Electrical properties and giant magnetoresistance of the CoFeB-SiO2 amorphous granular composites

The (Co41Fe39B20)(x) (SiO2)(100-x) metal-insulator granular films (x = 33. 43, 50, 72 and 100 at.%) with amorphous structure have been obtained by ion -beam sputtering technique. Resistivity and magnetoresistance have been stu died in these materials. It has been observed that all the granular composi tes crystallize within the same temperature region 700-900 K independent of the concentration. Electrical conductance by hopping mechanism with a vari able jump length is found to dominate in the (Co41Fe39B20)(x) (SiO2)(100-x) granular composites containing less than 72 at.% of the metal phase (33, 4 3 and 50 at.% Co41Fe39B20) at temperatures below 300 K. The negative giant magnetoresistance (GMR) was observed in the same granular composites. The m aximum value of the GMR (3.4%) was found in the (Co41Fe39B20)(50)(SiO2)(50) film which is close to the percolation threshold. The GMR is associated wi th the electron tunneling through the insulator barriers separating the fer romagnetic granules. (C) 2001 Elsevier Science B.V. All rights reserved.