Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y50: Molecular Nanomagnets, Clusters, and NetworksFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Mark Meisel, University of Florida Room: 397 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y50.00001: NMR of small frustrated electron spin systems: example of V15 molecular magnet Viatcheslav Dobrovitski Frustrated spin systems with multiply degenerate ground state exhibit interesting properties, including formation of the macroscopic spin liquid state [1]. The nuclear magnetic resonance (NMR) is particularly valuable for studying frustration: it allows local probe of the electron spin systems and provides important information about the frustrated many-spin states [2,3]. However, the standard theory of NMR is not directly applicable to the frustrated system, because it assumes large separation between the spin states of the electronic subsystem (fast electron spin dynamics). We investigate how the NMR spectra are formed in the presence of frustration, taking as an example the V15 magnetic molecule, whose low-energy properties are defined by three frustrated electron spins with a doubly degenerate ground state. Considering the coupled electron-nuclear system, we show that the electron and the nuclear spins form a set of joint entangled states that define the NMR spectrum. We revise the earlier NMR experiments on V15 [3], and provide an alternative view of the experimental results. \\ {[1]} L. Balents, Nature 464, 199 (2010) [2] M. Fu et al, Science 350, 655 (2015) [3] Y. Furukawa et al, Phys. Rev. B 75, 220402(R)(2007) [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y50.00002: Reaching the Landauer limit at high speeds with a quantum nanomagnet Rocco Gaudenzi, Enrique Burzuri, Herre van der Zant, Fernando Luis The erasure of a bit of information, regardless of the physical system on which it is performed, is an irreversible operation bound to dissipate an amount of heat $Q = k_{B}T\ln 2$. As a result, work $W \geq Q$ -- where equal sign means reversible operation -- has to be applied to the physical system to restore the erased information content. This principle, due to Rolf Landauer, sets a universal minimal energy limit inherent to any classical computation. In the pursuit of the fastest and most efficient means of computation, the ultimate challenge is to produce a memory device combining the lowest intrinsic dissipation with the smallest possible relaxation time, i.e. minimising the product $W \cdot \tau_{\text{rel}}$. Here we use a crystal of molecular nanomagnets as a spin memory device and measure the work needed to carry out a storage operation. Full magnetic field control over these isolated spin systems allows quantum tunneling of magnetization to be exploited, yielding performance bordering the reversible limit while maintaining short relaxation times. The product $W \cdot \tau_{\text{rel}} $ results orders of magnitude lower than any existing memory device to date. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y50.00003: Long lived excitations in fully compensated antiferromagnetic nanomagnets Jacob Burgess, Luigi Malavolti, Steffen Rolf-Pissarczyk, Gregory McMurtrie, Shichao Yan, Sebastian Loth Extensive interest is directed towards finding long lived states in atomic scale magnetic structures. Applications include classical and quantum spintronics schemes. Here we use a recently described method of applying a single atom exchange bias, using a magnetic scanning tunneling microscope tip [1], to control the quantum states of fully compensated nano-antiferromagnetic atomic chains. We apply time-resolved spin-polarized scanning tunneling microscopy to measure the energy relaxation of the chains as a function of the tip interaction strength. With strong coupling to the microscope tip, the excited state lifetimes can extend to the millisecond scale. [1] Nature Nanotech. 10, 40 (2015). [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y50.00004: Amplification of the diamagnetic response in small Hubbard rings Amir Caldeira, Thais Trevisan We present a brief resume of a study of the electric transport properties of small discrete rings with $3\leq N\leq 6$ sites and $N_{e}<2N$ electrons, which can be seen as a simplified version of real aromatic molecules. In particular, the ring with six sites and six electrons is our prototype of the benzene molecule. It is already known that the Hubbard model itself cannot account for the anisotropy of the diamagnetic susceptibility of the aromatic molecules, which is observed when they are subjected to an external magnetic field perpendicular to their basal plane. Therefore, we propose an extension of the Hubbard model, with an \textit{ad hoc} extra interaction term, with two adjustable parameters. Our results show that this extension of the Hubbard model is able to amplify the persistent currents established in the ground state of our rings and, moreover, promotes an enhancement of the magnetic susceptibility anisotropy depending on the tuning of the adjustable parameters. