Atomically engineered cobaltite layers for robust ferromagnetism

Emergent phenomena at heterointerfaces are directly associated with the bonding geometry of adjacent layers. Effective control of accessible parameters, such as the bond length and bonding angles, offers an elegant method to tailor competing energies of the electronic and magnetic ground states. In this study, we construct unit-thick syntactic layers of cobaltites within a strongly tilted octahedral matrix via atomically precise synthesis. The octahedral tilt patterns of adjacent layers propagate into cobaltites, leading to a continuation of octahedral tilting while maintaining substantial misfit tensile strain. These effects induce severe rumpling within an atomic plane of neighboring layers, further triggering the electronic reconstruction between the splitting orbitals. First-principles calculations reveal that the cobalt ions transit to a higher spin state level upon octahedral tilting, resulting in robust ferromagnetism in ultrathin cobaltites. This work demonstrates a design methodology for fine- tuning the lattice and spin degrees of freedom in correlated quantum heterostructures by exploiting epitaxial geometric engineering.

Automated summary

In this study, a unit-thick syntactic layer of cobaltites was constructed within a strongly tilted octahedral matrix through atomically precise synthesis. The tilting patterns of the octahedral matrix propagated into the cobaltites and induced severe rumpling within neighboring layers, triggering electronic reconstruction and resulting in robust ferromagnetism. This work demonstrates a design methodology for fine-tuning lattice and spin degrees of freedom in correlated quantum heterostructures through epitaxial geometric engineering.