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Sample records for reentrant spin glass

  1. Reentrant spin glass ordering in an Fe-based bulk metallic glass

    SciTech Connect

    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.

  2. Reentrant spin-glass state in a geometrical frustrated multiferroic system: Role of disorder

    SciTech Connect

    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}.

  3. Transversal spin freezing and re-entrant spin glass phases in chemically disordered Fe-containing perovskite multiferroics.

    PubMed

    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

  4. GMI in the reentrant spin-glass Fe90Zr10 alloy: Investigation of the spin dynamics in the MHz frequency regime

    NASA Astrophysics Data System (ADS)

    Ribeiro, P. R. T.; Ramírez, J. M. M.; Vidyasagar, R.; Machado, F. L. A.; Rezende, S. M.; Dahlberg, E. Dan

    2016-09-01

    Giant magnetoimpedance (GMI) in the reentrant spin-glass (SG) phase of ferromagnetic Fe90Zr10 is reported. The temperature (T) dependence of the GMI allows the investigation of the spin dynamics in the SG phase in the MHz frequency regime and thus very short relaxation times τ (˜10-8 s). The GMI shows a broad maximum around 150 K and diminishes with decreasing T below the glass temperature Tg of 15 K. The magnetic permeability data obtained from the GMI data show the general features observed in the ac magnetic susceptibility measured at lower frequencies (10 ≤ f ≤ 104 Hz), yielding values of Tf (=Tg(f)) that allow testing the validity of the power-law scaling used for describing the dynamics of SG-phases up to 15 MHz. A log-log plot of τ (=1/f) versus the reduced critical temperature shows two distinct regimes in the time-domain: (1) a critical slowing-down is observed for values τ > 3 × 10-3 s; and (2) for 7 × 10-8 ≤ τ ≤ 3 × 10-3 s. In the latter case a fitting to the power-law yields the value 7.4 for the product of the critical exponents zν, and 1.6 × 10-7 s for the microscopic relaxation time τ0. The product of the exponents is appropriate for an Ising spin glass.

  5. Correlation between reentrant spin glass behavior and the magnetic order-disorder transition of the martensite phase in Ni-Co-Mn-Sb Heusler alloys.

    PubMed

    Nayak, Ajaya K; Suresh, K G; Nigam, A K

    2011-10-19

    We have performed ac susceptibility and dc magnetization measurements in Ni(50-x)Co(x)Mn(38)Sb(12) Heusler alloys. From the ac susceptibility measurements, the existence of reentrant spin glass (RSG) state is observed for x=0-5. It is found that the signature of RSG behavior diminishes with increase in x. This behavior is in contrast to the fact that the exchange bias field increases with x, which reveals that the origins of RSG and exchange bias are different in the present system. It is found that the system enters a frustrated ferromagnetic state just below the Curie temperature of the martensite phase (T(M)(C)) and then the RSG state at low temperature. The strength of the RSG state is critically dependent on the sharpness of the magnetic transition at (T(M)(C)). This proposition is further supported by the thermo-remanent magnetization and low field thermomagnetic measurements.

  6. Experimental evidence of the formation of a reentrant spin-glass phase in alloying two ferromagnetic CoPt3 and MnPt3 compounds

    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 0spin-glass orderings. This phase diagram is well described in the theoretical infinite-range model of Gabay and Toulouse. The randomness of the average exchange interaction is suggested to arise from competing magnetic interactions between the positive values of J2ndCoCo and J2ndMnMn and the negative value of J2ndCoMn for 3d atoms in position of second-nearest neighbors.

  7. Spin freezing process in a reentrant ferromagnet studied by neutron depolarization analysis

    SciTech Connect

    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.

  8. On the dynamics of the reentrant spin-glass state of the Fe{sub 100−x}Zr{sub x} (x = 9, 10) amorphous alloys

    SciTech Connect

    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.

  9. Complexity of vector spin glasses.

    PubMed

    Yeo, J; Moore, M A

    2004-08-13

    We study the annealed complexity of the m-vector spin glasses in the Sherrington-Kirkpatrick limit. The eigenvalue spectrum of the Hessian matrix of the Thouless-Anderson-Palmer free energy is found to consist of a continuous band of positive eigenvalues in addition to an isolated eigenvalue and (m-1) null eigenvalues due to rotational invariance. Rather surprisingly, the band does not extend to zero at any finite temperature. The isolated eigenvalue becomes zero in the thermodynamic limit, as in the Ising case (m=1), indicating that the same supersymmetry breaking recently found in Ising spin glasses occurs in vector spin glasses.

  10. Observation of re-entrant spin reorientation in TbFe1-xMnxO3.

    PubMed

    Fang, Yifei; Yang, Ya; Liu, Xinzhi; Kang, Jian; Hao, Lijie; Chen, Xiping; Xie, Lei; Sun, Guangai; Chandragiri, Venkatesh; Wang, Chin-Wei; Cao, Yiming; Chen, Fei; Liu, Yuntao; Chen, Dongfeng; Cao, Shixun; Lin, Chengtian; Ren, Wei; Zhang, Jincang

    2016-01-01

    We report a spin reorientation from Γ4(Gx, Ay, Fz) to Γ1(Ax, Gy, Cz) magnetic configuration near room temperature and a re-entrant transition from Γ1(Ax, Gy, Cz) to Γ4(Gx, Ay, Fz) at low temperature in TbFe1-xMnxO3 single crystals by performing both magnetization and neutron diffraction measurements. The Γ4 - Γ1 spin reorientation temperature can be enhanced to room temperature when x is around 0.5 ~ 0.6. These new transitions are distinct from the well-known Γ4 - Γ2 transition observed in TbFeO3, and the sinusoidal antiferromagnetism to complex spiral magnetism transition observed in multiferroic TbMnO3. We further study the evolution of magnetic entropy change (-ΔSM) versus Mn concentration to reveal the mechanism of the re-entrant spin reorientation behavior and the complex magnetic phase at low temperature. The variation of -ΔSM between a and c axes indicates the significant change of magnetocrystalline anisotropy energy in the TbFe1-xMnxO3 system. Furthermore, as Jahn-Teller inactive Fe(3+) ions coexist with Jahn-Teller active Mn(3+) ions, various anisotropy interactions, compete with each other, giving rise to a rich magnetic phase diagram. The large magnetocaloric effect reveals that the studied material could be a potential magnetic refrigerant. These findings expand our knowledge of spin reorientation phenomena and offer the alternative realization of spin-switching devices at room temperature in the rare-earth orthoferrites. PMID:27634299

  11. Observation of re-entrant spin reorientation in TbFe1‑xMnxO3

    NASA Astrophysics Data System (ADS)

    Fang, Yifei; Yang, Ya; Liu, Xinzhi; Kang, Jian; Hao, Lijie; Chen, Xiping; Xie, Lei; Sun, Guangai; Chandragiri, Venkatesh; Wang, Chin-Wei; Cao, Yiming; Chen, Fei; Liu, Yuntao; Chen, Dongfeng; Cao, Shixun; Lin, Chengtian; Ren, Wei; Zhang, Jincang

    2016-09-01

    We report a spin reorientation from Γ4(Gx, Ay, Fz) to Γ1(Ax, Gy, Cz) magnetic configuration near room temperature and a re-entrant transition from Γ1(Ax, Gy, Cz) to Γ4(Gx, Ay, Fz) at low temperature in TbFe1‑xMnxO3 single crystals by performing both magnetization and neutron diffraction measurements. The Γ4 ‑ Γ1 spin reorientation temperature can be enhanced to room temperature when x is around 0.5 ~ 0.6. These new transitions are distinct from the well-known Γ4 ‑ Γ2 transition observed in TbFeO3, and the sinusoidal antiferromagnetism to complex spiral magnetism transition observed in multiferroic TbMnO3. We further study the evolution of magnetic entropy change (‑ΔSM) versus Mn concentration to reveal the mechanism of the re-entrant spin reorientation behavior and the complex magnetic phase at low temperature. The variation of ‑ΔSM between a and c axes indicates the significant change of magnetocrystalline anisotropy energy in the TbFe1‑xMnxO3 system. Furthermore, as Jahn-Teller inactive Fe3+ ions coexist with Jahn-Teller active Mn3+ ions, various anisotropy interactions, compete with each other, giving rise to a rich magnetic phase diagram. The large magnetocaloric effect reveals that the studied material could be a potential magnetic refrigerant. These findings expand our knowledge of spin reorientation phenomena and offer the alternative realization of spin-switching devices at room temperature in the rare-earth orthoferrites.

  12. Observation of re-entrant spin reorientation in TbFe1−xMnxO3

    PubMed Central

    Fang, Yifei; Yang, Ya; Liu, Xinzhi; Kang, Jian; Hao, Lijie; Chen, Xiping; Xie, Lei; Sun, Guangai; Chandragiri, Venkatesh; Wang, Chin-Wei; Cao, Yiming; Chen, Fei; Liu, Yuntao; Chen, Dongfeng; Cao, Shixun; Lin, Chengtian; Ren, Wei; Zhang, Jincang

    2016-01-01

    We report a spin reorientation from Γ4(Gx, Ay, Fz) to Γ1(Ax, Gy, Cz) magnetic configuration near room temperature and a re-entrant transition from Γ1(Ax, Gy, Cz) to Γ4(Gx, Ay, Fz) at low temperature in TbFe1−xMnxO3 single crystals by performing both magnetization and neutron diffraction measurements. The Γ4 − Γ1 spin reorientation temperature can be enhanced to room temperature when x is around 0.5 ~ 0.6. These new transitions are distinct from the well-known Γ4 − Γ2 transition observed in TbFeO3, and the sinusoidal antiferromagnetism to complex spiral magnetism transition observed in multiferroic TbMnO3. We further study the evolution of magnetic entropy change (−ΔSM) versus Mn concentration to reveal the mechanism of the re-entrant spin reorientation behavior and the complex magnetic phase at low temperature. The variation of −ΔSM between a and c axes indicates the significant change of magnetocrystalline anisotropy energy in the TbFe1−xMnxO3 system. Furthermore, as Jahn-Teller inactive Fe3+ ions coexist with Jahn-Teller active Mn3+ ions, various anisotropy interactions, compete with each other, giving rise to a rich magnetic phase diagram. The large magnetocaloric effect reveals that the studied material could be a potential magnetic refrigerant. These findings expand our knowledge of spin reorientation phenomena and offer the alternative realization of spin-switching devices at room temperature in the rare-earth orthoferrites. PMID:27634299

  13. 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.

  14. Antibacterial properties of laser spinning glass nanofibers.

    PubMed

    Echezarreta-López, M M; De Miguel, T; Quintero, F; Pou, J; Landin, M

    2014-12-30

    A laser-spinning technique has been used to produce amorphous, dense and flexible glass nanofibers of two different compositions with potential utility as reinforcement materials in composites, fillers in bone defects or scaffolds (3D structures) for tissue engineering. Morphological and microstructural analyses have been carried out using SEM-EDX, ATR-FTIR and TEM. Bioactivity studies allow the nanofibers with high proportion in SiO2 (S18/12) to be classified as a bioinert glass and the nanofibers with high proportion of calcium (ICIE16) as a bioactive glass. The cell viability tests (MTT) show high biocompatibility of the laser spinning glass nanofibers. Results from the antibacterial activity study carried out using dynamic conditions revealed that the bioactive glass nanofibers show a dose-dependent bactericidal effect on Sthaphylococcus aureus (S. aureus) while the bioinert glass nanofibers show a bacteriostatic effect also dose-dependent. The antibacterial activity has been related to the release of alkaline ions, the increase of pH of the medium and also the formation of needle-like aggregates of calcium phosphate at the surface of the bioactive glass nanofibers which act as a physical mechanism against bacteria. The antibacterial properties give an additional value to the laser-spinning glass nanofibers for different biomedical applications, such as treating or preventing surgery-associated infections.

  15. Muon spin relaxation in spin glass PdMn

    SciTech Connect

    Heffner, R.H.; Leon, M.; Schillaci, M.E.; Dodds, S.A.; Gist, G.A.; MacLaughlin, D.E.; Mydosh, J.A.; Nieuwenhuys, G.J.

    1983-01-01

    Muon spin relaxation (..mu..SR) rates have been measured in transverse, longitudinal, and zero applied field for the spin glass PdMn (7 at. %), and are compared with a previous study of the disordered ferromagnet PdMn (2 at. %). The calculated paramagnetic state transverse field relaxation rate for noninteracting spins is much larger than the observed rate in spin glass PdMn, but is in good agreement with ferromagnetic PdMn. The zero field relaxation rate shows a sharp cusp at T/sub g/=5K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glss PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below T/sub g/=5K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glass PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below T/sub g/, a distribution of quasistatic local fields is observed in zero field, which has the same temperature dependence for both samples. Comparisons with model calculations are discussed.

  16. 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.

  17. Ground State Studies of Spin Glass Models.

    NASA Astrophysics Data System (ADS)

    Kolan, Amy Joanne

    The ground state energy and degeneracy for a set of spin glass models, PQR models, has been studied in detail. For the pure frustration case, a subset of the general PQR case, we have studied the spacial distribution of frustrated plaquettes at T = 0. We investigated the "frustration -frustration" correlation function, which involved a series expansion analysis and a computer analysis, to examine a phase transition mechanism proposed by Schuster (1981). Schuster suggested that a pair of plaquettes is bound together above, and dissociated below a critical concentration of antiferromagnetic bonds. Our analysis, however, led us to conclude that there is no sharp "unbinding" of frustration pairs. We have developed an efficient algorithm to compute the ground state energy and degeneracy of sample PQR lattices and have studied the general PQR model numerically. Our algorithm is similar in essence to Morgenstern and Binder's (1980) transfer matrix approach used to calculate the partition function of a sample of spins in the pure frustration case. The algorithm involves computing times of order ALM 2('L), where L is the width of the lattice, M is the length, and A is a constant of proportionality. We have used the results of our analysis to investigate the possibility of a paramagnetic (<--->) spin glass phase transition in the PQR model at T = 0. Although scatter in our results for the ground state degeneracy/spin obscures evidence of a possible non-analyticity in this function, we do see evidence of a "break" in the curves for the ground state energy/spin. We have used this "break" to plot the phase transition line between the spin glass and paramagnetic regimes.

  18. Correlated rattling-ion origins of dielectric properties in reentrant dipole glasses BaTiO3-BiScO3

    NASA Astrophysics Data System (ADS)

    Krayzman, Victor; Levin, Igor; Woicik, Joseph C.; Bridges, Frank

    2015-11-01

    The local structure of the pseudo-cubic solid solution 0.6BaTiO3-0.4BiScO3, 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.

  19. Correlated rattling-ion origins of dielectric properties in reentrant dipole glasses BaTiO{sub 3}-BiScO{sub 3}

    SciTech Connect

    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.

  20. 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)].

  1. Almost sure convergence in quantum spin glasses

    SciTech Connect

    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)].

  2. Quantum spin glass and the dipolar interaction.

    PubMed

    Schechter, Moshe; Laflorencie, Nicolas

    2006-09-29

    Anisotropic dipolar systems are considered. Such systems in an external magnetic field are expected to be a good experimental realization of the transverse field Ising model. With random interactions, this model yields a spin glass to paramagnet phase transition as a function of the transverse field. We show that the off-diagonal dipolar interaction, although effectively reduced, induces a finite correlation length and thus destroys the spin-glass order at any finite transverse field. We thus explain the behavior of the nonlinear susceptibility in the experiments on LiHo(x)Y(1-x)F(4), and argue that a crossover to the paramagnetic phase, and not quantum criticality, is observed.

  3. PREFACE: Viewing the World through Spin Glasses

    NASA Astrophysics Data System (ADS)

    Coolen, Ton; Nishimori, Hidetoshi; Sourlas, Nicolas; Wong, Michael

    2008-08-01

    This special issue of Journal of Physics A: Mathematical and Theoretical collects papers by speakers and participants of the conference `Viewing the World through Spin Glasses', held in Oxford (UK) on 31 August and 1 September 2007 in honour of Professor David Sherrington. It also includes contributions by many other active researchers in the field of spin glasses and related problems. The theory of spin glasses has a history of more than 30 years and continues to develop within itself as well as into an unexpectedly vast range of interdisciplinary subjects, including neural networks, error-correcting codes, optimization problems and social problems. Most of these amazing developments have their formal basis in the ground-breaking work of David Sherrington with Scott Kirkpatrick, centred on the SK model and the techniques devised to analyse it via the replica method. In this 'classic-of-classics' paper, a theoretical paradigm was suddenly established which became the common tool of analysis for thousands of papers in the following decades. It also led to deep developments in probability theory, through the efforts to understand the enigmatic Parisi solution of the SK model. The work of Professor Sherrington will continue to be an infinite source of our inspiration in many years to come. The purpose of the conference `Viewing the World through Spin Glasses' was to provide an overview of the present status of the fields which Professor Sherrington initiated, on the occasion of his 65th birthday, organized by John Cardy, Juan P Garrahan and the present Guest Editors. The first contribution in this special issue, by Professor Paul Goldbart, reflects his salute delivered at the conference dinner, and conveys its atmosphere very well. The papers that follow, ordered by the date of acceptance, represent the current activities of leading researchers in spin glasses and related fields, and we expect these to serve as milestones for future developments. We thank all the

  4. Critical slowing down mechanism and reentrant dipole glass phenomena in (1-x)BaTiO3-xBiScO3 (0.1⩽x⩽0.4): The high energy density dielectrics

    NASA Astrophysics Data System (ADS)

    Bharadwaja, S. S. N.; Kim, J. R.; Ogihara, H.; Cross, L. E.; Trolier-McKinstry, S.; Randall, C. A.

    2011-01-01

    The dielectric and ferroelectric switching properties of high temperature-high energy density (1-x)BaTiO3-xBiScO3 (0.1⩽x⩽0.4) dielectrics were investigated over a broad temperature range. It was found that these ceramics possess dipole glass features such as critical slowing down of the dielectric relaxation, polarization hysteresis aging, rejuvenation, and holelike memory below the dipole glass transition temperature (TDG). The dielectric relaxation behavior is consistent with a three-dimensional Ising model with critical slowing exponents (zυ)=10±1 and composition-dependent glass transition temperatures. At lower temperatures, (1-x)BaTiO3-xBiScO3 ceramics transform into a reentrant dipole glass state owing to the breakup of local polar ordering. A phase diagram is developed marking the paraelectric, ferroelectric, and dipole glass regimes as a function of composition with the reentrant features.

  5. 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.

  6. Chiral Potts spin glass in d =2 and 3 dimensions

    NASA Astrophysics Data System (ADS)

    Ćaǧlar, Tolga; Berker, A. Nihat

    2016-09-01

    The chiral spin-glass Potts system with q =3 states is studied in d =2 and 3 spatial dimensions by renormalization-group theory and the global phase diagrams are calculated in temperature, chirality concentration p , and chirality-breaking concentration c , with determination of phase chaos and phase-boundary chaos. In d =3 , the system has ferromagnetic, left-chiral, right-chiral, chiral spin-glass, and disordered phases. The phase boundaries to the ferromagnetic, left- and right-chiral phases show, differently, an unusual, fibrous patchwork (microreentrances) of all four (ferromagnetic, left-chiral, right-chiral, chiral spin-glass) ordered phases, especially in the multicritical region. The chaotic behavior of the interactions, under scale change, are determined in the chiral spin-glass phase and on the boundary between the chiral spin-glass and disordered phases, showing Lyapunov exponents in magnitudes reversed from the usual ferromagnetic-antiferromagnetic spin-glass systems. At low temperatures, the boundaries of the left- and right-chiral phases become thresholded in p and c . In d =2 , the chiral spin-glass Potts system does not have a spin-glass phase, consistently with the lower-critical dimension of ferromagnetic-antiferromagnetic spin glasses. The left- and right-chirally ordered phases show reentrance in chirality concentration p .

  7. Reentrant phase transitions of a coupled spin-electron model on doubly decorated planar lattices with two or three consecutive critical points

    NASA Astrophysics Data System (ADS)

    Čenčariková, Hana; Strečka, Jozef; Lyra, Marcelo L.

    2016-03-01

    The generalized decoration-iteration transformation is adapted for the exact study of a coupled spin-electron model on 2D lattices in which localized Ising spins reside on nodal lattice sites and mobile electrons are delocalized over pairs of decorating sites. The model takes into account a hopping term for mobile electrons, the Ising coupling between mobile electrons and localized spins as well as the Ising coupling between localized spins (J ‧). The ground state, spontaneous magnetization and specific heat are examined for both ferromagnetic (J ‧ > 0) as well as antiferromagnetic (J ‧ < 0) interaction between the localized spins. Several kinds of reentrant transitions between the paramagnetic (P), antiferromagnetic (AF) and ferromagnetic (F) phases have been found either with a single critical point, or with two consecutive critical points (P - AF / F - P) and three successive critical points AF / F - P - F / AF - P. Striking thermal variations of the spontaneous magnetization depict a strong reduction due to the interplay between annealed disorder and quantum fluctuations in addition to the aforementioned reentrance. It is shown that the specific heat displays diverse thermal dependencies including finite cusps at the critical temperatures.

  8. The Ising Spin Glass in dimension four

    NASA Astrophysics Data System (ADS)

    Lundow, P. H.; Campbell, I. A.

    2015-09-01

    The critical behaviors of the bimodal and Gaussian Ising spin glass (ISG) models in dimension four are studied through extensive numerical simulations, and from an analysis of high temperature series expansion (HTSE) data of Klein et al. (1991). The simulations include standard finite size scaling measurements, thermodynamic limit regime measurements, and analyses which provide estimates of critical exponents without any consideration of the critical temperature. The higher order HTSE series for the bimodal model provide accurate estimates of the critical temperature and critical exponents. These estimates are independent of and fully consistent with the simulation values. Comparisons between ISG models in dimension four show that the critical exponents and the critical constants for dimensionless observables depend on the form of the interaction distribution of the model.

  9. Reentrant phenomenon and inverse magnetocaloric effect in a generalized spin-(1/2,  s) Fisher's super-exchange antiferromagnet.

    PubMed

    Gálisová, Lucia

    2016-11-30

    The thermodynamic and magnetocaloric properties of a generalized spin-(1/2,  s) Fisher's super-exchange antiferromagnet are investigated precisely by using the decoration-iteration mapping transformation. Besides the critical temperature, sublattice magnetization, total magnetization, entropy and specific heat, the isothermal entropy change and adiabatic temperature change are also rigorously calculated in order to examine the cooling efficiency of the model in the vicinity of the first- and second-order phase transitions. It is shown that an enhanced inverse magnetocaloric effect occurs around the temperature interval [Formula: see text] for any magnetic-field change [Formula: see text]. The most pronounced inverse magnetocaloric effect can be found nearby the critical field, which corresponds to the zero-temperature phase transition from the long-range ordered ground state to the paramagnetic one. The observed phenomenon increases with an increasing value of decorating spins. Furthermore, sufficiently high values of decorating spins have also been linked to the possibility of observing reentrant phase transitions at finite temperatures. PMID:27662179

  10. 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.

  11. 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.

  12. Thermodynamic glass transition in a spin glass without time-reversal symmetry

    PubMed Central

    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

  13. Dynamical properties of the hypercell spin-glass model

    NASA Astrophysics Data System (ADS)

    Gleiser, P. M.; Tamarit, F. A.

    1998-02-01

    The spreading of damage technique is used to study the dynamical phase diagram of the spin-glass hypercubic cell model in a heat bath Monte Carlo simulation. Since the hypercubic cell in dimension 2D and the hypercubic lattice in dimension D resemble each other closely at finite dimensions and both converge to a mean field when dimension goes to infinity, we can study the effects of dimensionality on the dynamical behavior of spin glasses.

  14. 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.

  15. Efficient Cluster Algorithm for Spin Glasses in Any Space Dimension.

    PubMed

    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.

  16. 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.

  17. Low-Temperature Phase Transformations in Weakly Doped Quantum Paraelectrics: Novel Features and Quantum Reentrant Dipolar Glass State in KTa0.982Nb0.018O3

    SciTech Connect

    Trepakov, V. A.; Prosandeev, S. A.; Savinov, M. E.; Galinetto, P.; Samoggia, G.; Kapphan, S. E.; Jastrabik, L.; Boatner, Lynn A

    2004-01-01

    An unusual sequence of phase transitions (PT) and reentrant dipole glass-like phase formation at low temperatures was found recently in KTaO{sub 3} weakly doped with Li and Nb (K{sub 0.9986}Li{sub 0.0014}Ta{sub 0.976}Nb{sub 0.024}O{sub 3}) [Phys. Rev. B 63 (2001) 172]. We report on detailed low frequency (100 Hz-1 MHz) permittivity and Raman light scattering studies of similar composition, but without Li admixture, KTa{sub 1-x}Nb{sub x}O{sub 3} with x = 0.018 (KTN1.8). The aim of the study is to answer the question if the reentrant dipole glass-like phase exists in KTN1.8 and what is the microscopic origin of this phase. A detailed study of the sharp low-temperature PT observed at T{sub C} {approx} 27 K revealed properties inherent to the reentrant glass-type state at lower temperatures. The substitution of Nb for Ta influences the TO{sub 1} soft lattice mode and leads to PT with the long-range ferroelectric ordering. A crossover to an order-disorder polar microregion dynamics with a non-standard {var_epsilon}(T) behaviour and dipole glass-like formation were found below T{sub C} (at {approx}15 K), which is attributed to the randomness of the Nb distribution. A crossover to the long-range order was found under a dc bias field.

  18. 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.

  19. The Spin Glass-Kondo Competition in Disordered Cerium Systems

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F.; Coqblin, B.

    2013-10-01

    We discuss the competition between the Kondo effect, the spin glass state and a magnetic order observed in disordered Cerium systems. We present firstly the experimental situation of disordered alloys such as CeNi1 - xCux and then the different theoretical approaches based on the Kondo lattice model, with different descriptions of the intersite exchange interaction for the spin glass. After the gaussian approach of the Sherrington-Kirkpatrick model, we discuss the Mattis and the van Hemmen models. Then, we present simple cluster calculations in order to describe the percolative evolution of the clusters from the cluster spin glass to the inhomogeneous ferromagnetic order recently observed in CeNi1 - xCux disordered alloys and finally we discuss the effect of random and transverse magnetic field.

  20. Are Magnetically Doped Transition-metal Oxides Spin-glasses?

    NASA Astrophysics Data System (ADS)

    Lussier, A.; Dvorak, J.; Idzerda, Y. U.; Ogale, S. B.; Shinde, S. R.; Venkatesan, T.; Lofland, S. E.

    2004-03-01

    Many magnetic impurity doped transition-metal oxides exhibit ferromagnetism at room temperature. Some also exhibit strange magnetic aging behavior. One such material is Co-doped SnO2 which displays a saturation magnetization decrease over time, as well as with successive field applications. From the theoretical perspective, there are two prerequisites for spin-glass behavior which are both satisfied for these samples: disorder and frustration. Disorder is readily satisfied because the dilute magnetic impurities are randomly scattered. Additionally, the suggested RKKY interaction between magnetic impurities, coupled with their random spacing, likely results in frustration. Magnetometry, XAS, and XMCD measurements, with temperature, measurement time, and history dependence help elucidate the magnetic order in these materials, and are consistent with spin-glass character. We would like to acknowledge the support of NSF (MSU), the Office of Naval Research (MSU), DARPA SpinS (UMD) and NSF-MRSEC (UMD).

  1. 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.

  2. Cumulative overlap distribution function in realistic spin glasses

    NASA Astrophysics Data System (ADS)

    Billoire, A.; Maiorano, A.; Marinari, E.; Martin-Mayor, V.; Yllanes, D.

    2014-09-01

    We use a sample-dependent analysis, based on medians and quantiles, to analyze the behavior of the overlap probability distribution of the Sherrington-Kirkpatrick and 3D Edwards-Anderson models of Ising spin glasses. We find that this approach is an effective tool to distinguish between replica symmetry breaking-like and droplet-like behavior of the spin-glass phase. Our results are in agreement with a replica symmetry breaking-like behavior for the 3D Edwards-Anderson model.

  3. On the p-spin interaction transverse Ising spin-glass model without replicas

    NASA Astrophysics Data System (ADS)

    De Cesare, L.; Lukierska-Walasek, K.; Rabuffo, I.; Walasek, K.

    1995-02-01

    The p-spin interaction Ising spin glass model in the presence of a transverse field is studied in the large p-limit by means of a convenient operator extension of the cavity fields method avoiding replicas and the Trotter-Suzuki transformation. The results appear quite consistent with those recently obtained for the same model using conventional treatments within the replica trick. This gives additional support to the cavity fields approach as a promising tool towards a general theory of classical and quantum spin glasses.

  4. Glass Nanofibers from Fragile Melts Produced by Laser Spinning

    NASA Astrophysics Data System (ADS)

    Dieste, O.; Penide, J.; Quintero, F.; Riveiro, A.; Comesaña, R.; Lusquiños, F.; Pou, J.

    Laser Spinning is a new technique enabling the production of large quantity of very long amorphous ceramic nanofibers. This technique has been successfully tested with different material compositions, probing its capability to produce fibers of inorganic oxides that cannot be produced by any other technique. Precise control of the process allows for the production of amorphous nanofibers of non-ready glass former materials and the unprecedented synthesis of glass nanofibers from very fragile melts. This outcome demonstrates the capability for the synthesis of glass nanofibers with applications in the field of fire retardant fabrics, catalysis or high refractory materials.

  5. Non-self-averaging in Ising spin glasses and hyperuniversality.

    PubMed

    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 U_{22}(T,L) for the spin glass susceptibility [and for higher moments U_{nn}(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 U_{nn}(β,L)=[K_{d}ξ(T,L)/L]^{d} and so follow a renormalization group law due to Aharony and Harris [Phys. Rev. Lett. 77, 3700 (1996)PRLTAO0031-900710.1103/PhysRevLett.77.3700]. Empirically, it is found that the K_{d} values are independent of d to within the statistics. The maximum values [U_{nn}(T,L)]_{max} are almost independent of L in each dimension, and remarkably the estimated thermodynamic limit critical [U_{nn}(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 XY 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. PMID:26871035

  6. 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.

  7. Dynamical scaling in Ising and vector spin glasses

    NASA Astrophysics Data System (ADS)

    Katzgraber, Helmut G.; Campbell, I. A.

    2005-07-01

    We have studied numerically the dynamics of spin glasses with Ising and XY symmetry (gauge glass) in space dimensions 2, 3, and 4. The nonequilibrium spin-glass susceptibility χne(tw,T) and the nonequilibrium energy per spin, ene(tw,T) , of samples of large size Lb are measured as a function of anneal time tw after a quench to temperatures T . The two observables are compared to the equilibrium spin-glass susceptibility χeq(L,T) and the equilibrium energy eeq(L,T) , respectively, measured as functions of temperature T and system size L for a range of system sizes. For any time and temperature a nonequilibrium time-dependent length scale L*(tw,T) can be defined by writing χne(tw,T)=χeq(L*,T) (or the equivalent expression for the energy). Our analysis shows that for all systems studied, an “effective dynamical critical exponent” parametrization L*(tw,T)=A(T)t1/z(T) fits the data well at each temperature within the whole temperature range studied, which extends from well above the critical temperature Tc to near T=0 for dimension 2 or to well below Tc for the other space dimensions studied. In addition, the data suggest that the dynamical exponent z varies smoothly when crossing the transition temperature.

  8. Effect of glass structure on spin Hamiltonian parameters: Cu doped tellurite glasses

    NASA Astrophysics Data System (ADS)

    Ramamoorthy, Raj Kumar; Bhatnagar, Anil K.

