Engineering Unequal Antipolar Displacement in Ferromagnetic Layered Oxide Heterostructures

Multiferroic materials that simultaneously display ferroelectricity and magnetic ordering are highly sought after for next-generation electronics applications. The combination of these properties is very rare in single-phase materials, thus heterostructure engineering represents a promising alternative pathway. In this context, heterostructures comprising the insulating and ferromagnetic double perovskites La₂NiMnO₆ and RE₂NiMnO₆ (RE=rare earth≠La) represent an intriguing system. These superlattices are predicted to exhibit unequal antipolar displacement of the La and RE ions [1], which, when combined with odd periodicity superlattice layering, could potentially lead to hybrid improper ferroelectricity.

La₂NiMnO₆/Sm₂NiMnO₆ superlattices are grown with atomic precision using a sputtering system equipped with high-energy electron diffraction (RHEED). The heterostructures display robust ferromagnetism [2], as confirmed by in-house magnetometry and synchrotron measurements. Scanning transmission electron microscopy (STEM) in conjunction with first-principles calculations has validated the predicted unequal antipolar displacement in our superlattices. This represents a significant advance towards the establishment of hybrid improper ferroelectricity in artificially layered heterostructures.


References
[1] H. J. Zhao, W. Ren, Y. Yang, J. Íñiguez, X. M. Chen, L. Bellaiche, Nat. Comm. 5 4021 (2014)
[2] J. Spring et al., arXiv:2406.09937 (2024)