Emergent double perovskite phase at LaMnO3/LaNiO3 interfaces: Coupled charge transfer and structural reconstruction

Abstract

We report [( LaNiO3)(n)/(LaMnO3)(n)] M/SrTiO3(111) superlattices [n = 20, 10, 5, 2, and 1 unit cells (u.c.)] as "precursor" heterostructures for a double perovskite La2NiMnO6. A charge transfer at the LaNiO3/LaMnO3 interfaces and formation of the emergent La2NiMnO6 phase with Ni2+ and Mn4+ oxidation states was evidenced by in situ optical ellipsometry and supported by magnetic and Raman measurements. The 10/10 and 5/5 superlattices revealed a complex magnetic behavior with two ferromagnetic phase transitions with TC-low = 170K and TC-high similar to 250-280K, originating from the ferromagnetic LaMnO3 and the emergent interfacial La2NiMnO6 phase, respectively. With decreasing thickness of individual layers, the magnetism of 2/2 and 1/1 superlattices transforms into that of the ordered double perovskite La2NiMnO6. Furthermore, a structural reconstruction into a monoclinic (P-12) structure of the ordered La2NiMnO6 at the interface, evidenced by Raman spectroscopy, goes ahead with the charge transfer and magnetic La2NiMnO6 behavior.