Interfacial ferromagnetism in an atomically ordered three-component manganite superlattice*

Lattice distortions play a key role in the ferromagnetic-metallic ground state of the mixed valent manganite, La_2/3Sr_1/3MnO₃. To explore the effect of such distortions on the electronic and magnetic properties, we substitute 50% of the La atoms with Y to grow La_1/3Y_1/3Sr_1/3MnO₃ thin films where the La, Y and Sr atoms all randomly occupy the A-site. But the random occupancy also leads to disorder. We decouple this disorder by constructing an ordered superlattice of three manganite phases, LaMnO₃, YMnO_3, and SrMnO₃, stacked at the atomic layer limit. Our electronic transport measurements show an insulating ground state in both the ordered superlattice and the random alloy samples although a crossover to a metallic state around 120K is observed in the ordered superlattice. We find a quasiparticle peak due to interfacial reconstruction at the oxygen K-edge in the ordered superlattice when probed with resonant soft x-rays. Furthermore, a more than four times stronger dichroic signal is observed in the ordered superlattice compared to the random alloy sample. These measurements point to ferromagnetic metallic tendencies at the Mn³⁺/Mn⁴⁺ interfaces in the ordered superlattice.