Emergent Ferromagnetism in CaRuO₃/CaMnO₃ (111)-Oriented Superlattices

The boundary between CaRuO₃ and CaMnO₃ is an ideal test bed for emergent magnetic ground states stabilized through interfacial electron interactions. In this system, nominally antiferromagnetic and paramagnetic materials combine to yield interfacial ferromagnetism in CaMnO₃ due to electron leakage across the interface. In this work, we show that the crystal symmetry at the surface is a critical factor determining the nature of the interfacial interactions. Specifically, by growing CaRuO₃/CaMnO₃ heterostructures along the (111) instead of the (001) crystallographic axis, we achieve a 3-fold enhancement of the magnetization and involve the CaRuO₃ layers in the ferromagnetism, which now spans both constituent materials. The stabilization of a net magnetic moment in CaRuO₃ through strain effects has been long-sought but never consistently achieved, and our observations demonstrate the importance of interface engineering in the development of new functional heterostructures.