Engineering unequal antipolar displacement in ferromagnetic layered oxide heterostructures

Abstract

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.