Quantum dynamics of the Neel vector in the antiferromagnetic molecular wheel CsFe8

TL;DR

This study investigates the quantum dynamics of the Neel vector in CsFe8 using inelastic neutron scattering, modeling the system with a microscopic spin Hamiltonian to accurately describe low-energy magnetic states and their transitions.

Contribution

The paper introduces an effective spin Hamiltonian approach to accurately model INS spectra and low-energy magnetism in CsFe8, overcoming computational challenges.

Findings

Low-energy states are well described by the effective Hamiltonian.

Transitions correspond to L-band state changes, including tunneling and rotational modes.

The model accurately reproduces experimental INS spectra.

Abstract

The inelastic neutron scattering (INS) spectrum is studied for the antiferromagnetic molecular wheel CsFe8, in the temperature range 2 - 60 K, and for transfer energies up 3.6 meV. A qualitative analysis shows that the observed peaks correspond to the transitions between the L-band states, from the ground state up to the S = 5 multiplet. For a quantitative analysis, the wheel is described by a microscopic spin Hamiltonian (SH), which includes the nearest-neighbor Heisenberg exchange interactions and uniaxial easy-axis single-ion anisotropy, characterized by the constants J and D, respectively. For a best-fit determination of J and D, the L band is modeled by an effective SH, and the effective SH concept extended such as to facilitate an accurate calculation of INS scattering intensities, overcoming difficulties with the dimension of the Hilbert space. The low-energy magnetism in CsFe8 is excellently described by the generic SH used. The two lowest states are characterized by a tunneling of the Neel vector, as found previously, while the higher-lying states are well described as rotational modes of the Neel vector.