Spin-lattice interaction in the quasi one-dimensional helimagnet LiCu_2O_2

TL;DR

This study investigates the electron spin resonance in LiCu_2O_2, revealing how magnetic excitations and spin gaps evolve across phase transitions, and presents a magnon model incorporating exchange interactions and anisotropy.

Contribution

It provides the first ESR analysis of LiCu_2O_2 and develops a comprehensive magnon model including exchange parameters and spin anisotropy.

Findings

Broad ESR line in paramagnetic state with g-factor of 2.3

Resonance broadens and shifts near phase transition

Spin gap of 1.5 meV at low temperature

Abstract

The field dependence of the electron spin resonance in a helimagnet, LiCu_2O_2, was investigated for the first time. In the paramagnetic state a broad resonance line was observed corresponding to a g-factor of 2.3. In the critical regime around the paramagnetic to helimagnetic phase transition the resonance broadens and shifts to higher frequencies. A narrow signal is recovered at low temperature, corresponding to a spin gap of 1.5 meV in zero field. A comprehensive model of the magnons is presented, using exchange parameters from neutron scattering (T. Masuda et al, Phys. Rev. B 72, 014405), and the spin anisotropy determined here. The role of the quantum fluctuations is discussed.