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 studied in these materials. It has been observed that all the granular composites crystallize within the same temperature region 700–900 K independent of the concentration. Electrical conductance by hopping mechanism with a variable 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, 43 and 50 at.% Co41Fe39B20) at temperatures below 300 K. The negative giant magnetoresistance (GMR) was observed in the same granular composites. The maximum 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 with the electron tunneling through the insulator barriers separating the ferromagnetic granules.