Effects of Mg doping and sintering temperature on the magnetoresistance of sintered Fe/sub 3/O/sub 4/ ferrites

Fe/sub 3/O/sub 4/ powder was mixed with MgO powder and then sintered in an atmosphere of argon at various temperatures for 3 h to form Mg-doped Fe/sub 3/O/sub 4/ ferrites. The effects of the sintering temperature, microstructure, and Mg content on the magnetoresistance of sintered Fe/sub 3/O/sub 4/ ferrites were investigated. X-ray diffraction and chemical titration analysis of Fe/sup 2+/ and Fe/sup 3+/ ions indicate that the nonstoichiometric phases of Fe/sub 3/O/sub 4+X/ and MgFe/sub 2/O/sub 4-x/ coexisted in the sintered sample. The temperature dependence of resistivity was examined. A plot of log /spl rho/ against T/sup -1/2/ of the sintered samples exhibits a linear relationship, indicating that the dominant magnetoresistance effect is spin-dependent tunneling. The maximum magnetoresistance of the sintered sample is about 7.3% at room temperature at a magnetic field of 12 kOe. The Mg content of this sample is 0.93 at.%.