Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session M39: Single-Molecule Magnets and QubitsFocus Live
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Sponsoring Units: GMAG DMP Chair: Selvan Demir, Michigan State University |
Wednesday, March 17, 2021 11:30AM - 12:06PM Live |
M39.00001: Lanthanide Organometallic Compounds as Single-Molecule Magnets Invited Speaker: Richard Layfield Organometallic sandwich compounds have played a leading role in the development of lanthanide chemistry. However, the magnetic properties of f-element organometallics have not been studied extensively, which is surprising given the prominent roles played by lanthanides in magnetic materials and their applications medical settings, notably MRI. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M39.00002: Vibronic coupling in candidate spin qubit material: Na9[Ho(W5O18)2]x35H2O Avery Blockmon, Aman Ullah, Kendall D Hughey, Yan Duan, Ken ONeal, Mykhaylo Ozerov, Juan Arago, Alejandro Gaita-Arino, Janice Musfeldt In order to unravel decoherence pathways in a candidate spin qubit system, we measured the vibrational properties of single molecule magnet Na9[Ho(W5O18)2]x35H2O. We compared our findings with complementary lattice dynamics calculations and models for spin-phonon and vibronic coupling. Magneto-infrared spectroscopy revealed field-induced changes near 63 and 370 cm−1 that we model in terms of f-manifold crystal field excitations activated by odd-symmetry vibrations. These findings advance the understanding of vibronic coupling in molecular magnets, place severe constraints on the spin energy levels in this system, and provide a strategy for designing molecular qubit materials with improved lifetimes. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M39.00003: Investigating the Magnetic Properties of the Giant Mn84 Torus Dian-Teng Chen, Henry F Schurkus, Matthew J O'Rourke, Ashlyn R Hale, George Christou, Garnet Chan, Hai-Ping Cheng The giant single-molecule magnet Mn84 has a shape of torus of eighty-four Mn3+ ions (S=2). As the manganese atoms in Mn84 are all bridged by O2- or MeO- groups, strong pairwise exchange interactions between these manganese atoms are expected. Even though the magnetic susceptibility of this system has been measured experimentally, its electronic-magnetic structure and spin-spin couplings remain unknown. In this work, we investigate these interactions using first-principles calculations, from which a Heisenberg model is developed. The exchange coupling constants are extracted by fitting to the total energies of different spin configurations of Mn84. In addition, we compute the magnetic anisotropy energy by including spin-orbital couplings. |
Wednesday, March 17, 2021 12:30PM - 1:06PM Live |
M39.00004: Symmetries, pseudo-symmetries and single-molecule magnets Invited Speaker: Akseli Mansikkamäki In recent years, one of the key frameworks for constructing lanthanide-based single-molecule magnets with high operational temperatures has been the so-called symmetry strategy. Under certain point-group symmetries the crystal-field operator corresponding to the molecular complex commutes with the angular momentum projection. This then leads to vanishing of several important transition magnetic moment matrix elements and to slower relaxation of magnetization. For example, local symmetries have been used to explain the relatively high effective energy barriers for the reversal of magnetization in several lanthanide complexes with pentagonal bipyramidal structure.[1] In the present work we will show by quantitative evaluation of the crystal-field using ab initio methods that the symmetry of the crystal-field operator does not match that of an ideal pentagonal bipyramidal environment. Furthermore, the best-performing single molecule magnets are based on dysprosium metallocene cations that do not have any obvious molecular point group symmetry.[2] We will discuss to what extent molecular point-group symmetry – exact or approximate – actually plays a role in determining the magnetic properties of lanthanide single-molecule magnets. We will propose that the magnetic properties are better described by considering the interaction between the ligands and the vacant lanthanide 5d oribtals, which then produces an indirect effect on the open 4f shell. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M39.00005: Magnetic Properties of Single-Molecule Magnets Derived from Equation-of-Motion Coupled-Cluster Wave Functions Maristella Alessio, Anna Krylov This work presents validation studies for magnetic properties of transition metal complexes that are proposed as single-molecule magnets (SMMs). |
Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M39.00006: Relativistic Hyperfine Interaction in Single-Molecule Magnets: Multiconfigurational Study Aleksander Wysocki, Kyungwha Park Accurate calculations of hyperfine interaction parameters in single molecule magnets are of crucial importance for quantum information applications. Relativistic treatment of hyperfine operators is essential in such calculations especially in the presence of a significant Fermi contact contribution. Here, we describe an implementation of a first-principles computational methodology for magnetic hyperfine and electric quadrupole interactions within the framework of multiconfigurational quantum chemistry methods. The relativistic effects are included based on the Douglas-Kroll-Hess Hamiltonian. Hyperfine interaction parameters are calculated for simple molecules and compared with the literature. The method is then used to study electronic-nuclear spectra and magnetization dynamics in different single molecule magnets. Further, the effect of an external electric field on hyperfine interactions is studied. Conditions necessary for realization of a strong hyperfine Stark effect are discussed. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Live |
