Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session P6: Quantum Spin Dynamics in Molecular Nanomagnets |
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Sponsoring Units: GMAG Chair: Andrew Kent, New York University Room: Baltimore Convention Center 310 |
Wednesday, March 15, 2006 11:15AM - 11:51AM |
P6.00001: Quantum Dynamics of the Neel Vector of Antiferromagnetic Nanomagnets Invited Speaker: |
Wednesday, March 15, 2006 11:51AM - 12:27PM |
P6.00002: Universal Mechanism of Spin Relaxation in Solids Invited Speaker: Conventional elastic theory ignores internal local twists and torques. Meantime, spin-lattice relaxation is inherently coupled with local elastic twists through conservation of the total angular momentum (spin + lattice). This coupling gives universal lower bound (free of fitting parameters) on the relaxation of the atomic or molecular spin in a solid [1] and on the relaxation of the electron spin in a quantum dot [2]. \newline \newline [1] E. M. Chudnovsky, D. A. Garanin, and R. Schilling, Phys. Rev. B \textbf{72}, 094426 (2005). \newline [2] C. Calero, E. M. Chudnovsky, and D. A. Garanin, Phys. Rev. Lett. \textbf{95}, 166603 (2005). [Preview Abstract] |
Wednesday, March 15, 2006 12:27PM - 1:03PM |
P6.00003: Organization of Single Molecule Magnets on Surfaces Invited Speaker: The field of magnetic molecular clusters showing slow relaxation of the magnetization has attracted a great interest for the spectacular quantum effects in the dynamics of the magnetization that range from resonant quantum tunneling to topological interferences. Recently these systems, known as Single Molecule Magnets (SMMs), have also been proposed as model systems for the investigation of flame propagation in flammable substances. A renewed interest in SMMs also comes from the possibility to exploit their rich and complex magnetic behavior in nano-spintronics. However, at the crystalline state these molecular materials are substantially insulating. They can however exhibit significant transport properties if the conduction occurs through one molecule connected to two metal electrodes, or through a tunneling mechanism when the SMM is grafted on a conducting surface, as occurs in scanning tunnel microscopy experiments. Molecular compounds can be organized on surfaces thanks to the self assembly technique that exploits the strong affinity of some groups for the surface, e.g. thiols for gold surfaces. However the deposition of large molecules mainly comprising relatively weak coordinative bonds is far from trivial. Several different approaches have started to be investigated. We will briefly review here the strategies developed in a collaboration between the Universities of Florence and Modena. Well isolated molecules on Au(111) surfaces have been obtained with sub-monolayer coverage and different spacers. Organization on a large scale of micrometric structures has been obtained thanks to micro-contact printing. The magnetic properties of the grafted molecules have been investigated through magneto-optical techniques and the results show a significant change in the magnetization dynamics whose origin is still object of investigations. [Preview Abstract] |
Wednesday, March 15, 2006 1:03PM - 1:39PM |
P6.00004: First Principles Calculations and Spin Models Invited Speaker: Single magnetic molecules are fascinating entities. The individual transition metal ions have well defined spin states associated with localized d-orbitals bonded to ligands, which mediate the effective exchange or magnetic coupling among spins. At low temperatures and magnetic fields the internal complexity of the molecule can often (but not always) be ignored, with only the total collective spin determining the ground state and first few excited states. Using Mn$_{12}$ and V$_{15}$ as prototypes, this talk will describe a more reductionist approach and describe first principles electronic structure calculations used to gain insight into the electronic and magnetic structure of the individual transition metal ions and their interactions. Various spin coupling schemes and phenomenological Hamiltonians will be presented and compared to a variety of experimental results. Many colleagues and students from a number of institutions have contributed to this work and will be acknowledged during the talk. [Preview Abstract] |
Wednesday, March 15, 2006 1:39PM - 2:15PM |
P6.00005: Density-Functional Theory of Molecular Magnets Invited Speaker: Molecular magnets are large (a few nanometers in diameter), well-defined, discrete molecules consisting of several transition metal ions interacting through organic and/or inorganic ligands. Among thousands of synthesized molecular magnets, there is a class of molecular magnets known as single-molecule magnets (SMMs) which have large effective magnetic moments and behave as single-domain magnetic nanoparticles in an external magnetic field. They are particularly interesting because of observed quantum tunneling of magnetization and their possible applications in magnetic recording and molecular electronics. In this talk, I will demonstrate how quantum mechanics can be used to study the properties of SMMs from a first-principles vantage point. In particular, I will present density-functional calculations of the electronic, vibrational, and magnetic properties of selected SMMs, such as the total magnetic moment, electronic energy gaps, Raman scattering spectra, exchange constants, spin excitation energetics, and magnetic anisotropy barriers. I will also discuss what types of molecular environmental changes can significantly influence the exchange interaction, magnetic anisotropy, and observed quantum tunneling in the SMMs. [Preview Abstract] |
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