Synthesis of <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{\gamma}$</EquationSource> </InlineEquation>-Fe<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mathsf{_2}$</EquationSource> </InlineEquation>O<InlineEquation ID="Equ3"> <EquationSource Format="TEX">$\mathsf{_3}$</EquationSource> </InlineEquation> nanoparticles coated on silica spheres: Structural and magnetic ...
The structural and magnetic properties of <InlineEquation ID="Equ4"> <EquationSource Format="TEX">$\gamma$</EquationSource> </InlineEquation>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles dispersed on silica spheres prepared by sol-gel method were investigated. The properties of <InlineEquation ID="Equ5"> <EquationSource Format="TEX">$\gamma$</EquationSource> </InlineEquation>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles without silica were compared with those on silica spheres. Both the nanoparticle assemblages were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Mössbauer (20, 80 and 300 K) and electron paramagnetic resonance (EPR) (80, 300 K) measurements. The XRD spectra clearly indicated the formation of pure <InlineEquation ID="Equ6"> <EquationSource Format="TEX">$\gamma$</EquationSource> </InlineEquation>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles and the absence of any other form of iron oxide. TEM images showed a uniform distribution of the nanoparticles of size <InlineEquation ID="Equ7"> <EquationSource Format="TEX">$\sim$</EquationSource> </InlineEquation>6 nm on the surfaces of silica spheres (diameter <InlineEquation ID="Equ8"> <EquationSource Format="TEX">$\sim$</EquationSource> </InlineEquation> 35-60 nm). The size of the individual nanoparticles (without silica) varied within 5-6 nm. The low temperature (20 K) Mössbauer spectra consisted of a partially split sextet superimposed on a doublet. The partial magnetic splitting of the sextet at 20 K revealed the effect of surface magnetization and surface modifications of the <InlineEquation ID="Equ9"> <EquationSource Format="TEX">$\gamma$</EquationSource> </InlineEquation>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles coated on silica spheres. The gradual collapse of the partially split sextet into a doublet with increasing temperature indicated the superparamagnetic relaxation exhibited by the <InlineEquation ID="Equ10"> <EquationSource Format="TEX">$\gamma$</EquationSource> </InlineEquation>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles with/without silica. The surface magnetization arising out of mis-aligned spins at the surface as evidenced by Mössbauer spectra was further confirmed by electron paramagnetic resonance (EPR) studies. Copyright Springer-Verlag Berlin/Heidelberg 2003