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y50.00005: Core and shell size dependences on strain in core@shell Prussian blue analogue (PBA) nanoparticles and the effect on photomagnetism. J. M. Cain, C. F. Ferreira, A. C. Felts, S.~A. LoCicero, J. Liang, D. R. Talham, M. W. Meisel Rb$_x$Co[Fe(CN)$_6$]$_y$@K$_a$Ni[Cr(CN)$_6$]$_b$ core@shell heterostructures have been shown to exhibit a photoinduced decrease in magnetization that persists up to the $T_c = 70$~K of the KNiCr-PBA component, which is not photoactive as a single-phase material. A magnetomechanical effect can explain how the strain in the shell evolves from thermal and photoinduced changes in the volume of the core. Moreover, a simple model has been used to estimate the depth of the strained region of the shell, but only one size of core ($347 \pm 35$~nm) has been studied. Since the strain depth in the shell is expected to be dependent on the size of the core, three distinct RbCoFe-PBA core sizes were synthesized, and on each, three different KNiCr-PBA shell thicknesses were grown. The magnetization of each core-shell combination was measured before and after irradiation with white light. Our results suggest the strain depth, as expected, increases from $\approx 56$~nm in heterostructures with a core size of $328 \pm 29$~nm to more than 90~nm in heterostructures with a core size of $575 \pm 113$~nm. The data from the smallest core size also shows features indicating the model may be too simple. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y50.00006: Non-Collinearity in Small Cobalt-Benzene Molecular Clusters Andrés Ayuela, J. W. Gonzalez, T. Alonso-Lanza, F. Delgado, F. Aguilera Cobalt clusters covered with benzene in the form of bowl-like structures have recently been synthesized using laser ablation. Here, we investigate the types of magnetic order such clusters have, and whether they retain any magnetic order at all. We use different density functional theory (DFT) methods to study three cobalt atoms surrounded by benzene rings since, in addition to its inherent simplicity, this cluster is more stable. We found that the benzene rings induce a ground state with non-collinear magnetization, with the magnetic moments localized on the cobalt centers and lying on the plane formed by the three cobalt atoms. This is surprising because nanostructures and small clusters based on pure cobalt typically have a predominantly ferromagnetic order, and additional organic ligands such as benzene tend to remove the magnetization. We analyze the magnetism of such a cluster using an anisotropic Heisenberg model where the involved parameters are obtained by a comparison with the DFT results. Moreover, we propose electron paramagnetic resonance as an experimental tool to study the anisotropic response. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y50.00007: Magnetic Behavior of the larger network of triangles in Dy$_{8}$ molecule Qing Zhang, Michael L. Baker, Shiqi Li, Myriam P. Sarachik, Theocharis Stamatatos Qubits with chiral symmetry promise to allow denser packing because the magnetic field produced by toroidal moments decays much faster than that of normal magnetic dipoles. Prompted by the chiral symmetry found for Dy$_{3}$ [1], we have embarked on a study of the toroidal magnetism in a larger network of triangles in a Dy$_{8}$ molecule with the formula (Et$_{4}$N)$_{4}$[Dy$_{8}$O(nd)$_{8}$(NO$_{3}$)$_{10}$(H$_{2}$O)$_{2}$]2MeCN [2]. The effect of exchange coupling within a triangular network of eight oxo-bridged Dy(III) ions is investigated. Single crystal magnetization follows the 4-fold structural symmetry of the Dy$_{8}$ molecule. The angular dependence of single crystal magnetization data is consistent with an Ising type exchange Hamiltonian, the single ion easy axes are determined by an electrostatic crystal field model. [1] J. Luzon, et al., Phys. Rev. Lett. 100, 247201 (2008). [2] D. I. Alexandropoulos, et al., Inorg. Chem. 53, 5420 (2014). [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y50.00008: Electron transport through a single chalcogenide Ni$_9$Te$_6$(PEt$_3$)$_8$ cluster Guangpu Luo, Vikas Chauhan, Shiv Khanna, Kyungwha Park Recently nanoscale chalcogenide-based superatoms have been synthesized in the form of solids and also patterned at the surface of two-dimensional transition metal dichalcogenides as dopants in the laboratory. The superatoms were also theoretically shown to transform from electron donor to acceptor by modifying the ligands. One such superatom consists of a Ni$_9$Te$_6$ cluster with a rock-salt structure surrounded by eight PEt$_3$ ligands which are connected to Ni atoms at the vertices. The superatom has cubic magnetic anisotropy with magnetic anisotropy barrier of 31.55 K in the neutral state. Here we investigate electron transport through an individual Ni$_9$Te$_6$(PEt$_3$)$_8$ cluster in a single-molecule transistor setup, by considering only two charge states within the sequential electron tunneling limit. We calculate current-voltage characteristics without and with an external magnetic field by using the giant spin model with parameter values obtained from density-functional theory and by solving the master equation. