Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A19: Spin Chains: ExperimentFocus Session
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Sponsoring Units: GMAG DMP Chair: Matthew Stone, Oak Ridge National Laboratory Room: LACC 308A |
Monday, March 5, 2018 8:00AM - 8:12AM |
A19.00001: Quantum Criticality in a Strongly Coupled S=1 Spin Chain System at Ambient Field and Pressure Kirill Povarov, Alexandra Mannig, Gerard Perren, Johannes Möller, Erik Wulf, Jacques Ollivier, Andrey Zheludev We report spontaneous appearance of antiferromagnetic order in a model gapped quantum paramagnet Ni(Cl1-xBrx)2-4SC(NH2)2 induced by a change in bromine concentration x. The linear soft-mode spin waves, as well as magnetic Bragg peaks are observed directly in a Br-rich material [1]. Comparison with the preceding studies on specimen with lower bromine concentration [2,3] allows us to reconstruct the overall phase diagram. The transition is qualitatively similar to a z=1 magnetic quantum critical point. However, the observed critical scaling of thermodynamic and magnetic properties has rather unusual critical exponents. |
Monday, March 5, 2018 8:12AM - 8:24AM |
A19.00002: Tunable spin-phonon scattering in low-D spin chain compounds AB2O6 (A= Co, Ni; B= Sb, Ta) Narayan Prasai, Joshua Cohn, Aaron Christian, John Neumeier We report measurements of thermal conductivity (κ) in the range 5 K ≤ T ≤ 300 K for single crystals of the low-dimensional antiferromagnetic spin-chain compounds CoSb2O6, NiSb2O6, CoTa2O6 and NiTa2O6. While all of these compounds share the same tetragonal trirutile structure with space group P42/mnm, Co2+ has a spin-3/2 and Ni2+ a spin-1 state. The Ta compounds show a strongly suppressed κ over a broad range of temperature relative to the Sb compounds that is typically ascribed to resonant spin-phonon scattering.a We will discuss the possibility that this difference is caused by changes in the energy overlap of the magnon and phonon spectra associated with the B-site ion substitution. |
Monday, March 5, 2018 8:24AM - 8:36AM |
A19.00003: Molecular architecture and universality-class control in S =1 quantum magnets§ Jamie Manson, John Singleton, Paul Goddard, Samantha DeAbreu, Jamie Brambleby, Will Blackmore, Rob Williams, Junjie Liu, Andrew Ozarowski, Danielle Villa, Cecelia Villa We have studied a large class of low-dimensional quantum magnets based on S = 1 Ni(II) ions. When coordinated to varying numbers of organic ligands and halides, we can observe all three universality classes; Heisenberg, Ising and XY. We show that the trend in the magnitude of the single-ion anisotropy (D) coincides with predictions from the spectrochemical series. Also, it is found that NiX2N4 coordination spheres (X = Br, I, NCS) have D < 0 (Ising-like) whereas X = Cl and F exhibit ground states with large, positive D (XY-like). Increasing the number of halide or oxygen donor atoms around the Ni(II) ion, to form NiX4N2 or NiO4N2, induces an Ising-like ground state in the existing examples. In the absence of frustrated interactions, we demonstrate an ability to predict the orientation of the Ni(II) spin direction in simple systems, regardless of dimensionality or presence of long-range magnetic order, based solely on the single-ion anisotropy. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A19.00004: Low-dimensional Quantum Magnetism in Cu(NCS)2, a Molecular Framework Material Matthew Cliffe, Jeongjae Lee, Joseph Paddison, Sam Schott, Paromita Mukherjee, Michael Gaultois, Pascal Manuel, Henning Sirringhaus, Sian Dutton, Clare Grey Low dimensional magnetic materials with spin-1/2 moments can host a range of exotic magnetic phenomena due to the intrinsic importance of quantum fluctuations to their behaviour. In this work we report the structure, magnetic structure and magnetic properties of copper(II) thiocyanate, Cu(NCS)2, a one-dimensional coordination polymer which displays low-dimensional quantum magnetism. Magnetic susceptibility, electron paramagnetic resonance spectroscopy, 13C magic angle spinning nuclear magnetic resonance spectroscopy, and density functional theory investigations indicate that Cu(NCS)2 behaves as a two dimensional array of weakly coupled antiferromagnetic spin chains (J2=133(1)K, α=J1/J2=0.08). Powder neutron diffraction measurements confirm that below TN=12 K Cu(NCS)2 orders as a commensurate G-type antiferromagnet with a strongly-reduced ordered moment (0.3 μB) due to quantum fluctuations. