the Parisi Ansatz takes the simple "one step replica symmetry breaking form," (2) the replica free-energy as a function of the order parameters is simple enough to allow for numerical maximization with arbitrary precision. We present the essential ideas of the proof, we stress its connections with the theory of effective potentials for glassy systems, and we reduce the technically more difficult part of the Talagrand's analysis to an explicit evaluation of the solution of a variational problem.
NASA Astrophysics Data System (ADS)
Said, Moh'd. Rida
1990-01-01
Standard magnetization measurements on Tb _{0.15}Y_{0.85 }Zn, Tb_{x} Y_{1-x}Ag, and Gd_{x}Y _{1-x}Ag for x <= 0.5 show that these compounds exhibit spin-glass behavior, as evidenced by the irreversibility of the magnetization (M) versus temperature (T) curves and by the thermoremanence (TRM) induced by field cooling. In the case of Tb_{x}Y _{1-x}Ag, spin -glass ordering coexists with the long-range antiferromagnetic order seen by neutron diffraction, which presumably also exists in Gd_{x}Y _{1-x}Ag. In the case of Tb_{0.15}Y _{0.85}Zn, our magnetization measurements show no spontaneous moment and thus the absence of the ferromagnetic order that exists in undiluted TbZn. Detailed measurements of the TRM versus T for different fields applied during cooling (H_{cool}), produce isotherms of TRM versus H_{cool}, which are found to scale to a universal curve for each sample. Resistivity measurements (rho) as a function of temperature were performed on Tb _{x}Y_ {1-x}Ag and Gd_ {x}Y_{1-x}Ag, from which we found that the residual resistivity at T(<
Josephson, Mark E
2016-01-01
Atrioventricular nodal reentrant tachycardia (AVNRT) should be classified as typical or atypical. The term ‘fast-slow AVNRT’ is rather misleading. Retrograde atrial activation during tachycardia should not be relied upon as a diagnostic criterion. Both typical and atypical atrioventricular nodal reentrant tachycardia are compatible with varying retrograde atrial activation patterns. Attempts at establishing the presence of a ‘lower common pathway’ are probably of no practical significance. When the diagnosis of AVNRT is established, ablation should be only directed towards the anatomic position of the slow pathway. If right septal attempts are unsuccessful, the left septal side should be tried. Ablation targeting earliest atrial activation sites during typical atrioventricular nodal reentrant tachycardia or the fast pathway in general for any kind of typical or atypical atrioventricular nodal reentrant tachycardia, are not justified. In this review we discuss current concepts about the tachycardia circuit, electrophysiologic diagnosis, and ablation of this arrhythmia.
NASA Astrophysics Data System (ADS)
Baños, R. A.; Cruz, A.; Fernandez, L. A.; Gil-Narvion, J. M.; Gordillo-Guerrero, A.; Guidetti, M.; Iñiguez, D.; Maiorano, A.; Mantovani, F.; Marinari, E.; Martin-Mayor, V.; Monforte-Garcia, J.; Muñoz Sudupe, A.; Navarro, D.; Parisi, G.; Perez-Gaviro, S.; Ricci-Tersenghi, F.; Ruiz-Lorenzo, J. J.; Schifano, S. F.; Seoane, B.; Tarancón, A.; Tripiccione, R.; Yllanes, D.
2011-11-01
We study the sample-to-sample fluctuations of the overlap probability densities from large-scale equilibrium simulations of the three-dimensional Edwards-Anderson spin glass below the critical temperature. Ultrametricity, stochastic stability, and overlap equivalence impose constraints on the moments of the overlap probability densities that can be tested against numerical data. We found small deviations from the Ghirlanda-Guerra predictions, which get smaller as system size increases. We also focus on the shape of the overlap distribution, comparing the numerical data to a mean-field-like prediction in which finite-size effects are taken into account by substituting delta functions with broad peaks.
NASA Astrophysics Data System (ADS)
Rinaldi-Montes, N.; Gorria, P.; Martínez-Blanco, D.; Fuertes, A. B.; Fernández Barquín, L.; Rodríguez Fernández, J.; de Pedro, I.; Fdez-Gubieda, M. L.; Alonso, J.; Olivi, L.; Aquilanti, G.; Puente-Orench, I.; Blanco, J. A.
2015-11-01
The unexpected appearance of magnetic hysteresis and exchange bias effects in nominally antiferromagnetic NiO nanoparticles is usually explained in terms of a core/shell morphology, where a spin glass-like shell is exchange coupled to an antiferromagnetic core. However, recent studies have challenged the validity of this assumption for small enough NiO nanoparticles. In this work we present proof of the core/shell model for NiO nanoparticles with sizes below 10 nm by combining neutron powder diffraction and magnetic measurements. In addition, we have verified that the exchange bias effect persists even when the particle size is reduced down to 4 nm.
Maiti, R. P. Mitra, M. K.; Chakravorty, Dipankar
2014-04-24
Sm{sub 2}CoMnO{sub 6} samples with particle sizes ∼70 nm were synthesized by a sol-gel technique. Field cooled magnetization study exhibited a ferromagnetic transition with a Curie temperature at ∼139K. This was attributed to ferromagnetic Co{sup 2+}−O−Mn{sup 4+} superexchange interaction. The results of magnetic relaxation measurements could be fitted to a stretched exponential function indicating the presence of both ferromagnetic and spin glass components in the system.
Cluster-spin-glass behavior in layered LiNi0.4Mn0.4Co0.2O2
NASA Astrophysics Data System (ADS)
Du, Fei; Bie, Xiaofei; Chen, Yan; Wei, Yingjin; Liu, Lina; Wang, Chunzhong; Zou, Guangtian; Chen, Gang
2009-09-01
Layered LiNi0.4Mn0.4Co0.2O2 has been synthesized by citrate precursor method. Its magnetic properties are investigated by dc magnetization. The high-temperature susceptibility curve follows the Curie-Weiss law with Curie and Weiss constant 1.435(2) emu K/mol Oe and -112(4) K, respectively, larger than those values reported in previous researches, which possibly results from the difference in the synthesis process and sintered temperature. Our dc susceptibility differs from that of the homogeneous spin glass in that below Tirr field cooled (FC) curve continues to rise, while the FC curve is almost flat for homogeneous spin glass. Together with the de Almeida-Thouless line analysis, cluster spin glass is suggested to be the ground state of LiNi0.4Mn0.4Co0.2O2. Frustration parameter |θ|/Tf in this system is estimated to be about four, lower than the value that frustration effect is strong enough to give rise to spin glass state. This fact indicates that the cluster-spin-glass results from the short-range structure disorder rather than the geometrical frustration.
Spin glass freezing and superconductivity in YBa2(Cu(1-x)Fe(x))3O7 alloys
NASA Technical Reports Server (NTRS)
Mirebeau, I.; Hennion, M.; Dianoux, J.; Caignaert, V.; Phillips, T. E.; Moorjani, K.
1991-01-01
The dynamics were studied of the iron spins in superconducting YBa2(Cu(0.94)Fe(0.06))3O7 by neutron time of flight measurements. Two samples were studied with slightly different characteristics, as shown by resistivity and neutron diffraction measurements. The same dynamical anomalies are observed by neutrons in both samples. Differences appear qualitative but not quantitative. In the whole temperature range, the q-dependence of the magnetic intensity mainly reflects the magnetic form factor of iron which shows that the iron spins are almost uncorrelated. The elastic and quasielastic intensities strongly vary with temperature. A spin glass like freezing is revealed at low temperature by a sharp decrease of the quasielastic intensity, an increase of the 'elastic' or resolution limited intensity and a minimum in the quasielastic width. The freezing temperature (T sub f - 18 K) corresponds to that already determined by a magnetic splitting in Mossbauer experiments. Above T sub f, the relaxation of the iron spins in the paramagnetic state is modified by the occurrence of superconductivity. An increase was observed of the quasielastic intensity and of the quasielastic width at the superconducting transition.
Contrasting energy scales of reentrant integer quantum Hall states
NASA Astrophysics Data System (ADS)
Deng, Nianpei; Watson, J. D.; Rokhinson, L. P.; Manfra, M. J.; Csáthy, G. A.
2012-11-01
We report drastically different onset temperatures of the reentrant integer quantum Hall states in the second and third Landau level. This finding is in quantitative disagreement with the Hartree-Fock theory of the bubble phases which is thought to describe these reentrant states. Our results indicate that the number of electrons per bubble in either the second or the third Landau level is likely different than predicted.
Pressure variation of reentrant transition temperature in liquid crystals.
Srivastava, A; Sa, D; Singh, S
2007-02-01
High pressure experimental studies show that in certain mesogenic materials, the nematic-smectic A (N-Sm A) transition temperature T(AN) exhibits nonlinear pressure dependence. As a consequence, the material shows reentrant phenomena that is a phase sequence nematic -- smectic A -- reentrant nematic appears. The characteristic features of this phenomenon have been addressed here within the framework of Landau-de-Gennes theory, where the coupling between nematic and smectic A order parameters (gamma, lambda(eff)) plays an important role. The cubic coupling gamma is chosen to be negative in order to form Sm A phase whereas the biquadratic coupling lambda(eff) is made large and positive to obtain reentrant behaviour. In the present work, we incorporate the pressure dependence in the theory through gamma and lambda(eff) which justifies the experimental pressure dependence in the reentrant transition temperature [Formula: see text]. The pressure dependence of gamma and lambda(eff) are employed in the calculation of excess specific heat capacity near the reentrant transition. The computed heat capacity shows strong pressure dependence near the reentrant transition which can be confirmed from high pressure measurement. PMID:17342375
Replica analysis of the generalized p-spin interaction glass model.
Schelkacheva, T. I.; Chtchelkatchev, N. M.
2011-10-13
We investigate the stability of replica symmetry breaking solutions in generalized p-spin models. It is shown that the kind of the transition to the one-step replica symmetry breaking state depends not only on the presence or absence of the reflection symmetry of the generalized 'spin'-operators {cflx U} but on the number of interacting operators and their individual characteristics.
NASA Astrophysics Data System (ADS)
Kehrle, J.; Zdravkov, V. I.; Obermeier, G.; Garcia-Garcia, J.; Ullrich, A.; Müller, C.; Morari, R.; Sidorenko, A. S.; Horn, S.; Tagirov, L. R.; Tidecks, R.
2012-01-01
Ferromagnet/Superconductor/Ferromagnet (F/S/F) trilayers, in which the establishing of a Fulde-Ferrell Larkin-Ovchinnikov (FFLO) like state leads to interference effects of the superconducting pairing wave function, form the core of the superconducting spin valve. The realization of strong critical temperature oscillations in such trilayers, as a function of the ferromagnetic layer thicknesses or, even more efficient, reentrant superconductivity, are the key condition to obtain a large spin valve effect, i.e. a large shift in the critical temperature. Both phenomena have been realized experimentally in the Cu 41 Ni 59 /Nb/Cu 41 Ni 59 trilayers investigated in the present work.
Aspelmeier, T; Wang, Wenlong; Moore, M A; Katzgraber, Helmut G
2016-08-01
The one-dimensional Ising spin-glass model with power-law long-range interactions is a useful proxy model for studying spin glasses in higher space dimensions and for finding the dimension at which the spin-glass state changes from having broken replica symmetry to that of droplet behavior. To this end we have calculated the exponent that describes the difference in free energy between periodic and antiperiodic boundary conditions. Numerical work is done to support some of the assumptions made in the calculations and to determine the behavior of the interface free-energy exponent of the power law of the interactions. Our numerical results for the interface free-energy exponent are badly affected by finite-size problems. PMID:27627255
NASA Astrophysics Data System (ADS)
Aspelmeier, T.; Wang, Wenlong; Moore, M. A.; Katzgraber, Helmut G.
2016-08-01
The one-dimensional Ising spin-glass model with power-law long-range interactions is a useful proxy model for studying spin glasses in higher space dimensions and for finding the dimension at which the spin-glass state changes from having broken replica symmetry to that of droplet behavior. To this end we have calculated the exponent that describes the difference in free energy between periodic and antiperiodic boundary conditions. Numerical work is done to support some of the assumptions made in the calculations and to determine the behavior of the interface free-energy exponent of the power law of the interactions. Our numerical results for the interface free-energy exponent are badly affected by finite-size problems.
Spin-glass behavior and anomalous magnetoresistance in ferromagnetic Ge{sub 1-x}Fe{sub x}Te epilayer
Liu, Jindong; Cheng, Xiaomin Tong, Fei; Miao, Xiangshui
2014-07-28
We report that the Ge{sub 1-x}Fe{sub x}Te thin film exhibits spin-glass behavior when the Fe concentration increases to 0.08. A large bifurcation between the zero-field cooling and field cooling temperature-dependent magnetization was observed. The hysteresis loops after zero-field cooling and field cooling show an exchange bias effect. A time-dependent thermoremanent magnetization follows power-law decay, which confirms the existence of spin glass. The anomalous magnetotranport properties present a further evidence for spin-glass behavior and give a freezing temperature T{sub g} ∼ 5 K in the Ge{sub 0.92}Fe{sub 0.08}Te thin film.
Spin glass and semiconducting behavior in one-dimensional BaFe2-dSe3 (d~2) crystals
Saparov, Bayrammurad I; Calder, Stuart A; Sipos, Balazs; Cao, Huibo; Chi, Songxue; Singh, David J; Christianson, Andrew D; Lumsden, Mark D; Sefat, A. S.
2011-01-01
We investigate the physical properties and electronic structure of BaFe{sub 1.79(2)}Se{sub 3} crystals, which were grown out of tellurium flux. The crystal structure of the compound, an iron-deficient derivative of the ThCr{sub 2}Si{sub 2}-type, is built upon edge-shared FeSe{sub 4} tetrahedra fused into double chains. The semiconducting BaFe{sub 1.79(2)}Se{sub 3} ({rho}{sub 295K} = 0.18 {Omega} {center_dot} cm and E{sub g} = 0.30 eV) does not order magnetically; however, there is evidence for short-range magnetic correlations of spin glass type (T{sub f} {approx} 50 K) in magnetization, heat capacity, and neutron diffraction results. A one-third substitution of selenium with sulfur leads to a slightly higher electrical conductivity ({rho}{sub 295K } = 0.11 {Omega} {center_dot} cm and E{sub g} = 0.22 eV) and a lower spin glass freezing temperature (T{sub f} {approx} 15 K), corroborating with higher electrical conductivity reported for BaFe{sub 2}S{sub 3}. According to the electronic structure calculations, BaFe{sub 2}Se{sub 3} can be considered as a one-dimensional ladder structure with a weak interchain coupling.
(Tb_1-xY_x)Ni_2Ge_2: From Ising Antiferromagnet to Ising Spin Glass.
NASA Astrophysics Data System (ADS)
Canfield, P. C.; Wiener, T.; Bud'Ko, S. L.
2000-03-01
Recent measurements [1,2] on single crystals of RNi_2Ge2 compounds have revealed complex, anisotropies and H-T phase diagrams. In addition recent work on (Gd_1-xEu_x)Ni_2Ge2 has demonstrated our ability to change the band filling so as to tune the ordering wave-vector of the magnetically ordered state [3]. In this talk we will present the results of measurements on another pseudo- ternary series: (Tb_1-xY_x)Ni_2Ge_2. The Tb local moments are aligned along the crystallographic c-axis for all concentrations of Y and as Y replaces Tb the two magnetic transition temperatures decrease rapidly. For x > 0.6 the low temperature ground state of the magnetic sublattice is that of an Ising spin glass. T -x phase diagrams and detailed characterization of the spin glass state will be presented. [1]S.L.Bud'ko et al. JMMM 205, 53 (1999). [2]Z.Islam et al. PRB 58, 8522 (1998). [3]Z.Islam et al. PRL 83, 2817 (1999). Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences.
Light scattering by a reentrant fractal surface.
Mendoza-Suárez, A; Méndez, E R
1997-05-20
Recently, rigorous numerical techniques for treating light scattering problems with one-dimensional rough surfaces have been developed. In their usual formulation, these techniques are based on the solution of two coupled integral equations and are applicable only to surfaces whose profiles can be described by single-valued functions of a coordinate in the mean plane of the surface. In this paper we extend the applicability of the integral equation method to surfaces with multivalued profiles. A procedure for finding a parametric description of a given profile is described, and the scattering equations are established within the framework of this formalism. We then present some results of light scattering from a sequence of one-dimensional flat surfaces with defects in the form of triadic Koch curves. Beyond a certain order of the prefractal, the scattering patterns become stationary (within the numerical accuracy of the method). It can then be argued that the results obtained correspond to a surface with a fractal structure. These constitute, to our knowledge, the first rigorous calculations of light scattering from a reentrant fractal surface. PMID:18253371
Reentrant stability of BEC standing wave patterns
Kalas, Ryan M; Solenov, Dmitry; Timmermans, Eddy M
2009-01-01
We describe standing wave patterns induced by an attractive finite-ranged external potential in a large Bose-Einstein Condensate (BEC). As the potential depth increases, the time independent Gross-Pitaevskii equation develops pairs of solutions that have nodes in their wavefunction. We elucidate the nature of these states and study their dynamical stability. Although we study the problem in a two-dimensional BEC subject to a cylindrically symmetric square-well potential of a radius that is comparable to the coherence length of the BEC, our analysis reveals general trends, valid in two and three dimensions, independent of the symmetry of the localized potential well, and suggestive of the behavior in general, short- and large-range potentials. One set of nodal BEC wavefunctions resembles the single particle n node bound state wavefunction of the potential well, the other wavefunctions resemble the n - 1 node bound-state wavefunction with a kink state pinned by the potential. The second state, though corresponding to the lower free energy value of the pair of n node BEC states, is always unstable, whereas the first can be dynamically stable in intervals of the potential well depth, implying that the standing wave BEC can evolve from a dynamically unstable to stable, and back to unstable status as the potential well is adiabatically deepened, a phenomenon that we refer to as 'reentrant dynamical stability'.
Capillary surface discontinuities above reentrant corners
NASA Technical Reports Server (NTRS)
Korevaar, H. J.
1982-01-01
A particular configuration of a vertical capillary tube for which S is the equilibrium interface between two fluids in the presence of a downward pointing gravitational field was investigated. S is the graph a function u whose domain is the (horizontal) cross section gamma of the tube. The mean curvature of S is proportional to its height above a fixed reference plane and lambda is a prescribed constant and may be taken between zero and pi/2. Domains gamma for which us is a bounded function but does not extend continuously to d gamma are sought. Simple domains are found and the behavior of u in those domains is studied. An important comparison principle that has been used in the literature to derive many of the results in capillarity is reviewed. It allows one to deduce the approximate shape of a capillary surface by constructing comparison surfaces with mean curvature and contact angle close to those of the (unknown) solution surface. In the context of nonparametric problems the comparison principle leads to height estimates above and below for the function u. An example from the literature where these height estimates have been used successfully is described. The promised domains for which the bounded u does not extend continuously to the boundary are constructed. The point on the boundary at which u has a jump discontinuity will be the vertext of a re-entrant corner having any interior angle theta pi. Using the comparison principle the behavior of u near this point is studied.
Magnetic Field Reentrant Superconductivity in Aluminum Nanowires
NASA Astrophysics Data System (ADS)
Bretz-Sullivan, Terence; Goldman, Allen
Reentrance to the superconducting state through the application of a magnetic field to quasi-one dimensional superconductors driven resistive by current, is counter to the expected properties of superconductors. It was not until recently that a microscopic mechanism explaining the phenomenon was proposed in which superconductivity and phase slip driven dissipation coexist in a non-equilibrium state. Here we present additional results of magnetic field induced reentrance into the superconducting state in quasi-one-dimensional aluminum nanowires with an in-plane magnetic field both transverse to, and along the wire axis. The reentrant behavior is seen in the magnetic field dependence of the I-V characteristic and resistance vs. temperature, and in the wire's magnetoresistance at 450mK. This work was supported by DOE Basic Energy Sciences Grant DE-FG02-02ER46004. Samples were fabricated at the Minnesota Nanofabrication Center. Parts of this work were carried out in the University of Minnesota Characterization Facility, a member of the Materials Research Facilities Network (www.mrfn.org) funded via the NSF MRSEC program.
Strong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3
NASA Astrophysics Data System (ADS)
Katukuri, Vamshi M.; Nishimoto, Satoshi; Rousochatzakis, Ioannis; Stoll, Hermann; van den Brink, Jeroen; Hozoi, Liviu
2015-10-01
With large spin-orbit coupling, the electron configuration in d-metal oxides is prone to highly anisotropic exchange interactions and exotic magnetic properties. In 5d5 iridates, given the existing variety of crystal structures, the magnetic anisotropy can be tuned from antisymmetric to symmetric Kitaev-type, with interaction strengths that outsize the isotropic terms. By many-body electronic-structure calculations we here address the nature of the magnetic exchange and the intriguing spin-glass behavior of Li2RhO3, a 4d5 honeycomb oxide. For pristine crystals without Rh-Li site inversion, we predict a dimerized ground state as in the isostructural 5d5 iridate Li2IrO3, with triplet spin dimers effectively placed on a frustrated triangular lattice. With Rh-Li anti-site disorder, we explain the observed spin-glass phase as a superposition of different, nearly degenerate symmetry-broken configurations.
Identical band gaps in structurally re-entrant honeycombs.
Zhu, Zhu-Wei; Deng, Zi-Chen
2016-08-01
Structurally re-entrant honeycomb is a sort of artificial lattice material, characterized by star-like unit cells with re-entrant topology, as well as a high connectivity that the number of folded sheets jointing at each vertex is at least six. In-plane elastic wave propagation in this highly connected honeycomb is investigated through the application of the finite element method in conjunction with the Bloch's theorem. Attention is devoted to exploring the band characteristics of two lattice configurations with different star-like unit cells, defined as structurally square re-entrant honeycomb (SSRH) and structurally hexagonal re-entrant honeycomb (SHRH), respectively. Identical band gaps involving their locations and widths, interestingly, are present in the two considered configurations, attributed to the resonance of the sketch folded sheets, the basic component elements for SSRH and SHRH. In addition, the concept of heuristic models is implemented to elucidate the underlying physics of the identical gaps. The phenomenon of the identical bandgaps is not only beneficial for people to further explore the band characteristics of lattice materials, but also provides the structurally re-entrant honeycombs as potential host structures for the design of lattice-based metamaterials of interest for elastic wave control. PMID:27586722
NASA Astrophysics Data System (ADS)
Kaul, S. N.; Messala, Umasankar
2016-03-01
Weak itinerant-electron ferromagnet Ni3Al is driven to magnetic instability (quantum critical point, QCP, where the long-range ferromagnetic order of the bulk ceases to exist) by reducing the average crystallite size to d=50 nm. 'Zero-field' (H=0) linear and nonlinear ac-susceptibilities, measured on Ni3Al nanoparticle aggregates, with d=50 nm (S1) and d=5 nm (S2), provide strong evidence for two spin glass (SG)-like thermodynamic phase transitions: one at Ti(H = 0) ≃ 30 K (Ti† (H = 0) ≃ 230 K) and the other at a lower temperature Tp(H = 0) ≃ 8 K (Th(H = 0) ≃ 52 K) in S1 (S2). 'In-field' (H ≠ 0) linear ac-susceptibility and dc magnetization demonstrate that the thermodynamic nature of these transitions is preserved in finite fields. The presently determined H-T phase diagrams for the samples S1 and S2 are compared with those predicted by the Kotliar-Sompolinsky and Gabay-Toulouse mean-field models and Monte Carlo simulations, based on the chirality-driven spin glass (SG) ordering scenario, for a three-dimensional nearest-neighbor Heisenberg SG system with or without weak random anisotropy. Such a detailed comparison permits us to unambiguously identify various 'zero-field' and 'in-field' SG phase transitions as: (i) the simultaneous paramagnetic (PM)-chiral glass (CG) and PM-SG phase transitions at Ti(H), (ii) the PM-CG transition at Ti† (H), (iii) the replica symmetry-breaking SG transition at Tp(H), and (iv) the continuous spin-rotation symmetry-breaking SG transition at Th(H). In the presence of random anisotropy, magnetization fails to saturate even at 90 kOe in S1 whereas negligibly small anisotropy allows even fields as weak as 1 kOe to saturate magnetization and induce ferromagnetism in S2. Due to the proximity to CG/SG-QCP, magnetization and susceptibility both exhibit non-Fermi liquid behavior over a wide range at low temperatures.
12-Metal 36-membered ring based W(V)-Co(II) layers showing spin-glass behavior.
Zhao, Liang; Duan, Ran; Zhuang, Peng-Fei; Zheng, Hui; Jiao, Cheng-Qi; Wang, Jun-Li; He, Cheng; Liu, Tao
2015-07-28
The present study describes the designed synthesis, X-ray structures, and magnetic properties of two 2D cyano bridged heterobimetallic W(V)-Co(II) networks, {[W(CN)8]2[Co(phpy)4]3}·2CH3OH·2H2O (1) and {[W(CN)8]2[Co(4-spy)4]3}·6H2O (2) (phpy = 4-phenylpyridine, 4-spy = 4-styrylpyridine). Both compounds consist of cyano-bridged 12-metal 36-membered ring units, Co6W6(CN)12, joined by organic linkers into a 2D plane. The layer presents a corrugated configuration in compound 1 and a plane configuration in compound 2 due to different π-π stacking interactions. Magnetic measurements reveal that both 1 and 2 have a transition to the spin glass-like phase due to competitive magnetic interactions. PMID:26076432
NASA Astrophysics Data System (ADS)
Lee, Seong-Joo; Jung, Hyunok; Lee, Soonchil; Dho, Joonghoe
2009-02-01
The present study investigates the magnetic properties of a natural haematite (α-Fe2O3) crystal at the temperature of liquid helium using magnetometry and 57Fe nuclear magnetic resonance (NMR) methods. The magnetization curve shows that the net magnetization in the (111) plane vanishes at the Morin temperature (260 K) but weakly reappears as the temperature decreases below 40 K. A comparison of the magnetization and NMR results indicates that the spin state, direction and canting angle, at a low temperature, is identical to that in a weak-ferromagnetic state above the Morin temperature. Its volume, however, occupies only 3% of the entire sample. The relaxation of magnetization with time, the difference of the zero-field-cooled and field-cooled magnetization, and the rise of the NMR echo intensity with increasing magnetic field exhibit the superparamagnetic behaviour of the reentrant weak ferromagnetic phase. The cluster size of the weak ferromagnetic phase is smaller than 102 nm and the blocking temperature is higher than 40 K. The fact that the results from the natural crystal and pure powder are similar implies that the reentrant weak-ferromagnetic phase at a low temperature is due to the intrinsic magnetic instability of haematite.
Spin glass behavior in the Dy{sub 3-x}Y{sub x}TaO{sub 7} (0≤x≤1) system
Gomez-Garcia, J. Francisco; Escudero, Roberto; Tavizon, Gustavo
2014-09-15
Several x-compositions of the polycrystalline Dy{sub 3−x}Y{sub x}TaO{sub 7} system, crystallizing in the weberite-type structure, were synthesized and structurally characterized using Rietveld refinements based on X-ray diffraction data. In previous magnetic characterization of Dy{sub 3}TaO{sub 7} (x=0), with the same crystal structure, an antiferromagnetic transition at T=2.3 K has been assigned to this compound. On the basis of DC and AC magnetic susceptibilities analyses, we show in this work that all compounds in the range of 0≤x≤1.0 exhibit a spin glass behavior. The nature of the spin glass behavior in Dy{sub 3−x}Y{sub x}TaO{sub 7}, can be attributed to the highly frustrated antiferromagnetic interaction of the Dy{sup 3+} sublattice and to the Dy{sup 3+}–Dy{sup 3+} distorted tetrahedra array in the weberite-type structure of this system. By fitting AC susceptibility data, using dynamical scaling theory equations, we conclude that a cluster spin glass is present in Dy{sub 3−x}Y{sub x}TaO{sub 7} in the low temperature range. Depending on the x-composition, T{sub g}∼2.2–3.2 K. In the range 15–300 K the system obeys a Curie–Weiss magnetic behavior. - Graphical abstract: Weberite-type crystal structure of the Dy{sub 3−x}Y{sub x}TaO{sub 7} compounds. In this structure the magnetic sublattice is formed by Dy{sup 3+} cations in an arrangement of distorted tetrahedra at the second-nearest neighbor site; this arrangement suggests geometric frustration that leads to a spin glass behavior. - Highlights: • Spin glass of Dy{sub 3−x}Y{sub x}TaO{sub 7} is associated to highly frustrated AFM interaction. • Quasi-one-dimensional feature of the crystal structure. • Suggest the existence of a cluster spin glass in Dy{sub 3−x}Y{sub x}TaO{sub 7}. • Dy{sub 3−x}Y{sub x}TaO{sub 7} system (x=0.33, 0.66, and 1.0) also display spin glass behavior.
Miwa, Yohei; Yamamoto, Katsuhiro
2012-08-01
A combination of the microwave power saturation (MPS) method of electron spin resonance (ESR) and spin probing is proposed as a simple and practical technique for detecting the glass transition temperatures, T(g), of polymers with high sensitivity. Effects of the spin-probe size and concentration on the T(g) value of polystyrene (PS) determined by MPS, T(g,ESR), were first evaluated. Spin-probed PS with four types of nitroxides, namely, di-tert-butyl nitroxide (DBN), 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BZONO), and 4',4'-dimethyl-spiro(5α-cholestane-3,2'-oxazolidin)-3'-yloxy free radical (CHOL), having molecular weights of 144, 156, 276, and 473, respectively, and spin-labeled PS with TEMPO were prepared. The T(g,ESR) values for the spin-probed PS with DBN, TEMPO, BZONO, and CHOL and spin-labeled PS were determined to 360, 363, 374, 374, and 375 K, respectively, within experimental uncertainties of 2 K, whereas the glass transition temperature determined by DSC, T(g,DSC), was 375 K for all samples. A significant decrease in T(g,ESR) for small spin probes was shown to be due to decoupling between the mobilities of small spin probes and PS segments. Concerning the concentration, a decrease in the saturation factor, S, induced by shortening of the spin-spin relaxation time was observed for the spin-probed PS with CHOL when the concentration of CHOL was more than 1.0 wt %. Furthermore, T(g,ESR) decreased slightly with increasing weight fraction of CHOL because of the "plasticizer effect" of CHOL. However, the T(g,ESR) and T(g,DSC) values corresponded for each concentration. Thus, large spin probes, such as CHOL and BZONO, are appropriate for the determination of T(g,ESR) values; the concentration of the spin probes does not affect the T(g,ESR) value unless the overall T(g) value is reduced by blending of excess spin probes. Finally, measurements of T(g,ESR) in PS/silica composites containing more than 95 wt
NASA Astrophysics Data System (ADS)
Wang, Bo-Kun; Wu, Shao-Yi; Yuan, Zi-Yi; Liu, Zi-Xuan; Jiang, Shi-Xin; Liu, Zheng; Yao, Zi-Jian; Teng, Bao-Hua; Wu, Ming-He
2016-08-01
The spin Hamiltonian parameters and local structures are theoretically studied for Cu2+-doped alkaline earth lead zinc phosphate (RPPZ, R=Mg, Ca, Sr, and Ba) glasses based on the high-order perturbation calculations for a tetragonally elongated octahedral 3d9 cluster. The relative elongation ratios are found to be ρ≈3.2%, 4.4%, 4.6%, and 3.3% for R=Mg, Ca, Sr, and Ba, respectively, because of the Jahn-Teller effect. The whole decreasing crystal-field strength Dq and orbital reduction factor k from Mg to Sr are ascribed to the weakening electrostatic coulombic interactions and the increasing probability of productivity of nonbridge oxygen (and hence increasing Cu2+-O2- electron cloud admixtures) under PbO addition, respectively, with increasing alkali earth ionic radius. The anomalies (the largest Dq and the next highest k among the systems) for R=Ba are attributed to the cross linkage of this large cation in the network. The overall increasing order (Mg≤Ba
Dynamics of bright and dark localized excitonic magnetic polarons in CdMnTe spin glass compound
NASA Astrophysics Data System (ADS)
Gnatenko, Yuriy; Bukivskij, Petro; Piryatinski, Yuriy
2015-03-01
The measurements of the magnetic properties of spin glass (SG) system indicate that the magnetic relaxation is characterized by a broad range of times below Tf. Here, for the first time, we have investigated time-resolved photoluminescence spectra of Cd0.70Mn0.30Te SG compound at the temperature below the freezing temperature Tf. This enables us to study the dynamics of different localized excitonic magnetic polarons (LEMPs) at T = 0.7Tfexcited in the crystal regions where various microscopic magnetic spin states (MMSSs) are formed. It was found that there is a broad distribution of the lifetimes of the LEMPs which have different lifetimes but same energies. It was shown that the presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states as a result of the local magnetic fields formation. The lifetimes of these dark LEMPs correspond to hundreds of nanoseconds. It was also found that the decay process of the PL exciton band intensity is described by the Kohlrausch-Williams-Watts stretched exponential function which describes the recombination processes which correspond to the emission of the LEMPs formed in the crystal region of the finite clusters as well as the infinite cluster. These complex dynamical phenomena, observed for Cd1-XMnXTe at low temperatures, reflect the spatially heterogeneous dynamics in the SG system which is due to the presence of different MMSSs below Tf.
Highly optimized simulations on single- and multi-GPU systems of the 3D Ising spin glass model
NASA Astrophysics Data System (ADS)
Lulli, M.; Bernaschi, M.; Parisi, G.
2015-11-01
We present a highly optimized implementation of a Monte Carlo (MC) simulator for the three-dimensional Ising spin-glass model with bimodal disorder, i.e., the 3D Edwards-Anderson model running on CUDA enabled GPUs. Multi-GPU systems exchange data by means of the Message Passing Interface (MPI). The chosen MC dynamics is the classic Metropolis one, which is purely dissipative, since the aim was the study of the critical off-equilibrium relaxation of the system. We focused on the following issues: (i) the implementation of efficient memory access patterns for nearest neighbours in a cubic stencil and for lagged-Fibonacci-like pseudo-Random Numbers Generators (PRNGs); (ii) a novel implementation of the asynchronous multispin-coding Metropolis MC step allowing to store one spin per bit and (iii) a multi-GPU version based on a combination of MPI and CUDA streams. Cubic stencils and PRNGs are two subjects of very general interest because of their widespread use in many simulation codes.
