<p>Radar absorbing materials (RAMs) for electromagnetic wave attenuation and EMI mitigation are increasingly required to exhibit broadband microwave absorption and low density. However, pure graphite suffers from poor impedance matching, lack of magnetic loss (resulting in weak low-frequency absorption), and excessive thickness requirements, while pure Fe₃O₄ has limited broadband absorption capability. To address these issues, Fe₃O₄/graphite composites with mass ratios ranging from 5:0 to 5:8 were prepared via an in-situ solvothermal method, integrating magnetic loss from Fe₃O₄ and dielectric loss from graphite to achieve synergistic microwave absorption. XRD, SEM–EDS, VSM, and vector network analyzer measurements were carried out. Results showed that Fe₃O₄ formed a pure cubic spinel phase, with nanoparticles uniformly dispersed on graphite sheets, creating layered mixed interfaces. As the graphite content increased, saturation magnetization decreased steadily, consistent with the magnetic phase dilution model. The microwave absorption originated from the synergistic effect of Fe₃O₄’s natural resonance (magnetic loss) and graphite’s dielectric loss (via multiple scattering and interface polarization). Among the samples, the 5:4 ratio composite exhibited a minimum reflection loss of –62.48&#xa0;dB at 4.88&#xa0;GHz with a thickness of 4.5&#xa0;mm, attributed to near-optimal impedance matching and a high attenuation constant. The 5:2 ratio composite achieved the widest effective absorption bandwidth of 4.48&#xa0;GHz (13.28–17.76&#xa0;GHz) at 1.5&#xa0;mm thickness. These Fe₃O₄/graphite composites demonstrate promising microwave absorption performance with low density, making them strong candidates for lightweight radar-absorbing structures, where broadband effectiveness and mass efficiency are critical design considerations.</p>