TL Phan, N Tran, HH Nguyen, DS Yang, NT Dang, BW Lee
Hexagonal BaCo1-xMnxFe11O19 (x = 0-1) compounds were prepared by the co-precipitation method. Morphological analyses indicated that the particle size gradually increased with increasing Mn content (x). An increase of x also caused a strong change of the lattice constants. This is due to the substitution of Mn3+ and Mn4+ for Co2+ and/or Fe3+ in the BaCoFe11O19 host lattice together with the Jahn-Teller distortions, in which Mn ions preferably occupy the 12k, 4f2, 2a, and 2b sites. The oxidation state of these ions in BaCo1-xMnxFe11O19 was almost unchanged when x increased. The analyses of magnetization data indicated that all BaCo1-xMnxFe11O19 compounds belong to the class of hard-magnetic materials. Though the saturation magnetization (Ms) gradually decreased with increasing x, the coercivity (Hc) increased remarkably. Concurrently, both the squareness ratio (Mr/Ms) and energy product (BH)max obtained from a hysteresis loop also increased, with Mr/Ms ≈ 0.53 and (BH)max ≈ 6.3 kJ/m3 for x = 1. These features prove the improvement of the hard-magnetic properties of BaCo1-xMnxFe11O19 when x increases.