Spin waves near the edge of halogen substitution induced magnetic order in Ni(Cl$_{1-x}$Br$_x$)$_2$$\cdot$4SC(NH$_2$)$_2$

TL;DR

This study investigates magnetic excitations near the edge of induced magnetic order in a chemically substituted quantum magnet using inelastic neutron scattering, revealing insights into spin wave behavior and disorder effects.

Contribution

It provides a detailed analysis of magnetic excitations in Ni(Cl$_{1-x}$Br$_x$)$_2$·4SC(NH$_2$)$_2$ with x=0.21, employing generalized spin wave theory to understand the effects of chemical substitution.

Findings

Spectrum well explained by generalized spin wave theory

Determined effective Hamiltonian parameters for comparison

Addressed magnon lifetimes and structural disorder effects

Abstract

We report an inelastic neutron scattering study of magnetic excitations in a quantum paramagnet driven into a magnetically ordered state by chemical substitution, namely Ni(Cl$_{1-x}$Br$_x$)$_2$$\cdot$4SC(NH$_2$)$_2$ with $x=0.21(2)$. The measured spectrum is well accounted for by the generalized spin wave theory (GSWT) approach [M. Matsumoto and M. Koga, [J. Phys. Soc. Jap. 76, 073709 (2007)]. This analysis allows us to determine the effective Hamiltonian parameters for a direct comparison with those in the previously studied parent compound and `underdoped' system. The issue of magnon lifetimes due to structural disorder is also addressed.