F. El Hallak

Publications (4)7.37 Total impact

• Source

  Available from: Giuseppe Amoretti

  Article: Inelastic neutron scattering and frequency-domain magnetic resonance studies of S= 4 and S= 12 Mn_ {6} single-molecule magnets

  O. Pieper, T. Guidi, S. Carretta, J. van Slageren, F. El Hallak, B. Lake, P. Santini, G. Amoretti, H. Mutka, M. Koza, M. Russina, A. Schnegg, C. J. Milios, E. K. Brechin, A. Julià, J. Tejada
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  ABSTRACT: We investigate the magnetic properties of three Mn6 single-molecule magnets by means of inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The experimental data reveal that small structural distortions of the molecular geometry produce a significant effect on the energy-level diagram and therefore on the magnetic properties of the molecule. We show that the giant spin model completely fails to describe the spin-level structure of the ground spin multiplets. We analyze theoretically the spin Hamiltonian for the low-spin Mn6 molecule (S=4) and we show that the excited S multiplets play a key role in determining the effective energy barrier for the magnetization reversal, in analogy to what was previously found for the two high spin Mn6 (S=12) molecules [ S. Carretta et al. Phys. Rev. Lett. 100 157203 (2008)].
  Phys. Rev. B. 03/2010; 81(17).
• Source

  Available from: Tatiana Guidi

  Article: Neutron spectroscopy and magnetic relaxation of the Mn$_6$ nanomagnets

  S Carretta, T Guidi, P Santini, G Amoretti, O. Pieper, B. Lake, J van Slageren, F. El Hallak, W. Wernsdorfer, H Mutka, M. Russina, C. J. Milios, E. K. Brechin
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  ABSTRACT: Inelastic neutron scattering has been used to determine the microscopic Hamiltonian describing two high-spin variants of the high-anisotropy Mn$_6$ nanomagnet. The energy spectrum of both systems is characterized by the presence of several excited total-spin multiplets partially overlapping the S=12 ground multiplet. This implies that the relaxation processes of these molecules are different from those occurring in prototype giant-spin nanomagnets. In particular, we show that both the height of the energy barrier and resonant tunnelling processes are greatly influenced by low-lying excited total-spin multiplets.
  09/2008;
• Article: Breakdown of the giant spin model in the magnetic relaxation of the Mn6 nanomagnets.

  S Carretta, T Guidi, P Santini, G Amoretti, O Pieper, B Lake, J van Slageren, F El Hallak, W Wernsdorfer, H Mutka, M Russina, C J Milios, E K Brechin
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  ABSTRACT: We study the spin dynamics in two variants of the high-anisotropy Mn6 nanomagnet by inelastic neutron scattering, magnetic resonance spectroscopy and magnetometry. We show that a giant-spin picture is completely inadequate for these systems and that excited S multiplets play a key role in determining the effective energy barrier for the magnetization reversal. Moreover, we demonstrate the occurrence of tunneling processes involving pair of states having different total spin.
  Physical Review Letters 04/2008; 100(15):157203. · 7.37 Impact Factor
• Article: Neutron spectroscopy and magnetic relaxation of the Mn6 nanomagnets

  T Guidi, P Santini, G Amoretti, O. Pieper, B. Lake, J van Slageren, F. El Hallak, W. Wernsdorfer, H Mutka, M. Russina, CJ Milios, EK Brechin
  [show abstract] [hide abstract]
  ABSTRACT: Inelastic neutron scattering has been used to determine the microscopic Hamiltonian describing two high-spin variants of the high-anisotropy Mn6 nanomagnet. The energy spectrum of both systems is characterized by the presence of several excited total-spin multiplets partially overlapping the S = 12 ground multiplet. This implies that the relaxation processes of these molecules are different from those occurring in prototype giant-spin nanomagnets. In particular, we show that both the height of the energy barrier and resonant tunnelling processes are greatly influenced by low-lying excited total-spin multiplets.