    2015-06-01

    Cu-doped glasses with compositions [(70TeO2-(30-x)ZnO-xPbO)0.98- (CuO)0.02] (x = 5, 10, 15, 20) were prepared using the melt quenching technique and characterized by EPR. Cu2+ 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 Cu2+ ions are correlated with the help of EPR and earlier Raman analysis.

  9. Effect of glass structure on spin Hamiltonian parameters: Cu doped tellurite glasses

    SciTech Connect

    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.

  10. Avalanches and hysteresis in frustrated superconductors and XY spin glasses.

    PubMed

    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

  11. Avalanches and hysteresis in frustrated superconductors and XY spin glasses

    NASA Astrophysics Data System (ADS)

    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.

  12. Avalanches and hysteresis in frustrated superconductors and XY spin glasses.

    PubMed

    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.

  13. Reconstruction on Trees and Spin Glass Transition

    NASA Astrophysics Data System (ADS)

    Mézard, Marc; Montanari, Andrea

    2006-09-01

    Consider an information source generating a symbol at the root of a tree network whose links correspond to noisy communication channels, and broadcasting it through the network. We study the problem of reconstructing the transmitted symbol from the information received at the leaves. In the large system limit, reconstruction is possible when the channel noise is smaller than a threshold. We show that this threshold coincides with the dynamical (replica symmetry breaking) glass transition for an associated statistical physics problem. Motivated by this correspondence, we derive a variational principle which implies new rigorous bounds on the reconstruction threshold. Finally, we apply a standard numerical procedure used in statistical physics, to predict the reconstruction thresholds in various channels. In particular, we prove a bound on the reconstruction problem for the antiferromagnetic "Potts" channels, which implies, in the noiseless limit, new results on random proper colorings of infinite regular trees. This relation to the reconstruction problem also offers interesting perspective for putting on a clean mathematical basis the theory of glasses on random graphs.

  14. 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.

  15. Ordering of the Heisenberg spin glass in two dimensions

    NASA Astrophysics Data System (ADS)

    Kawamura, Hikaru; Yonehara, Hitoshi

    2003-10-01

    The spin and the chirality orderings of the Heisenberg spin glass in two dimensions with the nearest-neighbour Gaussian coupling are investigated by equilibrium Monte Carlo simulations. Particular attention is paid to the behaviour of the spin and the chirality correlation lengths. In order to observe the true asymptotic behaviour, a fairly large system size L gap 20 (L the linear dimension of the system) appears to be necessary. It is found that both the spin and the chirality order only at zero temperature. At high temperatures, the chiral correlation length stays shorter than the spin correlation length, whereas at lower temperatures below the crossover temperature T×, the chiral correlation length exceeds the spin correlation length. The spin and the chirality correlation-length exponents are estimated above T× to be ngrSG = 0.9 ± 0.2 and ngrCG = 2.1 ± 0.3, respectively. These values are close to the previous estimates on the basis of the domain-wall-energy calculation. Discussion is given about the asymptotic critical behaviour realized below T×.

  16. Replica symmetry breaking in cold atoms and spin glasses

    NASA Astrophysics Data System (ADS)

    Rotondo, P.; Tesio, E.; Caracciolo, S.

    2015-01-01

    We consider a system composed by N atoms trapped within a multimode cavity, whose theoretical description is captured by a disordered multimode Dicke model. We show that in the resonant, zero-field limit the system exactly realizes the Sherrington-Kirkpatrick model. Upon a redefinition of the temperature, the same dynamics is realized in the dispersive, strong-field limit. This regime also gives access to spin-glass observables which can be used to detect replica symmetry breaking.

  17. Spin-glass structures in biological systems (abstract)

    NASA Astrophysics Data System (ADS)

    Tsapin, Alexandre I.; Blumenfeld, L. A.

    1994-05-01

    We have discovered spin-glass structures in different biological systems like animal and plant tissues, cells, chloroplasts, mitochondria, etc. These structures were detected by the ESR method. This work has been done using a synchronous culture of yeasts, saccharomyces cer. To detect spin-glass structures in a biological system, the sample must be cooled in the presence of a strong magnetic field, from 77 to 10 K. After such cooling, we recorded the ESR signal at g factor about 3.0 caused by spin-glass structures. The rotation of the sample at 10 K relative to the permanent magnetic field (always present in ESR experiments) leads to the significant change in the intensity of the ESR signal as well as in its shape. The curve of the dependence of the ESR signal intensity on the magnetic field in which the sample was cooled is S-shaped. The cooling of the same sample in zero magnetic field resulted in the absence of the ESR signal at g=3,0. It had been shown that the maximum ESR signal at g factor about 3,0 was reached 15 min before the beginning of mitosis. The study of the properties of the ESR signal at g=3,0 allowed us to make the conclusion that the paramagnetic centers responsible for this signal have been formed by Fe(II) ions localized at the chromosomes. Formed during mitosis, spin-glass structures which play a significant role in cell biology, can be detected only by the ESR method in field cooling experiments.

  18. Percolation Problem Describing +/- J Ising Spin Glass System

    NASA Astrophysics Data System (ADS)

    Kasai, Y.; Okiji, A.

    1988-05-01

    The critical concentration of the extended percolation problem on the simple cubic lattice is determined with reference to Bhatt, Young, Ogielski and Morgenstern's simulation data of transition temperature. A relation of dimensional invariants for the critical concentration suggests that in the spin glass phase an infinite number of infinitely-large clusters coexist and each of those clusters is confined in a domain with a connectivity dimension ~ 1.4.

  19. Barrier Response Upon a Magnetic Field Change for Spin Glasses

    NASA Astrophysics Data System (ADS)

    Joh, Y. G.; Orbach, R.; Hammann, J.

    1998-03-01

    Djurberg et al.(C. Djurberg et al. Europhys. Lett., 29) 163 (1995) reported that the maximum of the relaxation rate of the zero-field-cooled spin glass magnetization, S(t)≡ partial M_ZFC(t) / partial log t, shifts to shorter waiting times with increasing magnetic field strength. We propose that these shifts allow an absolute calibration of the change in barrier structure upon a magnetic field change:(Y. G. Joh et al. Phys. Rev. Lett. 77) 4648 (1996) a reduction of the barrier heights Δ by an amount proportional to the change in Zeeman energy, E_z∝ δΔ. Analysis of the shifts contained in the data of Djurberg et al.^1 shows that Ez is proportional to B^2, where B is the applied magnetic induction, confirming an assumption of the hierarchical barrier model.^2 We find that the barrier response parameter β≡δΔ/kB T B^2 ≈ 2.5× 10-2 for the metallic spin glass (Fe_0.15Ni_0.85)_75P_16B_6Al_3,^1 2× 10-3 for the thiospinel CdCr_1.7In_0.3S_4,(E. Vincent et. al., Phys. Rev. B 52) 1050 (1995). and 5× 10-5 for the canonical spin glass CuMn 6%. These value of β scale with \\chi_FC, the field-cooled susceptibility per spin, for each compound. We believe that β decreases with decreasing tendencies for ferromagnetic clustering in the different alloys.

  20. Spin-polarized nitroxide radicals in organic glasses.

    SciTech Connect

    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.

  1. A generalization of spin glass theory in marketing: the coordination of interdependent country markets

    NASA Astrophysics Data System (ADS)

    Cremer, Jörg

    1997-02-01

    A spin model is suggested for making strategies of multinational corporations. We have generalized a a Heisenberg spin glass and random field model to describe the interrelatedness of a multinational corporation's marketing strategies. Preliminary simulations have brought about realistic results.

  2. Coexistence of exponentially many chaotic spin-glass attractors.

    PubMed

    Peleg, Y; Zigzag, M; Kinzel, W; Kanter, I

    2011-12-01

    A chaotic network of size N with delayed interactions which resembles a pseudoinverse associative memory neural network is investigated. For a load α = P/N < 1, where P stands for the number of stored patterns, the chaotic network functions as an associative memory of 2P attractors with macroscopic basin of attractions which decrease with α. At finite α, a chaotic spin-glass phase exists, where the number of distinct chaotic attractors scales exponentially with N. Each attractor is characterized by a coexistence of chaotic behavior and freezing of each one of the N chaotic units or freezing with respect to the P patterns. Results are supported by large scale simulations of networks composed of Bernoulli map units and Mackey-Glass time delay differential equations.

  3. Simulating Ising spin glasses on a quantum computer

    NASA Astrophysics Data System (ADS)

    Lidar, Daniel A.; Biham, Ofer

    1997-09-01

    A linear-time algorithm is presented for the construction of the Gibbs distribution of configurations in the Ising model, on a quantum computer. The algorithm is designed so that each run provides one configuration with a quantum probability equal to the corresponding thermodynamic weight. The partition function is thus approximated efficiently. The algorithm neither suffers from critical slowing down nor gets stuck in local minima. The algorithm can be applied in any dimension, to a class of spin-glass Ising models with a finite portion of frustrated plaquettes, diluted Ising models, and models with a magnetic field.

  4. Inference from matrix products: a heuristic spin glass algorithm

    SciTech Connect

    Hastings, Matthew B

    2008-01-01

    We present an algorithm for finding ground states of two-dimensional spin-glass systems based on ideas from matrix product states in quantum information theory. The algorithm works directly at zero temperature and defines an approximation to the energy whose accuracy depends on a parameter k. We test the algorithm against exact methods on random field and random bond Ising models, and we find that accurate results require a k which scales roughly polynomially with the system size. The algorithm also performs well when tested on small systems with arbitrary interactions, where no fast, exact algorithms exist. The time required is significantly less than Monte Carlo schemes.

  5. Spin-glass-like behaviour in IrSr{sub 2}RECu{sub 2}O{sub 8} (RE=Sm and Eu)

    SciTech Connect

    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.

  6. 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

  7. From Spin Glass to Spin Liquid Ground States in Pyrochlore Molybdates

    NASA Astrophysics Data System (ADS)

    Clark, Lucy

    Magnetic pyrochlores continue to generate intense interest due to the wealth of interesting behaviours that they can display as a result of their highly frustrated nature. Here we will present our study of the molybdate pyrochlore Lu2Mo2O7, which contains non-magnetic Lu3+ and an antiferromagnetic network of corner-sharing tetrahedra of Mo4+ 4d2 S = 1 ions. Magnetic susceptibility data show that Lu2Mo2O7 enters an unconventional spin glass state at Tf ~ 16 K that displays a quadratic dependence of the low temperature magnetic heat capacity, akin to that observed for its well-studied sister compound Y2Mo2O7. This spin glass transition is also clearly marked in our inelastic (CNCS, SNS) and diffuse elastic magnetic (D7, ILL) neutron scattering data. Furthermore, we will show that it is possible to topochemically substitute the oxide, O2-, ions within Lu2Mo2O7 for nitride, N3-, to produce an oxynitride molybdate pyrochlore of composition Lu2Mo2O5N2. Magnetic susceptibility measurements confirm that strong antiferromagnetic correlations persist within the oxynitride, which contains Mo5+ 4d1 S =1/2 ions and is thus a prime candidate to host exotic quantum spin liquid behavior. We will discuss how the enhanced quantum spin fluctuations in Lu2Mo2O5N2 appear to suppress the spin freezing transition observed in its parent oxide and instead support the formation of a gapless spin liquid phase that displays a linear dependence of the low temperature magnetic heat capacity.

  8. Magnetic transitions and spin-glass reentrance in two-dimensional [MnII(TCNE)(NCMe)2]X (X = PF6,AsF6,SbF6) molecular magnets.

    PubMed

    Olson, C S; Heth, C L; Alema, F L; Lapidus, S H; Stephens, P W; Pokhodnya, K I

    2013-06-26

    The structural, spectroscopic and magnetic properties of the two-dimensional (2D) molecule-based magnets of [Mn(II)(TCNE)(NCMe)2]X (X = PF6, AsF6, SbF6; TCNE = tetracyanoethylene, NCMe = acetonitrile) composition are reported. It is shown that the alteration of the interlayer distance by increasing the anion size has little effect on the critical magnetic ordering temperature, Tc, suggesting that it depends predominantly on the intra-plane magnetic exchange. The observed field-induced irreversibility in static magnetization, a slow decay of isothermal remanence below Tc, and the dynamic susceptibility data are in accord with a re-entrant spin-glass nature of the ground state of all materials. In contrast to the isostructural Fe-based magnets, in which strong magnetocrystalline anisotropy facilitates the finite temperature magnetic ordering with the magnetization easy axis perpendicular to the μ4-TCNE(•-) plane, in the studied Mn-based magnets the easy axis is canted away from the normal direction, due to a small magnetocrystalline anisotropy. The two magnetic transitions observed on cooling are assigned to the ferrimagnetic long-range ordering of the normal magnetization component followed by the re-entrant spin-glass type transition resulting from a random freezing of the in-plane magnetization component.

  9. Microwires fabricated by glass-coated melt spinning

    SciTech Connect

    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.

  10. Finite-size critical scaling in Ising spin glasses in the mean-field regime

    NASA Astrophysics Data System (ADS)

    Aspelmeier, T.; Katzgraber, Helmut G.; Larson, Derek; Moore, M. A.; Wittmann, Matthew; Yeo, Joonhyun

    2016-03-01

    We study in Ising spin glasses the finite-size effects near the spin-glass transition in zero field and at the de Almeida-Thouless transition in a field by Monte Carlo methods and by analytical approximations. In zero field, the finite-size scaling function associated with the spin-glass susceptibility of the Sherrington-Kirkpatrick mean-field spin-glass model is of the same form as that of one-dimensional spin-glass models with power-law long-range interactions in the regime where they can be a proxy for the Edwards-Anderson short-range spin-glass model above the upper critical dimension. We also calculate a simple analytical approximation for the spin-glass susceptibility crossover function. The behavior of the spin-glass susceptibility near the de Almeida-Thouless transition line has also been studied, but here we have only been able to obtain analytically its behavior in the asymptotic limit above and below the transition. We have also simulated the one-dimensional system in a field in the non-mean-field regime to illustrate that when the Imry-Ma droplet length scale exceeds the system size one can then be erroneously lead to conclude that there is a de Almeida-Thouless transition even though it is absent.

  11. Finite-size critical scaling in Ising spin glasses in the mean-field regime.

    PubMed

    Aspelmeier, T; Katzgraber, Helmut G; Larson, Derek; Moore, M A; Wittmann, Matthew; Yeo, Joonhyun

    2016-03-01

    We study in Ising spin glasses the finite-size effects near the spin-glass transition in zero field and at the de Almeida-Thouless transition in a field by Monte Carlo methods and by analytical approximations. In zero field, the finite-size scaling function associated with the spin-glass susceptibility of the Sherrington-Kirkpatrick mean-field spin-glass model is of the same form as that of one-dimensional spin-glass models with power-law long-range interactions in the regime where they can be a proxy for the Edwards-Anderson short-range spin-glass model above the upper critical dimension. We also calculate a simple analytical approximation for the spin-glass susceptibility crossover function. The behavior of the spin-glass susceptibility near the de Almeida-Thouless transition line has also been studied, but here we have only been able to obtain analytically its behavior in the asymptotic limit above and below the transition. We have also simulated the one-dimensional system in a field in the non-mean-field regime to illustrate that when the Imry-Ma droplet length scale exceeds the system size one can then be erroneously lead to conclude that there is a de Almeida-Thouless transition even though it is absent. PMID:27078308

  12. 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.

  13. Evolution of ferromagnetic interactions from cluster spin glass state in Co-Ga alloy

    NASA Astrophysics Data System (ADS)

    Mohammad Yasin, Sk.; Saha, Ritwik; Srinivas, V.; Kasiviswanathan, S.; Nigam, A. K.

    2016-11-01

    Low temperature magnetic properties of binary CoxGa100-x (x=54-57) alloy have been investigated. Analysis of frequency dependence of ac susceptibility provided a conclusive evidence for the existence of cluster spin glass like behavior with the freezing temperature ~8, 14 K for x=54, 55.5 respectively. The parameters for conventional 'slowing down' of the spin dynamics have been extracted from the acs data, which confirm the presence of glassy phase. The magnitude of Mydosh parameter obtained from the fits is larger than that reported for typical canonical spin glasses and smaller than those for non-interacting ideal superparamagnetic systems but comparable to those of known cluster-glass systems. Memory phenomena using specific cooling protocols also support the spin-glass features in Co55.5Ga44.5 composition. Further the development of ferromagnetic clusters from the cluster spin glass state has been observed in x=57 composition.

  14. Irreversible transitions in the exchange-striction model of spin-glass state

    NASA Astrophysics Data System (ADS)

    Valkov, V. I.; Golovchan, A. V.

    2014-08-01

    Based on the assumption of a negative volume dependence of random exchange integrals, it is possible to switch to a compressible Sherrington-Kirkpatrick spin-glass model. Within the proposed model, temperature-pressure phase diagrams were calculated and pressure- and magnetic-field-induced first-order phase transitions from the initial paramagnetic and spin-glass states to the ferromagnetic state were predicted. It was shown that the application of pressure in the spin-glass state not only increases and shifts magnetic susceptibility, but also reduces the critical magnetic fields of irreversible induced phase transitions from the spin-glass to the ferromagnetic state. The obtained results are used to describe the spin-glass state in (Sm1-xGdx)0.55Sr0.45MnO3.

  15. Finite versus zero-temperature hysteretic behavior of spin glasses: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Katzgraber, Helmut G.; Hérisson, Didier; Östh, Michael; Nordblad, Per; Ito, Atsuko; Katori, Hiroko Aruga

    2007-09-01

    We present experimental results attempting to fingerprint nonanalyticities in the magnetization curves of spin glasses found by Katzgraber [Phys. Rev. Lett. 89, 257202 (2002)] via zero-temperature Monte Carlo simulations of the Edwards-Anderson Ising spin glass. Our results show that the singularities at zero temperature due to the reversal-field memory effect are washed out by the finite temperatures of the experiments. The data are analyzed via the first order reversal curve (FORC) magnetic fingerprinting method. The experimental results are supported by Monte Carlo simulations of the Edwards-Anderson Ising spin glass at finite temperatures which agree qualitatively very well with the experimental results. This suggests that the hysteretic behavior of real Ising spin-glass materials is well described by the Edwards-Anderson Ising spin glass. Furthermore, reversal-field memory is a purely zero-temperature effect.

  16. BZT and PMN: overt and covert soft quasi spin glasses?

    NASA Astrophysics Data System (ADS)

    Sherrington, David

    2014-03-01

    PMN (PbMg1 / 3Nb2 / 3O3) is probably the most famous relaxor ferroelectric. BZT (BaZr1 - xTixO3) is a more recently discovered relaxor, within an appropriate concentration range. Both exhibit sharp frequency-dependent susceptibility peaks as a function of temperature, with evidence of polar nanodomains above this region. It will be argued that both BZT and PMN are effectively analogs of soft spin glasses, the former fairly overtly, the latter more covertly, reminiscent of metallic alloys with minority elements that are itinerant magnets in the bulk but without good local moments in isolation in the host. A further analogy with a Anderson localization explains both the features mentioned above.

  17. Exchange bias training relaxation in spin glass/ferromagnet bilayers

    NASA Astrophysics Data System (ADS)

    Chi, Xiaodan; Rui, Wenbin; Du, Jun; Zhou, Shiming; Du, An; Hu, Yong

    2016-04-01

    A canonical spin glass (SG) FeAu layer is fabricated to couple to a soft ferromagnet (FM) FeNi layer. Below the SG freezing temperature, exchange bias (EB) and training are observed. Training in SG/FM bilayers is insensitive to cooling field and may suppress the EB or change the sign of the EB field from negative to positive at specific temperatures, violating from the simple power-law or the single exponential function derived from the antiferromagnet based systems. In view of the SG nature, we employ a double decay model to distinguish the contributions from the SG bulk and the SG/FM interface to training. Dynamical properties during training under different cooling fields and at different temperatures are discussed, and the nonzero shifting coefficient in the time index as a signature of slowing-down decay for SG based systems is interpreted by means of a modified Monte Carlo Metropolis algorithm.

  18. 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.

  19. 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.

  20. Magnetostriction of rare-earth random magnetic anisotropy spin glasses

    SciTech Connect

    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.

  1. Memory effects in Heisenberg spin glasses: Spontaneous restoration of the original spin configuration rather than preservation in a frozen state

    SciTech Connect

    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.

  2. 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.

  3. Inverse spin glass and related maximum entropy problems.

    PubMed

    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

  4. Evidence for Spin Glass Ordering Near the Weak to Strong Localization Transition in Hydrogenated Graphene.

    PubMed

    Matis, Bernard R; Houston, Brian H; Baldwin, Jeffrey W

    2016-04-26

    We provide evidence that magnetic moments formed when hydrogen atoms are covalently bound to graphene exhibit spin glass ordering. We observe logarithmic time-dependent relaxations in the remnant magnetoresistance following magnetic field sweeps, as well as strong variances in the remnant magnetoresistance following field-cooled and zero-field-cooled scenarios, which are hallmarks of canonical spin glasses and provide experimental evidence for the hydrogenated graphene spin glass state. Following magnetic field sweeps, and over a relaxation period of several minutes, we measure changes in the resistivity that are more than 3 orders of magnitude larger than what has previously been reported for a two-dimensional spin glass. Magnetotransport measurements at the Dirac point, and as a function of hydrogen concentration, demonstrate that the spin glass state is observable as the zero-field resistivity reaches a value close to the quantum unit h/2e(2), corresponding to the point at which the system undergoes a transition from weak to strong localization. Our work sheds light on the critical magnetic-dopant density required to observe spin glass formation in two-dimensional systems. These findings have implications to the basic understanding of spin glasses as well the fields of two-dimensional magnetic materials and spintronics. PMID:27064170

  5. Spin-glass attractor on tridimensional hierarchical lattices in the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Salmon, Octavio R.; Nobre, Fernando D.

    2009-05-01

    A nearest-neighbor-interaction Ising spin glass, in the presence of an external magnetic field, is studied on different hierarchical lattices that approach the cubic lattice. The magnetic field is considered as uniform or random (following either a bimodal or a Gaussian probability distribution). In all cases, a spin-glass attractor is found, in the plane magnetic field versus temperature, associated with a low-temperature phase. The physical consequences of this attractor are discussed, in view of the present scenario of the spin-glass problem.

  6. Exchange bias effect in spin glass CoCr2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhu, Changming; Tian, Zhaoming; Wang, Liguang; Yuan, Songliu

    2015-11-01

    CoCr2O4 nanoparticles are about 5.4 nm in diameter synthesized by a hydrothermal technique. Magnetization measurements reveal that the nanoparticles exhibit a spin glass behavior below glass transition temperature. Signature of memory effect is clear in reheating curve where the step-like shape increasing with the increase of temperature is recovered after cooling process. Magnetic relaxation is performed to prove memory effect. Ageing effect is also detected in CoCr2O4 nanoparticles to verify the spin glass behavior. As temperature decreases to 5 K, which is far below the glass transition temperature, exchange bias effect can be observed clearly accompanied with a shift in field-cooled hysteresis loop. As particle size decreases to 5.4 nm, spin glass behavior appears due to the increased spin disorder effect. The spin glass phase providing a pinning force from some frozen spins to the rotatable spins gives the key to explain the exchange bias effects.

  7. Reentrant formation of magnetic polarons in quantum dots

    NASA Astrophysics Data System (ADS)

    Pientka, J. M.; Oszwałdowski, R.; Petukhov, A. G.; Han, J. E.; Žutić, Igor

    2012-10-01

    We propose a model of magnetic polaron formation in semiconductor quantum dots doped with magnetic ions. A wetting layer serves as a reservoir of photogenerated holes, which can be trapped by the adjacent quantum dots. For certain hole densities, the temperature dependence of the magnetization induced by the trapped holes is reentrant: it disappears for some temperature range and reappears at higher temperatures. We demonstrate that this peculiar effect is not an artifact of the mean-field approximation and persists after statistical spin fluctuations are accounted for. We predict fingerprints of reentrant magnetic polarons in photoluminescence spectra.

  8. Dynamical Properties of a Diluted Dipolar-Interaction Heisenberg Spin Glass

    NASA Astrophysics Data System (ADS)

    Zhang, Kai-Cheng; Liu, Yong; Chi, Feng

    2014-02-01

    Up to now the chirality is seldom studied in the diluted spin glass although many investigations have been performed on the site-ordered Edwards—Anderson model. By simulation, we investigate the dynamical properties of both the spin-glass and the chiral-glass phases in a diluted dipolar system, which was manifested to have a spin-glass transition by recent numerical study. By scaling we find that both phases have the same aging behavior and closer aging parameter μ. Similarly, the domains grow in the same way and both phases have a closer barrier exponent Ψ. It means that both the spins and the chirality have the same dynamical properties and they may freeze at the same temperature.

  9. Some peculiarities in the behavior of non-Ising spin glasses

    NASA Astrophysics Data System (ADS)

    Tareyeva, E. E.; Schelkacheva, T. I.; Chtchelkatchev, N. M.

    2015-03-01

    This paper is a review. We outline the main directions in the modern theory of spin glasses. The main content is based on our recent papers, devoted to studying replica symmetry breaking in non-Ising spin glasses. Studying a series of generalized models showed a certain uniformity of the behavior of these generalized spin glasses. Essentially, we observe a significant difference between their behavior and the behavior of the known systems with random couplings of Ising spins—the Sherrington-Kirkpatrick model and the corresponding p-spin model. We find the bifurcation point for the solution with the first replica symmetry breaking, study the form and stability of the solution near the bifurcation point, and show in which cases the transition to the glass state occurs continuously and in which cases, with a jump of the order parameters.

  10. Rigorous Results for Spin Glass Neural Network Associative Memories

    NASA Astrophysics Data System (ADS)

    Inchiosa, Mario Emil

    1991-08-01

    We use the methods of mathematical physics to carry out a rigorous calculation of the average free energy density and average magnetization of a spin glass type neural network associative memory which uses the pseudoinverse learning rule and has an infinite storage capacity (as the size of the network goes to infinity). We perform the calculation in the regime where the number of patterns can grow logarithmically with the size of the network. Rather than using the replica method, which relies on analytic continuation and is not mathematically rigorous, we use an exact sublattice representation. We also define and study a modified, symmetric version of the Gardner learning algorithm, which is capable of storing patterns with optimal stability. We show that in the logarithmic storage regime, this algorithm produces a network with the same average free energy density and magnetization as the pseudoinverse and Hebb rule networks. Finally, we show that previously derived results for the spurious states and speed of recall in the Hopfield model with Hebbian learning also apply to the pseudoinverse and modified symmetric Gardner rule networks.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. Bimodal and Gaussian Ising spin glasses in dimension two.

    PubMed

    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

  16. Evidence of spin glass dynamics in dilute LiHoxY1-xF4.

    PubMed

    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.

  17. Aneesur Rahman Prize for Computational Physics Talk: Numerical Simulations of Spin Glasses and Related Systems

    NASA Astrophysics Data System (ADS)

    Young, A. Peter

    2009-03-01

    Systems with disorder and ``frustration'' occur in many branches of science. There has been considerable effort to understand one such type of system, known as the ``spin glass'', because it can be probed in fine detail experimentally by applying a magnetic field, and because it can be modeled by simple-looking Hamiltonians which are amenable to numerical simulation. Analytical work is very difficult and has been carried out mainly on models with unphysical features such as infinite-range interactions. Hence, much of what we know about spin glasses and related systems comes from numerical simulations on simplified models. In this talk I will describe some of the difficulties in performing reliable spin glass simulations. Then I will discuss several questions concerning phase transitions in spin glasses and related systems that have been addressed by simulations in recent years including (i) whether there is universality, (ii) whether there is a ``vortex glass'' transition in a disordered type-II superconductor in a magnetic field, (iii) whether ``chiralities'' play a crucial role in Heisenberg spin glasses, and (iv) whether there is a line of transitions (AT line) in a magnetic field.

  18. Classical spin glass system in external field with taking into account relaxation effects

    SciTech Connect

    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

  19. Evidence for a re-entrant character of magnetism of σ-phase Fe-Mo alloys: Non-linear susceptibilities

    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

  20. Evolution from a ferromagnetic to a spin-glass regime in the spinel-type Cu(Cr{sub 1-x}Ti{sub x}){sub 2}S{sub 4}

    SciTech Connect

    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.

  1. Reentrant phenomenon and inverse magnetocaloric effect in a generalized spin-(1/2,  s) Fisher’s super-exchange antiferromagnet

    NASA Astrophysics Data System (ADS)

    Gálisová, Lucia

    2016-11-01

    The thermodynamic and magnetocaloric properties of a generalized spin-(1/2,  s) Fisher’s super-exchange antiferromagnet are investigated precisely by using the decoration-iteration mapping transformation. Besides the critical temperature, sublattice magnetization, total magnetization, entropy and specific heat, the isothermal entropy change and adiabatic temperature change are also rigorously calculated in order to examine the cooling efficiency of the model in the vicinity of the first- and second-order phase transitions. It is shown that an enhanced inverse magnetocaloric effect occurs around the temperature interval {{T}\\text{c}}(B\

  2. Spin-glass splitting in the quantum Ghatak-Sherrington model.

    PubMed

    Kim, Do-Hyun

    2013-04-01

    We propose an expanded spin-glass model, called the quantum Ghatak-Sherrington model, which considers spin-1 quantum spin operators in a crystal field and in a transverse field. The analytic solutions and phase diagrams of this model are obtained by using the one-step replica symmetry-breaking ansatz under the static approximation. Our results represent the splitting within one spin-glass (SG) phase depending on the values of crystal and transverse fields. The two separated SG phases, characterized by a density of filled states, show certain differences in their shapes and phase boundaries. Such SG splitting becomes more distinctive when the degeneracy of the empty states of spins is larger than one of their filled states. PMID:23679392

  3. Magnetic nature of the austenite-martensite phase transition and spin glass behaviour in nanostructured Mn2Ni1.6Sn0.4 melt-spun ribbons

    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.

  4. 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

  5. Direct observation of a resolvable spin separation in the spin Hall effect of light at an air-glass interface

    SciTech Connect

    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.

  6. Evidence of exchange bias effect originating from the interaction between antiferromagnetic core and spin glass shell

    SciTech Connect

    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.

  7. 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.

  8. Quantum annealing for the number-partitioning problem using a tunable spin glass of ions.

    PubMed

    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

  9. Quantum annealing for the number-partitioning problem using a tunable spin glass of ions

    PubMed Central

    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

  10. Ising spin glasses: Corrections to finite size scaling, freezing temperatures, and critical exponents

    NASA Astrophysics Data System (ADS)

    Mari, P. O.; Campbell, I. A.

    1999-03-01

    We compare simulation data from different sources on two canonical three-dimensional Ising spin glasses (ISGs): the binomial +/-J near-neighbor interaction ISG and the Gaussian interaction ISG. We allow for the possibility of corrections to finite size scaling and estimate the correction exponent w. Consistent estimates for the critical temperatures Tg and for the critical exponents for each system are obtained. The data strongly indicate that critical exponents in the two systems are significantly different from each other. These results thus confirm a breakdown of standard universality rules in Ising spin glasses.

  11. Dynamic mean field theory of the SK-spin glass. II. Order parameters and gauge invariance

    NASA Astrophysics Data System (ADS)

    Horner, H.

    1984-03-01

    The probability distribution of overlaps proposed by Parisi as order parameter for the SK-spin glass is calculated via dynamics. It is deduced from dynamic response functions and also directly obtained from a treatment with replicas and dynamics. The replica trick is not required. The comparison of the two results shows in which sense fluctuation dissipation theorems hold. Overlaps between three or more states are found to agree with those obtained by Mézard et al. using the replica trick. The origin of the ultrametric topology of spin glass states is investigated within the dynamic mean field theory and a gauge invariance is explored.

