Exchange Interactions and High-Energy Spin States in Mn_12-acetate

Abstract

We perform inelastic neutron scattering measurements on the molecular nanomagnet Mn_12-acetate to measure the excitation spectrum up to 45meV (500K). We isolate magnetic excitations in two groups at 5-6.5meV (60-75K) and 8-10.5meV (95-120K), with higher levels appearing only at 27meV (310K) and 31meV (360K). From a detailed characterization of the transition peaks we show that all of the low-energy modes appear to be separate S = 9 excitations above the S = 10 ground state, with the peak at 27meV (310K) corresponding to the first S = 11 excitation. We consider a general model for the four exchange interaction parameters of the molecule. The static susceptibility is computed by high-temperature series expansion and the energy spectrum, matrix elements and ground-state spin configuration by exact diagonalization. The theoretical results are matched with experimental observation by inclusion of cluster anisotropy parameters, revealing strong constraints on possible parameter sets. We conclude that only a model with dominant exchange couplings J_1 ~ J_2 ~ 5.5meV (65K) and small couplings J_3 ~ J_4 ~ 0.6meV (7K) is consistent with the experimental data.

17 pages, 12 figures

References in corpus (1)

• Thermodynamic properties of ferromagnetic mixed-spin chain systems

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• Magnetic Properties and Thermal Entanglement on a Triangulated Kagome Lattice
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• Unravelling the Spin Dynamics of Molecular Nanomagnets with Four-Dimensional Inelastic Neutron Scattering
• Standing Spin Waves in an Antiferromagnetic Molecular Cr6 Horseshoe
• Incommensurate, helical spin ground states on the Hollandite lattice
• Exchange constants and spin dynamics in Mn12-acetate
• Low-spin ground state of the giant single-molecule magnets {Mn${}_{70}$} and {Mn${}_{84}$}