Preparation and magnetic properties of NiFe2O4–Fe2O3@SnO2 heterostructures

• NiFe2O4–Fe2O3@SnO2 heterostructures were synthesized by a multi-step method.
• The sequence of preparation influenced the structure of composite.
• Magnetic properties of NiFe2O4–Fe2O3@SnO2 heterostructures were investigated.

NiFe2O4–Fe2O3@SnO2 heterostructures were successfully synthesized by a multi-step method using nonstoichiometric Ni ferrite as a precursor. Through adjusting the sequence of solvothermal treatment and thermal calcination, core–shell and yolk–shell NiFe2O4–Fe2O3@SnO2 porous spheres can be obtained. Using NiFe2O4–Fe2O3 composite as a core, NiFe2O4–Fe2O3@SnO2 core–shell spheres can be synthesized by the solvothermal growth of SnO2. NiFe2O4–Fe2O3@SnO2 yolk–shell spheres have been prepared by using nonstoichiometric Ni ferrite as a core followed by the solvothermal growth of SnO2 and thermal calcination. The effects of composite structure and composition on magnetic properties were investigated. Because of subsequent deposition of SnO2, magnetization saturation of NiFe2O4–Fe2O3 porous spheres is higher than that of NiFe2O4–Fe2O3@SnO2. Magnetization saturation of core–shell NiFe2O4–Fe2O3@SnO2 composite is higher than that of yolk–shell NiFe2O4–Fe2O3@SnO2 composite.