Abstract
Granular NiFe/Ag multilayer film exhibits low saturation field and large giant magnetoresistance (GMR) effect, suited as low-field sensor materials.1 However, observed Barkhausen noise in the GMR measurements in these films have been limiting their practical applications.2 Here, we report a micromagnetic modeling study, focusing on the correlation between the micromagnetic properties and film microstructure. It is found that the spatial randomness of intergranular exchange coupling, likely to occur in the film due to its granular microstructure, can cause Barkhausen jumps in GMR response. Figure 1 shows calculated GMR value of a patterned NiFe/Ag/NiFe trilayer with a size of 1.28 μm×1.11 μm, as a function of external fields, applied along its hard axis direction. The Barkhausen jumps can be clearly identified along the GMR response due to its μm size domain switching. In addition to the spatial nonuniformity, effects of various intergranular and interlayer Heisenberg and non-Heisenberg exchange couplings are systematically studied. Figure 2 shows the calculated GMR response for a patterned planar isotropic trilayer film with an interlayer biquadratic exchange coupling. The triangular shape of the GMR response is the characteristics of the biquadratic interlayer exchange coupling.
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