Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G58: Single Molecule Magnets II |
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Sponsoring Units: GMAG Chair: Tao Hong, Oak Ridge National Lab Room: Room 302 |
Tuesday, March 7, 2023 11:30AM - 11:42AM |
G58.00001: Toward the Understanding of a Zero-Field Clock Transition in Borosilicate Glass Brendan C Sheehan, Guanchu Chen, Jonathan R Friedman Clock transitions (CTs) in molecular nanomagnets have potential for use as qubits because the decohering effects of magnetic fluctuations are suppressed to first order, leading to enhanced coherences times T2 [1,2]. While not a molecular nanomagnet, borosilicate glass, a structural SiO2-based glass enriched with B2O3, shows promise as a CT-based qubit with coherence times up to 5 μs at the clock transition. By employing the CPMG pulse sequence, T2 can be extended up to 25 μs at the clock transition. Using electron spin resonance techniques, we characterize the CT in borosilicate glass and similar materials, including borosilicate glass with different concentrations of B2O3, while ruling out the presence of a CT in pure B2O3, quartz (crystalline SiO2), and soda-lime glass. A comparison of the spin dynamics of these materials provides insight into the physics underlying the observed clock transition. We hypothesize that the CT is due to spin-1 boron vacancy centers within the borosilicate glass. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G58.00002: Ab-initio study of rare-earth adatoms on a MgO film Homa Karimi, Karolina Janicka, Aleksander L Wysocki, Kyungwha Park Individual magnetic adatoms at surfaces have been shown by using scanning tunneling microscopy and spectroscopy (STM/S) to function as single atom magnets with significant coercive field and remnant field, and long spin relaxation time at several tens of kelvin. A recent addition of a capability of electron spin resonance to STM/S allows unprecedented energy resolution in measurements and enables coherent controls of spin states of the adatoms. Among such single atom magnets, a family of rare-earth adatoms has emerged a promising candidate for magnetic storage due to strong spin-orbit coupling and isolated nature of 4f valence orbitals from environment. So far, most of theoretical studies of rare-earth adatoms at surfaces are performed using density-functional theory (DFT), although 4f valence states are not reliably characterized by DFT. Here we study electronic structure and magnetic properties of several rare-earth adatoms at surfaces of magnesium oxide films by applying the ab-initio multiconfigurational method including spin-orbit coupling along with the embedding potential method. We compare our results to experiments and propose new applications of magnetic adatoms for quantum information science. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G58.00003: Quantum Chemical Study of Nickelocene: From Magnetic Molecules to Materials Maristella Alessio, Anna I Krylov A reliable ab initio description of molecular magnets is key to developing novel molecule-based quantum devices, with the potential to be more efficient and easily tunable. However, quantum chemical calculations of such magnetic materials are limited to density functional theory (DFT) or DFT+U (Hubbard correction to DFT). We employ our recently developed protocol based on the equation-of-motion coupled-cluster (EOM-CC) framework to investigate magnetic behavior of nickelocene (NiCp2, Cp = cyclopentadienyl) molecular magnet. The protocol is implemented within the ezMagnet software. Our calculations agree well with experimentally derived magnetic anisotropy and susceptibility values. The calculations show that magnetic anisotropy in NiCp2 originates from the spin-orbit coupling between the ground state and the third singlet state, instead of the closest-lying singlet state. Benchmarking DFT against EOM-CC enables then reliable DFT calculations on a realistic model of the NiCp2/MgO(001) absorption complex. The analysis of the resulting spinless transition density matrices and their natural transition orbitals explains how magnetic properties of NiCp2 are retained upon adsorption on MgO, making NiCp2 attractive as a spin sensor. The protocol is general and can be combined with density embedding techniques, allowing us to investigate systems as large and complex as molecular magnets on metal surfaces and their self-assemblies. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G58.00004: Vanadyl Phthalocyanine single molecules on insulating layers; ultrathin MgO film and Titanyl Phthalocyanine monolayer Kyungju Noh, Luciano Colazzo, Corina Urdaniz, Jaehyun Lee, Denis Krylov, Parul Devi, Andrin Doll, Andreas Heinrich, Christoph Wolf, Fabio Donati, Yujeong Bae Molecular spin is drawing attention as quantum processing platform due to its chemical tunability and scalability. Vanadyl Phthalocyanine (VOPc) is one of the promising molecular qubit candidates, yet it shows signs of strong coupling with scattering electrons when directly sitting on metal surface. Herein, we investigate VOPc single molecules on different insulating layers, magnesium oxide (MgO) bilayer and Titanyl Phthalocyanine (TiOPc) monolayer. By combined study of