Neutron study of mesoscopic magnetic clusters:Mn12O12

Abstract

Neutron diffraction and inelastic neutron scattering in zero field have been performed on mesoscopic magnetic Mn 12 O 12 clusters, well known for their macroscopic quantum effects observed at low temperature. In addition to the static spin correlations of the cluster in its ground state, we have observed some energy levels related both to the anisotropy and to the exchange energies of the cluster, with their respective dynamical form factor. The temperature and Q dependences of the anisotropy energy levels can be qualitatively explained using a quantum model. Besides these expected modes, the most striking result is the observation of extended energy modes at energy values below those related to anisotropy. Their temperature and Q dependences differ from those expected for the energy levels of usual magnetic clusters. They indicate an additional spin coupling which must play a role in tunneling properties.

Many-spin effects and tunneling splittings in Mn12 magnetic molecules

“…[13], and their magnitude has been estimated in Ref. [14] based on the neutron scattering data [15]. The molecules of Mn 12 possess a fourfold rotational-reflection axis (symmetry S 4 ) imposing restrictions on the DM-vectors D i;j ; so that DM interactions can be described by only three parameters…”

From single-molecule magnetism to long-range ferromagnetism inHpyr[Fe17O16(OH)Vecchini1, Ryan2, Cranswick3 et al. 2008Phys. Rev. B151100View full textAdd to dashboardCite

“…22 These studies, which were preceded by an unpolarized neutron diffraction investigation of polycrystalline Mn 12 ͑Ref. 23͒ and a characterization of the ground-state static spin correlations, 24 were devoted exclusively to the internal magnetic structure of each cluster and confirmed the much more localized nature of the spin density for these molecular magnets. The presence of long-range ferromagnetic order in the prototypical molecular magnet Mn 12 was recently confirmed by singlecrystal neutron diffraction.…”

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].…”

“…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].…”

“…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.…”