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

TL;DR

This study investigates the complex magnetic behavior of Fe-Cr GMR multilayers, revealing coexistence of multiple magnetic phases and the influence of interface roughness and Cr layer thickness on magnetic properties.

Contribution

It provides new insights into how heterostructures and multiple magnetic phases affect low-field magnetization in Fe-Cr multilayers, highlighting the role of interface roughness and Cr thickness.

Findings

Different magnetization curves below $T_{irr}$ for ZFC and FC.

FC magnetization follows $T^{3/2}$ at low T, 1/T at high T.

Presence of spin-glass, superparamagnetic, FM, and AF phases.

Abstract

Zero-field-cooled (ZFC) and field-cooled (FC) magnetization along with ac-magnetization vs. temperature and m-h loop measurements are reported for two series of ion-beam sputtered Fe-Cr GMR multilayers where the interface roughness is different. The exchange coupling between the Fe layers varies from ferromagnetic (FC) to antiferromagnetic (AF) depending upon the Cr layer thickness. The ZFC and FC magnetization data follow different curves below an irreversible temperature ($T_{irr}$). The FC data shows a $T^{3/2}$ thermal demagnetization behavior at lower temperatures with very small spin-wave stiffness 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. temperature shows a peak at $T_g$. This peak shifts towards higher temperatures and its amplitude decreases with increasing frequency of the driving ac field.