Size and self-field effects in giant magnetoresistive thin-film devices

Giant magnetoresistance (GMR) was measured as a function of device size for patterned NiCoFe/Cu and NiFe/Ag films. For the quasi-granular NiCoFe/Cu films, the normalized maximum change in resistivity Δρ/ρ was 8% for most of the samples. For the NiFe/Ag films, antiparallel alignment was achieved through magnetostatic coupling, not exchange fields, with a Δρ/ρ of 4.5%. The films were patterned into stripes with Au current leads for size-effect measurements. The height of the stripes varied from 0.5 to 16 μm and the track width varied from 1 to 16 μm. Discrete switching events and anomalous low-field dips in the response were observed for both materials for small device sizes. Self-field and heating effects due to the applied current were investigated for the NiFeCo/Cu films. The effect of the self-field produced by the applied current was separated from the thermal contribution and was found to reduce the response by over 32% for a current density of 10⁷ A/cm²