Regensburg 2007 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)
MA 15.146: Poster
Dienstag, 27. März 2007, 15:00–19:00, Poster A
Spin-wave theory for magnetic molecules — •Roman Schnalle1 and Jürgen Schnack2 — 1Universität Osnabrück, Fachbereich Physik, D-49069 Osnabrück — 2Universität Bielefeld, Fakultät für Physik, PF 100131, D-33501 Bielefeld
Unfortunately exact diagonalization of the Heisenberg
Hamiltonian of some molecular systems like the famous
{Mo72Fe30} is limited by the huge size
of the related Hilbert space that quickly grows with system
size. Following Takahashi [1] finite-size spin-wave theory seems
to be appropriate to access low-temperature properties of huge
magnetic molecules. By comparing results calculated by spin-wave
theory with results obtained from exact diagonalization it is
investigated whether spin-wave theory is able to give reliable
information about magnetic and thermodynamic properties of
molecular systems. Within this theory rotational invariance of
the participating spins is restored by the introduction of a set
of Lagrange-multipliers. Then the modified Hamiltonian is
diagonalized numerically. The energy spectra and the
low-temperature thermodynamics are calculated and compared with
results from exact diagonalization for quasi-onedimensional
Neél-like systems, namely spin rings, and a frustrated system,
where twelve spins occupy the vertices of a
cuboctahedron.
[1] M. Takahashi, Phys. Rev. B 40, 2494 (1989)