Low energy magnetic excitations of the Mn_{12}-acetate spin cluster observed by neutron scattering

TL;DR

This study used high-resolution neutron scattering to analyze the energy levels and anisotropy parameters of Mn_{12}-acetate, revealing high-order anisotropy terms and the transverse component responsible for quantum tunneling.

Contribution

It provides precise measurements of high-order anisotropy terms and the transverse component in Mn_{12}-acetate using neutron scattering, advancing understanding of its quantum magnetic behavior.

Findings

Identification of high-order anisotropy terms in the spin Hamiltonian.

Quantitative determination of the transverse anisotropy component.

Observation of non-regular energy level spacing indicating complex anisotropy.

Abstract

We performed high resolution diffraction and inelastic neutron scattering measurements of Mn_{12}-acetate. Using a very high energy resolution, we could separate the energy levels corresponding to the splitting of the lowest S multiplet. Data were analyzed within a single spin model (S=10 ground state), using a spin Hamiltonian with parameters up to 4^{th} order. The non regular spacing of the transition energies unambiguously shows the presence of high order terms in the anisotropy (D= -0.457(2) cm^{-1}, B_4^0 = -2.33(4) 10^{-5}cm^{-1}). The relative intensity of the lowest energy peaks is very sensitive to the small transverse term, supposed to be mainly responsible for quantum tunneling. This allows an accurate determination of this term in zero magnetic field (B_4^4 = \pm 3.0(5) 10^{-5} cm^{-1}). The neutron results are discussed in view of recent experiments and theories.