  We report annealing induced exchange bias in Fe-Cu-Pt based heterostructures
with Cu as an intermediate layer (Fe/Cu/Pt heterostructure) and capping layer
(Fe/Pt/Cu heterostructure). Exchange bias observed at room temperature (300 K)
is found to be dependent on the annealing temperature. We obtained positive
exchange bias of 120 Oe on annealing both the heterostructures at 400 oC, while
on annealing these heterostructures at 500 and 600 oC a negative exchange bias
of ~ -100 Oe was found. X-ray reflectivity and polarized neutron reflectivity
measurements provided evolution of depth dependent structure and magnetic
properties of the heterostructures on annealing at different temperatures and
revealed coexistence of soft and hard (alloy) magnetic phases across the
thickness of the films. Rapid and long range interdiffusion at interfaces on
annealing the systems at a temperature above 400 oC resulted into formation of
a ternary alloy phase. These results can be understood within the context of a
very unusual interface exchange interaction at the interface of hard/soft
magnetic phases, which are dependent on the annealing temperature.
