Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session C17: Magnetic Theory I 
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Sponsoring Units: GMAG Chair: Marcu Eisenbach, Oak Ridge National Laboratory Room: 319 
Monday, March 18, 2013 2:30PM  2:42PM 
C17.00001: First principles calculation of finite temperature magnetism in Ni Markus Eisenbach, Junqi Yin, Don M. Nicholson, Ying Wai Li We harnesses the computational power of massively parallel computers to calculate finite temperature magnetic properties by combining classical MonteCarlo calculations with our first principles multiple scattering electronic structure code (LSMS) for constrained magnetic states. Our previous calculations of Fe and $\mathrm{Fe_3C}$ [J. Appl. Phys. 109, 07E138 (2011)] only considered fluctuations in the local moment directions. Recent advances, both in the understanding of the WangLandau method used in our calculations [Phys. Rev. E 84, 065702(R) (2011)] and more powerful computing resources have enabled us to investigate Ni where the fluctuation in the magnitude of the local magnetic moments is of importance equal to their directional fluctuations. Here we will present our recent results for Ni that axpands our method to an even wider class of 3d element based ferromagnets. This research was sponsored by the Offices of Basic Energy Science (M.E. and D.M.N) and the Office of Advanced Computing Research (J.Y. and Y.W.L) of the US Department of Energy. This research used resources of the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory, which is supported by the Office of Science of the Department of Energy under contract DEAC0500OR22725. [Preview Abstract] 
Monday, March 18, 2013 2:42PM  2:54PM 
C17.00002: Sheared Ising models in three dimensions Alfred Hucht, Sebastian Angst The nonequilibrium phase transition in sheared threedimensional Ising models is investigated using Monte Carlo simulations in two different geometries corresponding to different shear normals [A. Hucht and S. Angst, EPL 100, 20003 (2012)]. We demonstrate that in the high shear limit both systems undergo a strongly anisotropic phase transition at exactly known critical temperatures $T_c$ which depend on the direction of the shear normal. Using dimensional analysis, we determine the anisotropy exponent $\theta=2$ as well as the correlation length exponents $\nu_\parallel=1$ and $\nu_\perp=1/2$. These results are verified by simulations, though considerable corrections to scaling are found. The correlation functions perpendicular to the shear direction can be calculated exactly and show OrnsteinZernike behavior. [Preview Abstract] 
Monday, March 18, 2013 2:54PM  3:06PM 
C17.00003: Heat capacity and new classification of phase transitions of fractional order: Ising model Vladimir Udodov Though the onedimensional Ising model has been the subject of a wide variety of analysis, it remains one of significant interest. Here we show that within the framework of Gibbs distribution this model can undergo fractional and arbitrarily high order phase transitions (PT) as the temperature changes at zero magnetic field. We suggest a new formula to define the order of PT for a special case of $T_{c} =$ 0; it is expressed via the critical exponent $\alpha $ associated with the heat capacity C. The unusual values of $\alpha $ (for example, $\alpha $ \textless $$10) are predicted. An interesting transition from 2D to 1D Ising model is considered. It corresponds the situations when the interparticle interaction is gradually switched off along one of two dimensions. As the system approaches the 1D limit, the critical temperature T$_{\mathrm{c}}$ tends to zero during which the critical exponent $\alpha $ changes continuously . The general formula for an order of PT offered extending formula R. Baxter and it is correct as for $T_{C}$ \textgreater\ 0 and $T_{C} =$ 0. The developed approach is equally applicable to quantum phase transitions. [Preview Abstract] 
Monday, March 18, 2013 3:06PM  3:18PM 
C17.00004: Finitesize scaling behavior of the magnetization distribution for 5d Ising model P. H. Lundow, A. Rosengren We have previously established that the magnetization distribution of the 5dimensional Ising model can be fitted by a $p,q$binomial distribution. Our extensive sampled Monte Carlo data can be used to determine the parameters' finitesize behavior. Now we use a long series expansion of the $p,q$binomial coefficients to obtain finitesize scaling formulas not only for the Binder ratio and the susceptibility near $T_c$, but also for the entire magnetization distribution, including correctionstoscaling terms. [Preview Abstract] 
Monday, March 18, 2013 3:18PM  3:30PM 
