Room-temperature ferrimagnetism and polar phase in strained La₂CoRuO₆ films through 3d-4d cation engineering.

Abstract

Materials with room-temperature magnetic ordering and switchable polarization are essential for spintronic devices. Although 3 d transition metal oxides exhibit potential, their Curie temperature (T_C) remains unsatisfactory, and coexistence of magnetic and polar order has not been realized in 4 d/5 d oxides. Here, through epitaxial strain and 3d-4d cation ordering engineering, a ferrimagnetic insulating state (T_C ~ 623 K) is achieved in La₂CoRuO₆ films, coexisting with switchable short-range polar nanodomains. Atomic-scale investigations and density functional theory calculations reveal that compressive strain enhances lattice distortions. These distortions, combined with high-spin state of Co²⁺ ions and ordered B-site cations, significantly enhance Co-O-Ru antiferromagnetic superexchange, inducing the ferrimagnetic insulating state. Concurrently, the gradient BO₆ octahedral rotations with inhomogeneous evolution trigger B-site ions' displacements, driving the formation of polar nanodomains. Our work fills the experimental gap in realizing magnetic and polar order coexistence in 4 d/5 d oxides and opens new avenues for designing high-T_C multiferroics.