Co9S8 hexagonal aggregations were synthesized in hydrazine hydrate (N2H4·H2O) solvent at 150 °C for 12 h using cobalt(II) sulfate hydrate (CoSO4 · 7H2O) and sodium sulfite (Na2SO3) as starting materials through a hydrothermal controlled-reduction method. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM), and their magnetic properties were evaluated on a vibrating sample magnetometer (VSM). The results showed the samples were mainly composed of Co 9S8 hexagonal aggregations with an average diameter of 2.2 μm and a thickness of 200 nm. About 3 nm Co9S8 nanocrystallites deposited on its single-crystal flakes. The products exhibited ferromagnetism; the saturation magnetization (Ms) and coercivity (Hc) values of the samples were 80 emu/g and 320 Oe, respectively. The possible formation mechanism of Co9S8 hexagonal aggregations is discussed.
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