In Srivastava et al., 2010, an investigation on magnetic properties of α-Fe2O3 NPs "synthesized under surfactant-free condition by hydrothermal process" was proposed. Two different precursors, FeCl3.6H2O and Fe(NO3)3.9H2O have been used. Srivastava and coworkers used X-ray diffraction (XRD), Raman spectroscopy (RS), microscope (SEM and HR-TEM), and vibrating sample magnetometer (VSM). The average particle size of the nanoparticles synthesized with the two precursors is different. The magnetic properties of the nanoparticles are different too, because of the different size. The Raman peaks are (in cm -1 ): In Bagherzadeh et al., 2023, we can find the "preparation of Fe3O4/vine shoots derived activated carbon nanocomposite" to be used for removal of Cr (VI). This is a reference which is interesting for the proposed magnetic investigation. "According to the VSM [Vibrating-Sample Magnetometer] … it can be seen that the maximum magnetization of Fe3O4 is higher than Fe3O4/C nanocomposites, which is due to non-magnetic nature of the activated carbon. … However, the magnetic property of Fe3O4/C is strong enough that it can to be quickly separated from the heavy metal ion solution using an external magnetic field" . Experiment tells that "both samples are superparamagnetic; also composite saturation magnetization of 30.34 emu g -1 , gives the adsorbent the privilege of magnetic separation and good retrievability" .