scanning tunneling spectroscopy (STS) and X-ray circular dichroism (XMCD), we confirm that VOPc in both systems are well decoupled from the metallic substrate, while retaining the pristine molecular spin characteristics. Furthermore, we discuss the novel properties of VOPc - symmetry reduction when adsorbed on MgO film and formation of long-range ordering on molecular template - in combination with density function theory (DFT) calculations. Our work provides a viable method towards the future integration of molecular spin qubits into solid-state quantum devices. |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G58.00005: Scanning Tunneling Microscopy Study of Vanadyl Phthalocyanine on Ag(100) William H Koll, Corina Urdaniz, Christoph Wolf, Jay A Gupta Magnetic molecules such as vanadyl phthalocyanine (VOPc) have garnered attention for their numerous applications in quantum information, photovoltaics, and medical imaging. Recent progress has been made in controlling the spin degree of freedom in molecules adsorbed on conducting surfaces via chemical synthesis. We used scanning tunneling microscopy (STM) to characterize two different coverage levels of VOPc sublimated onto a Ag(100) surface. At sub-monolayer coverage, we observe two distinct adsorption configurations: one in which the V-O group protrudes up into vacuum, and one where it points down into the substrate. Density functional theory calculations support these assignments, and predict the adsorption sites relative to the Ag(100) lattice. At higher coverages, the molecules self-assemble with only one orientation into a square lattice with a periodicity of 1.36nm, in addition to a moiré pattern of 4.36nm related to the interlayer stacking. Topographic images show a preference for stacking of an even number of molecular layers stabilized by out-of-plane dipolar interactions. Scanning tunneling spectroscopy reveals distinct electronic structure of the even-layer and odd-layer coverages. |
Tuesday, March 7, 2023 12:30PM - 12:42PM Author not Attending |
G58.00006: Tuning Spin Interactions of Magnetic Molecules on Au(111) by Atomic Adsorbates MinHui Chang, Yun Hee Chang, Na-Young Kim, Yong-Hyun Kim, Se-Jong Kahng Detecting and tuning spin interactions of magnetic molecules have been actively studied due to possible applications in molecular spintronic and qubit devices. On metallic surfaces, exchange interactions between molecular spins and spins of conduction electrons of substrates have been detected as Kondo resonances at Fermi level. It has been demonstrated that Kondo resonances can be tuned by small molecule bindings, but not by atomic adsorbates. Here, we demonstrate that the Kondo resonances of Co-porphyrin on Au(111) can be tuned by various atomic adsorbates and be detected using scanning tunneling microscopy and spectroscopy (STM and STS). We observed several adsorbate-induced complexes in STM images, and proposed their atomic structures based on density functional theory calculation results. Our STS results were explained with the redistribution of unpaired spins of Co-porphyrin by atomic adsorbates. Our study shows the spin states and interactions of metallo-porphyrin can be tuned by atomic adsorbates. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G58.00007: Molecule-based magnetic thin film for spin-thermoelectric energy conversion Jung-Woo Yoo Inseon Oh, Jungmin Park, Daeseong Choe, Junhyeon Jo, Hyeonjung Jeong, Mi-Jin Jin, and Jung-Woo Yoo |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G58.00008: Electric Control of Spin Transitions at the Atomic Scale Piotr Kot, Maneesha Ismail, Robert Drost, Janis Siebrecth, Haonan Huang, Christian Ast The direct electric control of spin and magnetic properties has been a longstanding goal in the field of solid state physics, due to the potential for increased efficiency in information processing. This efficiency could further be optimized by bringing spin electric coupling down to the atomic scale by operating on single spin systems. Here, we show direct electric control of spin transitions in single atom spins by employing the relatively new technique electron spin resonance scanning tunneling microscopy (ESR-STM). We find strong linear shifts in the spin resonance on the order of ten times the linewidth of the signal, which we show is due to the electrically induced movement of the atom in the STM junction. Our findings show that the bias voltage in ESR-STM experiments can be used to tune the coupling between spin systems. Furthermore, this tuning parameter opens new avenues for ultrafast control of spins, which leads towards the actualization of quantum information processing on the atomic scale. