Proximity-induced fully ferromagnetic order with eightfold magnetic anisotropy in heavy transition metal oxide CaRuO${}_3$

Ferromagnetic materials with a strong spin-orbit coupling (SOC) have attracted much attention in recent years because of their exotic properties and potential applications in energy-efficient spintronics. However, such materials are scarce in nature. Here, a proximity-induced paramagnetic to ferromagnetic transition for the heavy transition metal oxide CaRuO${}_3$ in (001)-(LaMnO${}_3$/CaRuO${}_3$) superlattices is reported. Anomalous Hall effect is observed in the temperature range up to 180 K. Maximal anomalous Hall conductivity and anomalous Hall angle are as large as ∼15 Ω${}^{-1}$ cm${}^{-1}$ and ∼0.93%, respectively, by one to two orders of magnitude larger than those of the typical 3d ferromagnetic oxides such as La${}_{0.67}$Sr${}_{0.33}$MnO${}_3$. Density functional theory calculations indicate the existence of avoid band crossings in the electronic band structure of the ferromagnetic CRO layer, which enhances Berry curvature thus strong anomalous Hall effects. Further evidences from polarized neutron reflectometry show that the CaRuO${}_3$ layers are in a fully ferromagnetic state (∼0.8 µ${}_B$/Ru), in sharp contrast to the proximity-induced canted antiferromagnetic state in 5d oxides SrIrO${}_3$ and CaIrO${}_3$ (∼0.1 µ${}_B$/Ir). More than that, the magnetic anisotropy of the (001)-(LaMnO${}_3$/CaRuO${}_3$) superlattices is eightfold symmetric, showing potential applications in the technology of multistate data storage. (© 2023 Wiley‐VCH GmbH)