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The dynamics of the S = 3/2 kagome antiferromagnet chromium jarosite, KCr3(OD)(6)(SO4)(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-lifetime broadening as well as a pronounced kagome zero mode. Using linear spin wave theory, we estimate the exchange couplings. The system is highly two dimensional with the leading nearest-neighbor coupling being J(1) = 0.881 meV. Above T-N, diffuse excitations from the classical spin liquid regime dominate. We model the Q response and energy response separately and show that in both the ordered phase and the classical spin liquid regime they are strongly coupled.
Henrik Moodysson Rønnow, Ellen Fogh, Peter Babkevich, Sami Juhani Vasala