  12. Glass-wool study of laser-induced spin currents en route to hyperpolarized Cs salt

    SciTech Connect

    Ishikawa, Kiyoshi

    2011-07-15

    The nuclear spin polarization of optically pumped Cs atoms flows to the surface of Cs hydride in a vapor cell. A fine glass wool lightly coated with the salt helps greatly increase the surface area in contact with the pumped atoms and enhance the spin polarization of the salt nuclei. Even though the glass wool randomly scatters the pump light, the atomic vapor can be polarized with unpolarized light in a magnetic field. The measured enhancement in the salt enables study of the polarizations of light and atomic nuclei very near the salt surface.

  13. Monolithically integrated active waveguides and lasers using rare-earth doped spin-on glass

    SciTech Connect

    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.

  14. 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).

  15. 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.

  16. Magnetoelectric relaxor and reentrant behaviours in multiferroic Pb(Fe2/3W1/3)O3 crystal

    PubMed Central

    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

  17. Nature of reentrant state in Cr75-x Fe25+x (x=0, 5) thin films

    NASA Astrophysics Data System (ADS)

    Kumar, B. Ravi; Kaul, S. N.

    2016-11-01

    Real (χn‧) and imaginary (χn″) components of the linear (n=1) and nonlinear (n = 2 , 3 , 4 , 5) magnetic susceptibilities for the Cr75-x Fe25+x (x=0, 5) thin films have been measured over three decades of ac driving-field frequency in the presence or absence of superposed dc magnetic fields (Hdc) at temperatures embracing the critical regions near the ferromagnetic (FM)-paramagnetic (PM) and reentrant (RE) phase transitions. The temperature, TRE, which marks the onset of the transition to the RE state, manifests itself as a shoulder in the χ1‧ (T) curve. The frequency- and Hdc-induced shifts in TRE and the dynamic scaling of χ1″ (T) at temperatures T ≲TRE, characteristic of a spin glass (SG) state, have been observed. Concomitant with this SG-like behavior, a long-range FM order persists down to the lowest temperature in the RE region, as evidenced by the existence of experimental signatures, symptomatic of a FM state, such as spontaneous magnetization and the characteristic features in χ2‧ (T) and χ3‧ (T) at T ≲TRE. In the RE state, the Cr75-x Fe25+x thin films are, thus, endowed with the characteristic attributes of both a conventional ferromagnet and a spin glass.

  18. Monolithically integrated solid state laser and waveguide using spin-on glass

    DOEpatents

    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.

  19. Inverse transitions in a spin-glass model on a scale-free network.

    PubMed

    Kim, Do-Hyun

    2014-02-01

    In this paper, we will investigate critical phenomena by considering a model spin glass on scale-free networks. For this purpose, we consider the Ghatak-Sherrington (GS) model, a spin-1 spin-glass model with a crystal field, instead of the usual Ising-type model. Scale-free networks on which the GS model is placed are constructed from the static model, in which the number of vertices is fixed from the beginning. On the basis of the replica-symmetric solution, we obtain the analytical solutions, i.e., free energy and order parameters, and we derive the various phase diagrams consisting of the paramagnetic, ferromagnetic, and spin-glass phases as functions of temperature T, the degree exponent λ, the mean degree K, and the fraction of the ferromagnetic interactions ρ. Since the present model is based on the GS model, which considers the three states (S = 0, ± 1), the S = 0 state plays a crucial role in the λ-dependent critical behavior: glass transition temperature T(g) has a finite value, even when 2 < λ < 3. In addition, when the crystal field becomes nonzero, the present model clearly exhibits three types of inverse transitions, which occur when an ordered phase is more entropic than a disordered one. PMID:25353530

  20. Inverse transitions in a spin-glass model on a scale-free network

    NASA Astrophysics Data System (ADS)

    Kim, Do-Hyun

    2014-02-01

    In this paper, we will investigate critical phenomena by considering a model spin glass on scale-free networks. For this purpose, we consider the Ghatak-Sherrington (GS) model, a spin-1 spin-glass model with a crystal field, instead of the usual Ising-type model. Scale-free networks on which the GS model is placed are constructed from the static model, in which the number of vertices is fixed from the beginning. On the basis of the replica-symmetric solution, we obtain the analytical solutions, i.e., free energy and order parameters, and we derive the various phase diagrams consisting of the paramagnetic, ferromagnetic, and spin-glass phases as functions of temperature T, the degree exponent λ, the mean degree K, and the fraction of the ferromagnetic interactions ρ. Since the present model is based on the GS model, which considers the three states (S =0,±1), the S =0 state plays a crucial role in the λ-dependent critical behavior: glass transition temperature Tg has a finite value, even when 2<λ<3. In addition, when the crystal field becomes nonzero, the present model clearly exhibits three types of inverse transitions, which occur when an ordered phase is more entropic than a disordered one.

  1. Ferromagnetic spin-glass behaviour in single-crystalline U2 IrSi3.

    PubMed

    Szlawska, M; Majewicz, M; Kaczorowski, D

    2014-03-26

    A single crystal of the U-based ternary silicide U(2)IrSi(3) was investigated by means of magnetic, resistivity and heat-capacity measurements performed in wide ranges of temperature and external magnetic fields. The results hint at the formation of a non-trivial magnetic ground state in which ferromagnetic ordering coexists with spin-glass freezing. PMID:24594881

  2. Many-Body Mobility Edge in a Mean-Field Quantum Spin Glass

    NASA Astrophysics Data System (ADS)

    Laumann, C. R.; Pal, A.; Scardicchio, A.

    2014-11-01

    The quantum random energy model provides a mean-field description of the equilibrium spin glass transition. We show that it further exhibits a many-body localization-delocalization (MBLD) transition when viewed as a closed quantum system. The mean-field structure of the model allows an analytically tractable description of the MBLD transition using the forward-scattering approximation and replica techniques. The predictions are in good agreement with the numerics. The MBLD transition lies at energy density significantly above the equilibrium spin glass transition, indicating that the closed system dynamics freezes well outside of the traditional glass phase. We also observe that the structure of the eigenstates at the MBLD critical point changes continuously with the energy density, raising the possibility of a family of critical theories for the MBLD transition.

  3. Numerical study of the dynamics of some long range spin glass models

    NASA Astrophysics Data System (ADS)

    Billoire, Alain

    2015-07-01

    We present results of a Monte Carlo study of the equilibrium dynamics of the one dimensional long-range Ising spin glass model. By tuning a parameter σ , this model interpolates between the mean field Sherrington-Kirkpatrick model and a proxy of the finite dimensional Edward-Anderson model. Activated scaling fits for the behavior of the relaxation time τ as a function of the number of spins N (Namely \\ln (τ )\\propto {{N}\\psi} ) give values of \\psi that are not stable against inclusion of subleading corrections. Critical scaling (τ \\propto {{N}ρ} ) gives more stable fits, at least in the non mean field region. We also present results on the scaling of the time decay of the critical remanent magnetization of the Sherrington-Kirkpatrick model, a case where the simulation can be done with quite large systems and that shows the difficulties in obtaining precise values for dynamical exponents in spin glass models.

  4. Radiation dose from reentrant electrons.

    PubMed

    Badhwar, G D; Watts, J; Cleghorn, T E

    2001-06-01

    In estimating the crew exposures during an extra vehicular activity (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 that 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. PMID:11855420

  5. 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.

  6. The spin glass delafossite CuFe(0.5)V(0.5)O(2): a dipolar glass?

    PubMed

    Singh, Kiran; Maignan, Antoine; Simon, Charles; Hardy, Vincent; Pachoud, Elise; Martin, Christine

    2011-03-30

    The ferroelectric and spin glass properties of CuFe(0.5)V(0.5)O(2) have been studied. Magnetization, ac magnetic susceptibility and specific heat measurements reveal a spin glass behavior (T(f) = 20.5 K) for this delafossite. In CuFeO(2), substitution of trivalent diamagnetic cations for Fe(3 + ) is known to change the antiferromagnetic state and induce ferroelectricity. But partial occupation of the Fe(3 + ) site by V(3 + ) is responsible for disordered magnetism in CuFe(0.5)V(0.5)O(2). The dielectric permittivity shows a frequency dependence reminiscent of relaxor ferroelectrics in which different cations occupy the same crystallographic site. Polarization measurements show the existence of a ferroelectric state below T(f) with P(5 K)≈1.3 µC m( - 2). These results point towards a relaxor-type ferroelectricity originating from a disordered array of magnetic cations. A clear coupling between electronic charges and spins is evidenced by the magnetodielectric effect.

  7. Weak Te,Te interactions through the looking glass of NMR spin-spin coupling.

    PubMed

    Bühl, Michael; Knight, Fergus R; Křístková, Anezka; Malkin Ondík, Irina; Malkina, Olga L; Randall, Rebecca A M; Slawin, Alexandra M Z; Woollins, J Derek

    2013-02-25

    Across the bay: J((125)Te, (125)Te) spin-spin coupling is a highly sensitive probe into the electronic and geometric structure of 1,8-peri-substituted naphthalene tellurium derivatives. The coupling is related to the onset of multicenter bonding in these systems.

  8. Spin-glass freezing in a Ni-vermiculite intercalation compound.

    PubMed

    Marcos, C; Argüelles, A; Khainakov, S A; Rodríguez Fernández, J; Blanco, J A

    2012-08-29

    We report on the magnetic properties of a Ni(2+)-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 Ni(2+) 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.

  9. 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.

  10. 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.

  11. Cluster spin glass behavior in geometrically frustrated Zn3V3O8

    NASA Astrophysics Data System (ADS)

    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 cm3K 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’ (\\frac{\\left|\\theta_{CW}\\right|}{T_{N}}\\sim100) 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 Zn3V3O8.

  12. 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.

  13. 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.

  14. 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.

  15. Comparison of Ising spin glass noise to flux and inductance noise in SQUIDs.

    PubMed

    Chen, Zhi; Yu, Clare C

    2010-06-18

    Recent experiments implicate spins on the surface of metals as the source of flux and inductance noise in SQUIDs. We present Monte Carlo simulations of 2D and 3D Ising spin glasses that produce magnetization noise S(M) consistent with flux noise. At low frequencies S(M) is a maximum at the critical temperature T(C) in three dimensions, implying that flux noise should be a maximum at T(C). The second spectra of the magnetization noise and the noise in the susceptibility are consistent with experimentally measured SQUID inductance noise.

  16. Magnetic surfactants as molecular based-magnets with spin glass-like properties.

    PubMed

    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

  17. 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.

  18. Electron spin echo study of Nd3 + solvation in methanol glasses

    NASA Astrophysics Data System (ADS)

    Janakiraman, R.; Kevan, Larry

    1981-08-01

    Electron spin echo modulation studies have been carried out for Nd3+ in methanol glasses at 4.2 K. By using the partially deuterated methanols (CH3OD and CD3OH), analysis of deuterium modulation in three-pulse electron spin echo decay curves gives the distances and numbers of Nd-D(OD) and Nd-D(CD3) interactions. It is found that Nd3+ is coordinated by nine equivalent methanol molecules, with distances of Nd-H (OH) of 3.1 Å and Nd-H (CH3) of 4.0 Å. These distances establish that the molecular dipole of methanol is oriented toward Nd3+.

  19. Spin-glass transition in geometrically frustrated antiferromagnets with weak disorder

    NASA Astrophysics Data System (ADS)

    Andreanov, A.; Chalker, J. T.; Saunders, T. E.; Sherrington, D.

    2010-01-01

    We study the effect in geometrically frustrated antiferromagnets of weak, random variations in the strength of exchange interactions. Without disorder the simplest classical models for these systems have macroscopically degenerate ground states, and this degeneracy may prevent ordering at any temperature. Weak exchange randomness favors a small subset of these ground states and induces a spin-glass transition at an ordering temperature determined by the amplitude of modulations in interaction strength. We use the replica approach to formulate a theory for this transition, showing that it falls into the same universality class as conventional spin-glass transitions. In addition, we show that a model with a low concentration of defect bonds can be mapped onto a system of randomly located pseudospins that have dipolar effective interactions. We also present detailed results from Monte Carlo simulations of the classical Heisenberg antiferromagnet on the pyrochlore lattice with weak randomness in nearest-neighbor exchange.

  20. 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.

  1. Metal-ion spin-on glasses: Novel materials for active waveguides

    SciTech Connect

    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.

  2. Irreversible response in spin-glasses: An experimental study in amorphous Fe-Mn

    NASA Astrophysics Data System (ADS)

    Yeshurun, Y.; Sompolinsky, H.

    1982-08-01

    The equilibrium and nonequilibrium susceptibilities χe and χne of the spin-glass (Fe0.64Mn0.36)75P16B6Al3 have been measured as functions of temperature (4.2<=T<=80 K) and a cooling field (8 Oe<=H<=2 kOe). A phase transition occurs at a temperature Tc(H) below which the irreversible response Δ(T)~T(χe-χne) appears. Tc(H) decreases from the freezing temperature (Tf=41.6 K) as H0.75+/-0.1. For small τ≡1-TTc(H), Δ behaves as Aτ+Bτ2 with field-dependent coefficients A and B and A(H=0)=0. The results are compared with the predictions of the mean-field theory of spin-glasses.

  3. Spin glass in semiconducting KFe1.05Ag0.88Te2 single crystals

    DOE PAGESBeta

    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.

  4. Monolithically integrated solid state laser and waveguide using spin-on glass

    DOEpatents

    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.

  5. 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

  6. Observation of spin-glass behavior in nickel adsorbed few layer graphene

    SciTech Connect

    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.

  7. Phenomenological Theory of Spin-Glasses ---Static Non-Linear and Dynamical Linear Susceptibilities---

    NASA Astrophysics Data System (ADS)

    Honda, K.; Nakano, H.

    1981-01-01

    By talking into account a symmetry consideration in the theory proposed by the present authors (Prog. Theor. Phys. 65 (1981), 83), the expression for free energy of spin-glass is obtained as a function of the respective parameters g and m for spin-glass and ferromagnetic phases and of what was named the internal field parameter θ. It is found that the non-linear susceptibility χ2 diverges to minus infinity at the transition temperature T_g between the spin-glass and paramagnetic phases in proportion to |T-T_g|-1. On the basis of a conventional theory, the kinetic equation for g, m and θ are constructed to calculate the dynamical susceptibility χ(ω). A collective mode exhibiting the critical slowing down at T_g is found from the poles of χ(ω). The imaginary part of χ(ω) divided by the frequency ω diverges to infinity in the vanishing limit of ω with critical exponents different adjacently below and above T_g.

  8. 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.

  9. Diffusivity Maximum in a Reentrant Nematic Phase

    PubMed Central

    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

  10. 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.

  11. Investigation of sodium distribution in phosphate glasses using spin-echo {sup 23}Na NMR

    SciTech Connect

    Alam, T.M.; McLaughlin, J.; Click, C.C.; Conzone, S.; Brow, R.K.; Boyle, T.J.; Zwanziger, J.W.

    2000-02-24

    The spatial arrangements of sodium cations for a series of sodium phosphate glasses, xNa{sub 2}O{sm{underscore}bullet}(100{minus}x)P{sub 2}O{sub 5} (x {le} 55), were investigated using {sup 23}Na spin-echo NMR spectroscopy. The spin-echo decay rate is a function of the Na-Na homonuclear dipolar coupling, and is related to the spatial proximity of neighboring Na nuclei. The spin-echo decay rate in these sodium phosphate glasses increases nonlinearly with higher sodium number density, and thus provides a measure of the Na-Na extended range order. The results of these {sup 23}Na NMR experiments are discussed within the context of several structural models, including a decimated crystal lattice model, cubic dilation lattice model, a hard sphere (HS) random distribution model, and a pairwise cluster hard sphere model. While the experimental {sup 23}Na spin-echo M{sub 2} are described adequately by both the decimated lattice and the random HS models, it is demonstrated that the slight nonlinear behavior of M{sub 2} as a function of sodium number density is more correctly described by the random distribution in the HS model. At low sodium number densities the experimental M{sub 2} is inconsistent with models incorporating Na-Na clustering. The ability to distinguish between Na-Na clusters and nonclustered distributions becomes more difficult at higher sodium concentrations.

  12. Investigation of Sodium Distribution in Phosphate Glasses Using Spin-Echo {sup 23}Na NMR

    SciTech Connect

    ALAM, TODD M.; BOYLE, TIMOTHY J.; BROW, RICHARD K.; CLICK, CAROL C.; CONZONE, SAM; McLAUGHLIN, JAY; ZWANZIGER, JOE

    1999-09-16

    The spatial arrangement of sodium cations for a series of sodium phosphate glasses, xNa{sub 2}O(100-x)P{sub 2}O{sub 5} (x<55), were investigated using {sup 23}Na spin-echo NMR spectroscopy. The spin-echo decay rate is a function of the Na-Na homonuclear dipolar coupling and is related to the spatial proximity of neighboring Na nuclei. The spin-echo decay rate in these sodium phosphate glasses increases non-linearly with higher sodium number density, and thus provides a measure of the Na-Na extended range order. The results of these {sup 23}Na NMR experiments are discussed within the context of several structural models, including a decimated crystal lattice model, cubic dilation lattice model, a hard sphere (HS) random distribution model and a pair-wise cluster hard sphere model. While the experimental {sup 23}Na spin-echo M{sub 2} are described adequately by both the decimated lattice and the random HS model, it is demonstrated that the slight non-linear behavior of M{sub 2} as a function of sodium number density is more correctly described by the random distribution in the HS model. At low sodium number densities the experimental M{sub 2} is inconsistent with models incorporating Na-Na clustering. The ability to distinguish between Na-Na clusters and non-clustered distributions becomes more difficult at higher sodium concentrations.

  13. 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.

  14. From spin induced ferroelectricity to dipolar glasses: Spinel chromites and mixed delafossites

    SciTech Connect

    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.

  15. Nanocomposites of silver nanoparticles embedded in glass nanofibres obtained by laser spinning.

    PubMed

    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.

  16. 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.

  17. 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.

  18. Stable mean-field solution of a short-range interacting SO(3) quantum Heisenberg spin glass.

    PubMed

    da Conceição, C M S; Marino, E C

    2008-07-18

    We present a mean-field solution for a quantum, short-range interacting, disordered, SO(3) Heisenberg spin model, in which the Gaussian distribution of couplings is centered in an antiferromagnetic (AF) coupling J[over ]>0, and which, for weak disorder, can be treated as a perturbation of the pure AF Heisenberg system. The phase diagram contains, apart from a Néel phase at T=0, spin-glass and paramagnetic phases whose thermodynamic stability is demonstrated by an analysis of the Hessian matrix of the free-energy. The magnetic susceptibilities exhibit the typical cusp of a spin-glass transition.

  19. Replica symmetry breaking in a quantum spin glass-antiferromagnetic Kondo lattice

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.

    2008-04-01

    The competition between the Kondo effect and the glassy magnetic order has been studied in a theoretical model of a Kondo lattice with an intrasite Kondo interaction. The spin glass (SG) and the antiferromagnetic (AF) orderings are described by two Kondo sublattices with infinite-range Ising SG interactions among localized spins and the disordered interactions can occur with spins of same sublattices and between spins of distinct sublattices. A transverse field Γ is introduced in the effective model as a quantum mechanism to produce spin flipping. The problem is formulated in a Grassmann path integral formalism. The disorder is treated within the replica trick in one-step replica symmetry breaking (1S-RSB). The static ansatz is adopted to get a mean-field expression for the free energy and order parameters. Results show a transition from the AF order to an RSB region with a finite staggered magnetization (mixed phase) when temperature T decreases for low values of the Kondo interaction. The SG phase is not observed below the mixed phase for 1S-RSB solution, in contrast with previous replica symmetry (RS) results. The Γ field suppresses the Neel temperature leading it to a quantum critical point.

  20. 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.

  1. Re-entrant DNA gels

    PubMed Central

    Bomboi, Francesca; Romano, Flavio; Leo, Manuela; Fernandez-Castanon, Javier; Cerbino, Roberto; Bellini, Tommaso; Bordi, Federico; Filetici, Patrizia; Sciortino, Francesco

    2016-01-01

    DNA is acquiring a primary role in material development, self-assembling by design into complex supramolecular aggregates, the building block of a new-materials world. Using DNA nanoconstructs to translate sophisticated theoretical intuitions into experimental realizations by closely matching idealized models of colloidal particles is a much less explored avenue. Here we experimentally show that an appropriate selection of competing interactions enciphered in multiple DNA sequences results into the successful design of a one-pot DNA hydrogel that melts both on heating and on cooling. The relaxation time, measured by light scattering, slows down dramatically in a limited window of temperatures. The phase diagram displays a peculiar re-entrant shape, the hallmark of the competition between different bonding patterns. Our study shows that it is possible to rationally design biocompatible bulk materials with unconventional phase diagrams and tuneable properties by encoding into DNA sequences both the particle shape and the physics of the collective response. PMID:27767029

  2. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

    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.

  3. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses.

    PubMed

    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

  4. Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

    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.

  5. 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.

  6. 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.

  7. Dipolar magnets and glasses: Neutron-scattering, dynamical, and calorimetric studies of randomly distributed Ising spins

    SciTech Connect

    Reich, D.H.; Ellman, B.; Yang, J.; Rosenbaum, T.F. . James Franck Institute University of Chicago, Chicago, IL . Department of Physics); Aeppli, G. ); Belanger, D.P. )

    1990-09-01

    We have measured the magnetic correlations, susceptibility, specific heat, and thermal relaxation in the dipolar-coupled Ising system LiHo{sub {ital x}}Y{sub 1{minus}{ital x}}F{sub 4}. The material is ferromagnetic for spin concentrations at least as low as {ital x}=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF{sub 4}. In contrast, an {ital x}=0.167 sample behaves as a spin glass above its transition temperature, while an {ital x}=0.045 crystal shows very different glassy properties characterized by decreasing barriers to relaxation and nonexponential thermal relaxation as {ital T}{r arrow}0. We find the properties of the {ital x}=0.045 system to be consistent with a single low-degeneracy ground state with a large gap for excitations. The {ital x}=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the {ital x}=0.167 sample.

  8. Nonlinear and spin-glass susceptibilities of three site-diluted systems

    NASA Astrophysics Data System (ADS)

    Fernández, Julio F.

    2011-09-01

    The nonlinear magnetic χ3 and spin-glass χSG susceptibilities in zero applied field are obtained from tempered Monte Carlo simulations for three different spin glasses (SGs) of Ising spins with quenched site disorder. We find that the relation -T3χ3=χSG-2/3 (T is the temperature), which holds for Edwards-Anderson SGs, is approximately fulfilled in canonical-like SGs. For nearest-neighbor antiferromagnetic interactions on a 0.4 fraction of all sites in face-centered cubic (fcc) lattices, as well as for spatially disordered Ising dipolar (DID) systems, -T3χ3 and χSG appear to diverge in the same manner at the critical temperature TSG. However, -T3χ3 is smaller than χSG by over two orders of magnitude in the diluted fcc system. In DID systems, -T3χ3/χSG is very sensitive to the system’s aspect ratio. Whereas, near TSG, χSG varies by approximately a factor of 2 as system shape varies from cubic to long-thin-needle shapes, χ3 sweeps over some four decades.

  9. Avalanches and hysteresis in frustrated superconductors and XY spin-glasses

    NASA Astrophysics Data System (ADS)

    Sharma, Auditya; Andreanov, Alexei; Mueller, Markus

    2014-03-01

    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 no n-linear 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, sim ilarly 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.

  10. 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.

  11. Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles

    DOE PAGESBeta

    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

  12. Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles.

    PubMed

    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

  13. Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles

    PubMed Central

    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

  14. Complexity in mean-field spin-glass models: Ising p-spin

    SciTech Connect

    Crisanti, A.; Leuzzi, L.; Rizzo, T.

    2005-03-01

    The complexity of the Thouless-Anderson-Palmer (TAP) solutions of the Ising p-spin is investigated in the temperature regime where the equilibrium phase is one-step replica symmetry breaking. Two solutions of the resulting saddle point equations are found. One is supersymmetric (SUSY) and includes the equilibrium value of the free energy while the other is non-SUSY. The two solutions cross exactly at a value of the free energy where the replicon eigenvalue is zero; at low free energy the complexity is described by the SUSY solution while at high free energy it is described by the non-SUSY solution, the latter accounting for the total number of solutions. The relevant TAP solutions counted by the non-SUSY complexity share the same features of the corresponding solutions in the Sherrington-Kirkpatrick model; in particular their Hessian has a vanishing isolated eigenvalue. The TAP solutions corresponding to the SUSY complexity, instead, are well separated minima.

  15. Constructive interference between disordered couplings enhances multiparty entanglement in quantum Heisenberg spin glass models

    NASA Astrophysics Data System (ADS)

    Mishra, Utkarsh; Rakshit, Debraj; Prabhu, R.; Sen(De, Aditi; Sen, Ujjwal

    2016-08-01

    Disordered systems form one of the centrestages of research in many body sciences and lead to a plethora of interesting phenomena and applications. A paradigmatic disordered system consists of a one-dimensional array of quantum spin-1/2 particles, governed by the Heisenberg spin glass Hamiltonian with natural or engineered quenched disordered couplings in an external magnetic field. These systems allow disorder-induced enhancement for bipartite and multipartite observables. Here we show that simultaneous application of independent quenched disorders results in disorder-induced enhancement, while the same is absent with individual application of the same disorders. We term the phenomenon as constructive interference and the corresponding parameter stretches as the Venus regions. Interestingly, it has only been observed for multiparty entanglement and is absent for the single- and two-party physical quantities.

  16. 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.

  17. Spin-glass Behavior of Semiconducting KxFe2−yS2

    SciTech Connect

    Lei, H.; Abeykoon, M.; Bozin, E.S.; Petrovic, C.

    2011-05-16

    We report the discovery of K{sub x}Fe{sub 2-y}S{sub 2} single crystals, isostructural to K{sub x}Fe{sub 2-y}Se{sub 2} superconductors. The sulfide compound is a small gap semiconductor and shows spin-glass behavior below 32 K. Our results indicate that stoichiometry, defects, and the local environment of FeCh (Ch=S,Se) tetrahedra have important effects on the physical properties of isostructural and isoelectronic K{sub x}Fe{sub 2-y}Ch{sub 2} compounds.

  18. Dynamics in the Sherrington-Kirkpatrick Ising spin glass at and above Tg

    NASA Astrophysics Data System (ADS)

    Billoire, Alain; Campbell, I. A.

    2011-08-01

    A detailed numerical study is made of relaxation at equilibrium in the Sherrington-Kirkpatrick Ising spin glass (ISG) model, at and above the critical temperature Tg. The data show a long time stretched exponential relaxation q(t)˜exp{-[t/τ(T)]β(T)} with an exponent β(T) tending to ≈1/3 at Tg. The results are compared to those which were observed by A. T. Ogielski, [Phys. Rev. BPLRBAQ1098-012110.1103/PhysRevB.32.7384 32, 7384 (1985)] in the three-dimensional ISG model and are discussed in terms of a phase space percolation transition scenario.

  19. The cumulative overlap distribution function in spin glasses: mean field vs. three dimensions

    NASA Astrophysics Data System (ADS)

    Yllanes, David; Billoire, Alain; Maiorano, Andrea; Marinari, Enzo; Martin-Mayor, Victor

    2015-03-01

    We use a sample-dependent analysis, based on medians and quantiles, to analyze the behavior of the overlap probability distribution in spin glasses. Using analytical and numerical mean-field results for the Sherrington-Kirkpatrick model, as well as data from toy models, we show that this approach is an effective tool to distinguish the low-temperature behavior of replica symmmetry breaking systems from that expected in the droplet picture. An application of the method to the three-dimensional Edwards-Anderson models shows agreement with the replica symmetry breaking predictions. Supported by ERC Grant No. 247328 and from MINECO (Spain), Contract No. FIS2012-35719-C02.

  20. Soft Modes, Localization, and Two-Level Systems in Spin Glasses.

    PubMed

    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

  1. Thermodynamic Identities and Symmetry Breaking in Short-Range Spin Glasses.

    PubMed

    Arguin, L-P; Newman, C M; Stein, D L

    2015-10-30

    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. PMID:26565493

  2. 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.

  3. 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.

  4. A spinning thermometer to monitor microwave heating and glass transitions in dynamic nuclear polarization.

    PubMed

    Miéville, Pascal; Vitzthum, Veronika; Caporini, Marc A; Jannin, Sami; Gerber-Lemaire, Sandrine; Bodenhausen, Geoffrey

    2011-11-01

    As previously demonstrated by Thurber and Tycko, the peak position of (79)Br in potassium bromide (KBr) allows one to determine the temperature of a spinning sample. We propose to adapt the original design by using a compact KBr tablet placed at the bottom of the magic angle spinning rotor, separated from the sample under investigation by a thin disk made of polytetrafluoroethylene (or 'Teflon'®). This design allows spinning the sample up to at least 16 kHz. The KBr tablet can remain in the rotor when changing the sample under investigation. Calibration in the range of 98 < T < 320 K has been carried out in a static rotor by inserting a platinum thermometer. The accuracy is better than ± 0.9 K, even in the presence of microwave irradiation. Irradiation with 5 W microwaves at 263 GHz leads to a small temperature increase of 3.6 ± 1.4 K in either static or spinning samples. The dynamic nuclear polarization enhancement decreases with increasing temperature, in particular when a frozen glassy sample undergoes a glass transition.

  5. Duality, quantum skyrmions, and the stability of a SO(3) two-dimensional quantum spin glass

    NASA Astrophysics Data System (ADS)

    da Conceição, C. M. S.; Marino, E. C.

    2009-08-01

    Quantum topological excitations (skyrmions) are analyzed from the point of view of their duality to spin excitations in the different phases of a disordered two-dimensional, short-range interacting, SO(3) quantum magnetic system of Heisenberg type. The phase diagram displays all the phases, which are allowed by the duality relation. We study the large-distance behavior of the two-point correlation function of quantum skyrmions in each of these phases and, out of this, extract information about the energy spectrum and nontriviality of these excitations. The skyrmion correlators present a power-law decay in the spin-glass (SG) phase, indicating that these quantum topological excitations are gapless but nontrivial in this phase. The SG phase is dual to the AF phase, in the sense that topological and spin excitations are, respectively, gapless in each of them. The Berezinskii-Kosterlitz-Thouless mechanism guarantees the survival of the SG phase at T≠0 , whereas the AF phase is washed out to T=0 by the quantum fluctuations. Our results suggest a more symmetric way of characterizing a SG phase: one for which both the order and disorder parameters vanish, namely, ⟨σ⟩=0 and ⟨μ⟩=0 , where σ is the spin and μ is the topological excitation operators.

  6. Discovery of room-temperature spin-glass behaviors in two-dimensional oriented attached single crystals

    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.

  7. Quantum versus classical annealing: insights from scaling theory and results for spin glasses on 3-regular graphs.

    PubMed

    Liu, Cheng-Wei; Polkovnikov, Anatoli; Sandvik, Anders W

    2015-04-10

    We discuss an Ising spin glass where each S=1/2 spin is coupled antiferromagnetically to three other spins (3-regular graphs). Inducing quantum fluctuations by a time-dependent transverse field, we use out-of-equilibrium quantum Monte Carlo simulations to study dynamic scaling at the quantum glass transition. Comparing the dynamic exponent and other critical exponents with those of the classical (temperature-driven) transition, we conclude that quantum annealing is less efficient than classical simulated annealing in bringing the system into the glass phase. Quantum computing based on the quantum annealing paradigm is therefore inferior to classical simulated annealing for this class of problems. We also comment on previous simulations where a parameter is changed with the simulation time, which is very different from the true Hamiltonian dynamics simulated here.

  8. Why the dipolar response in dielectrics and spin-glasses is unavoidably universal.

    PubMed

    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.

