External Magnetic Field Effects on a Distorted Kagome Antiferromagnet

We report bulk magnetization, and elastic and inelastic neutron scattering measurements under an external magnetic field $H$ on the weakly coupled distorted kagome system, $\mathrm{C}{\mathrm{u}}_2(\mathrm{OD}{)}_3\mathrm{Cl}$. Our results show that the ordered state below 6.7 K is a canted antiferromagnet and consists of large antiferromagnetic $ac$ components and smaller ferromagnetic $b$ components. By first-principles calculations and linear spin wave analysis, we present a simple spin Hamiltonian with nonuniform nearest neighbor exchange interactions resulting in a system of coupled spin trimers with a single-ion anisotropy that can qualitatively reproduce the spin dynamics of $\mathrm{C}{\mathrm{u}}_2(\mathrm{OD}{)}_3\mathrm{Cl}$.