We present a first-principles study on the interface between perovskite ferroelectrics (PbTiO${}_3$) and conducting magnetic manganites (La${}_{1-x}$Sr${}_x$MnO${}_3$). We show that by switching the ferroelectric polarization, additional carriers are accumulated or depleted at the interfacial region of the manganite and that this change in carrier density can modify the magnetic spin configuration of the interfacial Mn, which is consistent with the experimentally observed anomalously large change in the magnetization. We also describe an unexpected purely interfacial phenomenon whereby the ferroelectric polarization of the interfacial region changes the magnetic energetics—a degree of freedom not present in bulk manganites. Theoretically, we show the the ground-state magnetic structure depends sensitively on the precise choice of Hubbard $U$ parameter within the widely used DFT+$U$ class of exchange correlation functionals. We provide a simple Ising-like model that explains the evolution of the magnetic structure with $U$ in tandem with a discussion of various different ways in which one might try to choose an appropriate $U$ parameter.

• Received 26 August 2011

DOI:https://doi.org/10.1103/PhysRevB.86.024433