C17.00005: E8 spectrum and the finite temperature spin dynamics in the transverse field Ising chain with a small longitudinal field Jianda Wu, Marton Kormos, Qimiao Si When the transverse field Ising chain at its quantum critical point is subjected to a small longitudinal field, the perturbed conformal field theory led to a field theory with an exotic E8 symmetry [1]. Recent neutron scattering experiments have provided evidence for the lightest two particles in this E8 model in the quasi1D Ising ferromagnet CoNb2O6 [2]. While the zero temperature dynamics of the model is well known, its finitetemperature counterpart has not yet been systematically studied. We study the lowfrequency dynamical structure factor at finite temperatures using the formfactor method. We show that the dominant contribution to the dynamical structure factor comes from the scattering between two lightest particles, and discuss the implications of our results for the NMR relaxation rate. [1]A.B.Zamolodchikov, Int. J. Mod. Phys. A4, 4235(1989) [2]R. Coldea et al, Science 327, 177 (2010) [Preview Abstract] 

C17.00006: ABSTRACT WITHDRAWN 

C17.00007: ABSTRACT WITHDRAWN 
Monday, March 18, 2013 3:54PM  4:06PM 
C17.00008: Critical Point Estimation and LongRange Behavior in the OneDimensional XY Model Using Thermal Quantum and Total Correlations Baris Cakmak, Goktug Karpat, Zafer Gedik We investigate the thermal quantum and total correlations in the anisotropic XY spin chain in transverse field. While we adopt concurrence and geometric quantum discord to measure quantum correlations, we use measurementinduced nonlocality and an alternative quantity defined in terms of WignerYanase information to quantify total correlations. We show that the ability of these measures to estimate the critical point at finite temperature strongly depend on the anisotropy parameter of the Hamiltonian. We also identify a correlation measure which detects the factorized ground state in this model. Furthermore, we study the effect of temperature on longrange correlations. [Preview Abstract] 
Monday, March 18, 2013 4:06PM  4:18PM 
C17.00009: General method for finding ground state manifold of classical Heisenberg model Zhaoxi Xiong, XiaoGang Wen What is the ground state manifold of a classical Heisenberg model for an infinite crystal? It sounds simple, but the intuitive approach gets stuck for more general interaction patterns and higher crystal dimensions. In this paper we present an essentially analytical method that can deal with all systems with onespin unit cells and a broad class of systems with multispin unit cells. We also prove a theorem that guarantees that these systems must have some ``spiral ground states,'' which are coplanar. The method can be applied to classify all such systems, so that one can read off the ground state manifold of a Hamiltonian from some of its ``spectral properties.'' It can also be generalized to XY models, finite crystals, and anisotropic couplings, and may be helpful for quantum anomalous Hall effect and spin liquids. [Preview Abstract] 
Monday, March 18, 2013 4:18PM  4:30PM 
C17.00010: Invariant correlation entropy as a signature of quantum phase transitions in spin1/2 systems Davida Kollmar, Lea Santos The invariant correlation entropy was introduced in the context of nuclear physics as a way to quantify the degree of complexity of quantum states. Contrary to the Shannon information entropy or the inverse participation ratio, this entropy is basis independent. We show that it peaks in critical regions and can therefore be used to signal quantum phase transitions. Our findings are based on the numerical analysis of onedimensional spin1/2 systems described by different Heisenberg models and by the anisotropic XY model in a transverse magnetic field. [Preview Abstract] 
Monday, March 18, 2013 4:30PM  4:42PM 
C17.00011: The Integrable Chiral Potts Model: Quantum Group Methods Applied to Superintegrable Case Jacques H.H. Perk, Helen AuYang The integrable chiral Potts model resulted in the 1980s from a search of new solutions of the startriangle (YangBaxter)\break equations for spin models with expected parafermionic excitations. Its structure relates to cyclic representations of quantum groups at roots of unity, while the socalled superintegrable subcase has additional Onsager algebra structure. Recently the authors have utilized this quantum algebraic information, to derive detailed explicit results for the eigenvectors in the ground state sectors and give new information for the eigenvectors in general. One result is the explicit derivation of the spontaneous magnetization without hidden assumptions, as both conjectures made earlier have now been proved. The explicit eigenvectors also lead to some results for correlation functions. We shall present a review of what has been done so far and discuss the current status of the research.\\ \\ Helen AuYang and Jacques H.H. Perk, J. Phys. A: Math. Theor. {\bf 41}, 275201 (2008); {\bf 42}, 375208 (2009); {\bf 43} (2010) 025203 (2010); {\bf 44} 025205 (2011); {\bf 44}, 445005 (2011); arXiv:1108.4713; arXiv:1210.5803. [Preview Abstract] 
