Enhanced ferromagnetism in (111)-oriented CaRuO₃/CaMnO₃ superlattices

Emergent ferromagnetism observed at (001) CaRuO₃/CaMnO₃ (CRO/CMO) interfaces is attributed to charge transfer from the itinerant metal CRO into antiferromagnetic CMO. Experiment and theory agree that the ferromagnetism is confined to the first unit cell of CMO. At the (111) CRO/CMO interface, emergent ferromagnetism is observed but with a comparably enhanced moment. Transmission electron microscopy, atomic force microscopy, and x-ray reflectivity indicate smooth, atomically sharp interfaces in the superlattices. SQUID magnetometry confirms emergent ferromagnetism with an increase in magnetic moment to 2.8 µ_B/interfacial Mn compared to the 1 µ_B/interfacial Mn found in previous (001) superlattices. Transport measurements show a hysteretic anomalous Hall effect below the observed Curie temp (T_C = 150 K) and a surprising change from n- to p-type carriers near T_c. Ab initio calculations indicate that the conductive CRO contributes to an additional magnetic moment. Thus, emergent ferromagnetism at (111) interfaces can be explained through charge transfer from CRO to CMO and proximity induced ferromagnetism in the CRO.