Electron spin resonance in S=1/2 antiferromagnets at high temperature

TL;DR

This paper investigates electron spin resonance in low-dimensional antiferromagnets at high temperatures, testing theoretical predictions and revealing differences in resonance behavior between finite and infinite systems.

Contribution

It provides new predictions for ESR linewidths and lineshapes in infinite systems using an interpolation method, and highlights the impact of anisotropies on resonance properties.

Findings

Finite systems show a double-peak resonance differing from Lorentzian.

Predicted linewidth and lineshape depend on anisotropy strength.

Dzyaloshinskii-Moriya anisotropies cause larger linewidths in 2D than exchange anisotropies.

Abstract

We study the electron spin resonance (ESR) of low-dimensional spin systems at high temperature, and test the Kubo-Tomita theory of exchange narrowing. In finite-size systems (molecular magnets), we found a double-peak resonance which strongly differs from the usual Lorentzian. For infinite systems, we have predictions for the linewidth and lineshape as a function of the anisotropy strength. For this, we have used an interpolation between a non-perturbative calculation of the memory function at short times (exact diagonalization) and the hydrodynamic spin-diffusion at long times. We show that the Dzyaloshinskii-Moriya anisotropies generally induce a much larger linewidth than the exchange anisotropies in two dimensions, contrary to the one-dimensional case.