Hamed, F.; Razavi, F.S.; Zaleski, H.; Bose, S.K. )
1991-02-01
The superconducting transition temperature {ital T}{sub {ital c}} of metallic glasses Fe{sub 20}Zr{sub 80}, Fe{sub 25}Zr{sub 75}, and Cu{sub 25}Zr{sub 75} were measured under quasihydrostatic pressure up to 10 GPa. The volume (pressure) dependence of the electron-phonon coupling parameter, {lambda}{sub {ital e}-ph}, for Cu{sub 25}Zr{sub 75} was calculated using the McMillan equation. Using this volume dependence of {lambda}{sub {ital e}-ph} and the modified McMillan equation, which incorporates spin fluctuations, we determined the volume dependence of the spin-fluctuation parameter, {lambda}{sub SF}, in Ni{sub 25}Zr{sub 75} and Fe{sub 100{minus}{ital x}}Zr{sub {ital x}} ({ital x}=80, 75). It was found that with increasing pressure spin fluctuations are suppressed at a faster rate in Fe{sub 100{minus}{ital x}}Zr{sub {ital x}} as the Fe concentration is increased. The rate of suppression of spin fluctuations with pressure was also found to be higher in the Fe-Zr glasses than in Ni-Zr glasses of similar composition.
NASA Astrophysics Data System (ADS)
Liu, Hui; Zou, Youming; Ling, Langsheng; Zhang, Lei; Zhang, Changjin; Zhang, Yuheng
2015-08-01
We have studied the magnetic properties of spin-frustrated compound Dy2Ti2-xVxO7 single crystals. Bulk magnetization data show that ferromagnetic interaction enhances with increasing content of V, resulting from the ferromagnetic interactions between Dy and V ions. It is also found from ac susceptibility that the modestly doped samples (x≤0.4) still keep ice state, demonstrating the robustness of spin ice. When the doped concentration increases up to 0.5, more disorder on B site and internal field associated with V4+ ions would affect the macroscopic ground-state degeneracy and relieve the frustration, leading to the disappearance of spin ice and occurrence of a spin-glass-like transition. The magnetic properties of the system are related to magnetic frustration and local structural disorder.
Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd
NASA Astrophysics Data System (ADS)
Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.
2016-01-01
We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.
Cr-doped TiSe2 - A layered dichalcogenide spin glass
Luo, Huixia; Tao, Jing; Krizan, Jason W.; Seibel, Elizabeth M.; Xie, Weiwei; Sahasrabudhe, Girija S.; Bergman, Susanna L.; Phelan, Brendan F.; Wang, Zhen; Zhang, Jiandi; et al
2015-09-17
We report the magnetic characterization of the Cr-doped layered dichalcogenide TiSe2. 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 (θcw) 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/θcw = 0.05. The CDW transition seen in the resistivity for pure TiSe2 is still present for 3% Cr substitution but is absent by 10% substitution, above which themore » materials are metallic and p-type. Structural refinements, magnetic characterization, and chemical considerations indicate that the materials are of the type Ti1–xCrxSe2-x/2 for 0 ≤ x ≤ 0.6.« less
Cr-doped TiSe_{2} - A layered dichalcogenide spin glass
Luo, Huixia; Tao, Jing; Krizan, Jason W.; Seibel, Elizabeth M.; Xie, Weiwei; Sahasrabudhe, Girija S.; Bergman, Susanna L.; Phelan, Brendan F.; Wang, Zhen; Zhang, Jiandi; Cava, R. J.
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% 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–x}Cr_{x}Se_{2-x/2} for 0 ≤ x ≤ 0.6.
Kathirvelu, Velavan; Eaton, Gareth R.; Eaton, Sandra S.
2009-01-01
Spin-lattice relaxation rates measured by long-pulse saturation recovery in glassy solvents for chlorinated aromatic radicals: perchlorotriphenylmethyl radical, 2,5-dichloro-3,6-dihydroxy-1,4-benzosemiquinone, and tetrachloro-1,4-benzosemiquinone, were compared with relaxation rates for non-chlorinated analogs. The impact of the quadrupolar chlorines is small, and less than the effects of changing the rigidity of the glass. The temperature dependence of relaxation rates below the glass transition temperature could be modeled as the sum of contributions from the direct, Raman, and local mode processes. PMID:20126423
NASA Astrophysics Data System (ADS)
Torikai, Eiko; Ito, Atsuko; Watanabe, Isao; Nagamine, Kanetada
2006-03-01
One of the distinguishing properties of spin glass (SG) systems is a long-time relaxation of magnetization below the SG transition temperature. Motivated by the interests on how the microscopic spin dynamics is related to the macroscopic behavior of spin system in the SG state, we have performed the μSR measurement for a typical Ising SG system Fe 0.50Mn 0.50TiO 3 under various experimental conditions. We also pay attention to how the spin dynamics responds to a sudden change of magnetic fields. Thus, we have discussed the spin dynamics of SG system which had not been detected before our μSR measurement. For example, we have shown that the switching-off of a magnetic field at the field-cooled state makes the spin fluctuations faster. Moreover, such spin fluctuations have shown to remain faster at least up to the order of 2 h, although the thermoremanent magnetization decays dramatically within 2 h.
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3
Zhou, S.Y.; Langner, M.C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T.E.; Hertlein, M.P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R.W.
2014-01-16
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.
Numerical study of the spin-glass transition in a dilute Ising model on a triangular lattice
NASA Astrophysics Data System (ADS)
Andérico, Carmen Z.; Fernández, Julio F.; Streit, Thomas S. J.
1982-10-01
We study an Ising model with nearest-neighbor antiferromagnetic interactions. It is placed on a triangular lattice, where each site is occupied by a spin with x probability. There is no applied magnetic field. Randomness and frustration, two essential ingredients of spin-glasses, are present in this model. We study its critical properties here. The entropy is obtained by a transfer-matrix calculation as a function of x at low temperature (T=0.3JkB) for systems on a lattice of 10 × 20 sites. A fairly shallow minimum appears near x~=0.9, which suggests that this case is the one most likely to show a transition into an ordered state at low temperature. We study the cases x=1, 0.9, and 0.74, which is about half-way to the critical percolation. We simulate systems on lattices of 50 × 50 sites and 30 × 30 sites by the Monte Carlo method. The specific heat has a broad maximum at T~=0.9 for x=0.74 and 0.9. χSG, defined by χSG=N-1 i,j<σiσj>2, and the relaxation time (τ) are obtained for T>=0.6JkB. Both quantities, τ and χSG, turn out to be proportional to exp[A(T-T0)c] and 0<=T0<~0.4 a fit with T0=0 yields c~1 for x=1 but c~2 for x=0.74 and 0.9.
NASA Astrophysics Data System (ADS)
Monthus, Cécile
2015-09-01
For Gaussian Spin-Glasses in low dimensions, we introduce a simple Strong Disorder renormalization at zero temperature in order to construct ground states for Periodic and Anti-Periodic boundary conditions. The numerical study in dimensions d = 2 (up to sizes 20482) and d = 3 (up to sizes 1283) yields that Domain Walls are fractal of dimensions ds(d = 2) ≃ 1.27 and ds(d = 3) ≃ 2.55, respectively.
Pressure effect on magnetic phase transition and spin-glass-like behavior of GdCo2B2
NASA Astrophysics Data System (ADS)
Guang-Hui, Hu; Ling-Wei, Li; Umehara, Izuru
2016-06-01
We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current (AC) susceptibility, AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa. A detailed magnetic phase diagram under pressure is determined. GdCo2B2 exhibits three anomalies that apparently reflect magnetic phase transitions, respectively, at temperatures T C = 20.5 K, T 1 = 18.0 K and T N = 11.5 K under ambient pressure. Under pressures up to 2.2 GPa, these anomalies are observed to slightly increase at T C and T 1, and they coincide with each other above 1.6 GPa. Conversely, they decrease at T N and disappear under pressures higher than 1.4 GPa. The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure. Moreover, the spin-glass-like behavior of GdCo2B2 is examined in terms of magnetization, aging effect and frequency dependence of AC susceptibility. A separation between the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves becomes evident at a low magnetic field of 0.001 T. A long-time relaxation behavior is observed at 4 K. The freezing temperature T f increases with frequency increasing. Project supported by JSPS KAKENHI (Grant No. 24540366, Grant-in-Aid for Scientific Research (C)).
SrFe{sub 0.9}Ti{sub 0.1}O{sub 3−δ}: A cluster spin glass
Sendil Kumar, A.; Babu, P.D.; Srinath, S.
2014-03-01
Graphical abstract: - Highlights: • Prepared SrFe{sub 0.9}Ti{sub 0.1}O{sub 3−δ} is in nanocrystalline form. • Arrott plot shows absence of spontaneous magnetization which rules out the possibility of long range ferromagnetic order. • AC susceptibility data is evidence of cluster spin glass. • There is no magnetic Bragg's reflection. • By substituting Ti{sup 4+}, helical antiferromagetic SrFeO{sub 3} is transformed to a cluster spin glass. - Abstract: The magnetic ground state of nanocrystalline SrFe{sub 0.9}Ti{sub 0.1}O{sub 3−δ} system has been investigated from 2 K to 300 K using AC Susceptibilty (ACS), magnetization and neutron diffraction measurements. The cusp in the temperature dependent magnetization and dispersion below T{sub max} (the temperature at which the maximum susceptibility is observed) in real part of ac susceptibility with frequency is observed. Arrott plot shows the lack of M{sub S} (spontaneous magnetization) down to 2 K, and the non-occurrence of magnetic Bragg reflections below the T{sub max} in neutron diffraction measurements, indicates the absence of long range ferro and antiferromagnetic order. The frequency dependence of T{sub max} obeys Vögel–Fulcher model establishing the cluster spin glass behavior in this system.
Ciaccio, Edward J; Ashikaga, Hiroshi; Kaba, Riyaz A; Cervantes, Daniel; Hopenfeld, Bruce; Wit, Andrew L; Peters, Nicholas S; McVeigh, Elliot R; Garan, Hasan; Coromilas, James
2008-01-01
Background Infarct border zone (IBZ) geometry likely affects inducibility and characteristics of postinfarction reentrant ventricular tachycardia, but the connection has not been established. Objective To determine characteristics of post infarction ventricular tachycardia in the IBZ. Methods A geometric model describing the relationship between IBZ geometry and wavefront propagation in reentrant circuits was developed. Based on the formulation, slow conduction and block was expected to coincide with areas where IBZ thickness (T) is minimal and the local spatial gradient in thickness (ΔT) is maximal, so that the degree of wavefront curvature ρ ∝ ΔT/T is maximal. Regions of fastest conduction velocity were predicted to coincide with areas of minimum ΔT. In seven arrhythmogenic postinfarction canine heart experiments, tachycardia was induced by programmed stimulation, and activation maps were constructed from multichannel recordings. IBZ thickness was measured in excised hearts from histologic analysis or magnetic resonance imaging. Reentrant circuit properties were predicted from IBZ geometry and compared with ventricular activation maps following tachycardia induction. Results Mean IBZ thickness was 231±140µm at the reentry isthmus and 1440±770µm in the outer pathway (p<0.001). Mean curvature ρ was 1.63±0.45mm−1 at functional block line locations, 0.71±0.18mm−1 at isthmus entrance-exit points, and 0.33±0.13mm−1 in the outer reentrant circuit pathway. The mean conduction velocity about the circuit during reentrant tachycardia was 0.32±0.04mm/ms at entrance-exit points, 0.42±0.13mm/ms for the entire outer pathway, and 0.64±0.16mm/ms at outer pathway regions with minimum ΔT. Model sensitivity and specificity to detect isthmus location was 75.0±5.7% and 97.2±0.7%. Conclusions Reentrant circuit features as determined by activation mapping can be predicted on the basis of IBZ geometrical relationships. PMID:17675078
Pacemaker interactions induce reentrant wave dynamics in engineered cardiac culture
NASA Astrophysics Data System (ADS)
Borek, Bartłomiej; Shajahan, T. K.; Gabriels, James; Hodge, Alex; Glass, Leon; Shrier, Alvin
2012-09-01
Pacemaker interactions can lead to complex wave dynamics seen in certain types of cardiac arrhythmias. We use experimental and mathematical models of pacemakers in heterogeneous excitable media to investigate how pacemaker interactions can be a mechanism for wave break and reentrant wave dynamics. Embryonic chick ventricular cells are cultured invitro so as to create a dominant central pacemaker site that entrains other pacemakers in the medium. Exposure of those cultures to a potassium channel blocker, E-4031, leads to emergence of peripheral pacemakers that compete with each other and with the central pacemaker. Waves emitted by faster pacemakers break up over the slower pacemaker to form reentrant waves. Similar dynamics are observed in a modified FitzHugh-Nagumo model of heterogeneous excitable media with two distinct sites of pacemaking. These findings elucidate a mechanism of pacemaker-induced reentry in excitable media.
Reentrant processing mediates object substitution masking: comment on Põder (2013).
Di Lollo, Vincent
2014-01-01
Object-substitution masking (OSM) occurs when a target stimulus and a surrounding mask are displayed briefly together, and the display then continues with the mask alone. Target identification is accurate when the stimuli co-terminate but is progressively impaired as the duration of the trailing mask is increased. In reentrant accounts, OSM is said to arise from iterative exchanges between brain regions connected by two-way pathways. In an alternative account, OSM is explained on the basis of exclusively feed-forward processes, without recourse to reentry. Here I show that the feed-forward account runs afoul of the extant phenomenological, behavioral, brain-imaging, and electrophysiological evidence. Further, the feed-forward assumption that masking occurs when attention finds a degraded target is shown to be entirely ad hoc. In contrast, the evidence is uniformly consistent with a reentrant-processing account of OSM. PMID:25136322
NASA Astrophysics Data System (ADS)
Franke, Deanna; Maxwell, Robert; Lathrop, David; Banks, Kesha; Eckert, Hellmut
1992-10-01
The structure of glasses in the system CdGeAs2-xPx is discussed on the basis of complementary solid-state NMR experiments, including 31P and 113Cd magic-angle spinning (MAS) and spin-echo techniques, as well as 31-113Cd spin-echo double resonance (SEDOR) NMR. Computer simulations of atomic distribution models and experimental studies on crystalline model systems are used to quantify the results. The analysis reveals striking differences in the short-range order between the glassy and the stoichiometrically analogous crystalline materials. The structure of glasses in the system CdGeAs2-xPx is characterized by the presence of a substantial fraction of homopolar pnictogen-pnictogen bonds and by a distribution of cadmium relative to phosphorus that is close to random. These results lend credence to the bond-switching model invoked for the structural description of amorphous tetrahedral semiconductors.
Reentrant Melting of RNA with Quenched Sequence Randomness
NASA Astrophysics Data System (ADS)
Hayrapetyan, G. N.; Iannelli, F.; Lekscha, J.; Morozov, V. F.; Netz, R. R.; Mamasakhlisov, Y. Sh.
2014-08-01
The effect of quenched sequence disorder on the thermodynamics of RNA secondary structure formation is investigated for two- and four-letter alphabet models using the constrained annealing approach, from which the temperature behavior of the free energy, specific heat, and helicity is analytically obtained. For competing base pairing energies, the calculations reveal reentrant melting at low temperatures, in excellent agreement with numerical results. Our results suggest an additional mechanism for the experimental phenomenon of RNA cold denaturation.
Strong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3
Katukuri, Vamshi M.; Nishimoto, Satoshi; Rousochatzakis, Ioannis; Stoll, Hermann; van den Brink, Jeroen; Hozoi, Liviu
2015-01-01
With large spin-orbit coupling, the electron configuration in d-metal oxides is prone to highly anisotropic exchange interactions and exotic magnetic properties. In 5d5 iridates, given the existing variety of crystal structures, the magnetic anisotropy can be tuned from antisymmetric to symmetric Kitaev-type, with interaction strengths that outsize the isotropic terms. By many-body electronic-structure calculations we here address the nature of the magnetic exchange and the intriguing spin-glass behavior of Li2RhO3, a 4d5 honeycomb oxide. For pristine crystals without Rh-Li site inversion, we predict a dimerized ground state as in the isostructural 5d5 iridate Li2IrO3, with triplet spin dimers effectively placed on a frustrated triangular lattice. With Rh-Li anti-site disorder, we explain the observed spin-glass phase as a superposition of different, nearly degenerate symmetry-broken configurations. PMID:26434954
NASA Astrophysics Data System (ADS)
Monthus, Cécile
2016-04-01
The finite temperature dynamics of the Dyson hierarchical classical spins models is studied via real-space renormalization rules concerning the couplings and the relaxation times. For the ferromagnetic model involving long-ranged coupling J(r)\\propto {{r}-1-σ} in the region 1/2<σ <1 where there exists a non-mean-field-like thermal ferromagnetic–paramagnetic transition, the RG flows are explicitly solved: the characteristic relaxation time τ (L) follows the critical power-law τ (L)\\propto {{L}{{z\\text{c}}(σ )}} at the phase transition and the activated law \\ln τ (L)\\propto {{L}\\psi} with \\psi =1-σ in the ferromagnetic phase. For the spin-glass model involving random long-ranged couplings of variance \\overline{{{J}2}(r)}\\propto {{r}-2σ} in the region 2/3<σ <1 where there exists a non-mean-field-like thermal spin-glass–paramagnetic transition, the coupled RG flows of the couplings and of the relaxation times are studied numerically: the relaxation time τ (L) follows some power-law τ (L)\\propto {{L}{{z\\text{c}}(σ )}} at criticality and the activated law \\ln τ (L)\\propto {{L}\\psi} in the spin-glass phase with the dynamical exponent \\psi =1-σ =θ coinciding with the droplet exponent governing the flow of the couplings J(L)\\propto {{L}θ} .
Terakado, Nobuaki Watanabe, Kouki; Kawamata, Takayuki; Yokochi, Yuudai; Takahashi, Yoshihiro; Koike, Yoji; Fujiwara, Takumi
2015-04-06
High thermal conductivity materials are in great demand for heat-flow control and heat dissipation in electronic devices. In this study, we have produced a glass-ceramics that contains spin-chain compound SrCuO{sub 2} and have found that the glass-ceramics yields high thermal conductivity of ∼5 W K{sup −1} m{sup −1} even at room temperature. The glass-ceramics is fabricated through crystallization of inhomogeneous melt-quenched oxides made from SrCO{sub 3}, CuO, Li{sub 2}CO{sub 3}, Ga{sub 2}O{sub 3}, and Al{sub 2}O{sub 3}. Transmission electron microscopy and X-ray and electron diffraction reveal that SrCuO{sub 2} crystallites with a size of 100–200 nm are precipitated in the glass-ceramics. The highness of the thermal conductivity is attributable to two sources: one is elongation of phonon mean free path due to the crystallization of the inhomogeneous structure or structural ordering. The other is emergence of the heat carriers, spinons, in the SrCuO{sub 2}. This highly thermal conductive glass-ceramics is expected to be utilized as base materials for heat-flow control devices.
Low-temperature formation of high-quality gate oxide by ultraviolet irradiation on spin-on-glass
Usuda, R.; Uchida, K.; Nozaki, S.
2015-11-02
Although a UV cure was found to effectively convert a perhydropolysilazane (PHPS) spin-on-glass film into a dense SiO{sub x} film at low temperature, the electrical characteristics were never reported in order to recommend the use of PHPS as a gate-oxide material that can be formed at low temperature. We have formed a high-quality gate oxide by UV irradiation on the PHPS film, and obtained an interface midgap trap density of 3.4 × 10{sup 11 }cm{sup −2} eV{sup −1} by the UV wet oxidation and UV post-metallization annealing (PMA), at a temperature as low as 160 °C. In contrast to the UV irradiation using short-wavelength UV light, which is well known to enhance oxidation by the production of the excited states of oxygen, the UV irradiation was carried out using longer-wavelength UV light from a metal halide lamp. The UV irradiation during the wet oxidation of the PHPS film generates electron-hole pairs. The electrons ionize the H{sub 2}O molecules and facilitate dissociation of the molecules into H and OH{sup −}. The OH{sup −} ions are highly reactive with Si and improve the stoichiometry of the oxide. The UV irradiation during the PMA excites the electrons from the accumulation layer, and the built-in electric field makes the electron injection into the oxide much easier. The electrons injected into the oxide recombine with the trapped holes, which have caused a large negative flat band voltage shift after the UV wet oxidation, and also ionize the H{sub 2}O molecules. The ionization results in the electron stimulated dissociation of H{sub 2}O molecules and the decreased interface trap density.
Low-temperature formation of high-quality gate oxide by ultraviolet irradiation on spin-on-glass
NASA Astrophysics Data System (ADS)
Usuda, R.; Uchida, K.; Nozaki, S.
2015-11-01
Although a UV cure was found to effectively convert a perhydropolysilazane (PHPS) spin-on-glass film into a dense SiOx film at low temperature, the electrical characteristics were never reported in order to recommend the use of PHPS as a gate-oxide material that can be formed at low temperature. We have formed a high-quality gate oxide by UV irradiation on the PHPS film, and obtained an interface midgap trap density of 3.4 × 1011 cm-2 eV-1 by the UV wet oxidation and UV post-metallization annealing (PMA), at a temperature as low as 160 °C. In contrast to the UV irradiation using short-wavelength UV light, which is well known to enhance oxidation by the production of the excited states of oxygen, the UV irradiation was carried out using longer-wavelength UV light from a metal halide lamp. The UV irradiation during the wet oxidation of the PHPS film generates electron-hole pairs. The electrons ionize the H2O molecules and facilitate dissociation of the molecules into H and OH-. The OH- ions are highly reactive with Si and improve the stoichiometry of the oxide. The UV irradiation during the PMA excites the electrons from the accumulation layer, and the built-in electric field makes the electron injection into the oxide much easier. The electrons injected into the oxide recombine with the trapped holes, which have caused a large negative flat band voltage shift after the UV wet oxidation, and also ionize the H2O molecules. The ionization results in the electron stimulated dissociation of H2O molecules and the decreased interface trap density.
Oxygen miscibility gap and spin glass formation in the pyrochlore Lu{sub 2}Mo{sub 2}O{sub 7}
Clark, L.; Ritter, C.; Harrison, A.; Attfield, J.P.
2013-07-15
Rare earth (R) molybdate pyrochlores, R{sub 2}Mo{sub 2}O{sub 7}, are of interest as frustrated magnets. Polycrystalline samples of Lu{sub 2}Mo{sub 2}O{sub 7−x} prepared at 1600 °C display a coexistence of cubic pyrochlore phases. Rietveld fits to powder neutron diffraction data and chemical analyses show that the miscibility gap is between a stoichiometric x=0 and an oxygen-deficient x≈0.4 phase. Lu{sub 2}Mo{sub 2}O{sub 7} behaves as a spin glass material, with a divergence of field cooled and zero field cooled DC magnetic susceptibilities at a spin freezing temperature T{sub f}=16 K, that varies with frequency in AC measurements following a Vogel–Fulcher law. Lu{sub 2}Mo{sub 2}O{sub 6.6} is more highly frustrated spin glass and has T{sub f}=20 K. - Graphical abstract: The cubic Lu{sub 2}Mo{sub 2}O{sub 7−x} system exhibits a miscibility gap between coexisting pyrochlore phases at 1600 °C. Neutron powder diffraction refinement and chemical analysis shows that the gap separates stoichiometric x=0 and oxygen-deficient x≈0.4 phases. Lu{sub 2}Mo{sub 2}O{sub 7−x} has a frustrated spin glass ground state that is sensitive to the oxygen content. - Highlights: • The cubic Lu{sub 2}Mo{sub 2}O{sub 7−x} system has a miscibility gap between coexisting pyrochlore phases at 1600 °C. • Neutron powder diffraction shows that the gap separates x=0 and oxygen-deficient x≈0.4 phases. • Lu{sub 2}Mo{sub 2}O{sub 7−x} has a frustrated spin glass ground state that is sensitive to the oxygen content.
Aging, rejuvenation, and memory effects in short-range Ising spin glass: Cu_0.5Co_0.5Cl_2-FeCl3 GBIC
NASA Astrophysics Data System (ADS)
Suzuki, M.; Suzuki, I. S.
2004-03-01
Cu_0.5Co_0.5Cl_2-FeCl3 GBIC undergoes a spin glass (SG) transition at Tg (= 3.92 ± 0.11 K). The system shows a dynamic behavior that has some similarities and some significant differences compared to a 3D Ising SG.^1 Here we report on non-equilibrium aging dynamics which has been studied using zero-field cooled (ZFC) magnetization and low frequency AC magnetic susceptibility.^2 The time dependence of the relaxation rate S(t) = (1/H)dM_ZFC/dln t for the ZFC magnetization after the ZFC aging protocol, shows a peak at a characteristic time t_cr near a wait time t_w, corresponding to a crossover from quasi equilibrium dynamics to non-equilibrium. The time t_cr strongly depends on t_w, temperature, magnetic field, and the temperature shift. The rejuvenation effect is observed in both i^' and i^'' under the T-shift and H-shift procedures. The memory of the specific spin configurations imprinted during the ZFC aging protocol can be recalled when the system is re-heated at a constant heating rate. The aging, rejuvenation, and memory effects are discussed in terms of the scaling concepts derived from numerical studies on 3D Edwards-Anderson spin glass model. 1. I.S. Suzuki and M. Suzuki, Phys. Rev. B 68, 094424 (2003) 2. M. Suzuki and I.S. Suzuki, cond-mat/0308285
Reentrant network formation in patchy colloidal mixtures under gravity
NASA Astrophysics Data System (ADS)
de las Heras, Daniel; Treffenstädt, Lucas L.; Schmidt, Matthias
2016-03-01
We study a two-dimensional binary mixture of patchy colloids in sedimentation-diffusion equilibrium using Monte Carlo simulation and Wertheim's theory. By tuning the buoyant masses of the colloids we can control the gravity-induced sequence of fluid stacks of differing density and percolation properties. We find complex stacking sequences with up to four layers and reentrant network formation, consistently in simulations and theoretically using only the bulk phase diagram as input. Our theory applies to general patchy colloidal mixtures and is relevant to understanding experiments under gravity.
Benjamin Michael Meyer
2003-05-31
As time progresses, the world is using up more of the planet's natural resources. Without technological advances, the day will eventually arrive when these natural resources will no longer be sufficient to supply all of the energy needs. As a result, society is seeing a push for the development of alternative fuel sources such as wind power, solar power, fuel cells, and etc. These pursuits are even occurring in the state of Iowa with increasing social pressure to incorporate larger percentages of ethanol in gasoline. Consumers are increasingly demanding that energy sources be more powerful, more durable, and, ultimately, more cost efficient. Fast Ionic Conducting (FIC) glasses are a material that offers great potential for the development of new batteries and/or fuel cells to help inspire the energy density of battery power supplies. This dissertation probes the mechanisms by which ions conduct in these glasses. A variety of different experimental techniques give a better understanding of the interesting materials science taking place within these systems. This dissertation discusses Nuclear Magnetic Resonance (NMR) techniques performed on FIC glasses over the past few years. These NMR results have been complimented with other measurement techniques, primarily impedance spectroscopy, to develop models that describe the mechanisms by which ionic conduction takes place and the dependence of the ion dynamics on the local structure of the glass. The aim of these measurements was to probe the cause of a non-Arrhenius behavior of the conductivity which has been seen at high temperatures in the silver thio-borosilicate glasses. One aspect that will be addressed is if this behavior is unique to silver containing fast ion conducting glasses. more specifically, this study will determine if a non-Arrhenius correlation time, {tau}, can be observed in the Nuclear Spin Lattice Relaxation (NSLR) measurements. If so, then can this behavior be modeled with a new single distribution
NASA Astrophysics Data System (ADS)
Harikrishnan, S.; Naveen Kumar, C. M.; Bhat, H. L.; Elizabeth, Suja; Rößler, U. K.; Dörr, K.; Rößler, S.; Wirth, S.
2008-07-01
Single crystals of Dy0.5Sr0.5MnO3 are grown using the optical floating zone technique, and their structural, magnetic, transport and thermal properties have been investigated. Magnetization measurements under field-cooled and zero-field-cooled conditions display irreversibility below 35 K. The magnetization does not saturate up to fields of 5 T in the temperature range 5-350 K. AC susceptibility shows a cusp around 32 K that shifts to higher temperature with increasing frequency. This frequency dependence of the peak temperature follows a critical slowing down with exponent zν = 3.6. Electrical resistivity shows insulating behavior, and the application of magnetic fields up to 10 T does not change this qualitative behavior. However, a marked negative magnetoresistance is observed in the paramagnetic phase reaching 80% at 70 K and 10 T. The observed resistivity behavior does not obey an activated type of conduction. These features are characteristic of spin-glass behavior in this half-doped insulating manganite. It is argued that the spin-glass-like state originates from the A-site disorder, which in turn results from the random distribution of cations with different ionic radii. Specific-heat measurements reveal a sizable linear contribution at low temperature that may be associated with the glassy magnetic ordering and a Schottky-like anomaly in a wide temperature range between 8 and 40 K. The distribution of Schottky levels is explained by the inhomogeneity of the molecular field in the spin-glass state that leads to variable splitting of the Kramers ground-state doublets in Dy3+.
Ehlers, Georg; Gardner, Jason; Qiu, Y.; Rule, K; Greedan, John E; Stewart, John Ross; Fouquet, Peter; Cornelius, A. L.; Adriano, Cris; Pagliuso, P G
2010-01-01
Neutron scattering, muon spin relaxation, and de susceptibility studies have been carried out on polycrystalline Tb{sub 2}Ti{sub 2}O{sub 7}, a pyrochlore antiferromagnet in which the Tb{sup 3+} moments reside on a network of corner-sharing tetrahedra. Unlike other geometrically frustrated systems, Tb{sub 2}Ti{sub 2}O{sub 7} remains paramagnetic down to {approx}0.07 K, rather than ordering into a conventional Neel or spin-glass-like state, despite the fact that short-range antiferromagnetic correlations (AFC) develop at {approx}50 K. At the first AFC wave vector, its low-lying, relatively flat magnetic excitation spectrum softens partially below 30 K.
Spin glass behavior in a highly oxygen deficient Perovskite BaBiO.28Co0.72O2.2
Klimczuk, Thomasz W; Zandbergen, H; Huang, Q; Mcqueen, T
2008-01-01
A highly oxygen deficient perovskite, BaBio.28Coo.n02.2, was synthesized by solid state reaction. The crystal structure was determined by neutron and x-ray powder diffraction. The material exhlbits semiconducting behavior with an energy gap of 1.8 eV. Magnetic susceptibility studies reveal spin-glass ordering, which may have its origin in the frustration caused by the presence of competing antiferromagnetic and ferromagnetic interactions. The electron diffraction study shows the existence of short range ordering in thls phase.
Spin glass in semiconducting KFe_{1.05}Ag_{0.88}Te_{2} single crystals
Ryu, H.; Lei, H.; Klobes, B.; Warren, J. B.; Hermann, R. P.; Petrovic, C.
2015-05-26
We report discovery of KFe_{1.05}Ag_{0.88}Te_{2} single crystals with semiconducting spin glass ground state. Composition and structure analysis suggest nearly stoichiometric I4/mmm space group but allow for the existence of vacancies, absent in long range semiconducting antiferromagnet KFe_{1.05}Ag_{0.88}Te_{2}. The subtle change in stoichometry in Fe/Ag sublattice changes magnetic ground state but not conductivity, giving further insight into the semiconducting gap mechanism.
Depletion, melting and reentrant solidification in mixtures of soft and hard colloids.
Marzi, Daniela; Capone, Barbara; Marakis, John; Merola, Maria Consiglia; Truzzolillo, Domenico; Cipelletti, Luca; Moingeon, Firmin; Gauthier, Mario; Vlassopoulos, Dimitris; Likos, Christos N; Camargo, Manuel
2015-11-14
We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft-hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star-polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid-polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft-hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures. PMID:26356800
Spin-glass behavior of Sn0.9Fe3.1N: An experimental and quantum-theoretical study
NASA Astrophysics Data System (ADS)
Scholz, Tanja; Dronskowski, Richard
2016-05-01
Based on comprehensive experimental and quantum-theoretical investigations, we identify Sn0.9Fe3.1N as a canonical spin glass and the first ternary iron nitride with a frustrated spin ground state. Sn0.9Fe3.1N is the end member of the solid solution SnxFe4-xN (0 < x ≤ 0.9) derived from ferromagnetic γ'-Fe4N. Within the solid solution, the gradual incorporation of tin is accompanied by a drastic weakening of the ferromagnetic interactions. To explore the dilution of the ferromagnetic coupling, the highly tin-substituted Sn0.9Fe3.1N has been magnetically reinvestigated. DC magnetometry reveals diverging susceptibilities for FC and ZFC measurements at low temperatures and an unsaturated hysteretic loop even at high magnetic fields. The temperature dependence of the real component of the AC susceptibility at different frequencies proves the spin-glass transition with the characteristic parameters Tg = 12.83(6) K, τ* = 10-11.8(2) s, zv = 5.6(1) and ΔTm/(Tm ṡ Δlgω) = 0.015. The time-dependent response of the magnetic spins to the external field has been studied by extracting the distribution function of relaxation times g(τ, T) up to Tg from the complex plane of AC susceptibilities. The weakening of the ferromagnetic coupling by substituting tin into γ'-Fe4N is explained by the Stoner criterion on the basis of electronic structure calculations and a quantum-theoretical bonding analysis.
NASA Astrophysics Data System (ADS)
Kirkpatrick, Scott
The 1975 EA paper by Sam Edwards and Phil Anderson proposed to understand a class of real materials as frustrated, glassy magnets with a novel type of weak order in time. It launched an exciting period of intense exploration of new directions for understanding random and composite materials. This work has had a lasting impact well beyond materials science, contributing powerful new methods for optimization of complex many-parameter systems as well as codes offering Shannon-bounded communications in extremely noisy channels.
Performance of a reentrant cavity beam position monitor
NASA Astrophysics Data System (ADS)
Simon, Claire; Luong, Michel; Chel, Stéphane; Napoly, Olivier; Novo, Jorge; Roudier, Dominique; Rouvière, Nelly; Baboi, Nicoleta; Mildner, Nils; Nölle, Dirk
2008-08-01
The beam-based alignment and feedback systems, essential operations for the future colliders, require high resolution beam position monitors (BPMs). In the framework of the European CARE/SRF program, a reentrant cavity BPM with its associated electronics was developed by the CEA/DSM/Irfu in collaboration with DESY. The design, the fabrication, and the beam test of this monitor are detailed within this paper. This BPM is designed to be inserted in a cryomodule, work at cryogenic temperature in a clean environment. It has achieved a resolution better than 10μm and has the possibility to perform bunch to bunch measurements for the x-ray free electron laser (X-FEL) and the International Linear Collider (ILC). Its other features are a small size of the rf cavity, a large aperture (78 mm), and an excellent linearity. A first prototype of a reentrant cavity BPM was installed in the free electron laser in Hamburg (FLASH), at Deutsches Elektronen-Synchrotron (DESY) and demonstrated its operation at cryogenic temperature inside a cryomodule. The second, installed, also, in the FLASH linac to be tested with beam, measured a resolution of approximately 4μm over a dynamic range ±5mm in single bunch.
