Neutron-diffraction evidence for the ferrimagnetic ground state of a molecule-based magnet with weakly coupled sublattices

The diruthenium compound [Ru₂(O₂CMe) ₄]₃[Cr(CN)₆] contains two weakly coupled, ferrimagnetically ordered sublattices occupying the same volume. Due to the weak, antiferromagnetic dipolar interaction K_c ≈ 5 × 10 ^-3 meV between sublattices, a small magnetic field H_c ∼ K_c/μ_B ≈ 800 Oe aligns the sublattice moments. Powder neutron-diffraction measurements on a deuterated sample confirm an earlier prediction that the sublattice moments are restricted by the anisotropy of the diruthenium 'paddle-wheels' to the cubic diagonals. Those measurements also suggest that quantum corrections to the ground state are significant.