Field dependence of the magnetic spectrum in anisotropic and Dzyaloshinskii-Moriya antiferromagnets: II. Raman spectroscopy

TL;DR

This study combines Raman spectroscopy experiments with theoretical analysis to investigate magnetic excitations in anisotropic Dzyaloshinskii-Moriya antiferromagnets Sr(2)CuO(2)Cl(2) and La(2)CuO(4), revealing magnetic interactions and anisotropies.

Contribution

It provides a detailed classification of Raman active one-magnon excitations and measures their evolution under magnetic fields, linking experimental data with theoretical predictions.

Findings

Determined the interlayer coupling J_/J rom the Dzyaloshinskii-Moriya gap jump.

Measured anisotropic gyromagnetic tensor components g_s^a, g_s^b, and g_s^c.

Observed agreement between Raman data and ESR magnon-gap measurements in Sr(2)CuO(2)Cl(2).

Abstract

We compare the theoretical predictions of the previous article [L. Benfatto and M. B. Silva Neto, cond-mat/0602419], with Raman spectroscopy experiments in Sr(2)CuO(2)Cl(2) and untwinned La(2)CuO(4) single crystals. We construct the magnetic point group for the magnetically ordered phase of the two compounds, Sr(2)CuO(2)Cl(2) and La(2)CuO(4), and we classify all the Raman active one-magnon excitations according to the irreducible co-representations for the associated magnetic point group. We then measure the evolution of the one-magnon Raman energies and intensities for low and moderate magnetic fields along the three crystallographic directions. In the case of La(2)CuO(4), we demonstrate that from the jump of the Dzyaloshinskii-Moriya gap at the critical magnetic field H_c ~ 6.6 T for the weak-ferromagnetic transition one can determine the value of the interlayer coupling J_\perp/J ~ 3.2 x 10^-5. We furthermore determine the components of the anisotropic gyromagnetic tensor as g_s^a=2.0, g_s^b=2.08, and the upper bound g_s^c=2.65. For the case of Sr(2)CuO(2)Cl(2), we compare the Raman data obtained in an in-plane magnetic field with previous magnon-gap measurements done by ESR. Using the very low magnon gap estimated by ESR (~ 0.05 meV), the data for the one-magnon Raman energies agree reasonably well with the theoretical predictions for the case of a transverse field (only hardening of the gap).