The structural and magnetic characterization of ironstone-derived magnetite ceramic nanopowders

This paper demonstrates how magnetite (Fe₃O₄) nanopowders with a controlled crystallite size are successfully synthesized from Indonesian ironstone by employing a co-precipitation method. The variation of acidic environments (i.e., pH 9, 10, and 11) during precipitation revealed the influences on their structure, magnetic and microwave absorption properties. The characterization of materials included a combined synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS), high-resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) techniques. The magnetic and microwave absorption properties were characterized by vibrating sample magnetometer (VSM) and vector network analyzer (VNA), respectively. The structural characterization of the materials confirmed the formation of a single-phase magnetite which showed sphere-like agglomerated particles with a decreased average crystallite size with precipitation pH. The powders exhibited crystallite sizes of 9.8–13.4 nm. Additionally, the linear combination fitting (LCF) analysis of the XANES data showed a Fe²⁺/Fe³⁺ varying composition with pH. We found that, through the EXAFS fitting analysis on the first and second shells, interatomic distance decreased with increasing pH. Moreover, the M–H hysteresis loop demonstrated a ferrimagnetic behavior where the magnetization increased from 51.75 to 77.79 emu/g with decreasing crystallite size. Finally, the microwave absorption properties showed a significant change in reflection loss value from – 4.42 to – 23.11 dB with decreasing crystallite size.