We carried out neutron powder diffraction experiments on the cluster-based Haldane compound fedotovite K2Cu3O(SO4)3. Weak magnetic reflections caused by a magnetic long-range order appeared below an antiferromagnetic transition temperature TN =3.1 K. We propose a possible magnetic structure that is consistent with the magnetic properties reported in the literature.

We investigated the magnetism of FeVMoO7 by performing magnetization, specific heat, electron spin resonance, and neutron diffraction experiments. We observed an antiferromagnetically ordered state below T_N = 10.8 K. We consider that the probable spin model is an interacting antiferromagnetic spin-5/2 dimer model where spin dimers are connected by interdimer interactions. The intradimer interaction was evaluated to be J = 10.5 +- 0.5 K. The magnitude of ordered magnetic moments is 4.00(7) mu_B at 4...