Magnetic excitations and phonons in the spin-chain compound NaCu2O2

TL;DR

This study investigates magnetic excitations and phonons in NaCu2O2, revealing detailed phonon modes, magnon features, and their temperature-dependent behavior, enhancing understanding of spin-chain compounds with helical magnetic order.

Contribution

It provides a combined experimental and theoretical analysis of phonons and magnons in NaCu2O2, including ab-initio calculations and polarization-dependent magnetic excitation characterization.

Findings

Good agreement between observed and calculated phonon modes

Identification of two-magnon and one-magnon features

Temperature-dependent magnetic excitation spectrum change

Abstract

We report an inelastic light scattering study of single-crystalline NaCu$_2$O$_2$, a spin-chain compound known to exhibit a phase with helical magnetic order at low temperatures. Phonon excitations were studied as a function of temperature and light polarization, and the phonon frequencies are compared to the results of ab-initio lattice dynamical calculations, which are also reported here. The good agreement between the observed and calculated modes allows an assignment of the phonon eigenvectors. Two distinct high-energy two-magnon features as well as a sharp low-energy one-magnon peak were also observed. These features are discussed in terms of the magnon modes expected in a helically ordered state. Their polarization dependence provides evidence of substantial exchange interactions between two closely spaced spin chains within a unit cell. At high temperatures, the spectral features attributable to magnetic excitations are replaced by a broad, quasielastic mode due to overdamped spin excitations.