Calcination temperature effect on formability and magnetic properties enhancement of anisotropic Ca-La-Co substituted M-Type Sr-hexaferrites permanent magnets

Abstract

In this study, Ca-La-Co substituted M-type Sr-Hexaferrites (Ca0.35La0.47Sr0.18Fe10.87Co0.22O19-δ) were prepared via conventional solid-state reaction, with the calcination temperature ranging from 1240℃ to 1290℃. The grain size of the calcined powder increased with the elevation of calcination temperature, and XRD characterization confirmed the formation of Sr-hexaferrite structure at higher temperatures. SEM analysis revealed hexagonal grain morphologies in the calcined samples. Additionally, the microstructure of the fine-milled magnetic powder transitioned from ultrafine particles to larger plate-like granules as the calcination temperature increased. Remarkably, the remanence (Br) showed an upward trend with increasing calcination temperature, peaking at 4571 Gauss, while the intrinsic coercivity (iHc) reached an optimized value of 5306 Oe at 1280℃. Notably, the formability of M-type Sr-hexaferrites was influenced by the calcination temperature, with the sintering radial shrinkage rate (Sh-D) being <12 % and the required molding pressure of magnetic powder being <500 kg/cm2, both contributing to improved yield and cost-effectiveness in ferrite permanent magnet production. These findings effectively address previous challenges associated with achieving high characteristics and formability, leading to comprehensive enhancements in magnetic properties, operability, and production efficiency. The anisotropic Ca-La-Co substituted M-Type Sr-hexaferrites permanent magnets produced in this study emerge as promising candidates for high-performance rare-earth-free permanent magnets, particularly showcasing the optimal effects achieved at the calcination temperature of 1280℃.