Elucidating Nonwetting of Re-Entrant Surfaces with Impinging Droplets.
Zhang, Bo; Zhang, Xianren
2015-09-01
Superomniphobic surfaces display both superoleophobic and superhydrophobic properties, having a contact angle greater than 150° for both water and oil droplets. In this work, lattice Boltzmann simulations on droplets impacting the surface textures of various topologies are performed to understand the mechanism of how the superomniphobic properties can be achieved by optimizing the geometry of re-entrant surfaces and the inherent hydrophobicity of substrates. Detailed kinetics for droplet impinging is analyzed for both liquid impalement and emptying, showing distinct dependences on geometrical details of re-entrant surfaces. The origins of the enhanced stability of Cassie states are ascribed to (i) the barrier of the Cassie-to-Wenzel transition for the impalement process, (ii) the driving force for liquid receding in the emptying process, and (iii) the contact line pinning from the entrance effect and the edge effect. Finally, we check the strategies proposed here by designing a new re-entrance structure that possesses an excellent property in maintaining the droplet Cassie state. PMID:26270084
Mangalam, R.V.K.; Sundaresan, A.
2009-03-05
The ferromagnetic metallic oxide, SrRuO{sub 3} (T{sub C} {approx} 165 K) undergoes structural, magnetic and metal-insulator transitions upon substitution of Cu at the Ru-site. For x = 0.2 in SrRu{sub 1-x}Cu{sub x}O{sub 3}, the structure becomes a tetragonal with the space group I4/mcm and there is a signature of both ferromagnetic (T{sub C} = 65 K) and antiferromagnetic (T{sub N} = 32 K) ordering due to possible magnetic phase separation. The antiferromagnetism arises due to short range ordering of Cu- and Ru-moments. Jahn-Teller distortion of (Ru,Cu)-O{sub 6} octahedra indicates that the copper ions are in 2+ oxidation state with t{sub 2g}{sup 6}e{sub g}{sup 3} electronic configuration. For x {>=} 0.1, narrowing of Ru-4d bandwidth by the substitution of Cu ions results in semiconducting behavior. For x = 0.3, the ac and dc susceptibility measurements indicate a spin glass behavior. The origin of spin glass behavior has been attributed to competing ferromagnetic and antiferromagnetic interactions.
Structural chemistry and spin-glass behaviour of Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39}
Thammajak, Nirawat; Battle, Peter D.; Grandjean, Fernande; Long, Gary J.; Ramos, Silvia
2012-03-15
Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39} has been synthesised and characterised by neutron powder diffraction, X-ray absorption spectroscopy, Moessbauer spectroscopy and magnetometry. The cubic structure (Pm3-bar n, a=11.97227(8) A) is based on intersecting Left-Pointing-Angle-Bracket 1 1 1 Right-Pointing-Angle-Bracket chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a Nd-O framework. The larger of the two crystallographically distinct octahedral sites, 8e, is occupied by iron, titanium and lithium in a ratio of 76:20:4; the smaller, 2a, is occupied by iron and titanium in a ratio of 79:21. The trigonal-prismatic site, 16i, is occupied by lithium and iron in a ratio of 98:2. The cations on the 2a sites are assigned as Ti{sup 4+}and low-spin Fe{sup 4+}, and those on the 16i sites as Li{sup +} and Fe{sup 3+}. The 8e sites are thought to be occupied by Li{sup +}, Fe{sup 3+} and Ti{sup 3+}. Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39} undergoes a transition to a spin-glass state at 4.25(5) K. - Graphical abstract: Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39} undergoes a transition to a spin-glass state at 4.25(5) K. Highlights: Black-Right-Pointing-Pointer Spin-glass behaviour in Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39} below 4.25 K. Black-Right-Pointing-Pointer Application of X-ray absorption spectroscopy to a complex mixed-metal oxide. Black-Right-Pointing-Pointer Mixed-valence cations in Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39}.
Collapse of Ferromagnetism and Fermi Surface Instability near Reentrant Superconductivity of URhGe.
Gourgout, A; Pourret, A; Knebel, G; Aoki, D; Seyfarth, G; Flouquet, J
2016-07-22
We present thermoelectric power and resistivity measurements in the ferromagnetic superconductor URhGe for a magnetic field applied along the hard magnetization b axis of the orthorhombic crystal. Reentrant superconductivity is observed near the spin reorientation transition at H_{R}=12.75 T, where a first order transition from the ferromagnetic to the polarized paramagnetic state occurs. Special focus is given to the longitudinal configuration, where both the electric and heat current are parallel to the applied field. The validity of the Fermi-liquid T^{2} dependence of the resistivity through H_{R} demonstrates clearly that no quantum critical point occurs at H_{R}. Thus, the ferromagnetic transition line at H_{R} becomes first order implying the existence of a tricritical point at finite temperature. The enhancement of magnetic fluctuations in the vicinity of the tricritical point stimulates the reentrance of superconductivity. The abrupt sign change observed in the thermoelectric power with the thermal gradient applied along the b axis together with the strong anomalies in the other directions is definitive macroscopic evidence that in addition a significant change of the Fermi surface appears through H_{R}. PMID:27494485
Collapse of Ferromagnetism and Fermi Surface Instability near Reentrant Superconductivity of URhGe
NASA Astrophysics Data System (ADS)
Gourgout, A.; Pourret, A.; Knebel, G.; Aoki, D.; Seyfarth, G.; Flouquet, J.
2016-07-01
We present thermoelectric power and resistivity measurements in the ferromagnetic superconductor URhGe for a magnetic field applied along the hard magnetization b axis of the orthorhombic crystal. Reentrant superconductivity is observed near the spin reorientation transition at HR=12.75 T , where a first order transition from the ferromagnetic to the polarized paramagnetic state occurs. Special focus is given to the longitudinal configuration, where both the electric and heat current are parallel to the applied field. The validity of the Fermi-liquid T2 dependence of the resistivity through HR demonstrates clearly that no quantum critical point occurs at HR. Thus, the ferromagnetic transition line at HR becomes first order implying the existence of a tricritical point at finite temperature. The enhancement of magnetic fluctuations in the vicinity of the tricritical point stimulates the reentrance of superconductivity. The abrupt sign change observed in the thermoelectric power with the thermal gradient applied along the b axis together with the strong anomalies in the other directions is definitive macroscopic evidence that in addition a significant change of the Fermi surface appears through HR.
Reentrant melting of a classical two-dimensional binary cluster
Nelissen, K.; Partoens, B.; Peeters, F.M.; Schweigert, I.
2005-10-31
A system of classical charged particles interacting through a dipole repulsive potential, which are confined in a two-dimensional hardwall trap, is studied. The cluster consists of 16 particles, together with 4 defect particles. The technique of Brownian dynamics is used to simulate experimental binary colloidal systems. The melting properties and the reentrant behavior of the system, which was studied before for clusters of identical particles, are studied for the binary mixture. The defect particles, which have a smaller charge than the other particles, stabilize the cluster, melt at a higher value of the coupling parameter {gamma} as compared to the other particles and have a strong influence on the melting properties of the other particles.
Reentrant ac Magnetic Susceptibility in Josephson-Junction Arrays
Araujo-Moreira, F.M.; Barbara, P.; Cawthorne, A.B.; Lobb, C.J.
1997-06-01
We have measured the complex ac magnetic susceptibility of unshunted Josephson-junction arrays as a function of temperature T , amplitude of the excitation field h{sub ac} , and external magnetic field H{sub dc} . For small h{sub ac} Meissner screening occurs. For larger h{sub ac} , however, the screening is reentrant in T . This reentrance is not thermodynamic but dynamic and arises from the paramagnetic contribution of multijunction loops. This result gives an alternative explanation of the paramagnetic Meissner effect observed in granular superconductors. Experimental results are in agreement with a simplified model based on a single loop containing four junctions. {copyright} {ital 1997} {ital The American Physical Society}
Birgeneau, R.J.; Belk, N.; Kastner, M.A.; Keimer, B. . Dept. of Physics); Endoh, Y. . Dept. of Physics); Erwin, R.W. ); Shirane, G. )
1991-01-01
We review the results of neutron scattering studies of the static and dynamic spin fluctuations crystals of La{sub 2-x}Sr{sub x}CuO{sub 4+{delta}} in the doping regime intermediate between the Neel and superconducting regions. In this regime the in-plane resistance is linear in temperature down to {approximately}80 K with a crossover due to logarithmic conductance effects at lower temperatures. The static spin correlations are well-described by a simple model in which the inverse correlation length {kappa}(x,T) ={kappa}(x,0) + {kappa}(0,T). The most dramatic new result is the discovery by Keimer et al. that the dynamic spin fluctuations exhibit a temperature dependence which is a simple function of {omega}/T for temperatures 10 K{le}T{le}500 K for a wide range of energies. This scaling leads to a natural explanation of a variety of normal state properties of the copper oxides. 21 refs., 4 figs.
NASA Astrophysics Data System (ADS)
Carneiro, V. H.; Puga, H.; Meireles, J.
2015-11-01
Materials with a negative Poisson's ratio (PR) are called auxetics; they are characterized by expansion/contraction when tensioned/compressed. Given this counterintuitive behavior, they present very particular characteristics and mechanical behavior. Geometrical models have been developed to justify and artificially reproduce such materials' auxetic behavior. The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters. It is shown that, even in the presence of protruding ribs, there may not be auxetic behavior, and this depends on the geometry of each reentrant structure. Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.
NASA Astrophysics Data System (ADS)
Carneiro, V. H.; Puga, H.; Meireles, J.
2016-04-01
Materials with a negative Poisson's ratio (PR) are called auxetics; they are characterized by expansion/contraction when tensioned/compressed. Given this counterintuitive behavior, they present very particular characteristics and mechanical behavior. Geometrical models have been developed to justify and artificially reproduce such materials' auxetic behavior. The focus of this study is the exploration of a reentrant model by analyzing the variation in the PR of reentrant structures as a function of geometrical and base material parameters. It is shown that, even in the presence of protruding ribs, there may not be auxetic behavior, and this depends on the geometry of each reentrant structure. Values determined for these parameters can be helpful as approximate reference data in the design and fabrication of auxetic lattices using reentrant geometries.
Upadhyay, Sanjay Kumar; Iyer, Kartik K.; Rayaprol, S.; Paulose, P. L.; Sampathkumaran, E. V.
2016-01-01
The area of research to discover new Li containing materials and to understand their physical properties has been of constant interest due to applications potential for rechargeable batteries. Here, we present the results of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to be a ferrimagnet below 80 K. While our neutron diffraction (ND) and isothermal magnetization (M) data support ferrimagnetism, more detailed magnetic studies establish that this ferrimagnetic phase exhibits some features similar to spin-glasses. In addition, we find another broad magnetic anomaly around 40–55 K in magnetic susceptibility (χ), attributable to cluster spin-glass phenomenon. Gradual dominance of cluster spin-glass dynamics with a decrease of temperature (T) and the apparent spread in freezing temperature suggest that the ferrimagnetism of this compound is a chaotic one. The absence of a unique freezing temperature for a crystalline material is interesting. In addition, pyroelectric current (Ipyro) data reveals a feature in the range 40–50 K, attributable to thermally stimulated depolarization current. We hope this finding motivates future work to explore whether there is any intriguing correlation of such a feature with cluster spin-glass dynamics. We attribute these magnetic and electric dipole anomalies to the crystallographic disorder, intrinsic to this compound. PMID:27545439
Upadhyay, Sanjay Kumar; Iyer, Kartik K; Rayaprol, S; Paulose, P L; Sampathkumaran, E V
2016-01-01
The area of research to discover new Li containing materials and to understand their physical properties has been of constant interest due to applications potential for rechargeable batteries. Here, we present the results of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to be a ferrimagnet below 80 K. While our neutron diffraction (ND) and isothermal magnetization (M) data support ferrimagnetism, more detailed magnetic studies establish that this ferrimagnetic phase exhibits some features similar to spin-glasses. In addition, we find another broad magnetic anomaly around 40-55 K in magnetic susceptibility (χ), attributable to cluster spin-glass phenomenon. Gradual dominance of cluster spin-glass dynamics with a decrease of temperature (T) and the apparent spread in freezing temperature suggest that the ferrimagnetism of this compound is a chaotic one. The absence of a unique freezing temperature for a crystalline material is interesting. In addition, pyroelectric current (Ipyro) data reveals a feature in the range 40-50 K, attributable to thermally stimulated depolarization current. We hope this finding motivates future work to explore whether there is any intriguing correlation of such a feature with cluster spin-glass dynamics. We attribute these magnetic and electric dipole anomalies to the crystallographic disorder, intrinsic to this compound. PMID:27545439
An Investigation of the Spin Glass Properties of the Solid Solution CuAl2-2xGa2xO4
NASA Astrophysics Data System (ADS)
Bullard, Thomas; Brant, Jacilynn; Ebbing, Charles; Dilley, Neil; Hamilton, J.; Haugan, Timothy
The complete anti-ferromagnetic oxide spinel solid solution between end members CuAl2O4 and CuGa2O4 has been synthesized. The crystallographic and magnetic properties are examined as Ga is replaced with iso-valent Al. Crystallographic results show the solid solution obeys Vegard's law, and the cation distribution among the tetrahedral and octahedral sites matches well with prior results. The evolution of the magnetic susceptibility is examined as a function of temperature and doping percentage. Evidence is presented that indicates that the majority of the solution displays paramagnetic behaviour at high temperatures and spin glass behaviour below 3K. Specifically, a freezing temperature in the AC susceptibility, irreversibility in the DC magnetization, and relaxation dynamics in the presence of a changing applied field are observed.
Spin-glass behavior and pyroelectric anomalies in a new lithium-based oxide, Li3FeRuO5.
Upadhyay, Sanjay Kumar; Paulose, P L; Iyer, Kartik K; Sampathkumaran, E V
2016-08-17
The results of dc and ac magnetization, heat capacity, (57)Fe Mössbauer spectroscopy, dielectric, pyroelectric current and isothermal magneto-capacitance measurements of a recently reported lithium-rich layered oxide, Li3FeRuO5, related to LiCoO2-type (rhombohedral, space group R3[combining macron]m), are presented. The results reveal that the compound undergoes spin-glass freezing at 15 K. There is a peak around 34 K in pyroelectric data, which cannot be attributed to ferroelectricity, but to the phenomenon of thermally stimulated depolarization current. As revealed by magnetocapacitance data above and below the magnetic ordering temperature, magnetic and electric dipoles appear to be coupled, thereby offering evidence for magnetodielectric coupling. PMID:27498689
Insulating and metallic spin glass in KxFe2-δ-yNiySe2 (0.06 ≤ y ≤ 1.44 ) single crystals
Ryu, Hyejin; Abeykoon, Milinda; Wang, Kefeng; Lei, Hechang; Lazarevic, N.; Warren, J. B.; Bozin, E. S.; Popovic, Z. V.; Petrovic, C.
2015-05-04
We report electron doping effects by Ni in KxFe2-δ-yNiySe₂ (0.06 ≤ y ≤ 1.44) single crystal alloys. A rich ground state phase diagram is observed. Thus, a small amount of Ni (~ 4%) suppressed superconductivity below 1.8 K, inducing insulating spin glass magnetic ground state for higher Ni content. With further Ni substitution, metallic resistivity is restored. For high Ni concentration in the lattice the unit cell symmetry is high symmetry I4/mmm with no phase separation whereas both I4/m + I4/mmm space groups were detected in the phase separated crystals when concentration of Ni < Fe. The absence of superconductivitymore » coincides with the absence of crystalline Fe vacancy order.« less
Tlili, M.T.; Bejar, M.; Dhahri, E.; Sajieddine, M.; Valente, M.A.; Hlil, E.K.
2011-02-15
AMn{sub 1-x}Fe{sub x}O{sub 3} (A = La{sub 0.75}Ca{sub 0.08}Sr{sub 0.17} and x = 0-0.23) compounds, sintered at 700 deg. C, were characterized by X-ray diffraction (XRD) at room temperature. Rietveld refinement has shown that samples can be indexed in the orthorhombic (Pnma) structure for low Fe-content (x {<=} 0.046) and rhombohedral (R-3c) structure for high Fe-content (x {>=} 0.115). The transmission Moessbauer spectra have revealed the same isomer shift {delta} value assigned to Fe{sup 3+} ion for all compounds. The magnetization behavior and the Curie temperature T{sub C} have shown a large dependence on the fractional composition x. In fact, the M(T) curves have revealed the presence of a long-range ferromagnetic state below T{sub C} for compounds with x {<=} 0.115, and a spin-glass state (SGS) at low temperature for high Fe-content (x {>=} 0.177). Research Highlights: {yields} La{sub 0.75}Ca{sub 0.08}Sr{sub 0.17}Mn{sub 1-x}Fe{sub x}O{sub 3} compounds undergo a transition ortho-rhombo at x=0.046. {yields} On the rhombohedral phase, the magnetization is governed by the DE interaction {yields} The magnetization undergoes a strong decrease at high x-values (x{>=}0.115). {yields} Compounds show a strong AFM interaction with a spin-glass state at high Fe-content {yields} Hysteresis loops, M(H) confirm this behavior.
Muon Spin Relaxation and Neutron Diffraction Studies of Cluster-Glass States in Sr1‑xLaxRuO3
NASA Astrophysics Data System (ADS)
Kawasaki, Ikuto; Fujimura, Kenji; Watanabe, Isao; Avdeev, Maxim; Tenya, Kenichi; Yokoyama, Makoto
2016-05-01
To clarify the magnetic properties of cluster-glass states in Sr1-xLaxRuO3 (0.3 <= x <= 0.5), we report herein the results of muon spin relaxation (muSR) and neutron powder diffraction measurements. The muSR experiments showed that magnetic clusters start developing well above the peak temperature T^* in the ac susceptibility. The volume fraction of the magnetically ordered region increases continuously with decreasing temperature, showing no anomaly at T^*, and reaches nearly 100% at the lowest temperature. The temperature variation of the volume fraction is essentially independent of the La concentration in the x range presently investigated, although the dc magnetization is significantly suppressed with increasing x. Neutron powder diffraction experiments revealed that the ground state for x = 0.3 is a long-range ferromagnetic ordered state. These results indicate that, with decreasing temperature, cluster-glass states in Sr1-xLaxRuO3 gradually develop into long-range ferromagnetic ordered states with decreasing temperature, and that the magnetic ordering process differs strikingly from that expected for a conventional second-order ferromagnetic transition.
Sen, Sabyasachi; Kaseman, Derrick C; Hung, Ivan; Gan, Zhehong
2015-04-30
The mechanism of (77)Se nuclear spin-lattice relaxation is investigated in binary Ge-Se glasses. The (77)Se nuclides in Se-Se-Se chain sites relax faster via dipolar coupling fluctuation compared to those in Ge-Se-Ge sites shared by GeSe4 tetrahedra that relax slower via the fluctuation of the chemical shift anisotropy. The relaxation rate for the Se-Se-Se sites decreases markedly with increasing magnetic field, whereas that for the Ge-Se-Ge sites displays no appreciable dependence on the magnetic field such that the extent of differential relaxation between the two Se environments becomes small at high fields on the order of 19.6 T. The corresponding dynamical correlation time is three orders of magnitude shorter (∼10(-9) s) for the Se-Se-Se sites, compared to that for the Ge-Se-Ge sites (∼10(-6) s). The large decoupling in the time scale between these Se environments provides direct experimental support to the commonly made assumption that the selenium chains are mechanically floppy, and the interconnected GeSe4 tetrahedra form the rigid elements in the selenide glass structure. PMID:25848959
Origin of spin-glass and exchange bias in La1/3Sr2/3FeO3-γ nanoparticles
NASA Astrophysics Data System (ADS)
da Silva, R. B.; de Araújo, J. H.; Soares, J. M.; Machado, F. L. A.
2014-03-01
The structure and the magnetic properties of nanopowdered samples of La1/3Sr2/3FeO3-γ with average particles size d in the range of 67-367 nm prepared by a sol-gel method were investigated in detail. The samples were characterized by X-ray diffraction, scanning electron microscopy, specific heat, Mössbauer spectroscopy, ac susceptibility, and magnetization measurements. Exchange bias with vertical magnetization shift was found in all samples. Charge ordering and antiferromagnetism were observed close to 200 K for large particles (d ≥ 304 nm) samples, while for particles with intermediated and smaller values (d ≤ 156 nm) a cluster-glass like behaviour and a short range charge ordering were seen near 115 K and 200 K, respectively. The spin-glass like and exchange bias behaviour in nanopowdered samples of La1/3Sr2/3FeO3-γ are associated to compact Fe3+ antiferromagnetic (AF) clusters caused by an oxygen deficiency, which was found to be higher in the samples with the smallest average particles sizes. The effect of exchange bias and vertical magnetization shifts are explained by a simple model involving the interaction of one AF phase with a canted AF phase.
Signatures of spin-glass behaviour in PrIr2B2 and heavy fermion behaviour in PrIr2B2C.
Anupam; Anand, V K; Hossain, Z; Adroja, D T; Geibel, C
2011-09-21
The magnetic and transport properties of PrIr(2)B(2) and PrIr(2)B(2)C have been investigated by dc and ac magnetic susceptibility, specific heat, electrical resistivity and magnetoresistance measurements. PrIr(2)B(2) forms in CaRh(2)B(2)-type orthorhombic crystal structure (space group Fddd). At low fields the dc magnetic susceptibility of PrIr(2)B(2) exhibits a sharp anomaly near 46 K which is followed by an abrupt increase below 10 K with a peak at 6 K, and split-up in ZFC and FC data below 46 K. In contrast, the specific heat exhibits only a broad Schottky type hump near 9 K which indicates that there is no long range magnetic order in this compound. The thermo-remanent magnetization is found to decay very slowly with a mean relaxation time τ = 3917 s. An ac magnetic susceptibility measurement also observes two sharp anomalies; the peak positions strongly depend on the frequency and shift towards high temperature with an increase in frequency, obeying the Vogel-Fulcher law as expected for a canonical spin-glass system. The two spin-glass transitions occur at freezing temperatures T(f1) = 36 K and T(f2) = 3.5 K with shifts in the freezing temperatures per decade of frequency δT(f1) = 0.044 and δT(f2) = 0.09. An analysis of the frequency dependence of the transition temperature with critical slowing down, τ(max)/τ(0) = [(T(f)-T(SG))/T(SG)](-zν), gives τ(0) = 10(-7) s and exponent zν = 8, and the Vogel-Fulcher law gives an activation energy of 84 K for T(f1) and 27.5 K for T(f2). While zν = 8 is typical for spin-glass system, the characteristic relaxation time τ(0) = 10(-7) s is very large and comparable to that of superspin-glass systems. An addition of C in PrIr(2)B(2) leads to PrIr(2)B(2)C which forms in LuNi(2)B(2)C-type tetragonal structure (space group I4/mmm) and remains paramagnetic down to 2 K. The specific heat data show a broad Schottky type anomaly, which could be fairly reproduced with CEF analysis which suggests that the ground state is a
Spatially resolved breakdown in reentrant quantum Hall states
NASA Astrophysics Data System (ADS)
Rossokhaty, Oleksandr; Folk, Joshua; Baum, Yuval; Stern, Ady; Watson, John; Gardner, Geoffrey; Manfra, Michael
Electrons in a two dimensional electron gas in the fractional quantum Hall regime may rearrange into a quasi-crystalline structure that gives rise to a reentrant Integer Quantum Hall (RIQH) effect in transport. As bias current increases, longitudinal and Hall resistivities measured for these states show multiple sharp breakdown transitions, a signature that is unique to RIQH states and has previously been ascribed to pinning-depinning transitions or to the development of bias-induced anisotropy. We present an alternate interpretation of the characteristic features of RIQH breakdown at high bias, based on spatially-resolved measurements that indicate a phase boundary between broken-down and unbroken regions propagating chirally from source and drain contacts as a function of bias current. As the phase boundary passes various contacts, its spreading generates multi-stage breakdown signatures like those reported elsewhere. Confirming numerical simulations, the chiral sense of the spreading is set not by the chirality of the edge state itself, but instead depends on electron- or hole-like character of the RIQH state.
IMPLOSION OF INDIRECTLY DRIVEN REENTRANT CONE SHELL TARGET
STEPHENS,RB
2003-08-01
OAK-B135 The authors have examined the implosion of an indirectly driven reentrant-cone shell target to clarify the issues attendant on compressing fuel for a fast ignition target. The target design is roughly hydrodynamic equivalent to a NIF cryo-ignition target, but scaled down to be driven by Omega. A sequence of backlit x-radiographs recorded each implosion. The collapse was also modeled with LASNEX, generating simulated radiographs. They compare experimental and simulated diameter, density and symmetry as functions of time near stagnation. The simulations were generally in good agreement with the experiments with respect to the shell, but did not show the opacity due to ablation of gold off the cone; non-thermal gold M-line radiation from the hohlraum wall penetrates the shell and drives this ablation causing some Au to mix into the low density center of the core and into the region between the core and cone. This might be a problem in a cryo-ignition target.
A re-entrant groove hydrogen heat pipe
NASA Technical Reports Server (NTRS)
Alario, J.; Kosson, R.; Mccreight, C.
1978-01-01
This paper extends the development of reentrant groove technology to hydrogen heat pipes. Parametric analyses are presented which optimize the theoretical design while considering the limitations of state-of-the-art extrusion technology. Acceptable production-type runs of extruded lengths (over 300 m) could only be achieved at the expense of a wider nominal groove opening than specified (0.33 mm vs. 0.20 mm). However, dimensional variations of other critical dimensions were within 0.05 mm, which exceeded expectations. The 6063-T6 aluminum extrusion is 14.6 mm OD with a wall thickness of 1.66 mm and contains 20 axial grooves which surround a central 9.3-mm-diam vapor core. Each axial groove is 0.775-mm-diam with a 0.33 mm opening. An excess vapor reservoir is provided at the evaporator to minimize the pressure containment hazard during ambient storage. Details of the instrumentation and helium-cooled test installation are also presented.
Role of stringlike, supramolecular assemblies in reentrant supernematic liquid crystals
NASA Astrophysics Data System (ADS)
Mazza, Marco G.; Greschek, Manuel; Valiullin, Rustem; Schoen, Martin
2011-05-01
Using a combination of isothermal-isobaric Monte Carlo and microcanonical molecular dynamics we investigate the relation between structure and self-diffusion in various phases of a model liquid crystal using the Gay-Berne-Kihara potential. These molecules are confined to a mesoscopic slit pore with atomically smooth substrate surfaces. As reported recently [seeM. G. Mazza , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.227802 105, 227802 (2010)], a reentrant nematic (RN) phase may form at sufficiently high pressures and densities. This phase is characterized by a high degree of nematic order and a substantially enhanced self-diffusivity in the direction of the director n∧ that exceeds that of the lower-density nematic and an intermittent smectic-A phase by about an order of magnitude. Here we demonstrate that the unique transport behavior in the RN phase may be linked to a confinement-induced packing effect that causes the formation of supramolecular, stringlike conformations. The strings consist of several molecules traveling in the direction of n∧ as individual “trains” consisting of chains of molecular “cars.”
Reentrant quantum oscillations in CeIn3
NASA Astrophysics Data System (ADS)
Coniglio, William A.; Graf, David E.; Stillwell, Ryan L.; Park, Ju-Hyun; Schlottmann, Pedro; Palm, Eric C.; Murphy, Tim P.; Cooley, Jason C.; Tozer, Stanley W.
2014-03-01
Heavy fermion conductor CeIn3 is a low temperature antiferromagnet with a Néel transition at 10 K, 2.6 GPa, and 62 T. We show that Néel and Lifshitz transitions both introduce Fermi surface reconstruction, and the difference in temperature dependence between them leads to surprising reentrant behavior of certain Shubnikov de Haas orbits as a function of field, temperature, and pressure. We use a diamond anvil cell in a helium-3 fridge in pulsed magnetic fields to cover almost the entire phase space of the antiferromagnetic state. Our high resolution resistivity probe is a Tunnel Diode Oscillator that is mounted adjacent to the pressure cell within the bore of the magnet. We confirm the extraordinary sensitivity of the technique by observing the 69 kT Shubnikov de Haas orbit in the resistivity of polycrystalline copper. We appreciate support from DOE NNSA SSAA DE-NA0001979. The National High Magnetic Field Laboratory is supported by NSF Cooperative Agreement DMR-1157490, the State of Florida, and the DOE. We thank Red Schwartz and Mike Pacheco for technical assistance.
Rheological properties of a reentrant nematic liquid crystal.
Ananthaiah, J; Rajeswari, M; Sastry, V S S; Dabrowski, R; Dhara, Surajit
2012-07-01
We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (N(R)) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-N(R) phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-N(R) phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density. PMID:23005440
Rheological properties of a reentrant nematic liquid crystal
NASA Astrophysics Data System (ADS)
Ananthaiah, J.; Rajeswari, M.; Sastry, V. S. S.; Dabrowski, R.; Dhara, Surajit
2012-07-01
We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (NR) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-NR phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-NR phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density.
Role of stringlike, supramolecular assemblies in reentrant supernematic liquid crystals.
Mazza, Marco G; Greschek, Manuel; Valiullin, Rustem; Schoen, Martin
2011-05-01
Using a combination of isothermal-isobaric Monte Carlo and microcanonical molecular dynamics we investigate the relation between structure and self-diffusion in various phases of a model liquid crystal using the Gay-Berne-Kihara potential. These molecules are confined to a mesoscopic slit pore with atomically smooth substrate surfaces. As reported recently [seeM. G. Mazza et al., Phys. Rev. Lett. 105, 227802 (2010)], a reentrant nematic (RN) phase may form at sufficiently high pressures and densities. This phase is characterized by a high degree of nematic order and a substantially enhanced self-diffusivity in the direction of the director n that exceeds that of the lower-density nematic and an intermittent smectic-A phase by about an order of magnitude. Here we demonstrate that the unique transport behavior in the RN phase may be linked to a confinement-induced packing effect that causes the formation of supramolecular, stringlike conformations. The strings consist of several molecules traveling in the direction of n as individual "trains" consisting of chains of molecular "cars." PMID:21728553
Reentrant phase coherence in a quasi-one-dimensional superconductor
NASA Astrophysics Data System (ADS)
Ansermet, Diane; Petrovic, Alexander P.; He, Shikun; Chernyshov, Dmitri; Hoesch, Moritz; Salloum, Diala; Gougeon, Patrick; Potel, Michel; Boeri, Lilia; Andersen, Ole K.; Panagopoulos, Christos
Short coherence lengths characteristic of low-dimensional superconductors are related to high critical fields or temperatures. Fatally, such materials are often sensitive to disorder and suffer from phase fluctuations in the order parameter which diverge with temperature T, magnetic field H or current I. To solve synthesis and fluctuation problems, we propose to build superconductors from inhomogeneous composites of nanofilaments. Single crystals of quasi-one-dimensional Na2-δMo6Se6 featuring Na vacancy disorder (δ ~ 0 . 2) behave as percolative networks of superconducting nanowires. Long range order is established via transverse coupling between individual filaments, yet phase coherence is unstable to fluctuations and localization in the zero-(T, H, I) limit. A region of reentrant phase coherence develops upon raising (T, H, I) and is attributed to an enhancement of the transverse coupling due to electron delocalization. The observed reentrance in the electronic transport coincides with a peak in the Josephson energy EJ at non-zero (T, H, I). Na2-δMo6Se6 is a blueprint for a new generation of low dimensional superconductors with resilience to phase fluctuations at high (T, H, I). This work was supported by the National Research Foundation, Singapore, through Grant NRF-CRP4-2008-04.
Basu, Tathamay; Paulose, P L; Iyer, K K; Singh, K; Mohapatra, N; Chowki, S; Gonde, B; Sampathkumaran, E V
2014-04-30
We report that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Néel temperature (TN) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10 K), mimicking the 'reentrant' multiglass phenomenon. Such a behavior is not known among undoped compounds. A new finding in the field of multiferroics is that the characteristic magnetic feature at low temperatures moves towards higher temperatures in the presence of a magnetic field (H), whereas the corresponding dielectric feature shifts towards lower temperatures with H, unlike the situation near TN. This observation indicates that the alignment of spins by external magnetic fields tends to inhibit glassy-like slow electric-dipole dynamics, at least in this system, possibly arising from peculiarities in the magnetic structure. PMID:24722401
Jana, Rajesh; Saha, Pinku; Pareek, Vivek; Basu, Abhisek; Kapri, Sutanu; Bhattacharyya, Sayan; Mukherjee, Goutam Dev
2016-01-01
We have carried out detailed experimental investigations on polycrystalline CuO using dielectric constant, dc resistance, Raman spectroscopy and X-ray diffraction measurements at high pressures. Observation of anomalous changes both in dielectric constant and dielectric loss in the pressure range 3.7-4.4 GPa and reversal of piezoelectric current with reversal of poling field direction indicate to a change in ferroelectric order in CuO at high pressures. A sudden jump in Raman integrated intensity of Ag mode at 3.4 GPa and observation of Curie-Weiss type behaviour in dielectric constant below 3.7 GPa lends credibility to above ferroelectric transition. A slope change in the linear behaviour of the Ag mode and a minimum in the FWHM of the same indicate indirectly to a change in magnetic ordering. Since all the previous studies show a strong spin-lattice interaction in CuO, observed change in ferroic behaviour at high pressures can be related to a reentrant multiferroic ordering in the range 3.4 to 4.4 GPa, much earlier than predicted by theoretical studies. We argue that enhancement of spin frustration due to anisotropic compression that leads to change in internal lattice strain brings the multiferroic ordering to room temperature at high pressures. PMID:27530329
Jana, Rajesh; Saha, Pinku; Pareek, Vivek; Basu, Abhisek; Kapri, Sutanu; Bhattacharyya, Sayan; Mukherjee, Goutam Dev
2016-01-01
We have carried out detailed experimental investigations on polycrystalline CuO using dielectric constant, dc resistance, Raman spectroscopy and X-ray diffraction measurements at high pressures. Observation of anomalous changes both in dielectric constant and dielectric loss in the pressure range 3.7–4.4 GPa and reversal of piezoelectric current with reversal of poling field direction indicate to a change in ferroelectric order in CuO at high pressures. A sudden jump in Raman integrated intensity of Ag mode at 3.4 GPa and observation of Curie-Weiss type behaviour in dielectric constant below 3.7 GPa lends credibility to above ferroelectric transition. A slope change in the linear behaviour of the Ag mode and a minimum in the FWHM of the same indicate indirectly to a change in magnetic ordering. Since all the previous studies show a strong spin-lattice interaction in CuO, observed change in ferroic behaviour at high pressures can be related to a reentrant multiferroic ordering in the range 3.4 to 4.4 GPa, much earlier than predicted by theoretical studies. We argue that enhancement of spin frustration due to anisotropic compression that leads to change in internal lattice strain brings the multiferroic ordering to room temperature at high pressures. PMID:27530329
NASA Astrophysics Data System (ADS)
Hirai, Makoto; Ikeya, Motoji
2004-08-01
Ball-milled Pyrex glass (Corning 7740) was irradiated by gamma-rays to a dose of 30 kGy to investigate the milling effect on the formation of paramagnetic centers with ESR. The formation efficiency of E' centers was increased markedly while that of boron oxygen hole centers (BOHCs) was suppressed by 40%. An annealing experiment showed that the milling process makes BOHCs unstable, which may be the reason for the suppression. Reduction in the ESR intensity, after etching with hydrofluoric acid, clarified that both types of center are concentrated in the near-surface region in different ratios. The milling effect on E' center formation can be explained by the formation of oxygen vacancies in the near-surface region. A similar effect has already been observed in quartz. By contrast, the suppression of BOHC formation in the bulk region needs to be described by a new mechanism. We assume that internal elastic stress induced in the milled grains suppresses BOHC formation. Internal stress in the thermally tempered glass (TTG) was relieved by breaking it to submillimeter size. The observed dependence of the BOHC formation efficiency on grain size allowed us to estimate that the suppression rate per 1 MPa is more than 0.4%, which is consistent with the milling effect assuming a stress of 100 MPa.
