Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V38: Spin Glasses and Disordered Magnetic SystemsFocus

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Sponsoring Units: GMAG DMP Chair: Zhenzhong Shi, Duke University Room: BCEC 206B 
Thursday, March 7, 2019 2:30PM  2:42PM 
V38.00001: A dynamic probe of finitesize effects near the spinglass transition temperature Gregory Kenning, Daniel Tennant, Qiang Zhai, David Harrison, E. Dan Dalhberg, Raymond Orbach

Thursday, March 7, 2019 2:42PM  2:54PM 
V38.00002: Seeking the spinglass state in a field through windows Dilina Perera, A. Peter Young, Helmut Katzgraber Although the presence of a finitetemperature transition in the threedimensional Ising spinglass is well established in zero field, the behavior in the presence of an external magnetic field has been a matter of longstanding controversy. For the infiniterange SherringtonKirkpatrick spin glass, meanfield theory predicts a transition line known as AlmeidaThouless (AT) line that separates the paramagnetic and spinglass phases in the temperaturefield plane. Despite extensive numerical efforts, no consensus has been reached with regard to the presence of an AT line in shortrange systems, mostly due to strong corrections to finitesize scaling. Here we investigate the transition in a threedimensional system via a method in which we perform population annealing Monte Carlo simulations for a large system, but only consider the thermodynamic properties of the system restricted to a small window. By computing the wavevectordependent spinglass susceptibility for the individual windows, as well as for the whole system, we investigate the effects of finitesize corrections to the twopoint correlation function. 
Thursday, March 7, 2019 2:54PM  3:06PM 
V38.00003: Evidence of transition between Heisenberg and Isinglike phases in mesoscale Ge:Mn spin glass Samaresh Guchhait The glassy dynamics of vector spin glasses in presence of a weak uniaxial anisotropy has been a subject of longstanding controversy. It has been predicted that in presence of such anisotropy Heisenberglike spin glass system first undergoes longitudinal moment freezing, followed by a transverse moment freezing at even lower temperature. Evidence of such phase transition is seen in the temperature chaos experiments in thin film Ge:Mn spin glass. Here the sample temperature is increased from the quench temperature after the correlation length has reached its thickness. For large enough positive change of temperatures the maximum barrier height increases monotonically, which is consistent with a phase change of lower temperature Heisenberglike phase to higher temperature Isinglike phase. 
Thursday, March 7, 2019 3:06PM  3:18PM 
V38.00004: Study of longitudinal fluctuations of the SherringtonKirkpatrick spin glass Leopoldo Sarra, Lorenzo Talamanca, G. Parisi Spin glasses are disordered systems with a complex behavior, caused by the very high degeneracy of low energy states. They have a phase transition between a paramagnetic phase and a spin glass phase, in which the ergodicity is broken in a hierarchical organization of states. This implies many peculiar properties such as aging, remanence and memory effect. In our work, we study finitesize corrections to the mean field model, the SherringtonKirkpatrick spin glass, whose solution is wellknown. The behavior of these corrections in the low temperature phase has been debated for several years. Because of the complicated form of the theory around the mean field solution and of the difficulty to perform a numerical estimate, no final value has been found so far. We investigate the role of longitudinal fluctuations, neglecting the transverse contribution. Since they can be calculated directly into the fullreplica symmetry breaking ansatz, it is easier to obtain a prediction for their behavior. 
Thursday, March 7, 2019 3:18PM  3:30PM 
V38.00005: Chaotic Behavior in CuMn_{13.5} Multilayer Thin Film Spin Glasses Qiang Zhai, Raymond Orbach, David Harrison The zero field cooled (ZFC) and field cooled (FC) magnetizations of an 11 nm CuMn_{13.5} multilayer thin film spin glass was measured using a superconducting quantum interference device (SQUID) over the time scale where the correlation length has grown to the film thickness, i.e. for time scales where the thin films crossover from 3 D to 2 D. Temperature chaos, the vulnerability of the quasiequilibrium state to temperature perturbations, was studied by a series of temperature drops after the crossover time. We find the ZFC and FC magnetization responses are sensitive to temperature changes after crossover. Both reversible and chaotic behavior, the latter characterized as rejuvenation, are observed. The traditional interpretation using a characteristic length for chaos, and the concept that chaos is “driven by rare events,” are discussed in comparison with experimental results. 
