Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A29: Spin Glasses and Disordered Magnetic Materials 
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Sponsoring Units: GMAG Chair: Ben Ueland, National Institute of Standards and Technology, Center for Neutron Research Room: 333 
Monday, March 16, 2009 8:00AM  8:12AM 
A29.00001: Probing the relation between structural glasses and 3spin spin glasses using onedimensional models Derek Larson, Helmut G. Katzgraber, A.P. Young Motivated by a proposed connection between 3spin spin glasses and structural glasses, we have performed Monte Carlo simulations on a onedimensional longrange Ising glass with powerlaw interactions involving 3spins. Varying the exponent of the powerlaw interactions is analogous to changing the space dimension of a corresponding shortrange 3spin model. We present results of a finitesize scaling analysis of the twopoint correlation length, and compare our results with the prediction of Moore and Yeo that the threespin model is in the same universality class as an Ising spin glass in a magnetic field. [Preview Abstract] 
Monday, March 16, 2009 8:12AM  8:24AM 
A29.00002: Study of the de AlmeidaThouless line using powerlaw diluted onedimensional Ising spin glasses Helmut G. Katzgraber, Derek A. Larson, A.P. Young We test the existence of a spinglass state in an externallyapplied (random) magnetic field via Monte Carlo simulations of a powerlaw diluted onedimensional Ising spin glass. The model has the advantage over conventional shortrange models in that by tuning the exponent of the powerlaw interactions we are able to scan the full range of possible behaviors from the infiniterange to the nonmeanfield regime. Furthermore, due to the average fixed connectivity very large linear system sizes can be studied. An analysis of the twopoint correlation length shows that the system in the nonmeanfield universality class does not order in a field. This suggests that there is no de AlmeidaThouless line for shortrange Ising spin glasses below the upper critical dimension. [Preview Abstract] 
Monday, March 16, 2009 8:24AM  8:36AM 
A29.00003: Reentrant and Forward Phase Diagrams of the Anisotropic ThreeDimensional Ising Spin Glass Can G\"uven, A. Nihat Berker, Michael Hinczewski, Hidetoshi Nishimori The spatially uniaxially anisotropic d=3 Ising spin glass is solved exactly on a hierarchical lattice.[1] Five different ordered phases, namely ferromagnetic, columnar, layered, antiferromagnetic, and spinglass phases, are found in the global phase diagram. The spinglass phase is more extensive when randomness is introduced within the planes than when it is introduced in lines along one direction. Phase diagram crosssections, with no Nishimori symmetry, with Nishimori symmetry lines, or entirely imbedded into Nishimori symmetry, are studied. The boundary between the ferromagnetic and spinglass phases can be either reentrant or forward, that is either receding from or penetrating into the spinglass phase, as temperature is lowered. However, this boundary is always reentrant when the multicritical point terminating it is on the Nishimori symmetry line. [1] C. G\"uven, A.N. Berker, M. Hinczewski, and H. Nishimori, Phys. Rev. E 77, 061110 (2008). [Preview Abstract] 
Monday, March 16, 2009 8:36AM  8:48AM 
A29.00004: The BlumeEmeryGriffiths Spin Glass and Inverted Tricritical Points V. Ongun \"Oz\c{c}elik, A. Nihat Berker The BlumeEmeryGriffiths spin glass is studied by renormalizationgroup theory in d=3.[1] The boundary between the ferromagnetic and paramagnetic phases has firstorder and two types of secondorder segments. This topology includes an inverted tricritical point, firstorder transitions replacing secondorder transitions as temperature is lowered. The phase diagrams show disconnected spinglass regions, spinglass and paramagnetic reentrances, and complete reentrance, where the spinglass phase replaces the ferromagnet as temperature is lowered for all chemical potentials. [1] V.O. \"Oz\c{c}elik and A.N. Berker, Phys. Rev. E 78, 031104 (2008). [Preview Abstract] 
Monday, March 16, 2009 8:48AM  9:00AM 
