The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet that displays long-range magnetic order below TC=4.2 K with a strongly reduced moment. Our inelastic neutron scattering data show clear spin-wave excitations that are well described by a Heisenberg Hamiltonian with ferromagnetic nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K across the hexagons of the kagome lattice. These values place haydeeite very close to the quantum phase transition between ferromagnetic order and non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic short-range ferromagnetic correlations observed above TC persist well into the ferromagnetically ordered phase with a behavior distinct from critical scattering.
@article{arxiv.1503.08023,
title = {Haydeeite: a spin-1/2 kagome ferromagnet},
author = {D. Boldrin and B. Fak and M. Enderle and S. Bieri and J. Ollivier and S. Rols and P. Manuel and A. S. Wills},
journal= {arXiv preprint arXiv:1503.08023},
year = {2015}
}