Synthesis, Structural Characterization, and Magnetic Behavior of Fe Core-Shell-like Nanoparticles Dispersed in Carbon Matrices.

Metallic and organometallic nanoparticles exhibit intriguing size- and morphology-dependent magnetic properties that differ markedly from their bulk counterparts. Here, we report a detailed synthesis and characterization of iron (Fe), copper (Cu), nickel (Ni), and cobalt (Co) nanostructures dispersed in carbon matrices derived from phthalocyanine (Pc), tetrakis(4-carboxyphenyl)porphyrin (TCPP), and tetraphenylporphyrin (TPP), with the detailed quantitative analysis focused primarily on iron phthalocyanine (FePc), iron tetrakis(4-carboxyphenyl)porphyrin (FeTCPP), and iron tetraphenylporphyrin (FeTPP). Using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and magnetometry, we systematically investigate how precursor composition, annealing conditions, and nanostructure formation impact the resulting magnetic behaviors. We introduce a validation-aware image-analysis workflow for morphological, local periodic-contrast, and two-dimensional connectivity descriptors while distinguishing these image-derived quantities from direct measurements of bulk crystallinity, porosity, and three-dimensional connectivity. Hysteresis measurements at low temperatures reveal that iron-based compounds, particularly iron phthalocyanine (FePc) and iron tetrakis(4-carboxyphenyl)porphyrin (FeTCPP), exhibit notable saturation-like magnetization and stronger coercivity, respectively, whereas other precursors (e.g., Cu tetraphenylporphyrin, CuTPP) show weaker magnetic responses. These contrasting behaviors underscore the importance of understanding how candidate phase composition (e.g., metallic Fe, graphite-like carbon, or iron-carbide-related contributions), local morphology, and carbon structure correlate with magnetic characteristics. Microscopy and EDS support Fe-rich regions dispersed within carbonaceous matrices, and a representative Fe/O/C STEM-EDS field provides local evidence for a core-shell-like morphology without establishing a uniform shell thickness, composition, or local core phase across the full population. Our findings highlight the feasibility of tuning carbon-metal nanocomposites through controlled synthesis and post-annealing, thereby motivating future application-specific evaluations in areas such as magnetic hyperthermia, drug delivery, sensing, and electromagnetic materials. The image-analysis workflow also offers a reproducible framework for future studies seeking to relate nanoparticle morphology and magnetic properties to controlled processing.