Effect of SiO2 coating on the magnetic properties of Ni–Zn ferrite

The Ni–Zn ferrite/SiO2 nanocomposites (ZNF/SiO2 NCs) with core-shell structure were synthesized using Stöber method and a modified one. The core-shell structure was confirmed by transmission electron spectroscopy (TEM). The product obtained by modified Stöber method was more uniform than by Stöber method. The strength of dipole–dipole interaction between Ni–Zn nanoparticles decreases and the coordination of surface atoms increases due to surface modification. The decrease of blocking temperature and coercivity of the magnetic particles at low temperature can be attributed to the coating of SiO2, which weakens the surface spin disorder of magnetic nanoparticles.