Haydeeite: a spin-1/2 kagome ferromagnet

TL;DR

Haydeeite is a S=1/2 kagome ferromagnet exhibiting long-range order below 4.2 K, with spin-wave excitations well described by a Heisenberg model, and it is near a quantum phase transition between ferromagnetic and cuboc2 antiferromagnetic states.

Contribution

This study provides detailed inelastic neutron scattering data and modeling for haydeeite, revealing its proximity to a quantum critical point and characterizing its magnetic interactions.

Findings

Spin-wave excitations consistent with a Heisenberg model

Ferromagnetic order below 4.2 K with reduced magnetic moments

Presence of dynamic short-range correlations above TC

Abstract

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.