Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F38: Molecular NanomagnetsFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Stephen Hill, Florida State University Room: BCEC 206B |
Tuesday, March 5, 2019 11:15AM - 11:27AM |
F38.00001: Experimental Evidence for Non-Collinear Antiferro-toroidic Ground State in a Dy8 Molecule Qing Zhang, Shiqi Li, Myriam Sarachik, Michael L Baker, Theocharis Stamatatos The single molecular toroics are a class of coordination complexes that exhibit spin vortex chiral ground states due to non-collinear arrangements of local magnetic moments. While ab initio methods can predict local magnetic moments, unequivocal experimental determination has proven more challenging. Typically, angular dependent single crystal magnetization would be a good method to obtain anisotropy information. However, periodicity resultant from the cluster symmetry has hindered the use of this method for the study of many complexes including Dy3 [1]. In this work, we consider a snub square molecule, Dy8 [2]. Multiple orientation single crystal magnetization, measured at 0.3 K, reveal the orientation of moments. These measurements, with a simple Ising model, are used to identify a zero toroidal ground state in Dy8, highlighting the robustness of vortex chirality within larger Dy based molecular lattices. |
Tuesday, March 5, 2019 11:27AM - 11:39AM |
F38.00002: Calculation of Exchange Coupling Constants in Mn-Ce Molecular Magnets Dianteng Chen, Xiangguo Li, Yun-Peng Wang, Sayak Das Gupta, Xiaoguang Zhang, George Christou, Hai-Ping Cheng Recently several Mn-Ce molecular magnets have been synthesized, including Mn3Ce2 and Mn5Ce3 with three different ligands, but their magnetic properties are yet to be detailed. We calculate the energies of all the spin configurations of each of these molecules by density functional theory. From the calculations of each molecule, we determine a Heisenberg Hamiltonian with antiferromagnetic or ferromagnetic exchange coupling constants using both spin-projected and non-spin-projected energies of the broken symmetry solutions and compare the results to the coupling constants fitted from experimental susceptibility data. |
Tuesday, March 5, 2019 11:39AM - 11:51AM |
F38.00003: Spin Echo Measurements with a Customized Electron Spin Resonance Spectrometer of an Atomic-clock Transition in the Molecular Nanomagnet Cr7Mn Kai-Isaak Ellers, Gajadhar Joshi, Charles Collett, Jonathan Friedman, Daniel Sava, Grigore Timco, Richard Winpenny Molecular nanomagnets are promising systems for quantum computation but such applications require sufficiently long coherence times (T2) to permit quantum logic operations. We report on the development of low-cost, customized instrumentation for measuring T2 in such molecules, as well as promising results from the spin-1 molecular nanomagnet Cr7Mn. We dilute Cr7Mn samples in toluene at concentrations between 0.00001% and 10% and perform spin echo measurements using our home-made electron-spin resonance spectrometer. This is achieved by coupling our samples to a loop-gap resonator with adjustable resonant frequency and irradiating with short (~100 ns) electromagnetic microwave pulses controlled by an FPGA. We observe spin echo and Rabi nutation from our sample and measure both T2 and T1, the spin-lattice relaxation time. Further, we find an enhancement of T2 by a factor of three at the avoided level crossing that occurs at zero field, evidence of an atomic-clock transition, where the dependence of the transition frequency on magnetic field vanishes to first order. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F38.00004: Enhancing spin-spin coherence times in a Cr7Mn molecular nanomagnet at a clock transition Gajadhar Joshi, Kai-Isaak Ellers, Charles Collett, Daniel Sava, Richard Winpenny, Grigore Timco, Jonathan Friedman The development of quantum computing based on the spin quibits is contingent on the synthesis of spin quibits with long spin coherence time. Molecular nanomagnets (MNMs) are unique systems that allow chemical engineering of physical parameters in order to enhance their spin relaxation times. Atomic-clock transitions afford a method to significantly increase the spin-spin relaxation times (T2) for MNMs [1]. In dilute samples of Cr7Mn MNM with effective spin S=1, we have measured T2 values as high as 3 µs near a clock transition. We find that the effects of the clock transition are more pronounced with increased dilution and reduced temperature. We present the results of detailed studies of these effects and suggest ways to increase the coherence times further. