Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W46: Low-Dimensional Magnetism and Single Molecule MagnetsFocus
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Sponsoring Units: GMAG Chair: Selvan Demir, Michigan State Univ Room: 708 |
Friday, March 6, 2020 8:00AM - 8:36AM |
W46.00001: Remarkable magnetic field effects in quasi-one dimensional Ising-like antiferromagnet BaCo2V2O8 studied by neutron scattering Invited Speaker: Beatrice Grenier BaCo2V2O8 is a realization of a spin-1/2 Ising-like quasi-one dimensional antiferromagnet (AF) with fascinating static and dynamical behaviors. In zero-field, the weak interchain interactions stabilize below 5.6 K a peculiar Néel ordering, characterized by magnetic moments aligned along the chain c-axis and dressed with confined two spinon excitations [1,2]. We have explored the influence of an external magnetic field both on the AF ordering and on the spin dynamics by single-crystal neutron scattering. Different behaviors are observed for a transverse and a longitudinal magnetic field (i.e. perpendicular and parallel to the direction of the moments, respectively), nicely reproduced by TEBD numerical calculations. |
Friday, March 6, 2020 8:36AM - 8:48AM |
W46.00002: Comparison of magnetic disorder at low temperature in Ca3Co2O6 and Ca3Co1.9Zn0.1O6 Benjamin White, Alexander B. C. Mantilla, Jani Jesenovec The compound Ca3Co2O6 undergoes a transition into a spin-density wave (SDW) state near 24 K. Below ~10 K, this unstable SDW state coexists with a nearly- degenerate commensurate antiferromagnetic state as well as short-range magnetic order. Clear signatures of this strong magnetic disorder have been observed in the response of entropy to changing magnetic field and temperature. We performed a calorimetry study of Ca3Co2O6 and Ca3Co1.9Zn0.1O6 in order to compare their entropic responses at low temperature. Our results for Ca3Co2O6 reveal that ΔS(T, H) ≡ S(T, H) - S(T, H = 0) increases as either temperature or magnetic field increase. In contrast, ΔS data for Ca3Co1.9Zn0.1O6 were relatively unresponsive to changes in temperature or field, suggesting that Zn substitution may reduce the low-temperature magnetic disorder observed in Ca3Co2O6. These results will be discussed within the context of two cases (Ca3Co2O6 under applied pressure and Ca2.75R0.25Co2O6 (R = Dy, Lu)) in which a single magnetic ground state is stabilized. |
Friday, March 6, 2020 8:48AM - 9:00AM |
W46.00003: Electronic and magnetic properties of the cluster magnet Ba3LaRu2O9 Qiang Chen, Amanda Clune, Jie Ma, Jinguang Cheng, Keith Taddei, Clarina Reloj Dela Cruz, Matthew Stone, Alexander Kolesnikov, Janice Lynn Musfeldt, Haidong Zhou, Adam Aczel Magnetic materials with electrons delocalized over small molecular clusters, so-called cluster Mott insulators, have recently attracted significant interest in the quest for novel magnetic properties. The extremely short metal-metal distances within the molecular clusters promote significant electron hopping, thus leading to the formation of unusual electronic ground state configurations based on quasi-molecular orbitals. In this talk, we discuss the electronic and magnetic properties of the cluster magnet Ba3LaRu2O9. We present magnetic susceptibility and inelastic neutron scattering data supporting an unusual spin-3/2 per dimer electronic ground state that cannot be understood in a local moment picture. We also present bulk characterization, muon spin relaxation, neutron diffraction, and inelastic neutron scattering data that are indicative of an ordered state arising from a quasi-2D frustrated lattice of Ru dimer building blocks. Finally, we present preliminary results of Raman spectroscopy and neutron diffraction under pressure that reveal a coincident structural/spin state transition at ~1 GPa. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W46.00004: Large positive zero field splitting in the cluster magnet Ba$_3$CeRu$_2$O$_9$ Adam Aczel, Qiang Chen, Shiyu Fan, Keith Taddei, Matthew Stone, Alexander Kolesnikov, Jinguang Cheng, Janice Lynn Musfeldt, Haidong Zhou We present the synthesis and magnetic characterization of a polycrystalline sample of the 6H-perovskite Ba$_3$CeRu$_2$O$_9$, which consists of Ru dimers based on face-sharing RuO$_6$ octahedra. Our low-temperature magnetic susceptibility, magnetization and neutron powder diffraction results reveal a non-magnetic singlet ground state for the dimers. Inelastic neutron scattering, infrared spectroscopy, and the magnetic susceptibility over a wide temperature range are best explained by a molecular orbital model with a zero-field splitting parameter $D$~$=$~85~meV for the $S_{tot}$~$=$~1 electronic ground state multiplet. This large value is likely due to strong mixing between this ground state multiplet and low-lying excited multiplets, arising from a sizable spin molecular orbital coupling combined with an axial distortion of the Ru$_2$O$_9$ units. Although the positive sign for the splitting ensures that Ba$_3$CeRu$_2$O$_9$ is not a single molecule magnet, our work suggests that the search for these interesting materials should be extended beyond Ba$_3$CeRu$_2$O$_9$ to other molecular magnets based on metal-metal bonding. |
Friday, March 6, 2020 9:12AM - 9:48AM |