Thursday, March 7, 2019 3:30PM  3:42PM 
V38.00006: Experimental Observation of Roomtemperature Anomalous Hall Mobility and Positive Magnetic Hysteresis in Amorphous FeDyO Thin Films Krishna Koirala, Aniruddha Deb, Ritesh Sachan, Deepak Sapkota, Venkatanarayana P Sandireddy, James E PennerHahn, Ramki Kalyanaraman FeDyTbO thin film system was recently reported with very high transparency, conductivity and room temperature ferromagnetism driven by partially filled d  and f  subshells. Here, we have synthesized and studied the FeDyO thin films. The thin film system was prepared by ebeam evaporation and its structural, transport, magnetic and optical characterizations were performed. The asgrown films were amorphous, as evidenced by transmission electron microscopy and Xray scattering. Xray absorption spectra revealed a progressive oxidation of thin films on reducing the dimension. The films showed high ordinary (~10 cm^{2}/Vs) and anomalous (~10^{2 }cm^{2}/Vs) Hall mobility with ntype semiconducting behavior. Cryogenic magnetic behaviors evinced the existence of spinglasslike transition at 79 K. Positive hysteresis loop and transverse magnetoresistivity up to 4% in the magnetic field of 5 T were observed at room temperature. Roomtemperature optical studies showed the existence of a band gap of 2.42 eV in the visible range. These unique set of properties make the system a rich toolbox for not only understanding condensed matter behavior but also realizing multifunctional devices. 
Thursday, March 7, 2019 3:42PM  3:54PM 
V38.00007: A Lower LowerCritical SpinGlass Dimension from Quenched MixedSpatialDimensional Spin Glasses: Continuously Variable Dimension in Physically Realizable Systems Bora Atalay, A Nihat Berker By quenchedrandomly mixing local units of different spatial dimensionalities, we have studied Ising spinglass systems on hierarchical lattices continuously in dimensionalities 1=<d =<3. The global phase diagram in temperature, antiferromagnetic bond concentration, and spatial dimensionality is calculated. We find that, as dimension is lowered, the spinglass phase disappears to zero temperature at the lowercritical dimension dc=2.431. Our system being a physically realizable system, this sets an upper limit to the lowercritical dimension in general for the Ising spinglass phase. As dimension is lowered towards dc, the spinglass critical temperature continuously goes to zero, but the spinglass chaos fully sustains to the brink of the disappearance of the spinglass phase. The Lyapunov exponent, measuring the strength of chaos, is thus largely unaffected by the approach to dc and shows a discontinuity to zero at dc. 
Thursday, March 7, 2019 3:54PM  4:06PM 
V38.00008: Luttinger Quantum Paramagnet from Dimensional Recombination in the Frustrated Spin1/2 Trimer Magnet Ba_{4}Ir_{3}O_{10} Hengdi Zhao, Hao Zheng, Yifei Ni, Yu Zhang, Feng Ye, Xiaoping Wang, Christina Hoffmann, Minhyea Lee, Itamar Kimchi, Michael A Hermele, Gang Cao We report a highly frustrated spin state persisting down to 0.2 K in the monoclinic Ba_{4}Ir_{3}O_{10} with Ir^{4+}(5d^{5}) ions, which consists of Ir_{3}O_{12} trimers of facesharing IrO_{6} octahedra and wavy twodimensional IrO sheets. This iridate conspicuously avoids any longrange magnetic order down to 0.2 K despite strong antiferromagnetic interaction with CurieWeiss temperature 766 K. The corresponding frustration ratio reaches an astonishing value of 3830. This frustrated spin state is further evidenced by a sizable, linear heat capacity, indicating substantial residual entropy even at milliKelvin temperatures. It is equally striking that a mere 2% nonmagnetic Sr substitution for Ba readily lifts frustration and precipitates a longrange antiferromagnetic order at 130 K, suggesting proximity to a quantum critical point potentially with emergent random spin nucleation. 
