AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+NS-TuA

Paper MI+NS-TuA1
Many-spin Hamiltonian for the Single-molecule Magnet Mn12-Ac

Tuesday, November 4, 2003, 2:00 pm, Room 316

Session: Self Assembly and Nanomagnetism
Presenter: K. Park, Naval Research Laboratory and Howard University
Authors: K. Park, Naval Research Laboratory and Howard University
M.R. Pederson, Naval Research Laboratory
S.L. Richardson, Howard University and Naval Research Laboratory
Correspondent: Click to Email
Nanoscale single-molecule magnets recently received great attention due to scientific and practical reasons: macroscopic quantum phenomena and possible utilization as magnetic storage devices or quantum computing. A single-molecule magnet (SMM) is a three-dimensional array of identical molecules, each of which consists of several transition metal ions surrounded by organic ligands and is independent of neighboring molecules. Among many kinds of SMMs, Mn12-Ac has been the most extensively studied for the past decade. Although the low-energy features of Mn12-Ac have been well understood by considering each molecule as an effective ground-state spin of S=10, there is still a big controversy over the energy gap between the first excited-state manifold and the ground-state manifold as well as the internal structure of the single molecule. To provide a guide to understanding the controversial many-spin features, we investigate the intramolecular exchange couplings and the projected single-ion anisotropies using density-functional theory (DFT). We use all-electron Gaussian-orbital-based Naval Research Laboratory Molecular Orbital Library (NRLMOL) within Perdew-Burke-Ernzerhof (PBE) generalized-gradient approximation (GGA). Based on the calculated exchange couplings and anisotropy parameters, we construct a model many-spin Hamiltonian which reproduces calculated single-spin results and allows for the extraction of many-spin features.