W46.00005: Lanthanide-based single molecule magnets through the prism of ab-initio calculations Invited Speaker: Boris LeGuennic In the beginning of the century, the emergence of lanthanide-based systems exhibiting slow relaxation of their magnetization opened a new chapter in the field of molecular magnetism. These so called Single-Molecule Magnets (SMMs) may find in a near future many important applications such as high-density data storage, molecular spintronic or quantum computing. Over the recent years, quantum chemical approaches, going from multiconfigurational wavefunction-based methodologies to (periodic) density functional theory have shown to be powerful tools to gain deep insight into electronic and magnetic features of such lanthanide-based SMMs. This presentation will focus on recent applications of such state-of-the-art computational protocols in the understanding of Ln-based SMMs behaviors. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W46.00006: Nature of hyperfine interactions in TbPc2 single-molecule magnets: Multireference ab-initio study Aleksander Wysocki, Kyungwha Park Lanthanide-based single-ion magnetic molecules can have large magnetic hyperfine interactions as well as large magnetic anisotropy. Recent experimental studies reported the tunability of these properties by changes of chemical environments or by application of external stimuli for device applications. In order to provide insight into the origin and mechanism of such tunability, here we investigate the magnetic hyperfine and nuclear quadrupole interactions of TbPc2 single-molecule magnets using first-principles multireference methods including spin-orbit interaction. The microscopic Hamiltonian is mapped onto an effective Hamiltonian with an electronic pseudo-spin S=1/2. We discuss the physical origin of ab-initio-calculated hyperfine interaction parameters and their dependence on the experimental molecular geometry and structure distortions. We show the ab-initio-calculated electronic-nuclear spectrum and compare it with experimental data. We further analyze the role of the non-axial quadrupole interactions in the formation of avoided level crossings and magnetization dynamics. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W46.00007: A first-principles study of the phase stability and electronic properties of monolayer Vanadium-based Janus dichalcogenides Dibyendu Dey, Antia S. Botana We investigate the vibrational and electronic properties of 2D van der Waals Vanadium-based Janus dichalcogenides (VSSe, VSeTe, VSTe) at the monolayer level in both 2H and 1T phases by using first-principles calculations. We have found the 2H phase is energetically favorable in VSSe and VSeTe, whereas the 1T phase is lower in energy in VSTe. Within density functional theory, ferromagnetism (FM) allows splitting of the d-bands in the 2H phase with a trigonal prismatic environment, leading to a low-bandgap S=1/2 ferromagnetic insulator. On the other hand, no such splitting is observed in the distorted octahedral environment of the 1T phase, and the system remains metallic. In the presence of electronic correlations, we have found the magnetic ground state is FM for VSSe and VSeTe. On the contrary, a 120o canted AFM state is the magnetic ground state for VSTe. The semiconducting nature of FM two-dimensional Janus VSSe and VSeTe makes them potential materials for spintronics. |
Friday, March 6, 2020 10:12AM - 10:24AM |
W46.00008: Strong anisotropic spin-dipole coupling in electron-withdrawing Br-based system Cu2(OH)3Br Tathamay Basu, Heda Zhang, Zhiying Zhao, Xianglin Ke The compound Cu2(OH)3Br, belonging to an interesting hydroxyl salts of potential interests, crystallizes in monoclinic structure. This system consists of quasi-1D Cu-chains and undergoes complex antiferromagnetic ordering below around 10 K, with a magnetic field (H) induced spin-flop transitions below ordering. Here, we have investigated the detailed dielectric behavior of single crystalline compound in different orientations. We show that the temperature dependent dielectric constant clearly traces the magnetic ordering in presence of magnetic field, indicating the presence of magnetodielectric (MD) coupling. The MD coupling is further confirmed by isothermal H-dependent dielectric constant which captures the spin-flop transitions. These features are ascribable to electron withdrawing Br-atom to break the spatial inversion symmetry of the Cu-system, which creates local dipole moment and thereby governs strong MD coupling. This will create a path to design new magnetoelectric materials. |
Friday, March 6, 2020 10:24AM - 11:00AM |
W46.00009: Tailoring Non-Innocence in a Family of 2D Coordination Solids Invited Speaker: Kasper Pedersen Metal-organic frameworks (MOFs) and their non-porous analogues, coordination solids, constitute a new class of materials with highly multifaceted physical and chemical properties and virtually unlimited possibilities for synthetic modification and tuning. The realization of magnetic MOFs has been hampered by the large spatial separation between spin-carriers leading to magnetic order setting in at only low temperatures. A particularly attractive approach to magnetic MOFs is rooted in the use of radical ligands as spacers between paramagnetic metal ions, which alleviates the inter-metallic distance issue and have resulted in materials featuring extremely strong super-exchange interactions. Unfortunately, relatively few isolatable radical ligands possess the stability to allow their incorporation into MOF structures. An interesting approach to realize otherwise elusive radical ligands consists in the use of highly reducible metal ions, that will reduce even ligands considered wholly redox-inactive. We recently reported a quadratic, 2D coordination solid, CrCl2(pyrazine)2, that features Cr(III) and a partially reduced ligand scaffold, ensuing strong magnetic Cr(III)-radical exchange interactions [1]. |
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