  Doping at the rare-earth site by divalent alkaline-earth ions in perovskite
lattice has witnessed a variety of magnetic and electronic orders with
spatially correlated charge, spin and orbital degrees of freedom. Here, we
report an antisite disorder driven spontaneous exchange bias effect as a result
of hole carrier (Sr2+) doping in La2-xSrxCoMnO6 (0 < x < 1) double perovskites.
X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder
with the increase of Sr content up to x = 0.5 and thereby decreases from x =
0.5 to 1. X-ray absorption spectroscopy has revealed that only Co is present in
mixed valent Co2+ and Co3+ states with Sr doping to compensate the charge
neutrality. Magnetotransport is strongly correlated with the increase of
antisite disorder. The antisite disorder at the B-site interrupts the
long-range ferromagnetic order by introducing various magnetic interactions and
instigates reentrant glassy dynamics, phase separation and canted type
antiferromagnetic behavior with the decrease of temperature. This leads to
novel magnetic microstructure with unidirectional anisotropy that causes
spontaneous exchange bias effect that can be tuned with the amount of antisite
disorder.
