Influence of annealing condition on giant magnetoresistance of FeCo–Cu granular films

Abstract

FeCo–Cu granular films were prepared by DC magnetron sputtering using mixed targets. Two kinds of annealing procedures named `isochronous annealing' and `cumulative isothermal annealing' were used to promote the grain growth or phase segregation of as-deposited films. The influence of annealing condition on magnetoresistance has been investigated systematically for the films with optimal composition. It is found that for the films with same composition, the cumulative isothermal annealed samples have larger giant magnetoresistance (GMR) in comparison with the isochronous annealed ones. Transmission Electron Microscope study shows that the isochronous annealing promotes the grain growth a little excessively sometimes which is not in favor of the GMR improvement. The short-time isothermal annealing at a modest higher temperature, however, limits the grain growth due to the very short annealing time. By repeating this annealing step several times, more and homogenous fine particles are obtained, which leads to the larger GMR. Therefore, a cumulative isothermal annealing at an optimal temperature is recommended.