Correlation Between the Degradation of Perpendicular Anisotropy and the Double Hysteresis Behavior in [Pd/Co]$_{rm n}$/FeMn Exchange Biased Thin Films

We clearly detected double hysteresis by increasing Co layer thickness and decreasing the number of bilayers in perpendicular exchange biased [Pd(0.6)/Co$(t)$] $_{rm n}$/FeMn(11.6 nm) thin films. In-plane tensile stress calculations confirmed that the appearance of double hysteresis is closely related to the degradation of stress-induced perpendicular anisotropy in the [Pd/Co] multilayers. Furthermore, annealing at the magnetic field applied perpendicular to the film plane directly verified that the enhancement of thermally induced perpendicular anisotropy, $K_{rm eff-induced}$, in the [Pd/Co] multilayers is the main physical reason for removal of the double hysteresis. All our experimental and theoretical results demonstrated that perpendicular anisotropy is the dominant factor in controlling the double hysteresis behavior of perpendicularly magnetized [Pd/Co]$_{rm n}$/FeMn exchange biased thin films.