  9. Low-temperature spin-glass behavior in a diluted dipolar Ising system

    NASA Astrophysics Data System (ADS)

    Alonso, Juan J.

    2015-03-01

    Using Monte Carlo simulations, we study the character of the spin-glass (SG) state of a site-diluted dipolar Ising model. We consider systems of dipoles randomly placed on a fraction x of all L3 sites of a simple cubic lattice that point up or down along a given crystalline axis. For x ≲0.65 these systems are known to exhibit an equilibrium spin-glass phase below a temperature Tsg∝x . At high dilution and very low temperatures, well deep in the SG phase, we find spiky distributions of the overlap parameter q that are strongly sample dependent. We focus on spikes associated with large excitations. From cumulative distributions of q and a pair correlation function averaged over several thousands of samples we find that, for the system sizes studied, the average width of spikes, and the fraction of samples with spikes higher than a certain threshold, does not vary appreciably with L . This is compared with the behavior found for the Sherrington-Kirkpatrick model.

  10. Why the dipolar response in dielectrics and spin-glasses is unavoidably universal

    PubMed Central

    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

  11. Spin-glass phase transitions and minimum energy of the random feedback vertex set problem

    NASA Astrophysics Data System (ADS)

    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), 10.1140/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 βl at which the replica-symmetric mean-field theory loses its local stability, the inverse temperature βd of the dynamical (clustering) phase transition, and the inverse temperature βs of the static (condensation) phase transition. These critical inverse temperatures all change with the mean vertex degree in a nonmonotonic way, and βd is distinct from βs for regular random graphs of vertex degrees K >60 , while βd are identical to βs 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.

  12. Why the dipolar response in dielectrics and spin-glasses is unavoidably universal.

    PubMed

    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

  13. Spin-glass phase transitions and minimum energy of the random feedback vertex set problem.

    PubMed

    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

  14. 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.

  15. Complex replica zeros of ±J Ising spin glass at zero temperature

    NASA Astrophysics Data System (ADS)

    Obuchi, Tomoyuki; Kabashima, Yoshiyuki; Nishimori, Hidetoshi

    2009-02-01

    Zeros of the nth moment of the partition function [Zn] are investigated in a vanishing temperature limit β → ∞, n → 0 keeping y = βn ~ O(1). In this limit, the moment parameterized by y characterizes the distribution of the ground-state energy. We numerically investigate the zeros for ±J Ising spin-glass models with tree and several other systems, which can be carried out with a feasible computational cost by a symbolic operation based on the Bethe-Peierls method. For several tree systems we find that the zeros tend to approach the real axis of y in the thermodynamic limit implying that the moment cannot be described by a single analytic function of y as the system size tends to infinity, which may be associated with breaking of the replica symmetry. However, examination of the analytical properties of the moment function and assessment of the spin-glass susceptibility indicate that the breaking of analyticity is relevant to neither one-step nor full replica symmetry breaking.

  16. 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).

  17. Dealing with correlated choices: how a spin-glass model can help political parties select their policies.

    PubMed

    Moore, M A; Katzgraber, Helmut G

    2014-10-01

    Starting from preferences on N proposed policies obtained via questionnaires from a sample of the electorate, an Ising spin-glass model in a field can be constructed from which a political party could find the subset of the proposed policies which would maximize its appeal, form a coherent choice in the eyes of the electorate, and have maximum overlap with the party's existing policies. We illustrate the application of the procedure by simulations of a spin glass in a random field on scale-free networks. PMID:25375448

  18. Dealing with correlated choices: How a spin-glass model can help political parties select their policies

    NASA Astrophysics Data System (ADS)

    Moore, M. A.; Katzgraber, Helmut G.

    2014-10-01

    Starting from preferences on N proposed policies obtained via questionnaires from a sample of the electorate, an Ising spin-glass model in a field can be constructed from which a political party could find the subset of the proposed policies which would maximize its appeal, form a coherent choice in the eyes of the electorate, and have maximum overlap with the party's existing policies. We illustrate the application of the procedure by simulations of a spin glass in a random field on scale-free networks.

  19. Dealing with correlated choices: how a spin-glass model can help political parties select their policies.

    PubMed

    Moore, M A; Katzgraber, Helmut G

    2014-10-01

    Starting from preferences on N proposed policies obtained via questionnaires from a sample of the electorate, an Ising spin-glass model in a field can be constructed from which a political party could find the subset of the proposed policies which would maximize its appeal, form a coherent choice in the eyes of the electorate, and have maximum overlap with the party's existing policies. We illustrate the application of the procedure by simulations of a spin glass in a random field on scale-free networks.

  20. 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)].

  1. 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.

  2. 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.

  3. The infinite-range quantum transverse Ising spin glass: new estimate of the critical line via thermo-field method

    NASA Astrophysics Data System (ADS)

    Kopeć, T. K.; Büttner, G.; Usadel, K. D.

    1990-10-01

    The infinite-range quantum Ising spin glass in a transverse field Γ is studied by means of the thermo-field dynamics as a substitute for the n-replica trick. A new estimate of the critical line Tc(Γ) is obtained by the improved treatment of the dynamic self-interaction - in considerable agreement with the Trotter-Suzuki method.

  4. 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.

  5. 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.

  6. Extremal Optimization for Ground States of the Sherrington-Kirkpatrick Spin Glass with Levy Bonds

    NASA Astrophysics Data System (ADS)

    Boettcher, Stefan

    Ground states of Ising spin glasses on fully connected graphs are studied for a broadly distributed bond family. In particular, bonds J distributed according to a Levy distribution P(J) / 1/|J|1+α; |J| > 1; are investigated for a range of powers α. We determine ground state energy density variation with α and their finite-size corrections. We find that the energies attain universally the Parisi-energy of the SK as long as the second moment of P (J) exists (α > 2). They compare favorably with recent one-step replica symmetry breaking predictions well below α = 2. At and just below α = 2, the simulations deviate significantly from theoretical expectations. The finite-size investigation reveals that the corrections exponent ω decays from the putative SK value ωSK = = 2/3 already well above α = 2, at which point it reaches a minimum.

  7. Zero-temperature quantum annealing bottlenecks in the spin-glass phase.

    PubMed

    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

  8. Zero-temperature quantum annealing bottlenecks in the spin-glass phase

    PubMed Central

    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

  9. Phase Transition for Quenched Coupled Replicas in a Plaquette Spin Model of Glasses.

    PubMed

    Jack, Robert L; Garrahan, Juan P

    2016-02-01

    We study a three-dimensional plaquette spin model whose low temperature dynamics is glassy, due to localized defects and effective kinetic constraints. The thermodynamics of this system is smooth at all temperatures. We show that coupling it to a second system with a fixed (quenched) configuration leads to a phase transition, at finite coupling. The order parameter is the overlap between the copies, and the transition is between phases of low and high overlap. We find critical points whose properties are consistent with random-field Ising universality. We analyze the interfacial free energy cost between the high- and low-overlap states that coexist at (and below) the critical point, and we use this cost as the basis for a finite-size scaling analysis. We discuss these results in the context of mean-field and dynamical facilitation theories of the glass transition. PMID:26894718

  10. Spin-on-glass coatings for the generation of super-polishedsubstrates for extreme ultraviolet optics

    SciTech Connect

    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%.

  11. SEMICONDUCTOR TECHNOLOGY Development of spin-on-glass process for triple metal interconnects

    NASA Astrophysics Data System (ADS)

    Li, Peng; Wenbin, Zhao; Guozhang, Wang; Zongguang, Yu

    2010-12-01

    Spin-on-glass (SOG), an interlayer dielectric material applied in liquid form to fill narrow gaps in the sub-dielectric surface and thus conducive to planarization, is an alternative to silicon dioxide (SiO2) deposited using PECVD processes. However, its inability to adhere to metal and problems such as cracking prevent the easy application of SOG technology to provide an interlayer dielectric in multilevel metal interconnect circuits, particularly in university processing labs. This paper will show that a thin layer of CVD SiO2 and a curing temperature below the sintering temperature of the metal interconnect layer will promote adhesion, reduce gaps, and prevent cracking. Electron scanning microscope analysis has been used to demonstrate the success of the improved technique. This optimized process has been used in batches of double-poly, triple-metal CMOS wafer fabrication to date.

  12. Reentrant transition in coupled noisy oscillators

    NASA Astrophysics Data System (ADS)

    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.

  13. Reentrant transition in coupled noisy oscillators.

    PubMed

    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

  14. Scaling of the largest dynamical barrier in the one-dimensional long-range Ising spin glass

    NASA Astrophysics Data System (ADS)

    Monthus, Cécile; Garel, Thomas

    2014-01-01

    The long-range one-dimensional Ising spin glass with random couplings decaying as J(r )∝r-σ presents a spin-glass phase Tc(σ)>0 for 0≤σ<1 (the limit σ =0 corresponds to the mean-field Sherrington-Kirkpatrick model). We use the eigenvalue method introduced in our previous work (C. Monthus and T. Garel, J. Stat. Mech. 2009, P12017) to measure the equilibrium time teq(N ) at temperature T =Tc(σ)/2 as a function of the number N of spins. We find the activated scaling lnteq(N )¯˜Nψ with the same barrier exponent ψ ≃0.33 in the whole region 0≤σ<1.

  15. Large time zero temperature dynamics of the spherical p  =  2-spin glass model of finite size

    NASA Astrophysics Data System (ADS)

    Fyodorov, Yan V.; Perret, Anthony; Schehr, Grégory

    2015-11-01

    We revisit the long time dynamics of the spherical fully connected $p = 2$-spin glass model when the number of spins $N$ is large but {\\it finite}. At $T=0$ where the system is in a (trivial) spin-glass phase, and on long time scale $t \\gtrsim {\\cal O}{(N^{2/3})}$ we show that the behavior of physical observables, like the energy, correlation and response functions, is controlled by the density of near-extreme eigenvalues at the edge of the spectrum of the coupling matrix $J$, and are thus non self-averaging. We show that the late time decay of these observables, once averaged over the disorder, is controlled by new universal exponents which we compute exactly.

  16. Existence of a Thermodynamic Spin-Glass Phase in the Zero-Concentration Limit of Anisotropic Dipolar Systems

    NASA Astrophysics Data System (ADS)

    Andresen, Juan Carlos; Katzgraber, Helmut G.; Oganesyan, Vadim; Schechter, Moshe

    2014-10-01

    The nature of ordering in dilute dipolar interacting systems dates back to the work of Debye and is one of the most basic, oldest and as-of-yet unsettled problems in magnetism. While spin-glass order is readily observed in several RKKY-interacting systems, dipolar spin glasses are the subject of controversy and ongoing scrutiny, e.g., in LiHoxY1 -xF4, a rare-earth randomly diluted uniaxial (Ising) dipolar system. In particular, it is unclear if the spin-glass phase in these paradigmatic materials persists in the limit of zero concentration or not. We study an effective model of LiHoxY1 -xF4 using large-scale Monte Carlo simulations that combine parallel tempering with a special cluster algorithm tailored to overcome the numerical difficulties that occur at extreme dilutions. We find a paramagnetic to spin-glass phase transition for all Ho+ ion concentrations down to the smallest concentration numerically accessible, 0.1%, and including Ho+ ion concentrations that coincide with those studied experimentally up to 16.7%. Our results suggest that randomly diluted dipolar Ising systems have a spin-glass phase in the limit of vanishing dipole concentration, with a critical temperature vanishing linearly with concentration. The agreement of our results with mean-field theory testifies to the irrelevance of fluctuations in interactions strengths, albeit being strong at small concentrations, to the nature of the low-temperature phase and the functional form of the critical temperature of dilute anisotropic dipolar systems. Deviations from linearity in experimental results at the lowest concentrations are discussed.

  17. 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.

  18. Stability of topologically-protected quantum computing proposals as seen through spin glasses

    NASA Astrophysics Data System (ADS)

    Katzgraber, H. G.; Andrist, R. S.

    2013-12-01

    Sensitivity to noise makes most of the current quantum computing schemes prone to error and nonscalable, allowing only for small proof-of-principle devices. Topologically-protected quantum computing aims at solving this problem by encoding quantum bits and gates in topological properties of the hardware medium that are immune to noise that does not impact the entire system at once. There are different approaches to achieve topological stability or active error correction, ranging from quasiparticle braidings to spin models and topological colour codes. The stability of these proposals against noise can be quantified by their error threshold. This figure of merit can be computed by mapping the problem onto complex statistical-mechanical spin-glass models with local disorder on nontrival lattices that can have many-body interactions and are sometimes described by lattice gauge theories. The error threshold for a given source of error then represents the point in the temperature-disorder phase diagram where a stable symmetry-broken phase vanishes. An overview of the techniques used to estimate the error thresholds is given, as well as a summary of recent results on the stability of different topologically-protected quantum computing schemes to different error sources.

  19. 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.

  20. Integrated optical-fiber capillary electrophoresis microchips with novel spin-on-glass surface modification.

    PubMed

    Lin, Che-Hsin; Lee, Gwo-Bin; Fu, Lung-Ming; Chen, Shu-Hui

    2004-07-30

    This paper presents a novel micro-capillary electrophoresis (CE) chip with embedded optical fibers for the on-line detection of DNA samples. The optical fibers are pre-etched and then inserted directly into fiber channels incorporated within low-cost soda-lime glass substrates. The embedded optical fibers are precisely aligned with the microfluidic channels such that the induced fluorescence signals from labeled bio-samples can be detected. This arrangement avoids the requirement for delicate optical alignment procedures and equipment. Surface modification of the CE channels is accomplished by means of a simple and reliable organic-based spin-on-glass (SOG) method. The zeta potential distribution and the corresponding electroosmotic mobility of the fluid are simulated numerically for the modified and non-modified channel surfaces, and then both sets of results are verified experimentally. The present results indicate that the value of the zeta potential for a surface with an SOG coating is 19.3 times smaller than that of an untreated surface. A phiX-174 DNA marker fluid is used to evaluate the injection and separation performance of the developed micro-CE device. Furthermore, the long-term stability of the SOG-coated surface is also investigated. The experimental data reveal that the microchip device is capable of providing highly efficient separations of bio-molecules, and that the SOG layer retains its low zeta potential characteristics for at least 45 days. The present results confirm the effectiveness of the proposed micro-CE chip in performing the on-line detection of DNA samples, and indicate that the SOG process represents a simple and reliable solution for the surface modification of glass-based microchannels. PMID:15142580

  1. Spin-Glass Behavior in a Giant Unit Cell Compound Tb117Fe52Ge113.8(1)

    SciTech Connect

    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.

  2. Retrieving the ground state of spin glasses using thermal noise: Performance of quantum annealing at finite temperatures

    NASA Astrophysics Data System (ADS)

    Nishimura, Kohji; Nishimori, Hidetoshi; Ochoa, Andrew J.; Katzgraber, Helmut G.

    2016-09-01

    We study the problem to infer the ground state of a spin-glass Hamiltonian using data from another Hamiltonian with interactions disturbed by noise from the original Hamiltonian, motivated by the ground-state inference in quantum annealing on a noisy device. It is shown that the average Hamming distance between the inferred spin configuration and the true ground state is minimized when the temperature of the noisy system is kept at a finite value, and not at zero temperature. We present a spin-glass generalization of a well-established result that the ground state of a purely ferromagnetic Hamiltonian is best inferred at a finite temperature in the sense of smallest Hamming distance when the original ferromagnetic interactions are disturbed by noise. We use the numerical transfer-matrix method to establish the existence of an optimal finite temperature in one- and two-dimensional systems. Our numerical results are supported by mean-field calculations, which give an explicit expression of the optimal temperature to infer the spin-glass ground state as a function of variances of the distributions of the original interactions and the noise. The mean-field prediction is in qualitative agreement with numerical data. Implications on postprocessing of quantum annealing on a noisy device are discussed.

  3. Thermally driven asymmetric responses of grains versus spin-glass related distributions of blocking temperature in exchange biased Co/IrMn bilayers

    SciTech Connect

    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.

  4. Comparing Monte Carlo methods for finding ground states of Ising spin glasses: Population annealing, simulated annealing, and parallel tempering.

    PubMed

    Wang, Wenlong; Machta, Jonathan; Katzgraber, Helmut G

    2015-07-01

    Population annealing is a Monte Carlo algorithm that marries features from simulated-annealing and parallel-tempering Monte Carlo. As such, it is ideal to overcome large energy barriers in the free-energy landscape while minimizing a Hamiltonian. Thus, population-annealing Monte Carlo can be used as a heuristic to solve combinatorial optimization problems. We illustrate the capabilities of population-annealing Monte Carlo by computing ground states of the three-dimensional Ising spin glass with Gaussian disorder, while comparing to simulated-annealing and parallel-tempering Monte Carlo. Our results suggest that population annealing Monte Carlo is significantly more efficient than simulated annealing but comparable to parallel-tempering Monte Carlo for finding spin-glass ground states.

  5. Sustained phase separation and spin glass in Co-doped KxFe2 -ySe2 single crystals

    NASA Astrophysics Data System (ADS)

    Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.

    2015-11-01

    We present 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 the superconducting phase (stripe phase) are connected with the arrangement of K, Fe, and Co atoms. Semiconducting spin glass is found in proximity to the superconducting state, persisting for large Co concentrations. At high Co concentrations a ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell and arrangement and connectivity of the stripe conducting phase.

  6. Sustained phase separation and spin glass in Co-doped KxFe2-ySe2 single crystals

    DOE PAGESBeta

    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

  7. Short-range Ising spin glasses: The metastate interpretation of replica symmetry breaking

    NASA Astrophysics Data System (ADS)

    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 Wd -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)≠∫01dxq(x ), then the

  8. Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields

    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.

  9. Doping of ZnO nanowires using phosphorus diffusion from a spin-on doped glass source

    SciTech Connect

    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.

  10. Comment on ``Spin-glass attractor on tridimensional hierarchical lattices in the presence of an external magnetic field''

    NASA Astrophysics Data System (ADS)

    Berker, A. Nihat

    2010-04-01

    The effect of random or uniform magnetic fields on spin glasses on some d=3 hierarchical lattices has been studied, using renormalization-group theory, by Salmon and Nobre. In this work, the recursion relation for the local magnetic field is incorrect. It erroneously weakens the amplitude of the renormalization contribution to the magnetic field by a factor of 1/qμ , where qμ is the site coordination number.

  11. 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)

  12. 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.

  13. 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.

  14. Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers

    PubMed Central

    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

  15. Low-temperature behavior of the statistics of the overlap distribution in Ising spin-glass models

    NASA Astrophysics Data System (ADS)

    Wittmann, Matthew; Yucesoy, B.; Katzgraber, Helmut G.; Machta, J.; Young, A. P.

    2014-10-01

    Using Monte Carlo simulations, we study in detail the overlap distribution for individual samples for several spin-glass models including the infinite-range Sherrington-Kirkpatrick model, short-range Edwards-Anderson models in three and four space dimensions, and one-dimensional long-range models with diluted power-law interactions. We study three long-range models with different powers as follows: The first is approximately equivalent to a short-range model in three dimensions, the second to a short-range model in four dimensions, and the third to a short-range model in the mean-field regime. We study an observable proposed earlier by some of us which aims to distinguish the "replica symmetry breaking" picture of the spin-glass phase from the "droplet picture," finding that larger system sizes would be needed to unambiguously determine which of these pictures describes the low-temperature state of spin glasses best, except for the Sherrington-Kirkpatrick model, which is unambiguously described by replica symmetry breaking. Finally, we also study the median integrated overlap probability distribution and a typical overlap distribution, finding that these observables are not particularly helpful in distinguishing the replica symmetry breaking and the droplet pictures.

  16. Fragility of the mean-field scenario of structural glasses for disordered spin models in finite dimensions

    NASA Astrophysics Data System (ADS)

    Cammarota, Chiara; Biroli, Giulio; Tarzia, Marco; Tarjus, Gilles

    2013-02-01

    At the mean-field level, on fully connected lattices, several disordered spin models have been shown to belong to the universality class of “structural glasses” with a “random first-order transition” (RFOT) characterized by a discontinuous jump of the order parameter and no latent heat. However, their behavior in finite dimensions is often drastically different, displaying either no glassiness at all or a conventional spin-glass transition. We clarify the physical reasons for this phenomenon and stress the unusual fragility of the RFOT to short-range fluctuations, associated, e.g., with the mere existence of a finite number of neighbors. Accordingly, the solution of fully connected models is only predictive in very high dimension, whereas despite being also mean-field in character, the Bethe approximation provides valuable information on the behavior of finite-dimensional systems. We suggest that before embarking on a full blown account of fluctuations on all scales through computer simulation or renormalization-group approach, models for structural glasses should first be tested for the effect of short-range fluctuations and we discuss ways to do it. Our results indicate that disordered spin models do not appear to pass the test and are therefore questionable models for investigating the glass transition in three dimensions. This also highlights how nontrivial is the first step of deriving an effective theory for the RFOT phenomenology from a rigorous integration over the short-range fluctuations.

  17. Phase diagrams and the instability of the spin glass states for the diluted Hopfield neural network model

    NASA Astrophysics Data System (ADS)

    Canning, Andrew; Naef, Jean-Pierre

    1992-09-01

    The replica-symmetric order parameter equations derived in [2, 4] for the symmetrically diluted Hopfield neural network model [1] are solved for different degrees of dilution. The dilution is random but symmetric. Phase diagrams are presented for c=1, 0.1, 0.001 and cto 0, where c is the fractional connectivity. The line T_c where the memory states become global minima (having lower free energy than the spin glass states) is also found for different values of c. It is found that the effect of dilution is to destabilize the spin glass states and the line T_c is driven rapidly towards the line T_M; the phase transition line where the memory states first stabilize. All the results are derived in the context of replica symmetry so are expected to be incorrect in certain parts of the phase diagram (the error increasing the further below the replica symmetry breaking lines we are) but our results do suggest in a general way that dilution, even in small quantities, increases the stability of the memory states with respect to the spin glass states.

  18. Reentrant phase transition in granular superconductors

    NASA Astrophysics Data System (ADS)

    Fazekas, Patrik

    1982-09-01

    The conditions for the appearance of a reentrant superconducting phase in granular materials are studied in mean field approximation applied to periodic models. We assume that the relevant low-lying excitation is the transfer of a Cooper pair from a grain to one of its neighbours, and neglect pair breaking. Both on-grain ( U) and nearest neighbour ( V) Coulomb interactions are taken into account, and the Coulomb problem is treated in Bethe-Peierls approximation. When V/U is not too large, reentrance is predicted if V/U>(4+3 z)-1/2 where z is the coordination number. This result is different from a recent criterion suggested by Šimánek, which allows reentrance only in the immediate vicinities of certain discrete values of V/U. For strong enough V/U, the models treated here show a transition to an ionic-salt-like charge-ordered state. Reentrant superconductivity is shown to occur also on an ionic background. In actual systems, close-packing effects partially frustrate the ionic ordering and enhance the reentrant feature.

  19. 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

  20. Asymmetric electroresistance of cluster glass state in manganites

    SciTech Connect

    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.

  1. Asymmetric electroresistance of cluster glass state in manganites

    NASA Astrophysics Data System (ADS)

    Lourembam, James; Ding, Junfeng; Bera, Ashok; Lin, Weinan; Wu, Tom

    2014-03-01

    We report the electrostatic modulation of transport in strained Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films grown on SrTiO3 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.

  2. Flux 1/fα noise in two-dimensional Heisenberg spin glasses: Effects of weak anisotropic interactions

    NASA Astrophysics Data System (ADS)

    Atalaya, Juan; Clarke, John; Schön, Gerd; Shnirman, Alexander

    2014-07-01

    We study the dynamics of a two-dimensional ensemble of randomly distributed classical Heisenberg spins with isotropic RKKY and weaker anisotropic dipole-dipole couplings. Such ensembles may give rise to the flux noise observed in SQUIDs with a 1/fα power spectrum with α ≲1. We solve numerically the Landau-Lifshitz-Gilbert equations of motion in the dissipationless limit. We find that Ising-type fluctuators, which arise from spin clustering close to a spin-glass critical behavior with Tc=0, give rise to 1/fα noise. Even weak anisotropic interactions lead to a crossover from the Heisenberg-type criticality to the much stronger Ising-type criticality. The temperature-dependent exponent α (T)≲1 increases and approaches unity when the temperature is lowered. This mechanism acts in parallel to the spin diffusion mechanism. Whereas the latter is sensitive to the device geometry, the spin-clustering mechanism is largely geometry independent.

  3. Mechanics of plasma exposed spin-on-glass (SOG) and polydimethyl siloxane (PDMS) surfaces and their impact on bond strength

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Shantanu; Gao, Yuanfang; Korampally, Venumadhav; Othman, M. T.; Grant, Sheila A.; Gangopadhyay, Keshab; Gangopadhyay, Shubhra

    2007-02-01

    Silicone polymer (PDMS), widely used for micro-fluidic and biosensor applications, possesses an extremely dynamic surface after it is subjected to an oxygen plasma treatment process. The surface becomes extremely hydrophilic immediately after oxygen plasma exposure by developing silanol bond (Si sbnd OH), which promotes its adhesion to some other surfaces like, silicon, silicon dioxide, glass, etc. Such a surface, if left in ambient dry air, shows a gradual recovery of hydrophobicity. We have found an identical behavior to occur to surfaces coated with a thin continuous film of SOG (methyl silsesquioxane). The chemistry induced by oxygen plasma treatment of a spin-on-glass (SOG) coated surface provides a much higher density of surface silanol groups in comparison to precleaned glass, silicon or silicon dioxide substrates thus providing a higher bond strength with polydimethyl siloxane (PDMS). The bonding protocol developed by using the spin coated and cured SOG intermediate layer provides an universal regime of multi level wafer bonding of PDMS to a variety of substrates. The paper describes a contact angle based estimation of bond strength for SOG and PDMS surfaces exposed to various combinations of plasma parameters. We have found that the highest bond strength condition is achieved if the contact angle on the SOG surface is less than 10°.

  4. 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).

  5. Spin-glass behaviors in carrier polarity controlled Fe{sub 3−x}Ti{sub x}O{sub 4} semiconductor thin films

    SciTech Connect

    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.

  6. Nicholas Metropolis Award for Outstanding Doctoral Thesis Work in Computational Physics Lecture: The Janus computer, a new window into spin-glass physics

    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.

  7. Implosion of indirectly driven reentrant cone shell target

    SciTech Connect

    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.

  8. Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles

    SciTech Connect

    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.

  9. Nonequilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar-coupled spin-glass LiHo0.5Er0.5F4

    NASA Astrophysics Data System (ADS)

    Piatek, J. O.; Kovacevic, I.; Babkevich, P.; Dalla Piazza, B.; Neithardt, S.; Gavilano, J.; Krämer, K. W.; Rønnow, H. M.

    2014-11-01

    We present a study of the model spin-glass LiHo0.5Er0.5F4 using simultaneous ac susceptibility, magnetization, and magnetocaloric effect measurements along with small angle neutron scattering (SANS) at sub-Kelvin temperatures. All measured bulk quantities reveal hysteretic behavior when the field is applied along the crystallographic c axis. Furthermore, avalanchelike relaxation is observed in a static field after ramping from the zero-field-cooled state up to 200-300 Oe. SANS measurements are employed to track the microscopic spin reconfiguration throughout both the hysteresis loop and the related relaxation. Comparing the SANS data to inhomogeneous mean-field calculations performed on a box of one million unit cells provides a real-space picture of the spin configuration. We discover that the avalanche is being driven by released Zeeman energy, which heats the sample and creates positive feedback, continuing the avalanche. The combination of SANS and mean-field simulations reveal that the conventional distribution of cluster sizes is replaced by one with a depletion of intermediate cluster sizes for much of the hysteresis loop.

  10. Laser-induced radial birefringence and spin-to-orbital optical angular momentum conversion in silver-doped glasses

    SciTech Connect

    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.

  11. Ferromagnetic superexchange interaction and spin glass behaviour in Sm{sub 2}CoMnO{sub 6} nanoparticles

    SciTech Connect

    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.

  12. 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.

  13. Reentrant Phase Coherence in Superconducting Nanowire Composites.

    PubMed

    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).

  14. Interface free-energy exponent in the one-dimensional Ising spin glass with long-range interactions in both the droplet and broken replica symmetry regions

    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.

  15. Interface free-energy exponent in the one-dimensional Ising spin glass with long-range interactions in both the droplet and broken replica symmetry regions.

    PubMed

    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.

  16. Spin-glass behavior and anomalous magnetoresistance in ferromagnetic Ge{sub 1-x}Fe{sub x}Te epilayer

    SciTech Connect

    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.

  17. Interface free-energy exponent in the one-dimensional Ising spin glass with long-range interactions in both the droplet and broken replica symmetry regions.

    PubMed

    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

  18. Quantum tricritical fluctuations driving mass enhancement and reentrant superconductivity in URhGe

    NASA Astrophysics Data System (ADS)

    Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Kambe, S.; Hattori, T.; Araki, S.

    2016-02-01

    The field-induced reentrant superconductivity (RSC) discovered near a quantum critical point (QCP) in a ferromagnetic superconductor URhGe highlights the close interplay between superconductivity and magnetism. While the origin of the RSC is broadly thought to be associated with quantum critical fluctuations, their exact nature had not been well identified. Here we review our recent 59Co NMR study in a single crystal of URh0.9Co0.1Ge. Our measurements of the NMR spin-spin relaxation reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced QCP at HR ≈ 13 T. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum wing-critical points. We show that these tricritical fluctuations enhance the effective mass of the conduction electrons and, further, drive the RSC near the HR.

  19. Typical Value of Susceptibilities in the Three Dimensional Edwards-Anderson Spin Glass Model in an External Field

    NASA Astrophysics Data System (ADS)

    Feng, Sheng; Tam, Ka-Ming; Fang, Ye; Ramanujam, J.; Moreno, Juana; Jarrell, Mark

    2015-03-01

    We study the Edwards-Anderson model on a simple cubic lattice with a finite constant external field using a Monte Carlo simulation code, which employs graphics processing units to dramatically speedup the simulation. Conventional indicators, such as the Binder ratio and correlation length, do not show any signs of a phase transition. We also studied R12, or the ratio of spin glass susceptibilities at finite wavenumbers, and show it is quite noisy that a systematic analysis cannot come to clear conclusion. This is largely due to the fact that the susceptibilities follow a broad, fat-tailed distribution, and the average is possibly dominated by rare events. Therefore we propose to study the typical value of these parameters by taking the geometric average over different disorder realizations, and compare it with the linear average measurements. We argue that the typical value should be also studied in additional to conventional linear average value, to provide another perspective for the study of phase transition in spin glasses. This work is sponsored by the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

  20. Thickness induced crossover from the ferromagnetic to cluster spin glass state in Cr{sub 70}Fe{sub 30} thin films

    SciTech Connect

    Kumar, B. Ravi; Srinath, S.; Kaul, S. N.

    2015-06-24

    First five harmonics of the ac magnetic response were measuredas functions of temperature at different frequencies and with or without superposed dc magnetic field on Cr{sub 70}Fe{sub 30} thin films. An elaborate analysis of the linear susceptibility data reveals that (i) a well-defined paramagnetic (PM) to ferromagnetic (FM) phase transition, characterized by three-dimensional Heisenberg critical exponents, occurs for film thickness down to t≃ 90 nm, and (ii) the film with t≃40 nm exhibits experimental signatures in the critical region that are characteristic of both ferromagnets and spin glasses while the spin glass behavior dominates the FM one when t≃ 20 nm.

  1. Classification, Electrophysiological Features and Therapy of Atrioventricular Nodal Reentrant Tachycardia

    PubMed Central

    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. PMID:27617092

  2. Classification, Electrophysiological Features and Therapy of Atrioventricular Nodal Reentrant Tachycardia

    PubMed Central

    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.

