Nguyen and coworkers continue clearly explaining that "The magnetic moments of Fe 3+ and Fe 2+ cations in octahedral holes are coupled ferromagnetically. However, the Fe 3+ ions in tetrahedral sites possess magnetic dipoles in the reverse direction of the Fe 3+ ions in the octahedral sites. Therefore, Fe3O4 is a ferrimagnetic material with high saturation magnetization (MS) and low coercivity (HC) due to the antiferromagnetically coupled Fe 3+ cations in tetrahedral and octahedral sites of its crystal structure" . Nguyen and coworkers are also stressing: "the term ferromagnetic properties or ferromagnetism is [sometimes] also used for Fe3O4, which indicates that it exhibits magnetic properties in the absence of a magnetic field" . In fact, we can find in