Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y48: Frustrated Magnetism: Spin Glasses and 2D MagnetsFocus

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Sponsoring Units: GMAG DMP Chair: Yoshitomo Kamiya, RIKEN Room: 395 
Friday, March 17, 2017 11:15AM  11:27AM 
Y48.00001: Magnetic and Structural Properties of the Solid Solutions $CuAl_{2(1x)}Ga_{2x}O_4$ Thomas Bullard, Charles Ebbing, Timothy Haugan We have synthesized the antiferromagnetic spinel solid solution $CuAl_{2(1x)}Ga_{2x}O_4$. The majority of the solution displays irreversibility in the FCZFC DC susceptibility, a frequency dependence of the temperature of the cusp in the AC susceptibility, memory effects and slow relaxation dynamics as a result of changing magnetic field. We quantitatively compare to similar systems in the literature to distinguish between spin glass, cluster glass, and superparamagnetic behavior. Diffraction and CurieWeiss results suggest a rearranging of the Cu$^{2+}$ atoms as Al is replaced with Ga and offers a possible explanation for the quantitative differences in spin/cluster glass behavior within the solution. We also examine the irreversibility line distinguishing the stability regions in the HT plane for each solution member and find the de Almeida and Thouless line fits well to our results. [Preview Abstract] 
Friday, March 17, 2017 11:27AM  11:39AM 
Y48.00002: Length Scale Dependence of Glassy Dynamics at the Mesoscale Qiang Zhai, David Harrison, Daniel Tennant, E.Dan Dalhberg, Gregory Kenning, Raymond Orbach We have measured glassy dynamics for thin film mesoscopic CuMn multilayers, with CuMn thicknesses of 4.5 nm, 9.0 nm, and 20 nm. We compare our experimental results with the predictions for the growth rate of the spin glass correlation function for two spin glass dynamical models: power law and activated dynamics. The former predicts a logarithmic dependence of the maximum energy barrier height on length scale; the latter a power law dependence. In addition, the freezing temperature was measured for the three thin film thicknesses, and compared with the predictions of the two models. We find that power law dynamics can fit the length scale dependence of the maximum barrier height, while activated dynamics predicts a variation outside of the experimentally determined range. A similar conclusion is reached for the freezing temperature. In all, measurement of the length scale dependence of spin glass dynamics at the mesoscale proves to be a powerful tool for distinguishing between conflicting dynamical models. [Preview Abstract] 
Friday, March 17, 2017 11:39AM  11:51AM 
Y48.00003: Using neural networks to probe for the existence of a spinglass state in a field Humberto MunozBauza, Firas Hamze, Helmut G. Katzgraber The existence of a spinglass state in a field remains controversial. Most recently, machine learning techniques have found their way into condensed matter, as well as statistical physics, where neural networks have been trained to classify different phases of matter ranging from ice models to lattice gauge theories or strongly correlated electrons, to name a few. These promising results indicate that neural networks might also be able to discern if spin glasses  model systems that do not display any spatial order but do have a finitetemperature phase transition into a glassy phase at zero field  show signs of criticality when an external field is applied. [Preview Abstract] 
Friday, March 17, 2017 11:51AM  12:03PM 
Y48.00004: Waiting time effects in CuMn thin films Daniel Tennant, Gregory Kenning We report dynamical measurements of Cu$_{86.5}$Mn$_{13.5}$ 4.5nm thin films separated within a multilayer structure by 60nm layers of Cu. Systematic measurements of the waiting time effect on the thermoremanent magnetization (TRM) decays are made between 16K and the onset of irreversibility at $T_f $= 24K, which occurs at 0.45 $T_g$, the bulk transition temperature. At temperatures well below the freezing temperature up till approximately 21K, waiting time effects are observed with the effect going to zero at approximately 21K. Between 21K and 24K, we find, that while the waiting time effect is suppressed, the film remains in the spin glass phase as observed by the remnant magnetization. These observations are examined in light of the growth of the spin glass correlation length, $\xi(t, T)$, from nucleation to length scales comparable to the thin film thickness $\mathcal {L}$. The vanishing of the waiting time effect for times and temperatures such that $\xi(t, T) \geq \mathcal {L}$ is confirmatory evidence that $\xi(t, T)$ has reached the film thickness. [Preview Abstract] 