Pandey, Suchita; Kumar, Jitender; Awasthi, A M
2016-03-01
The magneto-dielectric spectroscopy of La0.95Ca0.05CoO3 covering the crossover of spin states reveals the strong coupling of its spin and dipolar degrees of freedom. The signature of the spin-state transition at 30 K clearly manifests in the magnetization data at a 1 Tesla optimal field. Our Co L3,2-edge X-ray absorption spectrum on the doped specimen is consistent with its suppressed low-to-intermediate spin-state transition temperature at ∼30 K compared to ∼150 K, documented for pure LaCoO3. The dispersive activation step in the dielectric constant with the associated relaxation peak in imaginary permittivity characterize the allied influence of coexistent spin-states on the dielectric character. Dipolar relaxation in the low-spin regime below the transition temperature is partly segmental (Vogel-Fulcher-Tamman (VFT) kinetics) and features magnetic-field tunability, whereas in the low/intermediate-spin disordered state above ∼30 K, it is uncorrelated (Arrhenic kinetics) and almost impervious to the magnetic field H. Kinetics-switchover defines the dipolar-glass transition temperature Tg(H) (=27 K|0T), below which their magneto-thermally-activated cooperative relaxations freeze out by the VFT temperature T0(H) (=15 K|0T). An applied magnetic field facilitates thermal activation in toggling the low spins up into the intermediate states. Consequently, the downsized dipolar-glass segments in the low-spin state and the independent dipoles in the intermediate state exhibit accelerated dynamics. A critical 5 Tesla field collapses the entire relaxation kinetics into a single Arrhenic behaviour, signaling that the dipolar glass is completely devitrified under all higher fields. The magneto-electricity (ME) spanning sizeable thermo-spectral range registers diverse signatures here in kinetic, spectral, and field behaviors, in contrast to the static/perturbative ME observed close to the spin-ordering in typical multiferroics. Intrinsic magneto-dielectricity (50%) along
Effects of structural parameters on flow boiling performance of reentrant porous microchannels
NASA Astrophysics Data System (ADS)
Deng, Daxiang; Tang, Yong; Shao, Haoran; Zeng, Jian; Zhou, Wei; Liang, Dejie
2014-06-01
Flow boiling within advanced microchannel heat sinks provides an efficient and attractive method for the cooling of microelectronics chips. In this study, a series of porous microchannels with Ω-shaped reentrant configurations were developed for application in heat sink cooling. The reentrant porous microchannels were fabricated by using a solid-state sintering method under the replication of specially designed sintering modules. Micro wire electrical discharge machining was utilized to process the graphite-based sintering modules. Two types of commonly used copper powder in heat transfer devices, i.e., spherical and irregular powder, with three fractions of particle sizes respectively, were utilized to construct the porous microchannel heat sinks. The effects of powder type and size on the flow boiling performance of reentrant porous microchannels, i.e., two-phase heat transfer, pressure drop and flow instabilities, were examined under boiling deionized water conditions. The test results show that enhanced two-phase heat transfer was achieved with the increase of particle size for the reentrant porous microchannels with spherical powder, while the reversed trend existed for the counterparts with irregular powder. The reentrant porous microchannels with irregular powder of the smallest particle size presented the best heat transfer performance and lowest pressure drop.
Kumar, Punith V. Manju, M. R. Dayal, Vijaylakshmi
2014-04-24
We present a comprehensive study on origin of Spin Glass (SG) property in polycrystalline La{sub 0.5}Bi{sub 0.5}MnO{sub 3} perovskite oxide using linear and higher order ac susceptibility (χ) measurements. The third order harmonic susceptibility (χ{sub 3}) vs. temperature (K) with varying magnetic fields from 0.95 to 9.45 Oe and the divergence in their χ{sub 3} (max) allows us to infer the SG behavior occurring in the sample possibly due to co-operative freezing of the spins.
Two-step depinning and re-entrant behavior of three-dimensional flux line lattices
NASA Astrophysics Data System (ADS)
Zhao, Z. G.; You, Y. X.; Wang, J.; Liu, M.
2008-05-01
We develop a three-dimensional flux line lattice (FLL) model with magnetic interactions between intraplane and interplane vortices to simulate the dynamic behavior of the flux flow in a disordered point-pinned system. A double-peak structure is found in the differential resistivity as a function of the driving current, corresponding to the two-step depinning behavior of the vortex motion. In between the two peaks there exists a new re-entrant pinning phase. The calculated results are summarized as a phase diagram of the interplane coupling strength of pancake vortices vs. the applied driving current. A huge peak effect and current-induced re-entrant pinning behavior appear in a narrow regime, where an unusual intrinsic pinning mechanism due to interlayer interactions dominates the peak effect. The phase diagram obtained is favorable for understanding the two-step depinning and re-entrant behavior observed recently experimentally.
Structure and Dynamics of Reentrant Nematics: Any Open Questions after Almost 40 Years?
Mazza, Marco G.; Schoen, Martin
2011-01-01
Liquid crystals have attracted enormous interest because of the variety of their phases and richness of their application. The interplay of general physical symmetries and specific molecular features generates a myriad of different phenomena. A surprising behavior of liquid crystals is the reentrancy of phases as temperature, pressure, or concentration are varied. Here, we review the main experimental facts and the different theoretical scenarios that have guided the understanding of bulk reentrant nematics. Recently, some computer simulations of a system confined to nanoscopic scales have found new dynamical features of the reentrant nematic phase. We discuss this prediction in relation with the available experimental evidence on reentrant nematics and with the dynamics of liquids in strongly confined environments. PMID:21954364
Why re-entrant surface topography is needed for robust oleophobicity.
Nosonovsky, Michael; Bhushan, Bharat
2016-08-01
Surface patterns affect wetting properties of solid materials allowing manipulation of the phase state of an adjacent fluid. The best known example of this effect is the superhydrophobic composite (Cassie-Baxter) interface with vapour/air pockets between the solid and liquid. Mathematically, the effect of surface micropatterns can be studied by an averaging technique similarly to the method of separation of motions in dynamics. However, averaged parameters are insufficient for robust superhydrophobic and superoleophobic surfaces because additional topography features are important: hierarchical organization and re-entrant roughness. The latter is crucial for the oleophobicity because it enhances the stability of a composite interface. The re-entrant topography can be achieved by various methods. Understanding the role of re-entrant surface topography gives us new insights on the multitude of wetting scenarios beyond the standard Wenzel and Cassie-Baxter models.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'. PMID:27354728
Splash and Re-entrant Albedo Fluxes Measured in the PAMELA Experiment
NASA Astrophysics Data System (ADS)
Mayorov, A. G.; Moiseeva, A. I.; Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; DeDonato, C.; DeSantis, C.; DeSimone, N.; DiFelice, V.; Formato, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Kvashnin, A. A.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorova, M. A.; Menn, W.; Merge', M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Pizzolotto, C.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.; Zverev, V. G.
This work devoted to the description of the method for splash albedo protons identification in the satellite-born experiment PAMELA. In contrast to the reentrant albedo particles, which enter into the main aperture of the instrument, the direct albedo particles enter from the opposite direction, so they pass a few detectors, including calorimeter, before being register by the magnetic spectrometer. The developed method take into account the influence of these detectors on the selection of events and measurements of their characteristics. To test this method the energy spectrum of reentrant albedo protons in various regions of the near-Earth space reconstructed; it is in a good agreement with the classical measurements in the main aperture. Therefore, this method can be useful to obtain a new physical data about fluxes of splash albedo protons in the PAMELA experiment, which, unlike the reentrant albedo, can be study even at high geomagnetic latitudes.
Tschabrunn, Cory M.; Roujol, Sébastien; Nezafat, Reza; Faulkner-Jones, Beverly; Buxton, Alfred E.; Josephson, Mark E.; Anter, Elad
2016-01-01
BACKGROUND Human ventricular tachycardia (VT) after myocardial infarction usually occurs because of subendocardial reentrant circuits originating in scar tissue that borders surviving myocardial bundles. Several preclinical large animal models have been used to further study postinfarct reentrant VT, but with varied experimental methodologies and limited evaluation of the underlying substrate or induced arrhythmia mechanism. OBJECTIVE We aimed to develop and characterize a swine model of scar-related reentrant VT. METHODS Thirty-five Yorkshire swine underwent 180-minute occlusion of the left anterior descending coronary artery. Thirty-one animals (89%) survived the 6–8-week survival period. These animals underwent cardiac magnetic resonance imaging followed by electrophysiology study, detailed electroanatomic mapping, and histopathological analysis. RESULTS Left ventricular (LV) ejection fraction measured using CMR imaging was 36% ± 6.6% with anteroseptal wall motion abnormality and late gadolinium enhancement across 12.5% ± 4.1% of the LV surface area. Low voltage measured using endocardial electroanatomic mapping encompassed 11.1% ± 3.5% of the LV surface area (bipolar voltage ≤1.5 mV) with anterior, anteroseptal, and anterolateral involvement. Reentrant circuits mapped were largely determined by functional rather than fix anatomical barriers, consistent with “pseudo-block” due to anisotropic conduction. Sustained monomorphic VT was induced in 28 of 31 swine (90%) (67 VTs; 2.4 ± 1.1; range 1–4) and characterized as reentry. VT circuits were subendocardial, with an arrhythmogenic substrate characterized by transmural anterior scar with varying degrees of fibrosis and myocardial fiber disarray on the septal and lateral borders. CONCLUSION This is a well-characterized swine model of scar-related subendocardial reentrant VT. This model can serve as the basis for further investigation in the physiology and therapeutics of humanlike postinfarction
NASA Astrophysics Data System (ADS)
Giri, S. K.; Panda, J.; Nath, T. K.
2012-06-01
The effect of doping of rare earth Pr3+ ion replacing Sm3+ in Sm0.5Sr0.5MnO3 is investigated in details. Measurements of linear and non linear ac magnetic susceptibility, resistivity, magnetoresistance on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 shows various interesting features with doping level x=0.15. Here we observe the frequency independent FM-PM transition at higher temperature followed by a frequency dependent re-entered magnetic transition at lower temperature through complex ac susceptibility measurements. We have ascribed our observation to the formation of finite size ferromagnetic clusters which are formed as a consequence of intrinsic phase separation and undergo Spin glass-like freezing below certain temperature in this manganite. The magnetoresistance of the samples also show strong irreversibility with respect to sweeping of the field between highest positive and negative values. All these experimental results have been attributed to phase separation effect and kinetic arrest of electronically phase separated system.
Gomez Sal, J.C.; Garcia Soldevilla, J.; Blanco, J.A.; Espeso, J.I.; Rodriguez Fernandez, J.; Luis, F.; Bartolome, F.; Bartolome, J.
1997-11-01
The low-temperature magnetic and transport properties of the orthorhombic CeNi{sub 0.4}Cu{sub 0.6} compound have been determined from the analysis of specific heat, ac magnetic susceptibility, electrical resistivity, elastic and inelastic neutron scattering. These measurements present intriguing experimental results that could not be explained within the usual phenomenology of Ce-based compounds. C{sub p} and {chi}{sub ac} present anomalies around 1 K corresponding to ferromagnetic order as confirmed by neutron diffraction. The magnetic structure is collinear with very reduced moments, 0.6{mu}{sub B}/Ce lying in the b direction. Additionally, a clear Kondo behavior is observed with a Kondo temperature T{sub K}=1.9K estimated from quasielastic neutron scattering. Above the ordering temperature, further anomalies are observed in C{sub p} and {chi}{sub ac} that could not be explained as originating from crystal electric field or Kondo effects. From the frequency and field dependence of the {chi}{sub ac}, above T{sub c}, a spin-glass state with a freezing temperature T{sub f}=2K is proposed for this compound. This unusual magnetic behavior is discussed in terms of mixed (positive and negative) Ruderman-Kittel-Kasuya-Yosida interactions, randomness (structural disorder), large hybridization (Kondo effect), and strong magnetocrystalline anisotropy (crystal electric field effects). {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Chandra, Sayan; Khurshid, H.; Li, Wanfeng; Hadjipanayis, G. C.; Phan, M. H.; Srikanth, H.
2012-07-01
A detailed study is presented on Fe/γ-Fe2O3 core-shell structured nanoparticles (mean size ˜10 nm) to understand the spin dynamics of the core and shell independently and their role in triggering exchange bias (EB) phenomena. The particle dynamics critically slow down at Tg ˜ 68 K, below which they exhibit memory effect in field-cooled and zero-field-cooled protocols associated with a superspin glass state. The field dependence of mean blocking temperature fits the de Almeida-Thouless line and shows two different linear responses in the low and high field regimes corresponding to the core and shell, respectively. We show that the energy barrier distribution estimated from the temperature decay of isothermal remanent magnetization shows two maxima that mark the freezing temperatures of the core (Tf-cr ˜ 48 K) and shell (Tf-sh ˜ 21 K). Last, hysteresis measurements after field cooling reveal strong EB indicated by a loop shift associated with unidirectional anisotropy. The onset of EB is at 35 K when the ferromagnetic core is frozen and the moments in the ferrimagnetic shell begin to block, resulting in enhanced exchange coupling.
Ding, Lei; Wang, Cong Sun, Ying; Colin, Claire V.; Chu, Lihua
2015-06-07
The Cu-doping effect on the lattice and magnetic properties in Mn{sub 3}Ni{sub 1−x}Cu{sub x}N (x = 0, 0.3, 0.5, 0.7, 1.0) was extensively investigated. We observed that the Cu-doping at the Ni site complicated the magnetic ground states, which induced the competition of antiferromagnetic and ferromagnetic interactions. Spin-glass-like behavior, arising from possible site-randomness and competing interactions of magnetism, was observed in compounds with x = 0.3, 0.5, and 0.7, and typically discussed by means of the measurement of ac magnetic susceptibility for x = 0.7. The negative thermal expansion (NTE) behavior, due to the magnetic ordering transition, was observed in Mn{sub 3}Ni{sub 1−x}Cu{sub x}N compounds using variable temperature x-ray diffraction. It reveals that the introduction of Cu effectively broadens the temperature range displaying negative thermal expansion. The relationship between the local lattice distortion and the competing magnetic ground states might play an important role in broadening the NTE temperature range in this antiperovskite compound.
NASA Astrophysics Data System (ADS)
Akmaldinov, Kamil; Ducruet, Clarisse; Alvarez-Herault, Jeremy; Baltz, Vincent
2015-03-01
For thermally-assisted magnetic random access memories (TA-MRAM), lowering bit-cells dispersions of exchange bias is necessary. In this study, we prove that spin-glass-like phases (SG) spread over the ferromagnetic/antiferromagnetic (F/AF) storage layer are the main cause of such distributions once the film is nanofabricated into a device. In particular, we show that the less the SG, the lower the bit-cell dispersion. More precisely, the amount of SG was varied from sample to sample by sputtering various AFs: IrMn, FeMn and their alloys. Blocking temperature distributions were measured to quantify the amount of SG at the wafer level. The wafers were then patterned to obtain 1kb devices and all the cells were tested electrically. Finally, the resulting loop shift cumulative distribution functions accounting for the bit-cell dispersions were correlated to the initial amount of SG. In addition to bridging the gap between fundamental SG and a technological application, we also demonstrated that blocking temperature distributions are a versatile method to qualify TA-MRAM production batches before processing. Univ. Grenoble-Alpes/CNRS/INAC-CEA, 38000 Grenoble, France.
Reentrant Origami-Based Metamaterials with Negative Poisson's Ratio and Bistability.
Yasuda, H; Yang, J
2015-05-01
We investigate the unique mechanical properties of reentrant 3D origami structures based on the Tachi-Miura polyhedron (TMP). We explore the potential usage as mechanical metamaterials that exhibit tunable negative Poisson's ratio and structural bistability simultaneously. We show analytically and experimentally that the Poisson's ratio changes from positive to negative and vice versa during its folding motion. In addition, we verify the bistable mechanism of the reentrant 3D TMP under rigid origami configurations without relying on the buckling motions of planar origami surfaces. This study forms a foundation in designing and constructing TMP-based metamaterials in the form of bellowslike structures for engineering applications. PMID:26001009
NASA Astrophysics Data System (ADS)
Zhu, Zheng; Ochoa, Andrew J.; Schnabel, Stefan; Hamze, Firas; Katzgraber, Helmut G.
2016-01-01
Recent tests performed on the D-Wave Two quantum annealer have revealed no clear evidence of speedup over conventional silicon-based technologies. Here we present results from classical parallel-tempering Monte Carlo simulations combined with isoenergetic cluster moves of the archetypal benchmark problem—an Ising spin glass—on the native chip topology. Using realistic uncorrelated noise models for the D-Wave Two quantum annealer, we study the best-case resilience, i.e., the probability that the ground-state configuration is not affected by random fields and random-bond fluctuations found on the chip. We thus compute classical upper-bound success probabilities for different types of disorder used in the benchmarks and predict that an increase in the number of qubits will require either error correction schemes or a drastic reduction of the intrinsic noise found in these devices. We restrict this study to the exact ground state, however, the approach can be trivially extended to the inclusion of excited states if the success metric is relaxed. We outline strategies to develop robust, as well as hard benchmarks for quantum annealing devices, as well as any other (black box) computing paradigm affected by noise.
NASA Astrophysics Data System (ADS)
Feng, Lang; Laderman, Bezia; Sacanna, Stefano; Chaikin, Paul
2015-01-01
In polymer-colloid mixtures, non-adsorbing polymers dispersed with much larger colloids provide a universal yet specific entropic attraction between the colloids. Such so-called depletion interaction arises from an osmotic-pressure imbalance caused by the polymers and is considered to be independent of temperature. Here we show that, for the most commonly used polymer-colloid depletion systems, the polymer undergoes a crossover from non-adsorbing to adsorbing and that, consequently, the effective colloidal interactions depend on temperature. We also find that a combination of the enthalpic (polymer bridging) and entropic (polymer exclusion) interactions, both attractive, leads to a re-entrant regime where the colloids are dispersed and form solids both on heating and on cooling. We provide a simple model to explain the observed transitions and to fill the theoretical gap at the polymer-adsorption crossover. Our findings open possibilities for colloidal self-assembly, the formation of colloidal crystals and glasses, and the behaviour of temperature-controlled viscoelastic materials.
Bundle branch reentrant tachycardia in a patient with normal ventricular function.
Fynn, Simon P; Kalman, Jonathan M
2004-06-01
We report an unusual case of bundle branch reentrant tachycardia, in a patient with normal left ventricular function, cured by radiofrequency catheter ablation. However, the long-term prognosis of these patients is uncertain. We discuss the indications for an implantable defibrillator in this group. PMID:15133364
Bohora, Shomu; Singh, Parvindar; Shah, Kaushal
2016-01-01
A 58 year old gentleman with complaints of palpitations and documented tachycardia was found to have a dilated right atrium, right ventricle and coronary sinus, which were due to partial unroofed coronary sinus without a left superior vena cava. He had upper septal ventricular tachycardia and atrio-ventricular nodal reentrant tachycardia, which was successfully treated by radiofrequency ablation. PMID:25852246
Dakshinamurthy, S.; Shetty, S.; Bhat, I.; Hitchcock, C.; Gutmann, R.; Charache, G.; Freeman, M.
1998-06-01
The GaInSb material system is attractive for application in thermophotovoltaic (TPV) cells since its band gap can be tuned to match the radiation of the emitter. At present, most of the TPV cells are fabricated using epitaxial layers and hence are expensive. To reduce the cost, Zn diffusion using elemental vapors in a semi-closed diffusion system is being pursued by several laboratories. In this paper, the authors present studies carried out on Zn diffusion into n-type (Te-doped) GaSb substrates in an open tube diffusion furnace. The dopant precursor was a 2,000 {angstrom} thick, zinc doped spin-on glass. The diffusion was carried out at temperatures ranging from 550 to 600 C, for times from 1 to 10 hours. The diffused layers were characterized by Hall measurements using step-and-repeat etching by anodic oxidation, secondary ion mass spectrometry (SIMS) measurements and TPV device fabrication. For diffusion carried out at 600 C, the junction depth was 0.3 {micro}m, and the hole concentration near the surface was 5 {times} 10{sup 19}/cm{sup 3}. The external quantum efficiency, measured without any anti-reflection coating, of the TPV cells fabricated using mesa-etching had a maximum value of 38%. Masked diffusion was also carried out by opening windows in a Si{sub 3}N{sub 4} coated, GaSb wafer. TPV cells fabricated on these structures had similar quantum efficiency, but lower dark current.
Ferrimagnetic and spin-glass transition in the Aurivillius compound SrBi5Ti4Cr0.5Co0.5O18
NASA Astrophysics Data System (ADS)
Yuan, B.; Yang, J.; Zuo, X. Z.; Song, D. P.; Tang, X. W.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Sun, Y. P.
2015-06-01
Single-phase polycrystalline SrBi5Ti4CrO18 and SrBi5Ti4Cr0.5Co0.5O18 were synthesized by a modified Pechini method. Both samples have an orthorhombic structure with the space group B2cb. The valence state of Cr is suggested to be +3 and the Co ions exist in the form of Co2+ and Co3+ based on the results of x-ray photoelectron spectroscopy. The sample SrBi5Ti4CrO18 exhibits the paramagnetic state, whereas SrBi5Ti4Cr0.5Co0.5O18 undergoes a ferrimagnetic transition at 89 K originating from the antiferromagnetic coupling of Cr-based and Co-based sublattices. In addition, SrBi5Ti4Cr0.5Co0.5O18 shows a typical spin-glass behavior below 89 K with zν = 6.02 and τ0 = (1.75 ± 0.33) × 10-14 s as evidenced by the results of the frequency dependence of ac susceptibility and magnetic relaxation measurements. In particular, both the dielectric constant and dielectric loss of SrBi5Ti4Cr0.5Co0.5O18 exhibit the characteristics of dielectric relaxation around 89 K with the activation energy of (0.14 ± 0.02) eV, which can be ascribed to the electron hopping of Co2+-VO-Co3+ through the bridging oxygen vacancies.
Glass and ceramics. [lunar resources
NASA Technical Reports Server (NTRS)
Haskin, Larry A.
1992-01-01
A variety of glasses and ceramics can be produced from bulk lunar materials or from separated components. Glassy products include sintered regolith, quenched molten basalt, and transparent glass formed from fused plagioclase. No research has been carried out on lunar material or close simulants, so properties are not known in detail; however, common glass technologies such as molding and spinning seem feasible. Possible methods for producing glass and ceramic materials are discussed along with some potential uses of the resulting products.
NASA Astrophysics Data System (ADS)
Nayek, Chiranjib; Samanta, S.; Manna, Kaustuv; Pokle, A.; Nanda, B. R. K.; Anil kumar, P. S.; Murugavel, P.
2016-03-01
We report the transition from robust ferromagnetism to a spin-glass state in nanoparticulate L a0.7S r0.3Mn O3 through solid solution with BaTi O3 . The field- and temperature-dependent magnetization and the frequency-dependent ac magnetic susceptibility measurements strongly indicate the existence of a spin-glass state in the system, which is further confirmed from memory effect measurements. The breaking of long-range ordering into short-range magnetic domains is further investigated using density-functional calculations. We show that Ti ions remain magnetically inactive due to insufficient electron leakage from L a0.7S r0.3Mn O3 to the otherwise unoccupied Ti -d states. This results in the absence of a Mn-Ti-Mn spin exchange interaction and hence the breaking of the long-range ordering. Total-energy calculations suggest that the segregation of nonmagnetic Ti ions leads to the formation of short-range ferromagnetic Mn domains.
Mundus, C; Müller-Warmuth, W
1995-10-01
27Al magic-angle spinning nuclear magnetic resonance satellite transition spectroscopy at 78 MHz has been applied to determine (true) chemical shift and quadrupole coupling parameters of glasses in the system K2O-Al2O3-SiO2 with 60-80 mol% SiO2 and K2O concentrations between 0 and 24 mol%. The powdered crystalline aluminosilicates andalusite and sillimanite have also been examined. In the glasses, all Al appears to be tetrahedrally bound in the aluminosilicate network unless x = mol% K2O:mol% Al2O3 becomes extremely small. Upon decreasing x the distortion of the tetrahedral Al(OSi)4 units increases in steps, and possible explanations are discussed. Six-coordinated aluminum observed for x < 0.2 is connected with the occurrence of interstitial Al3+ ions which charge-compensate the AlO4 units in addition to K+. PMID:8748646
NASA Astrophysics Data System (ADS)
Mishra, Chandan K.; Rangarajan, Amritha; Ganapathy, Rajesh
2013-05-01
We study experimentally the glass transition dynamics in quasi-two-dimensional suspensions of colloidal ellipsoids, aspect ratio α=2.1, with repulsive as well as attractive interactions. For the purely repulsive case, we find that the orientational and translational glass transitions occur at the same area fraction. Strikingly, for intermediate depletion attraction strengths, we find that the orientational glass transition precedes the translational one. By quantifying structure and dynamics, we show that quasi-long-range ordering is promoted at these attraction strengths, which subsequently results in a two-step glass transition. Most interestingly, within experimental certainty, we observe reentrant glass dynamics only in the translational degrees of freedom.
NASA Astrophysics Data System (ADS)
Dahlem, Markus A.; Graf, Rudolf; Strong, Anthony J.; Dreier, Jens P.; Dahlem, Yuliya A.; Sieber, Michaela; Hanke, Wolfgang; Podoll, Klaus; Schöll, Eckehard
2010-06-01
We present spatio-temporal characteristics of spreading depolarizations (SD) in two experimental systems: retracting SD wave segments observed with intrinsic optical signals in chicken retina, and spontaneously occurring re-entrant SD waves that repeatedly spread across gyrencephalic feline cortex observed by laser speckle flowmetry. A mathematical framework of reaction-diffusion systems with augmented transmission capabilities is developed to explain the emergence and transitions between these patterns. Our prediction is that the observed patterns are reaction-diffusion patterns controlled and modulated by weak nonlocal coupling such as long-range, time-delayed, and global coupling. The described spatio-temporal characteristics of SD are of important clinical relevance under conditions of migraine and stroke. In stroke, the emergence of re-entrant SD waves is believed to worsen outcome. In migraine, retracting SD wave segments cause neurological symptoms and transitions to stationary SD wave patterns may cause persistent symptoms without evidence from noninvasive imaging of infarction.
Late Proterozoic rift control on the shape of the Appalachians: The Pennsylvania reentrant
Gates, A.E. New York Geological Survey, Albany, NY ); Valentino, D.W. New York Geological Survey, Albany, NY )
1991-11-01
The Pennsylvania reentrant, the most prominent deviation in the trend of the Appalachians, is the product of Late Proterozoic rifting. The Peters Creek Formation, Pennsylvania-Maryland Piedmont, contains rift-generated, deep-water turbidite deposits of Late Proterozoic-Cambrian( ) age. These rocks are an extension of the Westminster terrane and lie well to the northeast of the southern Appalachian Late Proterozoic-Cambrian rift basin (Lynchburg-Chilhowee Group basin). The basin into which the Peters Creek Formation was deposited may have connected the southern rift basin with one to the north. The preservation of the Peters Creek Formation and other age equivalent units within the Pennsylvania reentrant indicates that the New York promontory acted as a buttress to Paleozoic orogenic activity.
Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures
Muller-Allinger; Mota
2000-04-01
We discuss the magnetic response of clean Ag coated Nb proximity cylinders in the temperature range 150 &mgr;K
Entropy-Driven Enhanced Self-Diffusion in Confined Reentrant Supernematics
NASA Astrophysics Data System (ADS)
Mazza, Marco G.; Greschek, Manuel; Valiullin, Rustem; Kärger, Jörg; Schoen, Martin
2010-11-01
We present a molecular dynamics study of reentrant nematic phases using the Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities above those characteristic of smectic A phases, reentrant nematic phases form that are characterized by a large value of the nematic order parameter S≃1. Along the nematic director these “supernematic” phases exhibit a remarkably high self-diffusivity, which exceeds that for ordinary, lower-density nematic phases by an order of magnitude. Enhancement of self-diffusivity is attributed to a decrease of rotational configurational entropy in confinement. Recent developments in the pulsed field gradient NMR technique are shown to provide favorable conditions for an experimental confirmation of our simulations.
Evaluating the role of reentrant output-to-input feedback in simultaneous pattern processing
Achler, Tsvi
2010-01-01
Simultaneous Pattern Processing (SPP) is defined as the ability to identify simultaneous-intermixed patterns without isolating them individually (e.g. without separating each pattern in space and processing it individually). Enhanced SPP ability is beneficial for many real-life applications such as scene understanding, separating simultaneous voices, and identifying odorant or taste mixes. The first part of this work identifies how SPP scenarios are problematic to models which train synaptic connections or implement lateral inhibition and quantifies how subtle difficulties lead to complex combinatorial issues. The second part of this work proposes and tests an algorithm motivated by Ubiquitous re-entrant 'output to input' connections found throughout sensory processing regions of the brain. Through these connections the model proposes a dynamic gain mechanism that can provide functionality normally achieved through variable synaptic connections. The re-entrant structure combined with enhanced perfonnance suggests the brain may utilize this configuration for SPP flexibility.
Entropy-driven enhanced self-diffusion in confined reentrant supernematics.
Mazza, Marco G; Greschek, Manuel; Valiullin, Rustem; Kärger, Jörg; Schoen, Martin
2010-11-26
We present a molecular dynamics study of reentrant nematic phases using the Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities above those characteristic of smectic A phases, reentrant nematic phases form that are characterized by a large value of the nematic order parameter S≃1. Along the nematic director these "supernematic" phases exhibit a remarkably high self-diffusivity, which exceeds that for ordinary, lower-density nematic phases by an order of magnitude. Enhancement of self-diffusivity is attributed to a decrease of rotational configurational entropy in confinement. Recent developments in the pulsed field gradient NMR technique are shown to provide favorable conditions for an experimental confirmation of our simulations. PMID:21231424
Rigorous analysis of highly tunable cylindrical transverse magnetic mode re-entrant cavities
NASA Astrophysics Data System (ADS)
Le Floch, J.-M.; Fan, Y.; Aubourg, M.; Cros, D.; Carvalho, N. C.; Shan, Q.; Bourhill, J.; Ivanov, E. N.; Humbert, G.; Madrangeas, V.; Tobar, M. E.
2013-12-01
Cylindrical re-entrant cavities are unique three-dimensional structures that resonate with their electric and magnetic fields in separate parts of the cavity. To further understand these devices, we undertake rigorous analysis of the properties of the resonance using "in-house" developed Finite Element Method (FEM) software capable of dealing with small gap structures of extreme aspect ratio. Comparisons between the FEM method and experiments are consistent and we illustrate where predictions using established lumped element models work well and where they are limited. With the aid of the modeling we design a highly tunable cavity that can be tuned from 2 GHz to 22 GHz just by inserting a post into a fixed dimensioned cylindrical cavity. We show this is possible, as the mode structure transforms from a re-entrant mode during the tuning process to a standard cylindrical transverse magnetic mode.
Phase Separation on Bicontinuous Cubic Membranes: Symmetry Breaking, Reentrant, and Domain Faceting
NASA Astrophysics Data System (ADS)
Paillusson, Fabien; Pennington, Matthew R.; Kusumaatmaja, Halim
2016-07-01
We study the phase separation of binary lipid mixtures that form bicontinuous cubic phases. The competition between the nonuniform Gaussian membrane curvature and line tension leads to a very rich phase diagram, where we observe symmetry breaking of the membrane morphologies and reentrant phenomena due to the formation of bridges between segregated domains. Upon increasing the line tension contribution, we also find faceting of lipid domains that we explain using a simple argument based on the symmetry of the underlying surface and topology.
Lin, Chin-Yu; Chung, Fa-Po; Lin, Yenn-Jiang
2015-01-01
We describe the case of a patient with severe hypertensive left ventricular hypertrophy and sustained hemodynamically unstable ventricular tachycardia (VT). Entrainment was demonstrated in the electrophysiological study. Activation mapping and pacemapping identified the location of the intramural reentrant VT with the exit site close to the epicardium. However, VT persisted after ablation at the epicardial exit site. Successful ablation was performed endocardially at the corresponding position. PMID:26617657
NASA Astrophysics Data System (ADS)
Klootwijk, Chris T.; Nazirullah, Russell; de Jong, Kees A.
1986-11-01
Successions of Lower to lower Middle Cambrian, Upper Permian to Upper Triassic and Lower Tertiary carbonates and arenites have been sampled in five sections, representative of the three main segments of the Mianwali reentrant in the (Trans-Indus) Salt Range (northern Pakistan), i.e.: the southern Khisor Range, the northern Surghar Range and the western Salt Range. Comparison of primary and secondary magnetization directions with the Indian APWP demonstrates the secondary origin of the Mianwali reentrant and shows a pattern of rotations which varies in sense and magnitude along the reentrant with the main structural trends. Data from the Trans-Indus and western Salt Range and published Early Cambrian, Early Permian and Late Tertiary palaeomagnetic results from the southern Salt Range and the Potwar Plateau show that the Hazara Arc underwent a 20-45° counterclockwise rotation relative to the Indian Shield. A contrasting clockwise rotation over about 45° has recently been established for thrust sheets in the opposing eastern limb of the Western Himalayan Syntaxis, i.e. for the Panjal Nappe [1] and the Riasi thrust sheet [2]. These palaeomagnetically established rotations conform with the about 75° azimuthal change in structural trend along the Syntaxis, and support Crawford's [3] suggestion that the Salt Range was originally in line with the northwestern Himalaya. The Salt Range front prograded and moved southwards as part of the Hazara Arc thrust sheet, detached from basement along the evaporitic Salt Range Formation. The Mianwali reentrant originated through obstruction of the southwards advancing thrust sheet by moulding around basement topography of the northwest oriented Sarghoda Ridge.