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G58.00009: Spin-vibrational resonances and coupling in Ln-based single-molecule magnets in different environmentsDaria D. Nakritskaia, Sergey A. Varganov*Department of Chemistry, University of Nevada, Reno, 1664 N. Virginia Street, Reno, NV 89557-0216, United States.svarganov@unr.edu Daria Nakritskaia, Sergey A Varganov Lanthanide-based single-molecule magnets (Ln-based SMMs) are of high interest because of their potential applications as qubits and building blocks for high-density memory materials. One of the main challenges is increasing the spin relaxation and decoherence times, which requires detailed understanding of the electronic structure and spin dynamics in Ln-based SMMs. Most electronic structure calculations are done on isolated SMMs assuming ideal gas conditions whereas the experiments are performed in the condensed phase environments. Interaction between electron spin and molecular vibrations is one of the important mechanisms responsible for spin relaxation and decoherence. The rate of spin relaxation depends on the presence of spin-vibrational resonances and on the magnitude of spin-vibrational couplings which are affected by their environments. We investigate these effects in Ln-terpyridine complexes using ab initio multireference electronic structure methods. The calculations are performed on the molecular structures sampled from the molecular dynamics simulations in the gas, solution, and crystal phases. While in many cases energies of the spin and vibrational transitions are not significantly affected by the SMMs environment, coordination of the solvent molecules to Ln can lead to a large increase of magnetic anisotropy barrier. This effect can improve the magnetic properties of Ln-based SMMs in solutions and open new direction in designing high-temperature SMMs. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G58.00010: Magnetic anisotropy and exchange coupling for a fullerene C74 containing a nearly linear Tb-O-Tb unit Kyungwha Park, Aleksander L Wysocki, James C Duchamp, Harry C Dorn, Mrittika Roy, Alan L Balch Fullerenes containing lanthanide elements have been extensively synthesized and characterized for increasing blocking temperature and coercive field in single-molecule magnets (SMMs) and for studies of lanthanide-lanthanide bonding which may be hard to achieve without fullerenes. Recently, the fullerene C80 with one carbon replaced by nitrogen, azafullerene C79N, containing a terbium (Tb) dimer has been shown to have high blocking temperature and large coercive as well as an unsually large exchange coupling between the Tb ions. Charge transfer between the Tb ions and the fullerene cage is crucial for these properties. Here we investigate magnetic properties of a newly synthesized fullerene C74 containing a nearly linear Tb-O-Tb unit, within ab-initio multiconfigurational methods including spin-orbit coupling, using the structure obtained from single crystal X-ray diffraction. We find that the individual Tb ions retain strong axiality in the magnetic anisotropy which may favor SMM behavior, and that a small deviation of the Tb-O-Tb unit from the linearity contributes to transverse ligand-field interactions. Our study also shows that the fullerene cage significantly enhances the axial and transverse magnetic anisotropy terms. The exchange coupling between the Tb ions turns out to be small and it favors ferromagnetic coupling. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G58.00011: Predicting magnetic properties and spin relaxation rates in lanthanide-based single-ion magnets Sergey A Varganov, Daria Nakritskaia, Vsevolod Dergachev Lanthanide-based single-ion magnets (SIMs) are promising building blocks for the development of new materials with applications in high-density magnetic memory, spintronics, quantum sensing, and quantum computing. These applications require SIMs with stable and controllable magnetic properties, which originate from the electron spin and orbital angular momentum in lanthanide ions. Spin relaxation is responsible for the loss of magnetization in high-density memory applications, while spin decoherence is related to the loss of quantum information in qubits used in quantum sensing and computing. We will describe our theoretical and computational efforts to understand the factors affecting the electron spin relaxation and decoherence in lanthanide complexes and to determine the design criteria for multifunctional lanthanide-based SIMs with useful opto-magnetic properties. The focus will be on the complexes with the terpyridine ligands and different lanthanide ions in the gas, solution, and crystal phases. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G58.00012: Supramolecular Spin Valve Effects in Graphene Quantum Dots Decorated with Mn12 Single Molecule Magnets Amjad Alqahtani, DaVonne Henry, Luke St. Marie, Lubomir Havlicek, Jakub Hruby, Antonin Sojka, Rachael L Myers-Ward, Daniel Pennachio, Jenifer Hajzus, Abdelouahad El Fatimy, David K Gaskill, Ivan Nemec, Petr Neugebauer, Amy Y Liu, Paola Barbara Single-molecule magnets (SMMs) are made of a core of magnetic ions embedded in a ligand shell. Their unique properties make them viable for applications in quantum computing and spintronics, making it essential to be able to read and manipulate their spin states. Previous work demonstrated an electronic read-out of SMMs magnetization switching with a supramolecular spin valve, a device made of a carbon nanotube or graphene quantum dot with a few SMMs (TbPc2) deposited on it [1, 2]. A parallel alignment of the SMMs spins gives higher conductance than an antiparallel one. All the measurements were done at T<1K, and a gate voltage tuned away from the Coulomb blockade region [1, 2].
