Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W52: Cooperative Magnetic Phenomena: SpinLattice Effects and DynamicsRecordings Available

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Sponsoring Units: GMAG Chair: Johanna Palmstrom, Los Alamos National Laboratory Room: McCormick Place W475A 
Thursday, March 17, 2022 3:00PM  3:12PM 
W52.00001: Magnetic properties near the quantum critical point in the pyrochlore iridates (Eu_{1x}La_{x})_{2}Ir_{2}O_{7} Qiang Chen, Bruce D Gaulin Pyrochlore iridates, R_{2}Ir_{2}O_{7} (R = rareearth and Y), have been extensively studied over the past decade. A wealth of emergent properties including metal insulator transitions (MITs) and nontrivial topological phases arise due to the combination of spin orbit coupling, geometric frustration and strong electron correlation. The ground state is highly sensitive to the ionic size of R, and evolves from an insulating AllIn AllOut (AIAO) antiferromagnetic (AFM) ground state for smaller rareearth ions (R = Gd, Tb, Dy, Ho, Er, Yb, Y), to a nonmagnetic metallic state for large R = Pr. The intermediate members with R = Nd, Sm and Eu, however, show a sharp MIT concurrent with AIAO type AFM longrange ordering. This quantum critical point is attributed to the change of the iridium electronic structure with chemical pressure, although direct experimental evidence remains elusive. Previous divalent (Ca) and trivalent (Bi) cation doping studies create either Ir^{4+}Ir^{5+} charge disproportionation or large Bi 6pIr 5d hybridization. Here we investigate this quantum critical point between R = Nd and Pr with a new doping strategy, replacing Eu^{3+} with larger La^{3+} in Eu_{2}Ir_{2}O_{7}, to produce (Eu_{1x}La_{x})_{2}Ir_{2}O_{7} with an expanded lattice. On doping to x = 0.5, a large lattice parameter is achieved that is equivalent to the critical point. We can then systematically study the magnetism which arises solely from the Irsublattice and see how it evolves with increasing chemical pressure on. Magnetic susceptibility studies show a field cooled, zero field cooled splitting at T_{c}, and the systematics of these dependencies in the vicinity of the quantum critical point will be presented and discussed. 
Thursday, March 17, 2022 3:12PM  3:24PM 
W52.00002: Piezomagnetism in uranium dioxide probed by xray diffraction in pulsed magnetic fields Krzysztof Gofryk, Daniel Antonio, Joel T Weiss, Katherine S Shanks, Jacob Ruff, Marcelo Jaime, Andres Saul, Thomas Swinburne, Myron B Salamon, Keshav Shrestha, Barbara Lavina, Daniel Koury, Sol M Gruner, David A Andersson, Christopher R Stanek, Tomasz Durakiewicz, James L Smith, Zahirul Islam 5felectron spin systems exhibit strong spinlattice coupling and electronic correlations and are predicted to host new emergent phenomena. One recent example is the observation of piezomagnetism and magnetoelastic memory effect in the antiferromagnetic MottHubbard insulator, UO_{2} [1]. Here, we give a short overview of piezomagnetic behavior in this material with a focus on Xray diffraction studies of oriented UO_{2} crystals under strong pulsed magnetic fields. We show how the highresolution singlecrystal diffraction allows us to study details of subtle unitcell distortions below and above the structural and magnetic phase transition in this material. We show that direct microstructural observations of the piezomagnetic and switching effects are being a direct consequence of the noncollinear 3k magnetic order that breaks timereversal symmetry in a nontrivial way. We also observe the presence of magnetic domains with distinct magneticfield evolution in the magnetically ordered state of UO_{2}, both when the field is applied repeatedly in a single direction and when the field direction is alternated. 
Thursday, March 17, 2022 3:24PM  3:36PM 
W52.00003: Probing antiferromagnetic domains and textures at criticality using singleshot Resonant Coherent Soft Xray Scattering Rourav Basak, Martin Bluschke, Andi Barbour, Ashley Warner, Katrin Fursich, Stuart Wilkins, Sujoy Roy, Georg Cristiani, Gennady Logvenov, Matteo Minola, Bernhard Keimer, Eva Benckiser, Claudio Mazzoli, Alex Frano Strongly correlated oxides host a rich phase diagram due to the strong interplay between structural, electronic and spin degrees of freedom. For example, the perovskite nickelate compound PrNiO3 (PNO) exhibits a firstorder phase transition from paramagnetic metal to bondordered antiferromagnetic insulator, in which structural, charge and spin degrees of freedom are all coupled. Here we investigate a thin film of PNO grown on a substrate of tensilestrain inducing (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT), and use coherent resonant soft xray scattering at the Ni L3 edge to study the emergence of the magnetic order parameter in the critical regime of the phase transition. We observe a smallq periodic modulation on the magnetic bragg peak which we argue to be the ‘fingerprint’ of a particular domain configuration. By analyzing the symmetry of these smallq modulations it was possible to directly guess the corresponding realspace domain arrangement and reproduce the observed diffraction patterns. This process is facilitated by the 2dimensional nature of the domain arrangement, and represents a powerful new approach to singleshot imaging of 2dimensional mesoscopic antiferromagnetic spin textures. 