Reconstructing three-dimensional reentrant cardiac electrical wave dynamics using data assimilation.
Hoffman, M J; LaVigne, N S; Scorse, S T; Fenton, F H; Cherry, E M
2016-01-01
For many years, reentrant scroll waves have been predicted and studied as an underlying mechanism for cardiac arrhythmias using numerical techniques, and high-resolution mapping studies using fluorescence recordings from the surfaces of cardiac tissue preparations have confirmed the presence of visible spiral waves. However, assessing the three-dimensional dynamics of these reentrant waves using experimental techniques has been limited to verifying stable scroll-wave dynamics in relatively thin preparations. We propose a different approach to recovering the three-dimensional dynamics of reentrant waves in the heart. By applying techniques commonly used in weather forecasting, we combine dual-surface observations from a particular experiment with predictions from a numerical model to reconstruct the full three-dimensional time series of the experiment. Here, we use model-generated surrogate observations from a numerical experiment to evaluate the performance of the ensemble Kalman filter in reconstructing such time series for a discordant alternans state in one spatial dimension and for scroll waves in three dimensions. We show that our approach is able to recover time series of both observed and unobserved variables matching the truth. Where nearby observations are available, the error is reduced below the synthetic observation error, with a smaller reduction with increased distance from observations. Our findings demonstrate that state reconstruction for spatiotemporally complex cardiac electrical dynamics is possible and will lead naturally to applications using real experimental data. PMID:26826859
Reconstructing three-dimensional reentrant cardiac electrical wave dynamics using data assimilation
NASA Astrophysics Data System (ADS)
Hoffman, M. J.; LaVigne, N. S.; Scorse, S. T.; Fenton, F. H.; Cherry, E. M.
2016-01-01
For many years, reentrant scroll waves have been predicted and studied as an underlying mechanism for cardiac arrhythmias using numerical techniques, and high-resolution mapping studies using fluorescence recordings from the surfaces of cardiac tissue preparations have confirmed the presence of visible spiral waves. However, assessing the three-dimensional dynamics of these reentrant waves using experimental techniques has been limited to verifying stable scroll-wave dynamics in relatively thin preparations. We propose a different approach to recovering the three-dimensional dynamics of reentrant waves in the heart. By applying techniques commonly used in weather forecasting, we combine dual-surface observations from a particular experiment with predictions from a numerical model to reconstruct the full three-dimensional time series of the experiment. Here, we use model-generated surrogate observations from a numerical experiment to evaluate the performance of the ensemble Kalman filter in reconstructing such time series for a discordant alternans state in one spatial dimension and for scroll waves in three dimensions. We show that our approach is able to recover time series of both observed and unobserved variables matching the truth. Where nearby observations are available, the error is reduced below the synthetic observation error, with a smaller reduction with increased distance from observations. Our findings demonstrate that state reconstruction for spatiotemporally complex cardiac electrical dynamics is possible and will lead naturally to applications using real experimental data.
Jiang, Yu; Huq, Ashfia; Booth, Corwin H.; Ehlers, Georg; Greedan, John E.; Gardner, Jason S.
2011-02-11
To understand the origin of the spin-glass state in molybdate pyrochlores, the structure of Tb{sub 2}Mo{sub 2}O{sub 7} is investigated using two techniques: the long-range lattice structure was measured using neutron powder diffraction (NPD), and local structure information was obtained from the extended x-ray absorption fine structure (EXAFS) technique. While the long-range structure appears generally well ordered, enhanced mean-squared site displacements on the O(1) site and the lack of temperature dependence of the strongly anisotropic displacement parameters for both the Mo and O(1) sites indicate some disorder exists. Likewise, the local structure measurements indicate some Mo-Mo and Tb-O(1) nearest-neighbor disorder exists, similar to that found in the related spin-glass pyrochlore, Y{sub 2}Mo{sub 2}O{sub 7}. Although the freezing temperature in Tb{sub 2}Mo{sub 2}O{sub 7}, 25 K, is slightly higher than in Y{sub 2}Mo{sub 2}O{sub 7}, 22 K, the degree of local pair distance disorder is actually less in Tb{sub 2}Mo{sub 2}O{sub 7}. This apparent contradiction is considered in light of the interactions involved in the freezing process.
Evidence for spin glass state of NdCo{sub 1−x}Ni{sub x}O{sub 3} (x = 0.3−0.5)
Kumar, Vinod Kumar, Rajesh; Singh, Kiran; Arora, S. K.; Shvets, I. V.; Kumar, Ravi
2014-08-21
Low-temperature magnetic properties of single phase NdCo{sub 1−x}Ni{sub x}O{sub 3}(x = 0.3−0.5) have been studied using ac and dc magnetic susceptibility measurements. Nickel substituted samples have been found to exhibit a different magnetic state at low temperature as compared to pristine NdCoO{sub 3}. The temperature dependent dc magnetization M (T) revealed the presence of a sharp cusp occurring at characteristic temperatures T{sub P}, for x = 0.3, 0.4, 0.5. Below T{sub P}, clear effect of magnetic field can be seen in M (T) curves and T{sub P} decreases with increasing magnetic field as well as Ni substitution content. The isothermal magnetization measurements at low temperatures shows small unsaturated hysteresis loop at lowest temperature (10 K). The ac susceptibility results show a clear frequency dependent feature. These results are analyzed to distinguish superparamagnetic and spin glass behavior by using Néel-Arrhennius, Vogel-Fulcher law, and power law fitting. This analysis ruled out the superparamagnet like state and suggests the presence of significant inter-cluster interactions, giving rise to spin-glass like cooperative freezing.
Ikeda, T; Wu, T J; Uchida, T; Hough, D; Fishbein, M C; Mandel, W J; Chen, P S; Karagueuzian, H S
1997-07-01
The mechanism(s) by which acetylcholine (ACh) increases atrial vulnerability to reentry and maintains its activity for longer durations remains poorly defined. In the present study we used high-resolution activation maps to test the hypothesis that ACh promotes meandering of atrial reentrant wave fronts, resulting in breakup and the generation of new wave fronts that sustain the activity. Reentry was induced in 11 isolated canine right atrial tissues (3.8 x 3.2 cm) by a premature point stimulus (S2) before and after superfusion with ACh (15 x 10(-6) M). Endocardial isochronal activation maps were constructed with the use of 509 bipolar electrodes (1.6-mm spatial resolution), and the dynamics of the activation wave fronts were visualized with animation. A vulnerable period was found during which an S2 current strength > 4.4 +/- 2.5 mA [lower limit of vulnerability (LLV)] and < 26 +/- 13 mA [upper limit of vulnerability (ULV)] induced a single stationary reentrant wave front that lasted 3 +/- 2.5 s with a period of 159 +/- 17 ms (16 episodes). AC shortened the refractory period from 100 +/- 12 to 59 +/- 9 ms (P < 0.001) and increased vulnerability to reentry induction by simultaneous decrease in the LLV (0.7 +/- 0.2 mA, P < 0.001) and an increase in the ULV (82 +/- 24 mA, P < 0.01). ACh accelerated the rate (period of 110 +/- 16 ms, P < 0.001) and converted the stationary reentrant wave front to a nonstationary (meandering) reentrant wave front showing polymorphic electrograms, i.e., "fibrillation-like" activity (22 episodes). Rapid meandering of the reentry tip led to wave front breakup (18 episodes) and the generation of new wave fronts (19 episodes). These wave front dynamics also led to sustained (76 +/- 224 s, P < 0.001) fibrillation-like electrograms. We conclude that ACh increases the ULV and promotes meandering of a single reentrant wave front, leading to breakup and the generation of new wave fronts. Single meandering and complex wave front dynamics cause
Mukherjee, Sumanta; Saha, Arnab; Santra, Pralay K; Sengupta, Surajit; Sarma, D D
2014-03-01
We study the phenomenon of evaporation-driven self-assembly of a colloid suspension of silica microspheres in the interior region and away from the rim of the droplet on a glass plate. In view of the importance of achieving a large-area, monolayer assembly, we first realize a suitable choice of experimental conditions, minimizing the influence of many other competing phenomena that usually complicate the understanding of fundamental concepts of such self-assembly processes in the interior region of a drying droplet. Under these simplifying conditions to bring out essential aspects, our experiments unveil an interesting competition between ordering and compaction in such drying systems in analogy to an impending glass transition. We establish a re-entrant behavior in the order-disorder phase diagram as a function of the particle density, such that there is an optimal range of the particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory. PMID:24490898
NASA Astrophysics Data System (ADS)
Deng, Nianpei
The two dimensional electron gas subjected to a magnetic field has been a model system in contemporary condensed matter physics which generated many beautiful experiments as well as novel fundamental concepts. These novel concepts are of broad interests and have benefited other fields of research. For example, the observations of conventional odd-denominator fractional quantum Hall states have enriched many-body physics with important concepts such as fractional statistics and composite fermions. The subsequent discovery of the enigmatic even-denominator nu=5/2 fractional quantum Hall state has led to more interesting concepts such as non-Abelian statistics and pairing of composite fermions which can be intimately connected to the electron pairing in superconductivity. Moreover, the observations of stripe phases and reentrant integer quantum Hall states have stimulated research on exotic electron solids which have more intricate structures than the Wigner Crystal. In contrast to fractional quantum Hall states and stripes phases, the reentrant integer quantum Hall states are very little studied and their ground states are the least understood. There is a lack of basic information such as exact filling factors, temperature dependence and energy scales for the reentrant integer quantum Hall states. A critical experimental condition in acquiring this information is a stable ultra-low temperature environment. In the first part of this dissertation, I will discuss our unique setup of 3He immersion cell in a state-of-art dilution refrigerator which achieves the required stability of ultra-low temperature. With this experimental setup, we are able to observe for the first time very sharp magnetotransport features of reentrant integer quantum Hall states across many Landau levels for the first time. I will firstly present our results in the second Landau level. The temperature dependence measurements reveal a surprisingly sharp peak signature that is unique to the reentrant
Optimizing glassy p-spin models
NASA Astrophysics Data System (ADS)
Thomas, Creightonk.; Katzgraber, Helmutg.
2011-04-01
Computing the ground state of Ising spin-glass models with p-spin interactions is, in general, an NP-hard problem. In this work we show that unlike in the case of the standard Ising spin glass with two-spin interactions, computing ground states with p=3 is an NP-hard problem even in two space dimensions. Furthermore, we present generic exact and heuristic algorithms for finding ground states of p-spin models with high confidence for systems of up to several thousand spins.
Coulomb blockade of spin-dependent shuttling
NASA Astrophysics Data System (ADS)
Park, Hee Chul; Kadigrobov, Anatoli M.; Shekhter, Robert I.; Jonson, M.
2013-12-01
We show that nanomechanical shuttling of single electrons may enable qualitatively new functionality if spin-polarized electrons are injected into a nanoelectromechanical single-electron tunneling (NEM-SET) device. This is due to the combined effects of spin-dependent electron tunneling and Coulomb blockade of tunneling, which are phenomena that occur in certain magnetic NEM-SET devices. Two effects are predicted to occur in such structures. The first is a reentrant shuttle instability, by which we mean the sequential appearance, disappearance and again the appearance of a shuttle instability as the driving voltage is increased (or the mechanical dissipation is diminished). The second effect is an enhanced spin polarization of the nanomechanically assisted current flow.
NASA Astrophysics Data System (ADS)
Yamaguchi, A.; Ishimoto, H.; Kojima, H.
2009-03-01
The superfluid component of ^3He A1 phase is spin-polarized. The process of forcing the superfluid component through a spin filtering structure, in a manner of mechano-magnetic effect, can be used to increase the spin polarization beyond the equilibrium under a given applied magnetic field. We have constructed a test cell in which a glass capillary array acts as the spin (and entropy) filter and an electrostatically actuated diaphragm forces the superfluid flow through it. Preliminary results show that a maximum relative increase of polarization by 50 % could be achieved. The maximum increase in polarization appears to be limited by the critical superfluid flow through the channels in the glass capillary array. The dependence of the observed effects on temperature, pressure and magnetic field will be presented.
Empowering Reentrant Projections from V5 to V1 Boosts Sensitivity to Motion.
Romei, Vincenzo; Chiappini, Emilio; Hibbard, Paul B; Avenanti, Alessio
2016-08-22
Evidence from macaques [1] and humans [2, 3] has shown that back projections from extrastriate areas to the primary visual area (V1) determine whether visual awareness will arise. For example, reentrant projections from the visual motion area (V5) to V1 are considered to be critical for awareness of motion [2, 3]. If these projections are also instrumental to functional processing of moving stimuli [4-8], then increasing synaptic efficacy in V5-V1 connections should induce functionally relevant short-term plastic changes, resulting in enhanced perception of visual motion. Using transcranial magnetic stimulation (TMS), we applied a novel cortico-cortical paired associative stimulation (ccPAS) protocol to transiently enhance visual motion sensitivity and demonstrate both the functional relevance of V5-V1 reentrant projections to motion perception and their plasticity. Specifically, we found that ccPAS aimed at strengthening reentrant connectivity from V5 to V1 (but not in the opposite direction) enhanced the human ability to perceive coherent visual motion. This perceptual enhancement followed the temporal profile of Hebbian plasticity [9-18] and was observed only when an optimal timing of 20 ms between TMS pulses [2, 3, 5, 6] was used, not when TMS pulses were delivered synchronously. Thus, plastic change is critically dependent on both the direction and timing of connectivity; if either of these requirements was not met, perceptual enhancement did not take place. We therefore provide novel causal evidence that V5-V1 back projections, instrumental to motion perception, are functionally malleable. These findings have implications for theoretical models of visual awareness and for the rehabilitation of visual deficits. PMID:27524488
Thermo-Chemical Ablation During Reentrant and High Altitude Skipping Flight
Havstad, M.; Carter, P.
2000-03-28
Thermo-chemical ablation during reentrant and high altitude skipping flights is treated using a variety of techniques. The solid material response is computed using heat-balance integrals, finite differences, and finite elements. The surface mass loss is computed using curve fits to the standard transport coefficient approach and by a surface kinetic model. Agreement between the approaches, when using the curve fits, is good. All approaches concur that for the skipping trajectory studied there is very little mass loss and surface temperatures remain in a range where the thermal protection system can be reused.
Reentrant valence transition in EuO at high pressures : beyond the bond-valence model
Souza-Neto, N.M.; Zhao, J.; Alp, E.; Shen, G.; Sinogeikin, S. V.; Lapertot, G.; Haskel, D.
2012-07-12
The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at {approx}45 GPa is accompanied by a reentrant Eu valence transition into a lower valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.
Phase Separation on Bicontinuous Cubic Membranes: Symmetry Breaking, Reentrant, and Domain Faceting.
Paillusson, Fabien; Pennington, Matthew R; Kusumaatmaja, Halim
2016-07-29
We study the phase separation of binary lipid mixtures that form bicontinuous cubic phases. The competition between the nonuniform Gaussian membrane curvature and line tension leads to a very rich phase diagram, where we observe symmetry breaking of the membrane morphologies and reentrant phenomena due to the formation of bridges between segregated domains. Upon increasing the line tension contribution, we also find faceting of lipid domains that we explain using a simple argument based on the symmetry of the underlying surface and topology. PMID:27517794
A quadrangular transverse Ising nanowire with an antiferromagnetic spin configuration
NASA Astrophysics Data System (ADS)
Kaneyoshi, T.
2015-11-01
The phase diagrams and the temperature dependences of magnetizations in a transverse Ising nanowire with an antiferromagnetic spin configuration are investigated by the use of the effective-field theory with correlations (EFT) and the core-shell concept. Many characteristic and unexpected behaviors are found for them, especially for thermal variation of total magnetization mT. The reentrant phenomenon induced by a transverse field in the core, the appearance of a compensation point, the non-monotonic variation with a compensation point, the reentrant phenomena with a compensation point and the existence of both a broad maximum and a compensation point have been found in the thermal variations of mT.
Insulating and metallic spin glass in K_{x}Fe_{2-δ-y}Ni_{y}Se_{2} (0.06 ≤ y ≤ 1.44 ) single crystals
Ryu, Hyejin; Abeykoon, Milinda; Wang, Kefeng; Lei, Hechang; Lazarevic, N.; Warren, J. B.; Bozin, E. S.; Popovic, Z. V.; Petrovic, C.
2015-05-04
We report electron doping effects by Ni in K_{x}Fe_{2-δ-y}Ni_{y}Se₂ (0.06 ≤ y ≤ 1.44) single crystal alloys. A rich ground state phase diagram is observed. Thus, a small amount of Ni (~ 4%) suppressed superconductivity below 1.8 K, inducing insulating spin glass magnetic ground state for higher Ni content. With further Ni substitution, metallic resistivity is restored. For high Ni concentration in the lattice the unit cell symmetry is high symmetry I4/mmm with no phase separation whereas both I4/m + I4/mmm space groups were detected in the phase separated crystals when concentration of Ni < Fe. The absence of superconductivity coincides with the absence of crystalline Fe vacancy order.
Sundaresan, A.; Maignan, A.; Raveau, B.
1997-03-01
Magnetic and magnetoresistance measurements were carried out on a distorted perovskite, Eu{sub 0.58}Sr{sub 0.42}MnO{sub 3}. In the absence of applied magnetic field, this compound is an insulator down to 5 K. Results of the ac- and dc-susceptibility measurements suggest a spin-glass ground state. An applied field of 7 T drives the insulator ground state to a ferromagnetic metallic state below T{sub C}=120 K. For a range of intermediate fields, the compound undergoes insulator-metal-insulator transitions which resemble those of 1:1 Mn{sup 3+}/Mn{sup 4+} charge-ordered compounds. A temperature-field phase diagram is established which depicts different magnetic and electronic states. {copyright} {ital 1997} {ital The American Physical Society}
Spin-glass behavior in Pr{sub 0.7}Ca{sub 0.3}CoO{sub 3} and Nd{sub 0.7}Ca{sub 0.3}CoO{sub 3}
Kundu, Asish K.; Nordblad, P.; Rao, C.N.R. . E-mail: cnrrao@jncasr.ac.in
2006-03-15
With a view to investigate the effect of small size of A-site cations on the magnetic properties of the rare earth cobaltates, Ln {sub 1-} {sub x}A{sub x} CoO{sub 3} (Ln=rare earth, A=alkaline earth), we have investigated Pr{sub 0.7}Ca{sub 0.3}CoO{sub 3} and Nd{sub 0.7}Ca{sub 0.3}CoO{sub 3} in detail. For this purpose, we have carried out low-field DC magnetization and ac susceptibility measurements including a study of magnetic relaxation and memory effects. Both Pr{sub 0.7}Ca{sub 0.3}CoO{sub 3} and Nd{sub 0.7}Ca{sub 0.3}CoO{sub 3} show frequency-dependent transitions at 70 and 55 K respectively in the ac susceptibility data, due to the onset of spin-glass like behavior. Their relaxation behavior exhibits aging effects. In addition, memory effects are found in the magnetization behavior. These characteristics establish spin-glass behavior in both these cobaltates, a behavior that is distinctly different from that of La{sub 0.7}Ca{sub 0.3}CoO{sub 3} and La{sub 0.5}Sr{sub 0.5}CoO{sub 3} which show well-defined ferromagnetic transitions, albeit without long-range ordering.
Current-biased Transition-edge Sensors Based on Re-entrant Superconductors
NASA Astrophysics Data System (ADS)
Gulian, A.; Nikoghosyan, V.; Tollaksen, J.; Vardanyan, V.; Kuzanyan, A.
Transition-edge sensors are widely recognized as one of the most sensitive tools for the photon and particles detection in many areas, from astrophysics to quantum computing. Their application became practical after understanding that rather than being biased in a constant current mode, they should be biased in a constant voltage mode. Despite the methods of voltage biasing of these sensors are well developed since then, generally the current biasing is more convenient for superconducting circuits. Thus transition-edge sensors designed inherently to operate in the current-biased mode are desirable. We developed a design for such detectors based on re-entrant superconductivity. In this case constant current biasing takes place in the normal state, below the superconducting transition, so that following the absorption of a photon it does not yield a latching. Rather, the sensor gains energy and shifts towards the lower resistant (e.g., superconducting) state, and then cools down faster (since Joule heating is now reduced), and resets in a natural way to be able to detect the next photon. We prototyped this kind of transition edge sensors and tested them operational in accordance with the outlined physics. The samples used in experiments were modified compositions of YBCO-superconductors in a ceramic form (which, as we discovered, reproducibly demonstrates re-entrant superconductivity). In this presentation we report their composition, methods of preparation, and the detection results. This approach, in some areas, may have practical advantage over the traditional voltage-biased devices.
Sa de Melo, C.A.R.
1996-02-01
The thermodynamics of quasi-one-dimensional superconductors in the presence of large magnetic fields is studied. When the quantum effects of the magnetic field are taken into account, several reentrant superconducting phases persist at very high fields. In the last reentrant phase the free energy change, the specific heat jump and the excess magnetization are estimated near the critical temperature. In particular, the excess magnetization is found to be paramagnetic as opposed to diamagnetic in weak fields and its sign is controlled by the slope of H{sub c{sub 2}} (T). The authors further generalize this result to the entire phase diagram (including all quantum phases) and to different physical systems using general thermodynamic relations which show that the sign of the excess magnetization {Delta}M of the superconducting state near H{sub c{sub 2}}(T) follows dH{sub c{sub 2}}(T)/dT. These relations provide a scenario for the evolution of the sign of {Delta}M from weak fields to strong fields.
NASA Astrophysics Data System (ADS)
Weisensee, Patricia B.; Torrealba, Eduardo J.; Raleigh, Mark; Jacobi, Anthony M.; King, William P.
2014-09-01
This paper presents the fabrication of metallic micro-mushroom re-entrant structures and the characterization of their hydrophobicity and oleophobicity. Five different microstructure geometries are introduced, with typical feature sizes in the range of 10-100 μm. These microstructures are realized in steel, and are fabricated over the cm-scale using micro electrical discharge machining (mEDM). The liquid repellency of these surfaces is characterized using droplets of either water (surface energy γlg = 72.4 mN m-1), RL-68H oil (γlg = 28.6 mN m-1), or Isopropanol (IPA) (γlg = 21.7 mN m-1). The water droplets form nearly perfect spheres, with contact angles in the range 146-162°, and contact angle hysteresis of 19-35°. The oil droplet contact angles are in the range 106-152° and the IPA contact angles are in the range 75-123°. Strong re-entrant features and close spacing are necessary to support a fully non-wetting state for use with oil and IPA. Water forms the highest contact angles with narrow, post-like, and widely spaced micro-mushroom geometries.
Reentrant excitation in an analog-digital hybrid circuit model of cardiac tissue
NASA Astrophysics Data System (ADS)
Mahmud, Farhanahani; Shiozawa, Naruhiro; Makikawa, Masaaki; Nomura, Taishin
2011-06-01
We propose an analog-digital hybrid circuit model of one-dimensional cardiac tissue with hardware implementation that allows us to perform real-time simulations of spatially conducting cardiac action potentials. Each active nodal compartment of the tissue model is designed using analog circuits and a dsPIC microcontroller, by which the time-dependent and time-independent nonlinear current-voltage relationships of six types of ion channel currents employed in the Luo-Rudy phase I (LR-I) model for a single mammalian cardiac ventricular cell can be reproduced quantitatively. Here, we perform real-time simulations of reentrant excitation conduction in a ring-shaped tissue model that includes eighty nodal compartments. In particular, we show that the hybrid tissue model can exhibit real-time dynamics for initiation of reentries induced by uni-directional block, as well as those for phase resetting that leads to annihilation of the reentry in response to impulsive current stimulations at appropriate nodes and timings. The dynamics of the hybrid model are comparable to those of a spatially distributed tissue model with LR-I compartments. Thus, it is conceivable that the hybrid model might be a useful tool for large scale simulations of cardiac tissue dynamics, as an alternative to numerical simulations, leading toward further understanding of the reentrant mechanisms.
Sarsam, Sinan; Sidiqi, Ibrahim; Shah, Dipak; Zughaib, Marcel
2015-01-01
Patient: Male, 54 Final Diagnosis: WPW and AVNRT Symptoms: Palpitations • shorthness of breath Medication: — Clinical Procedure: EP Study/Radiofrequency Ablation Specialty: Cardiology Objective: Rare co-existance of disease or pathology Background: Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of supraventricular tachycardia. In contrast, Wolff-Parkinson-White (WPW) pattern consists of an accessory pathway, which may result in the development of ventricular arrhythmias. Frequent tachycardia caused by AVNRT and accessory pathways may play a role in left ventricular systolic dysfunction. Case Report: A 54-year-old man presented with palpitations and acute decompensated congestive heart failure. His baseline EKG showed Wolff-Parkinson-White (WPW) pattern. While hospitalized, he had an episode of atrioventricular nodal reentrant tachycardia (AVNRT). He underwent radiofrequency catheter ablation for AVNRT, and his accessory pathway was also ablated even though its conduction was found to be weak. He was clinically doing well on follow-up visit, with resolution of his heart failure symptoms and normalization of left ventricular function on echocardiography. Conclusions: This case raises the question whether the accessory pathway plays a role in the development of systolic dysfunction, and if there is any role for ablation in patients with asymptomatic WPW pattern. PMID:26655223
Complex Structures in the Reentrant Phase Diagram of HoNi_2B_2C
NASA Astrophysics Data System (ADS)
Childers, J.; Zhang, J.; Olinger, A., Jr.; Metlushko, V.; Delong, L.; Canfield, P.
1996-03-01
HoNi_2B_2C exhibits a resistive onset to superconductivity near 9.0 K, followed by transitions to incommensurate magnetic order (IMO) at 6.0 K and 5.5 K, and commensurate antiferromagnetic order (AFM) at TN = 5.2 K. Vibrating reed (VR) and resistance data reveal two previously unobserved lines of magnetic anomalies in both the upper superconducting (SC) and lower reentrant SC regions for H || a*b*. The wide region between the upper onset of SC and the first magnetic anomaly reflects weak vortex pinning, possibly due to a subtle buildup of IMO from well above 8K. The interplay between SC and magnetic order is evident in abrupt displacements of transition lines to IMO near their crossing with the reentrant normal transition line for 5.2
Reentrant-Like Band Jahn-Teller Effect and its Field Dependence
NASA Astrophysics Data System (ADS)
Gangadhar Reddy, G.; Venkatappa Rao, T.; Ramakanth, A.; Ghatak, S. K.; Behera, S. N.
In the presence of the electron-lattice interaction where the lattice strain is coupled to the difference in orbital occupancy, the metallic system whose Fermi level lies in an orbitally degenerate eg band undergoes a structural transition to a lower symmetric state with distortion. The distortion is the consequence of the band Jahn-Teller (J-T) effect, and results from the gain of the electronic energy against the increase in the elastic energy. The extent of distortion depends on the nature of the density of states (DOS) and carrier concentration. These effects are examined for a system described by a different model DOS, and an orbitally degenerate eg band with the J-T interaction. In a certain region of parameter space, the temperature dependence of distortion exhibits a reentrant-like behavior, and the magnetic field augments the distortion in this region. In the parameter space where there is no reentrant-like behavior, the field suppresses the distortion, and the normalized distortion becomes a universal function of the normalized field. A phase diagram is obtained in the magnetic field-temperature plane.
Reentrant superconductivity in HoNi5-NbN-HoNi5 nanostructures
NASA Astrophysics Data System (ADS)
Singh, Gyanendra; Joshi, P. C.; Hossain, Z.; Budhani, R. C.
2013-08-01
Superconductivity (S) and ferromagnetism (F) are probed through transport and magnetization measurements in nanometer scale HoNi5-NbN (F-S) bilayers and HoNi5-NbN-HoNi5 (F-S-F) trilayers. The choice of materials has been made on the basis of their comparable ordering temperatures and strong magnetic anisotropy in HoNi5. We observe the normal state reentrant behavior in resistance vs. temperature plots of the F-S-F structures just below the superconducting transition in the limited range of HoNi5 layer thickness dHN (20\\ \\text{nm}) when d_{\\textit{NbN}} is fixed at{}\\simeq 10\\ \\text{nm} . The reentrance is quenched by increasing the out-of-plane (H_{\\perp} ) magnetic field and transport current where as in-plane (H_{\\parallel} ) field of \\leq 1500\\ \\text{Oe} has no effect on the reentrance. The origin of the reentrant behavior seen here in the range T_{\\textit{Curie}}/T_C \\leq 0.92 is attributed to a delicate balance between the magnetic exchange energy and the condensation energy in the interfacial regions of the trilayer.
Lammers, W J; Schalij, M J; Kirchhof, C J; Allessie, M A
1990-10-01
In isolated superfused left atria of the rabbit, inhomogeneity in conduction was quantified using the activation times measured with a high-density mapping system. At each recording site, the maximal difference with neighboring activation times (i.e., phase difference) was calculated. Local phase differences were plotted in a phase map, revealing the spatial distribution of inhomogeneities in conduction, and from each map a total index of inhomogeneity was calculated. During slow pacing (2 Hz) local differences in conduction velocity, depending on the direction of propagation, were found already. Inhomogeneity in conduction increased significantly during single early premature beats (inhomogeneity index increased from 2.3 to 3.1; P less than 0.001). The application of multiple premature beats further increased inhomogeneity in conduction, whereas rapid pacing induced the highest level of inhomogeneity (inhomogeneity index 5.3; P less than 0.001). An analysis of the spatial distribution of maximal phase differences revealed that during premature beats inhomogeneities in conduction were limited to an area of 6 mm around the point of origin of the premature impulse, whereas during rapid pacing inhomogeneities in conduction were found throughout the whole preparation. Phase maps constructed during the initiation of reentrant tachyarrhythmias showed that reentry occurred at sites with the highest phase differences. Quantification of spatial inhomogeneities in conduction is a useful tool to evaluate the vulnerability of the myocardial substrate for reentrant arrhythmias. PMID:1699438
Origin of spin-glass and exchange bias in La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} nanoparticles
Silva, R. B. da; Araújo, J. H. de; Soares, J. M.; Machado, F. L. A.
2014-03-21
The structure and the magnetic properties of nanopowdered samples of La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} with average particles size d in the range of 67-367 nm prepared by a sol-gel method were investigated in detail. The samples were characterized by X-ray diffraction, scanning electron microscopy, specific heat, Mössbauer spectroscopy, ac susceptibility, and magnetization measurements. Exchange bias with vertical magnetization shift was found in all samples. Charge ordering and antiferromagnetism were observed close to 200 K for large particles (d ≥ 304 nm) samples, while for particles with intermediated and smaller values (d ≤ 156 nm) a cluster-glass like behaviour and a short range charge ordering were seen near 115 K and 200 K, respectively. The spin-glass like and exchange bias behaviour in nanopowdered samples of La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} are associated to compact Fe{sup 3+} antiferromagnetic (AF) clusters caused by an oxygen deficiency, which was found to be higher in the samples with the smallest average particles sizes. The effect of exchange bias and vertical magnetization shifts are explained by a simple model involving the interaction of one AF phase with a canted AF phase.
NASA Astrophysics Data System (ADS)
Suzuki, Itsuko S.; Suzuki, Masatsugu
2008-12-01
Cu0.5Co0.5Cl2-FeCl3 graphite bi-intercalation compound is a three-dimensional short-range spin glass with a spin freezing temperature TSG (=3.92±0.11K) . The time evolution of the zero-field-cooled magnetization MZFC(t) has been measured under various combinations of wait time (tw) , temperature (T) , temperature shift (ΔT) , and magnetic field (H) . The relaxation rate SZFC(t) [=(1/H)dMZFC(t)/dlnt] shows a peak at a peak time tcr . The shape of SZFC(t) in the vicinity of tcr is well described by stretched exponential relaxation (SER). The SER exponent b and the SER relaxation time τSER are determined as a function of tw , T , H , and ΔT . The value of b at T=TSG is nearly equal to 0.3. There is a correlation between τSER and 1/b , irrespective of the values of tw , T , H , and ΔT . These features can be well explained in terms of a simple relaxation model for glassy dynamics.
NASA Astrophysics Data System (ADS)
Lv, Yi-Fei; Xiang, Jian-Yong; Wen, Fu-Sheng; Lv, Wei-Ming; Hu, Wen-Tao; Liu, Zhong-Yuan
2015-03-01
Single phase of Fe3+-doped α-Ga2-xFexO3 (α-GFxO, x = 0.1, 0.2, 0.3, 0.4) is synthesized by treating the β-Ga2-xFexO3 (β-GFxO) precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe3+ content. Calorimetric measurements show that the temperature of the phase transition from α-GFxO to β-GFxO increases, while the associated enthalpy change decreases upon increasing Fe3+ content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe3+ content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe3+ ions is antiferromagnetic. Remnant magnetization is observed in the Fe3+-doped α-GFxO and is attributed to the spin glass in the magnetic sublattice. At high Fe3+ doping level (x = 0.4), two evident peaks are observed in the image part of the AC susceptibility . The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α-GF0.4O is suggested to be the behavior of two spin glasses. Project supported by the National Basic Research Program of China (Grant No. 2010CB731605), the National Science Fund for Distinguished Young Scholars of China (Grant No. 51025103), the National Natural Science Foundation of China (Grant Nos. 51172198 and 51102206), the Natural Science Foundation of Hebei Province, China (Grant No. E2014203144), the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province, China (Grant No. YQ2014009), and the Research Program of the College Science & Technology of Hebei Province, China (Grant No. QN2014047).
Ciaccio, Edward J.; Coromilas, James; Ashikaga, Hiroshi; Cervantes, Daniel O.; Wit, Andrew L.; Peters, Nicholas S.; McVeigh, Elliot R.; Garan, Hasan
2015-01-01
Background When the infarct border zone is stimulated prematurely, a unidirectional block line (UBL) can form and lead to double-loop (figure-of-eight) reentrant ventricular tachycardia (VT) with a central isthmus. The isthmus is composed of an entrance, center, and exit. It was hypothesized that for certain stimulus site locations and coupling intervals, the UBL would coincide with the isthmus entrance boundary, where infarct border zone thickness changes from thin-to-thick in the travel direction of the premature stimulus wavefront. Method A quantitative model was developed to describe how thin-to-thick changes in the border zone result in critically convex wavefront curvature leading to conduction block, which is dependent upon coupling interval. The model was tested in 12 retrospectively analyzed postinfarction canine experiments. Electrical activation was mapped for premature stimulation and for the first reentrant VT cycle. The relationship of functional conduction block forming during premature stimulation to functional block during reentrant VT was quantified. Results For an appropriately placed stimulus, in accord with model predictions: (1) The UBL and reentrant VT isthmus lateral boundaries overlapped (error: 4.8±5.7 mm). (2) The UBL leading edge coincided with the distal isthmus where the center-entrance boundary would be expected to occur. (3) The mean coupling interval was 164.6±11.0 ms during premature stimulation and 190.7±20.4 ms during the first reentrant VT cycle, in accord with model calculations, which resulted in critically convex wavefront curvature with functional conduction block, respectively, at the location of the isthmus entrance boundary and at the lateral isthmus edges. Discussion Reentrant VT onset following premature stimulation can be explained by the presence of critically convex wavefront curvature and unidirectional block at the isthmus entrance boundary when the premature stimulation interval is sufficiently short. The
Glass liquid glass reentrance in mono-component colloidal dispersions
NASA Astrophysics Data System (ADS)
Ramírez-González, P. E.; Vizcarra-Rendón, A.; Guevara-Rodríguez, F. de J.; Medina-Noyola, M.