Friday, March 17, 2017 12:03PM  12:15PM 
Y48.00005: Corrections to scaling in the bonddiluted nextnearestneighbor Ising spinglass Andrew J. Ochoa, Helmut G. Katzgraber For spin glasses, model systems that have both frustration and disorder, calculating accurate critical exponents is difficult due to significant corrections to scaling and long equilibration times in Monte Carlo simulations that limit numerical studies to small system sizes. The study of critical phenomena of such systems requires a careful control of the scaling corrections, as emphasized in the works of, e.g., Hasenbusch {\em et al.}~[J. Stat. Mech., L02001 (2008)] and Katzgraber {\em et al.}~[Phys. Rev. B 73, 224432 (2006]. In an attempt to reduce corrections to scaling, we introduce an average over both disorder and lattice structures. We study a threedimensional nextnearestneighbor Ising spin glass with Gaussian disorder  that shares the same universality class as the standard threedimensional cubic lattice [Phys. Rev. B 73, 224432 (2006)]  but where we dilute the lattice such that the number of neighbors is on average six. Comparisons with simulations of the cubiclattice Ising spin glass with Gaussian disorder are performed. [Preview Abstract] 
Friday, March 17, 2017 12:15PM  12:27PM 
Y48.00006: Magnetic Field Dependence of Spin Glass Free Energy Barriers Samaresh Guchhait, Raymond Orbach Thin film spin glasses at mesoscopic thicknesses $\mathcal {L}$ achieve quasiequilibrium conditions when the spin glass correlation length $\xi(t, T)$ grows with time $t$ to $\mathcal {L}$ for times $t\geq t_{\text {co}}$, where $T$ is the temperature and $t_{\text {co}}$ is defined by the condition $\xi(t_{\text {co}}, T) = \mathcal {L}$. Because the spin glass lower critical dimension $d_\ell \approx 2.5>2$, no further growth of $\xi(t>t_{\text {co}}, T)$ takes place at constant temperature, generating a largest free energy barrier, $\Delta_{\text {max}}$. A barrier model predicts that $\Delta_{\text {max}}$ increases as a magnetic field $H$ decreases, proportional to the change in magnetic field $(\delta H)^2$. Experiments on a Ge:Mn thin film spin glass are reported that exhibit this proportionality, together with a small $(\delta H)^4$ term. The observed magnitude of the change of the spin glass free energy barriers is in near quantitative agreement with the predictions of a barrier model. Comparison is made with very recent numerical simulations on Janus and Janus II computers. The scaling laws that are derived from these simulations are of the same form as the results of our experiments. [Preview Abstract] 
Friday, March 17, 2017 12:27PM  12:39PM 
Y48.00007: Glassy phonons and magnonphonon coupling in the shape memory strain glass alloy Ni$_{\mathrm{45}}$Co$_{\mathrm{5}}$Mn$_{\mathrm{36.6}}$In$_{\mathrm{13.4}}$ Paul Stonaha, Michael Manley The magnetocaloric effect describes the coupling between a materials temperature and its magnetic state. Modern magnetocaloric devices employ materials which undergo a change in magnetic order coinciding with a martensitic (firstorder) phase transition. A drawback of the martensitic transformation is the requirement of large magnetic fields (\textgreater 2T) and the accompanying structural hysteresis. In this talk, we discuss the magnetocaloric effect in the shape memory alloy Ni$_{\mathrm{45}}$Co$_{\mathrm{5}}$Mn$_{\mathrm{36.6}}$In$_{\mathrm{13.4}}$ near its Curie temperature. In its austenite phase, this material exists in a frustrated ferromagnetic / antiferromagnetic state. We show that the TO [H00] phonon in this material is coupled to magnetism, and that the application of a magnetic field effects this phonon enough to appreciably change the vibrational entropy. We present the results of frozen phonon calculations that show how the phonon couples to magnetism at the atomic level. We also discuss the stain glass state of this material, in which the TA2 phonon is heavily damped both above and below the strain glass transition temperature. The results imply a new outlook on the source of the strain glass state. [Preview Abstract] 
