Giant magnetoresistance for ensembles of ferromagnetic granules in   variable range hopping conductivity regime
  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. 
V.I.Kozub, A.V. Shumilin
cond-mat.mes-hall