Peculiarity of Magnetoresistance of Composite Materials Based on Co and SiO

Abstract

A series of thin-film composite materials based on Co and SiO were deposited via electron-beam coevaporation technique using two independent sources. The concentration of Co atoms of thin-film composite materials varied from 35 to 90 at. %. It was controlled by using a scanning electron microscope (Tescan VE-GA3) with an energy-scattering X-ray (EDX) detector (Oxford Instruments). The total thickness of the nanocomposites was controlled by a system of two independent quartz resonators and amounted to 30 and 60 nm. The magnetoresistive properties of these structures deposited at room temperature were investigated. The results showed that the percolation threshold for the system based on Co and SiO is in the concentration range of сСо  60-70 at. %. From the field dependences of the magnetoresistance (MR) obtained at room temperature, it follows that the electrical resistance of the films decreases when they are introduced into the magnetic field (negative magnetoresistance). The negative MR indicates that the dominant effect observed is due to spin-dependent electron tunneling between ferromagnetic nanogranules. At the concentration range of сСо  40-60 at. %, isotropic MR of 1.5-2.5 % is realized. The maximum on the concentration dependences of MR shifts to the region of lower concentrations of Co with increasing sample thickness.