Tunnel magnetoimpedance in cobalt discontinuous films

We present the impedance and its variation in magnetic fields for discontinuous 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 fractions of Hz to 100 kHz. The samples present a distribution of relaxation times with a maximum width below the percolation point. For a given frequency, an external magnetic field induces a variation in the modulus and in the phase of the impedance. The evolution of the tunnel magnetoimpedance, whose real part is the usual tunnel magnetoresistance, as a function of frequency is presented and can be described in terms of the variations in the relaxation time.