2008-05-01
The self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics is employed to describe the ergodic-non-ergodic transition in model mono-disperse colloidal dispersions whose particles interact through hard-sphere plus short-ranged attractive forces. The ergodic-non-ergodic phase diagram in the temperature-concentration state space is determined for the hard-sphere plus attractive Yukawa model within the mean spherical approximation for the static structure factor by solving a remarkably simple equation for the localization length of the colloidal particles. Finite real values of this property signals non-ergodicity and determines the non-ergodic parameters f(k) and fs(k). The resulting phase diagram for this system, which involves the existence of reentrant (repulsive and attractive) glass states, is compared with the corresponding prediction of mode coupling theory. Although both theories coincide in the general features of this phase diagram, there are also clear qualitative differences. One of the most relevant is the SCGLE prediction that the ergodic-attractive glass transition does not preempt the gas-liquid phase transition, but always intersects the corresponding spinodal curve on its high-concentration side. We also calculate the ergodic-non-ergodic phase diagram for the sticky hard-sphere model to illustrate the dependence of the predicted SCGLE dynamic phase diagram on the choice of one important constituent element of the SCGLE theory.
Brow, R.K.; Kovacic, L.; Chambers, R.S.
1996-04-01
Hernetic glass sealing technologies developed for weapons component applications can be utilized for the design and manufacture of fuel cells. Design and processing of of a seal are optimized through an integrated approach based on glass composition research, finite element analysis, and sealing process definition. Glass sealing procedures are selected to accommodate the limits imposed by glass composition and predicted calculations.
Bimodality and re-entrant behaviour in the hierarchical self-assembly of polymeric nanoparticles.
C K, Sarika; Tomar, Gaurav; Basu, J K; Thiele, Uwe
2015-12-14
We show that a film of a suspension of polymer grafted nanoparticles on a liquid substrate can be employed to create two-dimensional nanostructures with a remarkable variation in the pattern length scales. The presented experiments also reveal the emergence of concentration-dependent bimodal patterns as well as re-entrant behaviour that involves length scales due to dewetting and compositional instabilities. The experimental observations are explained through a gradient dynamics model consisting of coupled evolution equations for the height of the suspension film and the concentration of polymer. Using a Flory-Huggins free energy functional for the polymer solution, we show in a linear stability analysis that the thin film undergoes dewetting and/or compositional instabilities depending on the concentration of the polymer in the solution. We argue that the formation via 'hierarchical self-assembly' of various functional nanostructures observed in different systems can be explained as resulting from such an interplay of instabilities. PMID:26406929
Reentrant superconducting behavior of the Josephson SFS junction. Evidence for the π-phase state
NASA Astrophysics Data System (ADS)
Ryazanov, V. V.; Veretennikov, A. V.; Oboznov, V. A.; Rusanov, A. Yu.; Larkin, V. A.; Golubov, A. A.; Aarts, J.
2000-11-01
Critical supercurrents, Ic in Nbsbnd Cu1- xNixsbnd Nb Josephson SFS junctions with F-layers prepared from ferromagnetic Cu1- xNix alloys have been studied. For value x=0.52 and particular F-layer thickness we have observed Ic( T) oscillations with Ic vanishing for some values of T. We associate this reentrant superconducting behavior with a crossover of the SFS junction from ‘0’- to ‘π’-state that is related to temperature dependence of spatial oscillation period of induced superconducting order parameter in the weak ferromagnet. We argue this is the first experimental evidence of the π-behavior of a Josephson junction, that is the special feature of superconducting pair flow through a ferromagnet predicted for SFS junctions by Bulaevskii, Buzdin et al [1].
Bragard, Jean Simic, Ana; Elorza, Jorge; Grigoriev, Roman O.; Fenton, Flavio H.; Cherry, Elizabeth M.; Gilmour, Robert F.; Otani, Niels F.
2013-12-15
In this article, we compare quantitatively the efficiency of three different protocols commonly used in commercial defibrillators. These are based on monophasic and both symmetric and asymmetric biphasic shocks. A numerical one–dimensional model of cardiac tissue using the bidomain formulation is used in order to test the different protocols. In particular, we performed a total of 4.8 × 10{sup 6} simulations by varying shock waveform, shock energy, initial conditions, and heterogeneity in internal electrical conductivity. Whenever the shock successfully removed the reentrant dynamics in the tissue, we classified the mechanism. The analysis of the numerical data shows that biphasic shocks are significantly more efficient (by about 25%) than the corresponding monophasic ones. We determine that the increase in efficiency of the biphasic shocks can be explained by the higher proportion of newly excited tissue through the mechanism of direct activation.
Cheng, Chao; Jia, Jun-Li; Ran, Shi-Yong
2015-05-21
In this study, we investigated the DNA condensation induced by polyethylene glycol (PEG) with different molecular weights (PEG 600 and PEG 6000) in the presence of NaCl or MgCl2 by using magnetic tweezers (MT) and atomic force microscopy (AFM). The MT measurements show that with increasing NaCl concentration, the critical condensation force in the PEG 600-DNA or PEG 6000-DNA system increased approximately linearly. PEG 6000 solution has a larger critical force than PEG 600 solution at a given NaCl concentration. In comparison, a parabolic trend of the critical condensation force was observed with increasing MgCl2 concentration, indicating that DNA undergoes a reentrant condensation. The AFM results show that the morphologies of the compacted DNA-PEG complexes depended on the salt concentration and were consistent with the MT results. PMID:25871460
Re-entrant phase behavior for systems with competition between phase separation and self-assembly
NASA Astrophysics Data System (ADS)
Reinhardt, Aleks; Williamson, Alexander J.; Doye, Jonathan P. K.; Carrete, Jesús; Varela, Luis M.; Louis, Ard A.
2011-03-01
In patchy particle systems where there is a competition between the self-assembly of finite clusters and liquid-vapor phase separation, re-entrant phase behavior can be observed, with the system passing from a monomeric vapor phase to a region of liquid-vapor phase coexistence and then to a vapor phase of clusters as the temperature is decreased at constant density. Here, we present a classical statistical mechanical approach to the determination of the complete phase diagram of such a system. We model the system as a van der Waals fluid, but one where the monomers can assemble into monodisperse clusters that have no attractive interactions with any of the other species. The resulting phase diagrams show a clear region of re-entrance. However, for the most physically reasonable parameter values of the model, this behavior is restricted to a certain range of density, with phase separation still persisting at high densities.
Reentrant superfluidity and pair density wave in single-component dipolar Fermi gases
NASA Astrophysics Data System (ADS)
Che, Yanming; Wang, Jibiao; Chen, Qijin
2016-06-01
We study the superfluidity of single-component dipolar Fermi gases in three dimensions using a pairing fluctuation theory, within the context of BCS-BEC crossover. The transition temperature Tc for the dominant pz wave superfluidity exhibits a remarkable reentrant behavior as a function of the pairing strength induced by the dipole-dipole interaction (DDI), which leads to an anisotropic pair dispersion. The anisotropy and the long-range nature of the DDI cause Tc to vanish for a narrow range of intermediate interaction strengths, where a pair density wave emerges as the ground state. The superfluid density and thermodynamics below Tc, along with the density profiles in a harmonic trap, are investigated as well. Implications for experiments are discussed.
Idiopathic intrafascicular reentrant left ventricular tachycardia in an elite cyclist athlete.
Riera, Andrés Ricardo Pérez; Ragognete, Ricardo Gitti; Filho, Celso Ferreira; Ferreira, Marcelo; Schapachnik, Edgardo; Dubner, Sergio; Ferreira, Celso; Mochon, Agnieszka; Zhang, Li
2009-01-01
A 32 year-old Caucasian male, an elite athlete, was admitted to the emergency department because of a sudden onset of palpitations which had lasted more than 12 hours and were associated with chest discomfort. He had a two-year history of recurrent stress-induced palpitations. He denied either episodes of syncope or any family history of sudden death. Physical examination was normal. He had no evidence of structural heart disease. The electrocardiography (ECG) documented during the event supported the diagnosis of idiopathic reentrant left ventricular tachycardia. Ventricular tachycardia ablation was successful. This case demonstrates that a careful physical examination and correct ECG diagnosis can lead to an appropriate arrhythmia management. PMID:19950094
Energy Scales of the Reentrant Integer Quantum Hall States in High Landau Levels
NASA Astrophysics Data System (ADS)
Deng, Nianpei; Watson, John; Manfra, Michael; Csathy, Gabor
2013-03-01
The reentrant integer quantum Hall states (RIQHS) have been identified with the electronic bubble phases. These bubble phases are exotic electronic solids similar to the Wigner crystal, but have more than one electron per lattice site. Recently we reported the presence of a peak in the temperature dependent magnetoresistence of the RIQHSs and we have associated this peak with the onset of the RIQHSs. We found that, contrary to the predictions of the bubble theory, the onset temperatures of the RIQHSs in the third Landau level are much higher than those in the second Landau level. We have extended such measurements of the onset temperatures to several high Landau levels. In this talk we will discuss the orbital dependence of the onset temperatures of RIQHSs and we will compare these quantitative results to the predictions of the bubble theory. This work was supported by the DOE BES contract no. DE-SC0006671.
Reentrant phase transitions and defensive alliances in social dilemmas with informed strategies
NASA Astrophysics Data System (ADS)
Szolnoki, Attila; Perc, Matjaž
2015-05-01
Knowing the strategy of an opponent in a competitive environment conveys obvious evolutionary advantages. But this information is costly, and the benefit of being informed may not necessarily offset the additional cost. Here we introduce social dilemmas with informed strategies, and we show that this gives rise to two cyclically dominant triplets that form defensive alliances. The stability of these two alliances is determined by the rotation velocity of the strategies within each triplet. A weaker strategy in a faster rotating triplet can thus overcome an individually stronger competitor. Fascinating spatial patterns favor the dominance of a single defensive alliance, but enable also the stable coexistence of both defensive alliances in very narrow regions of the parameter space. A continuous reentrant phase transition reveals before unseen complexity behind the stability of strategic alliances in evolutionary social dilemmas.
Re-entrant melting as a design principle for DNA-coated colloids
NASA Astrophysics Data System (ADS)
Angioletti-Uberti, Stefano; Mognetti, Bortolo M.; Frenkel, Daan
2012-06-01
Colloids functionalized with DNA hold great promise as building blocks for complex self-assembling structures. However, the practical use of DNA-coated colloids (DNACCs) has been limited by the narrowness of the temperature window where the target structures are both thermodynamically stable and kinetically accessible. Here we propose a strategy to design DNACCs, whereby the colloidal suspensions crystallize on cooling and then melt on further cooling. In a phase diagram with such a re-entrant melting, kinetic trapping of the system in non-target structures should be strongly suppressed. We present model calculations and simulations that show that real DNA sequences exist that should bestow this unusual phase behaviour on suitably functionalized colloidal suspensions. We present our results for binary systems, but the concepts that we develop apply to multicomponent systems and should therefore open the way towards the design of truly complex self-assembling colloidal structures.
NASA Astrophysics Data System (ADS)
Bragard, Jean; Simic, Ana; Elorza, Jorge; Grigoriev, Roman O.; Cherry, Elizabeth M.; Gilmour, Robert F.; Otani, Niels F.; Fenton, Flavio H.
2013-12-01
In this article, we compare quantitatively the efficiency of three different protocols commonly used in commercial defibrillators. These are based on monophasic and both symmetric and asymmetric biphasic shocks. A numerical one-dimensional model of cardiac tissue using the bidomain formulation is used in order to test the different protocols. In particular, we performed a total of 4.8 × 106 simulations by varying shock waveform, shock energy, initial conditions, and heterogeneity in internal electrical conductivity. Whenever the shock successfully removed the reentrant dynamics in the tissue, we classified the mechanism. The analysis of the numerical data shows that biphasic shocks are significantly more efficient (by about 25%) than the corresponding monophasic ones. We determine that the increase in efficiency of the biphasic shocks can be explained by the higher proportion of newly excited tissue through the mechanism of direct activation.
On the phase diagram of reentrant condensation in polyelectrolyte-liposome complexation
NASA Astrophysics Data System (ADS)
Sennato, S.; Bordi, F.; Cametti, C.
2004-09-01
Complexation of polyions with oppositely charged spherical liposomes has been investigated by means of dynamic light scattering measurements and a well-defined reentrant condensation has been observed. The phase diagram of charge inversion, recently derived [T. T. Nguyen and B. I. Shklovskii, J. Chem. Phys. 115, 7298 (2001)] for the complexation of DNA with charged spherical macroions, has been employed in order to define the boundaries of the region where polyion-liposome complexes begin to condense, forming larger aggregates, and where aggregates dissolve again, towards isolated polyion-coated-liposome complexes. A reasonable good agreement is observed in the case of complexes formed by negatively charged polyacrylate sodium salt polyions and liposomes built up by cationic lipids (dioleoyltrimethylammoniumpropane), in an extended liposome concentration range.
NASA Astrophysics Data System (ADS)
Thangavelu, Karthik; Asthana, Saket
2015-09-01
The effect of magnetic cation substitution on the phase stabilization, ferroelectric, dielectric and magnetic properties of a lead free Na0.5Bi0.5TiO3 (NBT) system prepared by O2 atmosphere solid state sintering were studied extensively. Cobalt (Co) was chosen as the magnetic cation to substitute at the Ti-site of NBT with optimized 2.5 mol%. Rietveld analysis of x-ray diffraction data favours the monoclinic Cc phase stabilization strongly rather than the parent R3c phase. FE-SEM micrograph supports the single phase characteristics without phase segregation at the grain boundaries. The stabilized Cc space group was explained based on the collective local distortion effects due to spin-orbit stabilization at Co3+ and Co2+ functional centres. The phonon mode changes as observed in the TiO6 octahedral modes also support the Cc phase stabilization. The major Co3+-ion presence was revealed from corresponding crystal field transitions observed through solid state diffuse reflectance spectroscopy. The enhanced spontaneous polarization (Ps) from ≅38 μC cm-2 to 45 μC cm-2 could be due to the easy rotation of polarization vector along the {(1\\bar{1}0)}{{pc}} in Cc phase. An increase in static dielectric response (ɛ) from ɛ ≅ 42 to 60 along with enhanced diffusivity from γ ≅ 1.53 to 1.75 was observed. Magneto-thermal irreversibility and their magnetic field dependent ZFC/FC curves suggest the possibility of a spin glass like behaviour below 50 K. The monoclinic Cc phase stabilization as confirmed from structural studies was well correlated with the observed ferroic properties in magnetically diluted NBT.
Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.
2015-11-19
We describe Co substitution effects in K_{x}Fe_{2-y-z}Co_{z}Se_{2 } (0.06 ≤ z ≤ 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K_{2}Fe_{4}Se_{5} and superconducting/metallic K_{x}Fe_{2}Se_{2} is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell, arrangement and connectivity of stripe conducting phase.
NASA Astrophysics Data System (ADS)
Chau, N.; Tho, N. D.; Luong, N. H.; Giang, B. H.; Cong, B. T.
2006-08-01
The mixed rare earth manganites Nd 0.5-xPr xSr 0.5MnO 3 ( x=0.1-0.5) have been prepared using solid state reaction technique. All samples are of single phase with orthorhombic structure. The microstructure of the samples was determined by SEM. The field-cooled (FC) and zero-field-cooled (ZFC) curves showed that samples with x⩾0.25 exhibit the spin glass-like state at low field and low temperatures, whereas, in the samples with x<0.25, there is the charge ordering (coexisting with FM-AFM transition) established at low temperatures. The Curie temperature of the samples increases with increasing Pr content due to increase of < rA>. Interesting feature is that at the FM-AFM transition region, the magnetic entropy change has positive value, in contrary to that at FM-PM transition region. The electrical property of the samples from 10 K to room temperature is examined in detail.
A transverse Ising bilayer film with an antiferromagnetic spin configuration
NASA Astrophysics Data System (ADS)
Kaneyoshi, T.
2015-10-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising bilayer film with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory (EFT) with correlations, in order to clarify whether the appearance of a compensation point is possible below the transition temperature in the system. From these investigations, we have found a lot of characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value, such as the reentrant phenomenon free from the disorder-induced frustration and the novel types of magnetization curve with a compensation point.
Coulomb Glass: a Mean Field Study
NASA Astrophysics Data System (ADS)
Mandra, Salvatore; Palassini, Matteo
2012-02-01
We study the Coulomb glass model of disordered localized electrons with long-range Coulomb interaction, which describes systems such as disordered insulators, granular metals, amorphous semiconductors, or doped crystalline semiconductors. Long ago Efros and Shklovskii showed that the long-range repulsion induces a soft Coulomb gap in the single particle density of states at low temperatures. Recent works suggested that this gap is associated to a transition to a glass phase, similar to the Almeida-Thouless transition in spin glasses. In this work, we use a mean field approach to characterize several physical properties of the Coulomb glass. In particular, following a seminal work of Bray and Moore, we show that the Edward-Anderson parameter qEA and the spin glass susceptibility χSG are directly related to spectrum distribution of the Hessian matrix around free energy minima. Using this result, we show that no glass transition is associated to the gap formation.
Brown, Philip S.; Bhushan, Bharat
2016-01-01
Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices. PMID:26876479
Brown, Philip S; Bhushan, Bharat
2016-01-01
Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices. PMID:26876479
NASA Astrophysics Data System (ADS)
Brown, Philip S.; Bhushan, Bharat
2016-02-01
Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices.
NASA Astrophysics Data System (ADS)
Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas
2015-08-01
In a previous paper [Phys. Rev. E 83, 021801 (2011), 10.1103/PhysRevE.83.021801] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ˜100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (μ SR ) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ˜100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the μ SR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings.
Kanaya, Toshiji; Ogawa, Hiroki; Kishimoto, Mizuki; Inoue, Rintaro; Suter, Andreas; Prokscha, Thomas
2015-08-01
In a previous paper [Phys. Rev. E 83, 021801 (2011)] we performed neutron reflectivity (NR) measurements on a five-layer polystyrene (PS) thin film consisting of alternatively stacked deuterated polystyrene (dPS) and hydrogenated polystyrene (hPS) layers (dPS/hPS/dPS/hPS/dPS, ∼100 nm thick) on a Si substrate to reveal the distribution of Tg along the depth direction. Information on the Tg distribution is very useful to understand the interesting but unusual properties of polymer thin films. However, one problem that we have to clarify is if there are effects of deuterium labeling on Tg or not. To tackle the problem we performed low-energy muon spin relaxation (μSR) measurements on the above-mentioned deuterium-labeled five-layer PS thin film as well as dPS and hPS single-layer thin films ∼100 nm thick as a function of muon implantation energy. It was found that the deuterium labeling had no significant effects on the Tg distribution, guaranteeing that we can safely discuss the unusual thin film properties based on the Tg distribution revealed by NR on the deuterium-labeled thin films. In addition, the μSR result suggested that the higher Tg near the Si substrate is due to the strong orientation of phenyl rings. PMID:26382423
Taylor, P.C.
1987-08-15
Although there are some significant exceptions, most important glass-forming systems contain elements from the sixth, or chalcogenide, column of the periodic table (oxygen, sulfur, selenium, or tellurium). The glasses that contain oxygen are typically insulators, while those that contain the heavier chalcogen elements are usually semiconductors. Even though oxygen is technically a chalcogen element, the term chalcogenide glass is commonly used to denote those largely covalent, semiconducting glasses contain sulfur, selenium, or tellurium as one of the constituents.
Creating tuneable microwave media from a two-dimensional lattice of re-entrant posts
Goryachev, Maxim; Tobar, Michael E.
2015-11-28
The potential capabilities of resonators based on two dimensional arrays of re-entrant posts is demonstrated. Such posts may be regarded as magnetically coupled lumped element microwave harmonic oscillators, arranged in a 2D lattices structure, which is enclosed in a 3D cavity. By arranging these elements in certain 2D patterns, we demonstrate how to achieve certain requirements with respect to field localisation and device spectra. Special attention is paid to symmetries of the lattices, mechanical tuning, design of areas of high localisation of magnetic energy; this in turn creates unique discrete mode spectra. We demonstrate analogies between systems designed on the proposed platform and well known physical phenomena such as polarisation, frustration, and Whispering Gallery Modes. The mechanical tunability of the cavity with multiple posts is analysed, and its consequences to optomechanical applications is calculated. One particular application to quantum memory is demonstrated with a cavity design consisting of separate resonators analogous to discrete Fabry–Pérot resonators. Finally, we propose a generalised approach to a microwave system design based on the concept of Programmable Cavity Arrays.
Mamontov, Eugene; O'Neill, Hugh Michael
2014-01-01
Recent studies have outlined the use of eutectic solution of lithium chloride in water to study microscopic dynamics of lysozyme in an aqueous solvent that is remarkably similar to pure water in many respects, yet allows experiments over a wide temperature range without the solvent crystallization. The eutectic point in (H2O)R(LiCl) system corresponds to R 7.3, and it is of interest to investigate whether less concentrated aqueous solutions of LiCl could be employed in low-temperature studies of a solvated protein. We have investigated a range of concentrations of lysozyme and LiCl in aqueous solutions to identify systems that do not show phase separation and avoid solvent crystallization on cooling down. Compared to the lysozyme concentration in solution, the concentration of LiCl in the aqueous solvent plays the major role in determining systems suitable for low-temperature studies. We have observed interesting and rich phase behavior reminiscent of reentrant condensation of proteins.
Creating tuneable microwave media from a two-dimensional lattice of re-entrant posts
NASA Astrophysics Data System (ADS)
Goryachev, Maxim; Tobar, Michael E.
2015-11-01
The potential capabilities of resonators based on two dimensional arrays of re-entrant posts is demonstrated. Such posts may be regarded as magnetically coupled lumped element microwave harmonic oscillators, arranged in a 2D lattices structure, which is enclosed in a 3D cavity. By arranging these elements in certain 2D patterns, we demonstrate how to achieve certain requirements with respect to field localisation and device spectra. Special attention is paid to symmetries of the lattices, mechanical tuning, design of areas of high localisation of magnetic energy; this in turn creates unique discrete mode spectra. We demonstrate analogies between systems designed on the proposed platform and well known physical phenomena such as polarisation, frustration, and Whispering Gallery Modes. The mechanical tunability of the cavity with multiple posts is analysed, and its consequences to optomechanical applications is calculated. One particular application to quantum memory is demonstrated with a cavity design consisting of separate resonators analogous to discrete Fabry-Pérot resonators. Finally, we propose a generalised approach to a microwave system design based on the concept of Programmable Cavity Arrays.
Re-Entrant Corner Flows of Oldroyd-B fluids in the Natural Stress Basis
NASA Astrophysics Data System (ADS)
Evans, J. D.; O'Byrne, A. T.
2008-07-01
We consider the steady planar flow of Oldroyd-B type fluids for re-entrant corners of angle π/α where 1/2⩽α<1. Additional mathematical results to Rallison and Hinch [9] are presented, where we place their physical arguments more systematically within the method of matched asymptotic expansions. The asymptotic regions are known to consist of an outer region in which the upper convected stress derivative dominates, together with inner (boundary) layers at the walls. An artificial small parameter is introduced (based on the assumption that we are considering small length scales) and used to systematically compare the sizes of terms and facilitate the matching procedure between the regions. Additional results relate to the balance for the natural stress variable v in the outer region (so that it is no longer a constant along streamlines), as well as the asymptotic behaviors of the boundary layer equations at the wall and in the far-field towards the outer region. Further results on the parameter dependence of the solution are given in terms of similarity parameters.
WO21.3 Direct Drive Reentrant Cone Targets for Fast Ignition
Stephens, R B; Nikroo, A; Hill, D; Smith, J N Jr.; Hatchett, S P; Stoeckl, C; Bonino, M J; Sangster, T C; Shiraga, H; Fujioka, S; Tanaka, K A
2003-08-23
Targets designed for fast ignition must have clear access for the ignitor laser to the compressed core. This is provided in current concepts by embedding a reentrant cone in the shell, the tip of the cone close to the center of the shell. We have designed a gas-tight direct-drive FI target as the first step in developing a FI ignition target, and have studied its implosion dynamics at Omega with back-lit and self-emission framing cameras. A step in the cone surface, and Al on the shell was required to make the assembly gas-tight; these assemblies withstood >10 atm and had a typical pressure half-life of 2-6 hrs. The implosion of these targets was substantially different from that of previous indirect drive targets; there was much less vaporization of the Au cone, much clearer structure in the collapsing shells, and a possibility that the hot core could escape around the cone rather than punch in its tip. Additionally self-emission images show the heating of the core gas, and its effect on the cone tip. These results will be compared to simulations.
NASA Astrophysics Data System (ADS)
Lyanda-Geller, Yuli; Simion, George
2015-03-01
We investigate a ground state of the two-dimensional (2D) electron liquid in the presence of disorder for Landau level filling factors, for which the re-entrant integer quantum Hall effect is observed. Our particular interest is the range of filling factors, which in a clean 2D system is favorable to formation of the two-electron (2e) bubble crystal. For the smooth random potential due to charged impurities placed far away from the 2D gas, the ground state is a lightly distorted 2e bubble crystal. However, for positively or negatively charged residual impurities located approximately within about three magnetic lengths from the 2D electrons, the ground state contains charged 2e complexes formed either by positively charged impurity and 3e defect bubble, or negatively charged impurity and 2e defect bubble. In the vicinity of 1e and 3e defect bubbles, the 2e bubbles of the crystal change their shape from round to elongated forming hedgehog (for 1e defect) or vortex (for 3e defect) textures. The topological textures due to these complexes interact with vortex and hedgehog excitations, generated as temperature increases that are not bound by residual impurities. The temperature of insulator to metal transition calculated with both bound and unbound defects agrees with experiment. Research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010544.
Magnetic field tuned reentrant superconductivity in out-of-equilibrium aluminum nanowires
NASA Astrophysics Data System (ADS)
Bretz-Sullivan, Terence M.; Goldman, A. M.
2016-05-01
Perpendicular-to-the-plane magnetic field tuned reentrant superconductivity in out-of-equilibrium, quasi-one-dimensional (quasi-1D) planar nanowires is a novel, counterintuitive phenomenon. It was not until recently that a microscopic mechanism explaining the phenomenon as arising from the coexistence of superconductivity with phase-slip driven dissipation was developed. Here we present results on reentrance phenomena in quasi-1D aluminum nanowires with in-plane magnetic fields, transverse and longitudinal to the nanowire axis. The response to in-plane transverse magnetic fields in this geometry is qualitatively different from that previously reported for perpendicular-to-the-plane field experiments and for in-plane longitudinal field studies. The different feature in the data is an abrupt return to the superconducting state with increasing field at values of field corresponding to a single flux quantum for a short wire and a fractional flux quantum for a long wire. Since these findings are dramatically different from those involving perpendicular-to-the-plane magnetic fields, a different mechanism, as yet unidentified, may be at work.
Implosion of indirect-drive fast ignition targets with CH coated reentrant cone
NASA Astrophysics Data System (ADS)
Zhou, Weimin; Shan, Lianqiang; Gu, Yuqiu; Zhang, Baohan; Fast Ignition Team
2014-10-01
Compared with central ignition of laser fusion, fast ignition separates compression and ignition thus it can relax the requirements on the implosion symmetry and the driven energy. The implosion of indirect-drive fast ignition targets with CH coated reentrant cone was experimentally researched on SHENGUANG (SG) II laser facility. The small scale cone-in-shell target fast ignition was pre-compressed by the SG II eight 260 J/1 ns/3 ω laser beams indirectly since beam smoothing was not available currently. The maximum density of the compressed cone-in-shell target 1.37 ns after the lasers' irradiation on the inside wall of hohlraum is about 8.7 g/cm3, and the areal density is close to 8.9 mg/cm2, which are well consistent with the simulation results with two-dimensional radiation hydrodynamic code. To minimize the mixing of the compressed fuel and high-Z vapor produced by the M-line emission from the gold holhraum, a 3 μm CH foil was coated on the full outer surface of the cone and guiding wire. Experimental results and simulation results also demonstrated the coated CH foil could minimize the mixing effectively. By the appropriate design, target can remain robust before the maximum compression, that is, the time while the hot electrons produced by ignition laser pulse deposit energy in the compressed fuel.
Modulated systems in external fields: Conditions for the presence of reentrant phase diagrams
NASA Astrophysics Data System (ADS)
Mendoza-Coto, Alejandro; Billoni, Orlando V.; Cannas, Sergio A.; Stariolo, Daniel A.
2016-08-01
We introduce a coarse-grained model capable of describing the phase behavior of two-dimensional ferromagnetic systems with competing exchange and dipolar interactions, as well as an external magnetic field. An improved expression for the mean-field entropic contribution allows us to compute the phase diagram in the whole temperature versus external field plane. We find that the topology of the phase diagram may be qualitatively different depending on the ratio between the strength of the competing interactions. In the regime relevant for ultrathin ferromagnetic films with perpendicular anisotropy we confirm the presence of inverse-symmetry breaking from a modulated phase to a homogeneous one as the temperature is lowered at constant magnetic field, as reported in experiments. For other values of the competing interactions we show that reentrance may be absent. Comparing thermodynamic quantities in both cases, as well as the evolution of magnetization profiles in the modulated phases, we conclude that the reentrant behavior is a consequence of the suppression of domain wall degrees of freedom at low temperatures at constant fields.
Osmancik, Pavel; Zdarska, Jana; Budera, Petr; Straka, Zbynek
2015-01-01
A case of macro-reentrant tachycardia associated with a box lesion after thoracoscopis left atrial surgical atrial fibrillation (AF) ablation yet to be described. The goal was to clarify the mechanisms and electrophysiological characteristics of this type of tachycardia. A patient was admitted for an EP study following surgical thoracoscopic AF ablation (box lexion formation by right-sided Cobra thoracoscopic ablation). Thoracoscopic ablation was done as the first step of the hybrid ablation approach to the persistent AF; the second step was the EP study. At the EP study, he presented with incessant regular tachycardia (cycle length of 226 ms). An EP study with conventional, 3D activation and entrainment mapping was done to assess the tachycardia mechanism. Two conduction gaps in the superior line (roofline) between the superior pulmonary veins were discovered. The tachycardia was successfully treated with a radiofrequency application near the gap close to the left superior pulmonary vein; however, following tachycardia termination, pulmonary vein isolation was absent. A second radiofrequency application, close to the roof of the right superior pulmonary, vein closed the gap in the box and led to the isolation of all 4 pulmonary veins. No atrial tachycardia recurred during the 6-month follow-up. Conduction gaps in box lesion created by thoracospcopic ablation can present as a novel type of man-made tachycardia after surgical ablation of atrial fibrillation. Activation and entrainment mapping is necessary for an accurate diagnosis. PMID:26937113
Osmancik, Pavel; Zdarska, Jana; Budera, Petr; Straka, Zbynek
2015-01-01
A case of macro-reentrant tachycardia associated with a box lesion after thoracoscopis left atrial surgical atrial fibrillation (AF) ablation yet to be described. The goal was to clarify the mechanisms and electrophysiological characteristics of this type of tachycardia. A patient was admitted for an EP study following surgical thoracoscopic AF ablation (box lexion formation by right-sided Cobra thoracoscopic ablation). Thoracoscopic ablation was done as the first step of the hybrid ablation approach to the persistent AF; the second step was the EP study. At the EP study, he presented with incessant regular tachycardia (cycle length of 226 ms). An EP study with conventional, 3D activation and entrainment mapping was done to assess the tachycardia mechanism. Two conduction gaps in the superior line (roofline) between the superior pulmonary veins were discovered. The tachycardia was successfully treated with a radiofrequency application near the gap close to the left superior pulmonary vein; however, following tachycardia termination, pulmonary vein isolation was absent. A second radiofrequency application, close to the roof of the right superior pulmonary, vein closed the gap in the box and led to the isolation of all 4 pulmonary veins. No atrial tachycardia recurred during the 6-month follow-up. Conduction gaps in box lesion created by thoracospcopic ablation can present as a novel type of man-made tachycardia after surgical ablation of atrial fibrillation. Activation and entrainment mapping is necessary for an accurate diagnosis. PMID:26937113
Liquid-glass transition in charge-stabilized colloidal dispersions
NASA Astrophysics Data System (ADS)
Lai, S. K.; Wang, G. F.; Peng, W. P.
2000-06-01
We model the inter-colloidal interactions in a charge-stabilized colloidal dispersion by a hard-core Yukawa potential φ(r)=σ0γ exp(-κr)/r, r>σ0 and apply the rescaled mean spherical approximation to calculate its static structure factor. In conjunction with the idealized mode-coupling theory, we determine the loci of the liquid-glass transition phase boundary for a salt-free suspension of charged colloids evaluated at different counter-ion environment (characterized by the κ) in terms of the macro-ion parameters: volume fraction ɛ, charge Z0 and size σ0. The calculated parametric phase diagrams are quite general since the results, with slight and straightforward modification, can be utilized to study the glass transition in a more realistic colloidal solution such as an aqueous monodisperse suspension of polystyrene charged spheres with an added electrolyte. Confining our discussion, then, to the simplest salt-free colloidal liquids, we extract from our analysis of the calculated liquid-glass transition boundaries some succinct features. Specifically, we show in this work that given a range of interaction Vkgr=κσ0<~3.8, there is a possibility of observing the liquid⇋glass⇋liquid⇋glass(LGLG) re-entrant phenomenon in restrictive regions of the phase diagram ɛ-σ0 or ɛ-Z0 for a monodisperse charge-stabilized solution. However, as the σ0 increases above a critical size, the LGLG re-entrant behavior vanishes. To delve into this re-entrant phenomenon, we compare, for a given Vkgr, the glassy Debye-Waller factor, static structure factor and their spatial counterparts for two cases-nnone for lower-Z0 colloids at a high ɛ and the other for higher-Z0 colloids at a low ɛ. For the former, the glassification is basically driven by the geometric restriction while that, for the latter, it is mainly induced by the Coulomb force. We conclude from this comparison that under the same screening environment both the excluded volume and the electrostatic effects are
Lindblad dynamics of a quantum spherical spin
NASA Astrophysics Data System (ADS)
Wald, Sascha; Henkel, Malte
2016-03-01
The coherent quantum dynamics of a single bosonic spin variable, subject to a constraint derived from the quantum spherical model of a ferromagnet, and coupled to an external heat bath, is studied through the Lindblad equation for the reduced density matrix. Closed systems of equations of motion for several quantum observables are derived and solved exactly. The relationship to the single-mode Dicke model from quantum optics is discussed. The analysis of the interplay of the quantum fluctuation and the dissipation and their influence on the relaxation of the time-dependent magnetisation leads to the distinction of qualitatively different regimes of weak and strong quantum couplings. Considering the model’s behaviour in an external field as a simple mean-field approximation of the dynamics of a quantum spherical ferromagnet, the magnetic phase diagram appears to be re-entrant and presents a quantum analogue of well-established classical examples of fluctuation-induced order.