A29.00005: QuenchedVacancy Induced SpinGlass Order G\"ul G\"ulpinar, A. Nihat Berker The ferromagnetic phase of an Ising model in d=3, with any amount of quenched antiferromagnetic bond randomness, is shown to undergo a transition to a spinglass phase under sufficient quenched bond dilution.[1] This general result, demonstrated here with the numerically exact renormalizationgroup solution of a d=3 hierarchical lattice, is expected to hold true generally, for the cubic lattice and for quenched site dilution. Conversely, in the ferromagneticspinglassantiferromagnetic phase diagram, the spinglass phase expands under quenched dilution at the expense of the ferromagnetic and antiferromagnetic phases. In the ferrospinglass phase transition induced by quenched dilution reentrance is seen, as previously found for the ferrospinglass transition induced by increasing the antiferromagnetic bond concentration. [1] G. G\"ulpinar and A.N. Berker, arXiv:0811.0025v1 [cond mat.disnn] (2008). [Preview Abstract] 
Monday, March 16, 2009 9:00AM  9:12AM 
A29.00006: Nonequilibrium spin glass dynamics with the Janus computer David Yllanes, F. Belletti, A. Cruz, L.A. Fernandez, A. GordilloGuerrero, M. Guidetti, A. Maiorano, F. Mantovani, E. Marinari, V. MartinMayor, J. Monforte, A. Munoz Sudupe, D. Navarro, G. Parisi, S. PerezGaviro, J.J. RuizLorenzo, S.F. Schifano, D. Sciretti, A. Tarancon, R. Tripiccione The out of equilibrium evolution of the EdwardsAnderson spin glass is followed for a tenth of a second, effectively halving the (logarithmic) temporal gap between previous simulations and experiments. In fact, we have been able to make safe predictions about the behavior at experimental times, using mild extrapolations. This work has been made possible by Janus, a special purpose computer designed by our collaboration. We have thoroughly studied the spin glass correlation functions and the growth of the coherence length for $L\!=\!80$ lattices in $3D$,using $L\!=\!24,40$ lattices to check for finite size effects. We present clear evidence for a replicon correlator. Our main conclusion is that these spin glasses follow noncoarsening dynamics, at least up to the experimentally relevant time scales. [Preview Abstract] 
Monday, March 16, 2009 9:12AM  9:24AM 
A29.00007: Chaotic Spin Correlations in Frustrated Ising Hierarchical Lattices Ne\c{s}e Aral, A. Nihat Berker Spinspin correlations are calculated in frustrated hierarchical Ising models that exhibit chaotic renormalizationgroup behavior. [1] The spinspin correlations, as a function of distance, behave chaotically. The far correlations, but not the near correlations, are sensitive to small changes in temperature or frustration, with temperature changes having a larger effect. On the other hand, the calculated free energy, internal energy, and entropy are smooth functions of temperature. The recursionmatrix calculation of thermodynamic densities in a chaotic band is demonstrated. The spectrum of Lyapunov exponents is calculated as a function of frustration. [1] N. Aral and A.N. Berker, arXiv:0810.4586v1 [condmat.disnn] (2008). [Preview Abstract] 
Monday, March 16, 2009 9:24AM  9:36AM 
A29.00008: Tunable domain pinning in a RandomField Ising Ferromagnet D. M. Silevitch, G. Aeppli, T.F. Rosenbaum The diluted magnetic salt $\mathrm{Li(Ho,Y)F}_4$ was shown recently [Nature {\bf 448} 567570 (2007)] to be the first ferromagnetic realization of the randomfield Ising model, where the strength of the random fields can be tuned by an external magnetic field. These randomfield effects can be used to continuously and reversibly vary the pinning potential of the magnetic domains, allowing us to tune the hysteretic behavior. Magnetization measurements reveal enhanced pinning in the randomfield regime as well as a temperaturedependent crossover into a regime dominated by quantum fluctuations. [Preview Abstract] 
Monday, March 16, 2009 9:36AM  9:48AM 
A29.00009: A strongly disordered spin glass and minimum spanning trees Thomas Jackson, Nicholas Read We investigate the ground state structure of a strongly
disordered spin glass model proposed by Newman and Stein (NS). In
the strong disorder limit, frustration is negligible and the
problem of identifying ground states is equivalent to the minimum
spanning tree (MST) problem in combinatorial optimization: given
an edgeweighted graph, the MST is the subset of edges that
connects all vertices, has no cycles, and minimizes the total
edge weight. Here the weights are quenched random variables, and
we use a relation between Kruskal's greedy algorithm for finding
the MST and percolation. We solve this random MST on the Bethe
lattice with appropriate boundary conditions, which defines a
meanfield theory valid above $d_c=6$ (NS proposed $d_c=8$).