Thursday, March 17, 2022 3:36PM  3:48PM 
W52.00004: Structural distortions and magnetism in transitionmetal cluster compound GaNb_{4}Se_{8} Julia L Zuo, Stephen D Wilson Lacunar spinels AB_{4}Q_{8} (A=Al, Ga, Ge; B=V, Nb, Mo, Ta; Q=S, Se) display a variety of novel phenomena including skyrmion lattices and pressureinduced insulatormetal transitions and superconductivity. The high temperature structure features unique tetrahedral transitionmetal clusters with S=1/2 moments on an FCC lattice. Low temperature distortions of these clusters are crucial to the properties of lacunar spinels. In GaNb_{4}Se_{8}, antiferromagnetic interactions lead to geometric frustration and a magnetic transition associated with a tetragonal distortion, proposed to be a singlet state at low temperatures. We present results of structural characterization on lacunar spinel GaNb_{4}Se_{8} under temperature and pressure in connection to its magnetic properties. 
Thursday, March 17, 2022 3:48PM  4:00PM 
W52.00005: Xray Photon Fluctuation Spectroscopy on amorphous FeGe near magnetic phase transition at LCLSII. Ryan Tumbleson, Nicolas Burdet, Emily M Hollingworth, ARNAB SINGH, Ahmad Us Saleheen, Margaret R McCarter, David Raftrey, Vincent Esposito, Assefa Tadesse, Sophie A Morley, Daisy O'Mahoney, FranzJosef Decker, Alexander Reid, Georgi Dakovski, Stephen D Kevan, Peter J Fischer, Frances Hellman, Joshua J Turner, Sujoy Roy Nontrivial magnetic spin textures, e.g. Skyrmions, have attracted attention lately due to their potential application in data storage and unique topological protection. Despite this, much is still unknown about the stabilization of these textures and how the symmetric (Hesienberg) and antisymmetric (DzyaloshinskiiMoriya interaction) exchange couplings compete. In this talk, I present results from a recent experiment at LCLSII where we probed subnanosecond time scales near the magnetic phase transition of amorphous FeGe. We investigated the transition between a helical and paramagnetic state, mediated by temperature. This work not only provides further insight into the competition between symmetric and antisymmetric exchange in chiral materials but also provides a blueprint for future subnanosecond experiments at Xray Free Electron Lasers. 
Thursday, March 17, 2022 4:00PM  4:12PM 
W52.00006: Welldefined paramagnons in YCo_{2} Benjamin G Ueland, Bing Li, Robert J McQueeney, Garrett E Granroth, Xiaoping Wang, Alannah M Hallas, Shiming Lei, ChienLung Huang, Emilia Morosan, Volodymyr Smetana, Anjaverena Mudring Cubic YCo_{2} is an exchangedenhanced metallic paramagnet on the verge of ferromagnetic order. In such itinerant magnets, competition between magnetic states can be seen in the magnetic excitation spectrum. Here we present results from inelastic neutron scattering, diffraction, and thermodynamic measurements on YCo_{2}. We find steep welldefined overdamped magnetic excitations centered at the Γ point of the Brillouin zone which extend past 100 meV. The excitations weaken with increasing temperature but exist up to at least 300 K. We will discuss the excitations in terms of the compound's itinerant ferromagnetism and proximity to ferromagnetic order. 
Thursday, March 17, 2022 4:12PM  4:24PM 
W52.00007: Scalar susceptibility of a diluted classical XY model Reece D BeattieHauser, Thomas Vojta The Higgs (amplitude) mode at the disordered superfluidMott glass quantum phase transition was recently shown to feature unusual localization properties that violate naive scaling [1,2,3]. To test whether analogous behavior also occurs in the classical case, we analyze the Higgs mode in a diluted 3D classical XYmodel near the magnetic phase transition. We calculate the amplitude correlation function and the corresponding scalar susceptibility by means of Monte Carlo simulations. In contrast to the quantum case, we find that the scalar susceptibility fulfills naive scaling (employing the clean critical exponents, as expected from the Harris criterion) as the temperature is varied across the phase transition for several dilutions. 