  3. Observation of the Spin-Glass Behavior in Co-Based Antiperovskite Nitride GeNCo3.

    PubMed

    Zu, Lin; Lin, Shuai; Lin, Jianchao; Yuan, Bin; Kan, Xucai; Tong, Peng; Song, Wenhai; Sun, Yuping

    2016-09-19

    Single-phase antiperovskite nitride GeNCo3 with space group Pm3̅m is successfully synthesized by a solid-gas reaction. The crystal structure, magnetism, specific heat at low temperatures, Hall effect, and electrical and thermal transport properties are widely investigated. Exhilaratingly, a canonical spin-glass (SG) behavior is observed in GeNCo3 with a freezing temperature T0 = 79.43 K, dynamical exponent zν = 6.156, and flipping time τ0 = 5.0 × 10(-12) s. The origin of the SG state in GeNCo3 is likely due to the atomic disorder introduced by the Ge vacancies. This is further proven by the measurements of Ge0.9NCo3 with more Ge deficiencies. PMID:27572498

  4. Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

    PubMed

    Roy, Anupam; Guchhait, Samaresh; Dey, Rik; Pramanik, Tanmoy; Hsieh, Cheng-Chih; Rai, Amritesh; Banerjee, Sanjay K

    2015-04-28

    Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

  5. 12-Metal 36-membered ring based W(V)-Co(II) layers showing spin-glass behavior.

    PubMed

    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

  6. Crossover of spin glass characteristics as a function of field in an NiMnSnAl alloy

    NASA Astrophysics Data System (ADS)

    Agarwal, Sandeep; Banerjee, S.; Mukhopadhyay, P. K.

    2013-10-01

    The magnetic state in martensitic phase of Ni50Mn34Sn6Al10 shows interesting glassy behaviour. The irreversibility was observed in d.c. magnetization measurement below martensitic transformation temperature. Further measurements at lower temperature showed the presence of exchange bias field in sample. H-T phase diagram of the irreversibility showed that the system was in Heisenberg like spin glass state at low field, which changed its type when the external field was above the exchange bias field. In order to determine the cause of cross over, a.c. susceptibility measurements were performed in zero and d.c. biasing fields. This switching of glassy nature of the system is a novel phenomenon.

  7. Spin glass behavior in the Dy{sub 3-x}Y{sub x}TaO{sub 7} (0≤x≤1) system

    SciTech Connect

    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.

  8. From spin induced ferroelectricity to spin and dipolar glass in a triangular lattice: The CuCr{sub 1−x}V{sub x}O{sub 2} (0≤x≤0.5) delafossite

    SciTech Connect

    Kumar, S.; Singh, K.; Miclau, M.; Simon, Ch.; Martin, C.; Maignan, A.

    2013-07-15

    The change from antiferromagnetism induced ferroelectricity to spin glass ferroelectric relaxor has been studied along the CuCr{sub 1−x}V{sub x}O{sub 2} (0≤x≤0.5) solid solution of polycrystalline samples. As x increases from CuCrO{sub 2} (x=0) to CuCr{sub 0.82}V{sub 0.18}O{sub 2}, it is found that the Néel temperature decreases from ∼24 K down to ∼13 K. This progressive weakening of the antiferromagnetism of CuCrO{sub 2} induces a rapid decrease of the spin induced ferroelectricity with polarization values going from ∼44 μC/m{sup 2} down to ∼1.5 μC/m{sup 2} for x=0.04 and x=0.08, respectively. Beyond x=0.18 (0.20≤x≤0.50), ac-magnetic susceptibility and magnetization measurements evidence a spin glass state while dielectric permittivity and polarization measurements point towards a relaxor behaviour. This shows that competing magnetic interactions in delafossites are an efficient way to transform a spin induced magnetoelectric into a multiglass (spin and dipolar) state. - Graphical abstract: The P(T) curves evidencing the aging effect on polarization in CuCr{sub 0.5}V{sub 0.5}O{sub 2}: E=135 kV/m is applied during cooling at different temperatures. The P values and the inflection point of the transition depend on the poling temperature suggesting a relaxor behaviour. This effect related to the spin glass state is not observed for the lowest vanadium content. - Highlights: • Samples of the CuCr{sub 1−x}V{sub x}O{sub 2} series have been studied. • The V content increase induces a change from antiferromagnetism to spin glass. • A behavior characterisitic of a spin and dipole glass is demonstrated. • The ferroelectricity is shown to go from spin induced to relaxor. • Competing magnetic interactions are efficient way to generate multiglass state.

  9. Theoretical Studies of the Spin Hamiltonian Parameters and Local Distortions for Cu2+ in Alkaline Earth Lead Zinc Phosphate Glasses

    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≤Baglasses containing copper dopants.

  10. The spin glass-antiferromagnetism competition in Kondo-lattice systems in the presence of a transverse applied magnetic field

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.

    2006-05-01

    A theory is proposed to describe the competition among antiferromagnetism (AF), spin glass (SG) and Kondo effect. The model describes two Kondo sublattices with an intrasite Kondo interaction strength JK and a random Gaussian interlattice interaction in the presence of a transverse field Γ. The Γ field is introduced as a quantum mechanism to produce spin flipping and the random coupling has average -2J0/N and variance 32J2/N. The path integral formalism with Grassmann fields is used to study this fermionic problem, in which the disorder is treated within the framework of the replica trick. The free energy and the order parameters are obtained using the static ansatz. In this many parameters problem, we choose J0/J≈(JK/J)2 and Γ/J≈(JK/J)2 to allow a better comparison with the experimental findings. The obtained phase diagram has not only the same sequence as the experimental one for Ce2Au1-xCoxSi3, but mainly, it also shows a qualitative agreement concerning the behavior of the freezing temperature and the Neel temperature which decreases until a quantum critical point (QCP).

  11. Large area, screen printed silicon solar cells with selective emitter made by laser overdoping and RTA spin-on glasses

    SciTech Connect

    Besi-Vetrella, U.; Pirozzi, L.; Salza, E.; Ginocchietti, G.; Ferrazza, F.; Ventura, L.; Slaoui, A.; Muller, J.C.

    1997-12-31

    In this paper the authors describe their work on a new solar cells fabrication process, based on the use of Rapid Thermal Diffusion (RTD) from spin-on techniques, laser assisted treatments to get selective emitter structures, and screen-printing. The homogeneous lightly doped emitter is first made by rapid thermal diffusion from a P-doped Spin-On Glass (SOG) film. Laser overdoping of contact regions follows, to form the selective emitter structure, by writing the grid pattern using a laser beam. Finally, screen-printing is used to get the contacts; proper solutions have been developed for optical realignment to laser pattern, with a resolution of about 10 microns. The authors have first prepared several batches of small area solar cells, made by using these processes separately, with the aim to study the influence of the main laser and dopant parameters on cell performances. A further step has been to use all the processes together. Large area devices preparation is in progress.

  12. 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.

  13. Reentrant stability of BEC standing wave patterns

    SciTech Connect

    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'.

  14. 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.

  15. 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.

  16. Light scattering by a reentrant fractal surface.

    PubMed

    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

  17. Real-space renormalization for the finite temperature statics and dynamics of the Dyson long-ranged ferromagnetic and spin-glass models

    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} .

  18. Re-Entrant Structure for Robust Superhydrophobicity and Drag Reduction

    NASA Astrophysics Data System (ADS)

    Zhao, Hong; Gad-El-Hak, Mohamed

    2014-11-01

    A re-entrant structure is required for superoleophobicity by effectively pinning low-surface-tension liquids from wetting the textures and forming a solid-liquid-air composite interface. In this work, we examine the contribution of a re-entrant structure to the robustness of superhydrophobicity and skin-friction reduction capabilities. Textured surfaces with wavy sidewall pillars provide re-entrant structures and are used as model surfaces. Gibbs energy analysis is conducted to study the pinning sites and wetting stability. The wetting robustness against pressure is characterized by breakthrough pressure, which is obtained by conservation of energy and force balance at the pinning sites. The slip length and slip velocity are evaluated through a shear stress and strain rate correlation, which is obtained using an Anton Paar rheometer. Gibbs energy analysis indicates that the breakthrough pressure provided by the wavy sidewall structure for water is about 18 times of that on the straight sidewall structure. This is mostly due to the energy barrier at the re-entrant structure. When a contact line advances onto and pins at the re-entrant structure, its slip performance degrades due to the increased no-slip fraction on the composite interface, but Cassie-Baxter state still remains.

  19. Identical band gaps in structurally re-entrant honeycombs.

    PubMed

    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

  20. 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.

  1. Cr-doped TiSe2 - A layered dichalcogenide spin glass

    DOE PAGESBeta

    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

  2. Cr-doped TiSe2 - A layered dichalcogenide spin glass

    SciTech Connect

    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 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 the 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.

  3. Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3

    SciTech Connect

    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.

  4. A re-entrant cavity for microwave-enhanced chemistry.

    PubMed

    Kalhori, Shirzad; Elander, Nils; Svennebrink, Jan; Stone-Elander, Sharon

    2003-01-01

    The electromagnetic aspect of microwave dielectric heating is analyzed. It is concluded that a re-entrant cavity may supply high electric field component that is theoretically favorable efficient microwave absorption process in a small liquid or solid chemical sample. A re-entrant cavity has been designed using both finite difference time domain and finite element time domain methods and constructed with a PC-driven control and power supply unit. The field distribution in the sample as well as Q-values for a water-loaded cavity are calculated and measured. Good agreement between designed and measured quantities were found.

  5. The Sherrington-Kirkpatrick spin glass model in the presence of a random field with a joint Gaussian probability density function for the exchange interactions and random fields

    NASA Astrophysics Data System (ADS)

    Hadjiagapiou, Ioannis A.

    2014-03-01

    The magnetic systems with disorder form an important class of systems, which are under intensive studies, since they reflect real systems. Such a class of systems is the spin glass one, which combines randomness and frustration. The Sherrington-Kirkpatrick Ising spin glass with random couplings in the presence of a random magnetic field is investigated in detail within the framework of the replica method. The two random variables (exchange integral interaction and random magnetic field) are drawn from a joint Gaussian probability density function characterized by a correlation coefficient ρ. The thermodynamic properties and phase diagrams are studied with respect to the natural parameters of both random components of the system contained in the probability density. The de Almeida-Thouless line is explored as a function of temperature, ρ and other system parameters. The entropy for zero temperature as well as for non zero temperatures is partly negative or positive, acquiring positive branches as h0 increases.

  6. FRACTAL DIMENSION OF SPIN-GLASSES INTERFACES IN DIMENSION d = 2 AND d = 3 VIA STRONG DISORDER RENORMALIZATION AT ZERO TEMPERATURE

    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.

  7. Monte Carlo study of the spin-glass phase of the site-diluted dipolar Ising model

    NASA Astrophysics Data System (ADS)

    Alonso, Juan J.; Fernández, Julio F.

    2010-02-01

    By tempered Monte Carlo simulations, we study site-diluted Ising systems of magnetic dipoles. All dipoles are randomly placed on a fraction x of all L3 sites of a simple cubic lattice, and point along a given crystalline axis. For xcspin-glass (SG) phase below a temperature given by kBTsg≃xɛd , where ɛd is a nearest-neighbor dipole-dipole interaction energy. We study (a) the relative mean-square deviation Δq2 of |q| , where q is the SG overlap parameter and (b) ξL/L , where ξL is a correlation length. From their variation with temperature and system size, we determine Tsg . In the SG phase, we find (i) the mean values ⟨|q|⟩ and ⟨q2⟩ decrease algebraically with L as L increases, (ii) double peaked, but wide, distributions of q/⟨|q|⟩ appear to be independent of L , and (iii) ξL/L rises with L at constant T but extrapolations to 1/L→0 give finite values. All of this is consistent with quasilong-range order in the SG phase.

  8. 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)).

  9. SrFe{sub 0.9}Ti{sub 0.1}O{sub 3−δ}: A cluster spin glass

    SciTech Connect

    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.

  10. Strong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3.

    PubMed

    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 5d(5) 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 4d(5) honeycomb oxide. For pristine crystals without Rh-Li site inversion, we predict a dimerized ground state as in the isostructural 5d(5) 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

  11. Spin-glass transition at nonzero temperature in a disordered dipolar Ising system: the case of LiHoxY(1-x)F4.

    PubMed

    Tam, Ka-Ming; Gingras, Michel J P

    2009-08-21

    The physics of the spin-glass (SG) state, with magnetic moments (spins) frozen in random orientations, is one of the most intriguing problems in condensed matter physics. In LiHoxY(1-x)F4, the Ho3+ moments, which are well described by Ising spins with only discrete "up or down" directions, interact predominantly via the inherently frustrated magnetostatic dipole-dipole interactions. The random frustration causing the SG behavior originates from the random substitution of dipole-coupled Ho3+ by nonmagnetic Y3+. In this Letter, we provide compelling evidence from extensive computer simulations that a SG transition at nonzero temperature occurs in a realistic microscopic model of LiHoxY(1-x)F4. This resolves the long-standing, and still ongoing, controversy about the existence of a SG transition in disordered dipolar Ising systems.

  12. Spin-glass behavior and incommensurate modulation in high-pressure perovskite BiCr0.5Ni0.5O3.

    PubMed

    Arévalo-López, Ángel M; Dos Santos-García, Antonio J; Levin, Jessica R; Attfield, J Paul; Alario-Franco, Miguel A

    2015-02-01

    The BiCr(0.5)Ni(0.5)O(3) perovskite has been obtained at high pressure. Neutron and synchrotron diffraction data show a Pnma orthorhombic structure with a = 5.5947(1) Å, b = 7.7613(1) Å, and c = 5.3882(1) Å at 300 K and random B-site Cr/Ni distribution. Electron diffraction reveals an incommensurate modulation parallel to the b axis. The combination of either Cr-O-Ni (J > 0) or Cr-O-Cr/Ni-O-Ni (J < 0) nearest-neighbor spin interactions results in a random-bond spin-glass configuration. Magnetization, neutron diffraction, and muon-spin-relaxation measurements demonstrate that variations in the local bonding and charge states contribute to the magnetic frustration.

  13. Toward more accurate loss tangent measurements in reentrant cavities

    SciTech Connect

    Moyer, R. D.

    1980-05-01

    Karpova has described an absolute method for measurement of dielectric properties of a solid in a coaxial reentrant cavity. His cavity resonance equation yields very accurate results for dielectric constants. However, he presented only approximate expressions for the loss tangent. This report presents more exact expressions for that quantity and summarizes some experimental results.

  14. Magnetic states of lightly hole-doped cuprates in the clean limit as seen via zero-field muon spin spectroscopy

    NASA Astrophysics Data System (ADS)

    Coneri, F.; Sanna, S.; Zheng, K.; Lord, J.; de Renzi, R.

    2010-03-01

    We have performed extensive zero-field μSR experiments on pure YBa2Cu3O6+y and diluted Y-rare-earth substituted Y0.92Eu0.08Ba2Cu3O6+y and Y0.925Nd0.075Ba2Cu3O6+y at light hole doping. A common magnetic behavior is detected for all the three families, demonstrating negligible effects of the isovalent Y-substituent disorder. Two distinct regimes are identified, separated by a crossover, whose origin is attributed to the concurrent thermal activation of spin and charge degrees of freedom: a thermally activated and a re-entrant antiferromagnetic regime. The peculiar temperature and hole density dependence of the magnetic moment m(h,T) fit a model with a (spin) activation energy for the crossover between the two regimes throughout the entire investigated range. The magnetic moment is suppressed by a simple dilution mechanism both in the re-entrant regime (0≤h≤0.056) and in the so-called cluster spin glass state coexisting with superconductivity (0.056

  15. Fabrication of glass-ceramics containing spin-chain compound SrCuO{sub 2} and its high thermal conductivity

    SciTech Connect

    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.

  16. Low-temperature formation of high-quality gate oxide by ultraviolet irradiation on spin-on-glass

    SciTech Connect

    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.

  17. 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.

  18. Random pinning glass model.

    PubMed

    Karmakar, Smarajit; Parisi, Giorgio

    2013-02-19

    Glass transition, in which viscosity of liquids increases dramatically upon decrease of temperature without any major change in structural properties, remains one of the most challenging problems in condensed matter physics despite tremendous research efforts in past decades. On the other hand, disordered freezing of spins in magnetic materials with decreasing temperature, the so-called "spin glass transition," is understood relatively better. A previously found similarity between some spin glass models and the structural glasses inspired development of theories of structural glasses based on the scenario of spin glass transition. This scenario, although it looks very appealing, is still far from being well established. One of the main differences between standard spin systems and molecular systems is the absence of quenched disorder and the presence of translational invariance: it often is assumed that this difference is not relevant, but this conjecture still needs to be established. The quantities, which are well-defined and characterized for spin models, are not easily calculable for molecular glasses because of the lack of quenched disorder that breaks the translational invariance in the system. Thus the characterization of the similarity between spin and the structural glass transition remains an elusive subject. In this study, we introduced a model structural glass with built-in quenched disorder that alleviates this main difference between the spin and molecular glasses, thereby helping us compare these two systems: the possibility of producing a good thermalization at rather low temperatures is one of the advantages of this model. PMID:23382186

  19. Oxygen miscibility gap and spin glass formation in the pyrochlore Lu{sub 2}Mo{sub 2}O{sub 7}

    SciTech Connect

    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.

  20. Investigation of the Spin-glass Regime Between the Antiferromagnetic and Superconducting Phases in Fe1+ySexTe1−x

    SciTech Connect

    Katayama, N.; Wen, J.; Ji, S.; Louca, D.; Lee, S.-H.; Fujita, M.; Sato, T.J.; Wen, J.S.; Xu, Z.J.; Gu, G.D.; Xu, G.; Lin, Z.W.; Enoki, M.; Chang, S.; Yamada, K.; Tranquada, J.M.

    2010-11-01

    Using bulk magnetization along with elastic and inelastic neutron scattering techniques, we have investigated the phase diagram of Fe{sub 1+y}Se{sub x}Te{sub 1-x} and the nature of magnetic correlations in three nonsuperconducting samples of Fe{sub 1.01}Se{sub 0.1}Te{sub 0.9}, Fe{sub 1.01}Se{sub 0.15}Te{sub 0.85}, and Fe{sub 1.02}Se{sub 0.3}Te{sub 0.7}. A cusp and hysteresis in the temperature dependence of the magnetization for the x=0.15 and 0.3 samples indicates spin-glass (SG) ordering below T{sub sg} = 23 K. Neutron scattering measurements indicate that the spin-glass behavior is associated with short-range spin density wave (SDW) ordering characterized by a static component and a low-energy dynamic component with a characteristic incommensurate wave vector of Q{sub m} = (0.46, 0, 0.50) and an anisotropy gap of -2.5 meV. Our high Q-resolution data also show that the systems undergo a glassy structural distortion that coincides with the short-range SDW order.

  1. Surface spin-glass, large surface anisotropy, and depression of magnetocaloric effect in La0.8Ca0.2MnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Xi, S. B.; Lu, W. J.; Wu, H. Y.; Tong, P.; Sun, Y. P.

    2012-12-01

    The surface magnetic behavior of La0.8Ca0.2MnO3 nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature TF does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer.

  2. Surface spin-glass, large surface anisotropy, and depression of magnetocaloric effect in La0.8Ca0.2MnO3 nanoparticles

    PubMed Central

    Xi, S. B.; Lu, W. J.; Wu, H. Y.; Tong, P.; Sun, Y. P.

    2012-01-01

    The surface magnetic behavior of La0.8Ca0.2MnO3 nanoparticles was investigated. We observed irreversibility in high magnetic field. The surface spin-glass behavior as well as the high-field irreversibility is suppressed by increasing particle size while the freezing temperature TF does not change with particle size. The enhanced coercivity has been observed in the particles and we attributed it to the large surface anisotropy. We have disclosed a clear relationship between the particle size, the thickness of the shell, and the saturation magnetization of the particles. The large reduction of the saturation magnetization of the samples is found to be induced by the increase of nonmagnetic surface large since the thickness of the spin-disordered surface layer increases with a decrease in the particle size. Due to the reduction of the magnetization, the magnetocaloric effect (MCE) has been reduced by the decreased particle size since the nonmagnetic surface contributes little to the MCE. Based on the core-shell structure, large relative cooling powers RCP(s) of 180 J/kg and 471 J/kg were predicted for a field change of 2.0 T and 4.5 T, respectively, in the small particles with thin spin-glass layer. PMID:23319829

  3. 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.

  4. Nuclear Spin Lattice Relaxation and Conductivity Studies of the Non-Arrhenius Conductivity Behavior in Lithium Fast Ion Conducting Sulfide Glasses

    SciTech Connect

    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

  5. Atrioventricular nodal reentrant tachycardia ablation and inferior vena cava agenesis.

    PubMed

    Galand, Vincent; Pavin, Dominique; Behar, Nathalie; Mabo, Philippe; Martins, Raphaël P

    2016-10-01

    Congenital anomalies of the inferior vena cava (IVC) are rare and very often diagnosed in asymptomatic patients during computed tomography performed for other purposes. These anomalies can have significant clinical implications, for example if electrophysiology procedures are needed. Diagnostic and ablation procedures are difficult since catheter manipulation and positioning are more complex. We present here a case of successful atrioventricular nodal reentrant tachycardia ablation in a patient with unexpected IVC agenesis, using an azygos route. PMID:27633734

  6. [Myotonic dystrophy and bundle-branch re-entrant tachycardia].

    PubMed

    Ramírez, Carlos J; Rodríguez, Diego A; Velasco, Víctor M; Rosas, Fernando

    2002-10-01

    We report the case of a 37-year-old man diagnosed with myotonic dystrophy who presented atrial fibrillation with high ventricular rate. While being treated with amiodarone, he suffered cardiac arrest. The electrophysiological study disclosed bundle-branch reentrant ventricular tachycardia and ventricular fibrillation. Catheter ablation of the right bundle branch was performed and a bicameral defibrillator was implanted. The mechanisms and treatment of arrhythmias in these patients are discussed. PMID:12383397

  7. 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.

  8. A high resolution neutron scattering study of Tb2Mo2O7: A geometrically frustrated and disorder-free spin glass

    SciTech Connect

    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.

  9. Spin glass behavior in a highly oxygen deficient Perovskite BaBiO.28Co0.72O2.2

    SciTech Connect

    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.

  10. Spin glass in semiconducting KFe1.05Ag0.88Te2 single crystals

    SciTech Connect

    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.

  11. Time-resolved photoluminescence spectroscopy of localized exciton magnetic polarons in Cd{sub 0.70}Mn{sub 0.30}Te spin glass compound

    SciTech Connect

    Gnatenko, Yu. P. Bukivskij, P. M.; Piryatinski, Yu. P.

    2014-04-07

    We have investigated dynamics of different localized exciton magnetic polarons (LEMPs) in Cd{sub 0.70}Mn{sub 0.30}Te spin glass (SG) compound below the freezing temperature T{sub f} in the crystal regions, where various microscopic magnetic spin states (MMSSs), namely, “loose” spins, finite, and infinite clusters, are formed. It was shown that there is a broad distribution of the LEMPs lifetimes. The presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states, i.e., the “brightening” of the dark LEMPs which exist along with the bright LEMPs. The lifetimes of the dark LEMPs correspond to hundreds of nanoseconds. It was found that the time decay of photoluminescence band intensity is approximated by the sum of two functions: a single exponential function and the Kohlrausch–Williams–Watts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite clusters as well as the infinite cluster. This reflects the appearance of spatially heterogeneous dynamics in Cd{sub 0.70}Mn{sub 0.30}Te SG compound below T{sub f} which is due to the disorder in the spin distribution caused by the formation of different MMSSs.

  12. 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.

  13. Non-fermi liquid and spin-glass behavior of the Sc{sub 1-x}U{sub x}Pd{sub 3} system

    SciTech Connect

    Gajewski, D.A.; Allenspach, P.; Seaman, C.L.; Maple, M.B. |

    1993-09-01

    Previous electrical resistivity {rho}T, magnetic susceptibility {chi}T, and specific heat C(T) measurements on the Y{sub 1-x}U{sub x}Pd{sub 3} system have revealed Kondo behavior for 0 < {times} < 0.2 and spin-glass-like behavior for 0.3 < {times} < 0.5. The Kondo behavior is unusual and characterized by non-Fermi liquid behavior at low temperatures T {much_lt} T{sub K}, where T{sub K} is the Kondo temperature: {rho}T/{rho}(0) {approximately} 1 {minus} T/(aT{sub K}), and C(T)/T {approximately} 1 {minus} (1/T{sub K})1nT with evidence for a finite T = 0 residual entropy S(0) = (R/2)1n(2). We report measurements of {rho}T, {chi}T, and C(T) on the Sc{sub 1-x}U{sub x}Pd{sub 3} system which reveal similar Kondo, non-Fermi liquid, and spin-glass behaviors.

  14. Structural chemistry and spin-glass behaviour of Nd{sub 18}Li{sub 8}Fe{sub 4}TiO{sub 39}

    SciTech Connect

    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}.

  15. An analysis of scattering from a reentrant wedge

    NASA Astrophysics Data System (ADS)

    Bhatta, Ambika

    In this thesis the scattering of acoustic pressure from a rigid wedge is examined. The wedges having re-entrant geometry are of particular interest. The incident field is considered from a time harmonic point source. The solution for the scattered pressure field is obtained by modal, image and asymptotic analysis. It is numerically shown that the exact modal solution and image based solution for different incident frequencies and source positions are the same. It is also shown that the asymptotic solution obtained matches with the image based solution.

  16. Depletion, melting and reentrant solidification in mixtures of soft and hard colloids.

    PubMed

    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.

  17. Non-collinearity and spin frustration in the itinerant kagome ferromagnet Fe(3)Sn(2).

    PubMed

    Fenner, L A; Dee, A A; Wills, A S

    2009-11-11

    Frustrated itinerant ferromagnets, with non-collinear static spin structures, are an exciting class of material as their spin chirality can introduce a Berry phase in the electronic scattering and lead to exotic electronic phenomena such as the anomalous Hall effect (AHE). This study presents a reexamination of the magnetic properties of Fe(3)Sn(2), a metallic ferromagnet, based on the two-dimensional kagome bilayer structure. Previously thought of as a conventional ferromagnet, we show using a combination of SQUID (superconducting quantum interference device) measurements, symmetry analysis and powder neutron diffraction that Fe(3)Sn(2) is a frustrated ferromagnet with a temperature-dependent non-collinear spin structure. The complexity of the magnetic interactions is further evidenced by a re-entrant spin glass transition ([Formula: see text] K) at temperatures far below the main ferromagnetic transition (T(C) = 640 K). Fe(3)Sn(2) therefore provides a rare example of a frustrated itinerant ferromagnet. Further, as well as being of great fundamental interest our studies highlight the potential of Fe(3)Sn(2) for practical application in spintronics technology, as the AHE arising from the ferromagnetism in this material is expected to be enhanced by the coupling between the conduction electrons and the non-trivial magnetic structure over an exceptionally wide temperature range.

  18. Static and dynamic spin fluctuations in the spin glass doping regime in La sub 2-x Sr sub x CuO sub 4+y

    SciTech Connect

    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.

  19. A rock-salt-type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers

    NASA Astrophysics Data System (ADS)

    Upadhyay, Sanjay Kumar; Iyer, Kartik K.; Rayaprol, S.; Paulose, P. L.; Sampathkumaran, E. V.

    2016-08-01

    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.

  20. A rock-salt-type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers

    PubMed Central

    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

  1. A rock-salt-type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers.

    PubMed

    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

  2. Insulating and metallic spin glass in KxFe2-δ-yNiySe2 (0.06 ≤ y ≤ 1.44 ) single crystals

    DOE PAGESBeta

    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

  3. Absence of conventional spin-glass transition in the Ising dipolar system LiHo(x)Y(1-x)F(4).

    PubMed

    Jönsson, P E; Mathieu, R; Wernsdorfer, W; Tkachuk, A M; Barbara, B

    2007-06-22

    The magnetic properties of single crystals of LiHo(x)Y(1-x)F(4) with x = 16.5% and x = 4.5% were recorded down to 35 mK using a micro-SQUID magnetometer. While this system is considered as the archetypal quantum spin glass, the detailed analysis of our magnetization data indicates the absence of a phase transition, not only in a transverse applied magnetic field, but also without field. A zero-Kelvin phase transition is also unlikely, as the magnetization seems to follow a noncritical exponential dependence on the temperature. Our analysis thus unmasks the true, short-ranged nature of the magnetic properties of the LiHo(x)Y(1-x)F(4) system, validating recent theoretical investigations suggesting the lack of phase transition in this system.

  4. Spin-glass behavior and pyroelectric anomalies in a new lithium-based oxide, Li3FeRuO5.

    PubMed

    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

  5. Observation of photonic paramagnetic to spin-glass transition in a specially designed TiO2 particle-based dye-colloidal random laser.

    PubMed

    Pincheira, Pablo I R; Silva, Andréa F; Fewo, Serge I; Carreño, Sandra J M; Moura, André L; Raposo, Ernesto P; Gomes, Anderson S L; de Araújo, Cid B

    2016-08-01

    Colloidal-based random lasers (RLs) are highly efficient and have been exploited in a wide range of geometries. However, in the particular case of ethanol solutions of rhodamines and TiO2 particles, the RL behavior is quite unstable due to the fast precipitation of the particles. In this Letter, specially designed amorphous TiO2 particles were synthesized by a sol-gel method, preventing the degradation of the RL for long operating lifetimes of over 105 shots. As a consequence, this modified colloidal RL allowed the observation of a clear replica-symmetry-breaking phase transition from the paramagnetic fluorescent to spin-glass RL behavior, which has not been observed in the system with nonfunctionalized TiO2 particles. PMID:27472593

  6. Structural and magnetic properties and evidence of spin-glass behavior induced by Fe-doping in perovskite manganites B-site

    SciTech Connect

    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.

  7. Collapse of Ferromagnetism and Fermi Surface Instability near Reentrant Superconductivity of URhGe.

    PubMed

    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

  8. Collapse of Ferromagnetism and Fermi Surface Instability near Reentrant Superconductivity of URhGe.

    PubMed

    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}.

  9. 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.

  10. (77)Se nuclear spin-lattice relaxation in binary Ge-Se glasses: insights into floppy versus rigid behavior of structural units.

    PubMed

    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.

  11. Quantum 3D spin-glass system on the scales of space-time periods of external electromagnetic fields

    SciTech Connect

    Gevorkyan, A. S.

    2012-10-15

    A dielectric medium consisting of rigidly polarized molecules has been treated as a quantum 3D disordered spin system. It is shown that using Birkhoff's ergodic hypothesis the initial 3D disordered spin problem on scales of space-time periods of external field is reduced to two conditionally separable 1D problems. The first problem describes a 1D disordered N-particle quantum system with relaxation in random environment while the second one describes statistical properties of ensemble of disordered 1D steric spin chains of certain length. Basing on constructions which are developed in both problems, the coefficient of polarizability related to collective orientational effects under the influence of external field was calculated. On the basis of these investigations the equation of Clausius-Mossotti (CM) has been generalized as well as the equation for permittivity. It is shown that under the influence of weak standing electromagnetic fields in the equation of CM arising of catastrophe is possible, that can substantially change behavior of permittivity in the X-ray region on the macroscopic scale of space.

  12. Twin plane re-entrant mechanism for catalytic nanowire growth.

    PubMed

    Gamalski, Andrew D; Voorhees, Peter W; Ducati, Caterina; Sharma, Renu; Hofmann, Stephan

    2014-03-12

    A twin-plane based nanowire growth mechanism is established using Au catalyzed Ge nanowire growth as a model system. Video-rate lattice-resolved environmental transmission electron microscopy shows a convex, V-shaped liquid catalyst-nanowire growth interface for a ⟨112⟩ growth direction that is composed of two Ge {111} planes that meet at a twin boundary. Unlike bulk crystals, the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center. We suggest that the nucleation barrier at the twin-plane re-entrant groove is effectively reduced by the line energy, and hence the twin acts as a preferential nucleation site that dictates the lateral step flow cycle which constitutes nanowire growth.