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Tuesday, March 7, 2023 1:54PM - 2:06PM |
G58.00013: Detecting Magnetic Switching in Single-Molecule Magnet Mn12 using Graphene Quantum Dots DaVonne Henry, Amjad Alqahtani, luke st marie, Samuel I Felsenfeld, Lubomir Havlicek, Jakub Hruby, Antonin Sojka, Jorge Navarro, Abdelouahad El Fatimy, Rachael L Myers-Ward, Kurt D Gaskill, Daniel Pennachio, Jenifer Hajzus, Albert F Rigosi, Ivan Nemec, Petr Neugebauer, Amy Y Liu, Paola Barbara Transport measurements through a graphene quantum dot device decorated with single-molecule magnet (SMM) Mn12 powder indicate stochastic switching of the magnetization in the molecules. Here we show that discrete changes in the graphene conductance can be attributed to magnetic switching of the molecules. The local magnetic field causes a change in the activation energy of the hot electrons in the quantum dot [1], allowing the graphene device to serve as a sensitive detector for the spin state of the proximate molecules and as a probe to measure the interaction between the SMMs and the graphene. The size of the activation energy change is too large to be explained by Zeeman effects owing to the dipole field, suggesting an exchange bias interaction between the graphene and the molecules. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G58.00014: Inelastic Electron Tunneling Spectroscopy in a Magnetic Molecule Vertical Heterojunction Xuanyuan Jiang, Shuanglong Liu, Duy Le, John J Koptur-Palenchar, Talat S Rahman, Xiaoguang Zhang, Haiping Cheng, Arthur F Hebard We have studied the inelastic electron tunneling spectroscopy (IETS) in EGaIn/H2Pc/MnPc/NCO heterojunctions where sublimated manganese phthalocyanine (MnPc) films as thin as 1 nm (3 layers) are sandwiched between ferrimagnetic bottom-layer NiCo2O4 (NCO) and top-layer soft-landing eutectic GaIn (EGaIn) electrodes, and the 1 nm hydrogen phthalocyanine (H2Pc) is used for the protection layer of MnPc. Through differential conductance measurements dI/dV, we observed conductance jumps at well defined threshold bias voltages, Vth, which indicates the energy exchange between the spins of magnetic molecules and the tunneling electrons. We also investigated the effects of magnetic field and temperature on the heterojunctions and found that they both have large influence on the Vth while the value of dI/dV of each conductance jump remains the same. We attribute the magnetic field dependence to the interaction between MnPc and our ferrimagnetic substrate NCO and attribute the temperature dependence to the correlation effect between tunneling electrons and molecular spins, as reported in a previous STM work [1]. Our work is important for electrical detection of spin qubits in magnetic molecules. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G58.00015: Conductance Peak Splitting in the Coulomb Blockade as Signature of Spin Interactions Eric D Switzer, Xiaoguang Zhang, Volodymyr Turkowski, Talat S Rahman Multi-spin device setups, such as triple quantum dots and dimer arrangements of magnetic molecules, show favorable characteristics for their use as spintronic and scalable quantum information devices[1,2]. There is a need to characterize single-electron transport properties of these systems to guide experimental realizations. In a step towards this aim, we use the generalized master equation under the Born and Markov approximation for a dimer system coupled to spin-polarized leads, with energy level positions controlled by a gate voltage, under an applied magnetic field. We predict multiple peaks in the steady-state conductance, as opposed to the single peak expected in traditional Coulomb blockade single molecule magnet experiments, related to the inclusion of excited state transitions between uncharged and charged electron manifolds. We find that by adjusting the exchange coupling of the electron with the system, these features turn on and off. This prediction opens the possibility of using spin-polarized current measurements to measure the exchange coupling between the iterant electron and multi-spin system. |
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