Interfacial Antiferromagnetic Coupling and Dual-Exchange Bias in Tetragonal SrRuO₃-PrMnO₃ Superlattices

The functional properties of oxide heterostructures depend on the interfaces accommodating ions, their spins, and structural mismatches. Here, by stabilizing tetragonal symmetry, we achieve the in-plane antiferromagnetic (AFM) ordering and dual-exchange bias in the superlattices consisting of two ferromagnets SrRuO₃ (SRO) and PrMnO₃ (PMO). The tetragonal symmetry of this superlattice system achieved after the octahedral rotations yield an elongation of the c-axis parameter with Ru-O-Mn bond angle close to 180°, induces an interfacial antiferromagnetic ordering, which is suppressed as the ferromagnetic (FM) ordering in the PMO layer increases. The 0.1 T in-plane cooling field (H_cool) leads to the shift (ca. -0.04 T) of minor hysteresis loop along the negative field axis due to the presence of -0.87 erg/cm² AFM interfacial exchange coupling energy density (E_Ru,Mn) at 20 K. The exchange bias field (H_EB) switches from negative to positive value with the increase in H_cool. For 5 T H_cool, the H_EB is positive, but the E_Ru,Mn is -1.25 erg/cm² for n ≤ 8 (n = number of unit cells of PMO) and 1.52 erg/cm² for n ≥ 8. The H_EB and its switching from negative to positive with the increase in H_cool are explained by the interplay of strong antiferromagnetic coupling energy and Zeeman energy at the interfaces. The results demonstrate that the SRO-PMO superlattice could be a model system for the investigation of the interfacial exchange coupling in functional oxides.