Diffuse spin waves, zero modes and cluster excitations in the spin-3/2 kagom\'e antiferromagnet chromium jarosite, KCr$_3$(OD)$_6$(SO$_4$)$_2$

TL;DR

This study investigates the spin dynamics of the S=3/2 kagome antiferromagnet chromium jarosite using neutron spectroscopy, revealing diffuse excitations, zero modes, and cluster excitations, and estimating exchange interactions.

Contribution

The paper provides the first detailed neutron spectroscopy analysis of chromium jarosite, identifying diffuse spin wave excitations and proposing a model for cluster excitations in the paramagnetic phase.

Findings

Diffuse spin wave excitations with incomplete gap and broadening

Identification of zero modes in the excitation spectrum

A model for two-dimensional magnetic cluster excitations

Abstract

The dynamics of the S = 3=2 kagome antiferromagnet chromium jarosite, KCr$_3$(OD)$_6$(SO$_4$)$_2$ was studied using high-resolution neutron time-of-flight spectroscopy on a polycrystalline sample with a nearly stoichiometric magnetic lattice (2.8(2)% Cr vacancies). Neutron spectroscopy reveals diffuse spin wave excitations in the ordered phase with an incomplete gap and significant finite life-time broadening as well as a pronounced zero mode. Using linear spin wave theory, we estimate the exchange couplings, with the leading nearest neighbor value being $J_1$ = 0:884 meV. Above $T_N$ diffuse excitations from cooperative paramagnetism dominate. A model for two-dimensional magnetic cluster excitations is shown to capture the essential features of the data in the cooperative paramagnetic phase.