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

The diruthenium compound [Ru-2(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 approximate to 5 x 10(-3) meV between sublattices, a small magnetic field H-c similar to K-c/mu(B) approximate to 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.