$^{133}$Cs NMR investigation of 2D frustrated Heisenberg antiferromagnet, Cs$_2$CuCl$_4$

TL;DR

This study uses $^{133}$Cs NMR to explore magnetic properties and spin excitations in the 2D frustrated Heisenberg antiferromagnet Cs$_2$CuCl$_4$, revealing a field-dependent spin gap and confirming magnetic behavior consistent with neutron and magnetization data.

Contribution

First application of $^{133}$Cs NMR to probe magnetic excitations and spin gaps in Cs$_2$CuCl$_4$, demonstrating its effectiveness in studying 2D frustrated antiferromagnets.

Findings

Spin excitation gap opens above saturation field

g-factor and saturation field match neutron and magnetization data

No structural changes down to lowest temperatures

Abstract

We report $^{133}$Cs nuclear magnetic resonance (NMR) measurements on the 2D frustrated Heisenberg antiferromagnet Cs$_2$CuCl$_4$ down to 2 K and up to 15 T. We show that $^{133}$Cs NMR is a good probe of the magnetic degrees of freedom in this material. Cu spin degrees of freedom are sensed through a strong anisotropic hyperfine coupling. The spin excitation gap opens above the critical saturation field. The gap value was determined from the activation energy of the nuclear spin-lattice relaxation rate in a magnetic field applied parallel to the Cu chains (b axis). The values of the g-factor and the saturation field are consistent with the neutron-scattering and magnetization results. The measurements of the spin-spin relaxation time are exploited to show that no structural changes occur down to the lowest temperatures investigated.