Reducing the magnetic dead layer to one unit cell in ultrathin films of manganites using spin-orbit coupling

For ultrathin films of manganites, it is commonly observed that the first several layers exhibit no magnetic signal, which are referred to as magnetic "dead layer." The existence of such a magnetic dead layer hinders the exploration of two-dimensional (2D) magnetism in strongly correlated systems. Various approaches including modulations of lattice, charge, and orbital of the ultrathin films have been used to reduce or even remove the magnetic dead layer. Although complete removal of the dead layer has not been achieved, noticeable success has been made in a model system of ultrathin films of La0.7Sr0.3MnO3/SrTiO3 (001), where the dead layer is reduced from 10 to 3 unit cells. In this work, we demonstrate that the dead layer can be further reduced to 1 unit cell with significantly enhanced magnetic moment and Curie temperature (T-C) using a strong spin-orbit coupling (SOC) effect. Specifically, we put two unit cells of SrIrO3 (SIO) either as the buffer or capping layers for the LSMO ultrathin films and similar results have been obtained. Density functional theory (DFT) calculations demonstrate that SIO dramatically enhances the magnetic anisotropy energy, in which the strong SOC effect of Ir atoms plays an important role. Our work indicates that enhancing spin-orbit coupling is an effective way to boost magnetism in 2D strongly correlated systems.