Effects of sintering temperature on the magnetoresistance and microstructure of the mixture of Fe/sub 3/O/sub 4/ and Cu-ferrite powder

The Fe/sub 3/O/sub 4/ powder was mixed with Cu-ferrite powder then sintered in an argon atmosphere at temperatures between 1000/spl deg/C and 1250/spl deg/C for 4 h. The Cu-ferrite content in the mixture powder was between 0 mol% and 30 mol%. The effects of Cu-ferrite content and sintering temperature on the magnetoresistance (MR) and microstructure of the sintered ferrite were investigated. It was found that the Cu ions were dispersed uniformly in all sintered samples by the analysis of Cu element mapping of the scanning electron microscopy. The maximum MR ratio of the sintered ferrite at room temperature is about 7.3% when Cu-ferrite content was 7.28 mol% and sintering temperature was 1200/spl deg/C. From the plot of log /spl rho/ versus T/sup -1/2/ curves and the measurement of the current versus voltage curves of the sintered samples, it can be known that the magnetoresistance mechanisms in these sintered samples are the contribution of spin-polarized tunneling effect.