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

We synthesized Sr 1- x Nd x Fe 12- y Co y O 19 ( x  = 0–0.25, y  = 0–0.1) using a conventional ceramic route. The crystal structures were analyzed using X-ray diffraction. With increasing Nd 3+ and Co 2+ 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 Co 2+ 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 M s  = 76.4 emu/g and H c  = 5115 Oe owing to the occupation of the 2 a site by divalent Fe 2+ . The occupancies of Co 2+ and Fe 2+ are further verified using Raman spectroscopy .