Exchange-coupling constants, spin density map, and Q dependence of the inelastic neutron scattering intensity in single-molecule magnets

TL;DR

This paper investigates how the Q dependence of inelastic neutron scattering intensity in single-molecule magnets can reveal exchange-coupling constants, using Mn12 as a case study, and discusses experimental feasibility.

Contribution

It demonstrates a method to infer exchange-coupling constants from Q dependence of INS transitions, linking spin density maps to exchange interactions in SMMs.

Findings

Q dependence varies significantly with exchange-coupling constants.

Experimental data can constrain exchange-coupling values but not determine them unambiguously.

Suitable experiments are feasible with current instrumentation.

Abstract

The Q dependence of the inelastic neutron scattering (INS) intensity of transitions within the ground-state spin multiplet of single-molecule magnets (SMMs) is considered. For these transitions, the Q dependence is related to the spin density map in the ground state, which in turn is governed by the Heisenberg exchange interactions in the cluster. This provides the possibility to infer the exchange-coupling constants from the Q dependence of the INS transitions within the spin ground state. The potential of this strategy is explored for the M = +-10 -> +- 9 transition within the S = 10 multiplet of the molecule Mn12 as an example. The Q dependence is calculated for powder as well as single-crystal Mn12 samples for various exchange-coupling situations discussed in the literature. The results are compared to literature data on a powder sample of Mn12 and to measurements on an oriented array of about 500 single-crystals of Mn12. The calculated Q dependence exhibits significant variation with the exchange-coupling constants, in particular for a single-crystal sample, but the experimental findings did not permit an unambiguous determination. However, although challenging, suitable experiments are within the reach of today's instruments.