Vol. 7, Issue 2, Part B (2025)

This study investigates how dopant concentration influences phase stability and magnetic behavior in diluted magnetic semiconductors (DMS). Using a series of metal-chalcogenide and oxide host matrices doped with transition-metal ions (Mn, Co, and Fe) across a wide concentration range (0.5-15 at.%), we combined controlled synthesis (solid-state reaction and pulsed-laser deposition), structural characterization (X-ray diffraction, transmission electron microscopy), chemical/valence analysis (XPS, EELS), and magnetic/electronic measurements (SQUID magnetometry, Hall effect, and temperature-dependent resistivity). We find a clear concentration-dependent evolution: at low dopant levels (<~3 at.%) dopants occupy substitutional lattice sites, preserving single-phase crystallinity and enabling carrier-mediated ferromagnetic coupling with low coercivity and Curie temperatures that scale with carrier density. Above a critical solubility threshold (host- and dopant-dependent, typically 3-8 at.%), dopant clustering and secondary-phase precipitates emerge, producing extrinsic ferromagnetism with larger magnetic moments, higher coercivity, and suppressed carrier mobility. First-principles calculations and mean-field models corroborate the experimental trend, showing that increasing dopant concentration both strengthens local exchange but destabilizes the host lattice thermodynamically. The results emphasize the trade-off between achieving strong magnetism and maintaining intrinsic, controllable DMS behavior, and they identify composition windows and processing guidelines to optimize magnetic ordering for spintronic applications.