Tunnel magnetoimpedance in cobalt discontinuous films

We present the impedance and its variation in magnetic fields for discontin uous Co films sandwiched by Al2O3. The Co nominal thickness varies from 0.7 to 2.5 nm and the room temperature impedance has been measured from fracti ons of Hz to 100 kHz. The samples present a distribution of relaxation time s with a maximum width below the percolation point. For a given frequency, an external magnetic held induces a variation in the modulus and in the pha se of the impedance. The evolution of the tunnel magnetoimpedance, whose re al part is the usual tunnel magnetoresistance, as a function of frequency i s presented and can be described in terms of the variations in the relaxati on time. (C) 1999 Elsevier Science B.V. All rights reserved.