Intra and inter-plane spin dependent tunneling in Co/SiO_x granular multilayers

Room temperature spin-dependent tunneling in Co/SiO_x granular multilayers has been analysed by the frequency dependence of the impedance and tunnel magnetoimpedance. In the samples, layers of Co grains are separated by SiO_x layers wich have different thickness for each sample. Mean relaxation, times were determined from the complex impedance versus frequency curves using Cole-Cole fitting procedures. For a intermediary insulator thickness two spin-dependent modalities have been found, They are explained, in terms of inter- and intra-plane tunnelling.