Direct observation of local Mn-Mn distances in the paramagnetic compound CsMnxMg1-xBr3

TL;DR

This paper presents a new neutron spectroscopy method for local structure determination in magnetic materials, revealing discrete Mn-Mn distances in CsMnxMg1-xBr3 that do not vary continuously with pressure.

Contribution

The study introduces a novel high-resolution local structure measurement technique applicable to magnetic clusters, enabling direct extraction of interatomic distances from excitation energies.

Findings

Mn-Mn distances are quantized and do not change continuously with pressure.

The method achieves a spatial resolution of about 0.01 Å.

Discrete Mn-Mn distances suggest a locking mechanism under pressure.

Abstract

We introduce a novel method for local structure determination with a spatial resolution of the order of 0.01 Angstroem. It can be applied to materials containing clusters of exchange-coupled magnetic atoms. We use neutron spectroscopy to probe the energies of the cluster excitations which are determined by the interatomic coupling strength J. Since for most materials J is related to the interatomic distance R through a linear relation dJ/dR={\alpha} (for dR/R<<1), we can directly derive the local distance R from the observed excitation energies. This is exemplified for the mixed one-dimensional paramagnetic compound CsMnxMg1 xBr3 (x=0.05, 0.10) containing manganese dimers oriented along the hexagonal c-axis. Surprisingly, the resulting Mn-Mn distances R do not vary continuously with increasing internal pressure, but lock in at some discrete values.