fig3

Figure 3. XRD patterns of Fe₃O₄ nanoparticles and Fe₃O₄@C microspheres. The Fe₃O₄ reflections match the cubic spinel Fe₃O₄ phase (JCPDS 19-629), and the broad feature centered at ~ 20-30° is assigned to amorphous carbon in Fe₃O₄@C. XRD: X-ray diffraction.