Synthesis, structure, and magnetic properties of Na3LnMn3O3(AsO4)3 (Ln = La, Sm, and Gd): a new 3d-4f series exhibiting one-dimensional manganese(III) oxide chains connected via LnO9 units.

In attempts to synthesize compounds containing mixed lanthanide and transition metal oxide magnetic nanostructures, a new 3d-4f arsenate phase, Na(3)GdMn(3)O(3)(AsO(4))(3), was isolated using high-temperature, molten-salt methods. The X-ray single-crystal structure analysis shows that Na(3)GdMn(3)O(3)(AsO(4))(3) crystallizes in a hexagonal space group with a = 11.091(2) A, c = 5.954(1) A, and V = 634.2(2) A(3); P6(3)/m (No.176); Z = 2. The structure has been refined by full-matrix, least-squares methods to a final solution with R1 = 0.0466, wR2 = 0.1318 and GOF = 1.101. This new three-dimensional framework consists of ferromagnetic one-dimensional MnO(4) chains, composed of edge-shared MnO(6) units propagating along c. The GdO(9) polyhedra connect three neighboring MnO(4) chains via oxygen atoms. Na(3)LaMn(3)O(3)(AsO(4))(3) (1), and Na(3)SmMn(3)O(3)(AsO(4))(3) (2), the isostructural derivatives of Na(3)GdMn(3)O(3)(AsO(4))(3) (3), were synthesized to acquire additional insight into the 3d-4f magnetic couplings. The Na(3)LnMn(3)O(3)(AsO(4))(3) series reveals an increase in chiT at low temperatures upon substitution of smaller Ln(3+) ions ranging from La(3+) to Gd(3+). The increase in chiT is likely due to the magnetic nature and size of the lanthanide ions present. It was expected that the Mn-O-Mn ferromagnetic interactions would dominate as 3d-4f magnetic interactions are generally weak. The magnetic data shows that the paramagnetic Ln(3+) ions in 2 (Sm) and 3 (Gd) do significantly enhance the bulk ferromagnetism compared to that of 1 (La), suggesting sizable contributions from the 4f magnetic ions.