Observation of magnetoresistance in core-shell Fe-Fe oxide systems

A negative magnetoresistance was measured between 15 and 300 K under a maximum field H=70 kOe on two granular systems obtained by compacting Fe nanoparticles surrounded by an oxide shell similar to2 nm thick. The effect depended on the Fe core average size D that was of 8 and 18 nm in the two samples, as by x-ray diffraction. The maximum relative resistance change, about 5%, was observed at 50 K in the sample with smaller D. The results have been interpreted considering intraparticle and interparticle magnetic correlations and microscopic mechanisms similar to those responsible for the magnetoresistance in other granular systems. (C) 2002 American Institute of Physics.