Asymmetry of the magnetization reversal mechanism probed by relaxation measurements in La-Ca-Mn-O ferromagnetic/antiferromagnetic multilayers

Abstract

In exchange-coupled ferromagnetic/antiferromagnetic ${\mathrm{La}}_{0.60}{\mathrm{Ca}}_{0.40}{\mathrm{MnO}}_{3}(\mathrm{FM})/{\mathrm{La}}_{0.33}{\mathrm{Ca}}_{0.67}{\mathrm{MnO}}_{3}(\mathrm{AF})$ multilayers the magnetization reversal mechanism is probed by magnetic viscosity and remanence measurements below (5 K) and above (80 K) the blocking temperature ${T}_{B}=70 \mathrm{K}.$ The magnetic relaxation follows the $\mathrm{ln}(t)$ behavior at 5 K, which is a universal feature of a slow relaxation process, whereas at 80 K the time decay requires an additional exponential term. Below ${T}_{B},$ the observed loop asymmetries in the irreversible susceptibility $({\ensuremath{\chi}}_{\mathrm{irr}})$ and the magnetic viscosity (S) reveal two inequivalent reversal mechanisms between the field increasing and field decreasing branches of the hysteresis loop.