O. Waldmann, C. Dobe, H. U. Güdel and H. Mutka
Quantum dynamics of the Néel vector in the antiferromagnetic molecular wheel
CsFe8
Phys. Rev. B 74, 054429/1-12 (2006)
Abstract:
The inelastic neutron scattering (INS) spectrum is studied for the
antiferromagnetic molecular wheel CsFe8, in the
temperature range 2–60 K, and for transfer energies up to 3.6 meV.
A qualitative analysis shows that the observed peaks correspond to
the transitions between the L-band states, from the ground
state up to the S=5 multiplet. For a quantitative analysis,
the wheel is described by a microscopic spin Hamiltonian (SH), which
includes the nearest-neighbor Heisenberg exchange interactions and
uniaxial easy-axis single-ion anisotropy, characterized by the constants
J and D, respectively. For a best-fit determination of
J and D, the L band is modeled by an
effective SH, and the effective SH concept extended such as to
facilitate an accurate calculation of INS scattering intensities,
overcoming difficulties with the dimension of the Hilbert space. The
low-energy magnetism in CsFe8 is excellently described by
the generic SH used. The two lowest states are characterized by a
tunneling of the Néel vector, as found previously, while the
higher-lying states are well described as rotational modes of the
Néel vector.