We unravel the effect of La substitution and hence antisite disorders on the
exchange bias (EB) mechanism in Sr2βxβLaxβCoNbO6β (x= 0, 0.2) double
perovskite samples using the detailed analysis of the field cooled
magnetization isotherms (M--H) and training effect. The field dependence of the
freezing temperature deviates from both Gabay-Toulouse (GT) and de
Almeida-Thouless (AT) lines and the analysis suggests that the x= 0 sample
follows a different universality class with moderate anisotropy in the frozen
spins. Interestingly, we find that the EB effect is significantly suppressed in
the x= 0.2 sample due to increase [decrease] in the size of ferromagnetic
(FM) [cluster glass (CG)] domain, which reduces the effective disordered
interface responsible for the EB. The changes in fraction of FM, AFM, and CG
like interactions with the La substitution and applied magnetic field are found
to be crucial in governing the EB effect in these samples. Further, the
training effect measurements show the unequal shift in the left and right
branches of the M--H loops and their different evolution with the field cycles
(n). The analysis reveals that the rotatable spins relax approximately one
order of magnitude faster than the frozen spins at the disordered interface. We
find a possible correlation between the observed EB effect and the antisite
disorders in these samples.Comment: submitte