Thursday, March 7, 2019 4:06PM  4:18PM 
V38.00009: Weird scaling for 2D avalanches: curing the faceting, and scaling in the lower critical dimension L. X. Hayden, Archishman Raju, James Patarasp Sethna The nonequilibrium randomfield Ising model (NERFIM) is very well studied and yet there are outstanding questions. In two dimensions, power law scaling approaches fail and the critical disorder is difficult to pin down. Additionally, the presence of faceting on the square lattice creates avalanches that are lattice dependent at small scales. We propose two methods which we find solve these issues. First, we perform large scale simulations on a Voronoi lattice to mitigate the effects of faceting. Secondly, the form of the nonlinear functions necessary to perform scaling collapses can be directly determined using our recent normal form theory of the Renormalization Group. This method has proven useful in cleanly capturing the complex behavior which occurs in both the lower and upper critical dimensions of systems and well describes the NERFIM in twodimensions. The obtained scaling collapses span over a range of a factor of ten in the disorder and a factor of 10^{4} in avalanche size. They are consistent with a critical disorder at zero and with a lower critical dimension for the model equal to two. 
Thursday, March 7, 2019 4:18PM  4:30PM 
V38.00010: Critical behavior of the Ising model on a lattice with fractional space dimension Chao Fang, Maoxin Liu, Helmut Katzgraber Disorder can have a drastic effect on the critical behavior of a magnetic system. The Harris criterion states that if the critical exponent of the correlation length $\nu$ fulfills the inequality $\nu \ge 2/d$, with $d$ the space dimension, disorder does not affect the universality class of the magnetic systems. A recent study reported a violation of this criterion for a twodimensional threestate Potts model on a Voronoi lattice. To better understand the effects of disorder on the critical behavior of magnetic systems on disordered lattices, we study the critical behavior of a twodimensional Ising ferromagnet on the largest component of a percolating cluster on a twodimensional square lattice. There are two possible scenarios: In the weak universality scenario the disordered structure of the underlying lattice slowly changes the critical exponents, whereas in the strong universality scenario the critical exponents are not affected by the fractional space dimension of the system. Our results suggest a strong universality scenario with weak (logarithmic) corrections. 
Thursday, March 7, 2019 4:30PM  4:42PM 
V38.00011: Maximally Random DiscreteSpin Systems with Symmetric and Asymmetric Interactions and Maximally Degenerate Ordering A Nihat Berker, Bora Atalay Discretespin systems with maximally random nearestneighbor interactions that are symmetric or asymmetric, ferromagnetic or antiferromagnetic, including offdiagonal disorder, are studied for q=3,4 states in d dimensions, using renormalizationgroup theory exact for hierarchical lattices and approximate (MigdalKadanoff) for hypercubic lattices. For all d>1 and all noninfinite temperatures, the system eventually renormalizes to a random single state, signaling qxq degenerate ordering, which is maximally degenerate ordering. For hightemperature initial conditions, the system crosses over to this highly degenerate ordering after many renormalizationgroup iterations near the disordered infinitetemperature fixed point. Thus, a temperature range of shortrange disorder in presence of longrange order occurs, as previously seen in underfrustrated Ising spinglasses. The calculated entropy behaves similarly for ferromagnetic and antiferromagnetic interactions and shows a derivative maximum at the shortrange disordering temperature. The system is disordered at all temperatures for d=1. 