Thursday, March 17, 2022 4:24PM  4:36PM 
W52.00008: Local structure of giant magnetocaloric system (Mn,Fe)_{2}(P,Si) Benjamin A Frandsen (Mn,Fe)_{2}(P,Si) is a promising system for magnetocaloric applications, with a tunable magnetostructural transition that ranges from about 320 K to 200 K, depending on the precise composition. As with other giant magnetocaloric systems with firstorder magnetostructural transitions, the local interactions between neighboring atoms and magnetic moments are of crucial importance for the behavior of the system. To probe the local structure of (Mn,Fe)2(P,Si), we have conducted pair distribution function (PDF) analysis of xray and neutron total scattering data collected from powder samples with a range of Mn:Fe ratios, including measurements with an in situ magnetic field. A significant rearrangement of the local atomic structure is observed as a function of temperature and applied magnetic field. We present an analysis of the local atomic structure of these compounds and discuss the relevance to the observed magnetocaloric properties. 
Thursday, March 17, 2022 4:36PM  4:48PM 
W52.00009: Asymmetry of Critical Exponents of O(N) Model due to Spontaneous Symmetry Breaking Akimitsu Kirikoshi, Takafumi Kita It has widely been believed that the critical exponents are equivalent above and below the secondorder phase transition point. On the contrary, we show that asymmetry develops in the critical exponents of the O(N) symmetric model due to spontaneous symmetry breaking. Whereas only the fourpoint vertices are relevant in the symmetric phase, threepoint vertices also become relevant in the ordered phase. One of the authors recently formulated a functional renormalization group that can reduce the number of the renormalization parameters to analyze the ordered phase[1]. Using this method to the O(N) symmetric model, we show numerically that the threepoint vertices are finite at the fixed point in the ordered phase. Around the fixed point, we also find that the critical exponent of the correlation length has a value different from that of the isotropic fixed point in the symmetric phase. Our mechanism for the emergence of asymmetry in critical exponents is different from the one proposed recently[2]. 
Thursday, March 17, 2022 4:48PM  5:00PM 
W52.00010: The extraordinary boundary transition in the 3d O(N) model via conformal bootstrap Jaychandran S Padayasi, Ilya A Gruzberg, Abijith Krishnan, Max Metlitski, Marco Meineri We study the critical behavior of the 3d classical O(N) model with a boundary. Recently, it was established that upon treating N as a continuous variable, there exists a critical value N_{c} > 2 such that for 2 ≤ N < N_{c} the model exhibits a new extraordinarylog boundary universality class, if the symmetry preserving interactions on the boundary are enhanced. N_{c} is determined by a ratio of universal amplitudes in the normal universality class, where instead a symmetry breaking field is applied on the boundary. We investigate the normal universality class using the numerical conformal bootstrap. We found truncated solutions to the crossing equation that indicate N_{c} ≈ 5. Additionally, we used semidefinite programming to place rigorous bounds on the boundary CFT data of interest to conclude that N_{c} > 3, under a certain positivity assumption which we checked in various perturbative limits. 
Thursday, March 17, 2022 5:00PM  5:12PM 
W52.00011: Search for a spin glass phase of the edgecubic spin model on 3D lattice Tasrief Surungan Discreteness is important for the existence of finite temperature 
Thursday, March 17, 2022 5:12PM  5:24PM 
W52.00012: Exploring potential energy surface of magnetic materials with noncollinear selfconsistent constrain method and deep learning model Zefeng Cai, Ben Xu, Linfeng Zhang, Han Wang In magnetic materials, the energy surface is a function of coordinates R and the magnetization vectors M of each atom. Therefore, exploring the energy surface concerning R and M using abinitial calculation methods has been a meaningful way to search magnetic candidate materials. However, this task is hindered by the difficulty of precisely anchoring the magnetization among the parameter space of arbitrarily varying direction or magnitude. In this talk, we would like to present our newly developed noncollinear selfconsistent magnetization constrain method and deep learningbased predicting model that explore the full M and R space, with the tolerance of magnetization up to 1e6 Bohr magneton. Moreover, using our deep learning model, the energy, atomic force and magnetic torque (or effective field) can be predicted with quantum accuracy with respective to variables R and M. We are confident that our method can provide the possibility for applications, for example the exploring the magenetic phase space and analyzing spin interaction hamiltonian, etc. 
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