Molecular nanomagnets (MNM) are model systems to study the spin dynamics and magnetic correlations in low dimensional magnets. Polycrystalline inelastic neutron scattering experiments are generally used to probe the spin dynamics of MNM through the position and the neutron momentum transfer Q dependence of the magnetic peaks. However, the random orientation of the crystallites results in an orientation average of the magnetic signal and therefore only the amplitude of scattering with respect to the modules of Q is obtained and part of the information is lost. On the other hand, when measuring single crystals, all the information expressed within the scattering profile may be exploited.
I will show how inelastic neutron scattering experiments on single crystals can be used to directly determine the Fourier components of the two-spin dynamical correlation functions at a given frequency. We measured a large portion of S(Q, ω) for a single crystal composed of isolated antiferromagnetic frustrated rings. I will show that from the fit of the S(Q) at a fixed energy transfer it is possible to univocally extract the two-spin correlation functions and that they are found to be in agreement with the values calculated using the spin Hamiltonian formalism. The described method can be used to determine the dynamical spin correlations when the Hilbert space is too large to perform calculations using the microscopic spin Hamiltonian.
ISIS facility-Rutherford Appleton Laboratory, Swindon UK