A Ferromagnetic Polar Metal With Efficient Electrical Switch of Magnetism.

Abstract

Materials that host intrinsic coexisting ferromagnetism, polar distortion, and metallicity, a ferromagnetic polar metal (FPM), can combine the advantages of both multiferroics and polar metals, and thus are expected to provide unforeseen opportunities for spintronics with ultra-low-power consumption. However, generalizable routes for creating FPMs with strong coupling between itinerant ferromagnetism and polar distortions are still limited. Meanwhile, efficient electrical control of magnetism in such systems remains unexplored. Herein, we introduce a design strategy based on interfacial oxygen-octahedral-rotation mismatch to create an intrinsic FPM state in superlattices composed of two nonpolar perovskites, SrRuO₃ and CaTiO₃. Unlike previous layered oxide systems, which often result in in-plane polarization, our superlattice FPM exhibits pronounced out-of-plane polar displacements directly within the perpendicular ferromagnetic RuO₆ metal network, enabling a strong entanglement between magnetic order and polarity. Consequently, the Rashba spin-orbit torque in the superlattice FPM gives rise to extraordinary current-driven magnetization self-switching at a current density as low as 2.5 × 10⁵ A cm^-2, about two orders of magnitude lower than that of conventional heavy-metal/ferromagnet heterostructures. Our work not only identifies a robust strategy for accessing FPM states but also provides a promising platform for exploring ultra-low-power spintronic devices.