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F38.00005: Forming a Two-Qubit System from Dimers of Molecular Nanomagnets Charles Collett, Paolo Santini, Stefano Carretta, Jonathan Friedman Molecular nanomagnets (MNMs) are a class of materials that can make good spin qubit candidates due to their chemical engineerability. We present a method for constructing two-qubit gates using dimers of Cr7Mn, a spin S=1 MNM that features a zero-field clock transition. Operating at this transition increases T2, allowing for more gates during the lifetime of the quantum state. We show that such a dimer system can be used to behave as a two-qubit system in which all of the transitions between states are clock transitions. One-qubit gates can be achieved using pulsed electron-spin resonance, and two-qubit gates can be implemented using an always-on exchange interaction between the molecules of the dimer. After truncating the Hamiltonian to its four lowest-energy states and transforming into the interaction picture, we simulated both a one-qubit gate as well as a CNOT gate sequence that has a duration of 85 ns, finding average fidelities of 99.5% for both gates. We will briefly discuss ongoing work to experimentally implement these protocols. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F38.00006: Pulsed Electron-Spin Resonance Studies of Atomic Clock Transitions in a Dimer of the Molecular Nanomagnet Cr7Mn Michael Cha, Jonathan Friedman, Daniel Sava, Grigore Timco, Richard Winpenny, Charles Collett Qubits, or quantum bits, rely on a quantum system that can hold any superposition of two states as opposed to just 0 or 1 as with a classical bit. Various systems have been explored as qubit candidates, including photons, trapped atoms, and both nuclear and electron spins. Our research focuses on constructing two-qubit systems using dimers of molecular nanomagnets (MNMs), a class of magnetic material that can be chemically engineered to achieve various desired attributes. The focus of our current work, dimers of the MNM Cr7Mn, features such an attribute: clock transitions between multiple spin states that increase the lifetime of the quantum state. We present pulsed electron-spin resonance (ESR) studies of dilute Cr7Mn dimers in loop-gap resonators, including spectroscopic exploration of two clock transitions in the dimer as well as progress on implementing two-tone ESR for two-qubit gates. |
Tuesday, March 5, 2019 12:27PM - 1:03PM |
F38.00007: Entanglement in a molecular magnet dimer Invited Speaker: Tatiana Guidi Entanglement is a crucial resource for quantum information processing and its detection and quantification is of paramount importance in many areas of current research. Weakly coupled molecular nanomagnets provide an ideal test bed for investigating entanglement between complex spin systems. However, entanglement in these systems has only been experimentally demonstrated rather indirectly by macroscopic techniques or by fitting trial model Hamiltonians to experimental data. We have exploited the capabilities of four-dimensional inelastic neutron scattering (INS) to portray entanglement in weakly coupled molecular qubits and to quantify it [1]. The INS measurements on the prototype (Cr7Ni)2 supramolecular dimer has allowed us to demonstrate the potential of this approach, which allows one to extract the concurrence in eigenstates of a dimer of molecular qubits. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F38.00008: Observation of Anisotropy-driven Quantum Dynamics of Single-Molecule Magnet Spins at 100mK Rebecca Cebulka, Enrique Del Barco We will present the continuing results of the implementation of our novel experimental technique to allow pulse EPR studies (spin echo) of condensed samples of single-molecule magnets and single-atom magnets (non-diluted crystals) at temperatures at or below 100mK. The aim is to eliminate dephasing due to dipolar fluctuations by freezing the spin state of all molecules in the crystal in the ground state without the need of applying strong magnetic fields. We expect that these conditions would allow us to study the quantum dynamics of the spins as governed by the intrinsic molecular magnetic anisotropy, which should give rise to non-well defined Rabi oscillations of the spin state, including metastable precessional spin states. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F38.00009: Combined THz and Pulsed EPR studies on a Yb(III) Single Ion Magnet Jonathan Marbey, Stergios Piligikos, Joscha Nehrkorn, Mykhaylo Ozerov, Stephen Hill Recently, the development of single molecule magnets has shifted rapidly away from the use of transition metals in favor of lanthanides due to their large single ion anisotropy. This is a direct consequence of the relatively strong spin-orbit coupling inherent to lanthanides, which, in the presence of the appropriate crystal field, gives rise to well separated spin-orbit projected states that can permit slow relaxation of the magnetization. The motivation for studying such systems presumes that the so-called Orbach process provides the primary pathway through which the magnetization relaxes. However, previous studies on Yb(trensal) (1) have shown that simply having a large zero field energy barrier is not a sufficient criterion to achieve a high blocking temperature. In doing so, it was demonstrated that 1 also has the additional potential for use as a molecular spin qubit. To further investigate these properties in 1, we employ both Fourier Transform Far Infrared spectroscopy and pulsed EPR measurements to: i) characterize the zero field splitting associated with the crystal field and ii) probe the interactions that limit both spin-lattice and spin-spin relaxation by measuring the dependence on temperature and magnetic field. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F38.00010: Zero field stability of holmium single atom magnets Patrick Forrester, François Patthey, Edgar Fernandes, Harald Brune, Fabian Natterer Since their magnetic remanence was first measured in 2016, holmium single atom magnets on MgO/Ag(100) have garnered significant attention due to their hour long spin lifetimes, read and write-ability with spin-polarized scanning tunneling microscopy (SP-STM), and high coercive magnetic field [1-3]. Despite having been characterized with X-Ray absorption, STM, and electron spin-resonance STM, the system has not been measured at zero field. This has led to ambiguities concerning the electronic ground state of Ho/MgO and the stability of the system at zero field [3]. Here we present SP-STM measurements demonstrating the zero-field stability of Ho single atom magnets. Using antiferromagnetic Mn88Ni12 tips, we read the atom’s magnetic state, allow it to evolve under zero field conditions, and read it again. We discuss how these measurements can be used to determine the electronic ground state of the system. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F38.00011: Interfacial Influence on Elastic Properties of Spin-Transition Nanoparticles John Cain, Mirko Mikolasek, Wanhong He, Ines E. Collings, José Elías Angulo Cervera, Lucía Piñeiro-López, Lucie Routaboul, Alin-Ciprian Bas, Maria D. Manrique-Juarez, Gábor Molnár, Daniel R. Talham, Mark Meisel In photo-excited RbxCo[Fe(CN)6]y@KaNi[Cr(CN)6]b core@shell spin-transition nanoparticles, the rate of the relaxation in the core is accelerated by more than an order of magnitude due to the presence of the shell [1]. In addition, the relaxation rate continues accelerating with increasing shell thickness, which an electro-elastic model explains as a change in the mechanical properties of the core due to its interface with an increasingly rigid shell [1,2]. Here, nuclear inelastic scattering (NIS) was used to study a series of heterostructures with different shells and selectively determine the stiffness of the core, using the low-energy phonon modes and the partial phonon density of states. The results show a significant softening of the low-temperature state in the core with increasing shell thickness, providing a possible explanation for the observed relaxation rate increase. The bulk modulus for each sample was determined using PXRD, and interestingly, shells of different compositions appear to have dissimilar effects on the stiffness of the low-spin state of the core, expected to predominate at low temperatures. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F38.00012: Detection of emergent magnetic states at molecular interfaces by LE-μSR Matthew Rogers, Rhea Stewart, Stephen Lee, Thomas Prokscha, Oscar Cespedes The interfacial states that form due to orbital hybridisation and charge transfer at molecular interfaces can lead to fascinating magnetic properties. Several approaches to the characterisation of these surface states have been taken in the recent past such as SQUID magnetometry and XMCD. However, the resolution of these methods is often tested due to the confinement of these effects to interfaces. In this study, we use low energy muon spin rotation (LE-μSR) to probe such phenomena. Probing the transition oscillations between hyperfine energy levels of C60 that has been interfaced with non-magnetic copper layers. We observe an increase in the transition frequency due to Zeeman splitting of the hyperfine tensor. We may eliminate this state through demagnetisation of the interface allowing us to attribute this observation to the emergent magnetic states at the CuC60 interface. In a second system comprised of a metal oxide-C60 interface. We have shown that optical gating of this photovoltaic device leads to increases in local fields at the interface due to a spin-dependent trapping of charge, thereby acting as a 'spin capacitor'. These measurements demonstrate the capability of the μSR technique for the characterisation of novel thin film molecular structures and devices. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700