A universal description of ultraslow glass dynamics
Martinez-Garcia, Julio Cesar; Rzoska, Sylwester J.; Drozd-Rzoska, Aleksandra; Martinez-Garcia, Jorge
2013-01-01
The dynamics of glass is of importance in materials science but its nature has not yet been fully understood. Here we report that a verification of the temperature dependencies of the primary relaxation time or viscosity in the ultraslowing/ultraviscous domain of glass-forming systems can be carried out via the analysis of the inverse of the Dyre–Olsen temperature index. The subsequent analysis of experimental data indicates the possibility of the self-consistent description of glass-forming low-molecular-weight liquids, polymers, liquid crystals, orientationally disordered crystals and Ising spin-glass-like systems, as well as the prevalence of equations associated with the ‘finite temperature divergence’. All these lead to a new formula for the configurational entropy in glass-forming systems. Furthermore, a link to the dominated local symmetry for a given glass former is identified here. Results obtained show a new relationship between the glass transition and critical phenomena. PMID:23652011
Geometrical spin symmetry and spin
Pestov, I. B.
2011-07-15
Unification of General Theory of Relativity and Quantum Mechanics leads to General Quantum Mechanics which includes into itself spindynamics as a theory of spin phenomena. The key concepts of spindynamics are geometrical spin symmetry and the spin field (space of defining representation of spin symmetry). The essence of spin is the bipolar structure of geometrical spin symmetry induced by the gravitational potential. The bipolar structure provides a natural derivation of the equations of spindynamics. Spindynamics involves all phenomena connected with spin and provides new understanding of the strong interaction.
Gates, A.E. . Dept. of Geology)
1992-01-01
Deformation consistent with N-S compression is found in several Mesozoic rift basins and occurs throughout the bedrock of the Pennsylvania Reentrant-New York Promontory. This area records the compressional event because the structural grain is favorably oriented (east-west) whereas most of the Appalachians is not. East-west trending structures in western PA and NY were proposed to reflect the Main Phase of Alleghanian deformation and to post-date a local Lackawanna Phase that produced weak NE-trending structures. In the Monroe area, eastern NY, the NE-trending structures are dominant and of a classic Alleghanian form. Folding, and NW-directed thrust faulting are well-developed in Devonian Catskill facies clastic rocks in the Green Pond Outlier as well as older units. These features are overprinted by structures that are consistent with N-S compression. Thrust faults with slickensides showing NW-directed movement are overprinted by slickensides showing N-directed movement. Shales and silt to fine-grained sandstones contain E-W to E-NE striking crenulation cleavages superimposed on the pervasive NE-striking cleavage. These structures are delocalized to the area around an E-W to W-NW striking reverse-dextral oblique fault with 1 to 2km offset. In some areas of NE-trending structures, such as the Peters Creek Formation along the Susquehanna R., well-developed E-W striking crenulation cleavages post-date the pervasive foliation and indicate a consistent N-directed sense of shear. Farther south in the MD Piedmont, E-W trending folds and associated crenulation cleavage cross the dominantly NE trending Baltimore Gneiss domes in zones. The Phoenix dome among others trends E-W and exhibits a strong E-W crenulation cleavage with N-directed asymmetry that crosses a weaker NE-trending crenulation cleavage.
Goodwin, A.R.; Mehl, J.B.; Moldover, M.R.
1996-12-01
A reentrant rf cavity resonator has been developed for automated detection of phase separation of fluid mixtures contained within the cavity. Successful operation was demonstrated by redetermining the phase boundaries of a CO{sub 2}+C{sub 2}H{sub 6} mixture in the vicinity of its critical point. We developed an accurate electrical model for the resonator and used helium to determine the deformation of the resonator under pressure. With the model and pressure compensation, the resonator was capable of very accurate dielectric measurements. We confirmed this by remeasuring the molar dielectric polarizability {ital A}{sub {epsilon}} of argon and obtained the result {ital A}{sub {epsilon}}=(4.140{plus_minus}0.006) cm{sup 3}/mol (standard uncertainty) in excellent agreement with published values. We exploited the capability for accurate dielectric measurements to determine the densities of the CO{sub 2}+C{sub 2}H{sub 6} mixture at the phase boundaries and to determine the dipole moment of 1,1,1,2,3,3-hexafluoropropane, a candidate replacement refrigerant. Near the operating frequency of 375 MHz the capacitor in the resonator has an impedance near 14 {Omega}. This low impedance is more tolerant of electrical conductivity within the test fluid and in parallel paths in the support structures than comparable capacitors operating at audio frequencies. This will be an advantage for operation at high temperatures where some conductivity must be expected in all fluids. Of further value for high-temperature applications, the present rf resonator has only two metal{endash}insulator joints. These joints seal coaxial cables; neither joint is subjected to large mechanical stresses and neither joint is required to maintain precise dimensional tolerances. The resonator is rugged and may be operated with inexpensive electronics.
Reentrant disorder-disorder transitions in generalized multicomponent Widom-Rowlinson models
NASA Astrophysics Data System (ADS)
Krčmár, Roman; Šamaj, Ladislav
2015-11-01
In the lattice version of the multicomponent Widom-Rowlinson (WR) model, each site can be either empty or singly occupied by one of M different particles, all species having the same fugacity z . The only nonzero interaction potential is a nearest-neighbor hard-core exclusion between unlike particles. For M
Reentrant disorder-disorder transitions in generalized multicomponent Widom-Rowlinson models.
Krčmár, Roman; Šamaj, Ladislav
2015-11-01
In the lattice version of the multicomponent Widom-Rowlinson (WR) model, each site can be either empty or singly occupied by one of M different particles, all species having the same fugacity z. The only nonzero interaction potential is a nearest-neighbor hard-core exclusion between unlike particles. For M
Randomised Evaluation of modified Valsalva Effectiveness in Re-entrant Tachycardias (REVERT) study
Appelboam, Andrew; Reuben, Adam; Mann, Clifford; Lobban, Trudie; Ewings, Paul; Benger, Jonathan; Vickery, Jane; Barton, Andrew; Gagg, James
2014-01-01
Introduction The Valsalva manoeuvre (VM) is a recommended first-line physical treatment for patients with re-entrant supraventricular tachycardia (SVT), but is often ineffective in standard practice. A failed VM is typically followed by treatment with intravenous adenosine, which patients often find unpleasant. VM effectiveness might be improved by a modification to posture which exaggerates the manoeuvre's vagal response and reduces the need for further emergency treatment. Methods and analysis This is a multicentre randomised controlled clinical trial in 10 UK emergency departments (EDs). It compares a standard VM with a modified VM incorporating leg elevation and a supine posture after a standardised strain in stable adult patients presenting to the ED with SVT. The primary outcome measure is return to sinus rhythm on a 12-lead ECG. Secondary outcome measures include the need for treatment with adenosine or other antiarrhythmic treatments and the time patients spend in the ED. We plan to recruit approximately 372 patients, with 80% power to demonstrate an absolute improvement in cardioversion rate of 12%. An improvement of this magnitude through the use of a modified VM would be of significant benefit to patients and healthcare providers, and justify a change to standard practice. Ethics and dissemination The study has been approved by the South West—Exeter Research Ethics Committee (REC reference 12/SW/0281). The trial will be published in an international peer reviewed journal. Study findings will be sent to the European and International resuscitation councils to inform future revisions of arrhythmia management guidelines. Results The trial will also be disseminated at international conferences and to patients through the Arrhythmia Alliance, a patient support charity. Registration The study is registered with Current Controlled Trials (ISRCTN67937027) and has been adopted by the National Institute for Health Research (NIHR) Clinical Research Network. PMID
Thermopower of Interacting GaAs Bilayer Hole Systems in the Reentrant Insulating Phase Near ν=1
NASA Astrophysics Data System (ADS)
Faniel, S.; Tutuc, E.; Poortere, E. P.; Gustin, C.; Vlad, A.; Melinte, S.; Shayegan, M.; Bayot, V.
2005-02-01
We report thermopower measurements of interacting GaAs bilayer hole systems. When the carrier densities in the two layers are equal, these systems exhibit a reentrant insulating phase near the quantum Hall state at total filling factor ν=1. Our data show that, as the temperature is decreased, the thermopower diverges in the insulating phase. This behavior indicates the opening of an energy gap at low temperature, consistent with the formation of a pinned Wigner solid. We extract an energy gap and a Wigner solid melting phase diagram.
Thermopower of interacting GaAs bilayer hole systems in the reentrant insulating phase near nu=1.
Faniel, S; Tutuc, E; De Poortere, E P; Gustin, C; Vlad, A; Melinte, S; Shayegan, M; Bayot, V
2005-02-01
We report thermopower measurements of interacting GaAs bilayer hole systems. When the carrier densities in the two layers are equal, these systems exhibit a reentrant insulating phase near the quantum Hall state at total filling factor nu=1. Our data show that, as the temperature is decreased, the thermopower diverges in the insulating phase. This behavior indicates the opening of an energy gap at low temperature, consistent with the formation of a pinned Wigner solid. We extract an energy gap and a Wigner solid melting phase diagram. PMID:15783582
NASA Astrophysics Data System (ADS)
Kleinert, H.; Schmidt, S.; Pelster, A.
2004-10-01
We calculate the location of the quantum phase transitions of a Bose gas trapped in an optical lattice as a function of effective scattering length aeff and temperature T. Knowledge of recent high-loop results on the shift of the critical temperature at weak couplings is used to locate a nose in the phase diagram above the free Bose-Einstein critical temperature T(0)c, thus predicting the existence of a reentrant transition above T(0)c, where a condensate should form when increasing aeff. At zero temperature, the transition to the normal phase produces the experimentally observed Mott insulator.
Premnath, S; Devaradjane, G
2015-11-01
The emissions from the Compression ignition (CI) engines introduce toxicity to the atmosphere. The undesirable carbon deposits from these engines are realized in the nearby static or dynamic systems such as vehicles, inhabitants, etc. The objective of this research work is to improve the performance and emission characteristics of a diesel engine in the modified re-entrant combustion chamber using a diesel and Jatropha methyl ester blend (J20) at three different injection pressures. From the literature, it is revealed that the shape of the combustion chamber and the fuel injection pressure have an impact on the performance and emission parameters of the CI engine. In this work, a re-entrant combustion chamber with three different fuel injection pressures (200, 220 and 240bars) has been used in the place of the conventional hemispherical combustion chamber for diesel and J20. From the experimental results, it is found that the re-entrant chamber improves the brake thermal efficiency of diesel and J20 in all the tested conditions. It is also found that the 20% blend of Jatropha methyl ester showed 4% improvement in the brake thermal efficiency in the re-entrant chamber at the maximum injection pressure. Environmental safety directly relates to the reduction in the undesirable effects on both living and non-living things. Currently environmental pollution is of major concern. Even with the stringent emission norms new methods are required to reduce the harmful effects from automobiles. The toxicity of carbon monoxide (CO) is well known. In the re-entrant combustion chamber, the amount of CO emission is reduced by 26% when compared with the conventional fuel operation of the engine. Moreover, the amount of smoke is reduced by 24% and hydrocarbons (HC) emission by 24%. Thus, the modified re-entrant combustion chamber reduces harmful pollutants such as unburned HC and CO as well as toxic smoke emissions. PMID:26256249
Yuan, B.; Yang, J. Zuo, X. Z.; Tang, X. W.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Song, D. P.; Sun, Y. P.
2015-06-21
Single-phase polycrystalline SrBi{sub 5}Ti{sub 4}CrO{sub 18} and SrBi{sub 5}Ti{sub 4}Cr{sub 0.5}Co{sub 0.5}O{sub 18} were synthesized by a modified Pechini method. Both samples have an orthorhombic structure with the space group B2cb. The valence state of Cr is suggested to be +3 and the Co ions exist in the form of Co{sup 2+} and Co{sup 3+} based on the results of x-ray photoelectron spectroscopy. The sample SrBi{sub 5}Ti{sub 4}CrO{sub 18} exhibits the paramagnetic state, whereas SrBi{sub 5}Ti{sub 4}Cr{sub 0.5}Co{sub 0.5}O{sub 18} undergoes a ferrimagnetic transition at 89 K originating from the antiferromagnetic coupling of Cr-based and Co-based sublattices. In addition, SrBi{sub 5}Ti{sub 4}Cr{sub 0.5}Co{sub 0.5}O{sub 18} shows a typical spin-glass behavior below 89 K with zν = 6.02 and τ{sub 0} = (1.75 ± 0.33) × 10{sup −14} s as evidenced by the results of the frequency dependence of ac susceptibility and magnetic relaxation measurements. In particular, both the dielectric constant and dielectric loss of SrBi{sub 5}Ti{sub 4}Cr{sub 0.5}Co{sub 0.5}O{sub 18} exhibit the characteristics of dielectric relaxation around 89 K with the activation energy of (0.14 ± 0.02) eV, which can be ascribed to the electron hopping of Co{sup 2+}-V{sub O}-Co{sup 3+} through the bridging oxygen vacancies.
Thanh, T. D.; Manh, D. H.; Phuc, N. X.; Phan, T. L.; Yu, S. C.; Phong, P. T.; Hung, L. T.
2014-05-07
We have studied the magnetic and spin-glass (SG) properties of La{sub 0.7}Ca{sub 0.3}MnO{sub 3} single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (t{sub m}). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (T{sub f}) appearing on the real part curve of the ac susceptibility, χ′(T). The T{sub f} value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔT{sub f}/T{sub f}Δ(log{sub 10}f), and the power law τ = τ{sub 0}(T/T{sub g} − 1){sup −zν}. The obtained values of c ≈ 5 × 10{sup −2}, τ{sub 0} ≈ 10{sup −5} s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at T{sub g} below T{sub f}, which decreases with decreasing 〈D〉. Basing on ln(f) versus T{sub f} data, and the Néel-Arrhenius model [ln(f) = ln(f{sub 0}) - E{sub a}/k{sub B}T] and Vogel–Fulcher law [ln(f) = ln(f{sub 0}) - E{sub a}/k{sub B}(T - T{sub 0})], the Larmor frequency (f{sub 0}), activation energy (E{sub a}) and effective temperature (T{sub 0}) for the samples with different 〈D〉 were determined. Obtained results indicate the existence a strong interaction between nanoparticles.
A Unified Stability Property in Spin Glasses
NASA Astrophysics Data System (ADS)
Panchenko, Dmitry
2012-08-01
Gibbs' measures in the Sherrington-Kirkpatrick type models satisfy two asymptotic stability properties, the Aizenman-Contucci stochastic stability and the Ghirlanda-Guerra identities, which play a fundamental role in our current understanding of these models. In this paper we show that one can combine these two properties very naturally into one unified stability property.
Spin Glass Computations and Ruelle's Probability Cascades
NASA Astrophysics Data System (ADS)
Arguin, Louis-Pierre
2007-03-01
We study the Parisi functional, appearing in the Parisi formula for the pressure of the SK model, as a functional on Ruelle's Probability Cascades (RPC). Computation techniques for the RPC formulation of the functional are developed. They are used to derive continuity and monotonicity properties of the functional retrieving a theorem of Guerra. We also detail the connection between the Aizenman-Sims-Starr variational principle and the Parisi formula. As a final application of the techniques, we rederive the Almeida-Thouless line in the spirit of Toninelli but relying on the RPC structure.
Synthesis of new amorphous metallic spin glasses
Haushalter, Robert C.
1988-01-01
Amorphous metallic precipitates having the formula (M.sub.1).sub.a (M.sub.2).sub.b wherein M.sub.1 is at least one transition metal, M.sub.2 is at least one main group metal and the integers "a" and "b" provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.
Synthesis of new amorphous metallic spin glasses
Haushalter, Robert C.
1986-01-01
Amorphous metallic precipitates having the formula (M.sub.1).sub.a (M.sub.2).sub.b wherein M.sub.1 is at least one transition metal, M.sub.2 is at least one main group metal and the integers "a" and "b" provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.
Synthesis of new amorphous metallic spin glasses
Haushalter, R.C.
1985-02-11
Disclosed are: amorphous metallic precipitates having the formula (M/sub 1/)/sub a/(M/sub 2/)/sub b/ wherein M/sub 1/ is at least one transition metal, M/sub 2/ is at least one main group metal and the integers ''a'' and ''b'' provide stoichiometric balance; the precipitates having a degree of local order characteristic of chemical compounds from the precipitation process and useful electrical and mechanical properties.
Structural ordering and glass forming of soft spherical particles with harmonic repulsions
Sun, Bin; Sun, Zhiwei; Ouyang, Wenze Xu, Shenghua
2014-04-07
We carry out dissipative particle dynamics simulations to investigate the dynamic process of phase transformation in the system with harmonic repulsion particles. Just below the melting point, the system undergoes liquid state, face-centered cubic crystallization, body-centered cubic crystallization, and reentrant melting phase transition upon compression, which is in good agreement with the phase diagram constructed previously via thermodynamic integration. However, when the temperature is decreased sufficiently, the system is trapped into an amorphous and frustrated glass state in the region of intermediate density, where the solid phase and crystal structure should be thermodynamically most stable.
Mahmud, R; Denker, S T; Tchou, P J; Jazayeri, M; Akhtar, M
1988-01-01
The importance of activation sequence of an atrioventricular junctional reentrant (AVJRe) circuit, before delivery of an extrastimulus, has received little attention in studies concerned with clinical tachycardias. In this study a change in activation sequence was accomplished using bidirectional activation (V-A sequential pacing) during the basic drive (V1A1-V1A1). It was noted that, compared with an atrial extrastimulus (A2) after an atrial drive (A1-A1), earlier activation (by V1 impulse of the V1A1-V1A1 drive) consistently improved conduction, or decreased refractoriness, or both, in the anterograde as well as the retrograde pathway of the AVJRe circuit. In all patients, five with AV nodal reentry and six with Wolff-Parkinson-White syndrome, reentrant tachycardia could be prevented during V-A sequential pacing. In four of eleven patients, reentry was prevented despite achieving the so-called critical atrioventricular nodal delays that had previously caused reentry during control study. This finding suggested that conduction delay necessary for reentry was related to the site of block, which in turn was affected by V-A sequential pacing. We concluded that changing the activation sequence during basic drive modulates conduction and refractoriness in AVJRe circuits, and allows the study of a wide range of electrophysical factors that prevent or permit reentry. Images PMID:3335641
Snitzer, E
1966-10-01
After a general discussion of the merits of glass vs. crystals as host materials for laser ions, a summary is given of the various glass lasers. Because of its importance as an efficient, room temperature laser the properties of neodymium are considered in greater detail. This includes the nonlaser properties of Nd(3+) in glass, the spectral and temporal emission characteristics of Nd(3+) lasers, and Nd(3+) laser configurations. Separate sections deal with the other two room temperature lasers which use Yb(3+) or Er(3+). The problem of thermal stability of laser cavities is also discussed. Finally, a survey is given of the glasses that are useful as Faraday rotators. PMID:20057584
Hoffmann, H.J.
1990-12-31
This article deals with the general properties of photochromic inorganic glasses and the darkening and regeneration dynamics as well as the main photochemical and photophysical reactions occurring in the glasses. It concludes with applications of photochromic systems to self-adjusting window panes. This controlled flow of radiant energy could lead to important energy savings by decreasing the cooling and heating loads in buildings and automobiles.
NASA Astrophysics Data System (ADS)
Webb, A. G.; Yu, H.; Hendershott, Z.
2010-12-01
Orogenic wedges are standard elements of collisional plate tectonics, from accretionary prisms to retro-arc basins. Recent study of orogenic wedge development has focused on links between mechanisms of internal deformation and surface processes. Models of orogenic wedges are commonly presented in the cross-section plane, which is generally effective as wedges largely develop via plane strain. The 3rd dimension can be utilized to explore effects of differences in controlling parameters on wedge evolution. We are investigating a stretch of the western Himalayan orogenic wedge that has two prominent changes in along-strike morphology: (1) a tectonic window (the Kullu Window) that appears to be strongly influenced by erosion along the 3rd largest river in the Himalayan system, the Sutlej River and (2) the Kangra Re-entrant, the largest re-entrant along the Himalayan arc. In addition to the along-strike heterogeneity, a key advantage of the proposed study area is its rich stratigraphy, with the most known diversity in the Himalayan arc. The stratigraphic wealth, combined with the along-strike heterogeneity in exposure level, offers a high resolution view of regional structural geometry. Our preliminary reconstructions suggest that the Sutlej River erosion increases the exposure depth and shortening budget across a narrow segment of the orogen, strongly warping the Kullu Window. Previous models have suggested that the out-of-sequence Munsiari thrust is the main structure associated with Kullu window formation, while our work suggests that most of this uplift and warping is accomplished by antiformal stacking of basement thrust horses. Late Miocene ages (U-Pb ages of zircons and Th-Pb ages of monazites) from a leucogranite in the core of the Kullu Window along the Sutlej River further suggests that this segment of the orogen represents a middle ground between plane strain orogenic wedge development and a tectonic aneurysm model. We have constructed a palinspastic
NASA Astrophysics Data System (ADS)
Akbarzadeh, Hadi
A systematic study of the low-dc-field magnetic susceptibility and the specific heat has been carried out on mixes Hg(,1-x)Mn(,x)Te crystals, in the composition range 0 (LESSTHEQ) x (LESSTHEQ) 0.35. The alloy with x = 0.35 showed spin-glass behavior below T = 10.9 K. The observed spin-glass phase is ascribed to the frustration of the antiferromagnetic interactions. For x (LESSTHEQ) 0.25, the Hg(,1-x)Mn(,x)Te samples remain paramagnetic down to 1 K. Experimental results for the specific heat and the susceptibility for x < 0.1 are discussed in terms of a cluster model which leads to an estimated value of the antiferromagnetic exchange constant J/k (DBLTURN) -0.7 (+OR-) 0.3 K. When a random distribution of Mn ions over the fcc sublattice is assumed, calculated values for the specific heat and the susceptibility differ substantially from the experimental results for the low Mn concentration, leading to the conclusion that the magnetic ions prefer to cluster rather than to remain isolated in Hg(,1-x)Mn(,x)Te. Low temperature specific heat of the spin glass compounds Co(,x)Ga(,1-x). with x between 0.49 and 0.58 are presented. For all samples the excess specific heat in zero magnetic field initially contains a term linear in temperature, and for x > 0.52 it also has contributions by the cobalt nuclei, proportional to T('-2), and a spin wave contribution proportional to T('3/2). This last term indicates the coexistence of spin glass and ferromagnetic properties. A simple two level system model fits the spin glass specific heat very well. The agreement between experimental and calculated specific heat shows that individual AS defects are responsible for the thermal properties. To explain hysteresis and remanence objects containing thousands of AS defects have been proposed. On increasing the temperature some objects become unfrozen. We speculate that the individual AS defects in the unfrozen objects can adjust themselves over their own two levels and so contribute to the
Hyperpolarized cesium ions doped in a glass material
NASA Astrophysics Data System (ADS)
Ishikawa, Kiyoshi
2014-12-01
Hyperpolarized (HP) 133 Cs nuclear magnetic resonance signals were measured from borosilicate glass cell walls during optical pumping of cesium vapor at high magnetic field (9.4 T). Significant signal enhancements were observed when additional heating of the cell wall was provided by intense but non-resonant laser irradiation, with integrated HP 133 Cs NMR signals and line widths varying as a function of heating laser power (and hence glass temperature). Given that virtually no Cs ions would originally be present in the glass, absorbed HP Cs atoms rarely met thermally-polarized Cs ions already at the surface; thus, spin-exchange via nuclear dipole interaction cannot be the primary mechanism for injecting spin polarization into the glass. Instead, it is concluded that the absorption and transport of HP atoms into the glass material itself is the dominant mechanism of nuclear spin injection at high temperatures-the first reported experimental demonstration of such a mechanism.
Ciaccio, Edward J.; Coromilas, James; Ashikaga, Hiroshi; Cervantes, Daniel O.; Wit, Andrew L.; Peters, Nicholas S.; McVeigh, Elliot R.; Garan, Hasan
2015-01-01
Background When the infarct border zone is stimulated prematurely, a unidirectional block line (UBL) can form and lead to double-loop (figure-of-eight) reentrant ventricular tachycardia (VT) with a central isthmus. The isthmus is composed of an entrance, center, and exit. It was hypothesized that for certain stimulus site locations and coupling intervals, the UBL would coincide with the isthmus entrance boundary, where infarct border zone thickness changes from thin-to-thick in the travel direction of the premature stimulus wavefront. Method A quantitative model was developed to describe how thin-to-thick changes in the border zone result in critically convex wavefront curvature leading to conduction block, which is dependent upon coupling interval. The model was tested in 12 retrospectively analyzed postinfarction canine experiments. Electrical activation was mapped for premature stimulation and for the first reentrant VT cycle. The relationship of functional conduction block forming during premature stimulation to functional block during reentrant VT was quantified. Results For an appropriately placed stimulus, in accord with model predictions: 1. The UBL and reentrant VT isthmus lateral boundaries overlapped (error: 4.8±5.7 mm). 2. The UBL leading edge coincided with the distal isthmus where the center-entrance boundary would be expected to occur. 3. The mean coupling interval was 164.6±11.0 ms during premature stimulation and 190.7±20.4 ms during the first reentrant VT cycle, in accord with model calculations, which resulted in critically convex wavefront curvature and functional conduction block, respectively, at the location of the isthmus entrance boundary and at the lateral isthmus edges. Discussion Reentrant VT onset following premature stimulation can be explained by the presence of critically convex wavefront curvature and unidirectional block at the isthmus entrance boundary when the premature stimulation interval is sufficiently short. The double
Vector chiral phases in the frustrated 2D XY model and quantum spin chains.
Schenck, H; Pokrovsky, V L; Nattermann, T
2014-04-18
The phase diagram of the frustrated 2D classical and 1D quantum XY models is calculated analytically. Four transitions are found: the vortex unbinding transitions triggered by strong fluctuations occur above and below the chiral transition temperature. Vortex interaction is short range on small and logarithmic on large scales. The chiral transition, though belonging to the Ising universality class by symmetry, has different critical exponents due to nonlocal interaction. In a narrow region close to the Lifshitz point a reentrant phase transition between paramagnetic and quasiferromagnetic phase appears. Applications to antiferromagnetic quantum spin chains and multiferroics are discussed. PMID:24785067
NASA Astrophysics Data System (ADS)
Colicchia, Giuseppe; Hopf, Martin; Wiesner, Hartmut; Zollman, Dean
2008-01-01
Eye aberrations are commonly corrected by lenses that restore vision by altering rays before they pass through the cornea. Some modern promoters claim that pinhole glasses are better than conventional lenses in correcting all kinds of refractive defects such as myopia (nearsighted), hyperopia (farsighted), astigmatisms, and presbyopia. Do pinhole glasses really give better vision? Some ways to use this question for motivation in teaching optics have been discussed. For this column we include a series of experiments that students can complete using a model of the eye and demonstrate issues related to pinhole vision correction.
NASA Astrophysics Data System (ADS)
Nelson, J. J.; Goldman, A. M.
2015-03-01
Metal insulator transitions are usually observed in high mobility and low carrier density 2D electron systems. There are several open questions regarding the metallic state including its existence in the limit of zero temperature. The current experimental focus is on the production of higher mobility samples to push the critical carrier density to even lower values, which will increase the effects of the Coulomb interaction. Here we report an unexpected result, the observation of the onset of a metallic state at high carrier densities in silicon gated with the ionic liquid DEME-TFSI. In addition we have observed a return to the insulating state as the carrier density was further increased. This reentrant insulting behavior is an effect that was recently predicted. Supported in part by NSF/DMR-1263316. Part of this work was carried out at the Minnesota Nanocenter.
Discontinuous nature of the repulsive-to-attractive colloidal glass transition
van de Laar, T.; Higler, R.; Schroën, K.; Sprakel, J.
2016-01-01
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale. PMID:26940737
Discontinuous nature of the repulsive-to-attractive colloidal glass transition.
van de Laar, T; Higler, R; Schroën, K; Sprakel, J
2016-01-01
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale. PMID:26940737
Discontinuous nature of the repulsive-to-attractive colloidal glass transition
NASA Astrophysics Data System (ADS)
van de Laar, T.; Higler, R.; Schroën, K.; Sprakel, J.
2016-03-01
In purely repulsive colloidal systems a glass transition can be reached by increasing the particle volume fraction beyond a certain threshold. The resulting glassy state is governed by configurational cages which confine particles and restrict their motion. A colloidal glass may also be formed by inducing attractive interactions between the particles. When attraction is turned on in a repulsive colloidal glass a re-entrant solidification ensues. Initially, the repulsive glass melts as free volume in the system increases. As the attraction strength is increased further, this weakened configurational glass gives way to an attractive glass in which motion is hindered by the formation of physical bonds between neighboring particles. In this paper, we study the transition from repulsive-to-attractive glasses using three-dimensional imaging at the single-particle level. We show how the onset of cage weakening and bond formation is signalled by subtle changes in local structure. We then demonstrate the discontinuous nature of the solid-solid transition, which is marked by a critical onset at a threshold bonding energy. Finally, we highlight how the interplay between bonding and caging leads to complex and heterogeneous dynamics at the microscale.
ERIC Educational Resources Information Center
Colicchia, Giuseppe; Hopf, Martin; Wiesner, Hartmut; Zollman, Dean
2008-01-01
Eye aberrations are commonly corrected by lenses that restore vision by altering rays before they pass through the cornea. Some modern promoters claim that pinhole glasses are better than conventional lenses in correcting all kinds of refractive defects such as myopia (nearsighted), hyperopia (farsighted), astigmatisms, and presbyopia. Do pinhole…
Unveiling the photonic spin Hall effect with asymmetric spin-dependent splitting.
Zhou, Xinxing; Ling, Xiaohui
2016-02-01
The photonic spin Hall effect (SHE) manifests itself as the spin-dependent splitting of light beam. Usually, it shows a symmetric spin-dependent splitting, i.e., the left- and right-handed circularly polarized components are equally separated in position and intensity for linear polarization incidence. In this paper, we theoretically propose an asymmetric spin-dependent splitting at an air-glass interface under the illumination of elliptical polarization beam and experimentally demonstrate it with the weak measurement method. The left- and right-handed circularly polarized components show expectedly unequal intensity distributions and unexpectedly different spin-dependent shifts. Remarkably, the asymmetric spin-dependent splitting can be modulated by adjusting the handedness of incident polarization. The inherent physics behind this interesting phenomenon is attributed to the additional spatial Imbert-Fedorov shift. These findings offer us potential methods for developing new spin-based nanophotonic applications. PMID:26906868
NASA Astrophysics Data System (ADS)
Pyżuk, W.; Górecka, E.; Mieczkowski, J.; Przedmojski, J.
1992-07-01
Two series of liquid-crystalline compounds having three phenyl rings separated by flexible spacer —CH(CH{3})CH{2}—COO— and by rigid azo and azoxy group, were studied by DSC, optical and X-ray methods. For esters of dl-3-(4^{prime}-nitro)-phenylbutyric acid with 4^{prime}-alkoxy-phenylazo-phenol-4 having dodecyloxy or longer terminal chains, as well as for related azoxy compounds, a narrow (even below 5 K) reentrant or inverted nematic phase appearing between partly bilayer and monolayer smectics A was observed. For higher homologues of the azoxy series additional smectic phases appear, leading to the occurrence of new multicritical points, e.g. the critical end point Ad Cd N^re. On each of the lines, which separate nematic from smectic A phases, transitions are of weakly first or second-order and more than one tricritical point can occur. On the A{1} N/A{1} N^re line, a simple N A{1} tricritical point is observed at T_NI/T_AN = 0.834. The presence of further critical points depends on the components of the binary system involved. Four of the azoxy compounds studied undergo a second order phase transition between partly bilayer smectics, Ad and Cd. Such a transition is accompanied by a jumb in the specific heat, varying linearly with the length of the molecular tails. Various temperature dependences of the layer spacing in the Ad phase are observed for subsequent homologues from the azoxy series. Plusieurs cristaux liquides composés de trois groupements phényl séparés par un groupement —CH(CH{3})CH{2}—COO—, ainsi que par des groupements azo et azoxy, ont été examinés par AED, méthodes optiques et par rayons X. Pour des esters de l'acide dl-3-(4^{prime}-nitro)phénylbutyrique et de 4^{prime}-alkoxy-phénylazo-phénol-4 ayant comme terminaison une chaîne dodecyloxy ou bien plus longue, ainsi que pour des composés azoxy relatif, on observe (même au-dessous de 5 K) une étroite phase nématique réentrante ou inverse entre les phases smectiques
NASA Astrophysics Data System (ADS)
Tatsuno, Taro; Mizoguchi, Eriko; Nasu, Joji; Naka, Makoto; Ishihara, Sumio
2016-08-01
Magnetic field (H) effects on a correlated electron system with a spin-state degree of freedom are examined. The effective Hamiltonian derived from the two-orbital Hubbard model is analyzed by the mean-field approximation. Applying a magnetic field to the low-spin (LS) phase induces an excitonic insulating phase as well as a spin-state ordered phase where the LS and high-spin (HS) states are ordered alternately. When H is applied to the HS phase, a reentrant transition for the HS phase appears. A rich variety of the phase diagrams is attributed to the spin-state degree of freedom and their combinations in the wave function as well as in the real-space configuration. The present results provide a possible interpretation for the recent experimental observation of LaCoO3 under a strong magnetic field.
Structure of rhenium-containing sodium borosilicate glass
Goel, Ashutosh; McCloy, John S.; Windisch, Charles F.; Riley, Brian J.; Schweiger, Michael J.; Rodriguez, Carmen P.; Ferreira, Jose M.
