Origin of large positive magnetoresistance in permalloy(Ni0.8Fe0.2)–graphite granular composites

Abstract We report the magnetoresistance (MR) of ball milled nano-granular (Ni 0.8 Fe 0.2 ) x C 100− x ( x = 0–50%) composites. Structural characterization has been carried out using X-ray diffraction and TEM measurements; while the electrical transport measurements were carried out by conventional four probe technique. Longitudinal ( L ) and transverse ( T ) magnetoresistance measurements were performed at room temperature upto 50 kOe magnetic field. Magnetic measurements on the composites show all the composites to be ferromagnetic. Although magnetic properties show significant changes in magnetization values, comparable variations could not be detected in MR measurements, suggesting the origin of large positive magnetoresistance is non-magnetic. The existing models for the electron transport behavior fail to explain the H 3/2 dependence of the MR. We have attempted to explain the origin of large positive MR values in these composites.