Magnetic domain transformations in polycrystallinehard-soft giant-magnetoresistive-effect spin valves withCo-Cu-based artificial antiferromagnetic subsystems

Abstract

The magnetic and transport properties of hard-softgiant-magnetoresistive-effect spin valves, with a Co/Cu/Coantiferromagnetically coupled sandwich as the hard layer, areinvestigated. The irreversibilities in the antiferromagneticallycoupled Co/Cu/Co sandwiches prepared by DC-magnetron (DC = direct current) sputtering are shown to strongly depend on themagnetic history of the samples. The irreversibilities, evidencedfrom analysis of the giant-magnetoresistance and magnetizationresponses along minor loops, are attributed to domain-phasetransformations. First, the effect of the buffer stack on thestructural properties and on the quality of the antiferromagneticcoupling is investigated. Coupling strengths larger than 0.4 erg cm-2 have been achieved for deposition on bufferscontaining a Cr/Fe bilayer. A method is given for estimating theamount of remanence in the Co/Cu/Co sandwich, based on the analysisof the giant-magnetoresistive response upon switching themagnetization direction of the soft magnetic layer located in thebuffer. The perfect antiferromagnetic alignment at zero field isattributed to the formation of a magnetic state with relativelylarge domains. The small amount of remanence detected in somesamples is ascribed to the persistence at zero field of asignificant density of domain walls. Small fluctuations in thethickness of the layers causing a lateral distribution of thecoupling strength are expected to influence the remanence magneticstate and induce differences between samples.