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

• Published in: Nanoscale research letters Vol. 15; no. 1; p. 192
• Main Authors: Al-Kindi, Umaima S. H., Al-Harthi, Salim H., Widatallah, Hisham M., Elzain, Mohamed E., Myint, Myo T. Z., Kyaw, Htet H.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-10-2020; Springer Nature B.V; SpringerOpen
• Subjects: Amplitudes; Chemical reduction; Chemical synthesis; Chemistry and Materials Science; Core-shell structure; Curie; Curie temperature; Dipping; Doping; Ferric oxide; Iron oxides; Irreversible; Legislation; Maghemite; Magnetic fields; Magnetite; Magnetization; Materials Science; Modified Bloch law; Molecular Medicine; Nano Express; Nanochemistry; Nanoparticles; Nanoscale Science and Technology; Nanotechnology; Nanotechnology and Microengineering; Oxidation; Parameter modification; Tuning; Magnetite; Curie; Irreversible; Modified Bloch law; Dipping; Maghemite
• ISSN: 1556-276X; 1931-7573; 1556-276X
• DOI: 10.1186/s11671-020-03423-9

Doped magnetite (Sn
x
Fe
3-2/3
x
O
4
) nanoparticles (NPs) (12–50 nm) with different amount of Sn
2+
ions (
x
) were synthesized using co-precipitation method. Sn
2+
doping reduces the anticipated oxidation of Fe
3
O
4
NPs to maghemite (γ-Fe
2
O
3
), 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-Fe
2
O
3
at the NPs surfaces. Along with an increase in the dipping temperature, we found that doping with Sn
2+
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
=
M
0
[1 −
γ
(
T
/
T
C
)]
β
) and a modified Curie–Weiss law (
M
= − 
α
[1/(
T
−
T
C
)
δ
]) is developed in order to explain the observed
M
-
T
behavior at different applied external magnetic fields and for different Sn
2+
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.