Friday, March 17, 2017 12:39PM  12:51PM 
Y48.00008: Measurements of $1/f$ Noise in Cu$_{86.5}$Mn$_{13.5}$ Thin Films David Harrison, E Dan Dahlberg, Raymond Orbach We have measured the $1/f$ noise in the spin glass state of Cu$_{86.5}$Mn$_{13.5}$ films. Our results are consistent with previous measurements that have demonstrated lowfrequency resistance fluctuations abruptly increase in magnitude as a spin glass is cooled through its glass temperature [1]. The noise originates from fluctuations in the orientation of the local magnetic moments (``spins'') within the spin glass. The importance of developing techniques to study the spin glass state in films such as these is the measurements require less material for an acceptable signaltonoise than conventional magnetometry (e.g. SQUID) measurements. This reduced volume of material required for experiments makes noise measurements ideal for mesoscale studies of the spin glass state and the effects of reduced dimensionality. For example, one might observe in the noise spectrum the crossover from time dependent correlation length growth $\xi(t, T)$ to saturation when $\xi(t, T) = {\mathcal {L}}$, where $\mathcal {L}$ is a dimension characteristic of the mesoscale. [1] Israeloff, N. E., et al. ``Electrical noise from spin fluctuations in CuMn.'' Physical review letters 63.7 (1989): 794. [Preview Abstract] 
Friday, March 17, 2017 12:51PM  1:03PM 
Y48.00009: Going beyond meanfield theory for frustrated magnetism with extended ThoulessAndersonPalmer method Matthew Enjalran 
Friday, March 17, 2017 1:03PM  1:15PM 
Y48.00010: Abstract Withdrawn Our work has shown the successful doping of BN with atomic Li resulting in a material with the stoichiometry Li(BN)$_3$. Magnetisation measurements showed various anomalies throughout the temperature range 2 – 300 K, where there is the emergence of a glassy magnetic ground state below 100 K. Muon spin spectroscopy measurements elaborated on this, where the at low temperatures and in zero field the sample shows a frozen disordered magnetic state, but on heating there is evidence of a diffusive process kicking in, which is likely due to the onset of Li diffusion. It is believed that within this sample, the atomic Li is able to diffuse freely, but on cooling the Li freezes and becomes static, injecting spin and charge into the BN layers. 
Friday, March 17, 2017 1:15PM  1:27PM 
Y48.00011: Magnonphonon coupling effects on the indirect Kedge RIXS spectrum of a 2D Heisenberg antiferromagnet Trinanjan Datta, Zijian Xiong, Kenny Stiwinter, DaoXin Yao We compute the effects of magnonphonon coupling on the indirect Kedge bimagnon RIXS intensity in a square lattice antiferromagnet. Including spin wave expansion up to 1/S order, the BetheSalpeter ladder approximation scheme for the bimagnon interacting channel, and considering a second order magnonphononmagnon scattering interaction we study the role of magnonphonon effect on the bimagnon RIXS spectrum. Considering the damping effects due to longitudinal acoustic phonon we find that the spectrum is indeed affected with prominent magnonphonon damping contributions along the Brillouin zone edge. The maximal damping effects are at the zone edge points of ($\pm \pi$,0) or (0, $\pm \pi$). Using magnonphonon coupling parameters pertinent to cuprates, we find that the RIXS bimagnonphonon peak can be observed as a discernible shoulder in the bimagnon RIXS spectrum. We also investigate the interplay of phonons with spatial anisotropy and magnetic frustration through next nearest neighbor interaction on the bimagnon RIXS spectrum to highlight the importance of RIXS in strongly correlated systems such as cuprates and pnictides. [Preview Abstract] 
Friday, March 17, 2017 1:27PM  1:39PM 
