Giant magnetoresistance for ensembles of ferromagnetic granules in variable range hopping conductivity regime

• We discuss the variable range hopping conduction over an array of metallic granules.
• VRH conduction occurs due to co-tunneling through states on Coulomb blockaded granules.
• The magnetoresistance depends exponentially on the number of these intermediate granules.

We study an effect of moderate magnetic field on variable range hopping conductivity in arrays of ferromagnetic granules separated by tunnel barriers. It is shown that the resulting magnetoresistance can be significantly larger than the standard “giant” magnetoresistance in Fe–N–Fe–N… multilayers. The effect is related to a gain in densities of states available for the virtual processes within the intermediate granules due to magnetic-field induced alignment of the granule magnetizations.