Nb-Zn Co-doping Cooperative Modulating Fe3+ Magnetic Moment Arrangement to Enhance the Saturation Magnetization of Strontium Ferrite

M-type strontium ferrite (SrFe12O19) is widely used in various fields due to its low cost and excellent stability. However, its relatively low saturation magnetization (Ms) significantly restricts its broader applications. Enhancing Ms through non-rare-earth doping via the solid-state reaction method is of significant practical importance. The primary challenge lies in simultaneously maintaining lattice stability and regulating Fe3+ spin alignment through doping. In this study, a series of non-rare-earth Nb-Zn co-doped SrFe12-x(NbaZnb)xO19 (a:b = 1:1, a:b = 4:5, x = 0.1-0.5) were synthesized using the solid-state reaction method. XRD phase analysis indicated that a single M-type strontium ferrite phase was obtained at the stoichiometric doped (a:b = 1:1). In contrast, for the non-stoichiometric doped (a:b = 4:5), a trace amount of the secondary phase SrNb0.5Fe0.5O3 was detected in Nb-Zn doped samples with x >= 0.2. Ms of both stoichiometric and non-stoichiometric doped samples increased within the range of 0 <= x <= 0.3 but gradually decreased when x exceeded 0.3. Notably, for the composition with a: b = 4:5, Ms reached a maximum value of 79.33 emu/g at x = 0.3, accompanied by a synchronous enhancement of 18.5 % in coercivity (Hc). Raman spectroscopy analysis revealed the enhancement mechanism of Ms: the synergistic occupation of Nb5+ and Zn2+ ions. Specifically, Zn2+ preferentially occupies the 4f1 tetrahedral sites, while Nb5+ incorporates into the 4f2 sites. This co-substitution effectively replaces the spin-down Fe3+ ions, leading to a significant increase in Ms. The presence of a trace amount of the secondary phase SrNb0.5Fe0.5O3 in the non-stoichiometrically doped samples, effectively inhibited grain growth, thereby contributing to the enhancement of Hc. This study successfully synthesized non-rare-earth-doped strontium ferrite materials via a solid-state reaction method, achieving a significant enhancement in Ms. Furthermore, the underlying mechanism for the improvement in Ms through Nb-Zn co-doping was elucidated for the first time. Our findings are of significance for the development of high-performance, cost-effective ferrite materials.