In situ annealing achieves an ultrafast synthesis of high coercive strontium ferrite foams and beyond.

Strontium ferrite nanostructures have attracted intensive interest recently due to the increasing demand for cost-effective features and good chemical corrosion resistance of magnetic materials, yet the ultrafast synthesis of strontium ferrite with desired coercivity is still experiencing a severe challenge. Herein, porous strontium ferrite foams with a coercivity up to 23.35 kOe were prepared by ultrafast in situ annealing for 1 min based on an auto-combustion strategy. The high coercivity of strontium ferrite benefits from the increasing magnetocrystalline anisotropy caused by the ion substitution and the appropriate grain size close to the critical single-domain size of strontium ferrite. In addition, this ultrafast synthesis can be extended to prepare a series of porous spinel, lanthanide-based perovskites, and their high-entropy counterpart foams. We also demonstrate that this strategy is feasible for preparing biphasic composite oxide foams. Furthermore, this work provides important guidance for the design of porous permanent magnet materials and the efficient preparation of porous oxide foam materials.