Magnetic Behavior of NiFe$_{2}$O $_{4}$/SiO $_{2}$ Nanocomposite Hollow Spheres

We present a simple process to prepare magnetic NiFe
₂
O
₄
/SiO
₂
nanocomposite hollow spheres. The ionic poly(methyl methacrylate-co-methacrylic acid) copolymer sphere (500 nm) was used as a core template to synthesize polymer/NiFe
₂
O
₄
/SiO
₂
hybrid core-shell composite spheres by coprecipitating metallic oxides of nickel and iron on the ionic polymer spheres and coating with tetraethyl orthsilicate (TEOS). To create hollow spherical structures with various sizes of NiFe
₂
O
₄
nanoparticles, the hybrid core-shell spheres were subsequently calcined in the temperature range from 450 to 900degC for 4 h. Scanning electron microscope and transmission electron microscope photographs show that the hollow spheres are uniform and the thickness of shell of hollow spheres is about 40 nm. Moreover, the concentration of NiFe
₂
O
₄
involved in NiFe
₂
O
₄
/SiO
₂
hollow spheres is about 83.1 wt % which is higher than any ferrite/SiO
₂
composites system.