  We explore the role of interfacial antiferromagnetic interaction in coupled
soft and hard ferromagnetic layers to ascribe the complex variety of
magneto-transport phenomena observed in $La_{0.7}Sr_{0.3}MnO_3/SrRuO_3$
(LSMO/SRO) superlattices (SLs) within a one-band double exchange model using
Monte-Carlo simulations. Our calculations incorporate the magneto-crystalline
anisotropy interactions and super-exchange interactions of the constituent
materials, and two types of antiferromagnetic interactions between Mn and Ru
ions at the interface: (i) carrier-driven and (ii) Mn-O-Ru bond super-exchange
in the model Hamiltonian to investigate the properties along the hysteresis
loop. We find that the antiferromagnetic coupling at the interface induces the
LSMO and SRO layers to align in anti-parallel orientation at low temperatures.
Our results reproduce the positive exchange bias of the minor loop and inverted
hysteresis loop of LSMO/SRO SL at low temperatures as reported in experiments.
In addition, conductivity calculations show that the carrier-driven
antiferromagnetic coupling between the two ferromagnetic layers steers the SL
towards a metallic (insulating) state when LSMO and SRO are aligned in
anti-parallel (parallel) configuration, in good agreement with the experimental
data. This demonstrate the necessity of carrier-driven antiferromagnetic
interactions at the interface to understand the one-to-one correlation between
the magnetic and transport properties observed in experiments. For high
temperature, just below the ferromagnetic $T_C$ of SRO, we unveiled the
unconventional three-step flipping process along the magnetic hysteresis loop.
We emphasize the key role of interfacial antiferromagnetic coupling between
LSMO and SRO to understand these multiple-step flipping processes along the
hysteresis loop.
