Sn2+ Doping: A Strategy for Tuning of Fe3O4 Nanoparticles Magnetization Dipping Temperature/Amplitude, Irreversibility, and Curie Point

Nanoscale Research Letters

Mohamed E. Elzain¹  Hisham M. Widatallah¹  Myo T. Z. Myint¹  Salim H. Al-Harthi¹  Umaima S. H. Al-Kindi¹  Htet H. Kyaw² 

[1] Department of Physics, College of Science, Sultan Qaboos University, P.O. Box 36, Al-Khoudh, 123, Muscat, Sultanate of Oman;Nanotechnology Research Center, Sultan Qaboos University, P.O. Box 33, Al-Khoudh, 123, Muscat, Sultanate of Oman;

关键词: Curie;    Dipping;    Irreversible;    Maghemite;    Magnetite;    Modified Bloch law;   

DOI  :  10.1186/s11671-020-03423-9

来源: Springer

【 摘 要 】

Doped magnetite (SnxFe3-2/3xO4) nanoparticles (NPs) (12–50 nm) with different amount of Sn2+ ions (x) were synthesized using co-precipitation method. Sn2+ doping reduces the anticipated oxidation of Fe3O4 NPs to maghemite (γ-Fe2O3), making them attractive in several magnetic applications. Detailed characterizations during heating–cooling cycles revealed the possibility of tuning the unusual observed magnetization dipping temperature/amplitude, irreversibility, and Curie point of these NPs. We attribute this dip to the chemical reduction of γ-Fe2O3 at the NPs surfaces. Along with an increase in the dipping temperature, we found that doping with Sn2+ reduces the dipping amplitude, until it approximately disappears when x = 0.150. Based on the core-shell structure of these NPs, a phenomenological expression that combines both modified Bloch law (M = M0[1 − γ(T/TC)]β) and a modified Curie–Weiss law (M = − α[1/(T − TC)δ]) is developed in order to explain the observed M-T behavior at different applied external magnetic fields and for different Sn2+ concentrations. By applying high enough magnetic field, the value of the parameters γ and δ ≈ 1 which are the same in modified Bloch and Curie–Weiss laws. They do not change with the magnetic field and depend only on the material structure and size. The power β for high magnetic field was 2.6 which is as expected for this size of nanoparticles with the core dominated magnetization. However, the β value fluctuates between 3 and 10 for small magnetic fields indicating an extra magnetic contribution from the shell structure presented by Curie–Weiss term. The parameter (α) has a very small value and it turns to negative values for high magnetic fields.

【 授权许可】

CC BY