https://doi.org/10.1140/epjb/e2010-00028-3
Inelastic neutron scattering study and Hubbard model description of the antiferromagnetic tetrahedral molecule Ni4Mo12
1
Physikalisches Institut, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany
2
Universität Bielefeld, Fakultät für Physik,
Postfach 100131, 33501 Bielefeld, Germany
3
Universität Osnabrück, Fachbereich Physik, 49069 Osnabrück, Germany
4
Institut Laue-Langevin, BP 156, 6 Rue
Jules Horowitz, 38042 Grenoble Cedex 9, France
Corresponding author: joscha.nehrkorn@physik.uni-freiburg.de
Received:
16
June
2009
Revised:
12
November
2009
Published online:
27
January
2010
The tetrameric Ni(II) spin cluster Ni4Mo12 has been studied by INS. The data were analyzed extensively in terms of a very general spin Hamiltonian, which includes antiferromagnetic Heisenberg interactions, biquadratic 2-spin and 3-spin interactions, a single-ion magnetic anisotropy, and Dzyaloshinsky-Moriya interactions. Some of the experimentally observed features in the INS spectra could be reproduced, however, one feature at 1.65 meV resisted all efforts. This supports the conclusion that the spin Hamiltonian approach is not adequate to describe the magnetism in Ni4Mo12. The isotropic terms in the spin Hamiltonian can be obtained in a strong-coupling expansion of the Hubbard model at half-filling. Therefore detailed theoretical studies of the Hubbard model were undertaken, using analytical as well as numerical techniques. We carefully analyzed its abilities and restrictions in applications to molecular spin clusters. As a main result it was found that the Hubbard model is also unable to appropriately explain the magnetism in Ni4Mo12. Extensions of the model are also discussed.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2010