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.

本文演示了磁铁矿（Fe ₃ O ₄）采用共沉淀法成功地从印尼铁矿中合成了具有可控微晶尺寸的纳米粉。沉淀过程中酸性环境（即pH 9、10和11）的变化揭示了对其结构，磁性和微波吸收特性的影响。材料的表征包括同步加速器X射线衍射（XRD）和X射线吸收光谱（XAS），高分辨率透射电子显微镜（HRTEM）和选择区域电子衍射（SAED）技术的组合。分别通过振动样品磁力计（VSM）和矢量网络分析仪（VNA）表征了磁性和微波吸收特性。材料的结构特征证实了单相磁铁矿的形成，该单相磁铁矿显示出球形的团聚颗粒，其平均微晶尺寸随沉淀pH值降低。这些粉末的微晶尺寸为9.8-13.4 nm。此外，XANES数据的线性组合拟合（LCF）分析显示出Fe²⁺ / Fe ³⁺随pH的变化而变化。我们发现，通过对第一壳和第二壳的EXAFS拟合分析，原子间距离随pH值的增加而减小。此外，MH磁滞回线表现出亚铁磁行为，其中随着微晶尺寸的减小，磁化强度从51.75 emu / g增加到77.79 emu / g。最后，随着微晶尺寸的减小，微波吸收特性的反射损耗值从– 4.42显着变化到– 23.11 dB。