The annealing effect on structure, magnetoresistance and magnetic properties of Co/Bi/Co thin films

摘要

Co/Bi/Co thin films were prepared by alternately sputtering at substrate temperature 460 K. Their structure, magnetoresistance and magnetic properties were studied using transmission electron microscopy (TEM), software-hardware complex with current-in-plane geometries, and vibrating sample magnetometer (VSM). The trilayer systems have been investigated as functions of the Bi layer thickness and temperature. The film structure in both as-deposited and annealed at 680K states is a granulated structure which consists of a Co magnetic matrix with embedded Bi granules. The film structure after annealing at 900K depends on Bi concentrations and changes from the fcc-Co+amorphous Bi to a fcc-Co+tetragonal phase of Bi2O3 of around 17 at.%. Magnetoresistance has demonstrated independence from annealing processes in the temperature range from 300 to 680 K. Besides, the oscillation dependence of magnetoresistance with Bi thickness has been observed. The saturation and remanent magnetization are reduced with the increase of Bi thickness and increase with increasing the annealing temperature; the coercivity slightly depends on Bi thickness in as-deposited state and increases more than 10 times at t(Bi) = 30nm after annealing at 680 K.