Modulating the Magnetism of LaCoO₃ Thin Films Via Strain Engineering

LaCoO₃ thin films grown on SrTiO₃ (100) single crystals exhibit an anomalous ferromagnetic transition at T_c= 87 K. This material is normally not ferromagnetic and the mechanism of the transition is not well understood, although the O-Co-O bond angle is believed to play a crucial role. It is shown that the compound is not ferromagnetic when grown on LaAlO₃. Further strain, which presumably alters the bonding angle, can be achieved by growing LaCoO₃ on large angle miscut SrTiO₃ substrates in a layer-by-layer growth mode with the angle of miscut being α ~10°. Films are grown using pulsed laser deposition employing a a 248nm KrF excimer laser to ablate a stoichiometric LaCoO₃ target. The growth is studied via in-situ reflection high energy electron diffraction (RHEED), which can detect layer-by-layer growth when the RHEED intensity oscillates as a function of growth time. Crystallinity and topography are measured using X-ray diffraction and atomic force microscopy, respectively, and magnetometry as a function of temperature and magnetic field is measured using a superconducting quantum interference device (SQUID) magnetometer.