Simultaneous improvement of coercivity and saturation magnetization of M-type strontium ferrite by Nd3+-Co2+unequal co-substitution

We synthesized Sr1-xNdxFe12-yCoyO19 (x = 0-0.25, y = 0-0.1) using a conventional ceramic route. The crystal structures were analyzed using X-ray diffraction. With increasing Nd3+ and Co2+ contents, lattice constant a increases, while lattice constant c decreases. In terms of magnetic properties, the saturation magnetization and coercivity are simultaneously increased when x = y = 0.1 (equal co-substitution). This is mainly because the bivalent Co2+ has a smaller magnetic moment and unquenched orbital moments. When substitution amount x is further increased (unequal co-substitution), the magnetic properties are further improved and reach the optimum values of Ms = 76.4 emu/g and Hc = 5115 Oe owing to the occupation of the 2a site by divalent Fe2+. The occupancies of Co2+ and Fe2+ are further verified using Raman spectroscopy.