Monday, March 18, 2013 4:42PM  4:54PM 
C17.00012: Accounting for spin fluctuations beyond LSDA in the density functional theory Luciano Ortenzi, Igor I. Mazin, Peter Blaha, Lilia Boeri We present a method to correct the magnetic properties of itinerant systems in local spin density approximation (LSDA) and we apply it to the ferromagneticparamagnetic transition under pressure in a typical itinerant system, Ni$_{3}$Al. We obtain a scaling of the critical fluctuations as a function of pressure equivalent to the one obtained within Moryia's theory. Moreover we show that in this material the role of the bandstructure is crucial in driving the transition. Finally we calculate the magnetic moment as a function of pressure, and find that it gives a scaling of the Curie temperature that is in good agreement with the experiment. The method can be easily extended to the antiferromagnetic case and applied, for instance, to the Fepnictides in order to correct the LSDA magnetic moment. [Preview Abstract] 
Monday, March 18, 2013 4:54PM  5:06PM 
C17.00013: Firstprinciples investigation of deviations from Matthiessen's rule due to the interplay of phonon and spin disorder scattering in iron and gadolinium James Glasbrenner, Kirill Belashchenko Magnetic materials contain an anomalous contribution to the electrical resistivity due to thermal spin fluctuations, which saturates in the disordered phase and is called the spindisorder resistivity (SDR). Experimental determination of the SDR involves fitting to hightemperature resistivity data and extrapolating to T=0 K. Recent calculations of the SDR of the heavy rareearth metals revealed strong underestimations of this quantity, particularly for Gd, while the results for transition metals were in good agreement with experiments. In order to understand this discrepancy, here we evaluate the mutual effects of phonon and spindisorder scattering in Fe and Gd. Calculations are performed using the supercell approach within the linear muffintin orbital method. The atomic positions are displaced according to the Gaussian distribution, and the resistivity is evaluated as a function of the meansquare displacement $\Delta^2 \propto T$. The deviations from Matthiessen's rule (DMR) are large in Gd and moderate in Fe. Fitting the linear region of $\rho$ vs $\Delta^2$ in Gd yields an intercept $\sim 2.5$ times larger than the ``bare'' SDR, significantly improving the agreement with experiment. Large DMR suggest large variations of the relaxation time on the anisotropic Fermi surface. [Preview Abstract] 
Monday, March 18, 2013 5:06PM  5:18PM 
C17.00014: Quantum torus chain Mingpu Qin, Jon Magne Leinaas, Shinsei Ryu, Eddy Ardonne, Tao Xiang, DungHai Lee We introduce a set of onedimensional quantum lattice models which we refer to as the quantum torus chain. These models have discrete global symmetry and projective onsite representations. They possess an integervalued parameter which controls the presence or absence of frustration. Depending on whether this parameter is even or odd, these models exhibit either gapped symmetrybreaking phases with isolated critical points or gapped symmetrybreaking phases separated by gapless phases.We discuss the property of these phases and phase transitions for two special values of the parameter and point out many open problems. [Preview Abstract] 
Monday, March 18, 2013 5:18PM  5:30PM 
C17.00015: Exchange and Magnetic Anisotropic Interactions of Magnetic Ions in Antiferromagnetic Materials Alexander Bazhan Investigations of antiferromagnetic orderings, based on theory of crystallographic and magnetic symmetry, which indicates quadratic forms of thermodynamic potentials, invarianted with respect to operations of magnetic symmetry groups and presented in irreducible representations of magnetic moments, are caring out, using vector magnetometer, introducing $\chi \cdot $(1$\chi_{\mathrm{//\thinspace }}$(\textbf{l}$_{\mathrm{i}}^{2})$/$\chi )\cdot $( $\gamma_{\mathrm{i}}$\textbf{H})$^{2}$ terms in discussions. Magnetic field dependencies of samples three magnetic moments components directly indicate magnetic ions interactions. Symmetric, Anderson, and antisymmetric, DzyaloshinskiiMoria, exchange interactions in antiferromagnetic orderings, in rhombohedral structures, as example, H$_{\mathrm{ex}}=\sum_{\mathrm{i,j}}$J$_{\mathrm{i,j}}\cdot $(\textbf{S}$_{\mathrm{i}}$\textbf{S}$_{\mathrm{j}})\sum _{\mathrm{i,j}}$D$_{\mathrm{i,j,z}}\cdot $(\textbf{S}$_{\mathrm{i,x}}$\textbf{S}$_{\mathrm{j,y}}$\textbf{S}$_{\mathrm{i,y}}$\textbf{S}$_{\mathrm{j,x}})$, determine weak ferromagnetic states at selected orientations of antiferromagnetic vectors. Weak ferromagnetic states, of second and higher orders interactions of magnetic ions, are presented in the report. [Preview Abstract] 
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