Above $d_c$, NS showed that the spin glass model has infinitely
many ground states, but only a single pair below $d_c$. For
$d 

A29.00010: ABSTRACT WITHDRAWN 
Monday, March 16, 2009 10:00AM  10:12AM 
A29.00011: Overlap as a Measure of SpinGlass Memory and a Probe of Free Energy Landscape Wen Luo, Michael Mihalco, Thomas E. Stone, Susan R. McKay The degree of history dependence and the structure of the free energy landscape of the spin glass are both indicators of the complexity of this ordered phase. Using the Ising antiferromagnet on a triangular lattice, diluted with quenched random ferromagnetic bonds, we probe these indicators through repeated cycling between two temperatures. We consider cases in which both temperatures are within the spinglass phase, and systematically vary the temperature difference between initial and final states. These results are compared with the same cycling pattern with one temperature inside and the other outside of the spinglass phase. The average overlap between lowtemperature states provides a quantitative measure of the system's memory, and is nonzero when the system remains within the spinglass phase during cycling. A plot of the overlaps of the low temperature states and their differences in internal energy shows no simple relationship between overlap and internal energy. States with almost identical internal energies often have very little overlap. [Preview Abstract] 
Monday, March 16, 2009 10:12AM  10:24AM 
A29.00012: Quantum Effects for Interaction of Electron with coupled magnetic local spin chains Fatih Dogan, Lucian Covaci, Wonkee Kim, Frank Marsiglio In this talk, we will look at time dependent interaction of an electron with ferromagnetic chain. We will show that ferromagnetic interactions between magnetic spins cause the electron interacting with them to change its energy and depending on the strength of interactions form a bound state. These effects are visible through the resulting state of the electron. Experimental suggestions will be given to observe this quantum behavior. [Preview Abstract] 
Monday, March 16, 2009 10:24AM  10:36AM 
A29.00013: Avalanche Spatial Structure: Viewing Crackling Noise through Windows YanJiun Chen, Stefanos Papanikolaou, James P. Sethna, Gianfranco Durin, Stefano Zapperi In imaging experiments of Barkhausen noise in thin films, magnetic avalanches at the boundaries present challenges to analysis. Large avalanches are removed from the distribution, and the portion inside the viewing window may sometimes be treated as smaller avalanches. We analyze the scaling behavior of different categories of avalanches in artificiallywindowed simulations of Barkhausen noise to examine the effect of window size on scaling relations. In passing, we discuss the average spatial shapes of avalanches, multivariable scaling functions, and the use of nonlinearleastsquares methods for exploring and reporting universal scaling functions. [Preview Abstract] 
Monday, March 16, 2009 10:36AM  10:48AM 
A29.00014: Avalanche Average Shapes: Meanfield temporal average avalanche shape Stefanos Papanikolaou, Christopher R. Myers, Francesca Colaiori, Karen E. Daniels, Gianfranco Durin, Stefano Zapperi, James P. Sethna The average temporal shape of avalanches has been a fruitful application of universality and critical scaling, with experimental and theoretical investigations particularly in the field of magnetic Barkhausen noise. The meanfield shapes of these avalanches have been thought to come in two forms: inverted parabolas for the infiniterange model and one lobe of a sinusoid for the singledegree of freedom ABBM model. We show that the infiniterange model can be mapped onto the earlier ABBM model, and that the average shape for both mean field theories is an inverted parabola, seemingly resolving the ambiguity. However, we also propose a new meanfield model including the effects of local saddlenode bifurcations on the dynamics, and analyze both its predictions for dynamical exponents and temporal average shapes. We compare with experimental results on sheared granular materials. [Preview Abstract] 
Monday, March 16, 2009 10:48AM  11:00AM 
A29.00015: Permutation Symmetric Critical Phases in Disordered NonAbelian Anyonic Chains Lukasz Fidkowski, Gil Refael, HanHsuan Lin, Paraj Titum Topological phases supporting nonabelian anyonic excitations have been proposed as candidates for topological quantum computation. We study disordered nonabelian anyonic chains based on the quantum groups $SU(2)_k$, a hierarchy that includes the $\nu=5/2$ FQH state and the proposed $\nu=12/5$ Fibonacci state, among others. We find that for odd $k$ these anyonic chains realize infinite randomness critical {\it phases} in the same universality class as the $S_k$ permutation symmetric multicritical points of Damle and Huse (arXiv:condmat/0207244). Indeed, we show that the pertinent subspace of these anyonic chains actually maps to the ${Z}_k \subset S_k$ symmetric sector of the DamleHuse model, and this ${Z}_k$ symmetry stabilizes the phase. [Preview Abstract] 
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