Study of annealing effects on the giant magnetoresistance in ferromagnetic alloys

A self-consistent macroscopic theory is developed to improve on that of Gu et al (1996 Phys. Rev. B 53 11685) and to provide a physical understanding of some new experimental observations in ferromagnetic alloys. For composites with non-spherical inclusions, which is the general case in artificial granular systems, previous models based on the calculation of a spherical particle in the dilute limit are inadequate. By considering the particle shape distribution and its evolution with annealing effects, we have studied the shape dependence of the giant magnetoresistance (GMR) in ferromagnetic alloys. It is found that both the particle shape and its orientation are effective factors in determining the magnitude of the GMR. Based on a comparison between our calculations and experimental data, a comprehensive picture of the effects of annealing on GMR is obtained