Thursday, March 7, 2019 4:42PM  4:54PM 
V38.00012: Direct Observation of Magnetic Longrange Order in AmmannBeenker Artificial Quasicrystals Lance De Long, Barry W Farmer, John Unguris, Justin Woods Magnetic longrange order (LRO) in 3D AmmannBeenker tilings (ABT) has been modeled in simulations^{1,2}, but has yet to be experimentally observed^{3}. We fabricated artificial ABT composed of a connected wire network of elongated Permalloy film segments that mimic classical Ising spins interacting via longrange dipolar and shortrange exchange interactions. Our MC analysis of ABT (NN interactions) generated a magnetic ground state built upon distinct sublattices, similar to fivefold Penrose tilings^{4,5}. Highresolution images of the inplane magnetization of ABT were acquired with scanning electron microscopy with polarization analysis (SEMPA). An annealing protocol that yielded improved agreement with the MC ground state. We developed a novel cluster covering that introduces frustration among neighboring clusters, and suggests lowenergy, longrange interactions are required for full LRO, and provides a possible explanation for the nonexistence of magnetic LRO in atomic quasicrystals. 
Thursday, March 7, 2019 4:54PM  5:06PM 
V38.00013: Simulating spinwaves in strongly disordered magnets Tom Berlijn, Randy Fishman, Gonzalo Alvarez, Weiguo Yin Many scientifically important magnets contain disorder which complicates the theoretical analysis of their magnetic excitations. Examples include Sr2(Ir,Ru)O4 [1] with 50% (Ir,Ru) substitutions, Mn1.13Sb [2] with 13% Mn interstitials and Fe2.7GeTe2 [3] with 30% of Fe vacancies. To simulate magnons in these types of strongly disordered magnets we combine linear spinwave theory [4] with the supercell approximation. [5] [1] Y. Cao, T. Berlijn et al PRB 95 (12), 121103 (2017) [2] A. E. Taylor, T. Berlijn, R. S. Fishman et al, PRB 91 (22), 224418 (2015) [3] G. D. Nguyen, T. Berlijn et al, PRB 97, 014425 (2018). [4] J. T. Haraldsen & R. S. Fishman, JPCM 21, 216001 (2009) [5] T. Berlijn et al, PRL 106, 077005 (2011). 
Thursday, March 7, 2019 5:06PM  5:18PM 
V38.00014: Study of a generalized XY model using the correlation length Nui Xuan Duong, Tuan Le, Kien DucTrung Nguyen, Huy Thanh Pham, Hung Dang, Viet Xuan Dao The correlation length is examined in a generalized XY model where, together with the usual ferromagnetic interaction between spins, there is an additional nematic interaction that allows for halfvortices. The power of the correlation length is demonstrated in distinguishing different phases, thus fully reconstructing the phase diagram of the model. Moreover, it allows for further investigation of the tricritical region in the phase diagram where the paramagnetic, the nematic and the quasilongranged phases meet. It shows that the Isingtype transition between the nematic and the quasilongrange ordered phases stops at the tricritical point. Starting from this tricritical point, there is an intermediate range of different physics separates the two regions corresponding to the Isingtype and the BerzinskiiKosterlitzThoulesstype transitions. 
Thursday, March 7, 2019 5:18PM  5:30PM 
V38.00015: Dangerously Irrelevant Field at Clock Models  A study with the Monte Carlo Based RG Flows Hui Shao, Wenan Guo, Anders W Sandvik The phase transitions between the paramagnetic phase and the $Z_q$ symmetrybreaking phase in the three dimensional XY model with $Z_q$anisotropic field is now well accepted as belonging to the 3D XY universality class for $q>q_c$, with the $Z_q$anisotropic field being irrelevant at the critical point. However, when $T<T_c$ it is always relevant as the symmetry is broken discretely. This is ”dangerous” because it leads to a larger length scale $\xi'$ than the normal correlation length $\xi$, which, by definition, governs the crossover behavior from $U(1)$ to $Z(q)$ symmetry breaking. While RG theory has provided generic pictures of the RG flow in coupling space, we here construct a quantitative Monte Carlo based RG flow using corresponding physical observables, where not only the crossover behaviors can be observed explicitly but also the critical exponents $\nu$ and $\nu'$ can be extracted accordingly. For this purpose, we have firstly restudied the anisotropy order parameter and confirm that its scaling dimension at the critical point is the same as that of the $Z_q$ field. We also clarify unsettled issues in several recent studies of this quantity. 
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