2013-03-01
A series of sodium borosilicate glasses were synthesized with increasing fractions of KReO4 or Re2O7, to 10000 ppm (1 mass%) target Re in glass, to assess the effects of large concentrations of rhenium on glass structure and to estimate the solubility of technetium, a radioactive component in typical low active waste nuclear waste glasses. Magic angle spinning nuclear magnetic resonance (MAS-NMR), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy were performed to characterize the glasses as a function of Re source additions. In general, silicon was found coordinated in a mixture of Q2 and Q3 structural units, while Al was 4-coordinated and B was largely 3-coordinate and partially 4-coordinated. The rhenium source did not appear to have significant effects on the glass structure. Thus, at the up to the concentrations that remain in dissolved in glass, ~3000 ppm Re by mass maximum. , the Re appeared to be neither a glass-former nor a strong glass modifier., Rhenium likely exists in isolated ReO4- anions in the interstices of the glass network, as evidenced by the polarized Raman spectrum of the Re glass in the absence of sulfate. Analogous to SO42-¬ in similar glasses, ReO4- is likely a network modifier and forms alkali salt phases on the surface and in the bulk glass above solubility.
NASA Astrophysics Data System (ADS)
Xu, Xiao; Nagasako, Makoto; Kataoka, Mitsuo; Umetsu, Rie Y.; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke
2015-03-01
Electronic, magnetic, and thermodynamic properties of Co2Cr(Ga,Si) -based shape-memory alloys, which exhibit reentrant martensitic transformation (RMT) behavior, were studied experimentally. For electric resistivity (ER), an inverse (semiconductor-like) temperature dependence in the parent phase was found, along with anomalous behavior below its Curie temperature. A pseudobinary phase diagram was determined, which gives a "martensite loop" clearly showing the reentrant behavior. Differential scanning calorimetry and specific-heat measurements were used to derive the entropy change Δ S between martensite and parent phases. The temperature dependence of the derived Δ S was analyzed thermodynamically to confirm the appearances of both the RMT and normal martensitic transformation. Detailed studies on the specific heat in martensite and parent phases at low temperatures were also conducted.
NASA Astrophysics Data System (ADS)
Orpin, A.; Carter, L.; Lewis, K.; Kuehl, S.; Alexander, C.
2003-04-01
The East Coast margin is characterised by high terrigenous sediment flux, dramatic effects of land-use changes, and by complex sediment-tectonic interactions on a steep and unstable continental slope. An estimated 18 cubic km of sediment has been deposited in an actively subsiding mid-shelf basin and outer shelf apron since 18 ka BP, with a maximum thickness of approximately 45 m. The shelf is boarded along its seaward edge by two growing anticlines, but a significant component of the sediment leaks through a 13 km-wide gap between the anticlines and cascades into a large structural re-entrant that is heavily incised by the Poverty submarine canyon system. 210Pb mass accumulation profiles indicate that the modern post-settlement sedimentation rate of around 0.9 cm/yr on the outer shelf is double that recorded at the mid-shelf. Hence, the modern sediment accumulation is inconsistent with the post-glacial sediment thicknesses, which show the largest volume has accumulated on the mid-shelf. This may suggest an increasing frequency of Waipaoa-derived hyperpycnal flows with the ability to transport sediment seawards, or a change in the storage pattern within Poverty Bay. Accumulation rates on the slope are an order of magnitude less, around 0.1 cm/yr. Cores and multibeam images suggest that Poverty Canyon is inactive as a modern sediment pathway. The mouth and floor of the canyon are composed of stiff Pleistocene mud, overlain by a thin drape of unconsolidated mud. The seabed at the canyon mouth is highly reflective, deeply scoured, and lacks a fan. These features indicate little or no sediment flux. Accepting near-full capture of riverine-derived sediment on the shelf and slope, accumulation rates indicate that the modern (post-settlement) sediment yield from the Waipaoa River is almost an order of magnitude higher than the average for the Holocene. This is broadly compatible with accelerated rates of landscape erosion measured onshore. A revised sediment budget
NASA Astrophysics Data System (ADS)
Acksteiner, Jozo
This dissertation addresses aspects within two different areas of the semiconductor industry: Manufacturing process optimization and supply chain management. The first part examines re-entrant lines motivated by manufacturing lines in chip production. Re-entrant lines are queueing networks in which jobs are processed several times by the same server. We call the nth processing step in the network the nth class of the network. If jobs from different classes are to be served by the same server, a dispatch policy decides which job is processed next. Such queueing networks are extremely difficult to study. In particular, the determination of rate stability, or whether the input rate into the system in the long-term equals the output rate of such networks, is often hopeless. Stochastic queueing networks can be approximated by deterministic fluid models, replacing the discrete job arrivals by continuous fluid flow. The results found in the fluid model can then be interpreted in the original queueing network setting. In particular stability in the fluid setting implies, under some technical conditions, rate stability in the original queueing network. In the fluid model, stability means that starting with any initial fluid levels, the system empties in finite time. The dissertation gives a first insight how to show stability in a 2-station re-entrant line under a fixed static buffer priority policy.
Gupta, Arti; Tandon, R. P.; Shinde, A. B.; Krishna, P. S. R.; Chatterjee, Ratnamala
2015-10-07
In this paper, we establish the negative spontaneous magnetization in Mn and Zn substituted cobalt ferrite Co{sub 0.6}Zn{sub 0.4}Fe{sub 1.7}Mn{sub 0.3}O{sub 4} (CZFMO). It is suggested that the origin of negative spontaneous magnetization is due to the substitution of small sized Mn{sup +4} ions (compared to Fe{sup +3} ions) at the octahedral B site in compound Co{sub 0.6}Zn{sub 0.4} Fe{sub 2}O{sub 4}. The low value of Poisson's ratio ∼0.202 for this compound possibly contributes towards the easy distortion in the bond length and bond angle, causing increase in Fe-O bond distance/decrease in Fe-O-Fe bond angle with Mn substitution, leading to considerably weak Fe-O-Fe superexchange interaction at the octahedral B site. The neutron diffraction data clearly illustrated the significant reduction in ordered magnetic moment at the B site, with the resultant negative spontaneous magnetization (M = M{sub B} − M{sub A}) in this mixed spinel system. The spin disorder also gives rise to an interesting semi-spin glass behavior in CZFMO.
Observation of transverse spin freezing by TDPAC
NASA Astrophysics Data System (ADS)
Webb, T. A.; Ryan, D. H.
2013-05-01
We use 181Hf time-differential perturbed angular correlation (TDPAC) spectroscopy to investigate magnetic ordering in the bond-frustrated metallic glass: a - Fe91Hf9. We show that TDPAC can be used to observe the magnetic fluctuations that are associated with the freezing of transverse spin components at T xy .
NASA Astrophysics Data System (ADS)
Deng, Nianpei; Watson, John; Manfra, Michael; Csathy, Gabor
2012-02-01
In the two-dimensional electron gas competing electron-electron interactions and disorder effects give rise to many-body ground states such as the fractional quantum Hall and the reentrant integer quantum Hall states (RIQHS). The latter are not yet well understood, but they are believed to be Wigner crystal-like electron solids with one or more electrons at each lattice nodes. We have recently shown that for the RIQHS in the second Landau level one can extract their onset temperature from the temperature-dependent magnetoresistance. We report similar studies of the RIQHS in the third Landau level. To our surprise, the onset temperatures of the RIQHSs in the third Landau level are about a factor of 3 larger than those in the second Landau level. This result clearly shows that the RIQHSs in the second and third Landau level have vastly different cohesion energies and may indicate different internal symmetries for these states. This work was supported by the DOE grant DE-SC0006671.
Proietti, Riccardo; Roux, Jean-Francois; Verma, Atul; Alturki, Ahmed; Bernier, Martin L; Essebag, Vidal
2016-05-01
The ablation strategy for ventricular tachycardia (VT) rapidly evolved from an entrainment mapping approach for identification of the critical isthmus of the re-entrant circuit during monomorphic VT, toward a substrate-based approach aiming to ablate surrogate markers of the circuit during sinus rhythm in hemodynamically nontolerated and polymorphic VT. The latter approach implies an assumption that the circuits responsible for the arrhythmia are anatomical or fixed, and present during sinus rhythm. Accordingly, the lines of block delimiting the channels of the circuits are often considered fixed, although there is evidence that they are functional or more frequently a combination of fixed and functional. The electroanatomical substrate-based approach to VT ablation performed during sinus rhythm is increasingly adopted in clinical practice and often described as scar homogenization, scar dechanneling, or core isolation. However, whether the surrogate markers of the VT circuit during sinus rhythm match the circuit during arrhythmias remains to be fully demonstrated. The myocardial scar is a heterogeneous electrophysiological milieu with complex arrhythmogenic mechanisms that potentially coexist simultaneously. Moreover, the scar consists of different areas of diverse refractoriness and conduction. It can be misleading to limit the arrhythmogenic perspective of the myocardial scar to fixed or anatomical barriers held responsible for the re-entry circuit. Greater understanding of the role of functional lines of block in VT and the validity of the surrogate targets being ablated is necessary to further improve the technique and outcome of VT ablation. PMID:26852719
NASA Astrophysics Data System (ADS)
Lascaris, Erik; Malescio, Gianpietro; Buldyrev, Sergey V.; Stanley, H. Eugene
2010-03-01
We introduce a family of bounded repulsive potentials, which we call the cut ramp potential, obtained by cutting a linear ramp potential at different heights. We find that for the uncut ramp potential the system shows a region of anomalous re-entrant melting (a negative slope of the melting line in the temperature-pressure phase diagram), with waterlike anomalies in the same pressure range. At high pressure the melting line recovers a positive slope, a feature that we associate with the formation of clusters of particles separated by a more or less density-independent distance, the cluster separation, which is approximately equal to the ramp width σ1 . As the ramp is cut at lower and lower heights, the region of anomalous behavior shrinks and eventually disappears while at the same time the formation of clusters becomes more favored, as it is energetically less unfavorable for particles to “climb up” the ramp. We relate the occurrence of anomalous behavior to the reduced efficacy of the soft repulsive length scale with increasing pressure. The clustering phenomenon partially restores this efficacy, giving rise to an approximately constant distance σ1 between the clusters. Our results may be useful to better understand the phase behavior of macromolecules as well as that of substances with nondirectional interactions that are capable of displaying liquid polymorphism.
Andersen, John A.; Flanigan, John J.; Kindley, Robert J.
1978-01-01
The disclosure relates to an apparatus for spin ejecting a body having a flat plate base containing bosses. The apparatus has a base plate and a main ejection shaft extending perpendicularly from the base plate. A compressible cylindrical spring is disposed about the shaft. Bearings are located between the shaft and the spring. A housing containing a helical aperture releasably engages the base plate and surrounds the shaft bearings and the spring. A piston having an aperture follower disposed in the housing aperture is seated on the spring and is guided by the shaft and the aperture. The spring is compressed and when released causes the piston to spin eject the body.
CRYSTALLIZATION IN MULTICOMPONENT GLASSES
KRUGER AA; HRMA PR
2009-10-08
In glass processing situations involving glass crystallization, various crystalline forms nucleate, grow, and dissolve, typically in a nonuniform temperature field of molten glass subjected to convection. Nuclear waste glasses are remarkable examples of multicomponent vitrified mixtures involving partial crystallization. In the glass melter, crystals form and dissolve during batch-to-glass conversion, melter processing, and product cooling. Crystals often agglomerate and sink, and they may settle at the melter bottom. Within the body of cooling glass, multiple phases crystallize in a non-uniform time-dependent temperature field. Self-organizing periodic distribution (the Liesegnang effect) is common. Various crystallization phenomena that occur in glass making are reviewed.
Kurkjian, C.R.
1985-01-01
This book presents information on the following topics: a look at the history of glass strength; atomistic theory of fracture; surface chemistry in relation to the strength and fracture of silicate glasses; high-speed photographic investigations of the dynamic localized loading of some oxide glasses; a correction for measurements of contact area using Newton's rings; envionmentally enhanced crack growth; fatigue in glass; behavior of flaws in fused silica fibers; fracture toughness of chalcogenide glasses and glass-ceramics; fracture analysis of glass surfaces; and fracture mechanics parameters for glasses - a compilation and correlation.
IMPACT STRENGTH OF GLASS AND GLASS CERAMIC
Bless, S.; Tolman, J.
2009-12-28
Strength of glass and glass ceramic was measured with a bar impact technique. High-speed movies show regions of tensile and compressive failure. The borosilicate glass had a compressive strength of at least 2.2 GPa, and the glass ceramic at least 4 GPa. However, the BSG was much stronger in tension than GC. In ballistic tests, the BSG was the superior armor.
NASA Astrophysics Data System (ADS)
Kiss, L. F.; Kemény, T.; Bednarčík, J.; Gamcová, J.; Liermann, H.-P.
2016-06-01
Despite the intensive studies for decades, it is still not well understood how qualitatively different magnetic behaviors can occur in a narrow composition range for the Fe-rich Fe-transition metal (TM) amorphous alloys. In this study of amorphous F e100 -xZ rx (x =7 , 9, 12) metallic glasses, normal ferromagnetism (FM) is found at 12 % Zr where only the FM-paramagnetic (PM) transition is observed at the Curie temperature, TC. In contrast, spin-glass (SG)-PM transition at a temperature, Tg, called SG temperature, is only observed at 7 % Zr, while in the transient re-entrant composition range (x =8 -11 ) , an SG-FM transition at a temperature, Tf, called spin-freezing temperature, is also observed at low temperature besides the normal FM-PM transition at TC. In order to understand this unusual behavior, a detailed characterization of pressure (atomic volume), composition, and temperature dependence of the magnetic properties is coupled with high pressure synchrotron x-ray diffraction determination of the pressure dependence of the atomic volume. The results on F e100 -xZ rx (x =7 , 9, 12) are compared to those obtained for the FM C o91Z r9 metallic glass not showing any kind of anomalous magnetic properties. It is confirmed that the unusual behavior is caused by a granularlike magnetic structure where weakly coupled magnetic clusters are embedded into a FM bulk matrix. Since the mechanism of the magnetization reversal was found to be of the curling type rather than homogeneous rotation, the energy barrier determining the blocking temperature of the clusters is calculated as AR, where A is the exchange constant and R is the cluster size, in contrast to the usual characterization of the energy barrier by KV where K is the anisotropy energy and V is the cluster volume. The volume fraction of the FM part is a fast changing function of the bulk composition: Almost 100% FM fraction is found at 12 % of Zr while no trace of real FM is observed at 7 at % Zr. The driving
Chemical Principles Revisited: The Chemistry of Glass.
ERIC Educational Resources Information Center
Kolb, Doris; Kolb, Kenneth E.
1979-01-01
Presents a detailed discussion on the chemistry of glass. Topics discussed include: natural glass, early history, modern glass composition, raw materials for glass melting, chemically modified glasses, modern glass forming, glass ceramics, and new developments in glass research. (BT)
Spin pumping and spin Seebeck effect
NASA Astrophysics Data System (ADS)
Saitoh, Eiji
2012-02-01
Utilization of a spin current, a flow of electrons' spins in a solid, is the key technology in spintronics that will allow the achievement of efficient magnetic memories and computing devices. In this technology, generation and detection of spin currents are necessary. Here, we review inverse spin-Hall effect and spin-current-generation phenomena recently discovered both in metals and insulators: inverse spin-Hall effect, spin pumping, and spin Seebeck effect. (1)Spin pumping and spin torque in a Mott insulator system We found that spin pumping and spin torque effects appear also at an interface between Pt and an insulator YIG.. This means that we can connect a spin current carried by conduction electrons and a spin-wave spin current flowing in insulators. We demonstrate electric signal transmission by using these effects and interconversion of the spin currents [1]. (2) Spin Seebeck effect We have observed, by using the inverse spin-Hall effect [2], spin voltage generation from a heat current in a NiFe, named the spin-Seebeck effect [3]. Surprisingly, spin-Seebeck effect was found to appear even in insulators [4], a situation completely different from conventional charge Seebeck effect. The result implies an important role of elementary excitation in solids beside charge in the spin Seebeck effect. In the talk, we review the recent progress of the research on this effect. This research is collaboration with K. Ando, K. Uchida, Y. Kajiwara, S. Maekawa, G. E. W. Bauer, S. Takahashi, and J. Ieda. [4pt] [1] Y. Kajiwara and E. Saitoh et al. Nature 464 (2010) 262. [0pt] [2] E. Saitoh et al., Appl. Phys. Lett. 88 (2006) 182509. [0pt] [3] K. Uchida and E. Saitoh et al., Nature 455 (2008)778. [0pt] [4] K. Uchida and E. Saitoh et al.,Nature materials 9 (2010) 894 - 897.
Spin freezing in the spin-liquid compound FeAl2O4
NASA Astrophysics Data System (ADS)
Nair, Harikrishnan S.; Ramesh Kumar, K.; Strydom, André M.
2015-02-01
Spin freezing in the A -site spinel FeAl2O4 , which is a spin-liquid candidate, is studied using remnant magnetization and nonlinear magnetic susceptibility and isofield cooling and heating protocols. The remnant magnetization behavior of FeAl2O4 differs significantly from that of a canonical spin glass, which is also supported by analysis of the nonlinear magnetic susceptibility term χ3(T ) . Through the power-law analysis of χ3(T ) , a spin-freezing temperature Tg=11.4 ±0.9 K and critical exponent γ =1.48 ±0.59 are obtained. A Cole-Cole analysis of magnetic susceptibility shows the presence of broad spin relaxation times in FeAl2O4 , however, the irreversible dc susceptibility plot discourages an interpretation based on conventional spin-glass features. The magnetization measured using the cooling-and-heating-in-unequal-fields protocol brings more insight into the magnetic nature of this frustrated magnet and reveals unconventional glassy behavior. Combining our results, we arrive at the conclusion that the present sample of FeAl2O4 consists of a majority spin-liquid phase with "glassy" regions embedded.
NASA Technical Reports Server (NTRS)
Helman, D. D.; Holt, J. W.; Smiser, L. V.
1979-01-01
Filing procedure consisting of machined lightweight fused-silica tiles coated with thin-layer of borosilicate glass produces homogeneous seal in thin glass. Procedure is useful in repairing glass envelopes, X-ray tub windows, Dewar flasks, and similar thin glass objects.
Sakhuja, Rahul; Smith, Lisa M; Tseng, Zian H; Badhwar, Nitish; Lee, Byron K; Lee, Randall J; Scheinman, Melvin M; Olgin, Jeffrey E; Marcus, Gregory M
2011-01-01
Summary Background Claims in the medical literature suggest that neck fullness and witnessed neck pulsations are useful in the diagnosis of typical AV nodal reentrant tachycardia (AVNRT). Hypothesis Neck fullness and witnessed neck pulsations have a high positive predictive value in the diagnosis of typical AVNRT. Methods We performed a cross sectional study of consecutive patients with palpitations presenting to a single electrophysiology (EP) laboratory over a 1 year period. Each patient underwent a standard questionnaire regarding neck fullness and/or witnessed neck pulsations during their palpitations. The reference standard for diagnosis was determined by electrocardiogram and invasive EP studies. Results Comparing typical AVNRT to atrial fibrillation (AF) or atrial flutter (AFL) patients, the proportions with neck fullness and witnessed neck pulsations did not significantly differ: in the best case scenario (using the upper end of the 95% confidence interval [CI]), none of the positive or negative predictive values exceeded 79%. After restricting the population to those with supraventricular tachycardia other than AF or AFL (SVT), neck fullness again exhibited poor test characteristics; however, witnessed neck pulsations exhibited a specificity of 97% (95% CI 90–100%) and a positive predictive value of 83% (95% CI 52–98%). After adjustment for potential confounders, SVT patients with witnessed neck pulsations had a 7 fold greater odds of having typical AVNRT, p=0.029. Conclusions Although neither neck fullness nor witnessed neck pulsations are useful in distinguishing typical AVNRT from AF or AFL, witnessed neck pulsations are specific for the presence of typical AVNRT among those with SVT. PMID:19479968
NASA Astrophysics Data System (ADS)
Lewis, K.; Orpin, A.
2003-04-01
Seabed bathymetric and backscatter images were collected using a Simrad EM300 multibeam from the Poverty indentation off Gisborne, on the active convergent margin of the New Zealand East Coast. The 1,500 km square Poverty indentation is a major depression of continental margin extending from a re-entrant in the deformation front at the Hikurangi Trough, which coincides with the mouth of the Poverty Canyon. The indentation outlines a triangular, enclosed depression, bounded along its landward flank by a high scarp incised by more than a dozen regularly-spaced, V-shaped, upper slope gullies that cut into the shelf break. The indentation has been partly in-filled by debris flow and avalanche deposits, which range from a few hundred metres to more than 25 km down-slope. At some places, cracks and scarps in the slopes indicate incipient avalanches. The indentation has been simultaneously eroded by a canyon system that exhibits many of the complexities of incised river systems onshore, including offset, capture and slump dams. At the mouth of the Poverty Canyon, scour holes are visible where hydraulic jumps have eroded the sea floor. A new canyon system appears to be in the process of forming a separate northern route to the Hikurangi Trough. On the lower slope, slumping seaward of a bulge indicates collapse in the wake of a small, subducting seamount. There is little evidence of sediment escaping the slope to form fan deposits along the Hikurangi Trough. These data are currently being used to assist in the structural and stratigraphic analysis of the margin. The high-resolution maps produced prompt a thorough re-interpretation of the Late Pleistocene "landscape evolution" of the Poverty indentation and highlight the complex interaction of tectonics and deformation with sea floor morphology along active plate boundaries in general.
Creutz, Michael
2014-03-15
Quantum mechanics and relativity in the continuum imply the well known spin–statistics connection. However for particles hopping on a lattice, there is no such constraint. If a lattice model yields a relativistic field theory in a continuum limit, this constraint must “emerge” for physical excitations. We discuss a few models where a spin-less fermion hopping on a lattice gives excitations which satisfy the continuum Dirac equation. This includes such well known systems such as graphene and staggered fermions. -- Highlights: •The spin–statistics theorem is not required for particles on a lattice. •Spin emerges dynamically when spinless fermions have a relativistic continuum limit. •Graphene and staggered fermions are examples of this phenomenon. •The phenomenon is intimately tied to chiral symmetry and fermion doubling. •Anomaly cancellation is a crucial feature of any valid lattice fermion action.
Quinn, Daniel B; Rosenberg, Brian J
2015-08-01
We present an analytical treatment of the acoustics of liquid-filled wine glasses, or "glass harps." The solution is generalized such that under certain assumptions it reduces to previous glass harp models, but also leads to a proposed musical instrument, the "inverted glass harp," in which an empty glass is submerged in a liquid-filled basin. The versatility of the solution demonstrates that all glass harps are governed by a family of solutions to Laplace's equation around a vibrating disk. Tonal analyses of recordings for a sample glass are offered as confirmation of the scaling predictions. PMID:26382336
NASA Astrophysics Data System (ADS)
Quinn, Daniel B.; Rosenberg, Brian J.
2015-08-01
We present an analytical treatment of the acoustics of liquid-filled wine glasses, or "glass harps." The solution is generalized such that under certain assumptions it reduces to previous glass harp models, but also leads to a proposed musical instrument, the "inverted glass harp," in which an empty glass is submerged in a liquid-filled basin. The versatility of the solution demonstrates that all glass harps are governed by a family of solutions to Laplace's equation around a vibrating disk. Tonal analyses of recordings for a sample glass are offered as confirmation of the scaling predictions.
Yu, Conrad M.
2003-12-30
A glass-silicon column that can operate in temperature variations between room temperature and about 450.degree. C. The glass-silicon column includes large area glass, such as a thin Corning 7740 boron-silicate glass bonded to a silicon wafer, with an electrode embedded in or mounted on glass of the column, and with a self alignment silicon post/glass hole structure. The glass/silicon components are bonded, for example be anodic bonding. In one embodiment, the column includes two outer layers of silicon each bonded to an inner layer of glass, with an electrode imbedded between the layers of glass, and with at least one self alignment hole and post arrangement. The electrode functions as a column heater, and one glass/silicon component is provided with a number of flow channels adjacent the bonded surfaces.
Aging and memory effects in the spin jam states of densely populated frustrated magnets
NASA Astrophysics Data System (ADS)
Samarakoon, Anjana; Lee, Seung-Hun; Sato, Taku; Zhou, Haidong; Sinclair, Ryan; Yang, Junjie; Chen, Tianran; Chern, Gia-Wei; Klich, Israel
Defects and randomness has been largely studied as the key mechanism of glassiness find in a dilute magnetic system. Even though the same argument has also been made to explain the spin glass like properties in dense frustrated magnets, the existence of a glassy state arise intrinsically from a defect free spin system, far from the conventional dilute limit with different mechanisms such as quantum fluctuations and topological features, has been theoretically proposed recently. We have studied field effects on zero-field cooled and field cooled susceptibility bifurcation and memory effects below freezing transition, of three different densely populated frustrated magnets which glassy states we call spin jam, and a conventional dilute spin glass. Our data show common behaviors among the spin jam states, which is distinct from that of the conventional spin glass. We have also performed Monte Carlo simulations to understand the nature of their energy landscapes.
NASA Astrophysics Data System (ADS)
Evans-Lutterodt, K. W.; Chung, J. W.; Ocko, B. M.; Birgeneau, R. J.; Chiang, C.; Garland, C. W.; Chin, E.; Goodby, J.; Tinh, Nguyen Huu
1987-08-01
We have carried out high-resolution x-ray scattering and heat-capacity studies of the nematic (N)-->smectic-A (SmA) transitions in 4'-(4''-n-alkoxybenzyloxy)-4-cyanostilbene with the alkyl chain of length 7 (T7) and 8 (T8). The material T7 exhibits only a single nematic-to-smectic-A1 transition where the SmA1 period is commensurate with the molecular length l. T8 exhibits with decreasing temperature the doubly reentrant sequence N-SmAd-N-SmA1 where the SmAd period is incommensurate with d~1.2l. For both T7 and T8 we find second-order N-SmA1 transitions with identical reduced amplitudes and exponents; the critical exponents so obtained are γ=1.22+/-0.06, ν=0.69+/-0.03, ν⊥=0.63+/-0.03, and α=0.06+/-0.06. These are close, but not identical, to those expected for an ideal XY transition and they give ν+2ν⊥+α-2=0.01+/-0.15, in good agreement with anisotropic hyperscaling. The lower N-SmAd transition in T8 gives γ=1.53+/-0.1, ν=0.88+/-0.05, and ν⊥=0.76+/-0.05, in disagreement with all models. The heat capacity associated with this transition is too small to yield a reliable value for the critical exponent α. In the reentrant nematic phase of T8, the SmAd and SmA1 fluctuations are essentially independent; the SmAd fluctuations change over from being SmA-like to SmC-like with decreasing temperature in the reentrant nematic phase.
Strong rejuvenation in a chiral-glass superconductor
NASA Astrophysics Data System (ADS)
Gardchareon, A.; Mathieu, R.; Jönsson, P. E.; Nordblad, P.
2003-02-01
The glassy paramagnetic Meissner phase of a Bi2Sr2CaCu2Ox superconductor (x=8.18) is investigated by superconducting quantum interference device magnetometry, using “dc-memory” experiments employed earlier to study spin glasses. The temperature dependence of the zero-field-cooled and thermoremanent magnetization is recorded on reheating after specific cooling protocols, in which single or multiple halts are performed at constant temperatures. The “spin” states equilibrated during the halts are retrieved on reheating. The observed memory and rejuvenation effects are similar to those observed in Heisenberg-like spin glasses.
Dioguardi, A. P.; Crocker, J.; Shcokley, A. C.; Lin, C. H.; Shirer, K. R.; Nisson, D. M.; Lawson, M. M.; Roberts-Warren, N.; Canfield, Paul C.; Budko, Sergey L.; Ran, Sheng; Curro, N. J.
2013-11-12
We present ^{75}As nuclear magnetic resonance data from measurements of a series of Ba(Fe_{1-x}Co_{x})_{2}As_{2} crystals with 0.00≤x≤0.075 that reveals the coexistence of frozen antiferromagnetic domains and superconductivity for 0.060≤x≤0.071. Although bulk probes reveal no long range antiferromagnetic order beyond x=0.06, we find that the local spin dynamics reveal no qualitative change across this transition. The characteristic domain sizes vary by more than an order of magnitude, reaching a maximum variation at x=0.06. This inhomogeneous glassy dynamics may be an intrinsic response to the competition between superconductivity and antiferromagnetism in this system.
Picture Wall (Glass Structures)
NASA Technical Reports Server (NTRS)
1978-01-01
Photo shows a subway station in Toronto, Ontario, which is entirely glass-enclosed. The all-glass structure was made possible by a unique glazing concept developed by PPG Industries, Pittsburgh, Pennsylvania, one of the largest U.S. manufacturers of flat glass. In the TVS glazing system, transparent glass "fins" replace conventional vertical support members used to provide support for wind load resistance. For stiffening, silicone sealant bonds the fins to adjacent glass panels. At its glass research center near Pittsburgh, PPG Industries uses the NASTRAN computer program to analyze the stability of enclosures made entirely of glass. The company also uses NASTRAN to simulate stresses on large containers of molten glass and to analyze stress effects of solar heating on flat glass.
Reaction cured glass and glass coatings
NASA Technical Reports Server (NTRS)
Goldstein, H. E.; Leiser, D. B.; Katvala, V. W. (Inventor)
1978-01-01
The invention relates to reaction cured glass and glass coatings prepared by reacting a compound selected from the group consisting of silicon tetraboride, silicon hexaboride, other boron silicides, boron and mixtures with a reactive glass frit composed of a porous high silica borosilicate glass and boron oxide. The glassy composites of the present invention are useful as coatings on low density fibrous porous silica insulations used as heat shields and for articles such as reaction vessels that are subjected to high temperatures with rapid heating and cooling and that require resistance to temperature and repeated thermal shock at temperatures up to about 1482C (2700PF).
Spin injection into semiconductors
NASA Astrophysics Data System (ADS)
Oestreich, M.; Hübner, J.; Hägele, D.; Klar, P. J.; Heimbrodt, W.; Rühle, W. W.; Ashenford, D. E.; Lunn, B.
1999-03-01
The injection of spin-polarized electrons is presently one of the major challenges in semiconductor spin electronics. We propose and demonstrate a most efficient spin injection using diluted magnetic semiconductors as spin aligners. Time-resolved photoluminescence with a Cd0.98Mn0.02Te/CdTe structure proves the feasibility of the spin-alignment mechanism.
Dynamics and Correlations among Soft Excitations in Marginally Stable Glasses
NASA Astrophysics Data System (ADS)
Yan, Le; Baity-Jesi, Marco; Müller, Markus; Wyart, Matthieu
2015-06-01
Marginal stability is the notion that stability is achieved, but only barely so. This property constrains the ensemble of configurations explored at low temperature in a variety of systems, including spin, electron, and structural glasses. A key feature of marginal states is a (saturated) pseudogap in the distribution of soft excitations. We examine how such pseudogaps appear dynamically by studying the Sherrington-Kirkpatrick (SK) spin glass. After revisiting and correcting the multi-spin-flip criterion for local stability, we show that stationarity along the hysteresis loop requires soft spins to be frustrated among each other, with a correlation diverging as C (λ )˜1 /λ , where λ is the stability of the more stable spin. We explain how this arises spontaneously in a marginal system and develop an analogy between the spin dynamics in the SK model and random walks in two dimensions. We discuss analogous frustrations among soft excitations in short range glasses and how to detect them experimentally. We also show how these findings apply to hard sphere packings.
Dynamics and Correlations among Soft Excitations in Marginally Stable Glasses.
Yan, Le; Baity-Jesi, Marco; Müller, Markus; Wyart, Matthieu
2015-06-19
Marginal stability is the notion that stability is achieved, but only barely so. This property constrains the ensemble of configurations explored at low temperature in a variety of systems, including spin, electron, and structural glasses. A key feature of marginal states is a (saturated) pseudogap in the distribution of soft excitations. We examine how such pseudogaps appear dynamically by studying the Sherrington-Kirkpatrick (SK) spin glass. After revisiting and correcting the multi-spin-flip criterion for local stability, we show that stationarity along the hysteresis loop requires soft spins to be frustrated among each other, with a correlation diverging as C(λ)∼1/λ, where λ is the stability of the more stable spin. We explain how this arises spontaneously in a marginal system and develop an analogy between the spin dynamics in the SK model and random walks in two dimensions. We discuss analogous frustrations among soft excitations in short range glasses and how to detect them experimentally. We also show how these findings apply to hard sphere packings. PMID:26197008
Spin-state configuration induced faster spin dynamics in epitaxial La1-xSrxCoO3 thin films
NASA Astrophysics Data System (ADS)
Cui, W. Y.; Li, P.; Bai, H. L.
2015-05-01
Two important features: spin-state configuration and spin dynamics in phase-separated ferromagnetic/spin-glass epitaxial La1-xSrxCoO3 thin films (x=0.07, 0.17, 0.26, 0.30, 0.40, 0.60) have been investigated and elaborated, proved by both magnetic analyses and first principle calculations. The configuration with high-spin (HS) state Co3+ and low-spin (LS) state Co4+ is considered to be the most stable spin-state configuration for La1-xSrxCoO3 at ground state, which was demonstrated by calculating the magnetic moments of La1-xSrxCoO3, as well as first principle calculation. The stretched Co-O bond by Sr doping causes the decrease of crystal field splitting, resulting in the HS state Co3+ and LS state Co4+. The spin dynamics in the La1-xSrxCoO3 thin films was found to be faster than the classic spin-glass compounds, which is attributed to the higher-spin Co3+, and rather smaller ferromagnetic cluster size (~2.16 to ~21.5 nm) in the epitaxial films than that in referenced polycrystalline compounds (~35 to ~240 nm).
Energy Science and Technology Software Center (ESTSC)
2011-09-16
GlassForm is a software tool for generating preliminary waste glass formulas for a given waste stream. The software is useful because it reduces the number of verification melts required to develop a suitable additive composition. The software includes property models that calculate glass properties of interest from the chemical composition of the waste glass. The software includes property models for glass viscosity, electrical conductivity, glass transition temperature, and leach resistance as measured by the 7-daymore » product consistency test (PCT).« less
Spin noise in mixed Spin Systems
NASA Astrophysics Data System (ADS)
Bauch, Erik; Junghyun, Paul; Singh, Swati; Devakul, Trithep; Feguin, Adrian; Hart, Connor; Walsworth, Ronald
2016-05-01
The spin noise due to interaction of multiple spin species in mixed spin systems provides a fundamental limit to ultra-sensitive ensemble sensing and quantum information applications. In our work, we investigate the interaction of dense nuclear 13C spins with electronic nitrogen spins using Nitrogen-Vacancy centers in diamond. Our work shows experimentally and theoretically, that under certain conditions, spin noise is greatly suppressed and the coherence time of NV centers improved by order of magnitudes, providing a pathway to engineering high density ensemble samples with long coherence times at room temperature.