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 LnO9Units

Abstract

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)](infinity) chains, composed of edge-shared MnO(6) units propagating along c. The GdO(9) polyhedra connect three neighboring [MnO(4)](infinity) 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.