Charge Transfer Control of Emergent Magnetism at SrMnO3/LaMnO3 Interfaces

Emergent phases at the interfaces in strongly correlated oxide heterostructures display novel properties not akin to those of constituting materials. The interfacial ferromagnetism in (LaMnO3)m/(SrMnO3)n (LMO)m/(SMO)n superlattices (SLs) with antiferromagnetic bulk LMO and SMO layers is believed to be a result of the interfacial charge transfer (CT). By using in situ optical ellipsometry, it is demonstrated directly that CT and emergent magnetism in (LMO)m/(SMO)n SLs are controlled by the LMO/SMO thickness ratio, chosen as m/n = 1 and 2. The enhanced CT in SLs with m/n = 2 favors the high-TC emergent ferromagnetism with TC = 350–360 K, whereas the reduced CT in m/n = 1 SLs suppresses it yielding TC = 300 K. A complex dependence of the saturation magnetization as a function of interface density Λ = (m + n)−1 with minima at Λ = 0.11 (m/n = 2) and Λ = 0.25 (m/n = 1) was observed and rationalized by the competition of ferromagnetic and antiferromagnetic contributions, originating from the volume of LMO and SMO layers as well as from the LMO/SMO interfaces. The role of epitaxy stress and MnO6 octahedral tilts in the emergent magnetic behavior is discussed.