Abstract: The rapid development of smart wireless electronic devices has led to severe multi-band electromagnetic pollution, driving the research, development, and application of multi-band electromagnetic wave (EMW) absorbers. Spinel ferrites possess excellent natural magnetic resonance characteristics, giving them broad application prospects in the field of multi-band EMW absorbers. However, their inherently low dielectric constant results in severe impedance mismatch, which significantly limits their performance. In this study, an innovative strategy of temperature-controlled heat treatment was employed to successfully synthesize spinel ferrite materials with a micrometer-scale layered structure. The slow heating process promoted the growth of magnetic domains, resulting in enhanced magnetic permeability and a broadened natural resonance peak. Due to the reduced natural resonance frequency and enhanced exchange resonance, the material’s strong magnetic loss band covers the entire low-frequency region. The construction of the layered structure effectively improved the material’s dielectric properties. Under electromagnetic synergy, the optimized sample ultimately achieved an effective absorption bandwidth of 10.72 GHz, successfully covering the S, C, X, and Ku bands. This study demonstrates that structural regulation through simple control of annealing kinetics is an effective strategy for optimizing the dielectric properties of ferrites, providing a novel process for designing high-performance multi-band electromagnetic wave absorbers.