Effect of Zn doping on the magnetoresistance of sintered Fe 3O 4 ferrites

The Zn doped Fe ₃O ₄ ferrites were prepared by mixing ZnO with Fe ₃O ₄ powder and then sintering in argon atmosphere at 1100°C for 3 h. The effects of Zn content and sintering temperature on the magnetoresistance (MR) and microstructure of sintered samples were investigated. From the analysis of Fe ²⁺ and Fe ³⁺ ions contents, X-ray diffraction, and scanning electron microscopy, we found that the nonstoichiometric phases of Fe ₃O _{4+ α} and ZnFe ₂O _{4- δ} coexisted in a sintered sample and Zn ions were dispersed uniformly in the sample. From the measurement of electrical resistivity ρ at temperatures between 80 K and room temperature, the relationship between log ρ and T^-1/2 is linear, which means that the dominant MR effect is spin-dependent tunneling. The sample with Zn=0.86 at% has the highest MR which is about 7% at room temperature under a magnetic field of 8 kOe.