Tunable structure and magnetic properties of iron ore-derived sumatran natural magnetite via high-energy shaker milling

The controlled production of submicron magnetite is critical for emerging applications in targeted drug delivery and advanced functional materials, where particle size, crystallinity, and magnetism must be tuned simultaneously. In this work, natural magnetite from Indonesian iron ore is milled in a PPF–Ultimate Gravity Shaker Mill (PPF–UG) to systematically elucidate the coupled effects of milling time and grinding media (alumina, steel, zirconia) on its physicochemical properties. X-ray diffraction reveals a progressive loss of crystallinity with increasing milling time, with zirconia media producing the strongest peak attenuation, consistent with higher impact energy and partial amorphization. Particle size analysis shows an initial comminution stage (up to 2 h) followed by agglomeration-dominated behavior; the highest submicron fraction (10.58 wt%) is obtained after 16 h of milling with zirconia balls. Laser diffraction and SEM corroborate the formation of finer, more homogeneous particles, accompanied by mild agglomeration of ultrafine magnetite. Vibrating sample magnetometry demonstrates a pronounced decrease in saturation magnetization (from 42.79 to 5.68 Am²·kg⁻¹) and remanence (from 8.20 to 0.74 Am²·kg⁻¹) with milling, while coercivity evolves toward nearly superparamagnetic behavior, attributable to increased surface disorder and reduced domain size. FTIR and DSC analyses indicate the development of surface hydroxyls, adsorbed species, and modified thermal responses associated with defect-rich, partially amorphous structures. Overall, the study establishes a direct process–structure–property relationship for PPF–UG milling of natural magnetite and demonstrates a viable route to tailor submicron magnetite derived from abundant Indonesian iron ore for prospective biomedical and functional material applications.