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

The diruthenium compound Ru(2)(O(2)CMe)(4)[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.