Neutron Spectroscopy for the Magnetic Anisotropy of Molecular Clusters

Single crystal EPR determination of the spin Hamiltonian parameters for Fe8 molecular clusters

“…Furthermore, the large zero-field splittings demand the use of frequencies and magnetic fields considerably higher than those typically used by the majority of EPR spectroscopists. Extrapolation of the frequency dependence of transitions to zero-field (for any orientation of the field) allows us to determine directly and accurately (to within 0.5%) the first five zero-field splittings, which are in good agreement with the neutron studies [19]. The dependence of these splittings on the applied field strength, and its orientation with respect to the crystal, enable us to identify (to within 1°) the easy, intermediate and hard magnetic axes.…”

“…z represent projections along the hard, intermediate and easy axes respectively; g is the Landé tensor, and B 6 is the applied magnetic field vector [16]. Inelastic neutron scattering [19] and high-frequency EPR studies [8,20] of powder samples have shown the need to include higher-order terms (fourth-order in the spin operators) in the above Hamiltonian; these terms are important, because they may provide clues as to the mechanism of the quantum tunneling phenomenon. However, the neutron and EPR studies published to date do not agree on the magnitudes of the higher-order Hamiltonian terms, or even on the exact D and E parameters [8,[19][20][21][22].…”

Probing spin frustration in high-symmetry magnetic nanomolecules by inelastic neutron scattering

“…Of paramount importance is the determination of the magnetic excitation spectrum. However, for a molecule with N magnetic ions of spin s the calculation of the (2s+ 1) N eigenstates and their energies quickly becomes impractical for increasing N and s. Neutron scattering is the most effective and direct technique for determining the magnetic energy levels, and there have been studies of excitations in several magnetic molecules containing up to 12 spins [2,3,4,5,6,7].In this Letter we report cold-neutron inelastic scattering results obtained on one of the largest magnetic molecules yet synthesized: the polyoxomolybdate cluster {Mo 72 Fe 30 }. The crystallographic structure is described by the space group R3 with the lattice constants: a ≈ 55.13Å, and c ≈ 60.19Å [9].…”

“…Of paramount importance is the determination of the magnetic excitation spectrum. However, for a molecule with N magnetic ions of spin s the calculation of the (2s+ 1) N eigenstates and their energies quickly becomes impractical for increasing N and s. Neutron scattering is the most effective and direct technique for determining the magnetic energy levels, and there have been studies of excitations in several magnetic molecules containing up to 12 spins [2,3,4,5,6,7].…”

“…Magnetic molecules are ideal prototypical systems for the study of fundamental problems in magnetism on the nanoscale level [1]. As a result, their properties have been the subject of many theoretical and experimental investigations [2,3,4,5,6,7,8,9,10,11,12]. Of paramount importance is the determination of the magnetic excitation spectrum.…”