Synergetic effect of site-controlled two-step Ca doping on magnetic and electrical properties of M-type strontium hexaferrites

Abstract

M-type strontium (SrM) hexaferrites exhibiting large magnetocrystalline anisotropy, high saturation magnetization and coercivity, and narrow ferrimagnetic resonance (FMR) linewidth have a great potential for applications in high-performance motors and self-biased circulators. Ca doping in SrM hexaferrites is an effective method for tailoring the intrinsic electromagnetic parameters and modifying polycrystalline microstructure to meet the application requirements. However, the regulation mechanism of Ca doping is still obscure, and its regulation effect is not optimized. Here, the magnetic and electrical properties of SrM hexaferrites with site-controlled two-step Ca doping are reported. The spatial concentration distribution and diffusion dynamics of Ca2+ ions are investigated when introduced by CaCO3 as the reactant and sintering additive, respectively. The existence of the Ca2+ ions in the crystallites added as the reactant reduces the diffusion of the Ca2+ ions in the grain boundaries added as the additive, which synergistically tailors the magnetocrystalline anisotropy field, crystallite orientation, and polycrystalline morphology, and further optimizes the coercivity, remanence, and maximum energy product. Moreover, the impact of the Ca2+ ions on the resistivities of the grain and grain boundary is also investigated, revealing the synergetic effect of Ca2+ ions at different sites on lowering the loss. These results prove the effectiveness of the site-controlled two-step Ca doping in synergistically enhancing the magnetic and electrical properties of SrM hexaferrites.