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A19.00005: 63Cu-NMR in pristine HKUST-1 MOF: static and dynamic effects near the Cu environment Greta O'Dea, Guo-meng Zhao, Engelbert Redel, Helmut Baumgart, Oscar Bernal NMR Spectroscopy is being used to explore magnetic and charge properties of the Cu(II)-based metal-organic framework (MOF) HKUST-1 and the change in conductivity that occurs between pristine HKUST-1 and HKUST-1 with tetracyano-quinodimethane (TCNQ) infiltration. The pulse NMR technique can be used to examine the interactions between the nuclei and the unpaired electrons in paramagnetic Cu(II) in pristine HKUST-1. This will allow for further understanding of the effect on the conductivity of the material when the pores of the MOF are occupied by TCNQ. Here we report on the 63Cu-NMR of pristine HKUST-1. We find that the 63Cu-NMR spectral linewidth in this system increases with decreasing temperature as would be expected for dipolar interactions of the paramagnetic Cu(II) ions with the nuclear moments. Surprisingly, we also find that the 63Cu line-shift with respect to a CuBr reference is very close to that of copper metal. To shed light on this intriguing experimental result, we will present preliminary measurements of lineshape, spin-lattice and spin-spin relaxation times as functions of temperature and applied magnetic field in pristine HKUST-1. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A19.00006: NBCT is an S = 1 antiferromagnetic nickel chain near the D/J quantum critical point Daniel Pajerowski, Jamie Manson, Mark Meisel, Andrei Podlesnyak, Timothy Prisk, Jacek Herbrych An S=1 antiferromagnetic chain, [Ni(HF2)(3-Clpy)4]BF4 (py = pyridine), henceforth NBCT, has been reported to be in the intermediate, in-plane anisotropy limit, which is a region of phase space that has not been tested quantitatively against theoretical predictions (large D and small D have both been investigated thoroughly). The best fit Hamiltonian parameters for NBCT from magnetization and specific heat have the easy-plane anisotropy D = 4.3 K, the intrachain antiferromagnetic interaction J = 4.86 K, and the interchain interaction J’ to be negligible, such that D/J = 0.88 in the vicinity of the D/J≈1 quantum critical point. Here, we present inelastic powder neutron scattering data that can be compared with density matrix renormalization group theory. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A19.00007: Study of quasi-one dimensional magnet Ti4MnBi2 by neutron scattering Ping Miao, Abhishek Pandey, Hua He, Mason Klemm, Zhijun Xu, Yang Zhao, Jeffrey Lynn, Xiaofeng Qian, Meigan Aronson We report the investigation of magnetic structure of Ti4MnBi2 that crystallizes into a tetragonal structure (space group: I 4/mcm, No. 140). The distance between two Mn-ions along the chain is relatively small (~2.5 A) while the distance between two adjacent chains is relatively large (~7.5 A), indicating the probable quasi-one dimensional magnetic character of the materials. T |
Monday, March 5, 2018 9:24AM - 9:36AM |
A19.00008: Magnetic Properties of the New Low Dimensional Fluoride Compound NaCuF3 Fan Xiao, Karl Krämer, Christian Rüegg Experimental work on a physical realization of the Hubbard model NaCuF3 has been carried out inspired by recent theoretical calculation. Large quantities of NaCuF3 single crystals have been successfully synthesized and characterized. The experiments have suggested that rather than a single-band Hubbard model, this fluoride compound forms low-dimensional quantum Heisenberg system with the superexchange pathway going through corner-sharing CuF6 octahedra and an exchange strength about 17 meV. Single crystal neutron diffraction experiments indicate a long range magnetic ordering at 18.85(1) K and excitation spectra revealed by recent inelastic neutron scattering experiment has shown a two-spinon continuum at low temperature, characteristic of isolated antiferromagnetic Heisenberg spin chain. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A19.00009: Spinon confinement and field-induced transition in a quasi-one-dimensional Ising-Heisenberg antiferromagnet Shintaro Takayoshi, Shunsuke Furuya, Quentin Faure, Virginie Simonet, Sylvain Petit, Beatrice Grenier, Thierry Giamarchi We study a quasi-one-dimensional antiferromagnet with Ising anisotropy. Low-energy excitations in this system are spinons, which are confined by the interchain interaction and have a discrete excitation spectrum. We calculate the dynamical susceptibility considering interchain effects by a mean field theory. The result shows a discrete dispersion relation and agrees well with inelastic neutron scattering (INS) experiments on the compound BaCo2V2O8. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A19.00010: THz Spectroscopy of the Quantum Criticality in a Transverse Field Ising Chain Compound CoNb2O6 Johan Viirok, Dan Hüvonen, Toomas Room, Urmas Nagel, Christopher Morris, Seyed Koohpayeh, Tyrel McQueen, Peter Armitage, Jason Krizan, Robert Cava The one-dimensional Ising chain in a transverse magnetic field is an ideal example of a system that undergoes an order-disorder transition at a quantum critical point. The columbite CoNb2O6 has been proposed as a good model system of the transverse field Ising chain allowing us to investigate the finite-temperature effects on quantum fluctuations near it’s quantum critical point. We studied the Ising chain material CoNb2O6 using THz spectroscopy in high magnetic fields up to 17T and down to 0.1K. The system shows a softening of the spectrum as one approaches the quantum critical point at about 5.5T from the ferromagnetic side. This collapse of energy scales is compared to predictions for quantum criticality in the 1D Ising model tuned by transverse field. |
Monday, March 5, 2018 10:00AM - 10:12AM |
A19.00011: Magnetic and thermal properties of a Haldane chain with one-dimensional ferromagnetic chains in square lattice Joon Han Lee, Marie Kratochvílová, Zahra-Sadat Yamani, Dae Hwan Park, Hong Eun Choi, Je-Guen Park, Yoon Seok Oh Since Haldane conjectured that ground state of one-dimensional Heisenberg antiferromagnet has a finite spin gap for integer spins, while gapless excitations for half-odd integer spins, it has inspired lots of theoretical and experimental studies on low-dimensional quantum magnets. Several one-dimensional chain systems of integer spins, so called Haldane chain, have been discovered and studied, such as CsNiCl3, Y2BaNiO5, PbNi2V2O8, SrNi2V2O8, AgVP2S6. It has been known that most of the Haldane chain has antiferromagnetic coupling for the intrachain exchange interaction. Recently, we have found a Haldane chain compound in which antiferromagnetic order is accompanied by antiferromagnetic interchain coupling between one-dimensional ferromagnetic chains below 30.5 Kelvin. In this presentation, we present comprehensive study of its magnetic and thermal properties. |
Monday, March 5, 2018 10:12AM - 10:24AM |
A19.00012: Magnetic and structural properties of ultra-short 1D ferromagnetic chains Nicolas Vargas, Carlos Monton, Ivan Schuller The magnetic properties of 1D Fe and varying composition Fe/Co chains are studied as a function of chain length and structural composition. Ultra-short chains, ~7 to 400 atoms long, can be grown by organic molecular beam epitaxy using Metallo-Phthalocyanine (MPc) superlattices (SLs). The orientation of the chains can be controlled by the appropriate choice of substrate whereas their length and composition can be controlled by the SL structure. Furthermore, the magnetic signal of ultra-short chains can be amplified by increasing the periodicity of the SL, which enables the use of conventional techniques such as VSM and SQUID to study their magnetic properties. In this work, we discuss the magnetic behavior of ultra-short 1D Fe chains as a function of length and composition. We have found that the coercive field decreases when the length of the chains is reduced from 400 to 7 atoms long. We correlate the observed magnetic behavior with structural information obtained from x-ray diffraction and refinement. |
