Interfacial antiferromagnetic coupling driven magnetotransport properties in ferromagnetic superlattices

We explore the role of interfacial antiferromagnetic interaction in coupled soft and hard ferromagnetic layers to ascribe the complex variety of magnetotransport phenomena observed in La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) superlattices (SLs) within a one-band double-exchange model using Monte Carlo simulations. Our model Hamiltonian incorporates magnetocrystalline anisotropy interactions and superexchange 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 superexchange to investigate the properties along hysteresis loop. We find that the antiferromagnetic coupling at the interface induces LSMO and SRO layers to align in antiparallel orientation at low temperatures. Our results reproduce the positive exchange bias of the minor 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 antiparallel (parallel) configuration, in good agreement with the experimental data. This demonstrates the necessity of carrier-driven antiferromagnetic interactions at the interface to understand the one-to-one correlation between magnetic and transport properties observed in experiments. For high temperature, just below the ferromagnetic TC of SRO, we unveil 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.