  Interface effect in complex oxide thin film heterostructures lies at the
vanguard of current research to design technologically relevant functionality
and explore emergent physical phenomena. While most of the previous works focus
on the perovskite/perovskite heterostructures, the study on
perovskite/brownmillerite interfaces remain at its infancy. Here, we
investigate spontaneously stabilized perovskite-ferromagnet
(SrCoO3-{\delta})/brownmillertite-antiferromagnet (SrCoO2.5) bi-layer with TN >
TC and discover an unconventional interfacial magnetic exchange bias effect.
From magnetometry investigations, it is rationalized that the observed effect
stems from the interfacial ferromagnet/antiferromagnet coupling. The
possibility for coupled ferromagnet/spinglass interface engendering such effect
is ruled out. Strikingly, a finite coercive field persists in the paramagnetic
state of SrCoO3-{\delta} whereas the exchange bias field vanishes at TC. We
conjecture the observed effect to be due to the effective external quenched
staggered field provided by the antiferromagtic layer for the ferromagnetic
spins at the interface. Our results not only unveil a new paradigm to tailor
the interfacial magnetic properties in oxide heterostructures without altering
the cations at the interface, but also provide a purview to delve into the
fundamental aspects of exchange bias in such unusual systems paving a big step
forward in thin film magnetism.
