Investigation of Fe $_{3}$O $_{4}$ Core/Mesoporous SiO $_{2}$ Shell Microspheres Based on Mössbauer Spectroscopy

The Fe
₃
O
₄
core/mesoporous SiO
₂
shell (Fe
₃
O
₄
@SiO
₂
) microspheres were prepared by a solvothermal reaction method. The crystal structure was determined to be cubic spinel with lattice constant a
₀
of 8.395 Å for core Fe
₃
O
₄
. Based on transmission electron microscopy (TEM) measurements, the core of Fe
₃
O
₄
particle diameter is 300-500 nm and shell thickness of 50 nm. From the magnetic hysteresis curves measured under 10 kOe, magnetization of Fe
₃
O
₄
and Fe
₃
O
₄
@SiO
₂
microspheres is determined to be 77.0 and 17.0 emu/g , respectively, at room temperature. The M-T curve confirmed that the magnetic moment transition temperature was around 110 K in Fe
₃
O
₄
and 32 K in Fe
₃
O
₄
@SiO
₂
. The Mössbauer spectra of the samples were analyzed with three six-line hyperfine patterns. It is noticeable that from the Mössbauer absorption area ratio between A(8a) and B(16d) sites, the area ratio of sextet increases from 40:60 for Fe
₃
O
₄
to 56:44 for Fe
₃
O
₄
@SiO
₂
, respectively. The Fe valence state of A site was determined to be ferric, and B (B
₁
, B
₂
) site was ferric (B
₁
site) and ferrous (B
₂
site) from the isomer shift values.