KNbO₃-based multiferroic heterostructures: a lead-free alternative for strain-driven magnetic modulations

Artificial multiferroic heterostructures offer a versatile platform for engineering magnetic properties through interfacial strain and magnetoelectric coupling. In this framework, we demonstrate the growth of both Ni and La_0.67Sr_0.33MnO₃ ferromagnetic thin films on KNbO₃ (100) single crystals. We show, by combining structural and magneto-optical characterizations, how their magnetic responses are affected by the structural transitions taking place in the substrate as a function of temperature. In particular, we observe sensitive modifications in the ferroelectric domain composition of KNbO₃, especially after cooling from orthorhombic to rhombohedral phase, leading to a transition from in-plane anisotropic to isotropic magnetization behaviour in Ni thin films. Temperature dependent magnetic characterizations show a coercivity modulation while crossing the structural transition for both Ni and La_0.67Sr_0.33MnO₃ films, signature of interfacial strain-driven coupling. To the best of our knowledge, these are the first reported KNbO₃-based multiferroic heterostructures, establishing this lead-free material as a potential functional host for both metallic magnetostrictive and complex oxide thin films.