  13. Reentrant melting of a classical two-dimensional binary cluster

    SciTech Connect

    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.

  14. Observation of a Reentrant Twist Grain Boundary Phase

    SciTech Connect

    Shankar Rao, D. S.; Krishna Prasad, S.; Raja, V. N.; Yelamaggad, C. V.; Anitha Nagamani, S.

    2001-08-20

    We report the occurrence of a reentrant twist grain boundary phase, which we designate as Re-TGB{sub A}. Microscopic observations on a nonsymmetric dimer showed the phase sequence Iso--N{sup *} --TGB{sub A} --Sm-A --Re--TGB{sub A} --TGB{sub C{sup *}}. Here N{sup *} and Sm-A stand for the chiral nematic and smectic-A phases, TGB{sub A} is the twist grain boundary phase with smectic-A blocks, and TGB{sub C{sup *}} that with smectic-C{sup *} blocks and exhibiting features of both the smectic-C{sup *} and TGB phases. The reentrance of the TGB{sub A} phase is unambiguously demonstrated using x-ray diffraction, selective reflection, and optical rotation data.

  15. Re-entrant Corner Singularity of the Giesekus Fluid

    NASA Astrophysics Data System (ADS)

    Evans, J. D.

    2009-09-01

    The local asymptotic behaviour is described for steady planar re-entrant corner flows of a Giesekus fluid with a solvent viscosity. The re-entrant corner angle is denoted by π/α where 1/2⩽α<1. Similar to another shear thinning model, namely the Phan-Thien-Tanner (PTT) fluid, Newtonian velocity and stress fields dominate near to the corner. However, in contrast to PTT, a weaker polymer stress singularity is obtained O(r-(1-λ0)(3-λ0)/4) with slightly thinner polymer stress boundary layers of thickness O(r(3-λ0)/2), where λ0 is the Newtonian flow field eigenvalue and r the radial distance to the corner. For comparison purposes in the benchmark case of a 270° corner, we thus have polymer stress singularities of O(r-2/3) for Oldroybd-B, O(r-0.3286) PTT and O(r-0.2796) for Giesekus. The wall boundary layer thicknesses are O(r4/3) for Oldroyd-B, O(r1.2278) for Giesekus and O(r1.1518) for PTT. As for the PTT model, these results for the Giesekus model breakdown in both limits of vanishing solvent viscosity and vanishing quadratic stress terms (i.e. the Oldroyd-B limit). It is also implicitly assumed that there are no regions of recirculation at the upstream wall i.e. we consider flow in the absence of a lip vortex.

  16. Magneto-thermally activated spin-state transition in La0.95Ca0.05CoO3: magnetically-tunable dipolar glass and giant magneto-electricity.

    PubMed

    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

  17. Magneto-thermally activated spin-state transition in La0.95Ca0.05CoO3: magnetically-tunable dipolar glass and giant magneto-electricity.

    PubMed

    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

  18. Features of re-entrant albedo deuteron trajectories in near Earth orbit with PAMELA experiment

    NASA Astrophysics Data System (ADS)

    Koldobskiy, S. A.; 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.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, AA; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergè, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, GI; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.

    2016-02-01

    The results of trajectory reconstruction for re-entrant albedo deuteron fluxes obtained in the PAMELA experiment are presented in this work. PAMELA is an international experiment aimed on measurements of cosmic ray particle fluxes in wide energy range. In particular, analysis of PAMELA data gives possibility to identify deuterons. Classification of re-entrant albedo deuterons with energies from 70 to 400 MeV/nucleon depending on theirs reconstructed lifetimes and generation zones is presented here at first time.

  19. Investigation of magnetic spin glass property in La{sub 0.5}Bi{sub 0.5}MnO{sub 3} sample using non-linear AC susceptibility measurements

    SciTech Connect

    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.

  20. Structural characterization and physical properties of P2O5-CaO-Na2O-TiO2 glasses by Fourier transform infrared, Raman and solid-state magic angle spinning nuclear magnetic resonance spectroscopies.

    PubMed

    Kiani, Azadeh; Hanna, John V; King, Scott P; Rees, Gregory J; Smith, Mark E; Roohpour, Nima; Salih, Vehid; Knowles, Jonathan C

    2012-01-01

    Phosphate-based glasses have been investigated for tissue engineering applications. This study details the properties and structural characterization of titanium ultra-phosphate glasses in the 55(P(2)O(5))-30(CaO)-(25-x)(Na(2)O)-x(TiO(2)) (0≤x≤5) system, which have been prepared via melt-quenching techniques. Structural characterization was achieved by a combination of X-ray diffraction (XRD), and solid-state nuclear magnetic resonance, Raman and Fourier transform infrared spectroscopies. Physical properties were also investigated using density, degradation and ion release studies; additionally, differential thermal analysis was used for thermal analysis of these glasses. The results show that with the addition of TiO(2) the density and glass transition temperature increased whereas the degradation and ion release properties are decreased. From XRD data, TiP(2)O(7) and CaP(2)O(6) were detected in 3 and 5 mol.% TiO(2)-containing glasses. Magic angle spinning nuclear magnetic resonance results confirmed that as TiO(2) is incorporated into the glass; the amount of Q(3) increases as the amount of Q(2) consequently decreases, indicating increasing polymerization of the phosphate network. Spectroscopy results also showed that the local structure of glasses changes with increasing TiO(2) content. As TiO(2) is incorporated into the glass, the phosphate connectivity increases, indicating that the addition of TiO(2) content correlates unequivocally with an increase in glass stability.

  1. Spin-glass freezing above the ordering temperature for the Kondo ferromagnet CeNi{sub 0.4}Cu{sub 0.6}

    SciTech Connect

    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}

  2. Spin-glass like behavior in a new ternary uranium cobalt aluminide, U 3Co 4+ xAl 12- x with x=0.55(2)

    NASA Astrophysics Data System (ADS)

    Tougait, O.; Noël, H.; Troc, R.

    2004-06-01

    The new compound U 3Co 4+ xAl 12- x, where x=0.55(2), was prepared by arc-melting of the elemental components, followed by a prolonged annealing at elevated temperature. Scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction were used to determine the deviation from the ideal stoichiometry. A small homogeneity range, that extends around the composition U 3Co 4+ xAl 12- x with 0.4(1) ⩽ x⩽0.7(1), could be detected. Single-crystal diffraction experiments revealed that U 3Co 4.55Al 11.45 crystallizes with the Gd 3Ru 4Al 12 type-structure, (space group P6 3/ mmc, Z=2) in a cell of dimensions at room temperature, a=8.6518(2) Å, c=9.2620(2) Å. The crystal structure can be viewed as an intergrowth of two distinct layers of Co and Al atoms, and U, Al and mixed Al/Co atoms that pile up along the hexagonal axis. The results of the DC magnetization suggest the occurrence of a spin glass state at low temperature ( Tf=8 K). The origin of freezing of the magnetic moments may arise from a topological frustration due to the location of the U atoms on the apexes of a distorted Kagomé lattice.

  3. Study of the changes in the infrared transmission of SiO sub 2 spin-on-glass due to ion implantation

    SciTech Connect

    Shacham-Diamand, Y. ); Finkman, E.; Pinkas, Y. ); Moriya, N. )

    1991-12-02

    The ion implantation of phosphorus into spin-on-glass (SOG) SiO{sub 2} thin-film films modified the infrared transmission spectrum of the films. Two SOG types, polysiloxane and silicate, were ion implanted with doses in the 1{times}10{sup 14}--1{times}10{sup 15} cm{sup {minus}2} range and an energy of 40 keV. The Fourier-transform infrared spectrum of such films on silicon substrates was measured and the results are presented as a function of the implanted dose. The effect of the ion implantation on the silicate SOG was minute while significant changes were observed in the polysiloxane SOG. The major absorption peaks in the transmission spectrum were numerically analyzed and fitted to a set of Lorentzian functions. The peak heights, width, and area were measured. The ion implantation reduces the number of CH{sub 3} groups while the location of the Si-O absorption peak is shifted towards a shorter wavelength, i.e., a denser material. A physical interpretation of the absorption peak dependence on the ion-implanted dose is presented.

  4. Spin-glass-like behavior and negative thermal expansion in antiperovskite Mn{sub 3}Ni{sub 1−x}Cu{sub x}N compounds

    SciTech Connect

    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.

  5. 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.”

  6. 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.

  7. IMPLOSION OF INDIRECTLY DRIVEN REENTRANT CONE SHELL TARGET

    SciTech Connect

    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.

  8. 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.

  9. Best-case performance of quantum annealers on native spin-glass benchmarks: How chaos can affect success probabilities

    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.

  10. High Pressure Experimental Studies on CuO: Indication of Re-entrant Multiferroicity at Room Temperature

    PubMed Central

    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

  11. High Pressure Experimental Studies on CuO: Indication of Re-entrant Multiferroicity at Room Temperature

    NASA Astrophysics Data System (ADS)

    Jana, Rajesh; Saha, Pinku; Pareek, Vivek; Basu, Abhisek; Kapri, Sutanu; Bhattacharyya, Sayan; Mukherjee, Goutam Dev

    2016-08-01

    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.

  12. High Pressure Experimental Studies on CuO: Indication of Re-entrant Multiferroicity at Room Temperature.

    PubMed

    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

  13. Electrophysiological predictors of propafenone efficacy in prevention of atrioventricular nodal re-entrant and atrioventricular re-entrant tachycardia

    PubMed Central

    Pintarić, Hrvoje; Zeljković, Ivan; Babić, Zdravko; Vrsalović, Mislav; Pavlović, Nikola; Bošnjak, Hrvojka; Petrač, Dubravko

    2012-01-01

    Aim To assess the efficacy of propafenone in prevention of atrioventricular nodal reentrant tachycardia (AVNRT) and orthodromic atrioventricular tachycardia (AVRT) based on the clinical results of arrhythmia recurrence and find the electrophysiological predictor of propafenone effectiveness. Methods This retrospective study included 44 participants in a 12-month period, who were divided in two groups: group A – in which propafenone caused complete ventriculo-atrial block and group B – in which propafenone did not cause complete ventriculo-atrial block. Results Group A had significantly lower incidence of tachycardia than group B (95% vs 70.8%, P = 0.038), and complete ventriculo-atrial block predicted the efficacy of propafenone oral therapy in the prevention of tachycardia (sensitivity 87.5%, specificity 52.8%, positive predictive value 95%, negative predictive value 29.2%). Patients with AVNRT in group B who did not experience the recurrences of tachycardia had significantly shorter echo zone before intravenous administration of propafenone than the patients who experienced episodes of sustained tachycardia (median 40 ms [range 15-60 ms] vs 79 ms [range 50-180 ms], P = 0.008). Conclusion In patients with non-inducible tachycardia, complete ventriculo-atrial block can be used as an electrophysiological predictor of the efficacy of propafenone oral therapy in the prevention of tachycardia. In patients with non-inducible AVNRT, but without complete ventriculo-atrial block, propafenone was more effective in patients with shorter echo zone of tachycardia. PMID:23275326

  14. 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.

  15. Coexistent Types of Atrioventricular Nodal Re-Entrant Tachycardia

    PubMed Central

    Marine, Joseph E.; Latchamsetty, Rakesh; Zografos, Theodoros; Tanawuttiwat, Tanyanan; Sheldon, Seth H.; Buxton, Alfred E.; Calkins, Hugh; Morady, Fred; Josephson, Mark E.

    2015-01-01

    Background— There is evidence that atypical fast–slow and typical atrioventricular nodal re-entrant tachycardia (AVNRT) do not use the same limb for fast conduction, but no data exist on patients who have presented with both typical and atypical forms of this tachycardia. We compared conduction intervals during typical and atypical AVNRT that occurred in the same patient. Methods and Results— In 20 of 1299 patients with AVNRT, both typical and atypical AVNRT were induced at electrophysiology study by pacing maneuvers and autonomic stimulation or occurred spontaneously. The mean age of the patients was 47.6±10.9 years (range, 32–75 years), and 11 patients (55%) were women. Tachycardia cycle lengths were 368.0±43.1 and 365.8±41.1 ms, and earliest retrograde activation was recorded at the coronary sinus ostium in 60% and 65% of patients with typical and atypical AVNRT, respectively. Thirteen patients (65%) displayed atypical AVNRT with fast–slow characteristics. By comparing conduction intervals during slow–fast and fast–slow AVNRT in the same patient, fast pathway conduction times during the 2 types of AVNRT were calculated. The mean difference between retrograde fast pathway conduction during slow–fast AVNRT and anterograde fast pathway conduction during fast–slow AVNRT was 41.8±39.7 ms and was significantly different when compared with the estimated between-measurement error (P=0.0055). Conclusions— Our data provide further evidence that typical slow–fast and atypical fast–slow AVNRT use different anatomic pathways for fast conduction. PMID:26155802

  16. Reentrant Superconductivity Driven by Quantum Tricritical Fluctuations in URhGe: Evidence from Co 59 NMR in URh0.9Co0.1Ge

    NASA Astrophysics Data System (ADS)

    Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Kambe, S.; Araki, S.

    2015-05-01

    Our measurements of the Co 59 NMR spin-spin relaxation in URh0.9Co0.1Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at HR≈13 T , around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We map out the strength of spin fluctuations in the (Hb,Hc ) plane of magnetic field components and show that critical fluctuations develop in the same limited region near the field HR as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum critical end points.

  17. Spin-glass behavior in single crystals of hetero-metallic magnetic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4

    NASA Astrophysics Data System (ADS)

    Arauzo, A.; Kazak, N. V.; Ivanova, N. B.; Platunov, M. S.; Knyazev, Yu. V.; Bayukov, O. A.; Bezmaternykh, L. N.; Lyubutin, I. S.; Frolov, K. V.; Ovchinnikov, S. G.; Bartolomé, J.

    2015-10-01

    Magnetic properties of heterometallic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 are presented, highlighting the effect of Co substitution on the magnetic properties of these compounds. The analysis of magnetization and heat capacity data has shown that these compounds exhibit a spin-glass transition below TSG=10, 20 and 22 K, respectively. Using zero field ac susceptibility as entanglement witness we find that the low dimensional magnetic behavior above TSG show quantum entanglement behavior χ(Τ)∝T-α(Τ) up to TE≈130 K. The α parameters have been deduced as a function of temperature and Co content, indicating the existence of random singlet phase in this temperature region. Above TE the paramagnetism is interpreted in terms of non-entangled spins giving rise to Curie-Weiss paramagnetism. The different intra- and inter-ribbon exchange interaction pathways have been calculated within a simple indirect coupling model. It is determined that the triangular motifs in the warwickite structure, together with the competing interactions, induce frustration. The spin-glass character is explained in terms of the substitutional disorder of the Mg, Fe and Co atoms at the two available crystallographic sites, and the frustration induced by the competing interactions. The Co substitution induces uniaxial anisotropy, increases the absolute magnetization and increases the spin-glass freezing temperature. The entanglement behavior is supported in the intermediate phase irrespective of the introduction of anisotropy by the Co substitution.

  18. Fabrication and characterization of GaSb based thermophotovoltaic cells using Zn diffusion from a doped spin-on glass source

    SciTech Connect

    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.

  19. 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.

  20. Why re-entrant surface topography is needed for robust oleophobicity.

    PubMed

    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'.

  1. Structure and Dynamics of Reentrant Nematics: Any Open Questions after Almost 40 Years?

    PubMed Central

    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

  2. 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.

  3. A swine model of infarct-related reentrant ventricular tachycardia: Electroanatomic, magnetic resonance, and histopathological characterization

    PubMed Central

    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

  4. Reentrant Origami-Based Metamaterials with Negative Poisson's Ratio and Bistability

    NASA Astrophysics Data System (ADS)

    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.

  5. 27Al magic-angle spinning nuclear magnetic resonance satellite transition spectroscopy of glasses in the system K2O-Al2O3-SiO2.

    PubMed

    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

  6. Brownmillerite CaCoO2.5: Synthesis, Re-entrant Structural Transitions and Magnetic properties

    NASA Astrophysics Data System (ADS)

    Zhang, Junjie; Zheng, Hong; Malliakas, Christos; Allred, Jared; Ren, Yang; Li, Qing'an; Han, Tianheng; Mitchell, John

    2015-03-01

    Cobalt oxides attract both fundamental and technological attention due to their physical properties including thermoelectricity, giant magnetoresistance, superconductivity and multiferroicity. Here we report the first synthesis of CaCoO2.5 single crystals using a high pressure optical-image floating zone technique. We find that it is an ordered oxygen-deficient perovskite of the brownmillerite type, and it undergoes an unprecedented re-entrant structural phase transitions (Pcmb --> P2/c11 --> P121/m1 --> Pcmb) with decreasing temperature. We describe its temperature-dependent structural, thermal, and magnetic properties, including AFM ordering near 240 K, with a weakly spin canted ferromagnet ground state below 140 K. The magnetic response of CaCoO2.5 depends markedly on the cooling rate and field history. Magnetization data also imply the potential of a distinct, field-induced phase arising uniquely from the P121/m1 structure, revealed as kinetically trapped by a rapid-cooling protocol. Work in the Materials Science Division at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Science and Engineering.

  7. Muon-spin rotation measurements of an unusual vortex-glass phase in the layered superconductor Bi2.15Sr1.85CaCu2O8+δ.

    PubMed

    Heron, D O G; Ray, S J; Lister, S J; Aegerter, C M; Keller, H; Kes, P H; Menon, G I; Lee, S L

    2013-03-01

    Muon-spin rotation measurements, performed on the mixed state of the classic anisotropic superconductor Bi(2.15)Sr(1.85)CaCu(2)O(8+δ), obtain quantities directly related to two- and three-body correlations of vortices in space. A novel phase diagram emerges from such local probe measurements of the bulk, revealing an unusual glassy state at intermediate fields which appears to freeze continuously from the equilibrium vortex liquid but differs both from the lattice and the conventional high-field vortex glass state in its structure.

  8. Development and experimental verification of a theory for high-field, ultralow-temperature magnetic linear dichroism of glasses containing molecular chromophores with spin doublet ground states

    NASA Astrophysics Data System (ADS)

    Bominaar, Emile L.; Peterson, Jim

    1999-10-01

    The first observation of magnetic linear dichroism in a metalloprotein Kramers system is reported, namely, that exhibited by the porphyrin moiety in ferricytochrome c (spin S=1/2). The measurements were conducted at low temperatures and in strong magnetic fields to maximize the signal intensity, which is intrinsicly weak in this case. The theory used in the interpretation of the wavelength dependence of this magneto-optical effect is based on the rigid-shift approximation in which the dichroic spectra are expressed as a sum of zeroth, first, and second derivatives of the underlying electronic absorption band. Similar to the case for magnetic circular dichroism, magnetic linear dichroism is caused by the Zeeman interactions of the molecular-chromophore electrons with an applied magnetic field. Two kinds of Zeeman interaction are considered, termed "inner state" and "outer state" depending on, respectively, whether or not they act between the components of a single Kramers doublet of the chromophore. It is formally demonstrated that the zeroth-derivative term for an electric-dipole transition between Kramers doublets arising from inner-state Zeeman interactions (nominally the strongest effect) completely cancels in the powder average over a randomly oriented ensemble of chromophores for all values of temperature and field. This cancellation has a profound effect on the magnetic linear dichroism of molecular chromophores suspended in glasses, as the effect now entirely relies on a set of weaker residual terms, each one having its own spectroscopic characteristics. The residual contributions have been estimated on the basis of electronic-term-energy differences and bandwidths in ferricytochrome c, resulting in the identification of the inner- and outer-state terms C1 and F0 as the dominant signatures. This prediction is in agreement with the experimental data for the shape and dependence on applied field and temperature of the magneto-dichroic spectrum for this

  9. Reentrant Solid-Liquid Transition in Ionic Colloidal Dispersions by Varying Particle Charge Density

    NASA Astrophysics Data System (ADS)

    Yamanaka, Junpei; Yoshida, Hiroshi; Koga, Tadanori; Ise, Norio; Hashimoto, Takeji

    1998-06-01

    The influence of the particle surface charge density on the solid-liquid phase transition in electrostatically stabilized colloidal silica and polymer latex dispersions is examined. Both systems show a reentrant transition with increasing charge density. This is not explainable in terms of the Yukawa potential and the charge-renormalization model.

  10. Recent volcano ice interaction and outburst flooding in a Mars polar cap re-entrant

    NASA Astrophysics Data System (ADS)

    Hovius, Niels; Lea-Cox, Andrew; Turowski, Jens M.

    2008-09-01

    Formation of chasms in the polar ice caps of Mars has been attributed to meltwater outburst floods, but the cause of melting has remained uncertain. In a cap re-entrant enveloping Abalos Colles, west of Casma Boreale in the north polar cap, we have found possible evidence of recent volcano-ice interaction and outburst flooding. In this paper we demonstrate that these two mechanisms can have acted together to form or expand the Abalos re-entrant. Flat-topped ridges and circular rims protruding above the ice cap surface in the re-entrant apex may be lava ridges and volcano craters, and can have caused melting of 3.3 to 7.7×10 km of ice. The surrounding cap surface appears to have subsided and the likely volume of missing ice matches the melt estimate. Outburst flooding from this area may have reached peak discharges of 0.3 to 1.5×10 ms according to scour patterns in one of the re-entrant channels. This required ponding of melt water during lava eruption and catastrophic release through a sub- or englacial melt water tunnel, the collapse of which has left a chasm in the ice cap margin. The flood features are geologically recent, and volcano-ice interaction may have occurred within the last 20,000 years.

  11. Visual binding through reentrant connectivity and dynamic synchronization in a brain-based device.

    PubMed

    Seth, Anil K; McKinstry, Jeffrey L; Edelman, Gerald M; Krichmar, Jeffrey L

    2004-11-01

    Effective visual object recognition requires mechanisms to bind object features (e.g. color, shape and motion) while distinguishing distinct objects. Synchronously active neuronal circuits among reentrantly connected cortical areas may provide a basis for visual binding. To assess the potential of this mechanism, we have constructed a mobile brain-based device, Darwin VIII, which is guided by simulated analogues of cortical and sub-cortical areas required for visual processing, decision-making, reward and motor responses. These simulated areas are reentrantly connected and each area contains neuronal units representing both the mean activity level and the relative timing of the activity of groups of neurons. Darwin VIII learns to discriminate among multiple objects with shared visual features and associates 'target' objects with innately preferred auditory cues. We observed the co-activation of globally distributed neuronal circuits that corresponded to distinct objects in Darwin VIII's visual field. These circuits, which are constrained by a reentrant neuroanatomy and modulated by behavior and synaptic plasticity, are necessary for successful discrimination. By situating Darwin VIII in a rich real-world environment involving continual changes in the size and location of visual stimuli due to self-generated movement, and by recording its behavioral and neuronal responses in detail, we were able to show that reentrant connectivity and dynamic synchronization provide an effective mechanism for binding the features of visual objects. PMID:15142952

  12. Structural classification and prediction of reentrant regions in alpha-helical transmembrane proteins: application to complete genomes.

    PubMed

    Viklund, Håkan; Granseth, Erik; Elofsson, Arne

    2006-08-18

    Alongside the well-studied membrane spanning helices, alpha-helical transmembrane (TM) proteins contain several functionally and structurally important types of substructures. Here, existing 3D structures of transmembrane proteins have been used to define and study the concept of reentrant regions, i.e. membrane penetrating regions that enter and exit the membrane on the same side. We find that these regions can be divided into three distinct categories based on secondary structure motifs, namely long regions with a helix-coil-helix motif, regions of medium length with the structure helix-coil or coil-helix and regions of short to medium length consisting entirely of irregular secondary structure. The residues situated in reentrant regions are significantly smaller on average compared to other regions and reentrant regions can be detected in the inter-transmembrane loops with an accuracy of approximately 70% based on their amino acid composition. Using TOP-MOD, a novel method for predicting reentrant regions, we have scanned the genomes of Escherichia coli, Saccharomyces cerevisiae and Homo sapiens. The results suggest that more than 10% of transmembrane proteins contain reentrant regions and that the occurrence of reentrant regions increases linearly with the number of transmembrane regions. Reentrant regions seem to be most commonly found in channel proteins and least commonly in signal receptors.

  13. Study on optical characterization of TGB and reentrant smectic-A phases in binary mixture of two liquid crystals

    NASA Astrophysics Data System (ADS)

    Govindaiah, T. N.; Sreepad, H. R.

    2015-04-01

    In this work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds, namely, cholesteryl nonanoate and p-methoxybenzylidene-p-ethylaniline, which exhibits a very interesting liquid crystalline twisted grain boundary (TGB) phase and reentrant smectic-A phase. The chiral liquid crystalline TGB phases and reentrant smectic-A phases have been observed at different concentrations and at different temperatures. The existence of TGB and reentrant smectic-A phases is confirmed by differential scanning calorimetry and optical microscopic studies. The variation of optical anisotropy has been discussed. The helical pitch of the cholesteric phase has also been discussed.

  14. EPR study of vanadyl ions in Li{sub 2}O-MoO{sub 3}-B{sub 2}O{sub 3} glasses[Electron Spin Resonance

    SciTech Connect

    Krishna, R.M.; Andre, J.J.; Seth, V.P.; Khasa, S.; Gupta, S.K.

    1999-05-01

    Electronic paramagnetic resonance (EPR) spectra of xLi{sub 2}O{center{underscore}dot}(30 {minus} x)MoO{sub 3}{center{underscore}dot}70B{sub 2}O{sub 3} glasses (0 {le} x {le} 25) containing 2 mol% V{sub 2}O{sub 5} were studied between room and liquid-helium temperatures at X-band frequencies. The spectra are typical of V{sup 4+} ions present in vanadyl (VO{sup 2+}) form in the glass. The spin-Hamiltonian parameters (SHP), g{sub {parallel}} g{sub {perpendicular}}, A{sub {parallel}}, and A{sub {perpendicular}}, the dipolar hyperfine coupling parameter, P, and the Fermi constant interaction parameter, k, were evaluated. It was found that these parameters are independent of the temperature. Results suggest that the tetragonal distortion of the V{sup 4+}O{sub 6} complex increases with increase in the Li{sub 2}O:MoO{sub 3} ratio. It was also found that the increase in this ratio results in an expansion of the 3d{sub xy} orbit of unpaired electrons in the vanadium ion and that the spin-Hamiltonian parameters do not depend on the value of theoretical optical basicity.

  15. Evidence for spin glass state of NdCo{sub 1−x}Ni{sub x}O{sub 3} (x = 0.3−0.5)

    SciTech Connect

    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.

  16. Order and disorder in the local and long-range structure of the spin-glass pyrochlore, Tb{sub 2}Mo{sub 2}O{sub 7}

    SciTech Connect

    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.

  17. Theory and simulations of quantum glass forming liquids.

    PubMed

    Markland, Thomas E; Morrone, Joseph A; Miyazaki, Kunimasa; Berne, B J; Reichman, David R; Rabani, Eran

    2012-02-21

    A comprehensive microscopic dynamical theory is presented for the description of quantum fluids as they transform into glasses. The theory is based on a quantum extension of mode-coupling theory. Novel effects are predicted, such as reentrant behavior of dynamical relaxation times. These predictions are supported by path integral ring polymer molecular dynamics simulations. The simulations provide detailed insight into the factors that govern slow dynamics in glassy quantum fluids. Connection to other recent work on both quantum glasses as well as quantum optimization problems is presented.

  18. Spin Glassiness and Ferromagnetism in Disordered Nickel-Manganese and Gold-Iron Alloys.

    NASA Astrophysics Data System (ADS)

    Abdul-Razzaq, Wathiq Nafee

    An initial magnetic study of disordered Ni(,100 -x)Mn(,x) for x = 23, 25, 27 showed that the latter two alloys have typical spin-glass (SG) properties below their susceptibility-peak temperatures (T(,g) = 120 K and 95 K, respectively). The x = 23 alloy, however, becomes ferro - magnetic at T(,c) = 160 K, below which (at T(,fg) = 60 K) it goes into a reentrant SG state, where its time-independent magnetizations (M) in various fixed fields applied during cooling (H(,cool)) reveal the existance of a spontaneous ferromagnetic moment. Its reentrant state is therefore mixed ferro-spin-glass (FSG),. Further study of Ni(,77)Mn(,23) showed that the narrow displaced hysteresis loops obtained at 4.2 K for high H(,cool) can be interpreted in terms of a single SG domain with a net magnetization (M(,S)) and a unidirectional anisotropy field (H(,K)). Its narrow symmetrical loop at 4.2 K for H(,cool) = 0 is shown to be consistent with the existence of an ensemble of smaller but similar domains of randomly oriented (')H(,K), which are coupled together antiferromagnetically via a weak average exchange field H(,E). With several additional Ni(,100-x)Mn(,x) alloys between x = 23 and x = 27, a detailed two-fold magnetic study was made. First, from the tem- perature dependence of the low-field M of each alloy, the variations of the magnetic transition temperatures (T(,g), T(,fg), and T(,c)) with compo- sition were determined. In the resulting magnetic phase diagram, the curves for these three temperatures meet at a multi-critical point located at x very close to 24, from which the boundary line separa- ting the FSG and SG phases extends vertically down in temperature. Secondly, from the hysteresis loops at 4.2 K obtained for high H(,cool) and for H(,cool) = 0, considered respectively as single=domain and multidomain behavior, values were deduced for the domain -model parameters (M(,S), H(,K), H(,E)), whose variations with composition are discussed briefly in physical terms. A similar but

  19. 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.

  20. Two-dimensional wave patterns of spreading depolarization: Retracting, re-entrant, and stationary waves

    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.

  1. Heating characteristics with a re-entrant type applicator in consideration of tissue blood flow rate.

    PubMed

    Ishimori, T; Ishihara, Y

    2012-01-01

    We have proposed the heating system based on a re-entrant cavity that can heat a localized deep region in a living body noninvasively. This system is superior in a local heating characteristic. However, when the living body was treated as a heating object during thermotherapy (hyperthermia), the effect of blood flow changes on a heating characteristic has to be examined. The purpose of this study was to establish the quantitative evaluation method of heating characteristics for a re-entrant type applicator. The numerical analyses by using three-dimensional finite element method in consideration of a blood flow and fundamental experiments with prototype system were carried out. Since the difference of numerical analyses and experiments was as small as about 4.2 [%] by evaluation with full width at half maximum (FWHM), the validity of this numerical analysis was confirmed.

  2. Evaluating the role of reentrant output-to-input feedback in simultaneous pattern processing

    SciTech Connect

    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.

  3. Palaeomagnetic constraints on formation of the Mianwali reentrant, Trans-Indus and western Salt Range, Pakistan

    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.

  4. 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.

  5. Reconstructing three-dimensional reentrant cardiac electrical wave dynamics using data assimilation.

    PubMed

    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

  6. Design, synthesis and characterization of a linear hydrogen bonded homologous series exhibiting reentrant smectic C ordering

    NASA Astrophysics Data System (ADS)

    Kavitha, C.; Madhu Mohan, M. L. N.

