Control of the Octahedral Tilts in Lanthanum Cobaltite and the Impact on Magnetic Properties

Strain can be accommodated in two ways in perovskite materials, either via the extension of bond lengths or the rotation of the relatively rigid BO$_{6}$ octahedra. To explore the effects of octahedral tilts on magnitism, we have used epitaxy to control the octahedral tilting in the unit cell of La$_{0.5}$Sr$_{0.5}$CoO$_{3}$ by growth on cubic La$_{0.3}$Sr$_{0.7}$Al$_{0.65}$Ta$_{0.35}$O$_{3}$ (LSAT) and orthorhombic NdGaO$_{3}$. From X-ray diffraction, the films grown on LSAT were shown to have a cubic structure whereas the films grown on NdGaO$_{3}$ show an orthorhombic distortion. Due to the large paramagnetic response of the NdGaO$_{3}$ polarized neutron reflectometery was used to probe the magnetic structure of the films. The polarized neutron reflectometry demonstrates that changes in the crystal structure due to the epitaxially imposed symmetries alter the magnetism in these materials.