Microwave Resonant and Zero-Field Absorption Study of Doped Magnetite Prepared by a Co-Precipitation Method

Fe3O4 and ZnxFe3-xO4 pure and doped magnetite magnetic nanoparticles (NPs) were prepared in aqueous solution (Series A) or in a water-ethyl alcohol mixture (Series B) by the co-precipitation method. Only one ferromagnetic resonance line was observed in all cases under consideration indicating that the materials are magnetically uniform. The shortfall in the resonance fields from 3.27 kOe (for the frequency of 9.5 GHz) expected for spheres can be understood taking into account the dipolar forces, magnetoelasticity, or magnetocrystalline anisotropy. All samples show non-zero low field absorption. For Series A samples the grain size decreases with an increase of the Zn content. In this case zero field absorption does not correlate with the changes of the grain size. For Series B samples the grain size and zero field absorption behavior correlate with each other. The highest zero-field absorption corresponded to 0.2 zinc concentration in both A and B series. High zero-field absorption of Fe3O4 ferrite magnetic NPs can be interesting for biomedical applications.J.C. Aphesteguy is grateful to the Group of Magnetism and Magnetic Materials of the Basque Country University UPV-EHU for advanced training and special support of his guest stay at the Department of Electricity and Electronics UPV-EHU. Technical and human support provided by SGIker services of UPV-EHU is gratefully acknowledged. Special thanks to A. Larranaga, I. Orue and A. A. Svalova for excellent support and helpful discussions. This work was supported under Key Excellence Center grant of the Department of Magnetism and Magnetic Nanomaterials Ural Federal University