    2012-10-01

    Design, synthesis and characterization of seven linear hydrogen bonded liquid crystal complexes derived from mesogenic p-n-decyloxy benzoic acid and p-n-alkyl benzoic acids designated as 10OØn (where n varied from ethyl to octyl) are reported. FTIR studies confirm the hydrogen bond formation in all these complexes. The phase transition temperatures and their corresponding enthalpy values are experimentally deduced from Differential Scanning Calorimetry (DSC) studies. POM and DSC data are further utilized for the construction of 10OØn phase diagram. Two Odd-even effects have been evinced, one in enthalpy values and the other in corresponding transition temperatures across the isotropic to nematic phase transition. An interesting result is the observation of re-entrant smectic ordering, designated as smectic CR in three higher ordered mesogens. A new smectic ordering, smectic X, has been observed which is sandwiched between traditional smectic C and re-entrant smectic CR. Magnitudes of optical tilt angle in smectic C, smectic X and smectic CR are experimentally found to attain saturation with decrement of temperature in the corresponding phase. The occurrence of smectic X and smectic CR are discussed with relation to the molecular chemical structure. The optical filtering action in smectic C and re-entrant smectic CR phases have been analyzed.

  7. Relationship between molecular association and re-entrant phenomena in polar calamitic liquid crystals.

    PubMed

    Mandle, Richard J; Cowling, Stephen J; Sage, Ian; Colclough, M Eamon; Goodby, John W

    2015-02-19

    The relationship between molecular association and re-entrant phase behavior in polar calamitic liquid crystals has been explored in two families of materials: the 4'-alkoxy-4-cyanobiphenyls (6OCB and 8OCB) and the 4'-alkoxy-4-nitrobiphenyls. Although re-entrant nematic phase behavior has previously been observed in the phase diagram of 6OCB/8OCB, this is not observed in mixtures of the analogous nitro materials. As there is no stabilization of the smectic A phase in mixture studies, it was conjectured that the degree of association for the nitro systems is greater than that for the cyano analogues. This hypothesis was tested by using measured dielectric anisotropies and computed molecular properties to obtain a value of the Kirkwood factor, g, which describes the degree of association of dipoles in a liquid. These computed values of g confirm that the degree of association for nitro materials is greater than that for cyano and offer a useful method for quantifying molecular association in systems exhibiting a re-entrant polymorphism.

  8. Magneto-thermally activated spin-state transition in La0.95Ca0.05CoO3: magnetically-tunable dipolar glass and giant magneto-electricity

    NASA Astrophysics Data System (ADS)

    Pandey, Suchita; Kumar, Jitender; Awasthi, A. M.

    Magneto-dielectric spectra of La0.95Ca0.05CoO3 covering the crossover of spin states reveals strong coupling of its spin and dipolar degrees of freedom. Signature of spin-state transition at 30K clearly manifests in magnetization, supported by Co L_3,2-edge XAS data on the doped-specimen as consistent with its suppressed T_SST vs. ~150K for pure LaCoO3. Dispersive activation-step {\\Delta}{\\epsilon}'(T_{\\omega})~O(10^2) and relaxation-peak {\\epsilon}"(T_{\\omega}) reflect the allied influence of coexistent spin-states on the dielectric character. Dipolar relaxation in the LS regime below T_SST is partly segmental (VFT kinetics) featuring magnetic-field tunability, whereas in the LS/IS-spin disordered state above 30K, it is uncorrelated (Arrhenic kinetics) and almost impervious to the H-field. Kinetics-switchover defines the dipolar-glass transition temperature Tg(H), below which the magneto-thermally-activated cooperative relaxations freeze-out by the VFT temperature T_0(H). Applied H-field facilitates thermally-activated SST and accelerates the dipolar relaxations; a critical 5T field collapsing the entire kinetics into a single Arrhenic behavior. Magneto-electricity (ME) spanning sizable thermo-spectral range registers diverse signatures here in the 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 with vanishing magneto-loss is obtained at (27K/50kHz)_9T. Sub-linear deviant field-hysteretic split seen in {\\epsilon}'(H)|_>4T suggests the emergence of robust dipoles organized into nano-clusters, realized by the internally-generated high magneto-electric field. An elaborate {\\omega}-T multi-dispersions diagram maps the rich variety of phase/response patterns, revealing the highly-interacting magnetic and electric moments in the system.

  9. Insulating and metallic spin glass in KxFe2-δ-yNiySe2 (0.06 ≤ y ≤ 1.44 ) single crystals

    SciTech Connect

    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 superconductivity coincides with the absence of crystalline Fe vacancy order.

  10. Origin of spin-glass and exchange bias in La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} nanoparticles

    SciTech Connect

    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.

  11. Transport studies of reentrant integer quantum Hall states forming in the two-dimensional electron gas

    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

  12. Viscous behavior in a quasi-1D fractal cluster glass.

    PubMed

    Etzkorn, S J; Hibbs, Wendy; Miller, Joel S; Epstein, A J

    2002-11-11

    The spin glass transition of a quasi-1D organic-based magnet ([MnTPP][TCNE]) is explored using both ac and dc measurements. A scaling analysis of the ac susceptibility shows a spin glass transition near 4 K, with a viscous decay of the thermoremanent magnetization recorded above 4 K. We propose an extension to a fractal cluster model of spin glasses that determines the dimension of the spin clusters (D) ranging from approximately 0.8 to over 1.5 as the glass transition is approached. Long-range dipolar interactions are suggested as the origin of this low value for the apparent lower critical dimension.

  13. Double spin-glass-like behavior and antiferromagnetic superexchange interaction between Fe3+ ions in α-Ga2-xFexO3 (0 ≤ x ≤ 0.4)

    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).

  14. Empowering Reentrant Projections from V5 to V1 Boosts Sensitivity to Motion.

    PubMed

    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

  15. Functional properties of the basal ganglia's re-entrant loop architecture: selection and reinforcement.

    PubMed

    Redgrave, P; Vautrelle, N; Reynolds, J N J

    2011-12-15

    Multifunctional agents with limited motor resources must decide what actions will best ensure their survival. Moreover, given that in an unpredictable world things don't always work out, considerable advantage is to be gained by learning from experience - instrumental behaviour that maximises reward and minimises punishment. In this review we will argue that the re-entrant looped architecture of the basal ganglia represents biological solutions to these fundamental behavioural problems of selection and reinforcement. A potential solution to the selection problem is provided for by selective disinhibition within the parallel loop architecture that connects the basal ganglia with external neural structures. The relay points within these loops permit the signals of a particular channel to be modified by external influences. In part, these influences have the capacity to modify overall selections so that the probability of re-selecting reinforced behaviours in the future is altered. This is the basic process of instrumental learning, which we suggest decomposes into two sub-problems for the agent: (i) learning which external events it causes to happen and learning precisely what it is doing that is causal; and (ii) having determined agency and discovered novel action-outcome routines, how best to exploit this knowledge to maximise future reward acquisitions. Considerations of connectional architecture and signal timing suggest that the short-latency, sensory-evoked dopamine response, which can modulate the re-entrant loop structure within the basal ganglia, is ideally suited to reinforce the determination of agency and the discovery of novel actions. Alternatively, recent studies showing that presence or absence of reward can selectively modulate the magnitude of signals in structures providing input signals to the basal ganglia, offer an alternative mechanism for biasing selection within the re-entrant loop architecture. We suggest that this mechanism may be better

  16. Enhanced self-termination of re-entrant arrhythmias as a pharmacological strategy for antiarrhythmic action

    NASA Astrophysics Data System (ADS)

    Aslanidi, O. V.; Bailey, A.; Biktashev, V. N.; Clayton, R. H.; Holden, A. V.

    2002-09-01

    Ventricular tachycardia and fibrillation are potentially lethal cardiac arrhythmias generated by high frequency, irregular spatio-temporal electrical activity. Re-entrant propagation has been demonstrated as a mechanism generating these arrhythmias in computational and in vitro animal models of these arrhythmias. Re-entry can be idealised in homogenous isotropic virtual cardiac tissues as spiral and scroll wave solutions of reaction-diffusion equations. A spiral wave in a bounded medium can be terminated if its core reaches a boundary. Ventricular tachyarrhythmias in patients are sometimes observed to spontaneously self-terminate. One possible mechanism for self-termination of a spiral wave is meander of its core to an inexcitable boundary. We have previously proposed the hypothesis that the spatial extent of meander of a re-entrant wave in the heart can be directly related to its probability of self-termination, and so inversely related to its lethality. Meander in two-dimensional virtual ventricular tissues based on the Oxsoft family of cell models, with membrane excitation parameters simulating the inherited long Q-T syndromes has been shown to be consistent with this hypothesis: the largest meander is seen in the syndrome with the lowest probability of death per arrhythmic episode. Here we extend our previous results to virtual tissues based on the Luo-Rudy family of models. Consistent with our hypothesis, for both families of models, whose different ionic mechanisms produce different patterns of meander, the LQT virtual tissue with the larger meander simulates the syndrome with the lower probability of death per episode. Further, we search the parameter space of the repolarizing currents to find their conductance parameter values that give increased meander of spiral waves. These parameters may provide targets for antiarrhythmic drugs designed to act by increasing the likelihood of self-termination of re-entrant arrhythmias.

  17. Paradoxical responses to pacing maneuvers differentiating atrioventricular node reentrant tachycardia and junctional tachycardia.

    PubMed

    Tokuda, Michifumi; Yamane, Teiichi; Matsuo, Seiichiro; Tokutake, Kenichi; Yokoyama, Kenichi; Hioki, Mika; Narui, Ryohsuke; Tanigawa, Shin-Ichi; Yamashita, Seigo; Inada, Keiichi; Yoshimura, Michihiro

    2016-02-01

    A 40-year-old female presented at our hospital because of heart palpitations. During an electrophysiological study, atrioventricular (AV) conduction showed dual AV nodal physiology. Three types of supraventricular tachycardia (SVT) were induced. The initiation of SVT was reproducibility dependent on a critical A-H interval prolongation. An early premature atrial contraction during SVT repeatedly advanced the immediate His potential with termination of the tachycardia, indicating AV node reentrant tachycardia (AVNRT). However, after atrial overdrive pacing during SVT without termination of the tachycardia, the first return electrogram resulted in an AHHA response, consistent with junctional tachycardia. The mechanism of paradoxical responses to pacing maneuvers differentiating AVNRT and junctional tachycardia was discussed.

  18. [Successful ablation of an atrioventricular nodal reentrant tachycardia ablation 2 years after orthotopic heart transplantation].

    PubMed

    Bellmann, Barbara; Reith, Sebastian; Gemein, Christopher; Schauerte, Patrick

    2015-09-01

    We report the case of a 48-year-old woman with an orthotopic heart transplantation. Two years after transplantation, the patient reported intermittent palpitations and dyspnea. The results of the 12-lead electrogram provided suspicion of AV nodal reentrant tachycardia (AVNRT), which was confirmed in the electrophysiological examination. The AVNRT was successfully eliminated without complications by radiofrequency catheter ablation of the slow pathway. The case shows that an AVNRT, even with existing sinus rhythm of the original heart, can also occur on the transplanted heart and ablation is safe and feasible. PMID:26208808

  19. Thermoelectric response of fractional quantized Hall and reentrant insulating states in the N=1 Landau level

    NASA Astrophysics Data System (ADS)

    Chickering, W. E.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.

    2013-02-01

    Detailed measurements of the longitudinal thermopower of two-dimensional electrons in the first excited Landau level are reported. Clear signatures of numerous fractional quantized Hall states, including those at ν=5/2 and 7/3, are observed in the magnetic field and temperature dependence of the thermopower. An abrupt collapse of the thermopower is observed below about T=40 mK at those filling factors where reentrant insulating electronic states have been observed in conventional resistive transport studies. The thermopower observed at ν=5/2 is discussed in the context of recent theories which incorporate non-Abelian quasiparticle exchange statistics.

  20. Reentrant Behavior of Divalent-Counterion-Mediated DNA-DNA Electrostatic Interaction

    NASA Astrophysics Data System (ADS)

    Lee, Seil; Le, Tung T.; Nguyen, Toan T.

    2010-12-01

    The problem of DNA-DNA interaction mediated by divalent counterions is studied using computer simulation. Although divalent counterions cannot condense free DNA molecules in solution, we show that if DNA configurational entropy is restricted, divalent counterions can cause DNA reentrant condensation similar to that caused by tri- or tetravalent counterions. DNA-DNA interaction is strongly repulsive at small or large counterion concentration and is negligible or slightly attractive for a concentration in between. Implications of our results to experiments of DNA ejection from bacteriophages are discussed. The quantitative result serves to understand electrostatic effects in other experiments involving DNA and divalent counterions.

  1. Thermo-Chemical Ablation During Reentrant and High Altitude Skipping Flight

    SciTech Connect

    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.

  2. Phase Separation on Bicontinuous Cubic Membranes: Symmetry Breaking, Reentrant, and Domain Faceting.

    PubMed

    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

  3. Slow pathway modification for atrioventricular node re-entrant tachycardia: fast junctional tachycardia predicts adverse prognosis

    PubMed Central

    Lipscomb, K; Zaidi, A; Fitzpatrick, A; LEFROY, D

    2001-01-01

    D LEFROY Deputy Editor OBJECTIVE—To examine the cycle length of the junctional tachycardia often seen during successful slow pathway ablation for atrioventricular (AV) node re-entrant tachycardia, to determine whether shorter cycle lengths predict imminent atrioventricular block.
DESIGN—Retrospective analysis of consecutive patients undergoing slow pathway modification. Intracardiac recordings were analysed after digital storage to determine the development of junctional tachycardia, its duration and maximum, minimum, and mean cycle length, occurrence of heart block, persistent slow pathway conduction, or later confirmed recurrence of AV node re-entrant tachycardia.
SETTING—Regional cardiac centre.
PATIENTS—136 consecutive patients undergoing electrophysiological study found to have typical "slow-fast" AV node re-entrant tachycardia and subject to 137 slow pathway modification procedures.
RESULTS—During successful temperature feedback controlled radiofrequency energy application, junctional tachycardia developed in 133 of 137 procedures. During ablation, 10 patients had evidence of AV block (first degree in seven patients and third degree in three), and 17 others had retrograde junctional atrial (JA) block. In these 27 patients, the junctional tachycardia was rapid, with a minimum (SD) cycle length 291 (47) ms. Conduction recovered quickly in all but two patients, one of whom required permanent pacing. Junctional tachycardia with normal AV and JA conduction in the other 111 patients was of a significantly slower minimum cycle length (537 (123) ms; p < 0.0001).
CONCLUSIONS—Fast junctional tachycardia with cycle lengths under 350 ms seen during slow pathway modification is a predictor of conduction block, suggesting proximity to the compact node. Radiofrequency energy application should be terminated immediately to prevent development of AV block. An "auto cut off" facility for cycle lengths shorter than 350 ms could be built into

  4. Glass sealing

    SciTech Connect

    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.

  5. Spin foams without spins

    NASA Astrophysics Data System (ADS)

    Hnybida, Jeff

    2016-10-01

    We formulate the spin foam representation of discrete SU(2) gauge theory as a product of vertex amplitudes each of which is the spin network generating function of the boundary graph dual to the vertex. In doing so the sums over spins have been carried out. The boundary data of each n-valent node is explicitly reduced with respect to the local gauge invariance and has a manifest geometrical interpretation as a framed polyhedron of fixed total area. Ultimately, sums over spins are traded for contour integrals over simple poles and recoupling theory is avoided using generating functions.

  6. 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

  7. 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.

  8. Hydrophobic and oleophobic re-entrant steel microstructures fabricated using micro electrical discharge machining

    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.

  9. Monoclinic Cc-phase stabilization in magnetically diluted lead free Na1/2Bi1/2TiO3—Evolution of spin glass like behavior with enhanced ferroelectric and dielectric properties

    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.

  10. Sustained phase separation and spin glass in Co-doped KxFe2-ySe2 single crystals

    SciTech Connect

    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 stripe conducting phase.

  11. Model of unidirectional block formation leading to reentrant ventricular tachycardia in the infarct border zone of postinfarction canine hearts

    PubMed Central

    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

  12. 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.

  13. Bose glass behavior in (Yb1 -xLux)4As3 representing randomly diluted quantum spin-1/2 chains

    NASA Astrophysics Data System (ADS)

    Kamieniarz, G.; Matysiak, R.; Gegenwart, P.; Ochiai, A.; Steglich, F.

    2016-09-01

    The site-diluted compound (Yb1-xLux) 4As3 is a scarce realization of the linear Heisenberg antiferromagnet partitioned into finite-size segments and is an ideal model compound for studying field-dependent effects of quenched disorder in the one-dimensional antiferromagnets. It differentiates from the systems studied so far in two aspects—the type of randomness and the nature of the energy gap in the pure sample. We have measured the specific heat of single-crystal (Yb1-xLux) 4As3 in magnetic fields up to 19.5 T. The contribution C⊥ arising from the magnetic subsystem in an applied magnetic field perpendicular to the chains is determined. Compared to pure Yb4As3 , for which C⊥ indicates a gap opening, for diluted systems a nonexponential decay is found at low temperatures which is consistent with the thermodynamic scaling of the specific heat established for a Bose-glass phase.

  14. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results.

    PubMed

    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

  15. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results

    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.

  16. Distribution of glass transition temperatures Tg in polystyrene thin films as revealed by low-energy muon spin relaxation: A comparison with neutron reflectivity results.

    PubMed

    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.

  17. Shock-induced termination of reentrant cardiac arrhythmias: Comparing monophasic and biphasic shock protocols

    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.

  18. Incessant slow bundle branch reentrant ventricular tachycardia in a young patient with left ventricular noncompaction.

    PubMed

    Barra, Sérgio; Moreno, Nuno; Providência, Rui; Gonçalves, Helena; Primo, João José

    2013-06-01

    A 15-year-old girl was admitted to the cardiology outpatient clinic due to mild palpitations and documented incessant slow ventricular tachycardia (VT) with left bundle branch block (LBBB) pattern. The baseline electrocardiogram revealed first-degree atrioventricular block and intraventricular conduction defect. Transthoracic echocardiography showed prominent trabeculae and intertrabecular recesses suggesting left ventricular noncompaction (LVNC), which was confirmed by cardiac magnetic resonance imaging. During electrophysiological study, a sustained bundle branch reentrant VT with LBBB pattern and cycle length of 480 ms, similar to the clinical tachycardia, was easily and reproducibly inducible. As there was considerable risk of need for chronic ventricular pacing following right bundle ablation, no ablation was attempted and a cardioverter-defibrillator was implanted. To the best of our knowledge, no case reports of BBR-VT as the first manifestation of LVNC have been published. Furthermore, this is an extremely rare presentation of BBR-VT, which is usually a highly malignant arrhythmia.

  19. Polyethylene glycol and divalent salt-induced DNA reentrant condensation revealed by single molecule measurements.

    PubMed

    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.

  20. Reentrant reversible remanent magnetization in superconducting submicron YBaCuO particles

    NASA Astrophysics Data System (ADS)

    Blinov, E. V.; Laiho, R.; Lyublinsky, A. G.; Lähderanta, E.; Traito, K. B.

    1999-05-01

    Reversible properties of the remanent magnetic moment, Mrem, in superconducting submicron- and micron-size Y-Ba-Cu-O particles and thin films are investigated with a SQUID magnetometer. In micron-size particles and thin films a monotonic increase of Mrem was observed when decreasing the temperature. In submicron particles, the same monotonic behaviour is observed at first but at low temperatures an unusual reentrant behaviour was found: Mrem decreased when cooling the sample below 6 K. This phenomenon is independent of the direction of the thermal cycle. Possible mechanisms of this effect, such as midgap states in the quasiparticle excitation spectrum and defect-induced localization of Cooper pairs, are discussed.

  1. 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.

  2. Reentrant phase transition in charged colloidal suspensions: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Tata, B. V. R.; Arora, Akhilesh K.; Valsakumar, M. C.

    1993-05-01

    Monte Carlo simulations of aqueous charged colloidal suspensions interacting via an effective pair potential are carried out with a view to elucidate the mechanism of the reentrant phase transition reported in these systems. The computed pair-correlation functions show that a weakly interacting homogeneous suspension phase separates into dense and rare phases and thereafter reenters into a homogeneous state with crystalline or liquidlike order when the concentration of the ionic impurities is decreased. The cluster-size distribution indeed shows the existence of dense-phase droplets for the intermediate range of impurity-ion concentrations where the phase separation occurs. Some of the recent experimental results are discussed in the light of the present simulation results.

  3. Re-entrant melting and freezing in a model system of charged colloids

    NASA Astrophysics Data System (ADS)

    Royall, C. Patrick; Leunissen, Mirjam E.; Hynninen, Antti-Pekka; Dijkstra, Marjolein; van Blaaderen, Alfons

    2006-06-01

    We studied the phase behavior of charged and sterically stabilized colloids using confocal microscopy in a low polarity solvent (dielectric constant 5.4). Upon increasing the colloid volume fraction we found a transition from a fluid to a body centered cubic crystal at 0.04150.0005, followed by reentrant melting at 0.11650.0015. A second crystal of different symmetry, random hexagonal close packed, was formed at a volume fraction around 0.5, similar to that of hard spheres. We attribute the intriguing phase behavior to the particle interactions that depend strongly on volume fraction, mainly due to the changes in the colloid charge. In this low polarity system the colloids acquire charge through ion adsorption. The low ionic strength leads to fewer ions per colloid at elevated volume fractions and consequently a density-dependent colloid charge.

  4. Reentrant BCS-BEC crossover and a superfluid-insulator transition in optical lattices.

    PubMed

    Shen, Zhaochuan; Radzihovsky, L; Gurarie, V

    2012-12-14

    We study the thermodynamics of a two-species Feshbach-resonant atomic Fermi gas in a periodic potential, focusing in a deep optical potential where a tight binding model is applicable. We show that for a more than half-filled band the gas exhibits a reentrant crossover with decreased detuning (increased attractive interaction), from a paired BCS superfluid to a Bose-Einstein condensate (BEC) of molecules of holes, back to the BCS superfluid, and finally to a conventional BEC of diatomic molecules. This behavior is associated with the nonmonotonic dependence of the chemical potential on detuning and the concomitant Cooper-pair or molecular size, larger in the BCS and smaller in the BEC regimes. For a single filled band we find a quantum phase transition from a band insulator to a BCS-BEC superfluid, and map out the corresponding phase diagram. PMID:23368340

  5. Reentrant BCS-BEC Crossover and a Superfluid-Insulator Transition in Optical Lattices

    NASA Astrophysics Data System (ADS)

    Shen, Zhaochuan; Radzihovsky, L.; Gurarie, V.

    2012-12-01

    We study the thermodynamics of a two-species Feshbach-resonant atomic Fermi gas in a periodic potential, focusing in a deep optical potential where a tight binding model is applicable. We show that for a more than half-filled band the gas exhibits a reentrant crossover with decreased detuning (increased attractive interaction), from a paired BCS superfluid to a Bose-Einstein condensate (BEC) of molecules of holes, back to the BCS superfluid, and finally to a conventional BEC of diatomic molecules. This behavior is associated with the nonmonotonic dependence of the chemical potential on detuning and the concomitant Cooper-pair or molecular size, larger in the BCS and smaller in the BEC regimes. For a single filled band we find a quantum phase transition from a band insulator to a BCS-BEC superfluid, and map out the corresponding phase diagram.

  6. Shock-induced termination of reentrant cardiac arrhythmias: Comparing monophasic and biphasic shock protocols

    SciTech Connect

    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.

  7. Experimental heating properties of re-entrant type resonant cavity applicator for deep tumor hyperthermia.

    PubMed

    Nakano, A; Kato, K; Tsuchiya, K; Nakazawa, K; Yabuhara, T; Uzuka, T; Takahashi, H

    2006-01-01

    This paper discusses the heating properties of a new type hyperthermia system composed of a re-entrant type resonant cavity applicator for a deep tumor of the abdominal region. In this heating method, a human body is placed between the two inner electrodes, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human body and the applicator. First, the experimental heating results of an agar-muscle equivalent phantom were presented. Second, we performed an experiment with a lard-agar phantom. The center region of the agar phantom could be heated selectively without generating hot spots in the lard layers. From these results, it was found that our newly developed heating method is useful for a deep-seated tumor hyperthermia treatment.

  8. Structure and interaction in the polymer-dependent reentrant phase behavior of a charged nanoparticle solution

    NASA Astrophysics Data System (ADS)

    Kumar, Sugam; Ray, D.; Aswal, V. K.; Kohlbrecher, J.

    2014-10-01

    Small-angle neutron scattering (SANS) studies have been carried out to examine the evolution of interaction and structure in a nanoparticle (silica)-polymer (polyethylene glycol) system. The nanoparticle-polymer solution interestingly shows a reentrant phase behavior where the one-phase charged stabilized nanoparticles go through a two-phase system (nanoparticle aggregation) and back to one-phase as a function of polymer concentration. Such phase behavior arises because of the nonadsorption of polymer on nanoparticles and is governed by the interplay of polymer-induced attractive depletion with repulsive nanoparticle-nanoparticle electrostatic and polymer-polymer interactions in different polymer concentration regimes. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. However, the increase in polymer concentration enhances the depletion attraction to give rise to the nanoparticle aggregation in the two-phase system. Further, the polymer-polymer repulsion at high polymer concentrations is believed to be responsible for the reentrance to one-phase behavior. The SANS data in polymer contrast-matched conditions have been modeled by a two-Yukawa potential accounting for both repulsive and attractive parts of total interaction potential between nanoparticles. Both of these interactions (repulsive and attractive) are found to be long range. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the depletion interaction leading to reentrant phase behavior. The nanoparticle clusters in the two-phase system are characterized by the surface fractal with simple cubic packing of nanoparticles within the clusters. The effect of varying ionic strength and polymer size in tuning the interaction has also been examined.

  9. Structure and interaction in the polymer-dependent reentrant phase behavior of a charged nanoparticle solution.

    PubMed

    Kumar, Sugam; Ray, D; Aswal, V K; Kohlbrecher, J

    2014-10-01

    Small-angle neutron scattering (SANS) studies have been carried out to examine the evolution of interaction and structure in a nanoparticle (silica)-polymer (polyethylene glycol) system. The nanoparticle-polymer solution interestingly shows a reentrant phase behavior where the one-phase charged stabilized nanoparticles go through a two-phase system (nanoparticle aggregation) and back to one-phase as a function of polymer concentration. Such phase behavior arises because of the nonadsorption of polymer on nanoparticles and is governed by the interplay of polymer-induced attractive depletion with repulsive nanoparticle-nanoparticle electrostatic and polymer-polymer interactions in different polymer concentration regimes. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. However, the increase in polymer concentration enhances the depletion attraction to give rise to the nanoparticle aggregation in the two-phase system. Further, the polymer-polymer repulsion at high polymer concentrations is believed to be responsible for the reentrance to one-phase behavior. The SANS data in polymer contrast-matched conditions have been modeled by a two-Yukawa potential accounting for both repulsive and attractive parts of total interaction potential between nanoparticles. Both of these interactions (repulsive and attractive) are found to be long range. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the depletion interaction leading to reentrant phase behavior. The nanoparticle clusters in the two-phase system are characterized by the surface fractal with simple cubic packing of nanoparticles within the clusters. The effect of varying ionic strength and polymer size in tuning the interaction has also been examined.

  10. Highly re-entrant profiles in a thick photosensitive material for nanotechnology applications

    NASA Astrophysics Data System (ADS)

    Flack, Warren W.; Nguyen, Ha-Ai; Shaw, Mark; do Canto, Manny

    2006-03-01

    The requirements for highly specialized photosensitive materials for nanotechnology and Micro-Electro-Mechanical Systems (MEMS) applications are being driven by the rapid growth of consumer products incorporating these devices. These high volume consumer devices including accelerometers for air-bag sensors, biomedical sensors, optical switches and ink jet print heads. These applications all require ultra-thick photosensitive materials with highly controllable lithographic properties. For ink-jet print head applications, the lithography requirements include the formation of high aspect ratio structures with a negative (re-entrant) profile for nozzle formation. In order to form the required nozzle geometry for high resolution ink-jet printers, photosensitive materials need to be capable of providing up to 10 degree negative profiles at a film thickness of up to 25 microns. For consistent print dot size it is necessary to maintain excellent control and repeatability of the sidewall angle of the nozzle. Since this material remains on the substrate as a permanent part of the ink-jet print head, the mechanical and adhesive properties of the material are as important as the lithographic properties. This paper investigates modifications to an existing MicroChem epoxy-based SU8-4000 thick photoresist to generate highly re-entrant sidewall angles for next-generation high resolution ink-jet nozzle formation. Multiple versions of SU8-4000 with different levels of dye tuned for the exposure wavelength are exposed using a 1X lithography system optimized for thick photoresist processing. This stepper uses a combination of low numerical aperture, broadband exposure and large focus offsets for optimal processing of thick photosensitive materials. Basic photoresist characterization techniques in conjunction with cross sectional SEM analysis are used to establish lithographic capabilities for nozzle formation.

  11. Glass Artworks

    NASA Technical Reports Server (NTRS)

    1988-01-01

    Several NASA technologies have played part in growth and cost containment of studio glass art, among them a foam type insulation developed to meet a need for lightweight material that would reduce flame spread in aircraft fire. Foam comes in several forms and is widely used by glass artists, chiefly as an insulator for the various types of ovens used in glass working. Another Spinoff is alumina crucibles to contain molten glass. Before alumina crucibles were used, glass tanks were made of firebrick which tended to erode under high temperatures and cause impurities; this not only improved quality but made the process more cost effective. One more NASA technology that found its way into glass art working is a material known as graphite board, a special form of graphite originally developed for rocket motor applications. This graphite is used to exact compound angles and creates molds for poured glass artworks of dramatic design.

  12. Glass Research

    NASA Technical Reports Server (NTRS)

    Weinberg, M. C.

    1985-01-01

    Research efforts span three general areas of glass science: glass refining, gel-derived glasses, and nucleation and crystallization of glasses. Gas bubbles which are present in a glass product are defects which may render the glass totally useless for the end application. For example, optical glasses, laser host glasses, and a variety of other specialty glasses must be prepared virtually defect free to be employable. Since a major mechanism of bubble removal, buoyant rise, is virtually inoperative in microgravity, glass fining will be especially difficult in space. On the other hand, the suppression of buoyant rise and the ability to perform containerless melting experiments in space allows the opportunity to carry out several unique bubble experiments in space. Gas bubble dissolution studies may be performed at elevated temperatures for large bubbles with negligible bubble motion. Also, bubble nucleation studies may be performed without the disturbing feature of heterogeneous bubble nucleation at the platinum walls. Ground based research efforts are being performed in support of these potential flight experiments.

  13. Phase transitions of Ising mixed spin 1 and 3/2 with random crystal field distribution

    NASA Astrophysics Data System (ADS)

    Sabri, S.; EL Falaki, M.; EL Yadari, M.; Benyoussef, A.; EL Kenz, A.

    2016-10-01

    The thermal and magnetic properties of the mixed spin-1 and spin-3/2 in the presence of the random crystal field are studied within the mean field approach based on the Bogoliubov inequality for the Gibbs free energy. The model exhibits first, second order transitions, a tricritical point, triple point and an isolated critical end point. It is found that the system displays simple and double compensation temperatures, five topologies of the phase diagrams. A re-entrant phenomenon is also discussed and the thermal dependences of total magnetization according to extended Neel classification have been also given.

  14. Successful radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia in a patient with dextrocardia due to unilateral pulmonary agenesis: a case report

    PubMed Central

    Aksu, Tolga; Guler, Tumer Erdem; Golcuk, Ebru; Erden, Ismail; Ozcan, Kazım Serhan

    2015-01-01

    Radiofrequency catheter ablation of the slow pathway is considered to be the treatment of choice for patients with atrioventricular nodal reentrant tachycardia. We report a 34-year-old female with mirror image dextrocardia due to unilateral pulmonary agenesis who underwent successful slow pathway ablation for typical atrioventricular nodal reentrant tachycardia. Using contrast injection, cardiac anatomy was identified in a short time and successfully ablated. PMID:25674017

  15. A universal description of ultraslow glass dynamics

    PubMed Central

    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

  16. Durable, superoleophobic polymer–nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation

    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.

