Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering

TL;DR

This paper demonstrates a groundbreaking method using four-dimensional inelastic neutron scattering to directly determine the quantum spin dynamics of molecular nanomagnets without relying on model Hamiltonians, exemplified by the Cr8 ring.

Contribution

The study introduces a novel experimental approach that captures the full spin dynamics of molecular nanomagnets directly from data, bypassing the need for approximate models.

Findings

First direct, model-free observation of spin dynamics in a molecular nanomagnet.

Ability to visualize quantum fluctuation propagation along the nanomagnet.

Validation of the Néel-vector-tunneling model through experimental data.

Abstract

Molecular nanomagnets are among the first examples of spin systems of finite size and have been test-beds for addressing a range of elusive but important phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to the an appropriate cluster spin-Hamiltonian, whose structure can be tailored at the synthetic level to meet specific requirements. Unfortunately, to this point it has been impossible to determine the spin dynamics directly. If the molecule is sufficiently simple, the spin motion can be indirectly assessed by an approximate model Hamiltonian fitted to experimental measurements of various types. Here we show that recently-developed instrumentation yields the four-dimensional inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal space and enables the spin dynamics to be determined with no need of any model Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this new approach. For the first time we extract a model-free picture of the quantum dynamics of a molecular nanomagnet. This allows us, for example, to examine how a quantum fluctuation propagates along the ring and to directly test the degree of validity of the N\'{e}el-vector-tunneling description of the spin dynamics.