Evidence of domain wall scattering in thin films of granular CoFe-AgCu

Thin films of the giant magnetoresistive granular CoFe-AgCu system prepared by rf sputtering displayed a great variety of domain-like microstructures with a net out-of-plane component of the magnetization for ferromagnetic vo lume concentrations above about 0.25. Therefore, magnetic percolation takes place at ferromagnetic concentrations much lower than the physical percola tion threshold. The out-of-plane structure of the as-deposited samples in m agnetic virgin state consisted of a distribution of both quasi-circular dom ains and short stripes depending on the ferromagnetic content. Furthermore, these samples present high metastability and a variety of remanent in-plan e and out-of-plane microstructures can be achieved as a function of the mag netic history. Besides, the evolution of the magnetic microstructure yields strong training effects on magnetotransport properties, due to the extra c ontribution of the electron scattering at the domain walls. All in all, the observed behavior is the result of a subtle correlation between perpendicu lar anisotropy produced by residual stresses, exchange interparticle intera ctions due to CoFe alloyed in the matrix, and dipolar interactions. Thus, a s high structural evolution occurs through annealing, the features of rando mly distributed ferromagnetic particles are recovered and, the out-of-plane domain structures and the training effects disappear.