Hi, If both samples synthesized by the same methods, they will obey the smaller the particle size with smaller the coercivity (Hc). Since, you have two different synthesized methods, crystalline nature and magnetic anisotropy will also be play along with particle size. The thickness of magnetic dead layer for each sample will also affect their magnetic properties. So, I suggest you do a detailed analysis on structural and magnetic properties of these two samples to get clear picture.

Dear Sir,

I also recommend that you check three points: the shape, the purity and their oxidation state of the particles.

A slight shape anisotropy can indeed contribute to the increase in the coercivity.

The presence of hematite can also be the source of mechanical stresses contributing to the increase in Hc. It would also be consistent with a decrease in saturation magnetization.

Finally, the partial oxidation of magnetite into a maghemite or bertholide-type oxide can also have a similar effect (increase in Hc and decrease in Ms). Surface oxidation can indeed develop a spinel oxide (maghemite or bertholide) with a lower crystal parameter than that of magnetite. The crystalline accommodation of the epitaxial surface layer to the particle core then causes mechanical stresses responsible for a slight increase in the coercive field. You can find additional information in the attached articles.

Sincerely,

Philippe.

Additional remark:

Some information on oxidation state of the particles could be obtained by X-ray measurements (lattice constant) and by thermogravimetry (deduction of the oxidation state from the study of the mass gain after total oxidation).

Regards.

Ph.

I reccomend to send question to prof. Julia Fedotova [email protected]

Alexander K Fedotov Might I ask for his contact information ?