Resistive and magnetoresistive properties of granular amorphous CoFeB-SiOncomposites

The electrical and magnetic properties of amorphous granular (CoFeB)(x)(SiO n)(100-x) (x = 20, 30, 36, 43.5, 46, 59, and 100, 1.6 less than or equal to n less than or equal to 2) thin films obtained by ion-beam sputtering of c omposite targets were studied. It was established that the size of the amor phous granules varied from 2-3 nm to 5-7 nm with an increase in the fractio n of the metallic phase (CoFeB) from 30 to 59 at. %. Tunneling is the domin ating conductivity mechanism in these films, although the probability of va riable-range hopping conductivity is high For the concentrations,fis of the metallic phase between 43.5 and 46 at. %. A giant magnetoresistance (GMR) reaching 4%, in a field of 11 kOe at room temperature was found. The GMR is due to the spin-dependent tunneling of etectrons between the metallic gran ules. The magnetic investigations performed suggest the existence of super- paramagnetism in the amorphous (CoFeB)(x)(SiOn)(100-x) composites.