Y48.00012: Phase Diagram of square lattice S=1 Mott insulators Julia Wildeboer, Jonathan Demidio, Ribhu Kaul We study the phase diagram of a spin1 Heisenberg Model with both 2 and 4 spin bilinearbiquadratic interactions on the square lattice. This model can be simulated signproblem free with means of a Stochastic Series Expansion Quantum Monte Carlo (SSE QMC). We study the competition between the N\’eel, quadrupolar, valence bond solid and Haldane phases, and the nature of the quantum phase transitions between these states of matter. [Preview Abstract] 
Friday, March 17, 2017 1:39PM  1:51PM 
Y48.00013: Multiple magnetic transitions on the pentagonal Cairo lattice in Bi$_4$Fe$_5$O$_{13}$F Alexander Tsirlin, Ioannis Rousochatzakis, Dmitry Batuk, Artem Abakumov Pentagonal Cairo lattice gives rise to an unusual frustrated scenario that was actively studied theoretically but still lacks experimental manifestation in real materials. In this talk, I will present a novel Cairolattice antiferromagnet Bi$_4$Fe$_5$O$_{13}$F that features a sequence of three magnetic transitions at $T_1=62$\,K, $T_2=71$\,K, and $T_N=178$\,K. Using a combination of neutron diffraction and M\"ossbauer spectroscopy, we show that the magnetic structure below $T_1$ is consistent with orthogonal spin order anticipated by theory. The collinear magnetic structure observed between $T_1$ and $T_2$ is also anticipated by theory, but only for the quantum version of the model, whereas Bi$_4$Fe$_5$O$_{13}$F with its spin$\frac52$ Fe$^{3+}$ should be close to the classical limit. Finally, the magnetic structure between $T_2$ and $T_N$ is again orthogonal, but individual spin directions are different from those below $T_1$. A microscopic magnetic model of Bi$_4$Fe$_5$O$_{13}$F will be presented, and possible origins of the spinreorientation transitions in this material will be discussed. [Preview Abstract] 
Friday, March 17, 2017 1:51PM  2:03PM 
Y48.00014: Dimensional Reduction in Quantum Dipolar Antiferromagnets Henrik Ronnow, Peter Babkevich, Minki Jeong, Yosuke Matsumoto, Ivan Kovacevic LiYbF$_4$ and LiErF$_4$ represent rare examples of materials where dipolar interactions dominate. Combining neutron scattering, specific heat and magetic susceptibility data for LiErF$_4$ and LiYbF$_4$, we demonstrate that dipolar interactions can lead to antiferromagnetic order. We establish the critical properties at respectively the thermal phase transition and the quantum phase transition as function of transverse magnetic field, and discover a surprising dimensional reduction. Despite dipolar interactions being threedimensional and longrange in nature, the critical exponents place these materials in the 2D $XY/h_4$ universality class. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which calls for theoretical efforts to elucidate the observation. [Preview Abstract] 
Friday, March 17, 2017 2:03PM  2:15PM 
Y48.00015: Unified Spin Model for Magnetic Excitations in Iron Chalcogenides Patricia Bilbao Ergueta, Zhentao Wang, WenJun Hu, Andriy H. Nevidomskyy Recent inelastic neutron scattering (INS) measurements on the iron chalcogenides FeSe and Fe(Te$_{1x}$Se$_{x}$) have sparked intense debate over the role of magnetism in these materials. We will argue that magnetic frustrations of the underlying Fe spin1 degrees of freedom are the key to understanding the nature of the ground states. We propose an effective bilinearbiquadratic spin model which is shown to consistently describe the evolution of lowenergy spin excitations in FeSe, both under applied pressure and upon Se/Te substitution. The phase diagram, studied using a combination of variational meanfield, flavorwave, and densitymatrix renormalization group (DMRG) calculations, exhibits a sequence of transitions between the nonmagnetic ferroquadrupolar phase attributed to FeSe and several other magnetically ordered phases{[1]}. The calculated spin structure factors mimic closely those observed with INS in FeSe and in the Fe(Te$_{1x}$Se$_x$) series{[2]}. In addition to the experimentally established phases, the possibility of incommensurate magnetic order is also predicted.\\ {[1]} P. Bilbao Ergueta, Z. Wang, W.J. Hu, and A. H. Nevidomskyy, arXiv: 1607.05295.\\ {[2]} Z. Xu \emph{et al.}, Phys. Rev. B. \textbf{93}, 104517 (2016). [Preview Abstract] 
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