Hyperfine interaction in CoCl$_2$ investigated by high resolution neutron spectroscopy

TL;DR

This study used high resolution neutron spectroscopy to observe hyperfine-induced nuclear spin excitations in CoCl₂, revealing temperature-dependent energy shifts linked to magnetic properties and orbital moments.

Contribution

First direct observation of hyperfine nuclear spin excitations in CoCl₂ using high resolution neutron spectroscopy, highlighting the role of unquenched orbital moments.

Findings

Detected inelastic peaks at 1.34 μeV at 2 K.

The inelastic peak energy decreases with temperature and vanishes at 25 K.

Nuclear spin excitation energies correlate linearly with Co magnetic moments in some compounds.

Abstract

We investigated low energy nuclear spin excitations in the layered compound CoCl$_2$ by high resolution back-scattering neutron spectroscopy. We detected inelastic peaks at $E = 1.34 \pm 0.03$ $\mu$eV on both energy loss and energy sides of the central elastic peak at $T = 2$ K. The energy of the inelastic peaks decrease with temperature continuously and become zero at $T_N \approx 25$ K at which the two ielastic peaks merge with the central elastic peak. We interpret the low energy excitations to be due to the transition between hyperfine field split nuclear levels. The present data together with the data on other Co compounds show that the energy of the nuclear spin excitations of a number of compounds follow a linear relationship with the electronic magnetic moment of the Co ion whereas that of other compounds deviate appreciably from this linear behaviour. We ascribe this anomalous behaviour to the presence of unquenched orbital moments of the Co ions.