Monday, March 5, 2018 10:24AM - 10:36AM |
A19.00013: Spinon Confinement and a Longitudinal Mode in One Dimensional Yb2Pt2Pb William Gannon, Liusuo Wu, Igor Zaliznyak, Alexei Tsvelik, Franz Demmel, Meigan Aronson The Yb3+ magnetic moments in Yb2Pt2Pb are seemingly classical, since the large spin-orbit coupling of the 4f-electrons and the crystal electric field dictate a J = +/-7/2 Yb ground state doublet. Surprisingly, the fundamental low energy magnetic excitations in Yb2Pt2Pb are spinons on one dimensional chains, shown to be in good agreement with the behavior expected with the XXZ Hamiltonian for nearly isotropic, S = +/-1/2 magnetic moments. We have performed new high resolution neutron scattering measurements to examine the properties of these excitations in a magnetic field. In fields larger than 0.5 T, the chemical potential closes the gap to the spinon dispersion, modifying the quantum continuum through the formation of a spinon Fermi surface. This leads to the formation of spinon bound states along the chains, coupled to a longitudinally polarized interchain mode at energies below the quantum continuum. The ground state doublet nature of the Yb ions ensures that at all fields, transverse excitations are virtually nonexistent, giving unprecedented access to only the longitudinal excitation channel without the presence of spin waves or other transverse damping mechanisms, allowing direct measurement of the mode dispersion. |
Monday, March 5, 2018 10:36AM - 10:48AM |
A19.00014: Spin-charge separation probed with resonant inelastic x-ray scattering on doped one-dimensional antiferromagnets Umesh Kumar, Alberto Nocera, Elbio Dagotto, Steven Johnston We propose a new method to observe spin-charge separation and other exotic excitations in doped Sr2CuO3 using the resonant inelastic x-ray scattering (RIXS) technique, which can simultaneously probe charge and spin degrees of freedom. Sr2CuO3 hosts corner-shared CuO3 plaquettes, in which the Cu spin moment-1/2 couples antiferromagnetically along a one-dimensional (1D) chain. Importantly, the spin-chain can be doped with Co, Ni or Zn. We model the spin-chain by exactly diagonalizing the 1D t-J Hamiltonian to study low energy spin and charge excitations of the doped system and provide predictions of the RIXS spectra at the oxygen K-edge for doped Sr2CuO3. Our results show that the RIXS spectra are rich, containing distinct two- and four-spinon excitations, dispersive antiholon excitations, and combinations thereof. We also study dynamical spin and charge structure factors using DMRG which complements the RIXS spectra and helps to identify the spin and charge excitations. |
Monday, March 5, 2018 10:48AM - 11:00AM |
A19.00015: Gapless Quantum Spin Liquid of the Kagome-Lattice Antiferromagnet Toru Sakai, Hiroki Nakano The S=1/2 kagome-lattice antiferromagnet is one of interesting frustrated quantum spin systems. The spin gap is an important physical quantity to characterize the spin fluid behavior. Whether the S=1/2 kagome-lattice antiferromagnet is gapless or has a finite spin gap, is still unsolved issue. Because any recently developped numerical calculation methods are not enough to determine it in the thermodynamic limit. Our large-scale numerical diazonalization up to 42-spin clusters and a finite-size scaling analysis indicated that the S=1/2 kagome-lattice antiferromagnet is gapless in the thremodynamic limit[1]. It is consistent with the U(1) Dirac spin liquid theory of the kagome-lattice antiferromagnet. On the other hand, the density matrix renormalization group calculations supported the gapped Z2 topological spin liquid theory. We propose one of better methods to determine whether the spin excitation is gapless or gapped, based on the finite-size scaling analysis of the spin susceptibility calculated by the numerical diagonalization. The present work indicates that the kagome-lattice antiferromagnet is gapless[2]. |
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