Role of heterostructures and multiple magnetic phases in the low-field magnetization of Fe-Cr GMR multilayers

摘要

Zero-field-cooled (ZFC) and field-cooled (FC) magnetization along withac-magnetization vs. temperature and m-h loop measurements are reported for twoseries of ion-beam sputtered Fe-Cr GMR multilayers where the interfaceroughness is different. The exchange coupling between the Fe layers varies fromferromagnetic (FC) to antiferromagnetic (AF) depending upon the Cr layerthickness. The ZFC and FC magnetization data follow different curves below anirreversible temperature ($T_{irr}$). The FC data shows a $T^{3/2}$ thermaldemagnetization behavior at lower temperatures with very small spin-wavestiffness constant (as compared with that of bulk Fe obtained from Bloch's$T^{3/2}$ law) but it goes as 1/T at higher temperatures (above ($T_{irr}$)).This behavior is interpreted in terms of the coexistence of spin-glass(SG)/superparamagnetic, FM and AF phases. ac-magnetization vs. temperatureshows a peak at $T_g$. This peak shifts towards higher temperatures and itsamplitude decreases with increasing frequency of the driving ac field.