Quasi-two-dimensional magnetic properties in atomic layer resolved La0.7Sr0.3MnO3/LaAlO3

Materials in low dimensions show interesting physics and excellent potential in practical applications. The atomic-level control of two-dimensional (2D) behavior in a traditional three-dimensional (3D) system is quite hard, and the ${({\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3})}_{n}/{(\mathrm{LaAl}{\mathrm{O}}_{3})}_{n}$ (LMSO/LAO) superlattice on a (001) $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate was investigated to explore its quasi-2D behavior. The number of magnetic phase transitions has a close relationship with the number of unit cells ($n$): only one phase transition for $n=2$ and four phase transitions for $n=8$. It was found that the local structure of each ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ atomic layer is responsible for the multiple phase transitions: the gradual change of the tetragonal ratio and the in-plane tensile strain-induced $3d$ electronic orbital occupancy control the magnetic properties of 2D-LSMO atomic layers. For the outmost 2D-LSMO atomic layer contacting $\mathrm{LaAl}{\mathrm{O}}_{3}$ directly, interface-related factors reduce the intensity of magnetic interaction significantly. With the increase of $n$, the properties around the LSMO/LAO interface changes, which demonstrates that the superlattice configuration and the lattice-mismatch strain could be employed to explore the quasi-2D behavior of a traditional 3D system.