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y50.00009: Evolution of the Spin Magnetic Moments and Atomic Valence of Vanadium in Vanadium doped Copper, Silver, and Gold Clusters. Arthur Reber, William Blades, Shiv Khanna The atomic structures, bonding characteristics, spin magnetic moments, and stability of VCu$_{\mathrm{x}}^{\mathrm{+}}$, VAg$_{\mathrm{x}}^{\mathrm{+}}$, and VAu$_{\mathrm{x}}^{\mathrm{+}}$ (x $=$ 3 - 14) clusters have been examined using density functional theory. Our studies indicate that the effective valence of vanadium is size-dependent and at small sizes some the valence electrons of vanadium are localized on vanadium while at larger sizes the 3$d$ orbitals of the vanadium participate in metallic bonding eventually quenching the spin magnetic moment. The electronic stability of the clusters may be understood through a split-shell model that partitions the valence electrons in either a delocalized shell or localized on the vanadium atom. A molecular orbital analysis reveals that in planar clusters the delocalization of the 3d orbital of vanadium is enhanced when surrounded by gold due to enhanced \textit{6s-5d} hybridization. Once the clusters become three-dimensional, this hybridization is reduced and copper most readily delocalizes the vanadium's valence electrons. By understanding these unique features, greater insight is offered into the role of a host materials electronic structure in determining the bonding characteristics and stability of localized spin magnetic moments in quantum confined systems. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y50.00010: Novel spintronic effects and nanoscale friction of Co-TBrPP/GNR/Au(111) heterostructures Yang Li, Kyaw Zin Latt, Anh Tuan Ngo, Andrew DiLullo, Yuan Zhang, Brandon Fisher, Peter Zapol, Saw-Wai Hla We synthesize heterostructures formed by cobalt-porphyrin (Co-TBrPP), graphene nanoribbon (GNR) and Au(111) substrate, and investigate topography, tribology and electronic properties of heterostructures using low temperature ultra high vacuum scanning tunneling microscopy (STM), tunneling spectroscopy, and atomic/molecular manipulation schemes. GNRs are formed by fusing 10,10'-dibromo-9,9'-bianthryl molecules on a Au(111) surface. Due to a weak binding, the Co-TBrPP molecules are mobile on GNR. The lateral manipulation scheme using the STM tip is employed to investigate the diffusion of the molecule on this surface. Guided by the edges of the GNR, the molecules diffuse in one-dimensional paths. Ultralow friction between Co-TBrPP is discovered and compared with the friction between Co-TBrPP and Au(111) substrate. We will also discuss novel spintronic effects of Co-TBrPP on GNR measured by using tunneling spectroscopy and spectroscopic mapping. We acknowledge the support of DOE SISGR grant: DE-FG02-09ER16109. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y50.00011: Dynamical simulation of spin-density-wave states in triangular-lattice Hubbard model Kipton Barros, Cristian Batista, Gia-Wei Chern We present a numerical framework for the dynamical simulation of quantum states with spin-density wave (SDW) order. Within a semiclassical approximation that retains electronic degrees of freedom, we demonstrate that the SDW order parameter field obeys a generalized Landau-Lifshitz (gLL) equation. To simulate this dynamics, we use the kernel polynomial method to solve the electron density matrix at every time step. Our linear scaling approach enables dynamical gLL simulations with $N \approx 10^5$ lattice sites. We apply our method to the triangular-lattice Hubbard model, and outline a phase diagram for filling fractions $n = 1/2$ and $3/4$. Our results at small and large Coulomb repulsion $U$ agree with those obtained from analytical calculations. At intermediate $U$ we uncover several intriguing SDW phases, including incommensurate structures. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y50.00012: Fluctuating charge density wave (CDW) in quasi-one-dimensional conductor Rb$_{0.3}$MoO$_{3}$ Guoqing Wu, Jun Dong, Yafang Xu, Xiao-shan Ye, Xianghua Zeng, Bing Wu, W. Gilbert Clark Fluctuating charge density wave (CDW) in quasi-one-dimensional conductor Rb$_{0.3}$MoO$_{3}$ Guoqing Wu, Jun Dong, Yafang Xu, Xiao-shan Ye, Xianghua Zeng$^{\ast}$, Yangzhou University Bing Wu, Fayetteville State University W. G. Clark, University of California, Los Angeles Various forms of charge and spin ordering exhibit in low dimensional conductors. They accompany with macroscopic coherence like superconductivity in some cases and sometimes compete or coexist with each other, while their significance is not fully understood. The quasi-one-dimensional blue bronze Rb$_{0.3}$MoO$_{3}$ is known to be a charge density wave (CDW) conductor and has been widely studied. Here we report spin-phase relaxation rate (1/$\math{T_2}$) measurements by $^{87}$Rb-NMR with a variation of field ($\math{B}$) alignments over the temperature rage 80 – 250 K (($\math{B}$ = 9 T). There is no clear evidence to support the model presented earlier in which the slow fluctuation of phasons are observed in the thermal fluctuations of CDW. *Supported by China NSF grant #: 61474096 [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y50.00013: Effects of pressure on the magnetic anisotropy of ferromagnetic insulator Cr$_{\mathrm{2}}$Ge$_{\mathrm{2}}$Te$_{\mathrm{6}}$ Zhisheng Lin, Mark Lohmann, Chi Tang, Junxue Li, Wenyu Xing, Jiangnan Zhong, Shuang Jia, Wei Han, Jing Shi Cr$_{\mathrm{2}}$Ge$_{\mathrm{2}}$Te$_{\mathrm{6}}$ is an interesting atomically layered ferromagnetic insulator with space group $R\overline 3 $ that has a Curie temperature of \textasciitilde 61 K and a band gap of \textasciitilde 0.2 eV. Owing to the van der Waals nature of the crystal structure, both electronic and magnetic properties depends on the interlayer coupling; therefore, it is interesting to study the effects of the interlayer spacing on physical properties. In this study, we apply a hydrostatic pressure to a CGT crystal up to 2000 PSI while measuring its magneto-transport properties with an external magnetic field applied along the c-axis of CGT. With increasing pressure, we observe a systematic increase in the anisotropic magnetoresistance ratio accompanied by a decrease in the band gap. In the meantime, the saturation field in the magnetoresistance increases as the pressure increases, indicating that the magnetization gradually favors to be in the ab-plane. This induced anisotropy change could be attributed to the increased interlayer coupling as the layers are bought closer to each other. [Preview Abstract] |
Friday, March 17, 2017 1:51PM - 2:03PM |
Y50.00014: Molecular Analogue of the Perovskete Repeating Unit Xiangguo Li, Yun-Peng Wang, Annaliese E. Thuijs, Khalil A. Abboud, George Christou, X.-G. Zhang, Hai-Ping Cheng The perovskite manganites AMnO$_{\mathrm{3}}$ and their doped analogues A$_{\mathrm{1-x}}$B$_{\mathrm{x}}$MnO$_{\mathrm{3}}$ are a fascinating family of magnetic oxides exhibiting a rich variety of properties. They are thus under intense investigation along multiple fronts, one of which is how their structural and physical properties are modified at the nanoscale when needed at this size regime. We investigate the electronic and magnetic properties of the molecular compound [Ce$_{\mathrm{3}}$Mn$_{\mathrm{8}}$O$_{\mathrm{8}}$(O$_{\mathrm{2}}$CPh)$_{\mathrm{18}}$(HO$_{\mathrm{2}}$CPh)$_{\mathrm{2}}$] (Ce$_{\mathrm{3}}$Mn$_{\mathrm{8}})$ that bears a striking structural resemblance to the repeating unit seen in the perovskite manganites, using first-principles method. We show that Ce$_{\mathrm{3}}$Mn$_{\mathrm{8}}$ exhibits both the combination of pairwise Mn$^{\mathrm{III}}_{\mathrm{2}}$ ferro- and antiferromagnetic exchange interactions and the resultant spin vector alignments that are found within the C-type antiferromagnetic perovskites. The first-principles calculations reveal not only the expected nearest-neighbor Mn$^{\mathrm{III}}_{\mathrm{2}}$ exchange parameters but also an unusual, direct metal-to-metal channel through the central Ce$^{\mathrm{IV}}$ for magnetic couplings, originating from a virtual exchange involving the Ce$^{\mathrm{IV}}$ f-orbitals. [Preview Abstract] |
Friday, March 17, 2017 2:03PM - 2:15PM |
Y50.00015: Novel phase transitions in coupled dipolar chains. paula mellado We study the properties of a classical magnetic system realized by two chains of U(1) rotors coupled via Coulomb interactions in the dumbbell approach. Magnets in chain I and chain II rotate in the x-z and y-z planes respectively. Ground state correlations and the system wave excitation spectrum are found using spin wave theory. The displacement "d" of chain II from chain I induces dynamics in the system and yields two first order magnetic phase transitions. The transitions happen at critical displacements, which notably, are independent of the magnetic charge at the tips of the magnets, suggesting a geometrical origin. [Preview Abstract] |
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