Novel aspects of magnetoresistance in nanogranular magnetic systems

Different measurements indicate that a negative isotropic magnetoresistance (MR) is a common feature of a wide class of nanogranular magnetic materials. Very similar effects emerge in various magnetic systems, whose common feature is a granularity (either structural or magnetic) on the nanometer scale. Basically, all MR effects have the same microscopic origin at an atomic level, i.e., a scattering cross-section explicitly depending on the angle between the spin of conduction electrons and the local direction of the magnetisation. In this work, analogies and differences among magnetotransport effects observed in nanogranular alloys will be highlighted.