  17. Reentrant transition from an incipient charge-ordered state to a ferromagnetic metallic state in a rare-earth manganate

    NASA Astrophysics Data System (ADS)

    Arulraj, Anthony; Biswas, Amlan; Raychaudhuri, A. K.; Rao, C. N. R.; Woodward, P. M.; Vogt, T.; Cox, D. E.; Cheetham, A. K.

    1998-04-01

    A reentrant transition from an incipient charge-ordered (CO) state to a charge-delocalized ferromagnetic (CDFM) state has been established in the manganate Nd0.25La0.25Ca0.5MnO3, in which the average A-site ionic radius is 1.19 Å. The reentrant CDFM phase is associated with a first-order phase transition that reduces the orthorhombic distortion of the lattice, in contrast to the CO transition in other manganates where the orthorhombically distorted CO state is stabilized at low temperatures. At the CO-CDFM transition, there is a collapse of the charge-ordering gap as measured by vacuum tunneling spectroscopy.

  18. Durable, superoleophobic polymer-nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation

    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.

  19. Durable, superoleophobic polymer–nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation

    PubMed Central

    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

  20. Chiral-glass transition in a diluted dipolar-interaction Heisenberg system

    NASA Astrophysics Data System (ADS)

    Zhang, Kai-Cheng; Liu, Gui-Bin; Zhu, Yan

    2011-05-01

    Recently, numerical simulations reveal that a spin-glass transition can occur in the three-dimensional diluted dipolar system. By defining the chirality of triple spins in a diluted dipolar Heisenberg spin glass, we study the chiral ordering in the system using parallel tempering algorithm and heat bath method. The finite-size scaling analysis reveals that the system undergoes a chiral-glass transition at finite temperature.

  1. Resetting and annihilation of reentrant activity in a model of a one-dimensional loop of ventricular tissue

    NASA Astrophysics Data System (ADS)

    Comtois, Philippe; Vinet, Alain

    2002-09-01

    Resetting and annihilation of reentrant activity by a single stimulus pulse (S1) or a pair (S1-S2) of coupled pulses are studied in a model of one-dimensional loop of cardiac tissue using a Beeler-Reuter-type ionic model. Different modes of reentry termination are described. The classical mode of termination by unidirectional block, in which a stimulus produces only a retrograde front that collides with the activation front of the reentry, can be obtained for both S1 and S1-S2 applied over a small vulnerable window. We demonstrate that another scenario of termination—that we term collision block—can also be induced by the S1-S2 protocol. This scenario is obtained over a much wider range of S1-S2 coupling intervals than the one leading to a unidirectional block. In the collision block, S1 produces a retrograde front, colliding with the activation front of the pre-existing reentry, and an antegrade front propagating in the same direction as the initial reentry. Then, S2 also produces an antegrade and a retrograde front. However, the propagation of these fronts in the spatial profile of repolarization left by S1 leads to a termination of the reentrant activity. More complex behaviors also occur in which the antegrade fronts produced by S1 and S2 both persist for several turns, displaying a growing alternation in action potential duration ("alternans amplification") that may lead to the termination of the reentrant activity. The hypothesis that both collision block and alternans amplification depend on the interaction between the action potential duration restitution curve and the recovery curve of conduction velocity is supported by the fact that the dynamical behaviors were reproduced using an integro-delay equation based on these two properties. We thus describe two new mechanisms (collision block and alternans amplification) whereby electrical stimulation can terminate reentrant activity.

  2. Geometrical spin symmetry and spin

    SciTech Connect

    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.

  3. Metallic glasses.

    PubMed

    Greer, A L

    1995-03-31

    Amorphous metallic alloys, relative newcomers to the world of glasses, have properties that are unusual for solid metals. The metallic glasses, which exist in a very wide variety of compositions, combine fundamental interest with practical applications. They also serve as precursors for exciting new nanocrystalline materials. Their magnetic (soft and hard) and mechanical properties are of particular interest.

  4. Consolidated silica glass from nanoparticles

    SciTech Connect

    Mayerhoefer, Thomas G. Shen Zhijian; Leonova, Ekaterina; Eden, Mattias; Kriltz, Antje; Popp, Juergen

    2008-09-15

    A dense silica glass was prepared by consolidating a highly dispersed silicic acid powder (particle size <10 nm) with the Spark Plasma Sintering (SPS) technique. The glass was characterized by ellipsometry, transmission electron microscopy (TEM), infrared reflectance and transmittance spectroscopy, as well as by Raman, UV-Vis-NIR and solid-state nuclear magnetic resonance (NMR) spectroscopy. The prototypic sample showed a transmittance of about 63% compared to silica glass in the UV-Vis spectral range. Based on the results of infrared transmittance spectroscopy this lower transparency is due to the comparably high water content, which is about 40 times higher than that in silica glass. {sup 1}H magic-angle spinning (MAS) NMR confirmed an increase in hydroxyl groups in the sample prepared by SPS relative to that of the conventional SiO{sub 2} reference glass. Aside from the comparably high water content, we conclude from the similarity of the IR-reflectance and the {sup 29}Si MAS NMR spectra of the SPS sample and the corresponding spectra of the conventionally prepared silica glass, that the short- and medium-range order is virtually the same in both materials. Raman spectroscopy, however, suggests that the number of three- and four-membered rings is significantly smaller in the SPS sample compared to the conventionally prepared sample. Based on these results we conclude that it is possible to prepare glasses by compacting amorphous powders by the SPS process. The SPS process may therefore enable the preparation of glasses with compositions inaccessible by conventional methods. - Graphical abstract: We report the preparation of SiO{sub 2} glass by consolidating a highly dispersed silicic acid powder with the Spark Plasma Sintering (SPS) technique. The glass was characterized by ellipsometry, transmission electron microscopy (TEM), infrared reflectance and transmittance spectroscopy, as well as by Raman-, UV-Vis-NIR- and solid-state nuclear magnetic resonance (NMR

  5. Reentrant condensation of lysozyme: Implications for studying dynamics of lysozyme in aqueous solutions of lithium chloride

    SciTech Connect

    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.

  6. Twin-plane reentrant edge growth of rhombohedra boron suboxide platelets

    NASA Astrophysics Data System (ADS)

    Yu, Zhiyang; Jiang, Jun; Yuan, Jun; Zhu, Jing

    2010-04-01

    Large quantities of rhombohedra and elongated rhombohedra boron suboxide platelets with flat (0 0 1) surface have been synthesized through conventional solid state reaction. Detailed structural investigations by selected area electron diffraction (SAED) and high-resolution electron microscopy (HRTEM) of these platelets are presented. We present the direct experimental observation of extensive lateral (0 0 1) microtwins in rhombohedra platelets and they give rise to the fractional diffractions spots. It is believed that the growth of these rhombohedra platelets is prompted by the twin-plane reentrant edge (TPRE) mechanism. The transition from rhombohedra platelets to elongated rhombohedra platelets in morphology is probably the result of catalytic growth at the apexes of the platelets. This proposed growth model can be representative of various platelets with low defects formation energy, especially in twinned crystals having a rhombohedra structure. Besides, the presence of extensive microtwins will yield interesting physical properties and probably results in the broadening of photoluminescence (PL) spectra from the rhombohedra and elongated rhombohedra platelets.

  7. Light scattering resonances in arbitrarily shaped one-dimensional reentrant surfaces

    NASA Astrophysics Data System (ADS)

    Negrete-Regagnon, Pedro; Hernandez-Walls, Rafael; Ruiz-Cortes, Victor

    2000-09-01

    Multiple scattering and shape-related effects are an active and important field of research in the area of diffraction and scattering of electromagnetic waves by rough surfaces. Most of the rigorous numerical techniques for dealing with this problem were limited to the treatment of single-valued surfaces. We have extended the formulation of Mendoza- Suarez and Mendez (1997) for dealing with multi-valued profile functions in order to study the scattering of reentrant surfaces or cavities in both, the near and far-field. We have evaluated the near-field in circular cavities with narrow entrances, as well as in the case of clusters of rods or cylinders. Resonant frequencies are clearly identified for these structures. We have also found that our model could be useful to predict wave-induced oscillations in harbors of arbitrary geometry. This comes form the fact that the mathematical formulation of the problem of light scattering by cavities (in the case of p polarization) is similar to the one employed in the case of harbors of arbitrary shape, when a water wave arrives at its entrance (Hwang and Tuck, 1970; Lee, 1971). The results obtained with our model are in close agreement with previously reported theories and experimental data.

  8. Topological textures and metal-insulator transition in Reentrant Integer Quantum Hall Effect: role of disorder

    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.

  9. Reentrant condensation of lysozyme: Implications for studying dynamics of lysozyme in aqueous solutions of lithium chloride.

    PubMed

    Mamontov, Eugene; O'Neill, Hugh

    2014-06-01

    Recent studies have outlined the use of eutectic solutions 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 solvent crystallization. The eutectic point in a (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 used 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. PMID:26819974

  10. Reentrant behavior of effective attraction between like-charged macroions immersed in electrolyte solution

    NASA Astrophysics Data System (ADS)

    Akiyama, Ryo; Sakata, Ryo; Ide, Yuji

    2011-03-01

    Strong effective attraction between like-charged macroions appears in electrolyte solution. The attraction between the monomers in DNA is experimentally measured[1,2]. The attraction depends on the concentration of electrolyte. When the electrolyte concentration is low, the effective interaction between like-charged macroions is repulsive. Addition of salt inverts the sign of the effective interaction. The dimer of macroions is strongly stabilized when the charges of the macroions are enough large and the electrolyte concentration is ˜1 mM. However the strong attraction disappears, when the electrolyte concentration becomes higher than 0.1 M. We studied this reentrant behavior on the basis of the HNC-OZ theory with a simple model. The attraction is caused by the overlap of ionic clouds which surround the macroions. This ionic "covalent" bond, namely shared-ion-bond, is similar to the molecular covalent bond consists of electronic cloud. (See Fig. 1.) Moreover, the result s indicates that the role of co-ions is important in disappearing the attraction.We will discuss the detail of our results and a model of molecular motor driven by the growth of actin filament in neutrophil (a kind of white blood cells) in our presentation.

  11. Novel phases and reentrant melting of two-dimensional colloidal crystals.

    PubMed

    Radzihovsky, L; Frey, E; Nelson, D R

    2001-03-01

    We investigate two-dimensional (2D) melting in the presence of a one-dimensional (1D) periodic potential as, for example, realized in recent experiments on 2D colloids subjected to two interfering laser beams. The topology of the phase diagram is found to depend primarily on two factors: the relative orientation of the 2D crystal and the periodic potential troughs, which selects a set of Bragg planes running parallel to the troughs, and the commensurability ratio p=a(')/d of the spacing a(') between these Bragg planes to the period d of the periodic potential. The complexity of the phase diagram increases with the magnitude of the commensurabilty ratio p. Rich phase diagrams, with "modulated liquid," "floating," and "locked floating" solid and smectic phases are found. Phase transitions between these phases fall into two broad universality classes, roughening and melting, driven by the proliferation of discommensuration walls and dislocations, respectively. We discuss correlation functions and the static structure factor in these phases, and make detailed predictions about the universal features close to the phase boundaries. We predict that for charged systems with highly screened short-range interactions, these melting transitions are generically reentrant as a function of the strength of the periodic potential, a prediction that is in accord with recent 2D colloid experiments. Implications of our results for future experiments are also discussed. PMID:11308653

  12. 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.

  13. 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.

  14. 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.

  15. Creating tuneable microwave media from a two-dimensional lattice of re-entrant posts

    SciTech Connect

    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.

  16. Binary mixtures of liquid crystalline compounds with a reentrant smectic-A* phase.

    PubMed

    Podoliak, Natalia; Novotná, Vladimíra; Glogarová, Milada; Pociecha, Damian; Gorecka, Ewa; Kašpar, Miroslav; Hamplová, Věra

    2011-12-01

    Binary mixtures of chiral liquid crystalline homologs have been studied. One compound designated 9ZBL exhibited reentrancy of a paraelectric smectic-A* phase, SmA*(RE), below the ferroelectric SmC* phase in the SmA*-SmC*-SmA*RE phase sequence. Stabilization of the SmA(RE) phase is established from studying binary mixtures of 9ZBL with its neighboring homologs 8ZBL and 10ZBL. Compound 8ZBL exhibits only SmA* phase in a wide temperature range and for 10ZBL the SmA*-SmC* phase sequence is observed on cooling. X-ray studies, dielectric spectroscopy, polarization, and tilt angle measurements have been carried out to characterize studied materials. For binary mixtures 9ZBL-10ZBL the reentrant SmA_(RE*) phase is observed for all studied concentrations. For binary mixtures 9ZBL-8ZBL a very small amount of 8ZBL (up to 0.5 mole %) causes disappearance of the SmC* phase. Nevertheless, a small anomaly in the temperature dependencies of the layer spacing, d(T), accompanied by a significant decrease in diffracted x-ray intensity occurs within the SmA* phase for mixtures containing up to 20 mole % of 8ZBL. This anomaly is evidence of the existence of a boundary between the SmA* and SmA(RE*) phases, thus proving their different nature.

  17. Coexistence of considerable inter-particle interactions and spin-glass behavior in La{sub 0.7}Ca{sub 0.3}MnO{sub 3} nanoparticles

    SciTech Connect

    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.

  18. Ferrimagnetic and spin-glass transition in the Aurivillius compound SrBi{sub 5}Ti{sub 4}Cr{sub 0.5}Co{sub 0.5}O{sub 18}

    SciTech Connect

    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.

  19. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    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.

  20. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    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.

  1. Synthesis of new amorphous metallic spin glasses

    DOEpatents

    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.

  2. Glass microspheres

    SciTech Connect

    Day, D.E.; Ehrhardt, G.J.

    1988-12-06

    This patent describes a glass microsphere having a diameter of about 54 micrometers or less and adapted for radiation therapy of a mammal. The glass consists of essentially an yttrium oxide-aluminosilicate glass composition lying substantially within a quadrilateral region of the ternary composition diagram of the yttria-alumina-silica system, the quadrilateral region being defined by its four corners having the following combination of weight proportions of the components: 20% silica, 10% alumina, 70% yttria; 70% silica, 10% alumina, 20% yttria; 70% silica, 20% alumina, 10% yttria; and 20% silica, 45% alumina, 35% yttria, the glass having a chemical durability such that subsequent to irradiation and administration of the microsphere to the mammal, the mircosphere will not release a significant amount of yttrium-90 into the mammal's system.

  3. Glass electrolytes

    SciTech Connect

    Not Available

    1984-06-25

    The objective of this research is a glass electrolyte for use in sodium/sulfur batteries that has a low resistivity (100 ohm-cm at 300/sup 0/C) and is stable in the cell environment. Experiments in this program are focussed on glasses in the quaternary system: soda, alumina, zirconia and silica. The FY 1983 research on glass analogs of NASICON, parallel thermodynamic calculations, and a review of the literature in the areas of glass conductivity and corrosion resistance led to selection of this system for more detailed investigation. The main program elements are: (1) conductivity measurements at 300 to 500/sup 0/C; (2) differential thermal analysis for determination of glass-transition and crystallization temperatures; (3) static corrosion tests at 400/sup 0/C using Na, Na/sub 2/S/sub 4/, and S; (4) mechanical strength and fracture toughness measurements; and (5) sodium/sulfur cell tests at 350/sup 0/C. Elements (1) and (2) are nearly completed; element (3) is being initiated using the glasses prepared for (1) and (2), and elements (4) and (5) will begin in the first and second quarters of FY 1985, respectively. Fourteen quaternary glasses having a broad range of compositions have been made. The resistivities of these glasses at 300/sup 0/C extended from 130 to 3704 ohm-cm; the activation energies for conduction extended from 0.488 to 0.684 eV, and the glass transition temperatures extended from 397 to 685/sup 0/C. Through a multiple linear regression analysis of these data response surfaces were generated for resistivity, activation energy for conduction, and glass transition temperature over the composition region within the quaternary system that is bounded by SiO/sub 2/, Na/sub 2/O/sub 3/, Na/sub 2/AlO/sub 4/ and Na/sub 2/ZrO/sub 3/. These response surfaces indicated a new region of high conductivity and high glass transition temperature in the neighborhood of 42% soda, 31% silica and 27% alumina plus zirconia.

  4. Low Temperature Calorimetric Investigation of the Spin Glasses: MERCURY(1-X)MANGANESE(X)TELLURIDE and COBALT(X)GALLIUM(1-X); and of the Compounds: Mercury-Telluride Alpha - Mercury Sulfide, Beta - Mercury Sulfide, THALLIUM(3)ARSENIC SELENIDE(3), THALLIUM(3)ANTIMONY SULFIDE(3), Silver-Thallium - and Silver-Thallium

    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

  5. Randomised Evaluation of modified Valsalva Effectiveness in Re-entrant Tachycardias (REVERT) study

    PubMed Central

    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

  6. An Appalachian Mesozoic compressional event: Evidence from the Pennsylvania Reentrant-New York Promontory

    SciTech Connect

    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.

  7. Reentrant radio-frequency resonator for automated phase-equilibria and dielectric measurements in fluids

    SciTech Connect

    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.

  8. Dipolar ferromagnets and glasses (invited)

    SciTech Connect

    Rosenbaum, T.F.; Wu, W.; Ellman, B.; Yang, J. ); Aeppli, G. ); Reich, D.H. )

    1991-11-15

    What is the ground state and what are the dynamics of 10{sup 23} randomly distributed Ising spins We have attempted to answer these questions through magnetic susceptibility, calorimetric, and neutron scattering studies of the randomly diluted dipolar-coupled Ising magnet LiHo{sub {ital x}}Y{sub 1{minus}{ital x}}F{sub 4}. The material is ferromagnetic for dipole concentrations at least as low as {ital x}=0.46, with a Curie temperature obeying mean-field scaling relative to that of pure LiHoF{sub 4}. In the dilute spin limit, an {ital x}=0.045 crystal shows very unusual glassy properties characterized by {ital decreasing} barriers to relaxation as {ital T}{r arrow}0. Its properties are consistent with a single low degeneracy ground state with a large gap for excitations. A slightly more concentrated {ital x}=0.167 sample, however, supports a complex ground state with no appreciable gap, in accordance with prevailing theories of spin glasses. The underlying causes of such disparate behavior are discussed in terms of random clusters as probed by neutron studies of the {ital x}=0.167 sample. In addition to tracing the evolution of the glassy and ferromagnetic states with dipole concentration, we investigate the effects of a transverse magnetic field on the Ising spin glass, LiHo{sub 0.167}Y{sub 0.833}F{sub 4}. The transverse field mixes the eigenfunctions of the ground-state Ising doublet with the otherwise inaccessible excited-state levels. We observe a rapid decrease in the characteristic relaxation times, large changes in the spectral form of the relaxation, and a depression of the spin-glass transition temperature with the addition of quantum fluctuations.

  9. Structural ordering and glass forming of soft spherical particles with harmonic repulsions

    SciTech Connect

    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.

  10. 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.

  11. Reentrant behavior in the superconducting phase-dependent resistance of a disordered two-dimensional electron gas

    SciTech Connect

    den Hartog, S.G.; van Wees, B.J.; Klapwijk, T.M.; Nazarov, Y.V.; Borghs, G.

    1997-12-01

    We have investigated the bias-voltage dependence of the phase-dependent differential resistance of a disordered T-shaped two-dimensional electron gas coupled to two superconducting terminals. The resistance oscillations first increase upon lowering the energy. For bias voltages below the Thouless energy, the resistance oscillations are suppressed and disappear almost completely at zero bias voltage. We find a qualitative agreement with the calculated reentrant behavior of the resistance and discuss quantitative deviations. {copyright} {ital 1997} {ital The American Physical Society}

  12. Dynamic phase transition properties for the mixed spin-(1/2, 1) Ising model in an oscillating magnetic field

    NASA Astrophysics Data System (ADS)

    Ertaş, Mehmet; Keskin, Mustafa

    2015-08-01

    Herein we study the dynamic phase transition properties for the mixed spin-(1/2, 1) Ising model on a square lattice under a time-dependent magnetic field by means of the effective-field theory (EFT) with correlations based on Glauber dynamics. We present the dynamic phase diagrams in the reduced magnetic field amplitude and reduced temperature plane and find that the phase diagrams exhibit dynamic tricitical behavior, multicritical and zero-temperature critical points as well as reentrant behavior. We also investigate the influence of frequency (ω) and observe that for small values of ω the mixed phase disappears, but for high values it appears and the system displays reentrant behavior as well as a critical end point.

  13. Improving the performance and emission characteristics of a single cylinder diesel engine having reentrant combustion chamber using diesel and Jatropha methyl esters.

    PubMed

    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.

  14. Improving the performance and emission characteristics of a single cylinder diesel engine having reentrant combustion chamber using diesel and Jatropha methyl esters.

    PubMed

    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

  15. Pinhole Glasses

    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.

  16. Pinhole Glasses

    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…

  17. Modulation of conduction and refractoriness in atrioventricular junctional reentrant circuit. Effect on reentry initiated by atrial extrastimulus.

    PubMed Central

    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

  18. Re-entrant nematic behavior in the 7OCB+9OCB mixtures: evidence for multiple nematic-smectic tricritical points.

    PubMed

    Cusmin, Paul; Salud, Josep; López, David O; de la Fuente, Maria R; Diez, Sergio; Pérez-Jubindo, Miguel A; Barrio, María; Tamarit, Josep Ll

    2006-12-28

    The metastable phase diagram of the two-component system heptyloxycyanobiphenyl (7OCB)+nonyloxycyanobiphenyl (9OCB) was determined by means of modulated differential scanning calorimetry (MDSC) and optical microscopy measurements. It was experimentally established that the 7OCB+9OCB two-component system exhibits a monotropic re-entrant nematic behavior. A complete quantitative thermodynamic analysis, through Oonk's equal G analysis, was performed, allowing for the calculation of the monotropic re-entrant behavior and the prediction of two tricritical points, one of them experimentally accessible for the SmAd-to-N transition and the other non-experimentally accessible for the RN-to-SmAd transition. From specific-heat measurements, latent heats were obtained for those mixtures displaying a first-order SmAd-to-N transition. Additionally, for some mixtures, the specific-heat critical exponents (alpha), through the second-order SmAd-to-N transition, were obtained. Both batches of data enable us to access to the experimental tricritical temperature for the SmAd-to-N transition.

  19. Rivers, re-entrants, and 3D variations in orogenic wedge development: a case study of the NW Indian Himalaya

    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

  20. Unveiling the photonic spin Hall effect with asymmetric spin-dependent splitting.

    PubMed

    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

  1. High-spin and low-spin states in Invar and related alloys

    NASA Astrophysics Data System (ADS)

    Moruzzi, V. L.

    1990-04-01

    Total-energy band calculations that show the coexistence of a high-spin and low-spin state in fcc transition metals and alloys are presented. The energy difference between the two states is shown to be a function of the electron concentration and to vanish at 8.6. At larger electron concentrations the low-temperature state is the high-spin state, and the thermal expansion is shown to pause at a system-dependent characteristic temperature. At lower electron concentrations the low-temperature state is the low-spin state, and enhanced thermal expansion is expected. An analysis that leads to a qualitative understanding of the thermal properties of Invar and that implies a connection with martensitic transformations and spin glasses in related alloys is presented. For Invar a magnetic collapse from the high-spin to the low-spin state at a pressure of 55 kbar is predicted.

  2. Unreachable glass transition in dilute dipolar magnet.

    PubMed

    Biltmo, A; Henelius, P

    2012-01-01

    In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo(0.045)Y(0.955)F(4) freezes, but that the transition is unreachable because of dynamics that are 10(7) times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

  3. Unreachable glass transition in dilute dipolar magnet

    NASA Astrophysics Data System (ADS)

    Biltmo, A.; Henelius, P.

    2012-05-01

    In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo0.045Y0.955F4 freezes, but that the transition is unreachable because of dynamics that are 107 times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

  4. Discontinuous nature of the repulsive-to-attractive colloidal glass transition.

    PubMed

    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.

  5. Children's Glasses

    NASA Astrophysics Data System (ADS)

    Akerskog, Gunnar; Soderlund, Jan

    1980-07-01

    There is a common opinion among eye specialists and opticians that children's glasses often are not shaped for optimal fitting. A fundamental reason for this is the lack of data for the shaping of the bows, with the result that most children's glasses are reduced copies of adult's glasses. This report describes a photogrammetric method for collection of primary data for manufac-turing bows for children. An ordinary amateur camera was equipped with a stereo-adapter. With a few arrangements, such as projecting a pattern on the face and keeping the hair away from the ears, 600 children were photographed. A calibration photograph was exposed at the beginning and end of each film or when the equipment had been transported or otherwise disturbed. The photographs were measured in a stereocomparator and the coordinates analytically corrected for distortion. After determination of model coordinates the requested geometric information, such as pupillar distance, eye-ear distance, location of the bridge of the nose etc, was calculated. The shapes of average noses were presented as profile plots.

  6. Reprint of 'Model of unidirectional block formation leading to reentrant ventricular tachycardia in the infarct border zone of postinfarction canine hearts'

    PubMed Central

    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

  7. XPS and SAM studies of the surface chemistry of lunar impact glasses including 12054

    NASA Technical Reports Server (NTRS)

    Housley, R. M.; Grant, R. W.; Cirlin, E. H.

    1979-01-01

    We report and discuss quantitative X-ray photoemission (XPS) analyses of mm size areas and qualitative scanning Auger microprobe (SAM) analyses of micron size areas on the surfaces of impact glass coatings found on fragments in the 14161 coarse fines and on the top surface, and a reentrant crack surface of rock 12054. The data suggest that some segregation occurs during impact glass formation leading to surface enrichments in Si and depletions in Mg, Al, Ca, and Ti. The magnitude of the effect appears fairly small, although the complexity of the surfaces severely complicates the data analysis. Because of the complexity of the surfaces, both XPS and SAM data were essential. A search for direct evidence of either solar wind sputter erosion or vapor deposition on the exposed top surface of 12054 provided interesting results which we cannot yet fully interpret. Both this surface and the surface from the re-entrant crack showed enrichments of more than a factor of two in Fe with respect to the bulk.

  8. Structure of rhenium-containing sodium borosilicate glass

    SciTech Connect

    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.

  9. Magnetic Field Effects in a Correlated Electron System with Spin-State Degree of Freedom — Implications for an Excitonic Insulator —

    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.

  10. Metallic 2D Surface State of Silicon by Ionic Liquid gating and observation of Reentrant Insulating behavior

    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.

  11. Negative spontaneous magnetization and semi-spin glass magnetic order in mixed spinel Co{sub 0.6}Zn{sub 0.4}Fe{sub 1.7}Mn{sub 0.3}O{sub 4}

    SciTech Connect

    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.

  12. Impact Strength of Glass and Glass Ceramic

    NASA Astrophysics Data System (ADS)

    Bless, Stephan; Tolman, John

    2009-06-01

    Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning, Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression and the steady-state strength. For both glasses, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic---as opposed to intrinsic---property.

  13. Spin ejector

    DOEpatents

    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.

  14. CRYSTALLIZATION IN MULTICOMPONENT GLASSES

    SciTech Connect

    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.

  15. Gamma radiation induced changes in nuclear waste glass containing Eu

    NASA Astrophysics Data System (ADS)

    Mohapatra, M.; Kadam, R. M.; Mishra, R. K.; Kaushik, C. P.; Tomar, B. S.; Godbole, S. V.

    2011-10-01

    Gamma radiation induced changes were investigated in sodium-barium borosilicate glasses containing Eu. The glass composition was similar to that of nuclear waste glasses used for vitrifying Trombay research reactor nuclear waste at Bhabha Atomic Research Centre, India. Photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques were used to study the speciation of the rare earth (RE) ion in the matrix before and after gamma irradiation. Judd-Ofelt ( J- O) analyses of the emission spectra were done before and after irradiation. The spin counting technique was employed to quantify the number of defect centres formed in the glass at the highest gamma dose studied. PL data suggested the stabilisation of the trivalent RE ion in the borosilicate glass matrix both before and after irradiation. It was also observed that, the RE ion distributes itself in two different environments in the irradiated glass. From the EPR data it was observed that, boron oxygen hole centre based radicals are the predominant defect centres produced in the glass after irradiation along with small amount of E’ centres. From the spin counting studies the concentration of defect centres in the glass was calculated to be 350 ppm at 900 kGy. This indicated the fact that bulk of the glass remained unaffected after gamma irradiation up to 900 kGy.

  16. Electron beam irradiation effects in Trombay nuclear waste glass

    NASA Astrophysics Data System (ADS)

    Mohapatra, M.; Kadam, R. M.; Mishra, R. K.; Dutta, D.; Pujari, P. K.; Kaushik, C. P.; Kshirsagar, R. J.; Tomar, B. S.; Godbole, S. V.

    2011-10-01

    Spectroscopic investigations were carried out on electron beam irradiated sodium barium borosilicate glasses, which is the base glass for immobilization of nuclear high level radioactive waste, generated from the research reactors at Bhabha Atomic Research Centre, Trombay. This was done in order to access the defects generated in it under long term irradiation. Electron paramagnetic resonance was used to identify the defect centers generated in the borosilicate glass after irradiation. In addition, positron annihilation spectroscopy and infrared investigations were done on the samples to evaluate the radiation induced changes in the glass. It was found that, boron-oxygen and silicon based hole centers along with E' centers are getting formed in the glass after irradiation due to the breaking of the Si sbnd O bonds at regular tetrahedron sites of Si sbnd O sbnd Si. The positron annihilation spectroscopy data gave an idea regarding the free volume size and fraction of the glasses before and after irradiation. It was seen that, after irradiation the free volume size in the glass increased with creation of additional sites. Microwave power variation and temperature variation studies suggested the formation of at least five different radicals in the irradiated glasses. The spin Hamiltonian parameter of all the radical species were determined by computer simulation. An electron paramagnetic resonance spin counting technique was employed to evaluate the defect concentration in the glasses after irradiation.

  17. IMPACT STRENGTH OF GLASS AND GLASS CERAMIC

    SciTech Connect

    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.

  18. Impact Strength of Glass and Glass Ceramic

    NASA Astrophysics Data System (ADS)

    Bless, S.; Tolman, J.

    2009-12-01

    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.

  19. Free-Energy Bounds for Hierarchical Spin Models

    NASA Astrophysics Data System (ADS)

    Castellana, Michele; Barra, Adriano; Guerra, Francesco

    2014-04-01

    In this paper we study two non-mean-field (NMF) spin models built on a hierarchical lattice: the hierarchical Edward-Anderson model (HEA) of a spin glass, and Dyson's hierarchical model (DHM) of a ferromagnet. For the HEA, we prove the existence of the thermodynamic limit of the free energy and the replica-symmetry-breaking (RSB) free-energy bounds previously derived for the Sherrington-Kirkpatrick model of a spin glass. These RSB mean-field bounds are exact only if the order-parameter fluctuations (OPF) vanish: given that such fluctuations are not negligible in NMF models, we develop a novel strategy to tackle part of OPF in hierarchical models. The method is based on absorbing part of OPF of a block of spins into an effective Hamiltonian of the underlying spin blocks. We illustrate this method for DHM and show that, compared to the mean-field bound for the free energy, it provides a tighter NMF bound, with a critical temperature closer to the exact one. To extend this method to the HEA model, a suitable generalization of Griffith's correlation inequalities for Ising ferromagnets is needed: since correlation inequalities for spin glasses are still an open topic, we leave the extension of this method to hierarchical spin glasses as a future perspective.

  20. 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)