S=2 quasi-one-dimensional spin waves in CrCl2

We examine the magnetic excitation spectrum in the $S=2$ Heisenberg antiferromagnet CrCl$_2$. Inelastic neutron scattering measurements on powder samples are able to determine the significant exchange interactions in this system. A large anisotropy gap is observed in the spectrum below the N\'{e}el temperature and the ratio of the two largest exchange constants is $J_c / J_b = 9.1 \pm 2.2$. However, no sign of a gapped quantum spin liquid excitation was found in the paramagnetic phase. The research was performed at Oak Ridge National Laboratory's Spallation Neutron Source and was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.