M39.00007: Impact of Heisenberg Coupling Strength of Ferromagnetic Electrodes on Temporal and Spatial Properties of Magnetic Tunnel Junction based Molecular Spintronics Devices (MTJMSD) Eva Mutunga, Bishnu Dahal, Marzieh Savadkoohi, Andrew Grizzle, Christopher D’Angelo, Vincent Lamberti, Pawan Tyagi Magnetic tunnel junction based molecular spintronics devices (MTJMSD) were fabricated by bridging single-molecule magnets (SMMs) across the insulating tunnel barrier on prefabricated magnetic tunnel junction1. The SMMs produced strong exchange coupling between the ferromagnetic electrodes. We used Monte Carlo (MC) simulations based on the Ising model analog of MTJMSD to investigate the effect of ferromagnetic electrodes on magnetic and physical properties of the device. We varied the Heisenberg coupling in the MTJMSD’s ferromagnetic electrodes as well as their Curie temperature. Here we will discuss: 1) The impact of ferromagnetic type on MTJMSD magnetization equilibrium state over time. 2) The effect of varying the molecular coupling strength and the ferromagnetic electrode's Heisenberg exchange coupling simultaneously. 3) The impact range of SMMs as a function of ferromagnetic electrode type elucidated by the spatial distribution of the magnetic moment of the ferromagnetic electrodes. Our MC study explains experimentally observed effects due to variation of the type of ferromagnetic electrodes2. |
Wednesday, March 17, 2021 1:42PM - 1:54PM Live |
M39.00008: Towards the extraction and control of the Hamiltonian parameters of spin-3/2 Co(II) antiferromagnets. William Blackmore, Jamie Brambleby, John Singleton, Martin Lees, Jamie L Manson, Paul Goddard Low-dimensional magnetism has potential applications in quantum computing and data storage, as well as furthering theoretical understanding of correlated systems, but challenges remain in designing suitable compounds. We will present a methodology to characterise S = 3/2 Co2+ antiferromagnets that make use of lab-based magnetometry and heat capacity techniques. We have synthesised and characterised four new materials: quasi-0-dimensional (Q0D) Co(HF2)2(3-Brpy)4, Q1D [Co(HF2)(3-Clpy)4]BF4, Q2D CoF2(pyz)2 and CoCl2(pyz-D4)2 to test this method. The results imply that by manipulating the starting components of the synthesis process, one can direct the Hamiltonian of these compounds. The effect structure has on the magnetic properties is described, as well as the influence of ligand and magnetic ion substitution by comparison to complexes containing [Ni(pyz)2]2+ sheets. |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M39.00009: Single-Molecule Magnet Mn12 on GaAs-supported Graphene: Gate Field Effects From First Principles Shuanglong Liu, Maher Yazback, James Nathan Fry, Xiaoguang Zhang, Hai-Ping Cheng We study gate field effects on the Mn12O12(COOH)16(H2O)4 | graphene | GaAs heterostructure via first-principles calculations. We find that under moderate doping levels electrons can be added to but not taken from the single-molecule magnet Mn12O12(COOH)16(H2O)4 (Mn12). The magnetic anisotropy energy (MAE) of Mn12 decreases as the electron doping level increases, due to electron transfer from graphene to Mn12 and change in the band alignment between Mn12 and graphene. At an electron doping level of -5.00 × 1013 cm-2, the MAE decreases by about 18% compared with that at zero doping. The band alignment between graphene and GaAs is more sensitive to electron doping than to hole doping since the valence band of GaAs is close to the Fermi level. The GaAs substrate induces a small bandgap in the supported graphene under the zero gate field and a nearly strain-free configuration. Finally, we propose a vertical tunnel junction for probing the gate dependence of MAE via electron transport measurements. |
Wednesday, March 17, 2021 2:06PM - 2:18PM Live |
M39.00010: Evolution of exchange interactions in XXYY spin tetramers Peter Dyszel, Jason Haraldsen The antiferromagnetic spin XXYY tetramer system consisting of two coupled dimers with exchange interactions α1 and α1' and dimer-dimer exchange interaction α2 is studied. Using exact diagonalization, we examine the evolution of the quantum energy levels and thermodynamic properties for various spin configurations and exchange interactions. Furthermore, we show the development of quantum phase transitions that are produced by the convergence of the Schottky anomaly with both exchange variance and external magnetic field. |
Wednesday, March 17, 2021 2:18PM - 2:30PM Live |
M39.00011: Electrically Tuned Hyperfine Coupling in Neutral Tb(II)-based Single-Molecule Magnet Robert L Smith, Aleksander L Wysocki, Kyungwha Park Electronic and nuclear spin levels of molecules and defects in solids have been shown to be good candidates for qubits. In order to control the level separations and qubit operations, an electric field or voltage was used for deep dopants in semiconductors. This is possible due to a strong interaction between the nuclear spin of the dopant and the electron spin density at the nucleus. Inspired by the solid-state systems, we propose that divalent lanthanide (Ln) complexes with unusual electronic configurations have a strong interaction between the Ln nuclear spin and the electronic degrees of freedom, which renders electrical tuning of the interaction. As a prototype example, we study hyperfine interaction of the Tb nucleus for a neutral Tb(II)(CpiPr5)2 molecule with long magnetization relaxation time, using the multiconfigurational quantum chemistry methods including spin-orbit coupling. We find that the hyperfine interaction is one order of magnitude greater than that for Tb(III)Pc2. We also uncover that the response of the Fermi contact term to an electric field results in electrical tuning of the nuclear level separations. |
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