Large positive magnetoresistance effect in metal-insulator nanocomposites in weak magnetic fields

Studies of the magnetoresistance of granular Fe/SiO2 films within the compositional range corresponding to insulators revealed a large positive magnetoresistance. The positive magnetoresistance reaches 10% in magnetic fields ∼100 Oe at room temperature and exhibits slow response times (∼2 min) to stepped magnetic-field variation. The nature of the effect is apparently associated with the influence of ferromagnetic cluster aggregates of iron nanoparticles on the magnetoresistance.